Unbalanced fuel tank reading

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birdistheword

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Hi folks

New to boating and to the site.
Advice needed please.
Recently purchased our Sealine S41with KAD300A's. Planning to sail from Plymouth to Cardiff. We set off ,with a skipper on board. Not too far into our maiden voyager noticed that the starboard fuel tank was starting to use fuel, OK no problem with that, but by the end of day 1, it had dropped to 1/2 tank and the post fuel tank reading full, it hadn't moved. WHY ?? Was fuel being taken from only one tank ? does it run from one tank then the other ? a lot of head scratching and finally the skipper said "we can't go on as we'll be forever needing to refuel if its only taking from one tank"

We have asked the marina for help but so far, 3 weeks later, no answers are forthcoming.

Bearing in mind that engines are defo not my thing, i usually leave it to the experts, if they can be bothered
, can you guys give me any clue.

Much appreciated in anticipation.
 
The obvious reason is the fuel supply valves are set incorrectly - however I would have expected a qualified/experienced skipper to sort that out. (it's very simple)
There is a set of valves ordinarily set so each engine draws from it's own tank and returns the excess fuel back to the same tank. However it is possible (and useful occasionally) to run both engines off one tank and return fuel to the same tank or the other tank.
Have a look at the Sealine S41 user manual (if you haven't got one post on here or the Sealine forum, someone will have a copy)

The other possible reason is the fuel tank senders or gauges are stuck/broken.
I am assuming both engines were running quite happily???

re: leaving engines etc to the experts - if you plan on going out to sea, it's definitely worth doing an engine maintenance training course. Boats usually break down because of a fuel issue or a cooling issue. Its well worth your while learning how to deal with it, and will make your boating life much easier and happier (and cheaper ;-))
 
Have you tried to fill the tanks and confirmed that the gauges are correct ( and the full tank in indeed full).

Changing tank selections is a conscious thing to do that normally requires some thought re the selections of the taps - so it is not an accidental thing.

You don't know the history from the last owner, but on balance gague issues are probably more likely and gagues are in general not that reliable mostly relying on a float.
.
To use half a tank in a day ( I dont know how far you went) on a delivery trip seems entirely plausible. So take the capacity of the tanks, the consumption of the engines ( google will give you a good enough figure - 41 foot boat 100 lph for both??) times the hours. if you had used half a tank on each does the roughly correlate to the fuel used calculation above?

Narrowing down the issue should only take moments. I am not sure how a Marina would help as they only operate the boat car park.

Finally in answer to your question no they do not take from one and then the other. Usually they draw and return from / to their own tank. The return references that fact that a diesel engine draws more fuel than it needs, injects what it requires and returns the rest to the tank.

If playing with the valves do be careful as shutting off the return completely will have devastating consequences ( high pressure fuel has nowhere to go and will find a route out come what may). Similarly if you send both returns to one tank it will possibly overflow. I have used return to balance fuel before when it was blowing a gale and the hose was too short to fill the other tank and I did not want to turn the boat. That is once in some 15 years of boating so messing about with it is relatively rare.
 
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S41 is a little odd in that it has "forward" and "aft" fuel tanks, with the Starboard engine drawing from the forward tank, and the Port engine drawing from the aft tank. Apart from the that, it's fairly conventional.

Normal running would be both fuel cocks open, and "all other taps pointing vertically".
i.e. both sides open, and both supply and return crossovers (on the small horizontal pipe sections) closed.

Also, when you filled up, was the Port engine tank really still full? (Stuck sender?).

p1hqEn.png
 
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thank you Kashurst. It appeared that both fuel gauges were working as they should prior to the trip i.e. both said half full and both took near enough 1/2 tank full of fuel.
Boat maintenance course is a great idea.
We are having a hopefully more reliable examination next week, i'll be there when they do this and hopefully learn something.
 
birdistheword said:
thank you Kashurst. It appeared that both fuel gauges were working as they should prior to the trip i.e. both said half full and both took near enough 1/2 tank full of fuel.
Boat maintenance course is a great idea.
We are having a hopefully more reliable examination next week, i'll be there when they do this and hopefully learn something.
Click to expand...
Don’t forget to let us know ,but did you try to fill up
 
Good advice above. +1 to fill up asap and record how many gallons each tank takes. QED.

I could be wrong but my hunch is that the push-on connectors to the fuel tank sensor have slightly corroded therefore are a bit resistive, so the gauge is seeing a higher resistance that it expects, and is reading full, or even 120% full in my case. :) Don't know the numbers for your boat, but to exaggerate: infinite resistance = tank full, zero resistance = empty. Pull off one of the connectors and check what the gauge does. BTW this can happen quite suddenly. Doesn't sound logical, you'd expect it to be slow over time, but true.
 
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You have it a little bit wrong return lines should not have isolating valves. Look at Flower Power's drawing of the fuel system and what you see is FEED isolating valves there are no other valves in the system. Stop the engine you stop the flow much safer. Jim
 
jim.howes said:
You have it a little bit wrong return lines should not have isolating valves. Look at Flower Power's drawing of the fuel system and what you see is FEED isolating valves there are no other valves in the system. Stop the engine you stop the flow much safer. Jim
Click to expand...

I’m not sure that’s correct.

Item 9 on the diagram looks like the return crossover / isolation (the dotted lines are the return path).
Item 5 is the feed isolation and crossover.

I have similar sets of valves on my SC35.

.
 
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Hi item 5 looks to me like fuel filters for the main engines and item 9 looks like a 3 way v/v with position # being return open to both tanks / position # return open to port or stbd tank/ position # return open to port or stbd tank depending on how the tanks are piped up but will not act as an isolating v/v as one way will always be open, and it looks to me as if both return lines have been drawn to pass the under the fuel filters. If you look at the top of the drawing there is what looks like a gen set (item 15) which also has an item 5 (fuel filter) but as far as I can see there are no isolating v/v's of any type in the gen set fuel system. The drawing is badly drawn as if I am right and item 15 is a gen set then it has 2 broken lines(returns) going to the gen set but no fuel feed. Jim
 
I should probably have posted the "key" to the diagram as well.
15 is indeed the gen set ... the dotted lines to it are because it's optional.
The other dotted lines are the return lines.



p1hqEn.png


1dPx24.png
 
jim.howes said:
Hi so are we agreed that there is no need for fuel return shut off v/v's in the system just changeover vv's. Jim
Click to expand...

I’ve managed to confuse myself.
Looking at the SC35 diagram, there are shutoff valves for the return lines, item 7. And they do exist on my SC35.
But closing either of them with a running engine would be disastrous unless that valve in the diagram is actually the other way around.

I’ll take a closer look at the actual layout at the weekend.
 
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Hi me again, I must agree in your drawing there are fuel return shut off v/v's in each of the return lines. The v/v's are set right for normal running. If you look at the legend item 7 is described as fuel (return?)cross connection valves(misprint ?) but no mention of shut off v/v's. Jim
 
So this is what's on the bulkhead.
The fuel supply shutoff valves are elsewhere in the cockpit.
The original poster will have something similar.

6pTAFh.jpg
 
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