Reply With QuoteI don't think it would be a good idea to not vent it permanently. So at the moment you don't have any connections as yet in the new tank?
Hey guys. I'm chasing some ideas to fix a venting issue with a newly built tank.
The tank has been built out of 3mm aluminium to fit into my existing kill bin area between my seats. ImageUploadedByTapatalk1406706663.828552.jpg
Underneath the lift out hatch I have 950mm long x 560mm wide x 150mm tall space which is utilised the best.
I have created a permanent fuel connection point into the aft wall using brass threaded fittings. 1/4" bsp elbow to either hold a threaded bung when not using the tank, Or a hose tail barb for when the tank is needed. This connection runs back to my water seperater filter with an inline 1/4 turn tap for each tank, main or aux. Keep it simple.
ImageUploadedByTapatalk1406706870.263175.jpg
Now I have had the tank built for a very neat fit inside the kill bin. 5mm clearance on the sides. And 140mm tall or a 10mm gap above. The lid fits over it easy now. But here lies my design issues.
1) Filler point options. I will need to find the slimmest deck filler cap possible to keep it from fouling on the hatch lid. 10mm clearance. Stainless steel is the slimmest option. But has electrolysis issues. The aluminium weld in options are too tall for my application. Plastic are also very tall.
2) Would I "need" a breather/vent if I only use this tank for the first part of my long distance trips? Could I simply crack the fuel cap a 1/4 turn and vent air into the system from there.
OR do I install a brass breather plug into each front corner of the tank?
Something like this.
ImageUploadedByTapatalk1406707888.082242.jpg
The tank will hold 70L approx, (yet to be filled). And only used in place of having to carry jerry cans offshore. Now if I normally seal up my jerry cans at sea. I can't see why I could not treat this tank any different to a big jerry can. Except that I plan on letting the outboard suck the fuel away.
Anybody used a sealed aluminium tank under the floor as an auxiliary for extended trips?
Last edited by Rip it up; 30-07-2014 at 06:12 PM. Reason: formating photos.
Damo's dodgy boat repairs.
1993 bermuda by Haines 530f - completed resto.
1976 cruisecraft rogue 14 - estuary weapon.
1984 vickers easyrider 156 - future project.
I don't think it would be a good idea to not vent it permanently. So at the moment you don't have any connections as yet in the new tank?
Virgin tank. Has a pick up tube welded against the rear wall. With the aft port corner cut away to allow hose connections to the brass fitting in the boat.
Damo's dodgy boat repairs.
1993 bermuda by Haines 530f - completed resto.
1976 cruisecraft rogue 14 - estuary weapon.
1984 vickers easyrider 156 - future project.
If you crack the filler to vent it's going to leak fuel while you're travelling.
The issue is the access to a vent higher than the tank. If I run a hose off the front of the tank I would not be able to keep it above the tank level to hide it. Running it back to the main tank breather it would have to go below the main tank and back up. Creating a fluid lock.
Damo's dodgy boat repairs.
1993 bermuda by Haines 530f - completed resto.
1976 cruisecraft rogue 14 - estuary weapon.
1984 vickers easyrider 156 - future project.
I'm headed to pirtek tomorrow to see if they have a brass fitting that incorporates a one way valve similar to a dirtbike fuel vent.
Damo's dodgy boat repairs.
1993 bermuda by Haines 530f - completed resto.
1976 cruisecraft rogue 14 - estuary weapon.
1984 vickers easyrider 156 - future project.
I'm thinking that if I use a standard 38mm deck filler it would enter the tank 50mm minimum. Creating a shield to the splashing. And a few strategic holes drilled into the neck would allow air to escape when filling.
Damo's dodgy boat repairs.
1993 bermuda by Haines 530f - completed resto.
1976 cruisecraft rogue 14 - estuary weapon.
1984 vickers easyrider 156 - future project.
Probably wouldn't matter if it goes down than up, Would suck any fuel through, if it gets in. As long as it will be high enough to not siphon while bow up.
So in theory I could create a second hose connection from the front of the tank and route it the 3metres back to the original main tank breather high on the transom.
This would leave a 2m section of 5/16" hose with fuel in it. Would the internal suction of the outboard pull the air from the breather past that much fuel?
Damo's dodgy boat repairs.
1993 bermuda by Haines 530f - completed resto.
1976 cruisecraft rogue 14 - estuary weapon.
1984 vickers easyrider 156 - future project.
Don't see why not. Can you get a filler like a portable tank with the screw vent? Although i used a portable tank on a 120 2 stroke once and couldn't vent enough.
My outboard should chew 40/45L per hour at a maximum. So that would need to be taken into consideration. I think I can find a vented flush deck filler cap.
If not I can always drill and tap a vent into the top of a stainless filler.
Damo's dodgy boat repairs.
1993 bermuda by Haines 530f - completed resto.
1976 cruisecraft rogue 14 - estuary weapon.
1984 vickers easyrider 156 - future project.
Ok I think I have my game plan.
I searched the online resources for a flush mounted filler cap in aluminium.
Two options. Thumb opening or recessed blade type.
ImageUploadedByTapatalk1406726123.632573.jpg
I like this option. 7mm high flange. Can be screwed or welded to the tank. Might get it welded at the factory if it fits properly.
The. I can create a vent in the bottom of the cap similar to this option.
ImageUploadedByTapatalk1406726169.484127.jpg
Large vent surface. 1/2" or 3/4" tapped into a blind hole from the underside of the filler cap.
Then a simple 2or3mm drill hole on the top surface.
It may not sound like a massive rush of air getting into the tank but it's all about equalising the pressure, not filling up 70L from a servo which the main tank breather must do.
What do you think?
Damo's dodgy boat repairs.
1993 bermuda by Haines 530f - completed resto.
1976 cruisecraft rogue 14 - estuary weapon.
1984 vickers easyrider 156 - future project.
I did a removable pipe set up ,recessed fuel filler and hoses back to a new breather . Down before up and a 3 way tap ..
Hi rip it up,
your doing what im going thru at the minute !
Listen, one thing that tank manufacturers INSIST on, especially marine aluminium, is an air flow, under the tank ! they have specified at least 15mm underneath the tank. the reason for this is that even if you can guarantee that there will be no water at all in the compartment, unless it has that flow underneath, you will get corrosion ! and they have told me that they have seen tanks fitted without that air flow in marine grade ali, that have only lasted a couple of years. I talked to 3 different manufacturers, one wouldn't make the tank for me unless it was installed using that method. hence my previous post on tanks under pods. by the time I allowed for the bottom clearance, and top clearance for vents, etc my tank was going to be 35mm smaller in height. airflow, airflow airflow underneath, important..
regards
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.
Damo's dodgy boat repairs.
1993 bermuda by Haines 530f - completed resto.
1976 cruisecraft rogue 14 - estuary weapon.
1984 vickers easyrider 156 - future project.
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