Darnell RN S class plans

Guys would this suffice for a ballast tank:-
http://www.ebay.co.uk/itm/FUEL-TANK-nitro-or-gas-petrol-500ml-rc-model-boat-with-clunk-pickup-500cc-/361061600190?_trksid=p2054897.l5662#ht_1692wt_1161

David

Hi David.

Are you going to Blank off the  fitting on the bottle side to give a pressurised tank
OR set the tank up as a vented system?

If the former, then check that the thread is sufficient to withstand pressure.

500cc with a pressure system = 300cc actual (say) which is 300gms weight,
will this be enough to overcome the boats buoyancy?

regards

John

Hi David, I don't think that tank could stand the pressure (about 300 KPa or 3 atmosphere) if you want to use the pressure tank system. It is a very good question so I have just started a thread on pressure ballast tanks in the Beginners section.

David

You might find this installation amusing but it works reliably.
The 150cc home made clunk tank is filled with a lorry windscreen pump (24v running on 12V) and the capacity is enough for a static dive. The air from the tank is displaced into a normal rubber balloon which helps to evacuate the water later and keeps the water from entering the WTC.
The balloon should be as thick as possible for safety, get mine from a party balloon shop.
Its due for renewal before the next sailing season.

I will stress that this is used in my first sub (over 10 years ago) when I didn't know any difference.









John.

Nice one John! I think I like that best of all the "baggy" & "bladdery" solutions. It will pressurise the WTC though and how do you stop the balloon from bursting if you run the pump for too long?

easy peasy, the balloon is inserted into a toilet roll tube (not shown in photo) which gives it a physical dimensional restraint to about the size of a conference pear which does not create too much of a WTC pressure. The boat is ballasted to dive with the tank 2/3 full so pump is switched off via the old Mk1 Eyeball system and the compressed air does give a fail safe effect.

I do recollect that the balloon would not have been used if I had found a bigger bottle.

John