Hi Vance. I haven't fabricated the tanks yet, so I have estimated the total weights and volumes. The tanks are made of 12 gage 304 stainless sheets and the support frames are made of 2 inch mild steel pipe. The back plate is 3/4 inch steel plate which supports the outboard motor, two Minnkota rear thrusters, swivel linkage, and prop shroud/rudder assemblies. The tank will weigh approximately 124 pounds with a capacity of 86 gallons. The rear support frame ( 3 legged) and back plate weighs 82 pounds. I haven't weighed the motors etc. but a rough estimate for the motor assemblies, extra scuba tank, outboard, and miscellaneous parts and pieces should be around 180 lbs. The fiberglass rear fairing weighs about 60 pounds and is mostly 3/8 inch thick except where a little extra was used at areas of high stress like the hinge area, rear "bump" zone, and side "bump" rails where it's 1/2 to 1 inch thick.
The front tank will weigh approximately 118 pounds with a capacity of 54 gallons. The front fairing weighs 52 pounds and the tube support frame ( 4 legged) with heavy nose piece weighs about 79 pounds.
The larger capacity rear tank is needed to "float" the extra weight of the two thruster/rudder assemblies and spare scuba tank.
I built a scale model of the sub and used it to size and locate the tanks, fairings, weights etc. This proved invaluable as I had to increase the front tank capacity so the model would sit level while at the surface. This was a balancing problem that took quite a bit of adjustment so that the submerged balance (front to back) remained equal.
I will be making further adjustments on the balance using the drop weight and internal ballast weights to fine tune the front/back balance after I float the sub on it's first "wet test".
I'll have two hard ballast trim tanks inside the sub to further fine tune the buoyancy while diving. the "Lite" propane tanks look to be the best way to go for these as I can visually see how much water is iem, and they are corrosion proof.
I made the steel tube frames so I can fill them with oil or argon gas, and if needed the lower legs can be filled with a steel shot/oil mixture for a little more weight.
Here's a sketch of the rear assembly and if you click on the other pictures you can see the scale model and front tank as well.
The final configuration of weights/balance will become apparent when I float the sub during it's first "wet test"
This will determine the exact location/capacity of the drop weight and internal lead brick ballast.
The displacement of the pressure hull is 6750 lbs. I estimate a total lead weight around 1800 pounds.( inside lead ballast and exterior drop weight) Frank D.