Design for 300 Gallon Diesel Fuel tank

[Barnacle Bob]

I want to build two integral epoxy and glass diesel fuel tanks into the hull of my 1972 Bertram motor yacht. The original Aluminum tanks are leaking and I have to do a floor and guest cabin wall tear up to get them out and will build the new tanks in place. The tanks will be rectangular and will conform to the "V" bottom of the hull which is about 1 inch solid fiberglass laminate. I am concerned with the baffles and how they are designed for this size tank and where they go in and how many. Any other ideas or suggestions to improve the tanks over the orginal ones would be welcome. Comments? Suggestions?

[On Vacation]

I beleive this was a lengthy discussion on another forum about one year ago. If you are going to do this in place, then go ahead and cut the tops off and pattern them in place. Then you can check out the baffles and cut them out to install in the new ones. Then remove the old pieces and build them in place.

[mmd]

Hey, BBob. I've designed tanks 'till they come out my wazoo. The primary idea of baffles is to defeat the free-surface effect of the liquid in the tank, and the effectiveness of this is a function of the surface area of the liquid versus the roll period of the vessel. A bunch of time & money is usually spent of calculating this on big boats with big tanks because the optimum is to control the free surface effects (stability) with the minimum amount of labour & materials to create the baffles (cost effectiveness). A secondary benefit of baffles is to reduce the noise of liquid sloshing about in the tank. This part is easy - the more baffles, the quieter it is. Since quiet is usually very desirable in a yacht, lots of baffles are usually installed, making the expensive engineering calcs to optimize the baffle configuration redundant. You are left with the limiting factors of cost and a configuration that is able to be readily built. As a rule of thumb, I would suggest that a free-surface area of 4 sq ft is maximum, allowing a tank "bay" to be 16" x 36" or some similar configuration. The longer dimension should always be oriented fore-and-aft. The tank baffles must be able to drain to the fuel pick-up from the tank bays without puddling in the corners, and allow air to freely move from bay to bay at the top of the tank. You should also arrange the tank & baffles do that you can open an inspection hatch and reach in to every bay with a rag or a mop to clean contamination away. Also, if possible, make all fittings & nipples easily accessable for inspection and service. Although not a requirement, I usually spec all openings in my tanks to be on the top to eliminate all possibility of leaks at the tank penetrations. Lastly, tanks must be built so that water or other exterraneous liquids cannot puddle on the top of the tank - crown it slightly. If you have access to AutoCAD I can send you a copy of one of my tank drawings by e-mail to use as an example.

[On Vacation]

I beleive the last time he discussed this , he had no way to remove the old ones without cutting half the boat up and installing new ones. He had stated he wished to do it in place. I think from that point, he was looking at less work with less baffles.