Having problems filling my fuel tanks

[Deleted User YDKXO]

There's a rather odd fuel tank set up on my boat. It has 2 fuel tanks forward of the engines but they are assymetric in that the port tank has a capacity of about 1200 litres and the starboard one about 800 litres. Both engines receive fuel from the port tank but the starboard engine returns fuel to the starboard tank. Then there is a 3rd tank aft of the engines with a capacity of about 500 litres. All tanks are connected by a pipe about 1" dia; this pipe has valves in it which I always keep in the open position. All 3 tanks have separate fillers on deck. There is only one fuel guage and it is attached to the port tank plus there is a sight guage on the port tank too. The starboard and aft tanks don't appear to have any guages.
When I bought the boat last year, I saw that all 3 tanks were interconnected and assumed that I could fill all 3 tanks from just one filler point. This works fine from the port filler but if I use the starboard filler, after a short while, the fuel blows back through the filler and I get fuel all over the deck (and me usually). As far as I can tell the vent pipes from all 3 tanks are open because I can feel air coming out of them when filling. Anyone got any idea what's going on here?
The second question concerns the aft tank. The top of this tank seems to be at the same level as the forward tanks when at rest but when on the plane, I'm wondering whether the top of the aft tank is lower than the forward tanks. Should I be concerned about fuel flowing back from the forward tanks into the aft tank and because of the difference in levels with the boat on the plane, could I be losing fuel out of the vent pipe from the aft tank? Needless to say, there's nothing in the manual on this but I'm now wondering whether I should close the connection pipe from the forward tanks to the aft tank after filling?
The last point concerns fitting fuel guages to the starboard and aft tanks. It would be useful to know levels in these tanks as well as the port tank. Are there any fuel guage systems on the market that I could fit without drilling holes in the tanks? All tanks are stainless steel

 

[MapisM]

if I use the starboard filler, after a short while, the fuel blows back through the filler and I get fuel all over the deck (and me usually).

My guess is that it's just a matter of time.
The stbd tank might fill more quickly than the connecting pipe (which works just by gravity) can transfer fuel to the other tanks. Did you try waiting a couple of minutes after the first diesel shower, and check if you can feed some more fuel before the second? That doesn't solve the problem of course, but at least you would know what's happening.

I'm wondering whether the top of the aft tank is lower than the forward tanks. Should I be concerned about fuel flowing back from the forward tanks into the aft tank and because of the difference in levels with the boat on the plane, could I be losing fuel out of the vent pipe from the aft tank?

I don't think so. It's possible in theory, but you should have also the vent pipe lower than the top fuel level of fwd tanks, and I'd be very surprised if that would be the case.

Are there any fuel guage systems on the market that I could fit without drilling holes in the tanks?

Not afaik, but if you have a sight gauge on port tank and you always leave the connecting pipes open, I can't see the point in fitting anything elese.

 

[kashurst]

Tek Tanks do a sensor made by Gobius that does not need holes drilling in the tank. don't know how accurate they are but might be worth a phone call

 

[DAKA]

As far as I can tell the vent pipes from all 3 tanks are open because I can feel air coming out of them when filling. Anyone got any idea what's going on here?

Day tanks are outside of my expertise but I have some experience with vent pipes........

They are usually fitted with a flame arrester gauze an inch or two from the hull fitting.

On a hot rough sunny day on the move sea spray can get sucked in which blocks the gauze.

Partially blocked vents may blow air but only when the tank reaches 2-5 psi .

You could be filling the tank with the breather blocked, as the pressure increases in the tank the breather starts to work reducing the pressure to say 3 psi , but you keep adding to the pressure and the blocked breather cant cope until eventually it backs out the filler.

I helped a guy with a sunseeker do this, you could hear the pressure building and about to erupt , it ejected diesel 6 ft into the air before covering the whole cockpit.

Clear it with a flat bladed screw driver carefully and then by misting fresh water into the vent to loosen the salt, then inject diesel into the breather to wash the salt away.

 

[Deleted User YDKXO]

Tek Tanks do a sensor made by Gobius that does not need holes drilling in the tank. don't know how accurate they are but might be worth a phone call

Thanks for that

 

[Deleted User YDKXO]

Day tanks are outside of my expertise but I have some experience with vent pipes........

They are usually fitted with a flame arrester gauze an inch or two from the hull fitting.

On a hot rough sunny day on the move sea spray can get sucked in which blocks the gauze.

Partially blocked vents may blow air but only when the tank reaches 2-5 psi .

You could be filling the tank with the breather blocked, as the pressure increases in the tank the breather starts to work reducing the pressure to say 3 psi , but you keep adding to the pressure and the blocked breather cant cope until eventually it backs out the filler.

I helped a guy with a sunseeker do this, you could hear the pressure building and about to erupt , it ejected diesel 6 ft into the air before covering the whole cockpit.

Clear it with a flat bladed screw driver carefully and then by misting fresh water into the vent to loosen the salt, then inject diesel into the breather to wash the salt away.

Thats exactly what happens to me. The fuel erupts from the s/b filler like a geyser. I'll try cleaning the vent pipe although it wont be easy as my boat doesn't have a gauze over the vent but a 90deg fitting through which it would be difficult to push anything. Maybe I can remove the pipe from the tank and blow air through?

 

[DAKA]

Thats exactly what happens to me. The fuel erupts from the s/b filler like a geyser. I'll try cleaning the vent pipe although it wont be easy as my boat doesn't have a gauze over the vent but a 90deg fitting through which it would be difficult to push anything. Maybe I can remove the pipe from the tank and blow air through?

Taking the vent pipe off would allow you to attach a water hose to the pipe which would clear it perfectly, (just remember to air clear the goose neck afterwards) if you cant get to the end easily then I would try the mister/diesel injection method first.


geyser, good description........I remember it well

you could hear the pressure building like a rocket going off , I would take several steps back, but Burt carried on filling

Whoosh up it went and down it came covering Burt and the cockpit, he carried on filling the Tank, the geyser went off at least 4 times ,until I plucked up enough courage to get close enough between the eruptions to stop him, I used a funnel to fill it which allowed the tank to breath through the filler, had a great day out so it was worth it