Re fuel remaining in place in some portion of the filler hose, typically rated only for A2 use, that is, to not have fuel permanently in the hose but suitable for enclosed spaces:
I agree that having fuel remain in the horizontal portion of the filler hose than crosses under the deck from the gunwale to the tank filler inlet can be a problem; the permeability of the A2 hose is not designated for having fuel present in the hose continually. For this reason when I am adding fuel to the boat I try to be mindful of this possibility. If we are adding fuel on the water, I try to keep the boat trim so the filler side (the port side on my boat) is raised higher than the other side. You can do this usually by moving a cooler to one side or just sitting on the gunwale on that side.
Once the boat is on the trailer and fuel will be added at a highway filling station, I try choose a pump so that, if there is any grade or slope involved, the trailer is aiming uphill. This helps to get the fuel drained out of the filler. Also, when loading the boat onto the trailer, it could be advantageous to have a slight tilt toward the non-filler side (again, on my boat, the starboard side) so that even when fueling on the highway the fuel tends to run downhill into the fuel tank and not remain in the filler hose.
The worst possible situation with the filler hose is for the hose to develop a dip or low spot in its path from gunwale to tank filler inlet, which then tends to collect fuel no matter what you do while fueling. You might be able to mitigate that problem whenever you get the boat in the water by having a couple of people sit on the other gunwale and get a rather steep list to that side, again encouraging the fuel to flow out of the filler hose. I try to do this when fueling on the water.
The worse situation is to add a lot of fuel for winter storage from a highway filling station with the boat on the trailer. If you then tow the trailer down any sort of big downhill grade, there is a good chance the fuel will move to the forward part of the tank and may rise into the filler hose; it will then sit there for six months of winter storage.
ASIDE: on our old sailboat the fuel tank was located directly below the cockpit deck level. The fuel filler inlet and cap were located on the cockpit deck, and the path into the tank was a straight vertical path. There were two advantages of this: when you added fuel, the fuel flowed directly down a short filler hose and into the tank, so there was no possibility of any fuel sitting in the hose; and, the tank level could be sounded with a stick to get the actual tank level. Because the fuel was diesel, the sounding stick was a smelly old pine dowel that would add a bit of fragrance to the locker in which it was stowed in a small section of PVC pipe fastened to a bulkhead. The other drawback of this arrangement was the location of the filler cap; being on the deck there was always some water sloshing round the deck when you did any cleaning or scrubbing of the deck. The filler cap had to have very good seals to keep the water out of the tank.
Braided hoses offer great abrasion resistance but are harder to assemble than smoother coatings as they need a cover/socket to prevent unravelling of the braided strands. The stainless steel braid can rub against other components wearing through them like a file. Braided nylon hoses have an inner stainless steel braid covered by an outer nylon mesh to prevent this abrasion. The nylon mesh however can get dirty and gunked up with contaminates. These types of hoses are typically used with crimp or reusable type AN fittings.
Push lock fitting use hoses with smooth outer skins over braided mesh. The braided mesh strengthens and protects the inner liner that handles the fluid. Push locks are often used with fuel and oil and therefore must be compatible with the harsh fluids. Common types include silicon or PTFE. Alcohol or e85 fuels can degrade some types of inner liners and so must be used with compatible hose types. The smooth outer cover hoses can look like generic rubber hose but don't be fooled these hoses have multi-layer designs often with specific mesh weaves for the application. The multiple layer design allows the hose to be flexible but still maintain strength under high temperatures and pressures.
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