WET-HULL AND DRY-HULL TYPE R/C SUBMARINES
(3-1, Brian kneeling over 1/32 Type-7 with WTC-3.5 mod 2)
R/C submarines can be categorized as either of the wet-hull or dry-hull type. The wet-type R/C submarines outer hull freely floods and drains; its interior - with the exception of specific spaces (or containers) housing the gear that has to be dry - is full of water. Since the wet-hull type model submarine outer hull is not subjected to differential pressures (as a consiquece of depth), it can be made quite light - a light weight above waterline structure requires less ballast tank volume, consiquecelly, less Propel gas/electicity to empty or flood the tank.
(3-2, Gordon Lewis' Type-202)
The dry-hull model submarine, on the other hand, has an outer hull that formes the watertight structure. All or a significant portion of a dry-hulls interior is dry. The principle advantage of the dry-hull sub model is the room the uncluttered and spacious interior of the model presents. Arrangement of servos, ballast tank, batteries, motors, etc. is an relatively eazy task. The only design considerations revolve around placement of the models c.g. and need to provid enough transverse bulkheads - if the hull is thin and/or of other than circular section - to prevent extreem hull distortion (and possible access hatch unseating) as a consiquece of increased hydrostatic pressure as the model dives deep.
Typically, dry-hull R/C submarines are constructed of GRP, wood, or blow-molded plastic. The wet-hull type hulls are usually made from GRP or vacuformed plastic.
(3-3, Johann holding superstructure over his Type-26)
Why is the distinction between the wet and dry-hull types important?
Let's take two imaginary examples: Make them of identical size and build them from identical GRP and cast resin parts. One is built up as a dry-hull 1/96 SKATE class SSN. The other model built as a wet-hull SKATE. Both are completely outfitted and trimmed for R/C operation.
Lift the wet-hull SKATE. It weighs in at five pounds.
Lift the dry-hull SKATE. Wow! It weights in at around 15 pounds!
The dry-hull presents a much larger 'envelop' when emerced in water than the wet-hull type.
A submerged submarine, in a state of 'neutrally buoyancy' has to weight as much as the weight of the water it displaces. Since the dry-hull type submarine in our example displaces so much more water than its wet dry-hull brother, the dry-hull boat had to be ballasted down with massive amounts of fixed weight to achieve neutral bouyancy.
The dry-hull R/C submarine is so heavy because the model displaces so much more water.
Ok, so the dry-hull SKATE is heavier than the wet-hull SKATE - so what! They both perform equally well in the water, that's what counts isn't it?
Well, yes, in water performace is the same, but what about the 99% of the time when the model is in the shop, on display, or being transported back and forth?
In addition to the back trouble you risk with such a heavy model, the dry-hull boats are very susceptibility to damage suffered as it is operated, transported and worked on. To make the point, let's get back to our twin SKATE models... your going to love this!
I'll make the point this way: Take the wet-hull version of the SKATE model and slam it up against a brick wall. Now, slam that heavy dry-hull SKATE model up against the same wall... and get that smirk off your face, your not supposed to be enjoying this!
Investigating the damage you'll note that the heavy wet-hull SKATE suffered much more damage than its light weight partner. The greater kinetic energy (as a consiquence of its greater inertia) of the heavier model was released upon impact by breaking appendages, bending shafts, and crushing portions of the hull and superstructure. The lighter model SKATE expended less energy trying to move the brick wall
Typically, wet-hull type R/C submarine models, because of their relatively light weight, are much easier to transport and are less suseptible to handling damage than the dry-hull types. Or to put it another way: most healthy guy's and gal's can easily move 15 pound 1/96 SKATE class models around, but what about that dry-hull 1/32 GATO... are you up to lugging a 200 pound model submarine around, Arnold?
DRY-HULL TYPE
Another problem with dry-hull models is the installation and maintenance of water tight seals within confined tapers at the stern and bow. A dry-hull boat typically has many more water tight seals penetrating its hull than employed aboard an equivalent wet-hull R/C submarine. However, that problem has been significantly lessened with the availability of the low profile water tight seal offered by SubTec.
It was not my intention to let the above introduction to this chapter become a slam against all dry-hull type designs. To the contrary, as the following examples show, there are good reasons to opt for the dry-hull design. As a practical matter, I recommend building an R/C submarine as a dry-hull providing the subject is under 55 inches in length and/or the equipment installation could not fit within a separte water tight space within the hull.
For example, Rainer Geriach outfits his R/C submairnes with what we in the West would consider exceptionally large amount of battery, a battery, composed of ni-cad cells that are not easily adaptable to storage within the flooded spaces within a wet-hull type model. Also, the German's favor a piston type ballast system aboard their models, another item that takes up valuable real estate within the dry spaces of the model.
Pictured is Rainer's latest R/C model, built up from the Thor Design and Development 1/72 ALFA kit. A fine example of an extremely well engineered application of a commercial kit intended to be employed as a wet-hull type submarine.
(3-11, Rainer Geriach's 1/72 ALFA opened up to show interior)
You'll notice that Rainer's ALFA opens up near the stern, the model hull separating into a forward and after section. With the forward section slide off to expose the inner workings, complete, unobstructed access is afforeded to just about every component that makes up the propulsion, control, and ballast systems. Notice that the stern and forward sections of hull are secured by two special bayonet type securing/sealing rings.
(3-12, matting rings for german boats)
First seen in the West during the 1994 SubRegatta, Norbert Bruggen's bayonet securing/sealing rings cought the interest of many long time and beginning R/C submariners. The device works to firmly hold the two hull halfs together as an installed o-ring seal make a perfect water tight seal at the joint. A series of inboard facing lugs on one ring locks, when rotated a few degrees, under a similar set of lugs within the other ring. Each ring is bonded permanently to a hull half with resin and reinforcing fiberglass tape. Of course this type hull fastener is only applicable to models of perfectly circular cross section at the break point - not too much of a problem as most modern type submarines feature a spindle shapped hull.
(3-4, Ray's NAUTILUS with superstructure removed)
A more traditional aproach to gaining entry within the dry-hull type R/C submarine in Ray Mason's beautiful Disney NAUTILUS. Other than a free flooding, removable superstructure piece to access the clear Lexan access lid, the entire model is water tight. The installation of equipment aboard Ray's model is further simplified by omission of any variable ballast tank system, this model being a dynamic-diving type R/C submarine.
(3-5, Tom Grafton with Krick U-Boat on bech)
Small sized model submarines (I'd say anything under 40 or so inches in length), such as the Krick U-boat kit, are great candidates to be built up as dry-type R/C submarine models. Here, Tom Grafton has departed substantielly (as he all too often does) from the kit instructions and has gouged out the hulls interior to a very thin wall thickness to increase its internal volume. The added room to acco odate installation of a 5-channel R/C system, a CO2 gas-type ballast system, and two propulsion motors, and other non-traditional items. The dry-hull type hull gives the modeler the flexibility to run route electrical wires, gas hoses, and to place equipment wherever needed within the length of the hull.
WET-HULL TYPE
(3-7, SKIPJACK with open hull with WTC-3 in it)
Accepted by most modelers today as the best arrangement, the wet-hull type model submarines biggist advantage is that it minimizes the problem of making water tight the mechanical outputs from the motor, servo, and actuator shaft. Those seals penatrating the watertight container within the hull - not the hull. Push-rods within the wet portions of the hull transmit servo motion to the control surfaces and other mechanical devices. Eleminating the water tight seal at the propeller shaft stern tube greatly simpliefies the design, installation, and maintenance of the running gear.
A wet-hull type model submarine lends itself to numerous control/propulsion/ballast system installation options:
The builder can simply install two or more transverse bulkheads within the hull to form water tight compartment(s) caped with one or more clear Lexan plastic access lids; he can construct a separate removable water tight box or cylinder; or the modeler may opt to purchase a pre-fabricated water tight cylinder like the one offered by our outfit, D&E Miniatures... hint, hint!
(3-6, Gene squatting over uncompleted GATO)
Most water tight spaces aboard wet-hull type submarines are formed by compartmentalizing portions of the hulls interior space. GRP sheet bulkheads are formed and glued into the bottom half of the hull, the top of the box or boxes terminating under the models superstructure -the upper portion of the box, exposed when the removable superstructure is pulled off, is capped with one or more sections of clear Lexan plastic sheet. Accross the top of the transverse bulkhead(s) and built into the hull sides within the boxed area are horizontal flanges that form both the foundation for access lid securing studs and a seating area for a water tight gasket that makes watertight the dry spaces when the lid(s) is secured in place.
(3-6B, AKULA's water tight box on table)
As mentioned, the water tight space(s) can be built separate and apart from the hull structure, securing it within the hull permanently during constuction, or making it a removable item, as I did with the pictured water tight box that was installed in my phas-2 AKULA model.
Two significant advantages are realized by the modeler using a removable control/propulsion and ballast system: Such an integrated system can be eazily swapped between different hulls. And the accessability of internal mechanisms makes makes for eazy adjustmen, repair, or replacement of system items.
In many wet-hull type installations, the propulsion battery, typically a sealed gel-cell, is housed in a wet portion of the model.
(3-8, Dave Copeland with OHIO and TYPHOON)
Another advantage of the wet-hull is its relatively light weight out of the water. Since the wet-hull does not have to resist hydrostatic force, only enough materials (fiberglass and resin lamination - in most hull kits) are used to assure structural integrity. And the wet-hull required only enough fixed ballast to assure good static roll stability - not the massive amount of fixed weight needed within a dry-hull to counter its considerable buoyancy.
(3-9, DK Models 1/48 Type-7 opened up to show WTC)
An important consideration while designing the internal layout of equipment and systems aboard the wet-hull type R/C model submarine is the need to place the ballast tank low enough within the hull so that no portion of it projects above the surfaced waterline. Any portion of the tank sticking in the air contibutes no buoyant force, therefore reprsenting un-needed ballast tank volume and wastage of Propellent gas or electricity.
(3-10, 1/96 STURGEON hull open and ready to receive WTC)
Several hull kit manufacturers are now recommending use of the WTC with their product. For example, Thor Design And Development recommends our WTC for both their 1/72 ALFA and 1/96 STURGEON R/C model submarine. Securing a WTC in a typical hull can be done with either 'Velcro' tape or rubber bands.
The only mechanical interface between submarine hull and WTC is a simple sliding connection between the propeller shaft(s) - a Dumas universal coupler, and snap type connectors for the servo output push-rods.