Fuel sloshing in flat tank

[druid]

Hi

I had a problem on my new-to-me Ontario 32 where the engine quit after the boat had been bounced around, and there was air in the fuel lines (and anyone who's bled a Yanmar knows that's a Pain In The Backside!).

Now, what I figured happened was that the fuel sloshed around in the tank and the inlet standpipe sucked air. Now, the tank was about 1/3 full, but it's VERY flat (80 cm x 40 cm x 20 cm deep). Do you think that was the problem (the engine ran fine for 2 days previous in quiet water and afterwards for a day and ever since). Have others had that problem with flat fuel tanks?

I DON'T think it was dirt getting stirred up because there was air in the lines - if it was dirt the engine would have just starved out. I suppose another possibility was a loose connection that flexed when I hit the wakes and allowed air in, but since the engine runs so well otherwise I don't think that was the problem.

Thoughts...?

druid
"Wind Drift" Ontario 32

 

[tommays]

My tank is only 14 gallons and has the minium of ONE baffel to help slosh

 

[alexco38]

An idea for you.

Some people use a "day tank". A much smaller tank hanging higher than the main and able to gravity feed to the engine. Of cause, the engine return goes there. You may have to rig a pump of some kind to fill the day tank from the main.

I think it is a beautiful concept. You can see the crap before it gets into the engine or filter. The main tank stays cool to reduce algae growth because no warm return fuel goes there.

 

[Stu Jackson]

I think you're onto something with the flat tank and air ingestion. You might want to consider getting an electric fuel pump, makes bleeding a LOT easier.

But you really need to avoid having the engine die because of the lack of fuel due to the shape of the tank. Have you discussed this with other similar Ontario 32 boat owners?

The day tank idea has great merit, you need an pump anyway for that, to get the fuel from the main tank to the day tank, and with a little design ingenuity, you could use one pump for dual service. Need to be careful to avoid using up the day tank on a short cruise and putting yourself right back where you started.

 

[alexco38]

Tug boat uses day tank.

http://www.cruisersforum.com/forums/f54/day-tank-for-diesel-fuel-17950.html

Say your trip typically last 5 hours, A day tank of 6 hours will be sufficient. You can even rig some tank monitor to sound an alarm it it gets too low and you have to reload it.

When the day tank if above the engine, it would solve your problem.

 

[kloudie1]

Druid, is the pickup on one end and one side? If so it becomes very easy to get air in the pickup .. The trig shows very small angles of heel to get the pickup uncovered with 1/3 tank full..
Something to consider.. if you have the room above the tank; put shims (or equivalent) under the tank to have it tipped toward the fuel pickup.. 3 or 4 cm higher on the side/corner furthest from the pickup would help a lot!..
I think you've diagnosed the problem correctly.

 

[Bill Roosa]

Just plumb the pick up to a small aux tank right next to the main tank that is connected at the tank bottom (the pick up) and tank top (to vent bubbles) and then draw fuel from there. If the aux tank is not as tall then any bubbles will get sucked in and float to the top of the aux tank and back to the main.
No extra pump or floats required.

 

[Bill Roosa]

Think of it as a "sediment blub" for air

 

[LloydB]

So could a second "sediment blub" installed upside down be a solution? just asking