Triming a submarine

[jimdavis]

Good day all
I need some advise on trimming out a new submarine. I am working on OTW Surcouf and yesterday I added lead to the bottom of the sub to bring it to waterline. it was floting level and jst over a 1/2 a tank of ballest (water) she will submerge. The problem is that she wants to roll to the right side as looking from the rear. My battery pack is under the WTC as I tried to keep the weight to the bottom. This is the first sub that I have done, but I have been building RC,models and trains for45 years. I have tried to keep the deck as free from weight as I could. I think I added between 8 to 10 lbs of lead to get to the waterline, with a good portion to the bow and stern. any ideas?
Thanks for reading and any input would be helpful
Have a good weekend
Jim

[Guest]

Re: Triming a submarine

Sounds like you've done all the right things.

This is a a OTW dive module too I take it?

The boat will be far more sensitive to trim once submerged, so either you need more weight in the bottom to lower the centre of gravity further, or perhaps you just need to offset the existing weight over to the portside to counter the roll.

I'd be surprised if you need to add foam- OTW tend to design the module with sufficient buoyancy so that you don't need to add extra floatation.

A member on here has built one of these up already, so he should be able to give you some pointers.

[jimdavis]

Re: Triming a submarine

Thank you for the advice I will try as you suggested. its is a OTW WTC
thanks again
Jim

[JWLaRue]

Re: Triming a submarine

I agree with what Andy has stated. For an OTW boat with an OTW dive module, start by only adding weight down in the keel area. That'll get you 90-100% of the way there.

I've built/completed three OTW boats and find that very little to no foam is required. Sometimes small pieces are needed above the waterline in the bow or stern to get that perfect submerged trim for pitch. The one exception for me is my Type XXIII. With that tall conning tower, it needed a little help with roll stability. I ended up placing foam right at the waterline to make it more stable.

-Jeff

[Guest]

Re: Triming a submarine

Must say that a Surcouf is an ambitious subject for a first sub. Here is a video I digitised and uploaded to Vimeo-

https://vimeo.com/20679846

Apologies for the somewhat poor quality of picture, I did what I could with it to clean it up after conversion but the tape is third or forth generation VHS.

If you look at it from 12:21 onwards you can see Bernie Woods Surcouf. This is one of the original hulls the OTW kit is now based on, which I think was mastered by Maurice Rickett. OTW have retooled the boat, and added some extras that weren't supplied with the original kit.

Nick Burge made a set of firing guns, which you can see firing in the video (they fire blanks, BTW), and adapted the ballast system from a gas type to a recirculating compressed air system.

If you look at about 13 minutes you can see something poking out of the bottom of the boat- that's the main battery, a lead acid cell. I understand that was done to get the boat stable, perhaps to offset the weight of the metal gun up top.

Fortunately, this boat has survived, and is currently under restoration. It's undergone a complete refit, including a new hybrid ballast system using a vented tank blown clear with a diaphragm pump (a la snort), and a trimmed down Engel piston tank which will allow the operator to trim the boat for neutral buoyancy.