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david f
dgp1957
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    Darnell RN S class plans

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    dgp1957
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    Darnell RN S class plans - Page 2 Empty Re: Darnell RN S class plans

    Post  dgp1957 Tue Sep 30, 2014 1:23 pm

    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
    John Wrennall
    John Wrennall
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    Darnell RN S class plans - Page 2 Empty Re: Darnell RN S class plans

    Post  John Wrennall Tue Sep 30, 2014 8:23 pm

    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
    david f
    david f
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    Darnell RN S class plans - Page 2 Empty Re: Darnell RN S class plans

    Post  david f Thu Oct 02, 2014 9:55 am

    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
    John Wrennall
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    Darnell RN S class plans - Page 2 Empty Re: Darnell RN S class plans

    Post  John Wrennall Thu Oct 02, 2014 4:34 pm

    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.

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    John.
    david f
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    Darnell RN S class plans - Page 2 Empty Re: Darnell RN S class plans

    Post  david f Fri Oct 03, 2014 5:51 pm

    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?
    John Wrennall
    John Wrennall
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    Darnell RN S class plans - Page 2 Empty Re: Darnell RN S class plans

    Post  John Wrennall Fri Oct 03, 2014 7:40 pm

    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

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