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    ballast and trimming

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    dgp1957
    AMS member

    Posts : 42
    Join date : 2012-12-30

    ballast and trimming

    Post  dgp1957 on Sun Dec 30, 2012 1:39 am

    hi folks i have just bought a darnell s type submarine
    all ready to go bar ballast and trimming, can anyone give me some hints?

    david
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    david f
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    Age : 68
    Location : Cumbria

    Re: ballast and trimming

    Post  david f on Wed Jan 02, 2013 5:09 pm

    Have you access to a test tank or will it fit in the bath.
    Basically you need to get the sub level on an even keel at neutral buoyancy, with the ballast tank full.

    Foam and lead can be used in combination if the boat is not very stable. I like using lead shot mixed with silicone rubber for the final fitting but don,t be afraid to place weights or foam pieces externally with ,say, rubber bands until you get close to a trial balance.

    David

    dgp1957
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    Join date : 2012-12-30

    Re: ballast and trimming

    Post  dgp1957 on Sat Jan 05, 2013 10:10 am

    thanks David, I have access to a test tank at my local club in Greenock. The sub sit level when the deck isnt on, but heels over to starboard when the deck is put on also the stern slips under when I apply the compressor to dive so I think that the water is coming into the tank area then the weight of the water is building up in the back of the tank causing the stern to go down first, does that sound right? so today Im going to try adding some foam to the stern on the upper part of the sub and we' ll see what happens then :-)

    Tom(ADMIN)
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    Re: ballast and trimming

    Post  Tom(ADMIN) on Sat Jan 05, 2013 11:31 am

    Might be worth mentioning to keep foam above the water line and lead ballast below the water line, otherwise one will be fighting the other. Oh yes...been there and done that, and wondered why I couldn't get the boat to sit level for more than ten seconds.

    dgp1957
    AMS member

    Posts : 42
    Join date : 2012-12-30

    Re: ballast and trimming

    Post  dgp1957 on Sat Jan 05, 2013 5:00 pm

    David finally got the level right (I think) however still listing to starboard would I be better adding weight to the bottom of the keel or add some foam to the starboard side above the waterline?
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    salmon
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    Re: ballast and trimming

    Post  salmon on Sat Jan 05, 2013 6:37 pm

    As long as the cause of the listing is static (fixed and not moving like a LiPo battery shifting) then move the weigh slightly to the port. You can add more weight and/or foam to counter act the listing issue as well. Testing, trial, and a bunch of patience.


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    david f
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    Re: ballast and trimming

    Post  david f on Sat Jan 05, 2013 8:19 pm

    As everyone has said, move the weight to port or starboard to counteract the list. (Don't tell anyone but I put Velcro on the underside of the model to easily fix and move small weights last minute at the pond side!)

    Foam and weight are used together to counteract listing. (Keep the weight as low as possible and the foam as high as possible (Metacentric height is the technical term) However you don't want much foam above the waterline because that volume has to be displaced by the balance tank (Remember Archimedes!) Keep the superstructure displacement as low as possible for the same reason. And the superstructure weight down to prevent listing)

    Oh dear, a lot of factors interact hence Salmon's suggestion for trial and error and patience!

    It may console you to know that small trim problems tend to be masked once the model is underway at a reasonable speed. Twin screw subs like yours also have the advantage of not listing because of propellor torque (turning forces).

    Have fun!

    David

    dgp1957
    AMS member

    Posts : 42
    Join date : 2012-12-30

    Re: ballast and trimming

    Post  dgp1957 on Sun May 05, 2013 9:02 pm

    hi guys still no success as yet. The sub is an old Darnell kit, it has a large chunk of lead attached at the bottom of the hull, was that a standard thing or would I be better cutting it off and starting from scratch?

    david
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    david f
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    Re: ballast and trimming

    Post  david f on Mon May 06, 2013 10:55 am

    I take it you still have a list to starboard?

    You have something heavy to one side.

    You may have to move that fixed weight, sorry. How is the overall waterline at the moment?

    David

    dgp1957
    AMS member

    Posts : 42
    Join date : 2012-12-30

    Re: ballast and trimming

    Post  dgp1957 on Mon May 06, 2013 4:54 pm

    Hi David its , as they say here in Greenock, "dain ma heed in" lol I'm just going to cut the lead from the hull strip it out and start from the begining :-)

    dgp1957
    AMS member

    Posts : 42
    Join date : 2012-12-30

    Re: ballast and trimming

    Post  dgp1957 on Mon May 06, 2013 8:27 pm

    Had some success tonight I took the cover off the middle section that is free flooding with two aerosol cans that hold air and are used to expel water (I think), had three bits of lead glued to the hull side I removed them and now the sub sits nice and level in the tank. Just need to get her diving and surfacing now. ;-)

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