Anyone know what this is?

Hey all,

I recently purchased a 34' sailboat and in the corner of the engine compartment is what looks to be another diesel tank, but much smaller than my main tank...it's only 23"x16"x5". Any hoses coming from this tank are no longer in service and have bolts in their ends.

The previous owner was clueless. I was told from the surveyor this it's possibly a 'day tank'...a tank that the diesel initially goes through first before the primary tank (for questionable fuel bought in other countries). But if so, how do you fill this tank up?

In total, there are 6 very small hose nipples protruding from it (4 on top and two on the bottom), plus one drain built on the very bottom in a 'cup' (where the heavier particles may settle?). Two of the nipples are actually attached to themselves from top to bottom by a hose (?).

This tank is connected to nothing else and is confusing the living hell out of me.

Any idea? I'm sure it's something very simple...

 

It could be a day tank, or a tank for the stove fuel.

 

Too many hoses and nipples for a day tank. Because it serves no purpose anymore it may be just a leftover from an unfinished experiment, like a heat exchanger to provide warm water.

 

Maybe.... it is a day tank, to transfer fuel to,
the hose top to bottom is to sight the level of fuel in the tank,
the other hose from the bottom is/was fuel to the engine,
the fitting on the bottom of the "cup" is to drain water off,
that leaves 3 on top, one is fuel return line from engine, one is vent & or bypass when pumping fuel in from.... the last is for fuel transfer from another source.
Just guessing but looks like a tiny tank set up, maybe 25 litres?
Jeff.

 

I came up with the same list as waikikin. It's not proper, though. Tanks shouldn't have fittings on the bottom. I'm thinking a tiny day tank can have a bottom drain, but only if it is ondeck, not in a hull. Also, you can see if waikikin's idea makes sense by looking at the height of the day tank and its connections relative to the engine, main tank, filters, and fuel pumps. It may have been abandoned because it wouldn't pass a survey. The correct way to get the junk out of the cup at the bottom is to run a pipe down from the top with holes in it just at the tank bottom level. When you remove the pipe, all the junk comes out with it. The pipe usually doubles as the tank fill and has a baffle. Nowadays, you can't do that either because of no-discharge rules, so you are left with Racors or similar.

 

Thanks everyone for your input. This tank sits higher than everything else, engine, filters, main tank, etc and there is also a small unused vent (possible fuel vent) right next to that tank, so waikikin's idea is a likely fit (though doesn't the engine's fuel return line have to be lower?). Now what to do with it....

 

What does the inside of the tank smell like?

 

looks like a fluid to fluid heat exchanger.

It might also be an accumulator tank for a dry sump oil system, not sure why that would be necessary on a sailboat, but in race cars and off road vehicles the oil stored in a separate tank rather than in the sump. a scavenger pump put the oil in the tank where any foaming might settle out and the oil supply is taken from the bottom of the tank below any foaming oil.

 

The vent should be higher, by a good margin, also when transfering fuel via a transfer pump some means of preventing overflow to the vent by height/valve & also to show on the bypass back to main tank a sightglass or similar to know when to stop. The system you have seems to incorperate the elements required but may have had a couple of flaws that led to it'd disuse.............
Who knows, pull it out think something up for it, blow through the holes, it may well have a internal circuit for heat transfer?
Jeff.

 

What you have is a proper day tank. Round sump on bottom is for water or sludge. Looks like it would drain through a valve on the threaded pipe stub on the bottom. Sight glass fittings should have spring loaded valve on the bottom that you would press to take a reading. Should be mounted up high in the engine room so that all engines can be fed by gravity (in case of fuel pump failure). It is properly designed, tall and narrow, so that in a seaway there is no sloshing at the bottom of the tank where the pick up is located (but above the grunge in the sump).

 

Thanks armatore, good to know. It does set high in the engine compartment. I have two questions being a novice in this category.

I always assumed that day tanks were filled separately than that of the main tank, settled, and then that fuel fed the main tank. But if this is the case how do you fill it? Most of the hoses are either not there or have bolts plugging them so no telling where they went at one time. I was thinking of using it as a spare fuel tank filling it with the return line off the injectors, but that fuel is already clean. Couldn't find any illustrations on line that would best tell me how these are usually hooked up.

And I'm guessing that this tank would need to be vented as well, so couldn't I just vent this tank with a 'T' into the main tank vent line (which goes into the lazerette)?

 

Day tanks are filled from the main bunkers by electric transfer pumps and in the best installations with a manual back up. Fuel in the main bunkers can be assumed to be "dirty" and the sump on the day tank provides and initial "polishing" step before being fed to the primary filters. The sump can be easily checked by bleeding a little into a small glass jar. This could be done as frequently as every time you fill the day tank if you worry about the quality of the fuel in your main tanks. Yes this tank should also be vented and it should have an overflow line that drains back to the main bunker should you forget to shut off the transfer pump! The engine return would also return to the day tank as that is where it is feeding. I can't picture all of the fittings on your tank, but there should be sump drain, feed line and lower sight glass fitting near the bottom and filling port, vent, engine return, overflow and upper sight glass fitting near the top. Also maybe a port for a high level sensor up high. This more of a "ship" type set up-seldom seen on yachts. Cheers

 

Good info! Thanks again.