Re: why aren't electric fuel pumps in the gas tank?
The engine manufacturers like Volvo and Mercrusier have no control over what boat, what shape fuel tank an engine is used for. The tanks are not designed for electriic fuel pumps either. Plus, with the present setup, Volvo and Merc have control how their fuel systems work. ON cars and trucks it's a different story. GM builds all of it.
It's also safer, no LONG pressureized hoses/lines from wherever the tank is to the engine along with a return line. What if a line breaks or comes loose between the pump and the engine. Pressureized fuel blowing into the bilge.
Then we have the dual fuel tank boats. Now you would have to have two pump and two return systems.
It's just not practical.
I agree with everything you've said except the safety issue.
I believe having the pump in the tank is actually safer.
#1. No chance of any siphon or drain. When power to the pump is shut off, the flow stops. Period. On setups with external pumps, the fuel can (and often does) continue to flow because of a siphoning effect.
#2. It protects the pump from mechanical damage. This is perhaps more relevant in a car, but during a crash, the fuel pump is a dangerous thing. You've got the potential for fuel leaks and sparks in one location. When the pump is in the tank, the tank usually absorbs the impact enough to prevent any kind of fuel leaks or sparks. Modern fuel tanks are pretty tough things, they can take quite a beating, and not burst or leak.
#3 Fewer fittings. with an external pump, you have the fitting at the tank, 2 fittings at the pump, and a fitting at the fuel rail.
Now, from a maintenance and repair point of few, having the pump in the tank is a PIA, you have to remove the tank to remove the pump (in most cases).
