Need help! How to calculate the tank sizes that will fit.

[Randy brandon]

Hi! I'm trying to find out if there is a calculator that will help me find the max size of a fuel tank I can fit in my boat. I cut out my old tank in sections and could bearly pull out the last section of the tank (59"l x 13"h.) I'm looking at some tanks that are not as long and taller and some that are longer and not as tall. Only thing I can come up with is to make a cardboard model to test sizes. Figured ther had to be somthing online, no luck tho. Any help would be appreciated!
Randy

 

[TANSL]

Welcome to the forum. There is no such calculator as there is no calculator for the maximum size of the owner's cabin sofa, but any CAD program, having the shapes of your boat and knowing the internal structure, will allow you to easily determine the size of the tanks. If you have that information, I could help you.

 

[Randy brandon]

Ok I have numbers. So the part of the tank pulled out is 59"l 28"w 13"h. The opening I cut in the deck is 30"w 57"l. The old tank was 90"l 28"w 13"h. From the bottom of the tank hold to where the tank was rubbing when I pulled it out is 16"h. The tank hold aft wall is 18"h and 35" from the top spot that was rubbing top of the tank.

 

[Barry]

and if you do not have access to a CAD program

Take the measurements of the side cross section view, draw a scaled down version on paper. Using the same scale, draw a profile of a tank that you are considering, and cut it out of a light cardboard, and see if it will
slip between the cross section of the opening.

There is a chance that you could slope the front of the bottom of the front of the tank upwards to permit the tank to slip between the obstructions. You would lose some volume from the ramp, but you would be able to
extend the length of the tank for additional volume. Certainly the CAD is a better way to go

Also the short bulkhead in front of the batteries could possibly be cut to allow a longer tank, then after the tank is in, re fibreglass it so long as you can rebuild this to assume its strength contribution to the frame.

Is this a diesel or gas fuel tank?

 

[TANSL]

and if you do not have the measurements of the side cross section....

 

[Randy brandon]

Good ideas, thanks. It is gas

 

[Randy brandon]

I'm looking at plastic tanks, so I have sizes in mind. Think I'm going to do some cardboard cutouts and see what fits.

 

[Barry]

I'm looking at plastic tanks, so I have sizes in mind. Think I'm going to do some cardboard cutouts and see what fits.

The reason that I asked is that FOR DIESEL only, I have seen single large fuel tanks removed in sections through small openings and as many as 3 fuel tanks of 1/3 the size, installed with hoses at the bottom of the tank
connecting three tanks. When I saw it, my first reaction was that it would not meet ABYC guidelines but evidently it does for DIESEL only

Should you decide to be environmentally compliant, evidently there are new
fuel fill and vent requirement when installing a new fuel tank. I think that it was IKE
a senior contributor here who was involved at some level with the Coast Guard compliance regs. I don't have all the details but you could PM him for info or perhaps find the thread as there were other learned contributors

 

[Ike]

I don't know if he would have to meet the EPA standards, but I can check. If he could buy a stock tank that would fit it would probably have all the necessary fittings for the EPA fuel systems.

He might want to have a look at Boat Building Regulations | Boat Fuel System https://newboatbuilders.com/pages/fuel.html

So let me see if I understand what he is trying to do. He wants to find a tank that will slide into the space under the sole through that opening. The advice to remove the bulkhead between the batteries and the tank compartment is good. It would give a much bigger opening and allow for a much longer and higher tank. Then replace the bulkhead.

 

[Ike]

I asked the folks at CG HQ about this. I had it right. The boat would be grandfathered. So As long as he maintains the current fuel system he's ok. But, if he wants to upgrade to the new standards that's good too.