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.
Originally Posted by Pikey Dave
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.