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johnharch 11-22-2011 11:26 PM

How low can you run your fuel tank
 
A quite a few years ago, in a different boat, I ran into problems with the fuel sloshing in the tank in rough water and the engine sucking air. The tank at this time was still half full. I was able to sail the boat in with no problem, but it has left me with a lasting fear of running the tank too low.

I am planning some exploring in the Inside Passage next summer where the winds will be fickle and the fuel stops scarce. Has anyone experience this sort of a problem? How low have you run your tank? I have a 35 gal capacity, but I'm wondering how much of that I can count on when calculating my maximum run time. I have never run this boat below half a tank.

John

Norstar 11-23-2011 08:00 AM

John, We typically never let our PSC 34 run less than 1/2 tank but have on occasion let it go to 1/4. Never experienced any problems with pick-up tube sucking air and we always run our engine while entering our inlet (Little River, SC) from offshore which can sometimes be quite spirited. Remember the tanks V shape has the fuel more concentrated in a smaller space near the bottom as opposed to a uniform shape all the way down in the bilge. Maybe this helps?
John S
PSC 34 #201
Norstar

AlLorman 11-23-2011 10:50 AM

I successfully ran the tank on my 31 all the way to empty (not intentionally, of course). The water way pretty flat, though.

Al Lorman
PSC 31 No. 55, Ann West
Annapolis

svjobeth 11-23-2011 12:55 PM

We've run down to 1/4 tank in Jo Beth with no issues. Sucking air would seem to be a relatively unusual event, even in very severe conditions, given the shape of the tanks and pick-up tube positioning I've seen in most PSC's. A more likely problem would be the stirring up of the sludge and gunk that lay in the nether regions of every fuel tank and that mess getting drawn into the fuel system. Of course, when a tank draws really, really low, water ingestion can also become a potential issue.

Because we go through a tank of fuel so slowly aboard Jo Beth, I've made it a customary practice to have the tank opened, cleaned and the fuel inside polished every three or four years. I also service the fuel system twice per year. Minor overkill perhaps, but so far, so good; no sludge or water issues.

ralopata 11-23-2011 03:45 PM

John:

Not sure about the tank on the 34 but on the 40 the tank is baffled, which helps reduce the possibility of sucking air in a lively sea.

I agree with the previous posts about the dangers inherent in getting water and/or gunk from a low tank.

However, it's not a bad idea to find out how much USABLE fuel your tank holds. While that stated capacity may be 35 gallons, no fuel pickup can actually get every last drop. Some fuel is always going to be in the very bottom of a tank. Some sailors run their tanks "dry" intentionally and then fill them up to develop a "usable" fuel number.

On JUNO, for instance, although the stated capacity of the tank is 67 gallons, we have discovered (the hard way) that the pickup sucks air at 58 gallons.

Best wishes and Happy Thanksgiving to all,

Roger Lopata
JUNO
PSC 40 -- #46

svjobeth 11-25-2011 07:25 AM

Quote:

Originally Posted by ralopata (Post 799964)
John:

Not sure about the tank on the 34 but on the 40 the tank is baffled, which helps reduce the possibility of sucking air in a lively sea.

I agree with the previous posts about the dangers inherent in getting water and/or gunk from a low tank.

However, it's not a bad idea to find out how much USABLE fuel your tank holds. While that stated capacity may be 35 gallons, no fuel pickup can actually get every last drop. Some fuel is always going to be in the very bottom of a tank. Some sailors run their tanks "dry" intentionally and then fill them up to develop a "usable" fuel number.

On JUNO, for instance, although the stated capacity of the tank is 67 gallons, we have discovered (the hard way) that the pickup sucks air at 58 gallons.

Best wishes and Happy Thanksgiving to all,

Roger Lopata
JUNO
PSC 40 -- #46

Excellent points Roger, on determining the useable fuel capacity of fuel tanks.

Jo Beth's fuel tank is baffled.

johnharch 11-25-2011 07:16 PM

Good points all. I'm not too worried about water and gunk as I'll have the tank cleaned this winter. I know it is baffled, but I don't know how well. I can see a fore and aft line on the top of the tank which would indicate a fore and aft baffle, but I don't know about side to side.

Those of you who have cleaned your tank, what kind of of access do you have? I have one square plate about 8 X 8. I can't imagine with the baffling that this will allow very good access. It is just bedded in and attached with what appear to be sheet metal screws. I'll have to have the fuel polished after removing and cleaning that.

Taking it out and running it until it ran dry would certainly give me the definitive answer, but may be a bit difficult. If I take it down to, say, 5 gallons remaining, that leaves me with still potentially needing to run for seven hours or more before it ran dry. So I would need to run for seven hours and be in a nonhazardous location when it went dry. Lots of tidal currents activity up here in the Northwest.

Looking back over my fuel log, I see that one time I actually did put 30 gallons in, but unfortunately I don't remember the circumstances, but I do know they were in flat water. I will keep better notes in the future!!!

I hate strapping fuel cans on deck, but I think I may have to resort to carrying a couple of 5 gal cans this year. Jeez, I'm already down to the water line. Run the engine at lower RPM and sail more. I'm still trying to figure out why I burn fuel faster than everyone else.

svjobeth 11-26-2011 08:20 AM

John -

Cleaning the fuel tank and polishing the fuel contained within is a job I hire out. It's messy, smelly, and very toxic. For me, it's one of those jobs that's worth paying someone else to do.

Our access plate is a single circular plate, secured with sheet metal screws and gasketed. Of course, when the tank is opened, the old gasket has to be cleaned off and a new one made. I'm not too sure about access; I think that our tank has a single fore and aft baffle, and that access is reasonable, considering. I'll ask the mechanic that does ours and report back.

johnharch 12-09-2011 06:45 PM

Update
 
Update...

I bit the bullet and drained the tank and opened it up today. This was very informative.

I emptied the tank by running the electric fuel pump and pumping into 5 gal cans. It was able to suck it right down to the bottom, leaving only about a cup of fuel.

1. My access port is about 6" square secured with 8 machine screws tapped into the tank top and sealed with some sort of sealant. The sealant was hard and poorly adhering so that the plate just lifted right off. No doubt this would leak if the tank were over filled, accounting for the diesel I once found in the bilge.

2. When the access port was installed, some of the squeezed out into the tank. Most of it was stuck to the sides, but a few drips on the bottom of the tank hadn't stuck and were floating around waiting to plug the intake line.

3. The tank was remarkably clean. There was a little sludge in places on the bottom totaling maybe 5 sq in. in spots about the size a quarter. The fuel level sensor is quite clean. Cleaning it looks to be a relatively easy job if I put in another access plate on the port side.

4. There is one baffle running front to back from top to bottom with the bottom corner cut off on the pickup end. There is no way to get past this baffle to clean the port side or even inspect it, without installing another access plate.

5. Without any lateral baffling, it still seems to me that sucking air in rough conditions is a big concern, I'm thinking I don't have to worry too much until I get down to the last 5 gallons or so.

Capt Len 12-10-2011 09:18 PM

Every system is unique. I'll tell you how mine works. Because I need a day tank for my diesel stove, I can fill it with a pulse pump or by return from injectors. It has a sight glass. The main tanks are vented thru this to outside.Because it's cold here the moisture from the air condenses in the day tank first and can be dealt with before it reaches either main tank by the drainable sump. Another line with it's own shut off and filter goes to the fuel manifold. If the unthinkable happens again I'll simply shut of the main fuel valve and open the day valve and be good for 4 more gallons TA DA!


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