Where to pass the fuel filling hose and vent fuel hose?

[s_explore]

Hello,

I am rebuilding a boat and now I'm at the point where I need to install the fuel tank. How this boat was made by the fabricant, thos hose were passing under the floor through the foam that help for flotaison under the floor. It was not accessible for repair or replacement. I am thinking passing the hose to the back of the boat and have the fuel cap at the back of the boat with the fuel vent. But I am not sure if that is a good idea, if anyone have any suggestion or new ideas I would greatly appreciate it. Here some picture

Also does anyone knows how high the engine mount needs to be? The two blocks where the mounts from the engine will be screwed? My old ones were all rotten and just desintegrated when I removed them.

 

[Chris1956]

Run the vent and fill hoses directly to the stern. Then route them to one side of the transom. The vent should go straight out the transom and the filler up thru the cap.

 

[Scott Danforth]

you have to mount the transom shield, install the engine (while hanging from the hook), and align it to get your block height

regarding the fuel fill and vent. I would go straight out the side of the boat by making a tube thru the stringers and then up the gunwale.

running to the back will create a dip in the line and you will never get fuel in the tank

 

[Chris1956]

Scott says "running to the back will create a dip in the line and you will never get fuel in the tank". That is simply not true. Many boats (including mine) have that configuration. The fuel filler hose is wire reinforced, quite rigid and doesn't sag easily.

I also do not recommend cutting 2" holes in the stringers. Of course, if you are a marine engineer, and you know them to be still strong enough, cut away.

 

[Grub54891]

Should have done what I did. Measure everything three times before teardown, and measure constantly during teardown. Everything fit pretty well when I was done.

 

[s_explore]

Run the vent and fill hoses directly to the stern. Then route them to one side of the transom. The vent should go straight out the transom and the filler up thru the cap.

This is what I am thinking. I don't want to do hole in the stringer, there is also foam there that I will need to cut and that would just be a mess.

"running to the back will create a dip in the line and you will never get fuel in the tank"
I am not sure how this would create a problem can you explain please.

 

[s_explore]

Should have done what I did. Measure everything three times before teardown, and measure constantly during teardown. Everything fit pretty well when I was done.

Yeah this is what I done but forgot to measure the engine mount... But Scott idea seems a good idea that I will tried.

 

[s_explore]

This is what I was thinking. See black line in pictures, but line goes from the front of the fuel tank to the rear. Hole in the bulkhead, hose run in the bilge and goes to one side of the boat.

 

[JASinIL2006]

Just in case this is helpful...
My boat has the fuel filler cap and vent in the back, just behind the sunpad. (See first pic below for interior detail of hose attachment to filler cap and vent.) This was when my boat was torn apart for restoration.

The hoses run down the transom on the starboard side of the keyhole, along the floor next to the engine bay (see second picture for detail) and then down under the floor, through a notch in the bulkhead and into the gas tank.
(The third pic shows the entry of the hoses under the floor, although the hoses would not be running through the engine bay when the engine is installed, of course.)

I don't have any problems with gas collecting in filler line. When sitting on the trailer, there is no dip in the filler hose that would allow gas to collect; it all runs downhill and straight into the tank. I think having a dip where gas would collect in the filler hose is what Scott was cautioning against.

 

[Chris1956]

From the original photo, I had though the fill and vent were in the rear of the tank. That makes them easy to route thru to the engine compartment. Cutting or notching a frame is much better than cutting or notching a stringer.

However, the way the picture looks with the black lines, (fill and vent in the bow) the fill and vent could be run forward and then up into the cap.

Alternatively, you could flip the tank around so the vent and fill route easily to the engine compartment. The fuel line is much thinner <1/2" so it can travel the length of the fuel tank, on top of the fuel tank and follow the filler and vent lines to the engine compartment.

However, a front fuel pickup could deprive you of some fuel capacity, since on a boat the bow is usually raised somewhat, so the height of the fuel level in the stern is higher.

If you install a length of fuel line on the inside end of the fuel pickup, with a 90* bend, so that the rubber line points rearward, you will restore much of the lost fuel capacity. Many tanks have this feature.

Just some ideas.

 

[flashback]

However, the way the picture looks with the black lines, (fill and vent in the bow) the fill and vent could be run forward and then up into the cap.

This was how my old scorpion was plumbed. the filler cap was in the starboard gunwale just forward of the helm. very convenient.

 

[s_explore]

However, the way the picture looks with the black lines, (fill and vent in the bow) the fill and vent could be run forward and then up into the cap.

Right the fill and vent are at the bow of the boat right now.

Alternatively, you could flip the tank around so the vent and fill route easily to the engine compartment. The fuel line is much thinner <1/2" so it can travel the length of the fuel tank, on top of the fuel tank and follow the filler and vent lines to the engine compartment.

This seem to be a good idea, I wasn't sure if it would be bad for the fuel line to be at the front.

"If you install a length of fuel line on the inside end of the fuel pickup, with a 90* bend, so that the rubber line points rearward, you will restore much of the lost fuel capacity. Many tanks have this feature."

I am not sure what do you mean here. I should install a fuel line with a 90deg inside the tank? Do you have an example like picture or something.

Thank you very much for the help very appreciated

 

[todhunter]

It's a similar idea of a "flop tube" in an aerobatic airplane fuel tank (google it). The tube essentially extends the end of the fuel pickup tube inside the tank to allow it to draw the fuel from the deepest part of the tank and/or where the fuel is at.

If you just flipped the tank around and had the fuel pickup at the front, you may starve the engine for fuel while trying to get up on plane if you have much less than a full tank, because all the fuel runs to the back / downhill end. Adding the fuel pickup extension will allow it to draw fuel out of the back of the tank, where all the gas will be most of the time.

 

[s_explore]

It's a similar idea of a "flop tube" in an aerobatic airplane fuel tank (google it). The tube essentially extends the end of the fuel pickup tube inside the tank to allow it to draw the fuel from the deepest part of the tank and/or where the fuel is at.

If you just flipped the tank around and had the fuel pickup at the front, you may starve the engine for fuel while trying to get up on plane if you have much less than a full tank, because all the fuel runs to the back / downhill end. Adding the fuel pickup extension will allow it to draw fuel out of the back of the tank, where all the gas will be most of the time.

Ooh thank you for the explanation that is very well explained.

Can I just use normal fuel hose and put it directly in the tank or it needs to be some sort of metal tube?

 

[Scott Danforth]

Ooh thank you for the explanation that is very well explained.

Can I just use normal fuel hose and put it directly in the tank or it needs to be some sort of metal tube?

USCG has very specific requirements on fuel systems.

 

[s_explore]

Finally I have check my fuel pickup and I don't think I could modify it without cutting it out and welding it back to the tank. I don't know how to weld so I would like to avoid that.

 

[Chris1956]

Most fuel pickups unscrew from the tank. I cannot tell from the photo whether your does.

I had a vent that was pressed in, that I needed to swap with the fuel pickup, which was threaded. The vent fitting would rotate but not come out. I ended up drilling it out and threaded the collar to accept a threaded nipple for the vent and the threaded fuel pickup fitting.

 

[Baylinerchuck]

Having a dip in the fill tube where fuel can sit acts as a trap in plumbing. Will you be able to fill the tank? Yes. Will it be a pain in the ass? Yes. The dip will cause the auto shut off on a fuel nozzle to trip off at high flow as fuel and vapors back up the fill tube. You’ll still be able to fill the tank, albeit slowly. It’s very annoying, especially when fuel spits on you out the fill port.

I posted a few pictures of how I did mine below. I like you did not want the fill and vent tubes stuck in the floatation foam.

 

[76SeaRay]

On mine, the fuel fill and vent lines ran through plastic "dryer" tube through a hole in the stringer on the starboard side and then forward about 3 feet then up the gunwale. I decided it was easier to use the same routing but I used ABS pipe and ran the hose through that so it can be changed if ever necessary. My stringer is 10 1/2 inches high at the point of the hole so the 2 1/2 inch hole won't affect it much if at all. The ABS pipe runs through the stringer.

Also, if you fill up at a dock while in the water then remember that you need to make sure the hose runs downhill while in the water. Sitting on the trailer may or may not simulate the angle of the hose when it sits in the water.

 

[s_explore]

On mine, the fuel fill and vent lines ran through plastic "dryer" tube through a hole in the stringer on the starboard side and then forward about 3 feet then up the gunwale. I decided it was easier to use the same routing but I used ABS pipe and ran the hose through that so it can be changed if ever necessary. My stringer is 10 1/2 inches high at the point of the hole so the 2 1/2 inch hole won't affect it much if at all. The ABS pipe runs through the stringer.

Also, if you fill up at a dock while in the water then remember that you need to make sure the hose runs downhill while in the water. Sitting on the trailer may or may not simulate the angle of the hose when it sits in the water.

Ok seems to be a good idea. I think I won't really have choice doing that, other option might cause dip in the fuel line.

Did you put foam under your floor? If yes, you were not concerned that the foam could expand and break the ABS pipe?