FC fuel tank

I’ve had my boat for a number of years now, and I try to consume my fuel before filling again. There are two questions/comments that I have:

  1. I can never get more than about 9 gal of fuel into the tank, so I suspected that my vent was clogged, trapping ulage and preventing a complete fill. I replaced the vent fitting and checked the hose. All is clear, and I seem to have have a full tank. I decided to verify the advertised 15 gal tank capacity, so I measured it. It is a trapezoidal solid, 10 in fore/aft, 9 in high on the aft side, 13 in high on the forward side, and 27 in wide. That volume computes to 2970 cu in or 1.72 cu ft, which is about 12.8 gal. I guess that the spec is not correct. This is a comment, and it is related to the next question.

  2. Here is the question … does anyone have an issue with getting air in the fuel system when heeling 25 - 30 deg on a low tank? I have this recurring problem, and it may be tank design related or I may have an air leak in the feed line, where it allows the fuel to drop back into the tank when the fuel pickup is exposed to the ulage. I am working on finding that leak, and I suspect a dubiously installed electric bleed pump that came with the boat. I will look there first, but I was wondering if anyone else experienced this problem.

Hi Tom,
My fuel tank measures 10 inch fore/aft, 10 inch high on aft side, 13 1/4 inch forward and 27 1/2 inch wide. This calculates to 3196.9 cubic inches or 1.85 cubic feet . Roughly calculates to 13.8 US gallons. This is still a bit shy of the posted 15 gallons. As my boat is FC39, Sam L Morse might have made some changes to the fuel tank since yours was build. I can not comment on your apparent airleak problem. My feed line is directly amidship near the bottom of the deepest part.

FC 39

I have not yet had this problem, but I think it is indeed possible for the fuel system to pick up air when the tank is low on fuel and the boat is heeled. Simple geometry says that in such a situation the fuel pickup could become “dry”. If the engine is started in that situation it would suck air up into the fuel system. It might also be possible that fuel in the system would leak back out if the fuel pickup was “dry” and thereby introduce air into the fuel system even without starting the engine.

ron walton

John - I used some rough measurments, but 10 in on the aft side would probably not fit in my hull. It was tight at 9 in high. Bet they are the same tank … probably did not go to a different supplier with hull numbers that are so close (mine is #33).

So, you have #39. I have done some business with Bob Baltierra, and he uses your boat to check the fit for my upholstery. Thank you for the use of your boat. I may have him make a winter cover for me this year, so you may be seeing Bob soon.

What do you know about the water tank below the engine? I assume that it is about 20 gal, but I can find no info on that particular tank. Ronco must have made it special for the FCs.

-Tom Frenock
FC 33

Ron -

Thanks for your input. I agree about sucking air while heeled, but my situation is where we sail, then with the boat relatively level, we start the engine and run it until the stall. Bleeding always works to get running again.

Someone suggested that my experience sounds like when you put your thumb on a soda straw and pull it out of the drink. Keep the thumb there and the liquid stays in the column within the straw. If you put the straw back into the drink, no problem. But, when an air leak allows the column of fuel to drop back into the ulage (caused by the 30 deg heel), there will be air in the line, just waiting to move into the fuel pump and cause the issue.

Some PO installed a small electric bleed pump in line, between the tank and the prefilter. The connections on the pump look suspicious, so I will concentrate on that area. I have a long wait until my fuel level is low enough again, though. I checked in here just to see if there were any other folks with a similar problem.

Will let you know what I find when I attack that fuel pump.

-Tom Frenock
FC 33


I would agree with Ron’s assessment that due to the design of the tank you could be pulling air when the fuel level is low and you are heeled far over.

I recently replaced my fuel tank. The new one measures to the specs listed by John, and also matched my old tank. It is a very tight fit, but no where does it rest on the cork lining. When filling for the first time I was able to put in 13.5 gallons with some room to spare, so it would seem very close to the rough calc of 13.8 that John mentioned. I had the tank made with a sight glass so I could easily monitor the fuel level. It also has a clean out/inspection plate on top, and additional pick up and return valves for a polishing system. All fittings and barbs were made from aluminum, and all pick ups incorporated Al shut off valves.

I haven’t measured the capacity of the water tank but plan to soon. There is a SLM drawing of it on the last page of what I believe is the second Falmouth Cutter Newsletter (June 1981). If you don’t have that let me know and I would be happy to send it to you as a pdf. After 30+ years I have a feeling that this will need to be replaced soon and from what I can tell involves pulling the engine to get the tank out.

Patrick Riley
FC 03

Thanks, Patrick. I too would agree with Ron, but I definitely waited until I was “level” before starting the engine … I sail as long as I can. I have some kind of air leak, and I think that I can fix it.

I will take more-precise measurements and compute my volume again. I appreciate all of the input from other FC people. There aren’t many of us, but this forum is clearly active. I must spend more time looking at the new posts, now that I have had my boat for about 5 years … I can’t believe it has been that long.

Another fuel topic … I have been keeping a sailing log on a spreadsheet. It is easy to compute fuel consumption, and I seem to be consuming 0.15 - 0.19 gal/hr. I have this spread because of having only two tanks of fill-up. Do you other FC sailors have a similar consumption? My engine is a Yanmar 1GM10. Just curious.

Hi again,

Diesel fuel might behave differently than water in a straw. But I am not sure. I am just saying that if the bottom of the fuel pick up becomes “dry” diesel fuel might leak out. But I would also definitely check for an airleak up stream.

The FC I have with an inboard had several leaks in its fuel tank. It appeared to me and several other people that to remove the tank intact without some disassembly of the boat was unlikely. By disassembly I mean removing a cockpit drain seacock or the bottom of the storage locker above the quarter berth. We chose to disassemble the tank with a saw.

Also, according to the Sam L. Morse Co. FC video, the fuel tank is put in before the deck is put on. So, if it is possible to remove the tank without taking the boat apart, that’s good news.

Regarding the water tank beneath the engine. The polyethylene version is a Ronco tank. Number 342, I think. Note that the drawing in their catalog seems a bit more asymmetric than the actual tank. I measured the volume of the one I installed in my FC and found it holds about 23 gallons. Ronco claims 27 gallons, but their measurement ignores the thickness of the tank walls and the constraints the bilge sides put on it. I timed the filling of a 5 gallon jerry jug and then transferred the fill hose to the tank and timed filling it. By using a very slow fill rate, I think I got a pretty accurate estimate. Note that I filled the tank through the inspection port and did not run it over, so a bit more water could probably be put in it if the deck fill is used.

ron walton

Ron -

Yep, I found the same one online (Ronco RH-342), and it is defineitely not our tank. Thanks for the info on your measurment. Your method is accurate enough for me. BTW, that method of measurement is a really good idea. With excess pressure on the supply side of your metering nozzle, there should be no effect of the hose length in timing your fill. I assumed that I had 20 gal, but 23 will be a good number for reference. I was interested, because I eliminated my forward tank group in the upper bilge to make room for house batteries.


You are correct- “some disassembly” was required to get the fuel tank out. I only had to take the cockpit drain seacock out, so not as bad as it could have been or looked. It did require a lot of boatyard yoga- patience, deep breathing, and getting the tank and myself oriented in the correct position to remove it. I did not need to remove any of the wood work of the storage locker or take anything else apart. The boat was already on the hard at the time and the seacocks needed to be greased and rebedded any way so it wasn’t too much of an issue.

I was very pleased with the folks who fabricated the new tank and the price was reasonable for the extras I wanted. They can work in stainless or aluminum and just about any size or shape is possible. If anyone is interested send me a PM and I’ll pass on their contact info and that of another fabricator who also gave a good quote.


I also have a Yanmar 1GM10 and seem to average about 0.2 gal/hr. That is in relatively calm conditions with the engine at approx 2250-2500 RPMs. I don’t want to get too far off subject here so I’ll send you a PM later today about your house battery location and some other things.


Hi Tom,

I checked the Ronco water tank number online and the #342 tank is the tank installed beneath the engine of Falmouth cutters. At least for those boats that have polyethylene water tanks there. Ronco’s drawing is wrong. I know the latter because I installed one of these tanks in an engineless Falmouth cutter which had no tank there. The #342 tank I installed did not look exactly like the drawing, but it fit perfectly.

ron walton