fuel tank venting

[bonneville]

hi all, I have a question
I currently have 2 under floor fuel tanks, with separate connections which have to be swapped over manually, that then go thru a fuel filter then to the motor. one is around 70 litres the other around 110 lts. both have no gauges set up on them.
here's where my question lies. the front tank vents straight into the back tank, which is then vented thru a water separator, then on to the fixed vent outlets in the engine well. is this normal for a 2 tank set up ? I was thinking that they should be vented separately ? I ask this because re-fueling is a long process and if I fill the back tank first, its hard to get the front one filled. in fact I have never been able to get the full 180 litres in total in them !
its not an ideal set up having 2 tanks with separate connections, although its a great way to tell how much is left when the front take runs out !
im looking at taking them out and putting just one tank in to make room for a kill tank, but that's on the bucket list at the minute.
the water separator allways has fuel in it, which I regularly drain, but my way of thinking is that there wouldn't be much venting from the front tank to the back tank if it was full ?
or have I got this all wrong ?

c

[scottar]

It does sound like a bit of an odd setup. Do you have issues with the system pushing fuel out of the breathers? I know the underfloor tank in my rig has 2 breathers - one at each end so it doesn't matter whether she is nose up or down it will vent. Another mate of mine has a 17c haines with twin tanks. Definately has independant breathers but he has to be careful with the bank tank. If the boat is facing the wrong way it's a pig to fill. Might be worth double venting your back tank and having an independant single on the front

[captain red beard]

Maybe just try filling the front tank first and see if it is any better.

Sent from my C6603 using Tapatalk

[bonneville]

yes it is definitely easy to fill the front tank when the back ones empty.
but, its more the venting issue im concerned about. the water separator was installed before I got the boat, maybe because of the venting set up, as I said the water separator has always got fuel in it. if my back tank is full to the brim, it must be imposible for the front to vent at all.
I haven't had any running issues as such, but was more interested in the venting set up.
I been mulling over the tank issue, and want to go to a single tank, around 130 ltrs, which would then alleviate any concerns I have with this set up. just looking at all the options, stainless or marine aluminium ? but as mentioned, that will probably be a next season project, just want to set these current ones up properly until then.

c

[scottar]

Missed that bit about the seperator. If the bank tank is full and the front is expanding it pretty much has to push the fuel out. For the cost of some hose and a "T" fitting or another breather I would do the mod. It is unusual to see a seperator on a breather outlet so I suspect you are right in guessing it may have been a problem for a while. American boats may have some sort of check valve installation as required by their regs, and I have seen some expansion chambers on some Kiwi rigs but can't ever recall seeing anything besides a water loop on an Aussie built boat.

[bonneville]

thanks for your input Scottar, I think that's what i'll do over the interim, till I fit the single tank.
I'll put a T junction in where it vents from one to the other and then run a hose to the connection at the water seperator
at least that will vent the front one a lot better and might help refuelling !
I can see the merits of a water separator on the vent hoses, it would be more of a fuel collector to save spilling fuel out the vents, the separator is tucked out of the way, so i'll leave it on there once I fit the new single tank, doing no harm I suppose.
cheers

c

[Nslfishing]

If your gonna sell one of those tanks let me know the dimensions and I might take it off your hands 😀

cheers nic

[Rip it up]

Yeah bonneville post up your tank sizes they would be very easy to sell.


Damo's dodgy boat building factory.

[Noelm]

Not too sure about the water separator on the breather side? That sounds kind of odd.

[docaster]

I have often wondered about that, but since the water is in vapour form it wouldn't work would it?

[bonneville]

I don't think the water separator is there as a separator/filter. my belief is that when the extra front tank was fitted, which I must point out, that the floor board is sitting hard on the end third of the tank, (crazy) as the compartment for the tank curves up over the last 300mm at the bow end, now with the way it was vented ( badly) there is a lot of pressure in the tanks and breather pipes, which causes at times the water separator to fill its glass bowl with fuel, so I believe the p/o or someone pryor, installed the water separator as a fuel catch, rather than spewing into the engine well. once the tanks are down in fuel, there doesn't seem to be an issue, but as previously described, the lack of venting makes it near impossible to fill with any speed.
the boats been sitting for a couple of months, work and other commitments, but I've just lifted the floor boards and cut the breather hose in readiness to fit a junction. at this stage I'll just route it through the water separator as it is now( then it goes on to a vent outlet ), that will make it easier to fill and get me out and about on the winter snapper. I'm pricing up new tanks at the minute, getting info on either stainless or the marine grade aluminium ones I'm seeing about. The trick then will be pushing the tank as far forward as I can, made with a taper on it to allow for the for the floor rising that last 300mm. Once fitted, I'll remove the water separator completely and rout the breather hose directly to the vent outlets, at the engine well, as they should be.
should of had this done months ago, weather has been dead set crap down here in Melbourne over that time, normally some pretty good winter days to be had locally at this time of the year, but its been a windy one !


bonneville

[MyWay]

is your tanks are inline or side by side ?

[bonneville]

there in line, up the centre.
I think the main tank, which I'd say is original ( 1989 c/c reef finder) which I believe has a sticker on it " cruise master" ?? approx. 110 ltrs
the extra one ( approx. 80 lt) put in is a no namer. both don't fit the space ecconomically, so the intention is to get the biggest size ( with minimum clearances ) in the space as far forward as possible, to create a kill tank in the space saved at the back. plus there's no fuel level senders in either ! so i'll be hooking up a fuel flow sensor at the same time.

bonneville