U-Boot: USS Nautilus - Eigenbauprojekt

I've elected to represent this USS NAUTILUS model in the 'as built' configuration. The display to look as this historic submarine did as it slid down the ways at Electric boat sixty-some years ago. My God, has it been that long?

Yet incredibly we (along with our UK partners -- who were the first to get the ball rolling) managed to harness the atom for 'useful' work such a short time ago!

There are subtle differences between how the boat looked then as to how it looks today as a museum ship. Originally the top of the sail was flat (not humped); there were two levels of free-flooding observation compartments with deadlights set into the leading edge of the sail; there were no sonar fairings on the deck; there was an array of large, square limber holes on the sides of the superstructure; it had five-blade propellers of traditional shape; and the stern was much more blunt of contour than it is today. Through the decades, the USS NAUTILUS has seen changes in mission as well as looks.

Andreas' kit is a bit of a hybrid: The sail has the hump, yet the stern is as originally built, the old style screws are provided, there are no deadlights in the leading edge of the sail, and the sides of the superstructure are neat. However, should you elect tor represent your model as the early version, this kit contains detailed instructions and illustrations that direct you on where the limber holes go as well as how they were shaped and sized.

I elected to enhance the 'step' between hull and superstructure -- a prominent feature seen on the actual boat, but lightly represented on the kit hull parts. Once I had built up this high relief longitudinal 'break' that ran around the superstructure I marked off and punched out the many superstructure limber holes.

The trough at the top of the hull (there to reduce the total displacement if the kit was to be assembled as a dry-hull type r/c submarine) presents a problem in that the two void areas, that run the entire length of the trough, form voids that if not vented would entrap air-bubbles once the boat made the transition from surfaced to submerged condition. These voids had to be opened up so that escaping air from within the hull could easily make it to the underside of the deck and out open holes placed there to insure a complete flooding of the hull as the model submarine assumes submerged trim.



I opened up most of the void areas either side of the trough. Only the removable upper hull piece had this trough. Note that the removed portions go all the way up to the underside of the deck -- bubbles will pass from the voids to the underside of the deck, then out vent holes to atmosphere. This work done for two reasons:

1. eliminating unneeded structure above the submarines waterline reduces the submerged boats displacement -- ballast tank volume is directly proportional to the volume of water displaced by the above waterline portions of the submarine.

2. since this is a free-flooding hull (only the SubDriver within is watertight) it is vital that all air within the superstructure be vented off as the submarine transitions from surfaced to submerged trim -- opening up the top of the hull like this insures that no bubbles of air get trapped in the 'high' portions of the trough, the voids either side of it.



I built up four layers of masking tap below where I wanted to represent the superstructure-hull slot -- represented on the kit hull as a simple angular transition between superstructure and hull.

Against the top edge of this masking tape dam I built up Bondo over both sides of the superstructure. The base of this build-up, once the tape dam was removed, would overhang the hull by about .030". This greatly increased the 'look' of the scale model.



Bondo, a two-part, exothermic curing filler -- often associated with automotive body work -- Is an excellent material where conformal, tightly bonding, yet easily filed and sanded material is demanded for surface re-contouring or gouge repair. Here you see it being used to build up the sides of the superstructure to produce the pronounced 'step'; simulating the slight stand-off of the upper superstructure plating over the rounded hull underneath.

Almost buried under the Bondo is the four ply masking tape used to produce this step. Once the Bondo has been knocked down with sanding blocks, to the level of the mask dams surface, and feathered up to the top of the superstructure side, the masking is removed -- it's edge producing a sharply defined step that denotes the break (artificial though it is) between hull and superstructure.



Once the Bondo had cured reasonably hard (it takes at least a day to cure to 90% of its solid state) I attacked it with descending grits of sandpaper till a reasonably smooth surface had been achieved. most of this work done with sanding blocks to insure that the sides of the superstructure assumed a flat surface.

To the right you see partially sanded work with the step producing masking tape dam still in place. As a section is finished the tape is pulled away revealing the simulated superstructure-hull step. There! … looks just like the real thing!



Wherever possible you want to to use a sanding block on long, simple curved surfaces, such as the Bondo build-up over the existing GRP. To refine the 'slot' I used CA adhesive stiffened pieces of sandpaper. Note that while I was working the slot I also faired in the slight miss-match between bonded bow hull pieces.

Some consider the automotive type fillers as unsuitable for r/c submarine use. That has not been my experience at all. Once well protected under coats of primer and paint this otherwise water absorbent material will stand the tests of time and use -- I have twenty-year-old r/c submarines, coated with Bondo like material, that today evidence no failure of the filler. Bondo is our friend!



The square limber holes on the sides of the superstructure run all the way up to either side of the bow. Only at the bow do these flooding holes differ in shape and size -- becoming a bit smaller and spaced very close together. All the dope about the shape, specific size and location of all limber holes is presented on two of the 'instruction' pages that accompany this very complete r/c submarine model kit. The illustrations are presented in orthographic, isometric and 'exploded' form.

The task of lofting the dimensional information (stated and drawing specific) onto the surface of the model was accomplished with metric scale (this is, after all, a European based kit), proportional dividers, two-point dividers, marking templates, pencil and scratch-awl.



I took a piece of .010" plastic card, trued it up to a perfect rectangle, then scribed a perpendicular line in the middle, and bent it to the angle described by the deck and superstructure side. I fixed that bend with some CA on the inboard side of this marking-scribing template blank and used to to mark verticals (the deck being the datum plane here) on the side of the hull. Each vertical line falling along the point where the leading edge of a square shaped limber hole would go -- those points indicated, in mille-meters, on one of the instruction sheets. You see those vertical pencil markings in this photograph, along with the scribed in outlines of each limber hole.

You might ask why not mark the holes with a pen or pencil. Sure, would have been simpler and less work, but a scribed line is much narrower than an external marking (ask any sheet-metal guy!). The difference between a pencil or scribed line is the difference between a sloppy hole and a tight hole.

(Sorry -- a left-over from Torpedoman A-school).



And here we have the four steps (evolutionary progression) of how I get from marking to completed hole:

1. at the extreme left we have the initial start of a square limber hole, two 1/16" holes punched within the previously scribed limber hole outline, that engraving done with the aid of a special scribing stencil

2. the the limber hole has been refined significantly using the same drill bit as a mill with the flutes doing the cutting, pushing the bit up-down-left-right, keeping the cut within the hole boarder defined by the engraving

3. second from the right is the further refined square hole, done with the smaller bit worked as a mill -- it's smaller diameter produces a tighter radius at the hole corners, the small bit is harder to hand-steer than the larger bit, so it's only used after the hole has been roughed out with the big bit

4. And the file refined square hole to the right using square and three-faced diamond files



Diamond dust coated files are the best tools for GRP detail cutting. They will never dull, and the industry has produced an incredible variety of these files in all sizes and cross sections. I found the most useful files for this job to be straight, Jeweler's sized square and triangle sectioned diamond shape. Those two files to the extreme right.

Also seen to advantage here are the open portions of upper hull -- done to reduce submerged displacement and to properly vent the free flooding hull when the model is commanded to dive beneath the surface.



Though the surface of the hull has been beat up with knife, file, rotary bit, and scribing over-strikes, the depth and severity of those boo-boo's are quickly fixed with air-dry touch-up putty and #400 grit sanding sticks used wet.

A quick shot of automotive lacquer primer (DuPont's Nason 421-23 gray primer) shows off the shadow thrown by the slot between superstructure and hull. This slot runs all the way aft, around the turtle-back and to the other side. Amazing what you can achieve with a little Bondo!

Roughly speaking, on the actual boat, this slot is the demarcation line between external hull and superstructure. It is through this slot that most of the flooding/draining water passes in/out of the free-flooding superstructure as the submarine transitions between surfaced and submerged trim. The USS NAUTILUS, as built -- in a time where marine Architects where still in the 'submerge as quickly as you can' mind set -- the square flood-drain limber holes were there to augmented the flooding/draining rate of the superstructure. However, as the navy came to realize that the mission of the submarine would forever abandon the need to cruise on the surface, the noise producing limber holes were (for the most part) plated over. This streamlining measure improving both the hydrodynamic and acoustic performance of the hull.

As I wanted to represent the early version of the NAUTILUS I was compelled to incorporate these iconic limber holes during assembly of this kit. Extra work? Sure. But well worth the effort.
 
Part-8
A notable departure from the kit instructions was my inclusion of additional sub-structure re-enforcement cross-braces. These to provide a more sound support under the very flimsy photo-etched (PE) deck pieces.

Though the kit supplied GRP transverse deck pieces served this function to a degree, I determined that there were not enough of them to do the job adequately. My fear is that I or some other idiot, while handling the model would accidently damage the very fragile PE deck, ruining it.

So, better now to strengthen the deck sub-structure than to repair a painted and weathered model after the inevitable deck damage occurred.

Concurrent with that I began the task of representing the clear deadlights at the leading edge of the sail. I could have painted these on with a gray or silver color later – that would have been the simple solution. However, nothing looks like clear windows like … well … clear windows!

These windows which provided visibility from within the sail to the forward deck were used by watch standers while the submarine cruised around on the surface in rough weather. There were three levels of these deadlights – the lower two levels represented by blocks of clear acrylic sheet, and the top level, forward of the bridge, would differ in that its deadlights would be represented by a build-up of clear, 12-hour cure epoxy glue – employing a very neat process advocated by David Manley. More on that later.



Though the kit provides transverse GRP deck supports, I believe that the very flimsy PE deck pieces will be subject to handling damage (pushed in by fat fingers!) if additional sub-structure bracing were not provided. That’s what you’re seeing here: .015” thick styrene sheet transverse deck braces being installed atop the superstructure. The position of these additional cross-braces fell under (and was hid by) a corresponding all-metal transverse section of the PE deck. Under normal lighting conditions these sub-structure braces will not be apparent through the open slots between simulated wood planks of the PE deck pieces.



You can see how I’ve arranged the additional sub-structure cross-braces, each sitting under the transverse all-metal portion of the slotted PE deck pieces. Later, after most of the painting is done, the PE deck pieces will be secured atop the superstructure with RTV adhesive.

Note how the top of each cross-brass has been outfitted with slots. These to permit the quick longitudinal movement of entrapped air bubbles so they can move about and find a vent hole in the deck so they can escape. Entrapped air within a wet-hull type r/c submarine is a major problem and one has to be ever mindful to provide for complete venting of the hull as it makes the transition from surfaced to submerged trim.



Making me the liar, this flash photography does show the additional transverse sub-structure elements added to strengthen the fragile PE deck. However, in the real-world, you won’t see much past the slots of the deck. This trick of lighting does show how I’ve placed the additional cross-bracing under the transverse ‘solid’ portions of PE decking.

I must comment again at my amazement at how well everything on this CAD designed and CNC and printed tooling of this kit insured all parts fit together almost perfectly-this thing literally falls together out of the box!



A Machinist’s surface-gauge was used to scribe the upper and lower edges of the yet-to-be-established deadlights. A right-angle triangle was used to guide a scribe as I cut in the deadlight vertical edges. Such lay-out precession was needed for the bridge deadlight cut-outs, but was over-kill for the plugs of clear acrylic actually used to represent the clear faces of the lower platform deadlights.

A holding fixture was cut from shelving stock and the sail screwed to it using the same fasteners and foundations that secure the sail atop the NAUTILUS’s hull.



The ballast sub-system employs a float activated snorkel valve within the sail. It was necessary to establish the where the bottom of the mast foundation piece sat within the sail so the snorkel could be made so it would not project above that line. On the outside of the sail I marked where the bottom of the mast foundation piece terminated and designed the snorkel mechanism to occupy the space beneath.



A trick that goes back at least a century is the use of clear plastic plugs, inserted into the portion of model where you want windows, and to then grind the outer surface of the plastic (usually acrylic) to conform to the outer contour of the model. Once the face of the clear part is ground and polished back to an optically clear item, the window frames are made by masking over where you want only clear areas to be, then paint, and remove the masking. That’s what’s going to happen here to the two lower platform deadlights.

Deadlight is navy-speak for windows.

Two ¼” thick pieces of acrylic sheet have been roughed out to approximate shape. Once set into the leading edge of the sail each is CA’ed in place, and ground, filed, sanded, and polished to conform to the curvature at the leading edge of the sail.

The drill was used to rough out the individual open deadlight ports up where the bridge will go. Diamond files were used to refine the square openings. Later these openings will be filled with clear epoxy glue. More on that later.



The solid acrylic pieces filed and polished to conform to the leading edge of the sail. The bridge open deadlight frames will later receive epoxy lenses. But, once it’s all masked out and painted you will be hard pressed to see the difference in materials and fabrication methodology between the three platform deadlights.

I could not use the acrylic trick on the upper deadlights as there is little space between the deadlights and forward section of bridge well – a cast resin piece that will later



The installed pieces of acrylic plastic within the two lower platform deadlight positions has been ground, filed, sanded, and polished to follow the contour of the sails leading edge.

The slabs of acrylic plastic were fine for the two lower levels, but not for the bridge level as those deadlights had to be of a thickness little more than the thin GRP of the sail.



When painting over masked clear parts you always want to go with the final color, from beginning to end. If you don’t, then the different colors (gray and/or red primer for example) will result in a disparity of color at the edges that denote transitions from clear to colored portion of the model.

So, if the final color will be a dark, dark, gray (the case with this model), then that’s the only color you will shoot over the clear part masks. Once the deadlight masks are in place I’ll lay down the first of many layers of final color. Paint does not typically have the heavy fill ability of a thick primer, but multiple coats will eventually get the job done around the deadlights.



The bridge level set of deadlights has yet to receive its clear lenses. The two lower platforms have had their individual deadlights (each set actually a single hunk of clear acrylic plastic) represented by pieces of masking tape followed by a coat of dark-gray paint. Here, with the masking removed, we see what appear to be closely spaced, deadlights along the two lower sail platforms.
 
Part-9
A statically diving type submarine submerges by taking on water ballast (variable ballast). The weight of the ballast water equal in weight to the water displaced by those portions of the submarine formerly above the surface.
The more structure above the surfaced submarines waterline, the more ballast water needed to counter the buoyancy of those structures once they are immersed in water. Good design practice would have you make the ballast tank as small as possible for two reasons:
First, is to minimize the volume given over to the ballast tank itself, leaving room for other devices needed to animate the submarine.
And less ballast water to be shoved in and out means less energy expended to move that water. Usually, as in this design, the air in the ballast tank is simply vented to atmosphere, done by a servo – not much energy expended there. However, to empty the ballast tank of water an air-pump has to be run, and that means a drain on the battery and wear and tear on the pump controller, pump, and its motor. Also, as my SD also employ’s an emergency gas back-up ballast blow sub-system, there is the kinetic energy stored within an on-board bottle of liquefied propellant, that energy given up each time an ‘unscheduled’ emergency surfacing occurs. We want to husband the vessels energy reserves. So ...
... Small ballast tank-- good; big ballast tank -- bad.

In a wet-hull type r/c submarine superstructure and sail wall thickness is the main driver of total above waterline displacement. Most of the appendages are solid cast items, and they too contribute to the total above waterline displacement.
This kit, designed and manufactured by a model aircraft guy – which makes him a GRP weight conscious fanatic -- has above waterline structures of very thin section. That’s why this r/c submarine kit, even though it represents a boat of high freeboard, requires a relatively small ballast tank.

(GRP and polyurethane resin have specific gravities close to 1, so in this game weight pretty much equals displacement).
Unfortunately, when I sized the ballast tank for this model, I still managed to wildly underestimate the total displacement of the above waterline portions of the surfaced model NAUTILUS. The first trimming trail with that SubDriver (SD for short, or for you old-school types, WTC) revealed that shortcoming immediately. Compelling me to build another SD with an enlarged ballast tank.
The SubDriver is a removable system comprising the propulsion, control, and ballast sub-systems that animate the model. I’ll outline the SD’s design, fabrication and functions in a later installment.

DSCF9927.jpg


The two machine screws that hold the upper hull down upon the lower hull are accessed through holes drilled through the PE deck – one forward, one aft. Great care was taken to secure the deck pieces onto the drill press bed: any drill chatter would easily tear the thin brass piece to shreds. Also, long before I determined securing screw locations I found spots on the PE deck pieces that were solid, and not impossible to drill slotted portions.
And that’s the case here. Note that the forward upper hull securing screw access hole will run through the PE deck where the solid deck hatch rescue-bell seating foundation is.



With the basic submarine structure completed and the SD and other internals worked out, time came to install the fixed ballast weight and buoyant foam – all arranged to work with the variable ballast water to set the boats displacement for both surfaced and submerged trim.

The trick is to make the center of gravity and center of buoyancy well distanced vertically; and for these two collectives of force to shift longitudinally, in unison, as the boat makes its transitions between surfaced and submerged trim.
Experience tells me that a four-foot long wet-hull type r/c submarine requires at a minimum two pounds of fixed lead ballast weight as low in the hull as possible. Here I’ve broken out some ingots of lead for a trial installation of fixed ballast weight.
A single screwed submarine would need more fixed lead ballast to better counter the torque of the propeller. However, as this submarine has two counter-rotating propellers (net torque is zero), I could get away with two pounds worth.



The USS NAUTILUS, in surface trim, has a very distinctive waterline: A high freeboard (distance from waterline to top of deck); the bow high, and the stern low. Unlike so many of the cold-war era American submarines, this conservatively designed -- first vessel to be nuclear powered -- submarine embodied many of the post-war, old-boat characteristics: hull form optimized for surface cruising; wide flat deck; and a high freeboard owing to its (by today’s standard) a significantly large amount of reserve buoyancy.
Before starting the trimming operation – a process, by trial-and-error of the amounts and location of fixed ballast weight and buoyant foam – I marked out onto the hull, with a wide Sharpie pen, the submarines surface trim waterline. The objective is to have the boat, with dry ballast tank, float at this waterline in surface trim; and, with a flooded ballast tank, to project only the top of the sail above the waters surface in submerged trim. The marking was laid down with the model rubber-banded to a flat work surface, pitched up the correct amount (that angle established by checking with a Machinist’s surface gauge as the bow was shimmed upward), and the waterline marking tool run around the model, laying down the waterline where it should go.



The first attempt to trim the boat revealed that I did not have enough ballast tank volume to get the boat up to the designed waterline once the tank was blown and emptied of water. From submerged trim I needed a weight of ballast water equal to the weight of water displaced by all the above waterline structures. Didn’t have it! Damn thing sat low in the water with the tank dry. The ballast tank was too small. Who was the dumb-ass who designed this system anyway?!.....
Nuts!



Nothing for it but to make a new SD with an enlarged ballast tank.
(Two, actually: one to replace my first attempt at the SD, and a second one for Andreas who’s putting together a wet-hull version of this kit back home in Germany)

The new SD features a ballast tank possessing 150% the volume of the first. Note that I retained the initial SD cylinder length by giving up space in the forward and after dry sections of the cylinder.
The aft dry section had excess space so that was easily given up to the forward section of ballast tank by moving the after ballast bulkhead aft a bit more. The forward dry section, containing the battery and mission switch was shortened by simply going to a shorter battery – cramming two of them in there and wiring them in parallel, giving the same capacity of the single long battery. The forward ballast bulkhead moved forward. Other than the bigger ballast tank and some minor relocation of ballast sub-system components, the length, function, and dry weight of the short and long ballast tank SD’s is identical.



Submerged trim is worked out first. The ballast tank is flooded. Once that’s set, you establish surfaced trim.
Yes, with all that foam hanging off the model it looks like hell.

Just the top of the sail projects above the water as the boat stabilizes at zero pitch and roll angles. Perfect submerged trim for a typical r/c model submarine equipped with a ballast tank. This is the condition of the submerged boat once the correct amount and location of buoyant foam has been established.

Working out foam amount and location to the outside of the hull is a lot easier than stuffing it within the hull and hoping you got it right. This way, the trimming is done in one, quick, sitting, without having to yank it out of the water numerous times.

“Are we done yet??!!!!”
Surface Trim, the ballast tank blown dry.
Some of the buoyant foam has been moved vertically, either above or below the surfaced waterline – the objective to get the boat to float at the designed waterline. There is more ballast tank volume than that needed using the new SD. That’s a good thing! The higher the center of buoyancy is over the center of gravity, the more statically stable becomes the vehicle.
Submerged and surface trim fixed, the model is taken back into the shop and all that foam is glued to the inside surfaces of the hull and superstructure.




The laborious process of shifting all that foam from the outside of the model to its inside has begun. It’s vital that the buoyant foam you select is of the closed-cell type. The blue and pink polystyrene expanded foam is of this type. Unlike open-cell type foam (usually white), the closed-cell type will not water-log over time. There is absolutely no need to ‘seal’ installed closed-cell type buoyant foam.
Here you see the installed fixed lead weights, and foam pieces ready to be installed within the hull. Note that some of the foam has already been shaped and bonded within the upper hull half.



The important thing is to get the longitudinal and vertical position of the foam correct. What was established during the trimming operation, placing the foam on the outside, now has to be replicated as the foam is glued to the inside of the model.
 
Davids Jungfernfahrt...meins fährt heute:

The first open-water run of the 1/87 USS NAUTILUS r/c submarine kit I acquired from Germany. Produced by Andreas Schmehl this is an easy to assemble and drive r/c submarine.

This outing presented in the following video was to establish surfaced and submerged turning radius. I find this to be a well running model submarine both on and under the surface. The initial run of this boat was in the rather confining boundaries of a local swimming pool which did not give me the opportunity to maneuver the model with any real freedom. However, that all changed when I went to some open water, as you can see in the video.

The model employs a Caswell-Merriman SubDriver -- the system that controls, propels, and manages ballast water. The system is removable and easy access to its devices through the two end bulkheads is quick, easy, and assured.

This SD, customized specifically for this r/c model submarine kit, will be available soon through the Caswell catalog.

I have posted the video to Youtube.
David
 
Meins ist heute gefahren. Was für eine Spaßfahrt. Es hat aufgetaucht schon nen ordentlichen Wendekreis, aber getaucht gehts schon viel besser. Hab es dann auch mehr unter als über Wasser gefahren. Sher gute Tiefenkontrolle trotz der starren Bugtiefenruder. Hier profitiert man von den hinteren Tiefenrudern direkt im Propellerstrom.

Die einzigen Spaßbremsen: Ordentlich Farbe am Rumpfunterteil verloren....über ein paar Steine geschrappelt. Der Lack hält auch nicht sonderlich gut. Beim nächsten wieder Epoxyprimer. Und der Fahrakku macht jetzt beim Aufladen Zicken....wahrscheinlich nur ein Balancer-Kabel.

Aber alles in allem: Sehr geil. Mein bestes Boot bisher.
 
This model kit WIP installment is exclusively dedicated to the NAUTILUS’ sail. And for good reason: Much as a scale model airplanes cockpit, the sail of a submarine model is the focal point of the viewer’s attention – the ‘front office’ of the vehicle; it’s where the machines intelligence and purpose are housed. The sail is where the people are. The sail also is one of the few places where you get a sense of the dynamic of the vehicle it represents: the optical and electronic sensors rising and descending upon their masts and faring; and It’s the last thing seen as the boat dives, and the first thing seen when it surfaces.

As a display, the sail is the most interesting aspect of the model. One must do it justice if the display is to be attractive and interesting. The model submarines sail is the focal point of the display, have no doubts about that.

The sail, with all those windows (deadlights); masts and fairings; antennas; periscopes; and open bridge with its deck, compass repeater, alarm boxes, platforms and such: all items that demand special care by the model kit assembler.




Since the earliest days of submarining the conning towers -- and fairings over those conning towers if used -- featured clear windows through which watch-standers could conn the boat, surfaced or submerged.

These windows, properly called deadlights, were quickly abandoned as pressure hull penetrations with the advent of the periscope. Deadlights of any significant size present a flooding hazard should the fragile glass lens fail as a consequence of collision or close aboard explosion. In any event, even with good underwater visibility, only on rare occasions could one see past the bow of the submarine – of little utility to the helmsman maneuvering the boat while submerged.

From the 30’s onward submarine deadlights were relegated to the free-flooding portions of the conning tower fairing where watch standers would seek refuge against the waves while navigating the boat on the surface.

Today, the use of sail mounted deadlights has been all but abandoned (The Russian Rubin design bureau being the last significant advocate). With the advent of nuclear power and AIP the imperative that a submarine ride out a storm on the surface was eliminated – no need for weather beaten watch standers to duck down to a protected platform and peer out through its deadlights. Today, if it’s rough, the boat submerges and everyone enjoys the ride beneath the waves – no longer must the watch standers take green water in the face while powers puking over the side as cold water streams down their backsides (I speak from grim experience!). God bless nuclear power!

DBF … my ass!

As built, the USS NAUTILUS featured no less than three levels within the leading edge of the sail outfitted with deadlights for outside observation. The bottom platform had three deadlights; the middle platform had five deadlights; and the bridge level platform had another five deadlights. That’s a lot of Plexiglas! The US Navy finally abandoning sail mounted platforms equipped with deadlights with the introduction of the THRESHER class submarine.




The kit provided sail-top represents the ‘armour’ bulged top aft of the bridge opening. This bulg afforded a few inches of protection over the tops of the retractable antennas, induction, and optical heads – an alteration of the origional flat sail top, prompted by the famous under-ice exploits of this world famous submarine.

However, my kit is being assembled to represent the ‘as launched’ boat, with the flat sail- top. I had to make a new sail-top.

I substituted a .031” thick piece of commercially available fiberglass sheet (G-10) for the kits sail-top. This very strong material is dimensionally stable, and takes to adhesives, primer and paint very well.

Note that the G-10 sail-top piece is temporarily held to the cast resin mast foundation piece with the aid of two machine screws (seen atop the sail-top between the masts and fairings). The ability to refine the shape and position of the many sail-top holes for wells, lookout stations, masts and fairings with the mast foundation piece out of the way makes those jobs a lot easier.



The kits cast resin mast foundation piece – used to both provide some of the housing wells and supports of the masts and some of the antennas atop them – had its sides milled down and a good portion of its bottom cut away to reduce total weight/displacement. This one piece, as it was, displaced nearly one- ounce. After the cut-down it displaced about a third of that. That’s a lot of weight removed from the tallest point on the model, aiding greatly in keeping the models center-of-gravity reasonably low. This weight reduction would minimize heeling in tight turns on the surface, and would contribute to better static stability about the roll axis.

Using the original resin sail-top piece as a template, I scribed onto the G-10 the sail outline as well as the shapes and locations of the holes for the bridge, lookout stations, antenna and optics retractable masts, and fairings. Those scribed lines highlighted by smearing some artist’s oil paint over the work.



The G-10 was cut out on the band saw to outline; and the well, mast and fairing holes punched out and shaped with drills, burrs, and diamond-dust jeweler’s files.

The only two retractable masts not represented in the raised position on this model will be the communications UHF-VHF whip-antenna mast-fairings. The top of those ‘retracted’ mast-fairings represented as engraved tear-drop shaped forms scribed upon the sail-top piece.

An aluminum scribing stencil used here – the cutting done with two scratch-awls: a starting scriber with a sharp point, and a widening scriber with a blunt point to widen the engraved line. GRP material is very, very tough to scribe owing to the glass content which quickly dulls the steel tools, which required their sharpening several times during the course of this work.

As a great deal of force is applied to the scribe, both down into the work and against the inside edge of the stencil, it’s a good practice to glue the stencil in place during the entire cutting operation least the stencil shift, resulting in a ruined engraving. It’s easy enough, once the scribing is done, to pop the glued stencil off the work and scrap away any remaining adhesive from the work. On occasion I will even use machine or wood screws to hold a scribing stencil down securely onto the work.

Engraving is hard.

Filling and fairing over screw holes and scraping away glue is not.



While I was integrating the G-10 sail-top and cast resin foundation pieces I kept the two registered together with two machine screws that temporarily pulled the two pieces together. This permitted me to easily access both pieces, separately, as I cut out the holes for the masts through the G-10 sail-top, and worked to bore or sleeve the mast foundation piece bores to imperial sizes.

Damned metric-system! Can’t these people count to twelve!?....



As I stated before, big blocks of clear acrylic were employed to represent the transparent elements of the two lower platform deadlights. However, a different means of producing clear deadlights at the bridge level was required owing to the very small space between the inside surfaces of those deadlights and the front of the cast resin bridge piece.

I opened up the deadlight openings; each framed as on the prototype, and then touched the edges of these holes with a clear self-curing resin, such as epoxy glue. Now, if those openings were small enough (they were not), the strong surface-tension of the liquid would hold its form and it would bridge the entire opening as the application tool was slowly removed. The clear resin would be left to changes state from a liquid to a solid.

However, the larger openings, like these deadlights, require additional steps as the deadlight holes are way too big to be bridged in one glue application. Though it did not bridge the opening entirely, that first application of glue did build up a significant radius of clear adhesive at the deadlight corners and did build-up along the edges, reducing the amount of glue (and reducing the risk of introducing air-bubbles in later applications) needed to complete the bridging of the deadlight openings.

(You plastic model plane and ship guys may recall the ‘crystal-clear’ product for representing port holes and the like – a thick, clear-drying liquid that had the surface tension to hold form once applied with a round tool to the edges of a hole. When applied correctly the goo would hold as a film within the opening where it would be permitted to harden into a not-quiet optically clear transparency).

What David Manley taught me, and I replicated here, is to place a masking tape damn around the leading edge of the sail and apply glue from the inside, building it up thick enough to conform to the inner curvature of the sails leading edge – bridging all the deadlight openings. The outside mask insuring that the forward face of the clear glue assumed the curvature at the leading edge of the sail.

After the clear epoxy glue has cured hard the masking tape is pulled away from the sails leading edge, the inside and outside surfaces of the clear deadlights are filed, sanded, and then polished to the contours of the sail, inside and out. Deadlight masks were applied and the black (very, very dark gray) exterior painted.

Nothing to it!





It’s my practice to keep as many model assemblies separable as long as possible during the course of the job.

The entire sail assembly, only some of which you see here, is a case in point: the removable sail-top (secured to the to the sail during the in-water trimming operation and when there is a need to integrate pieces that need clearance between both sail-top and sail) permits easy access to the inside of the sail for SD snorkel mechanism integration and installation; work on the three platforms of leading edge deadlights; finish and detailing tasks to those inside surfaces of the sail seen through the open bridge and lookout stations; detailing ;installation of the sail-to-hull screw foundations; and the manufacture and fitting of the hand-rails that run both sides of the sail.



Another departure from the kit-as-provided was to make the forward ‘tub’ -- that forms the open bridge atop the sail -- removable. Accomplished by gluing four RenShape drilled and taped foundations: two to the bottom of the sail-top and two to the back of the bridge tub. Once the sail-top is glued permanently atop the sail I retain the ability to install/remove the bridge tub as required.

The two ‘L’-shaped brass items, each projecting from a side of the sail, are the mounts that interface the UHF-VHF whip antennas (represented by lengths of stretched sprue or cat whisker …. “here, kitty, kitty, kitty!”) with their respective ‘retractable’ fairing. A RenShape block glued to the bottom of the sail-top receives a whip antenna mount. Cut-outs in the sail-top and sides of the sail permitted each mount, with its attached antenna, to project well clear from the side of the sail.




The completely assembled sail-top being test fitted atop the sail. Note that all the deadlight work is done and that each deadlight has been masked and dark paint applied and the masking removed to reveal the correct number and size of deadlights that, on the real thing, permit crew observation from the three platforms within the sail – but only on the surface as the entire sail (except for the bridge hatch access tunnel) is free-flooding.

At this point the mast foundation piece will be glued to the bottom of the sail-top, the two temporary screws holding the two assemblies together removed, and their holed filled and faired over. The bridge tub will be unscrewed, removed, and set aside. And the sail-top permanently CA’ed atop the sail and the edge between sail-top and sail will be filed and sanded to the proper radius.
 
Weil es fragen nach dem Modell gegeben hat. Ich habe meines jetzt gefahren, und alles was ich wissen muss gelernt um nach dem Prototypen jetzt das hoffentliche perfekte Boot zu bauen. Dazu gibts wieder einen Baubericht und parallel erstelle ich die Mantageanleitung. Danach wirds wahrscheinlich ne Kleinserie an Booten geben. Unter Montageanleitung stelle ich mir sowas vor (elende Arbeit....):

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Part-11
I assembled this NAUTILUS kit as a ‘wet-hull’ type r/c model submarine. The hull and sail are free-flooding and the only spaces aboard that are dry are those two compartments at either end of a removable cylinder. This water tight cylinder (WTC) -- also referred in Europe as a ‘module’ ... or, ‘Tupperware’ when they’re in a particularly mischievous frame of mind -- contains the three basic sub-systems needed to animate the model submarine, endowing it with the ability to cruise either on the surface or submerged. Propulsion, control, and ballast.

Pushing out ballast water is done either by water pump, air-pump, piston, an onboard gas, or a combination of methods.
The removable cylinder concept has been around since the 60’s and commercial product since the late 80’s.

(For the Record: In the States credit for the design and continued development of the WTC is mine. In Europe I believe the lion’s share of credit for what they call a module goes to Brittan’s Nick Berge – one of the most prolific and out-of-the-box thinkers this hobby has ever had. In the days before the internet Nick and I worked toward development and promotion of similar systems, initially we were not aware of the others similar work).

Typically a WTC is divided into three sections, partitioned by four bulkheads -- one at each end, and two near the center of the cylinder. Between the two internal bulkheads is formed the WTC’s ballast tank. There are variations on this theme. The work of Ron Perrott http://www.rcsubs.co.uk/ and Norbert Bruggen come to mind, but for brevities sake I will focus specifically on the 3” diameter, two-motor-two-shaft SAS type SD worked up for the 1/87 USS NAUTILUS kit – the subject of this rather comprehensive WIP.

Most WTC’s differ as to materials and method of ballast water management. The WTC is an old idea: I have a picture of what otherwise looks to be a current version of a clear cylinder WTC from an old issue of Model Boats dated 1967. However, its cylinder was formed from Acrylic plastic – a material prone to cracking and difficult to machine. Today most clear cylinders are formed from Lexan, the same tough clear plastic used for soft-drink bottles and clear r/c car bodies.



And here we have the WTC ‘system’ – a self-contained, removable, easily accessed water tight cylinder that contains the three sub-systems needed to effectively animate an r/c submarine: propulsion, control, and water ballast.

Atop is an assembled, outfitted, tested, and operational SubDriver (the proprietary name given our extensive line of WTC’s). These two sized and arranged specifically for the 1/87 scale USS NAUTILUS. Pictured are the significant components that go into the manufacture of this SubDriver (SD).

Four cast resin bulkheads divide the Lexan cylinder into three sections. The after dry section contains the propulsion and control elements; the center section forms the ballast tank; and the forward dry space houses the battery and mission switch.



Examine the above cut-away examples of a typical WTC bulkhead and pushrod watertight seal to get an idea how the conduit, bulkhead, and pushrods are made watertight to the SD.

All four resin bulkheads are made watertight to the cylinder through edge sealing O-rings. The conduit -- a brass tube that running the length of the ballast tank -- is made watertight to the ballast bulkheads via partially encapsulated O-rings during bulkhead manufacture.

The pushrod watertight seals are descrete items that are RTV’ed into holes punched through the motor and after ballast bulkheads. Each pushrod seal features a 1/16” diameter bore with an encasulated O-ring at the seal bodies center which effects the watertight seal between its axial running pushrod and SD proper. The three pushrods that project aft make up to the stern plane, rudder, and bow plane linkages – all of which are external of the SD and make up with
magnetic connectors. A single pushrod passes between the dry and wet side of the after ballast bulkhead and is part of the linkage that controls the operation of the ballast tank vent and emergency gas blow valve.



Three servos are mounted on the motor-bulkhead device tray. The one about to be made up to its 1/16” diameter brass pushrod drives the stern planes. This servo is tended by the ADF2 angle-keeper circuit (with operator input always available); the middle servo is for the rudders; and the port servo operates the bow planes.
Each servo pushrod goes through a watertight seal set into the motor-bulkhead. Those seal bodies made fast with RTV adhesive – this permits easy replacement if called for.



Like cramming ten-pounds of stuff into a five-pound bag!
That’s always been the situation with r/c model submarines. As illustrated here. All the devices that have to fit, coherently, onto the motor-bulkhead device tray and bulkhead can now be fit into a very tight package. Only with the development of small footprint devices (computer assisted circuit design and surface mount technology) and very selective receivers (signal processing in addition to detection) has this magic-trick been possible. Device size and receiver selectivity has been a boon to this hobby.

Pull the motor-bulkhead away from the cylinder and there are only two electrical connections to break to free the entire unit from the system: one pair of plug connectors interface the motor-bulkhead to the battery power cable, and the lead going to the ballast servo mounted to the dry-side of the after ballast bulkhead.
In order to better describe the function and arrangement of three sub-systems, I’ll discuss each in some detail with supporting pictures:

PROPULSION SUB-SYSTEM
The devices regarded as belonging to the propulsion sub-system include the battery, Electronic Speed Controller (ESC), mission switch, battery cable, battery, cable plugs, motors, motor spark- suppression, gear reduction and propulsion shaft seals.



BATTERY This particular SD is sized to fit the 1/87 USS NAUTILUS kit. As I found the size of the ballast tank left little room for both the forward and after dry spaces, this necessitated the use of ‘short’ 11.1-volt Lithium-polymer batteries. Two of these short batteries, wired in parallel, achieved the 3-Ampere hour capacity needed to keep the model running for a few hours between charges. Note the use of a three-plug adapter used to gang the two batteries together in parallel, permitting me to retain the original battery discharge plugs. One of these ganged batteries made up to the foreground

motor-bulkhead devices through a test/set-up power cable – this cable making set-up of the installed devices an easy matter, and is a perfect analog to the one that runs through the SD’s conduit tube.

ESC The electronic speed controller is a common, commercially available item that directs battery current of the desired polarity and intensity to the motor(s) as commanded by the transmitters throttle stick. I’m a big fan of the Mtroniks brand of brushed motor ESC’s. These units are waterproof, robust, and easy to program, and feature a relatively small footprint for the work they do. It’s a good practice to select an ESC with a maximum sustained current draw that approximates 2X the stall current of the motor(s) it’s connected to. For this application, where I’m driving two motors in parallel, I’ve found the fifteen-Ampere Mtroniks ESC to be more than adequate to the task. Though provided, you do not use the ESC’s battery eliminator circuit on the larger SD’s – it simply does not have the current capacity to meet the load presented to the receiver power bus. Either snip off or pull clear of the ESC’s lead the red wire to disable the ESC’s BEC .... NOT THE BLUE WIRE, OR WE ALL DIE IN A HORRIBLE EXPLOSION (for you WW-2 movie fans out there).




MISSION SWITCH The entire system is powered through a single battery – which provides power to control, propel manage ballast water. The mission switch is a simple, series connected single-pole, single-throw toggle-switch rated for 10-Amper’s at 110- volts. The on/off function is done at the forward face (wet side) of the SD’s forward bulkhead – simply flipping the toggle to either the ‘on’ or ‘off’ position. The switch itself is made waterproof by a rubber boot that fits over the toggle and makes a watertight union to the face of the bulkhead through an O-ring. The mission switch is wired in series to the battery power cable – the wiring passing through a strain-relief block within the forward bulkhead, its job to prevent breakage of the wires at the switch
terminals during handling.

BATTERY POWER CABLE To be capable of handling up to a sustained 20-Ampere’s at 12-volts it’s two conductors are of 16-gauge; enough copper cross section to preclude any significant voltage drop or heating. This is the main-line between the battery and all the devices requiring electrical power in the after dry space. The power cable runs aft through the brass tube conduit within the central ballast tank. A male Deans-plug at the forward end makes up to the battery (parallel battery harness in this case), and a female Deans plug at the after end of the cable makes up to the devices female Deans plug off to the side of the motor-bulkhead device tray, within the SD’s after dry space. As pictured below.



CABLE PLUGS As mentioned, the power cable plugs are of the Deans type. These are polarized to prevent accidental polarity screw-ups when making up the battery and devices to the power cable. Though four devices get battery power direct (BEC, MPC, BLM and ESC), it’s the ESC we’re interested in here. This vital propulsion device gets the lion’s share of current when the propulsion motors are running and accounts for why the power cable and connecting plugs, and mission switch are of such a robust nature.



MOTOR AND SPARK SUPRESSION Two 40 turn, three-pole, 12-volt, brushed, 380 sized motors are mounted within the dry side of the motor-bulkhead. Each motor is spark- suppressed with two .01 micro-Farad capacitor – each soldered to the motor case and one brush pole. These capacitors store and discharge at a low RF frequency the ‘electrical noise’ created by the arcing between brushes and commutator pads. Noise that if it got into the very tightly package array of electronic devices would drive them nuts! The two motors are wired to a single ESC in parallel, is such a way that each shaft turns counter to the other.



GEAR REDUCTION To better speed-match the high RPM motors to the low RPM propellers I usually employ a 3:1 gear reduction as pictured above. The typical motor bulkhead comprises two pieces: a forward back-plate to hold the motors with their press fit pinion gears; and the motor-bulkhead proper in which are housed the drive- shafts, spur gears, and drive-shaft cup type watertight seals. The motor-bulkhead also mounts the servo pushrod seals, receiver antenna extension, and SAS suction and discharge nipples. Screwed to the forward face of the motor-bulkhead back-plate is the aluminum tray and bulkhead, upon which all the devices are either screwed or double- back taped in place. The motor bulkhead is HEAVILY populated with stuff!





SHAFT SEALS Each 3/16” diameter motor drive shaft is made watertight to the motor- bulkhead through a cup-seal. A cup-seal is housed within a plastic shaft seal body and the seal backed up against transverse motion by an internal Oilite bearing. Cup type seals are ideal for rotating shafts as they offer minimal friction and have the feature of increasing their sealing pressure with increasing outside water pressure. Each shaft seal unit is affixed within the motor-bulkhead with RTV adhesive – this flexible material easily absorbs vibration and can be easily defeated if the occasion arises where the shaft seal either needs replacement or repair.

CONTROL SUB-SYSTEM The control sub-system constitutes the ‘brains’ of the SD system; devices that take the commands that originate in your massive brain, into the transmitter, then on to the receiver where that intelligence (or an autonomously functioning environment sensing device) emerges as modulated pulse-width. Each channel from the receiver feeds a device or devices with a command from the transmitter. Then, each device either converts that intelligence into physical motion (servos), applies a voltage to a motor or solenoid (ESC and MPC), or generates a pre-set pulse-width data stream to drive other devices to a pre-set ‘fail-safe’ position (Lipo- Guard, BLM, or ADF2).

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Most of the devices are common to the average r/c model vehicle user. The servos, ESC, BEC, transmitter-receiver, battery, and connectors can be found at any hobby shop or through the Internet. However, r/c model submarining places demands on the system, and employs special devices that are only available from a few dedicated on-line services, Such as the Caswell Company – the outfit I work for. Their catalog can be seen here: http://sub-driver.com/ This outfit also supplies a wide range of SD’s for the r/c submarine modeling community.



The above photo shows a typical hook-up arrangement of the devices that control, propel, and manage the ballast water aboard a SubDriver type WTC. And this is not all of it, just the devices that mount to the motor tray and bulkhead. If you look carefully you’ll see that four of these devices (ESC, BLM, MPC, and BEC) have their own red-black power wires. These red-black wires will all be ganged together in parallel and made up to a Deans male type plug which will make up to the battery cable.



BATTERY ELEMINATOR CIRCUIT Not actually a controlling device, but vital to the whole sub-system, is the BEC, the battery eliminator circuit. This devices takes the high-voltage battery current, reduces it to the 5-volts the other devices require (distributed through the receiver bus via each devices three-wire lead). But, unlike the low capacity ESC BEC’s, this dedicated BEC has the ass to pump out a continuous 8-Ampere’s of current (enough to smoke the receiver bus foils if ever attained ... but that’s another issue!). The stand-alone BEC in larger models (such as the case here) is used because of the higher stall current situations larger servos can present. The BEC is the circuit power source for all devices and as such is a vital element of the control sub-system. Smaller systems, using smaller servos, can get away with using the dinky ESC BEC.

BATTERY LINK MONITOR/LIPO-GUARD If your system employs Lithium batteries you must have on board either the old Lipo-Guard or the recently introduced (and much more capable) battery link monitor (BLM). Both devices monitor battery voltage and work to prevent a low voltage to damage the battery. When activated, the device locks you out of the ballast channel loop, so that the model must be returned to shore for re- set – by that time even the most dense r/c submarine driver will have figured out that his battery needs replacement/re-charging. The difference between the Lipo-Gurad and BLM is the added capability of the BLM. The BLM not only protects the battery but also serves as a loss-of-signal fail-safe; real-time battery voltage meter; and r/c system performance monitor -- actually counts and displays the number of frame drop-outs that have occurred since last switching on the system.



ADF2 The ADF2 is two devices in one: An angle-keeper and a fail-safe circuit. The angle- keeper plugs into channel-5 of the receiver. The circuit employs a position sensor (accelerometer) to detect and work out the displacement of the gravity line (established during device set-up/programming) to the model submarines axis. And that is what you see in the above hook-up between the ADF2, stern plane servo, and receiver. The angle- keeper is both an autonomous artificial stabilization device – working the stern planes to keep the boat at a near a zero pitch-angle while underway submerged -- yet able to permit operator input to the stern planes; mixing both driver and angle-keeper inputs into a viable command output to the servo. The fail-safe side of the ADF2, if used, plugs into either the Lipo-Guard or channel-4 receiver port. In this example the ADF2 fail-safe circuit is not used – its lead not used.

RECEIVER The r/c system receiver is the RF link between your transmitter and the devices that control, manage ballast water, and propel the r/c model submarine. Today’s receivers are so well designed and crafted that they have the signal selectivity to work in the very tight confines of a very RF noisy environment (The closer the receiver is to all those motors and signal-generators the more hideous becomes the inverse-square rule). Bottom line: we can cram the SD with so much stuff today and not have to worry excessively about the receiver being swamped and made stupid by all the electrical noise. At a minimum you want a five-channel receiver on any RF band below 75mHz if you want the ability to sail the model underwater with the antenna completely submerged (and then, only in fresh water). 2.4gHz r/c systems just won’t work with the receiver antenna under water.



MOTOR PUMP CONTROLLER The MPC is an electronic switch that solders directly to the back-plate of the small brushed motor that drives the low pressure blower (LPB), which produces the compressed air used to blow the ballast tank dry. The above photo demonstrates the low foot-print of the MPC. The larger unit above is used in my line of larger SD’s. The MPC gets its power from the battery cable through a voltage-dropping resister that permits the LPB motor to operate at its optimum 3-6 volts, not the 11.1- volts that comes directly off the battery. The MPC’s three-wire lead makes up to one leg of the Y-lead that comes out of the ADF2 fail-safe side or output side of the battery link monitor (BLM) – that signal shared with the ballast sub-system servo.



BALLAST SUB-SYSTEM Models that don’t employ a variable ballast (ballast tank) can only dive dynamically – they require forward motion to generate the dynamic force on the hull to drive the submarine beneath the surface. Submarines that can dive in place, without the need of hull produced dynamic force, do so by changing their weight; increasing it so that the added displacement caused by the above waterline structures being immersed is countered by the weight of the water taken into the ballast tank.
The ballast sub-system comprises the ballast tank and the means of flooding it with water and pushing all the water out as either commanded from the transmitter or automatically through one of the detected fail-safe conditions: loss of r/c system signal or low battery voltage.

Either the normal SAS type vent/blow cycle or a back-up emergency gas ballast blow will empty the tank. SAS normally. Gas and SAS when commanded by the fail-safe circuit. The ballast sub-system servo and its linkage are common to both the SAS and gas elements of the sub-system. Moderated travel of the linkage produces a SAS type blow. Extreme movement of the linkage results in both a SAS and gas type blow.



All our static diving type SD’s use the ‘soft’ type ballast tank – the tank is open at its bottom permitting the free flow of water in or out of it. If the vent valve is closed and air is in the tank, then it will compress to the ambient water pressure (usually, on the surface); opening the vent valve permits a pressure drop within the tank and water quickly floods in, displacing the water. The normal means of discharging the water is to compress air from either the dry-spaces of the cylinder or atmosphere and discharge that air into the ballast tank, forcing the water out as the higher air pressure displaces the water. Blowing air is selected in the Semi ASpirated (SAS) elements of the ballast sub-system by the snorkel mechanism.





SERVO The ballast sub-system servo drives a pushrod that runs through a watertight seal set within the after ballast bulkhead. The wet side of that bulkhead (within the ballast tank) has the linkage that translates the linear travel of the pushrod to a vertical motion which works to open/shut the vent valve atop the cylinder. Extreme motion of the servo in the ‘blow’ position not only keeps the vent valve shut it also causes the ballast linkage arm to open the emergency gas blow valve – the extreme motion can only be achieved through the fail-safe circuit or engagement of the transmitters channel-4 trim lever to the extreme ‘blow’ position.



MPC As mentioned, the motor pump controller is a form-fitting electronic switch that solders directly to the back of the low pressure blower motor. It is one of the four devices that takes battery current directly, and sends it to the motor as directed by the command that comes through the battery link monitor (as commanded by the transmitter or fail-safe circuit built within the BLM). Both the ballast sub-system servo and MPC get their control inputs through a Y-lead from the BLM, so they work in unison. (The above illustration shows both the small and larger type MPC’s we use with our line of SD’s – the USS NAUTILUS SD makes use of the smaller LPB-MPC unit).





LPB The low pressure blower is a positive displacement pump with the ability to pass a non-compressible fluid, like water, without damage. It is (the smaller unit) a two-stage diaphragm type – and it’s the flexibility of the diaphragm that permits it to pass water without getting hammered. A non-reversible type pump, it can only pass the air in one direction. And in this application the air is always directed into the ballast tank. That air pushing out the water within -- emptying the ballast tank. The air either comes from within the SD dry spaces or from atmosphere through an induction snorkel mechanism set up high within the sail, usually. Up high, the snorkel will broach the surface as the boat ascends. The above SAS layout illustrates both function and the devices used to draw air from either the cylinder or atmosphere and push it into the ballast tank.

BLM The battery link monitor is an upgrade from the Lipo-Guard. Unlike the Lipo- Guard -- which only monitored battery voltage and simulated a ‘loss of signal’ condition
to activate the ADF’s fail-safe circuit – the BLM produces a ‘blow’ signal when the battery voltage drops below the critical level. Also, the BLM is suitable for a number of different battery chemistries and cell counts; can be set for specific servo travel; as well as time delay between activation and ‘blow’ command. A very useful device regardless of battery type, but a must if you employ a battery of Lithium chemistry.

David
 
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