Part 1
- Kapitan Bill Thomas

Kapitan Bill Thomas reveals all about successful model
submarine construction and operation.


U789 on the surface. Captain Fastidious points out that U Boats were not in the habit of sailing around with their numbers in large print, but the compelling reason for doing same is that in certain conditions, submerged, all you can see of the boat is its number.


All waterborne craft, from the dock tug to the majestic battleship have their own particular appeal to the onlooker. Of them all, the submarine must rank as one of the most fascinating and intriguing. The story of their origins and development, and their war record, is one of sudden disaster, incredible danger and hardship, extreme ferocity and unbelievable courage, with appalling losses being both received and inflicted.

The construction of a fully operating model submarine is both rewarding and infuriating! I have been building models of various types since I was about ten, a period of 40 years. My many critics would assert that I have learnt little of the art ever since and at times during the construction of U789, there have been times I would have agreed. It is, however, easily the most interesting, in fact compelling boat I have ever built, and it attracts far more attention than the average model. Many magazine articles dealing with unusual models leave large information gaps, often with respect to vital detail, and leave the reader interested but little wiser. The aim of this article is to describe fairly fully how a working submarine model can be made, using orthodox techniques, and specifying dimensions, layouts, components, centres of gravity, tank capacities, specialised construction methods where applicable, and everything else I can think of that is relevant, the tribulations as well as the triumphs are included. 

Having said this, the job is not a pushover. Good, sound building is essential. Like the full-sized counterparts, model submarines are more prone to accident than normal surface craft. I suppose the submarine is, to the model boat builder, what the helicopter is to the aero modeller: more complex to build, and more critical to operate. I am really aiming at the modeller who has a track record of say half a dozen successful surface models to his credit, who knows how to build a straightforward hull, and install the appropriate ironmongery. You do not of course need to be a genius, though I personally found this attribute useful at times. I really mean that most sincerely.

 On a more serious note, in case I forget to mention it later, lead acid batteries should not be used in the confined hull space of a submarine. These batteries give off hydrogen. Motor commutators spark. The combination is explosive, in the literal sense ‑ remember the airship Hindenburg. It can happen. Long‑time readers of Model Boats will recall the sad episode of USS Perch, which blew up, almost causing serious injury to her owner. Sealed lead acid batteries may be a different matter, and the manufacturer's advice should be sought if you think of using these.

It is sound policy, in the long term, to get materials and modelling accessories from your local shops and firms. If we do not support them and they go out of business, we are into mail order ( and Internet - Mayhem ) whether we like it or not. However, many modellers do not have ready access to such items, and they may like to know that the following firms do supply the materials and tools needed to build one of these models:

Glasplies;  2 Crowland Street, Southport, Lancashire, PR9 7RL ‑ Telephone: 01704 540626. Fax: 01704 537322;

K. R. Whiston; New Mills, Stockport ‑ metals, (available in small quantities) tools.
( Not sure if they are still around! – Mayhem)

Both firms publish very useful catalogues. The other items I used, motors, batteries, pumps and other hardware are all readily obtainable at most well stocked model shops. I have in the past found it annoying when reading model‑building articles to find the author recommending the use of exotic, ridiculously expensive or simply unobtainable items. I plead not guilty to such a practice. U789 is built with commonplace gear throughout. 

In addition to GRP materials, a radio outfit with at least three channels, and preferably four or five, you need the usual hardware, prop shafts, couplings, and a few elementary model engineering tools such as drills and taps, and there is of course your supply of tranquilisers, headache treatments, anti‑depression pills, your nerve tonic and your fortified health wines, most of which are available through your family doctor. What's that? You don't need these things. Well, we'll soon see about that, after you've made a start. 

Having made the decision to become a submarine commander, you now need to recall the principles employed by submersibles to dive and surface. This is accomplished by two methods in conjunction, flooding or emptying ballast tanks, and using control surfaces, hydroplanes, which are similar in principle to the control surfaces of an aircraft, that is, they tilt the craft up or down, as the case may be. The diagrams show this. We can then consider these principles, and how they can be adopted or adapted to suit model purposes.

Into the cellar. The periscope, 'lain. diameter snake tube used for linkages, tells the depth of the boat. Note that even in slight chop, the boat becomes difficult to see just under the surface.

Working principles of a conventional submarine.
Nuclear submarines are a totally different concept, and we are not considering them. A conventional submarine is understood to be one which runs on air‑breathing diesel engines on the surface, and on electric motors powered by batteries when submerged. The batteries are recharged by the diesels, which can be arranged to rotate the electric motors, which then act as dynamos, and produce current instead of consuming it. To copy this practice in a model would be unnecessary as well as difficult. It means carrying two power plants around, only one of which is propelling the boat.

 Conventional submarines spent most of their time on the surface, at 'Surface Trim,' with the hull well out of the water, Fig. 1-1. In this trim, they were efficient sea boats, and could cope with very bad conditions. Their keel cavities were filled with iron bars, and this, together with the very small superstructure, gave tremendous stability.

Fig 1

 Diving was achieved by two principles in conjunction: (1) Ballast tanks, with a capacity of, typically 150 to 200 tons of water, would be flooded, and this brought the boat down to 'Diving Trim, ie. with the deck awash.
Fig. 1-2. The boat now had little or no positive buoyancy, and could be thrust down by a flow of water over its control surfaces ‑ hydroplanes ‑ which tilt the submarine in a manner similar to an aircraft's elevators. The angles of the planes are as shown in Fig. 1-3.

Some controversy exists about these angles, and there has been discussion in the club; people who should know say that the angles shown in Fig. 1-4 will also take a boat under. Both methods work. My own experience is that the first method is the better. Fig. 1-4 takes the boat under at a much shallower angle, and it takes a lot longer. I use Fig. 1-3 Having reached the required depth, the boat is then levelled out Fig. 1-5, which is a lot more difficult than it sounds, .

To surface the boat, the planes are angled as Fig. 1-6.

The main ballast tanks are supplemented, on full size boats, by trimming tanks, typically of 30 tons capacity. As the voyage continues, fuel, stores, torpedoes and other ammunition are expended, and water is admitted to the trim tanks to compensate for the reduction in weight. In theory, it is possible to trim a submarine to complete neutral buoyancy, i.e. where it is the same specific gravity as the water, and thus it should be able to 'hover.' In practical terms, however, a submarine is always either rising or sinking, albeit very slowly, when not moving backward or ­forward. A pint of water will cause a full size submarine to either sink or swim. In practice, a boat is able to fully control its depth by trickling along at well below walking pace, and in any case, the density of the water itself varies from place to place and affects the trim of the submarine. This applies on lakes as well as oceans. Some parts of Tynemouth lakes are colder than others, and it shows when you are trying to keep the boat at a steady depth. Impurities, e.g. salt, also affect the density of the water of course, and with it the trim of the submarine. 

From the diagrams, you may think, that all you do is set the hydroplanes to the dive position, then when you get to the required depth, you level out and finally apply up hydroplane in order to surface. Well, that may be true in theory. In practice, you are attempting a most difficult balancing feat. Though, under ideal conditions, the model may seem weightless in the water, it still has mass, and therefore momentum, up and down as well as backward and forward. Thus when you move the hydroplanes, they take time to overcome momentum. When the bow starts swinging into the required angle, you have to check well before you reach it, by putting on opposite plane angle at the right amount, and at the right time. You always have to be a couple of moves ahead of the submarine, because of the delay in response to the controls. Visualise a baulk of timber, about 4ft. long by say 4in square, balanced like a seesaw on a pivot at or near to its centre of gravity, free to swing up or down. Thus, the fullsizers used compressed air to blow the water from their ballast tanks. Modellers can use air, or other gases, such as CO2 or freon. For reasons which I will outline later, I discarded this idea. Instead, I opted for Mode 1, and subsequently progressed to Modes 2 and 3 of operation. Each has its pro's and con's.


Mode 1
Is the simplest. There is no diving trim as such. The flow of water over the planes alone takes the boat down. But a brisk speed, hence powerful motors, high current drain and low endurance are involved. The method is simple and reliable. Submerged control is difficult, that is, keeping it on an even keel ' due to the buoyancy of the boat and the relatively high speed needed to overcome the buoyancy.

Mode 2
Requires smaller motors, and an all round slower, more realistic operating speed. Conversion from Surface Trim to Diving Trim is achieved manually, that is, by clipping a metal bar (the ballast) to the keel of the model. The idea works well, though having to bring the model to the side to remove or replace the ballast bar, depending on whether you wish to motor round on the surface, or run submerged, gets a little tedious after a short time.

Mode 3
Ballast tanks are fitted, fore and aft. Electric pumps flood or drain them by radio control, though on the surface, normally taking about 45 seconds, with the boat on the move if required. Having tried this mode of operation, I would not consider going back to Modes 1 or 2.

U789 under way, under the surface and under control. The most beautiful part of this photo is the tiny wake from the periscope, called the feather.

I tried all three modes. They are all viable propositions, and I plan to describe each one in sufficient detail to enable a capable modeller to produce a satisfying working model. The same basic format ‑ hull, watertight compartment, propeller shafts and tubes, planes ‑ is common to all three. Thus you could start with a Mode 1 boat and proceed to Modes 2 or 3 without having to go back to square one, and build a new boat each time.

Imagine this is your submerged model. Visualise that you can tilt it, by radio, by shifting small weights, situated about 6in. in from each end, just as the hydroplanes are positioned. You can't shift them much, only say, 3in. each. This is the nature of the problem. You have to strive to keep the bulk of wood horizontal, by shifting the weights. You would most likely find that until you had a fair amount of practice, that the timber would tilt inadvertently very easily, and that once it starts tilting, it goes out of control, i.e. your model has either surfaced contrary to your wishes, or it has hit the bottom. It's quite a tough problem, but like all tough problems, you feel all beautiful inside when you start getting it right. You don't sail submarines, you fly them, odd though it may sound. Welcome to the Third Dimension. Both delight and despondency await you.

Decision time
Which submarine? I opted without hesitation for a Type IX U Boat. To the modeller who enjoys hull making, submarines are truly glorious subjects, the pleasing fishy shapes, the bulges, blisters, bumps and lovely knobbly bits and pieces are all there to be enjoyed in a leisurely fashion. But as a prospective submarine commander I wanted a 'now' boat, with clean, simple lines. The knobbly boat could wait for a while. So I came to the Type IX for more than one reason. The size had to be right, that is, it had to fit into my bath at home. This is a vital consideration. There is a great deal of testing, both of equipment and of flotation, there is balancing, mostly done by trial and error, and all this is time‑taking. Moreover it needs to be done in comfort, lest you are tempted to skimp the job. You need good light. You can't do sensitive checking with the wind howling round your jowls. Then there is transporting the model. My models have to share an average sized car with a family of four and a rather large dog with a low IQ. Hence it must fit in the luggage compartment. Those readers with swimming pools and pantechnicons of course can think bigger. I felt 46in. would be about right.

A large bonus is the shape of the Type IX. Not a. bulge in sight. Just a long, lovely sweeping curve from the shark like stem to the long slim stern. If you have never planked a hull in your life, you couldn't find a better one to start on. No blocks at bow and stern to carve. The shape is classic, with tumblehome nearly the full length. I built mine, inverted, on a plank about 4ft. long by 6ft. wide by 1 in. thick, without really trying. Then I made a fibreglass mould from the finished hull. Once you have the mould, you can turn out hulls of immense strength, inexpensively, for a couple of hours of working time. A 30p tinlet of No. 53 Humbrol paint can be added to the resin mixes. This is a dark grey colour with a satisfyingly sinister dull sheen about it. The hull could of course be made of wood, or ABS or metal, depending on personal preference. I have not regretted my decision to use GRP (Glass reinforced Plastic or Fibre-glass - Mayhem).  

About the drawing / plans.

( Plans -MM/471 are no longer on www.modelboats.co.uk – Mayhem).
At this stage it is essential to point out that the drawing is not a truly authentic scale representation. The radio installation depicts valve type gear, which puts the date of the drawing back to the days when information about U‑boats was scanty. The designer has grappled gamely with the problem within the limits of the knowledge and state of the art available to him, but there are inaccuracies, principally at the stern end, below the water line. The drawing can be very largely corrected, without too much difficulty by acquiring the book U‑Boats in Action, by Stern, Publisher Almark/ Signal/Squadron, www.amazon.co.uk or www.whsmith.co.uk etc. – Mayhem) This volume is full of photos and information about U‑boats, and the chapter on Type IX boats, which comprised a family of five sub classes, contains line drawings which enable the careful modeller to modify the drawing so as to satisfy everyone but Captain Fastidious. Scale considerations, carried, as they sometimes are, to the point of near fanaticism, do not play a very important part in my own philosophy. If a model looks good at a range of five or ten yards, on the water, where it belongs, and performs well, then I am satisfied. People who build for the judge's table are probably better equipped than myself for the hassle that all too often seems to plague such ventures. To each his own.


U789 shown in mode 1. The slots in the deck are over scale and would create havoc for the crew. This fact caused the author many sleepless nights, however the important‑thing is to let the air escape when diving.

Non‑Scale features of the model
The primary aim of the exercise was to finish up with a working model which would cruise well on the surface, dive well, remain controllable when submerged, and surface on command. Scale authenticity, while desirable, was pushed gently but firmly into second place. Simplicity was 'in,' complexity, where not essential to the actual operating of the boat, was 'out.' With this in mind, the following modifications (and probably several others which I don't recall at present) were featured, either to simplify and strengthen construction, or to improve performance. Despite them, the general consensus of opinion is that the model is quite a decent representation of a submarine.

The stern end below the waterline was redesigned to give improved access to the steering linkage.
A‑brackets were not included in the prop shaft assembly.
The conning tower was slimmed down and positioned in a more forward position.
The lower gun platform was omitted. (Needless drag submerged).
The number on the conning tower was not full‑size practice.
The free ports were enlarged. The deck slots are enlarged.
The propeller guard is not true scale.
Only one rudder is used. On balance I regret this; I would like a better turning circle.
Fore plane guard is not true scale.
No anchor or housing is incorporated at this stage.
The tank vents are not scale.
Propellers are not true scale.
The periscope is elongated.
The profile of the stem is modified.

"Ho!" says Captain Fastidious, "what right has he to talk of Type IX U‑boats when he has wilfully scorned authenticity in this callous manner?" Well, these are not so much alterations as improvements! U‑789 is what Type IX boats should have looked like. Indeed, it was truly fortunate for the Allied cause that Germany did not have men of my technical superiority designing their boats for them, or the Battle of the Atlantic would have taken a very different course. I really mean that most sincerely. Anyhow, there never was a U‑789. Numbers 780 to 790, due to be built Wilhelmshafen, were all cancelled.

The watertight compartment
The construction of this compartment is shown in the diagrams. The bulkheads and hatch rim should be tacked in position with dabs of top grade adhesive. I prefer Stabilit Express (www.pattex.de/ - Mayhem ), which sets hard in 20 minutes. Naturally, the hatch rim should by this time have been tapped and fitted with the screws, of which 43 were involved in my case. Great care should be taken not to deform the hatch rim when locating it in position, by bending or twisting it. After the glue has hardened, gel can be applied with a short stubby brush, from the interior of the compartment, to make a substantial fillet right round all the joints. When hard, fit the gasket and hatch cover, and tighten the nuts, as evenly as possible. Ideally, a little torque wrench would be used, but I haven't got round to that yet. Over tightening will damage the gasket. Test the compartment by plugging the end of the bilge pipe, immersing the hull in water, and blowing down the vent. Hopefully, no bubbles will appear.

The next items are the propeller shafts and tubes, 8in. long. They should be drilled 3/32" and have a ˝”  length of 3/32" brass or copper tube soldered into them, 1 ˝”. from the motor end. This is so a length of silicone tube can be fitted, down which you can blow a quick squirt of WD40, or LPS1 or whatever your favourite water disperser / lubricant may be.

To completely prevent water entering the boat through the propeller tubes is not easy, unless of course you pack from solid end to end with grease or petroleum jelly, in which case a lot of drag is caused. Initially I used oil, but even a single drop of this escaping causes a noticeable oil slick on the surface, and makes a bad impression. I tried emptying the tubes altogether, except for regular spurts of WD40. Water entered at the rate of lee per minute, i.e. a teaspoonful every five minutes. Only just acceptable. Then I injected a few cc's of petroleum jelly. The current drain, both motors running, props out of the water, rose from .4 amp to .8 amp. I. settled for this as a reasonable compromise.

Water does seep in, however, in very small quantities. I used 35mm three blade red plastic props. They did the job well enough, though they didn't pull very well astern. The red plastic irritated me after a while, and when I came to fitting smaller motors to U‑789, I made a pair of two bladed brass props, 30mm diameter. I like brass props, because you can alter the pitch easily to suit your motors. Captain Fastidious stands back in amazement. Two‑bladed props! On a IX Type U‑Boat! What heresy is this? Well, the fewer blades a propeller has, the more efficient it is, in my experience.

Bottom.. the plug for the GRP mould in wood. Centre is the left side and top the right side of the mould, with the hull shell still in place. Two halves are bolted together when the hull is being made.

Restricted space

It goes without saying that the alignment of the shafts and motors is crucial. I didn't get where I am today by not doing everything I can not to waste valuable battery power overcoming useless friction. I wish I had a quid for every time I have heard someone feeling sad about the rotten performance of his battery, when all the time the culprit is the appalling coupling and its equally appalling alignment. Time spent on alignment means extra time on the lake. Apart from the rather restricted space in the watertight compartment, there are no special problems. Items should be mounted as low as possible. There is not a lot to be gained by fastening stuff in so that you practically need dynamite to get it out. Every single item I installed, every single one, I later found it necessary to remove or replace. Modern adhesives are very good when properly used, and you don't have to slosh it on like jam. My motor mounts, for example, have a dab or Stability Express about the size of a drawing pin head, in each corner, it's all you need, provided the surfaces are clean. The same goes for servo mounts. I wouldn't be tempted to bond servos, motors etc., directly on to the hull. Go 'getability.' You should be able to shift any item out of the hull with a screwdriver or a tubular spanner in about five minutes or less. 

But you must not have stuff sculling around loose inside. Battery packs must be gently but firmly restrained from any movement. Finally, build light. You can always add extra weight, if necessary, to the keel, where it's going to do the most good. Getting rid of surplus weight is a tougher proposition altogether. 

Kapitain Bill Thompson.
( Part 2 coming soon - Mayhem)

U789 Mode 1. Stand / tool tray is a must. Two screwdrivers, one crosshead and one normal. Two syringes ‑ one to apply petroleum jelly to seal hatch ‑ this was before a gasket was fitted ‑ and one to suck water out of bilge via tube on right, silicone plugged with a 1/8" diameter.

Tubular spanner is a must, but use finger tight only without a Tommy bar. Tweezers are useful. The tool in front is a 48A socket grub screw wrench for the large number of grub screws. Jar contains 68A nuts. All photos by the author. 

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