Re: [PSUBS-MAILIST] Wetsub carrier water transport systems

[VBra676539@aol.com]

In a message dated 1/22/2005 1:59:01 PM Eastern Standard Time, lakins1@tampabay.rr.com writes:


> Dear Vance.
>  
> In theory your idea can work Vance, but practically it is very difficult. I have already considered exactly what you propose.
> First I would have to build a battery compartment into each hull and find a way to waterproof each hull's battery compartment. Now I have two battery compartments
> that might leak instead of one that are neither as strong nor as easy to seal as a pvc pipe with a screw on end cap with an o ring like my pvc pipe has.
> I would still have to have my air bladders in the nose and tail of the sub so they are above the center of gravity or else I could turn over if I inflated the pontoons underwater.
> Basically with what you propose I would be trading my pvc battery pod slung under the sub for two pontoons under the hull that would be much more difficult to construct a strong water pressure proof and leak proof
> battery compartment into. One option to your idea would be to buy oversize pontoons and actually put the pvc battery pods inside the able to be sealed middle of the pontoons and then only inflate the pontoons once I was awash on
> the surface to preclude turning upside down. Now that might work, but they would have to be pontoons that would accept a 12 inch pvc pod into their interior. The advantage of doing this would of course be that I do not
> have as much drag in the water with an exposed battery pod and a set of pontoons. In that case I would only have the pontoons exposed to drag. But what big pontoons they would be and then constructing all that AND 
> trying to pressure compensate the battery pod from within the pontoons would be more complicated than my current design idea. 
> The more I think about it the more I feel having a set of pontoons that the sub is slung under and disengages from for launching and then reengages and gets cranked up out of the water between them is the best way to go.
> No drag from the pontoons underwater decreasing both speed and battery power. And when I surface I can just float the awash sub between the pontoons sling the straps under the sub, crank it up out of the water and take off.
> I have thought about all kinds of options many of which I have posted already. But the more I think about underwater drag of pontoons permanently attached to the sub, and trying to find a way to constuct a battery compartment
> inside the pontoons that would be as strong and easy to seal as my pvc pipe, the more I become convinced that a detachable pontoon carrier for the sub is the way to go. It would be nice to have everything all in one, to have the pontoons 
> carry the batteries, even have an internal combustion engine located within the sub or the pontoons that could submerge and be sealed that I could use on the surface. But I am working with a 12 ft existing 1966 movie wetsub and trying to modify it
> with a battery pod, stronger electric motor and some way to get it to and from the dive site without speeding thousands of dollars on it. Someday I might build another wetsub from scratch out of kevlar wing tanks and incorporate all the things into it that I would 
> want from the beginning, but for now I gravitate to what is easy and simple. You can't beat the pvc with a screw on end cap and o ring for easy and simple and a pontoon carrier that the sub detaches from so there is no pontoon drag underwater.
> I will include a tow point on the pontoons at an advantageous position to preclude torque and wave slap as much as possible for the pontoon wetsub carrier but the tow boat will still have to take it easy towing my rig. 
> But thanks for your idea I always appreciate any input. Keep those ideas coming!
>  
> Kindest Regards,
> Bill Akins.


Bill,

I think you're making too much of the various complications. You're going to build pontoons, and battery pods, and a compensation system anyway. It just seems like a reasonable alternative to build them as a unit. If not, have a look at the LRPs they used so successfully in Hawaii. If you're dealing with surface chop, then submerging the pontoons on their own ballast system would let you garage the wet sub without banging it up.

I don't know which design you are using, but it doesn't take much to stick three or four batteries in a tube for 50 to 75 psi service. If you are going to use one, and that is certainly reasonable, then put it inside and sit on it, or do like Perry and shove the whole thing aft and get it completely out of the way. One nifty solution was to combine all this. We mounted a 3 hp thruster on the back plate of the battery pod, sort of like a DPV on steroids, and built it into the stern with just the prop sticking out of a faired section and the rudder and nozzle mounted to that. It worked (and still works) fine.

What kind of motors? The big Minn-Kotas give you a lot of push, and they are cheap. A couple of those ought to get you around pretty well. If you want a hot rod, try four. They put 4 of the 3/4 hp permanent magnet thrusters on the back of the Lotus wet sub, and it ran great. Batteries were 4 X 6volt 220 amp Trojans in an oil filled box with a couple of wraps of tygon tubing for compensation. Cost about 500 bucks start to finish and never caused a problem.

However, I still prefer the dry pods. Put a forced vent system on it, so that you can charge without disturbing the seals, and you'll be a much happier camper. I once took a ride in the PC-9 with a leaky pod. The fellow who was piloting on that dive was new, and had failed to switch the leak detectors on--didn't realize it until we were on the bottom. We got home without dropping the emergency weight, but it was a near thing, and cost us fifteen out of twenty-four batteries on that side. Sea water and batteries make green gas, and will turn the whole thing into a gigantic bazooka, so keep that in mind. It made me very cautious about my o-rings, I can tell you that. A piece of paper match across the seating surface caused the leak--a very small piece, I might add. It doesn't take much. 

Vance