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[tony23]

Hi ,
     I have been offered an OTW German type VIIc Kit plus a Sherline dive unit all untouched as I know nothing about subs I have many questions if I'm going to go ahead and take it on. What's the quality of these kits I know the Sherline dive unit is probably the best but I cannot find any build forums on the kit can anybody put a link up if there is one, I understand this sub is nearly seven feet long I'm wondering what type of turning circle do they have and will I need a huge lake to use it. If any members have one or owned one can they give me some information I might need to check if I go ahead and take this sub on.

[Subculture]

Have a look here- http://rc-sub.com/projects/viewproject.php5?id=33

Also the OTW website http://www.otwdesigns.com/Type7/type7.htm

Also get yourself along to a Dive-in. Next one is 27th March at Brockwell Lido. I can't guarantee an OTW Type VII, but there will be Sheerline boats there, and probably a Type VII or two which you can see being put through their paces.

http://www.diveintomodelsubmarines.co.uk

Turning circle wise they don't turn on a sixpence, but with twin rudders, they're better than British subs of the same period. But at the end of the day , you have a long narrow hull, so they need a bit of space. They turn tighter underwater than on the surface.

My only concern with a Sheerline module in a 1/32nd scale Type VII, is will it have a big enough tank? I think you need about 1.5 litres to lift that boat to the correct waterline. Perhaps an Ohio module would have enough volume?

Chris Cloke would be the best person to answer that one.

Andy

[tony23]

Hi Andy,
              The Sherline unit is 30" x5" complete with the motors ect. thanks for the link I'll have read 

[Subculture]

It's the size of the centre ballast tank that is the important bit, as opposed to the overall size of the module.

[admiral donuts]

Its all a question of bouyancy,simply weigh the the the top half moulding and add about a quarter of this weight
I.E top deck is about,say two kilos plus half a kilo equals two and a half kilos ( the all up weight of what you want to lift out of the water) so you would need a module the will hold two and a half litres, one litre weighs one kilo,
Sheerline modules pump water to about one atmosphere so the science means that it will onlly be possible to half fill the tank
On filling the air inside the tank is compressed and the pump cannot force any more water in past the one atmosphere mark
this roughly adds up to a module that will need a five litre tank to enable the pump to deliver a two and a half litre load

This explanation has been greatly simplified and I am sure the more maths minded people could be howling in derision
but as a rough rule of thumb coupled with years of experience i have found that it works for me

Regards Donuts

[Mankster]

The OTW hull is pretty thinly laid up and it has a brass deck as well, which has little vilume As long as you keep the WTC low, 1L balast tank should be plenty.

[Subculture]

You can still use empirical methods to size your tank without breaking out the pocket calculator- trying to calculate the tank volume for a wet hulled Type VII isn't my idea of fun, and you would still have to add in a large 'fudge factor'.

The best and easiest way, is to submerge the boat in test tank add polystyrene foam below the waterline until the boat is neutrally bouyant, or until say just the top of the periscope is above the surface. Now add more blocks of foam below the waterline until the boat reaches the desired waterline.

Once your goal is achieved, calculate the volume of the blocks you had to add to go from submerged trim to full waterline- that is your ballast tank volume, add 10-15% if you want a bit of extra weight to go fully negative (e.g. bottom your boat).

Andy