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Old 31 August 2016, 13:11   #1
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Fuel bladders

Thinking of having a fuel bladder made but I was thinking of fitting it each side of the inflateable keel below the floor protected by some neoprene rubber to prevent it chaffing.fuel filler and lead through two holes in the ply floor boards at the bow.

Any thoughts see any problems?

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Old 31 August 2016, 13:24   #2
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I see one.
Every time you hit a wave at some speed fuel will get forced into the engine.
Don't think the fuel pump and the carbs will love that.
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Old 31 August 2016, 13:28   #3
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I see one.
Every time you hit a wave at some speed fuel will get forced into the engine.
Don't think the fuel pump and the carbs will love that.

Won't the floats in the carbs stop that? (I'm not savvy with carbed outboards so could be talking borrox)


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Old 31 August 2016, 13:54   #4
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The needle valves operated by the floats are sufficient to stop the pressure the fuel pump generates from flooding the carbs and the engine with petrol, but I doubt they would be sufficient enough to stop the pressure created by what is in basically someone(in this case the wave) kicking a fuel bag against a hard surface(in this case the wooden floor). Even if the SIB has a soft (air) floor the pressure created would be considerable.

Imagine you keep pumping the primer ball while the engine is running. It'll cut out due to the mixture getting too rich eventually.
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Old 31 August 2016, 14:31   #5
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New Suzuki fuel injected fuel separator in line plus when pumping bulb it's as solid as a rock no where to go with surge ?, also why would the shock be any different? Not knocking your thoughts just dragging as much info as possible. I thought about shock but the whole boat is subject to it even a rib when it flys and lands hard with an air gap in the tank no baffle to stop surge? Or am I wrong
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Old 31 August 2016, 14:57   #6
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New Suzuki fuel injected fuel separator in line plus when pumping bulb it's as solid as a rock no where to go with surge ?, also why would the shock be any different? Not knocking your thoughts just dragging as much info as possible. I thought about shock but the whole boat is subject to it even a rib when it flys and lands hard with an air gap in the tank no baffle to stop surge? Or am I wrong

Hadn't realised it was a fuel injected engine. If you leave some airspace in the bladders it should act as a shock absorber & stop it hydraulic shocking. If you have the take off at the stern end it will stop air being drawn.


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Old 31 August 2016, 15:04   #7
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You aren't completly wrong and I'm not trying to knock your idea either. Storage wise, it's quite good.

Rigid fuel tanks behave differently in this case, as the Fuel tank itself isn't being compressed, but the fuel rather sloshes about inside it.

I'm talking about the motion of the boat on the plane cutting through a wave.
I own a wooden floored SIB with a wooden Keel (About as rigid as SIBs get) and when you hold your hand over openings in the floor boards whilst driving, you can feel the air rush out of the under-floor cavity every time the boat hits a wave. On a RIB
this is different as the hull itself does not flex.

Imagine having a flexible fuel tank and a rigid one. You kick the flexible one, fuel spurts out of the connector
You kick the rigid one, depending on how rigid it actually is, either some fuel comes out and the tank has a big dent in it, or the entire affair falls over =D

You propably see what I'm driving at.

With a EFI Four stroke it's obviously different as the injection system is under pressure, unlike carbed engines, even though, I doubt the fuel pump, and the connectors to and from the tank will love it being kicked over and over again.

I could be wrong of course, and I don't know where you are usually boating. It's just a possibility that springs to my mind, and a possible point of failure on the fuel system, a weakness that isn't really necessary.

You could fasten your flexible fuel tanks to the sides of the tubes, that way they are out of the way and don't get kicked by the action of the boat. And they are easier to refuel too.

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Hadn't realised it was a fuel injected engine. If you leave some airspace in the bladders it should act as a shock absorber & stop it hydraulic shocking. If you have the take off at the stern end it will stop air being drawn.
I hadn't thought of that, it's correct ofc, but could lead to the engine being starved of fuel, especially on a SIB that sits completly level at standstill.
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Old 31 August 2016, 15:06   #8
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So I could swap it round Dave filler and line coming out the stern the boat is more stern down and momentum forcing fuel back. Would surge be any different than hung on the tubes?
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Old 31 August 2016, 15:20   #9
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Mextl

See what your saying the outer skin is acting like a drum and would transmit that through the bladder thus might cause fatigue in the bladder.
The surge not sure how bad that would be but it must be considered.
the best option for me would be if tanks were available that were quadrant shaped in PVC and fitted in the corners under the tubes to floor out of the way I don't want to hang off the tubes.

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Old 31 August 2016, 15:20   #10
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Exactly that's what I was driving at. Eventually, everything will be a compromise, especially on a SIB. The entire existance of the SIBs is compromise!
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