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[Plastic - RIP]

When people make model battleships that are to be sunk in mock sea battle displays, is the sinking controlled in any way? I’ve watched a number of Youtube vids and the boats seem to go down randomly as they slip under the surface. 

Are there problems with the ship becoming unstable and capsizing as it fills with water?
I assume if it sinks upside down, the superstructure and fittings can be damaged when it hits the bottom.
 
Do people think about this and engineer accordingly or is controlled-sinking too difficult?
 
For displays, how difficult is it to do a half-sinking like having the bow under but the rest still afloat?
 
Are we going too far into submarine technology?
 

[Crossie]

 Quite easy to build, just make a simple valve on a floodeable container which is big enough to give the desired level of ''sink'' and operate it with a servo and you might need a simple pump. As you suggest, I would think that it might take a fair bit of time and effort to get the flooded section and some strategically placed buoyancy in the right place to prevent a capsize and in any event you would have to make sure that all the electrics were in watertight containers, and waterproof the boat interior, but you would not have to get too involved in submarine technology because your warships is now presumably no longer controllable. Our friends across the big pond go in for this sort of thing in a big way, co2 powered BB guns and all, which is a bit OTT really,

                                        Trevor

[Netleyned]

The lads in the Portsmouth Model Boats Display Team are
the ones to educate you Plastic.
Unbuilt Nautilus and his buddy's are the experts.


Ned

[unbuiltnautilus]

Expert here ..
We have sunk a fair number of models through the years, intentionally, some not so much!
1) SMS Leipzig. This was part of our Battle of the Falklands display. Built entirely from glass fibre, the RC compartment was underneath, accessed from below. The rest of the model was free flood, which introduced a stability issue as it filled with water. The model would roll over! This then had a keel weight, similar to a yacht fitted, a couple of inches under the hull. It used two caravan in-line pumps, one up, one down, to submerge and surface. Foam was fitted to control the sinking, stopping the model from fully submerging. Leaving just the props showing, and the breather tube above water to aid the pump up routine.
2) Merchant Ship. Built for the above display, this model is still going strong today. Designed to be blown in half in a spectacular fashion with a fairly small underwater charge. Once again all fibre glass, built as two seperate entities with an RC compartment aft and just foam forward. Big holes in the joining bulkhead ensure it sinks rapidly once 'separated'! Once again foam filled to limit the amount of 'sink'.
3) Drakes ship Revenge. Sinking sailing ship. Same system as Leipzig, also fitted with a large keel weight. Built as a waterproof 'submarine' up to deck level. The entire upper structure was separate. Now rebuilt as Chesapeake, sadly lacking its sinking component.
4) Merchant Ship. Same hull as the first merchant ship, but fitted with a series of pumps and valves, the builder was a proper engineer. Worked well but heavy. This model had bow to midships tanks with the aft area as RC compartment. Didn't need a keel, very controllable.
5) Whaler. part of our Vietnam Display back in the late nineties. This was 72" long, moored in place and operated via a long land line into a submarine style watertight box. This had a marine bilge pump to take it down, two hull mounted charges to go bang, and a three quarter height moon pool inside to speed up the sinking, titanic style, when water breached the top of said moon pool. Designed to sink completely, then be recovered by waders after the display, it was partly successful, mostly sinking early as the moon pool breached in the chop, and filled the model up before time! most embarrassing!
5) SS Ohio, see build thread elsewhere on the forum. This is designed to pump down to decks awash only, using two marine bilge pumps to pump down then up again. No stability issues so far, although at 100" long by 12.5" beam, unlikely! The fore and aft sections are mostly foam filled while midships is one great big ballast tank. Takes about 80 seconds to pump down and 100 seconds to pump back up. Its only been tried in our test tank so far, not out at 'sea'. All plywood and lots of waterproofing.
So, it can be a bit 'submarine' at times, with stability issues etc, but it seems to depend on the prototype being modelled. Low profile models mostly being fine, while the higher top hamper vessels needing ballast issues addressing. My suggestion; bath, hull, foam, water...have a play

[Plastic - RIP]

Cheers for that 

I'm thinking along similar lines with the hull divided into 2 parts with a bulkhead - the rear section with motors, radio, batteries sealed and watertight with the front half free-flooding with with an airbag that inflates to get up to the waterline and then vents to 'sink' down to decks-awash which is where any foam inside would support it from going any lower.

When there's less bouyancy and the hull is at an angle with stern up and bow down, I'm concerned that it might flip along the waterline axis and dunk the superstructure under. I'm planning of a boat around 55 inches so it can fit in the car.

I suppose the best way is to be able to get the whole deck on and off to be able to modify and muck about with the gubbins.

I'd like to have pyrotechnics to make it look like it's been torpedoed and I'll stick a couple of smoke generators in the hull to get it smoking well.

How difficult is it to get hold of and use pyrotechnics for this purpose? Any special licences needed?

[ballastanksian]

I believe so. I looked into it earlier this year as part of Geoff's ('Iron Duke' in Warships R&D) project. If you make your own maroons etc you need black powder and explosives transprtation liscenses, and certain fireworks need liscenses to store and operate. Modifying non liscensed fireworks to make them suitable for pyrotechnics may actually make them into liscensed items!

Then there's the issue of where you use them and insurance etc. We all know how some authorities can be especially if an occurance is not part of a recognised celebration such as 5th November

I don't think it is a great issue to apply for them providing your reasons are sound and you are showing that you are doing your homework. Like the silliest injuries thread elsewhere on this forum, you do not want to be showing us your smoke blackened stumps where a maroon went pop in your hand I remember seeing a hospital program including the case of a little boy who was mucking about and had a firework go off in his hand. It was a basket case with a large tear in his palm caused by the pressure of it detonating and some very red areas

[unbuiltnautilus]

If you keep the weight as low as possible in the bow section, with any foam as high as possible, possibly towards the centre bulkhead, that should reduce any chances of the model rolling uncontrollably. however, you can't beat trial and error!
As for pyrotechnics, mount them on the model and NOT in the water near or alongside the model..the effects on a hull not suitably beefed up can be quite terminal, speaking from past experience. however, this is exactly what I am planning to fit to SS Ohio. She is 3/8" ply skinned over 3/8" ply frames though. I shall still be taking big precautions with the design of the support for the charge..its all in my head at the moment

[Geoff]

To simulate a torpedo hit you probably don't need any pyrotechnics as a blast of compressed air from inside the ship would produce a satisfactory water column. Smoke generators can then simulate fire and smoke. Much safer and no Health and Safety issues.
 
If you don't believe me blow up a balloon and sink it in the bath with lots of weights then pop it! P.S. put some towels on the floor and ceiling!
 
Enjoy!
 
G