U789
Part 2
- Kapitan Bill Thomas
 


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


 


The watertight compartment

Radio gear these days is of good quality in the main, but the radio is only as good as the linkages. The rods need careful thought in this model, which is fairly full of equipment, and they need careful routing to avoid binding and chaffing. I used ball and socket joints throughout, these are one of the greatest advances in model making since the introduction of the left handed screwdriver in 1832.

I used 1/8,in. diameter brass rods, Where these pass through the bulkheads, rubber bellows by SHG were used, made for the job. I died a little when I heard the price, about 75p each ( About 3.50 if you can find them now-a-days - Mayhem ), but they really are very good. I coated mine inside out with petroleum jelly On a routine cheek, I discovered that one of them had slipped off its bulkhead spigot. I fitted a lip round it, as shown, and the problem has not recurred. Fig. 10.


Finally on the subject of sealing the compartment, there is the main hatch gasket. Initially, I used no gasket,  just applied petroleum jelly to the rim with a syringe, a-la cake icing. It never leaked a drop, but was a little messy. I tried making a gasket from what I thought was cork sheeting. It turned out to be micro thin cork facings on a core of paper. I discarded it. Now I use a form of floor covering, 1/8in thick. Half the thickness is a smooth black rubbery material, bonded to a layer of quite dense plastic foam. There is nothing special about it, there is no trademark or anything, so I fear I cannot specify exactly what you should seek. I have seen very similar material in shops, though faced with decorative colours and patterns, (Lino Vinyl?! - Mayhem).
 
I have mentioned acrylic sheet, for the hatch cover, I usually think of it as Perspex. It is funny stuff. It is brittle, and has poor resistance to shear and torsion stress. You have to be careful when working it. However, its compressive strength, which is what interests us, is adequate. Moreover, it is transparent; you can see what is going on inside the boat. When I laid up the glass fibre (GRP - Glass Reinforced Plastic - Mayhem)  for the hull, I also prepared sheets of GRP for the hatch rim and bulkheads, but acrylic sheet could also be used for these.

The vent tube, whose primary function is for blowing down, so that the boat can be checked for leaks, or if the bilge tube plug is removed, for expelling water, also has a secondary function. The tube I used, silicone tube, 1/8in bore, also houses the receiver aerial, which is thus kept dry. It can be clipped to the hatch top, or led up through into the conning tower, depending on which position gives the best range. Long radio range with these boats is not too important. Even at surface trim they tend to blend in to the background with their low profile and grey finish. You probably won't want more than 60 yards or so range.

At this stage I would like to record my appreciation of the ideas and suggestions that have cropped up from my club colleagues, the aerial idea just mentioned is such an idea. However, the next guy who suggests that I should motorise my 6BA tubular spanner for bolting down the hatch cover may come to a sticky end. (The 43 nuts take 4 1/2 minutes to bolt down, 2 1/2 minutes to take off).

The advantages of being a member of a club when tackling awkward projects are manifest. I have the honour to be an Honorary Member of Tynemouth Boat Club, established 1893, and I have found that if you have a technical query, there is almost always somebody who can shed light on it, or who knows someone who can. I know there are loners, who stay away from clubs because they feel they may be regimented or over controlled, but I think they miss out on a lot, in all sorts of ways.
 


Layout of watertight box - Mode 1


Mode 1
It is unnecessary for a submarine to be trimmed down from surface trim to diving trim in, provided there is a strong enough flow of water over the planes to enable them to exert enough effort to overcome the buoyancy of the model, and thrust it under the surface. The method has the merit of simplicity to commend it. I fitted a pair of Hummingbird 20 motors, honourably retired from front line service in my fast electric boats, but still with plenty of life. To drive them, I supplied 6 'D' cells (4 amp/hr) in series, giving a voltage of 7 volts. 35mm 3 Blade Graupner props were used. Ten amp micro switches controlled the set up. Three channel radio was used; one for steering, one for switching the motors, and one for the aft panes. The front (or as we experts say, the 'fore') planes were not radio controlled, but could be locked in any desired angle by 4BA socket head grub screws long. 1 hoped to find what the optimum angle was, and then leave it. Gibbering with excite merit, I placed the boat in the water, and switched on.


The boat tore across the water like a scalded cat. I applied dive to the planes, the bow dipped, the boat attempted to dive, but changed its mind and tried a slow roll instead, despite the contra‑rotating props, then it gave up and lay helplessly on its side with one propeller threshing uselessly out of the water. Part way through the sub merging process on a submarine, the centre of gravity and the centre of buoyancy momentarily coincide and the boat is unstable. Normally the boat goes through this condition without disaster. A C-of-G  which is correct on the surface may not be correct during diving, as I discovered. Screeches of hilarity from my loyal mates rang out. Strong men fell down, helplessly convulsed with laughter. I ran behind the clubhouse and wept bitterly.


Later, chewing my anti‑stress tablets thoughtfully, 1 diagnosed the causes of the disaster. The boat was too powerful. The motors needed controlling. The centre of gravity was not low enough.


I removed one of the cells, reducing the voltage to 6v. I fitted a Tamiya speed controller, a straightforward wiper job the car people use a lot, and I flitted a block of lead (21bs.) into the keel. 1 am somewhat prejudiced against speed controllers, having seen them proved unreliable and wasteful of power. To be fair, the Tamiya product was well made and proved infallible during the period when I used it. It did heat up, and in the restricted space inside the watertight compartment, it warmed the air, with the effect of pressurising the boat slightly, as indicated by a very slow succession of small bubbles which emerged from one of the propeller tubes after 10 minutes or so. The result was, very little water entered the boat. Using a small medical type syringe, I rarely sucked more than 3ccs of water out of the bilge after a 25 minute run. On the debit side, there was condensation, which on balance is probably more likely to affect radio gear than actual seepage of 'solid' water as opposed to a 'mist' type dampness. I did not however experience any radio problems, The rudder servo, if mounted between the couplings, needs protection from fine spray thrown off by centrifugal force.


With this Mode 1 format, I progressed steadily At first, I had the planes set far too coarsely. This did not show up to a great extent when diving. Incidentally, when Your boat slithers under the surface for the first time, taking with it all that precious gear that you can't really afford, you may feel that this is one of the more interesting' moments in your modelling life, followed by the moment when it surfaces for the first time. U789 initially used to surface in the most dramatic manner. leaping out of the water for nearly half its length rather like a Polaris (the missile not the sub). On one occasion, distracted for an instant, I lost sight of the boat. I panicked. It was a brisk mover, it could go a long way in a short time, or get well and truly entangled in weeds, I might never find it. I applied full power and put the planes to surface. I screened the lake, and took a quick swig of nerve tonic. Nothing. Then, about 4 feet away, U789 did its 'Jaws' act, leaping half out of the water literally under the nose of a small infant peacefully fishing. She squawked in terror, and fell down backwards. Her net went one way, and her jar, which contained about 24 million sticklebacks, toppled into the pond, doubtless to the relief of said sticklebacks. The male parent was adjacent. He was the human equivalent, at a rough estimate, of a heavy cruiser, and I was clearly outgunned. He advanced. I picked the kid up, gabbling profuse apologies. However, heavy cruiser was not hostile. He thought U789 was fantastic. He soothed his little daughter. When they had gone, I swaggered arrogantly into the clubhouse, "Ho! Ho!" Did you see the clever way I made it look like in accident?" I said. That's what you've got to have, when you're in submarines, like me. Charisma!


Later, after a few Phyllosans (??? - Mayhem), I reviewed the state of the game. Using a 'Y' lead con connected to another servo, I hooked up the front planes. Thus I had two sets of planes working off one channel. It could be done using only one servo with one very long linkage. However, I do not like long linkages, especially in a congested hull. I drastically reduced the movement of the aft planes down to a total of about 1/8 in. The aft planes, though smaller than the, fore planes, are much more sensitive placed as they are directly behind the propellers. The fore planes required a much coarser movement, about 25 degrees each side of neutral. Control improved, diving and surfacing were easy. Constant depth keeping was very hard. The boat, like, all conventional submarines, was not designed, and was the wrong shape, for good underwater performance  especially at the high speed required to keep U789 under the surface. These boats probably spent about 90% of their time on the surface in order to cover the often long distances to their patrol areas. A boat is either very good under water or very good on the surface.


I don't think you can be excellent at both, Nuclear submarines, with their roughly cylindrical shape, are ideal for almost permanent travel under water. On the surface I bet they are pigs to handle. So U789 had a problem, At slow speeds, when it might be more manageable submerged, it would not stay submerged. It had too much buoyancy. All the. time it was fighting to get back to surface trim. There was disharmony. The other, major snag, was the poor endurance.

The two Hummingbird 20's were very greedy, and after about 25 minutes of non-stop diving and attempts at depth keeping, the battery pack showed signs of tiredness. When this happens, the boat should be stopped forthwith. There is no future in bashing your meads. If you stop for a chat, with the boat stopped now and again, unjust mosey round on the surface at half speed, the endurance stretches out to just over an hour or even more, as the battery recuperates during rests. But this was not for me. To me, a submarine should spend most of its time where it belongs, underneath.


Round about this time, I received a most humiliating experience. I was accompanying  U789 round the lake, chewing nerve pills, juggling the sticks, and perspiring freely, and I was joined by Lieutenant Martin Young. whose own Type IX U boat was nearing completion at this stage. He is an accomplished aero modeller. He watched for a minute or two, by which time I was a cursing demoralised wreck. I readily handed him the transmitter on request. After about half a minute of sussing out the system he dived the boat. What is more, he kept it dived. Eventually, about 80 yards up the lake, the boat hit something, lost speed and surfaced. The longest underwater trip I had achieved was about 30 yards. Needless to say, I  was totally consumed with jealous rage and fury. I tried to hit him with my plastic binoculars, but my eyes were full of tears and my aim was poor. He went off, laughing. I recovered, after a long pull at my flask of Wincarnis (??? - Mayhem), and felt goaded into trying harder, eventually with some success. But that boat was tricky, submerged. Something had to be done to improve the endurance, and the submerged handling. On the surface, U789 was lovely, and still is. Tynemouth lake is about 70 yards from the North Sea, and about 70 feet above it. It gets rough when the wind is in the north, and it is no place for fair‑weather models. When its rough, its a waste of time diving the boat, you simply can't see it, but it's great motoring around on the surface. The boat sticks its long slim bow into the chop with surgical ease. No big bow wave or clouds of spray. When other models of similar weight (101bs.) are 'stetting' around like ping‑pong balls, U789 cruisers around with what looks remarkably like disdain.



U789 in calm conditions, seldom seen on Tynemouth lake.
She generates an impressive bow wave as she majestically glides through the water.
(All photos by the author.)


Competition Time

During the trials of U789, I entered a Club Scale Competition, for steering. The turning circle of the boat was about 20ft., which I was completely unused to. As a result,  by the time I was halfway round the course, it was clear to myself and everyone else that I was making what we experts call a 'bally‑toot' of the job. Unable to stand the shame any more, I dived the boat, and after a plausible interval, surfaced near the landing stage, in what I felt was a very good attempt at cheating. I claimed that I had negotiated the rest of the course faultlessly, below the surface, and I claimed the appropriate points. Raucous screeches of delight greeted this claim, and the judge laughingly disqualified me, despite my tears and the tantrum I laid on. I sulked and darted venomous glances at various people, but nobody noticed, so I swallowed a few anti depression tablets and went off to sail the boat on my own. Some weeks later, I had more or less got the hang of steering the boat, and I entered another of these steering competitions. The 5in beam enabled you to go through the gates at angles you would never normally consider, and the boat motored through the chop and stuck a couple of clear rounds in. This was enough to win the competition. I loaded my boat and the rest of the gear into my car, and checked that the engine would fire first time. Then I swaggered back to the clubhouse. They were drying their models, and clearing up. I positioned myself just inside the entrance, and intoned the following remarks:


"Kameraden, please try not to feel too  devastated and inferior as a result  of the crushing, humiliating defeat U789 has just inflicted so convincingly upon you all! It is no disgrace to be thrashed by U789! You all struggled to the best of your limited ability, with your crude, primitive boats, and it is not your fault that you were annihilated by the highly sophisticated, superbly designed U789 which incorporates the most overwhelmingly brilliant technology, not to mention my own dazzling navigational skills! I hope you will all persevere, even in the face of the invincible display of genius I have arrayed before you! It would be appropriate, when you wish to speak to me, to stand to attention, and address me as 'Herr Kapitan' "... At this stage, they rushed at me with the intention of removing my trousers. But my escape had been too well thought out, and I was off like a shot. That's how we U Boat Commanders are. Schemers, crafty as a barrow load of weasels. I was in the pub, and halfway through my second Ribena before they started trickling in."


Fore and aft planes setup.


Manoeuvrability
T
he original turning circle of U789 was about 20ft., and I found this a little tedious. I had installed the prop shafts well apart, so that I could fit large propellers if needed, As a result the prop wash missed the centrally located rudder to a large extent, causing a poor turn. Learning from my mistake, the builder of the next Type IX to appear at the lake, Martin Young, installed the prop shafts as close together as possible as the 30mm dia. propellers would allow,  which is quite close. His turning circle was 1Oft., a considerable improvement. Stung by this, I fitted twin rudders to U789, and this tightened the turn to about 1Oft. also. I was reasonably content with this until Herr W. Carpenter, who commands a large Type VII U Boat, also at Tynemouth, demonstrated his independent motor control. With one motor astern and one forward, the model slowly spun in its own length. If I hadn't seen it I wouldn't have believed it. My lower lip trembled. I only had 4‑channel gear. But I fought back the tears and pretended I wasn't impressed. How could I compete with this? It is an easy matter to enhance a turning circle by having the rudder servo cut out one of the motors. I wondered if it is possible with a little skulduggery, not only to stop a motor this way, but to reverse it. I bet it could be done. Three functions for the price of one! I smiled happily, and started U789 into a mock attack on a 575 (Model yacht), He saw the periscope, and spun out of the way, with a harsh cackle of triumph. My smile was replaced by a scowl. These tea‑drinking Englanders, they think they are so clever. I wonder if I could get U789 to lay a minefield. I bet I could. I chewed my Iron Jelloids  thoughtfully.....!


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