Aux fuel tank venting.

[bonneville]

Thanks bonneville.

This tank will be used as a portable Jerry can. So it won't live in that compartment. Just installed for my extended trips.

Yes I understand the air flow scenario.

ok, sorry, misunderstood.....

I've got 185 in height, which means, if I go to 1 tank full length it can only be about 160 finished size in height allowing for clearances and sender unit etc, so it dramatically reduces volume, so no kill tank at the back !
currently two tanks, the front one like yours, same position, with huge vent issues, venting really does play an important role as I've found out ! so put some good thought into your set up while your setting up now and will save you any issues later..
good luck with it all, make sure you put up finished pic's as its an interesting topic..
cheers
bonneville

[Rip it up]

Hey bonneville.
Here is the virgin tank. Yet to be molested.



You mention the venting issue you have. Are they filling related of suction related?

[bonneville]

that's a nice snug fit, looks good !
my situation, firstly no sender units, front tank vented into back tank, back tank two vent outlets, front tank one only ( which vents into the back one ) there's a lot of issues with the set up, filling the tanks are an issue, and I believe a sucking issue as well.
I've bitten the bullet and decided on one new tank, I'm probably going to leave out the sender unit to gain a few more centre meters in height and install a fuel flow meter connected up to the lowrance nmea system. also looking at doing what your doing, at maybe ( smaller than yours) around 40-50 litres, and either store it in the cuddy cabin forward, or under the seat pod purely as a removable reserve for longer trips, or just security/ peace of mind. the tanks are showing signs of degredation, rust at the welkds which look as though thev'e already had someone clean them up and brush primer on the area's, so, just time to fix it up properly !
cheers
bonneville

[Rip it up]

Yeah bonneville that's sounds like a need for a new tank. My main tank was built by NORWELD in cairns. Good design.
25mm space underneath. And overlaps the floor by 20mm. Heavy top checkplate 6mm. And has all the outlets at the rear.

Sender unit is there but only reads after 60% of tank is emptied. Then it goes down quick.

But I know if my tank still reads full when I get to my fishing spot, then I have enough to get home.

I've got nothing to loose with the single filler&vent in one. So I'll test run it. If I need to add a dedicated breather hose after that I will.

I had even thought of decanting the aux tank into the main with a 12v fuel pump when required. That's if the suction creates an issue for me.

[blairv70]

Looks like an awesome idea - where did you get the tank made?

I have two underfloor areas one between the seats and one at the rear - I am guessing the one at the rear would be less suitable than the one midships.

I was having the same thought of a fuel reserve and pump it into the main tank as opposed to running directly off it and transfer via a manually activated pump. Could you use a plastic tank?

[bonneville]

good plan rip it up, test it, then either vent it, or option to pump it if necessary.
I see your main tank in the photo ! hmm, currently I have two carpeted marine ply boards that slot down on top of the tanks, I have an aluminium channel which runs around the perimeter which the centre boards slot into. they all need to be replaced as well. I like how you've set your up, which had me ponder about my set up for a minute ! LOL
but I will just replace like for like, as it looks as though you have a rebate fibroglassed for the tank checker plate to slot into, where as that's what the aluminium reciprocates for my set up ! but I do like your set up.
regards
bonneville

[Rip it up]

ImageUploadedByTapatalk1406790708.869405.jpg
The main tank sits as the center piece in the cockpit. Pipe outlets tuck under the motor well. Away from the toes.


The aux tank was built by a local fab shop in Gladstone. $575

[Rip it up]

Blair I had no option with the plastic tanks getting a neat fit. Especially the 5mm gap i have for the aluminium.
This aluminium option allows me to neatly slide the tank into position when needed. No straps no fiddle issues. Just fill and go.

I took it out for a water test today with the virgin tank under the floor. Thinking it might cause a loud ratty box when empty. But it worked well no noises from below.

The killbin area does have two drain points in each aft corner. Headed back to the bilge pump area. So water will not sit under the tank when at sea. If I can find a suitable option I might put a 3mm rubber strip glued to the bottom of the tank to allow water to flow fore and aft.

It will be the first tank to empty and once dry will be removed at home for the next mission.

[bonneville]

ImageUploadedByTapatalk1406790708.869405.jpg
The main tank sits as the center piece in the cockpit. Pipe outlets tuck under the motor well. Away from the toes.


The aux tank was built by a local fab shop in Gladstone. $575

I like that set up, it looks schmick !!
ive had a quote for around $700 here in Melbourne, approx. 140-150 ltrs with the front part of the tank with a slight taper, as the floor of the tank recess lifts up over the last 300mm ( hence another reason to fix the current set up, the floor board at the front is sitting directly on the tank ). with a thirsty two stroke on the back at the minute, i'll need that reserve tank, ( currently 170 litres with the 2 tanks) but will be ideal when I re-power with a 4 stroke next year ( hopefully)
good luck with the tests on your aux tank rip it up
bonneville

[Rip it up]

That tank price sounds good. I did not chase the price down much as this fab shop is 400m from my house and had it knocked out in 4 days.

I'll be filling this tank late next week using this flush style aluminium cap. And headed out to the local reefs next weekend.

[Dignity]

Damo, I maybe reading this wrong but with the pic you had of the cap where you will be drilling a hole for venting, will you be venting into the cockpit of the boat or worse still under the floor. Excuse my poor interpretation if this isn't the case.

[Rip it up]

Dignity you stand correct. The flush cap for the tank will have a hole drilled from the top and a sintered metal breather installed on the under side to stop the liquid from slashing up.
Basically merging these two ideas.
ImageUploadedByTapatalk1406793936.064827.jpgImageUploadedByTapatalk1406793950.168685.jpg

I understand that venting into a closed floor space is not ideal but the 70L of fuel would be drained within 2hours of motoring to my extended fishing grounds.

The floor panel that is above the tank is only a loose fit and not screwed down etc.

[Dignity]

Damo, I would be greatly concerned as you end up with a pooling of fuel vapours, I understand you are using it within two hours but you don't need that much before you have a fire situation, witness the many boat fires that occur at a marina, these are usually caused by such an event. Are you going down this path because of the jerry can type situation, I would look at running a permanent vent to the outside that could easily be connected each time you wanted to use the portable tank.

[bonneville]

Damo, just looking at your set up..... could you not.... at the back end of the tank where the tank is angled, drill thru to the main tank cavity area and run a permanent vent hose along side the main tank ( presuming there's room ) and vent as the main tank would be out the back ?

I'm sure as you say the tank would empty quick enough, but this would allow you to save it as a true reserve, with out the need to use it first.

I think I hear where dignity is heading with his questioning, and im always very very suspect even of small tanks, a hot day etc etc if you know where im coming from. I just hate potential gases being anywhere near the cockpit area.... ????
bonneville

[Rip it up]

The laws of gravity will work against me to create the "standard vent line from the rear.

Let me explain.

When the boat takes off from rest the bow lifts high in the air before settling into trimmed position. This would force the fuel backwards I the tank and rushing down the breather hose on the back of the tank. Theoretically creating a possible syphoning effect.

Even if I create a loop high up on the transom wall or tee into the existing breather, I would still end up with a breather hose that would fill up with fuel. Now a small section of fuel 300/400mm might be overcome by the suction of the motor. But I have doubts that a 2m long section of fluid would be able to be sucked back into the tank by normal operating conditions. Maybe a inline fuel pump could do it. But that creates more issues.