The internal tank debate

[Chine]

I have a factory built FRG 5m runabout with an 85ltr internal fuel tank which is very slow to be filled owing to very poor design.

The rig was supplied with a single 19mm OD for'd breather and the same aft with a single 70mm OD filling line. To my way of thinking even if the breather lines were kink free (which they were NOT) this system design will not allow a normal filling rate. The other problem is plugs of fuel being spat out of the breather during filling. This particular system is a dog's breakfast.

The other point is that we all have the problem of degradation of octane rating and water in the fuel because the boats are being supplied with a permanently open fuel circuit. My filler is a screw seal and I am giving some consideration to fitting isolating valves just behind the breather heads. BUNGS IN, VALVES OPEN.........Naturally enough, if the boat were stored outside where the fuel may expand then the valves are left open or an in-line pressure/ vaccuum valve could be fitted My rig lives in the garage and this should not be a problem.

Any thoughts or similar experiences?

Regards

Chine

[FNQCairns]

Hi Chine, I suspect a 19mm air opening could pump 85L of air in 10 seconds at the same pressure the fuel is being pumped in at.

Your problem is possibly the length of the 70mm inlet (or something else)much more so than the breather (if it is clear and unobstructed).

I know these things are a right royal pain in the bum.

This is not advice, but some people have been known to insert the pump nossel into the filler then wrap a towel/rag around it to seal then pump, your breather would easily handle the volume of fuel.

cheers fnq

[FNQCairns]

Thought I better clarify - the rag is not there to prevent spit's or to pressurise to any extent, but simply to convince the displaced in tank air that the inlet is no longer the easiest route to equalisation.

cheers fnq

[Chimo]

Hi Chine

I know where you are coming from re filing the tank.

Can we assume you are dropping the nose of the boat (trailer jockey wheel?) when you are filling the tank?

I have a 190lt tank with single large inlet at the rear of the tank with two small breather outlets also off the rear of the tank and plumbed to the top of the outside of the motor well and the only way to fill the tank is to drop the bow. I have also put small covers on the breather outlets to restrict air flow and during filling spurting. The only way I can be sure the tank is full and avoid spurts is to drop the bow. 9 out of 10 fills I gravity fill the tank thru a tractor type water-catching diesel fuel filter funnel. Less than ideal; the bow down thing; but in the end, simple and certain.

Re the idea of sealing the tank as its stored inside, I don't think I would do it as the fuel does need to be able to expand which it will do even in your "well ventilated garage", I hope. If its not; you might be better of fitting a bilge blower to the garage! If the fuel is in a sealed container you do run the risk, over time, of a split tank.

Cheers

Chimo

[SgBFish]

Chine I feel your pain.
My last boat had breather hoses that dipped into the bottom of the boat and allowed fuel to sit in there and prevent air excaping.
This ment I could only fill by dribbling fuel in and rocking the boat on the trailer to let air out.
My current boat has a 150L tank with 2X 19 mm breathers and 50 mm filler and I have no probs it fills and breathes as fast as I can pump it.
The secret here is to make sure the breathers run straight up from the tank.
Scott

[Cheech]

I had/have a similar issue. But I have been able to improve it considerably.

The filler goes straight down from the filler to the floor, and then had a sharp 90 degree elbow, and then a straight pipe to the tank. The fuel would back up or create turbulence at the elbow. I replaced the sharp elbow with a length of flexible fuel hose, and thus increased the radius of the elbow. This allows the fuel to flow freely and increases the fill rate.

Cheech

[PADDLES]

am just going through the process of replacing the 170 litre tank in my signature. have had the same filling problems as you guys. some poor design things that i've noticed have been the sharp elbow in the filler pipe, the filler pipe enters the tank about an inch below the top of the tank (instantly turning my 170l tank into a 150l tank), there's only one breather and it's about 14 or 15mm hose, the worst one is that they used a brass fitting on the fuel pick-up and this is more than likely what has helped the tank to fail from corrosion.

[Chine]

Thanks for the feed back gents and I totally agree about dropping her by the head to improve filling. I decided to put this afternoon aside to lift the board and have a closer look at the system & took a few photographs.

A couple of things have come to light.
1. The for'd breather appears to be leaking with fresh residues apparent. I will drop the boat by the head this afternoon to confirm.
2. There is sufficient capacity to run two 19mm breathers from the front yet they have only supplied one.
3. The sales receipt and reviews stated that the boat came with an 85ltr tank whereas this polyethelene tank is stamped 75ltrs and has been tested to 3 psi.
4. It is easy to see why I am getting plugs of fuel out of both breathers
5. This is not a well designed system yet I will have to get used to it.::)

Regards

Chine

[Dignity]

Chine, same probs as you - have a 200L tank. No longer fill at bowser but buy fuel in 20 litre jerries when the price drops right down and have the 10cent discount, Use one of those self priming syphons to then fill the tank. Takes a little longer but saves me the hassle of tryin g to get into some of the servos around my place - who ever designs them never think of boaties.

My boat only has a single breather and the 90 degree bend in the filler pipe will cause the fuel to back up if using the bowser - not any more with jerries as I can monitor it much better. Haven't tried the rag trick and will give it a go.

Somrthing changed with my tank about a year ago. When filling it when it got close to full the vent would start whistling and I soon learnt to stop. Now it doesn't but there seems to be some sort of airlock which bangs loudly just before the tank is full so now rely on that.

[Blackened]

G'day

Geeze fellahs, all this drama makes me feel fortunate I have 2 12L portable tanks.

Dave

[Chine]

G'day

Geeze fellahs, all this drama makes me feel fortunate I have 2 12L portable tanks.

Dave

Dave,

Count yourself lucky. No filling problems and no stale fuel ;D .

Chine

[Chine]

am just going through the process of replacing the 170 litre tank in my signature. have had the same filling problems as you guys. some poor design things that i've noticed have been the sharp elbow in the filler pipe, the filler pipe enters the tank about an inch below the top of the tank (instantly turning my 170l tank into a 150l tank), there's only one breather and it's about 14 or 15mm hose, the worst one is that they used a brass fitting on the fuel pick-up and this is more than likely what has helped the tank to fail from corrosion.

Hello Paddles,

Mine also is a Signature and I experimented this afternoon to see how much I could squeeze into the tank before fuel backing up in the filler and/or spitting out of the breather......filling with 4 ltr mower fuel cans......the luxury of having a see through polyethelene tank.

I estimate that I was 5~10 litres shy of being full and fuel spat out of the rear breather with the filler backing up and the trailer coupling on the ground. Needless to say, the filling line is permanently carrying fuel.

I have decided to give the servo a miss and start topping up at home.

Cheers

Chine

[Dr DRIFT]

I too have a signature, its a 575f and everytime I go to fill up its just a pain as I need to fill slowly as it will not allow me to squeze the trigger at full.and 150ltrs takes along time at half speed... >:(

Will give the rag thing ago next time.....

? Its sounds like alot of signatures have these filling problems????

[PADDLES]

just be very careful if you are going to do the "rag trick" on a welded metal (stainless or alloy). what you are in fact doing is hydraulically pressurising the tank slightly and even 1psi across a large surface area (think of how many square inches of surface there is on your tank) will give a surprising amount of force. ie maybe into the many thousands of pounds. the metal ones may not like this:'(

[Dr DRIFT]

What do you mean "be carefull?". Should I do it or not? Is their any thing I should look out for? As my tank is under the floor so I cannot see it when I am filling, so I wouldnt know if it was pressurinsing or not....any tips....

[Dignity]

I too have a signature, its a 575f and everytime I go to fill up its just a pain as I need to fill slowly as it will not allow me to squeze the trigger at full.and 150ltrs takes along time at half speed... >:(

Will give the rag thing ago next time.....

? Its sounds like alot of signatures have these filling problems????

I think it is most boats where they seem to put a 90 degree bend in the fuel pipe - cars do not have such a restriction. Fill from jerrys, that way also manage to get the best price, at 1km = 1 litre it all goes a long way.

[PADDLES]

i've never seen it happen myself but was having a discussion with the guy who's welding my new tank up. he makes tanks for a couple of the bigger boat builders here in seq. he reckoned that the pressure issue across the surface area of a tank was one of the causes of failure in welded metal tanks. he actually told me of examples in bigger boats where the tank (water or fuel) is down low in a bilge area and the filler and outlets are up on deck or in a cabin area and the pressure from filling up so high has burst the tank. wouldn't have believed it myself, but he reckons it happens and the way he explained it makes sense when you consider a small psi across a large area giving a large force. :-/

[ngkala]

i had a signature 575 f until recently , same problem took forever to fuel up. i placed a piece of hose in the filler that went around bend into the tank and put the bowser nossle in that , improved it dramatically,solved the problem completley by buying a kevlacat

[FNQCairns]

Dr Drift read post number #3, exactly the reason I posted it, we are talking fractions of a PSI needed for the air to choose the easiest path to equilbrium.
Now if a breather is only 3mm and a person can obtain a compressed perfect seal with the rag or superfast pumps and/or faulty pumps are used things may become borderline with this method in the real world.

Why do fuel pump nossels trip off?

Of coarse this again is not advice just what I have known has been done to effect in the past but in now way do I advocate this practice yada yada.

cheers fnq

[Glenn Woods]

I also had a filler from the top of my transom to my 100ltr tank with the breather running off the filler line. Why the previous owner did this is beyond me:-/ . As i would fill, the tank would pressurise and spit out from both openings. I had the tank modified with a 13mm seperate breather line and a flush filler with no more problems. Not until i got a slug of water down the breather and past my raco water seperator and seized my 150 yamaha 4 stroke with only 24 hrs on the clock:'( :'( . Still in pieces in the shop waiting on the insurance company for the nod.

Woodsy