Graupner Shark Submarine

Here are some of the  factors that influenced my choice: 

It was small enough to carry without risking a hernia or back problems. I actually built a box that carries both the submarine and Tx, which fits under one arm. 

It was very maneuverable and did not need a massive area to operate in. I'd noticed that many of the larger static divers have very large turning circles and you often see models with the rudder enlarged by a piece of Perspex glued on. We have a fairly small lake. 

Cheaper than a Static Diver,  actually not by much in the end! 

Preparation for sailing was minimal. 

The only high tech additional equipment is a bicycle pump.

Controls  

Three controls are required which I arranged as follows;  

Right Stick:

Forward to dive, back to surface. Operates only the Forward Hydroplanes.

Usual Left and Right for Rudder

Left Stick:  (Ratchet) 

Throttle - Electronic Speed Control  (ESC)

Although the instructions recommended specific equipment for the batteries and ESC I could not easily find the suggested parts.  I ended up faxing a 1:1 drawing to Model Power Supplies (a UK Supplier) who made up the Drive and Rx batteries to fit the space available.  I did consider operating  with BEC but the balance of the submarine is dependent on this weight in the bow and I'd rather carry battery power than lead.  

The ESC was a difficult problem, size was critical, and normal ESC's would just not fit. I finally bought a RC Line "Sea Rover"  15Amp  ESC which appeared to fit with some clearance for the cooling fins. Having hot heat sinks touching a plastic hull would not keep the water out for long. There is only one motor, a SPEED 500 driving the two contra rotating props through a gearbox. With my final set up I'm getting about 50 minutes duration.  

A common question raised is about the aerial.  Many articles talk about keeping the aerial insulated from the water but Graupner just use a straight uninsulated piece of stainless steel wire.  To date I've never had any problems or doubts whatsoever.  As a word of caution, however, the model has never gone deeper that the bottom of our fresh water lake, say about 3ft, and never further away than the middle of the lake (~40ft). Max range is not yet an issue.  If it did lose the signal "theoretically" the motor would stop and the model surface, this has, fortunately, not yet been tested.  

Initial checks  

The usual marine test facility (bath) was used for ballasting the submarine statically, but it was of no use for checking a dynamic submarine which needs plenty of forward motion to dive.  Ballast supplied with the kit consisted of thin sheet that could be hand moulded to the required contours for fitting.  I erred very much on the side of caution with the amount I used, which proved to be an error.  The amount supplied is probably about right. This was also the time that I checked whether the radio worked with the aerial under water and it did. No leaks were found.  

Operation

Removing the main hatch is a pain which I really did not want to do just to switch the radio ON/OFF. I ended up cutting a circular hole under where the dummy crew hatch was located and glued a small tube underneath at the bottom of which are two reed switches in parallel both outside the sealed hull, but with the wires passing through to the inside.  Two reed switches for redundancy, as they cannot be easily replaced. I wasn't sure of their current rating and the Rx battery is also charged through them. So far they have worked well and I don't have to disassemble the hatch to switch ON/FF. To switch on a magnet attached to a dummy hatch cover is pushed down the tube, and is held in by friction.  

Remember the High Tech bicycle pump mentioned at the beginning, this is the point at which it is needed.  There is a bicycle tire valve fixed into the sail (conning tower or sail or fin) and just prior to sailing I do 2 pumps to slightly pressurise the interior.  Whilst I was originally sceptical it has proved very efficient. One side benefit is that if I see bubbles coming from the prop tubes I know it is time to repack the tubes.  I'm still working out what to use in the prop shafts, oils are too thin and some greases are not shirt/household/wife friendly, so I've been packing them with Vaseline. I pack a plastic syringe (from a model steam exhibition), no needle!, with Vaseline and warm it in the microwave, remove the prop shafts, and inject the Vaseline down the tubes.  It seems to work and lasts for a couple of months before I refill. I accept the losses due to the friction in exchange for no water up the tubes.

The initial trial, what a disaster!  High speed aeration of the lake, 15 minutes of battery life, and not much else. It was fairly clear what the problem was, as soon as the bow went down under the action of the forward dive planes the stern rose lifting the props out of the water. Experimentation was called for, it is almost impossible to fit any ballast aft of the centre of gravity, without a major disassembly, so I started by bolting some small lead discs  to the lower fixed fin. This had almost no effect. I next made some larger sized rear hydroplanes  which are fixed but can be adjusted manually, this also was not successful. Finally I succumbed to the suggestion of more internal ballast on the centre of gravity.  

Wow, what a difference!  It would now easily dive with very little forward motion and was highly manoeuvrable.  Control felt strange to begin with and underwater the controls are very sensitive.  The extra dimension means you have to be very careful with the speed underwater as the dive controls and speed are inversely proportional i.e. More speed less hydroplane down angle is needed otherwise the sub dives to the bottom VERY QUICKLY.  With less speed more down angle is needed to remain submerged.  Obviously a point is reached where if the speed is reduced too much then the sub surfaces regardless of hydroplane position.  The sub can be trimmed to sail "hands off" under the water but turning too tightly after a straight run tends to slow the sub and make it rise so a little down plane is needed.  

There have been a few comments about how the sub banks over when turning under water.  This is due to hydrodynamic effects on the sail whilst turning, as a submarine does not have to bank to turn like an aircraft.  I understand that this banking also happens on the full size submarines and can be very severe.  

Later Developments and Common Questions

A problem with submarines is that you cannot see when the prop becomes entangled with weed, plastic bags etc. A submarine seems to be much more likely to pick up these items as they tend to float just below the surface.  I suspect that at some point I damaged the ESC with a bag on the props, as while trying to sail I got some very erratic responses and the motor stopped.  The sub was pushed in, not easy as there are no right angles to push on, and a submarine tends to go under when pushed.  

I replaced the ESC with  a new design, M-Sonic-Marine, from Westbourne Models, Bournemouth, UK, and everything seems to be working again.  

The trim decals have still not been applied. The model tends to travels nose down under water. It probably need everything removing and the ballast repositioning. However, until I have to strip the inside for other reasons I'll probably leave this for the moment  

Graupner do offer some optional extra's of a Bow Light, Depth Regulator, and Water detector. However, I've got no idea how these could be fitted in with the present layout. I'm sure a better modeller than myself could probably fit them.  I've since talked to the owner of the model I'd previously seen and he has created extra room within the sail. On mine most of the sail volume is free flooding but it could be sealed off without causing any stability problems.  

How deep will it go?  I've got no idea, I suspect 6 to 8 ft would be the maximum and the only sure way to know would be to send it down until it reached crush depth, but then it wouldn't be coming back up!  

How fast will it go? Again I've got no idea.  Its fastest speed is underwater and my reactions are simply not quick enough (age?) to control it due to the hydroplane sensitivity.  

Well that is it so far, in spite of the problems, I've had loads of fun, which is the whole point and I've learnt a lot.  This is definitely not a project for  the scale enthusiasts or for beginners but it has certainly given me a lot to think about and it is definitely not as simple as many people might think.