GB36 Single screw fuel capacity

Boat is about 1985 single Lehman and need to know the individual capacity of the two fuel tanks.

The original tanks in our GB36 were 150 gallons each. There were three of them, one on each side of the engine room and one across the back. I don't know if the third tank was due to the boat being a twin. The tank configuration and capacity changed some through the life of this particular model.

According to the owners manual for GB36-790, also a twin, the tank capacity was 400 gallons in two, 200 gallon tanks. I don't know what year 790 was built. Our boat was built in 1973 and is hull 403.

This single has only two tanks, and we are beginning to think it has two 170-gallon tanks.

Look around on the tank. Usually the tank builder sticks a tag on it with lots of data, including capacity. Tag might be in hard to see place.

rgano said:

This single has only two tanks, and we are beginning to think it has two 170-gallon tanks.

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It's been a few years but I remember them having two 150 gallon tanks.

But now that I think about it, some build years it could be 400.

Our '88 GB36 single has 2 200 gal tanks if they are original. Suspect yours is the same.
Roger

Deck filler caps are typically stamped with the tank capacity.

Dream on, not for this old dog.

I previously owned 1984 GB classic hull #697 with a single. Tanks were 200 X 2 = 400 gallons.

Ski in NC said:

Look around on the tank. Usually the tank builder sticks a tag on it with lots of data, including capacity. Tag might be in hard to see place.

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I think that's a requirement but it might not have been back then. If the tanks are rectangular, it's a pretty simple task to measure them and figure out the capacity.

WesK said:

I think that's a requirement but it might not have been back then. If the tanks are rectangular, it's a pretty simple task to measure them and figure out the capacity.

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There is no requirement to have you deck fill caps marked with the tanks capacity.

That's what I have advised the owner to do, and he said he will do so this morning. Then I will calculate for him the ten-gallon increment rise in his sight gauges for the two sections of the tanks so he can place level marks with amount remaining next to the gauges like I did on my own GB42 and this Mainship I now own.

Capt.Bill11 said:

There is no requirement to have you deck fill caps marked with the tanks capacity.

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You are correct but that's not what I posted. I posted about the tanks themselves, not the deck fill caps. That was someone else.

We currently have a 1980 GB 36 single screw and there are two fuel tanks on board. Both starboard and port hold 212 gallons each.

Besides, one a four-tank boat like my GB42, one could conceivably mix the caps if they were not chained to the fills. I realize that is a stretch, but....

WesK said:

You are correct but that's not what I posted. I posted about the tanks themselves, not the deck fill caps. That was someone else.

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Your right of course. I mis-interpreted your post.

Measure the tanks. THe length, the depth, the height.

277.8 Cu inches is one Imperial gallon
231 cu inches is one US gallon.
You will be close.

You could allow for an estimate of tank wall thickness to get even closer.
If the tanks are tapered then that too can be estimated by measuring.

And after careful measurement, the winner is........ 200 gallons. He will mark the tank sides alongside the sight gauges at 25 gallons for the bottom five inches of the tank which have an angled portions out toward the hull sides. Then it is 1.5 inch interval marks to mark off each ten gallons above that point. Now he can accurately check fuel economy.

fuel

Single 135 Ford L. Both sides replaced with new aluminum tanks 2 seperate tanks per side. Total 350 gallons.

rgano wrote;
" Now he can accurately check fuel economy. "

Only if you want inaccurate numbers or if you run for days never touching your throttle lever. No way to accurately account for all the running below cruise speed. Many think this is the way to do it and probably because of the very low fuel burn numbers it always produces ... for obvious reasons. Soon he could be telling us he burns 1.5gph. And of course that will indicate he's running his boat on less than 30hp.

Terry,
That's a very desireable boat.