Fuel tank empty or full?

Many boats suffer from a bad O ring , so any water passing by the fill cap becomes a problem.

Our solution is cheap and sure.

Purchase (or find in the scrap pile) a piece of GRP at least 1/2 inch thick.

Cut it to match the fill hole in the deck and the OD or larger of the deck fitting

When the sealant under the fuel fill is renewed simply install the spacer .

Now any water running by will need to be deeper than the spaced up deck fill.

Could catch your toes tho.

This also works for stanchion bases , davit mounts and windlass mounting.

Tom.B said:

I have never seen any proof that full tanks or empty tanks matter either way. .

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TB

While I won't argue the full tank issue, I do find it interesting that many on this forum swear by the use of "fuel polishing" to keep their fuel clean. That being the case, how does it get "dirty" to begin with? Empty tanks maybe?

FF said:

Many boats suffer from a bad O ring , so any water passing by the fill cap becomes a problem.

Our solution is cheap and sure.

Purchase (or find in the scrap pile) a piece of GRP at least 1/2 inch thick.

Cut it to match the fill hole in the deck and the OD or larger of the deck fitting

When the sealant under the fuel fill is renewed simply install the spacer .

Now any water running by will need to be deeper than the spaced up deck fill.

Could catch your toes tho.

This also works for stanchion bases , davit mounts and windlass mounting.

Click to expand...

That is a good general idea! I'm putting on a anew windless soon and will think closely on your suggestion.

Regarding fuel fill seal, to keep it so that toe stub is not created...

In addition to making sure that "O" ring is in good condition I keep jar of Vaseline always handy. Each time I open fuel fill hole I put liberal amount of Vaseline onto the "O" ring and all the top's threads; also wipe some on female thread area too. When screwed tight the Vaseline squeezes out all around the cap's seam. Paper towel wipes it clean.

That way the seal against water intrusion is perfect and the Vaseline, made of fossil fuel ingredients and compatible with gas or diesel, poses no threat to fuel in tank.

Your in Mystic, CT. There is not a problem with condensation up here like in other parts of the country. I always just put the boat up with what is left in the tanks. If there at 1/4 or full it doesn't matter here. I've never had a condensation issue in 40 years of boating.

Want a read a sad story of how I managed to get water in my fuel? I really had to work on it too. This occurred when I had the Nordhavn. It carried 1000 gallons of fuel in 4 tanks.
I thought I had a sanitary tank vent plugged so I went and got a fresh water hose to flush it from outside, on the side of the boat. Yes, I had a hull diagram, self made, of all the hull opening and vents. Well, I ended up putting about 20 gallons of water back through the vent only to realize, I was filling one of my 4 fuel tanks. I called a company out to polish the fuel, clean and inspect that fuel tank. He unrolled his big bladder on the walkway, pumped all the fuel into it, pulled the tank inspection plate, cleaned out the tank, inspected it, pronounced it clean and undamaged. He polished the fuel as he refilled the tank after reinstalling the inspection plate.
How much did it cost to polish about 500 gallons of fuel? Ah, that's a good question. I do have a tendency to forget the price of things that 'cost too much'.

After that incident, I installed a fuel transfer pump with a Racor filter so as to transfer fuel between tanks for timing the boat.

That is my very sad, self imposed "How I got water in my fuel."
Oh, I corrected the 'hull opening chart' too.

FF said:

Many boats suffer from a bad O ring , so any water passing by the fill cap becomes a problem.

Our solution is cheap and sure.

Purchase (or find in the scrap pile) a piece of GRP at least 1/2 inch thick.

Cut it to match the fill hole in the deck and the OD or larger of the deck fitting

When the sealant under the fuel fill is renewed simply install the spacer .

Now any water running by will need to be deeper than the spaced up deck fill.

Could catch your toes tho.

This also works for stanchion bases , davit mounts and windlass mounting.

Click to expand...

FF,

What's GRP? And are there many fuel fills on the deck? Also, why would you want to raise up davit mounts, etc.? If they're bedded right, no issue, if you re bed them. What am I missing?

"What's GRP? "

Glass Reinforced Plastic , fiberglass , probably what your boat is made from.

"And are there many fuel fills on the deck? Also, why would you want to raise up davit mounts, etc.? If they're bedded right, no issue, if you re bed them. What am I missing? "

You are missing the reality that bedding compound fails in time , and has to be redone.

Some folks wait till the fitting leaks , which is fine on an all GRP built boat
but a horror for many TT where a leak rots the plywood core and major work is required.

By raising thru bolted fittings UP off the deck the amount of water needed to create a leak is raised.

That poor O ring on the fuel fill may never leak water into the tank , a huge plus.

0025 said:

As winter is approaching, should I fill my fuel tanks or leave them at 1/4.

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Wifey B: Winter? What? Approaching from what direction? Is it another Atlantic storm? Did we really get to W? Last I knew we were still on N. What is this winter stuff? I'll go Google it and maybe I can find out more. Doesn't sound like something I'd like.

My boat's owner's manual suggests keeping the tanks full to reduce the possibility of condensation introducing water to the (diesel) fuel.

I top off the tanks when I return from a cruise regardless so this isn't something I do for winter or summer, I just do it so I'll be ready for the next cruise.

FF said:

Many boats suffer from a bad O ring , so any water passing by the fill cap becomes a problem.

Our solution is cheap and sure.

Purchase (or find in the scrap pile) a piece of GRP at least 1/2 inch thick.

Cut it to match the fill hole in the deck and the OD or larger of the deck fitting

When the sealant under the fuel fill is renewed simply install the spacer .

Now any water running by will need to be deeper than the spaced up deck fill.

Could catch your toes tho.

This also works for stanchion bases , davit mounts and windlass mounting.

Click to expand...

You can buy those rungs pre made, with a split so you don't have to remove the hose, just raise the deck fitting and slip them on. No need to try and make one yourself.

FF said:

"What's GRP? "

Glass Reinforced Plastic , fiberglass , probably what your boat is made from.

"And are there many fuel fills on the deck? Also, why would you want to raise up davit mounts, etc.? If they're bedded right, no issue, if you re bed them. What am I missing? "

You are missing the reality that bedding compound fails in time , and has to be redone.

Some folks wait till the fitting leaks , which is fine on an all GRP built boat
but a horror for many TT where a leak rots the plywood core and major work is required.

By raising thru bolted fittings UP off the deck the amount of water needed to create a leak is raised.

That poor O ring on the fuel fill may never leak water into the tank , a huge plus.

Click to expand...

FF,

Good points. Guess I've been lucky, never had any bedding fail that couldn't be fixed with a tube of caulk, mostly cosmetic. But for older boats, great idea. I'd be more worried about water getting in the fill port than anything, and did have to put in a defector once to prevent that.

Art said:

In addition to making sure that "O" ring is in good condition I keep jar of Vaseline always handy. Each time I open fuel fill hole I put liberal amount of Vaseline onto the "O" ring and all the top's threads; also wipe some on female thread area too. When screwed tight the Vaseline squeezes out all around the cap's seam. Paper towel wipes it clean.

That way the seal against water intrusion is perfect and the Vaseline, made of fossil fuel ingredients and compatible with gas or diesel, poses no threat to fuel in tank.

Click to expand...

See above from a previous post of mine... I reiterate... simplest, least costly way to make sure water does not enter via fill hole into fuel tank.

WesK said:

You can buy those rungs pre made, with a split so you don't have to remove the hose, just raise the deck fitting and slip them on. No need to try and make one yourself.

Click to expand...

That would be "rings", not rungs. Too late to edit my post.

Never filled in 25 years, never condensation issue, figured less weigh while in dry dock is better.

Ski in NC said:

I routinely keep my tanks at a low level. Never had any water issues. I don't fill for the sake of filling.

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I keep tanks about 1/2 full unless wer'e going on a long trip.

Less fuel gets cycled more often and stays fresher. And my boat is hundreds of lbs lighter.

When I had new tanks made I asked for smaller tanks but they just made them like the original.

Over the years I've only found traces of water in my fuel. Now and then I pump up some fuel from the bottom of the tank through a 1/8" copper tube but because I've found so little water I don't do it very often now.

Had water concerns w ultralight aircraft too. They almost all have plastic tanks and I've never seen water in them. And of course at several thousands of feet above the ground we took engine stoppage fairly seriously.

Nomad Willy said:

Less fuel gets cycled more often and stays fresher. And my boat is hundreds of lbs lighter.

.

Click to expand...

Cycling fuel is not a problem we have.

We do keep the tanks full or nearly so but has nothing to do with condensation. Is simply we want to be ready to go and we fill by truck at home and get much better pricing.

We always add fuel at .20 left in tank. If going far we fill up. If not we put in .50 full.

BandB said:

Cycling fuel is not a problem we have.

We do keep the tanks full or nearly so but has nothing to do with condensation. Is simply we want to be ready to go and we fill by truck at home and get much better pricing.

Click to expand...

BandB,

What company do you use for home fueling? I've shopped and can't get anything better than the local marina, and with the marina I can pump out.

Nomad Willy said:

I keep tanks about 1/2 full unless wer'e going on a long trip.

Less fuel gets cycled more often and stays fresher. And my boat is hundreds of lbs lighter.

When I had new tanks made I asked for smaller tanks but they just made them like the original.

Over the years I've only found traces of water in my fuel. Now and then I pump up some fuel from the bottom of the tank through a 1/8" copper tube but because I've found so little water I don't do it very often now.

Had water concerns w ultralight aircraft too. They almost all have plastic tanks and I've never seen water in them. And of course at several thousands of feet above the ground we took engine stoppage fairly seriously.

Click to expand...

I hate when that happens.

Seevee said:

BandB,

What company do you use for home fueling? I've shopped and can't get anything better than the local marina, and with the marina I can pump out.

Click to expand...

In our area, Anchor, Luk, Peterson, Admiral, and Shoreline are a few. Peterson even delivers by barge. We've used Anchor and Peterson. Use Anchor since they are Valvtech. Palm Beach delivers north of us. We use AnchorIn your area, I'm familiar with Mobil and River and then Dockside delivers to your dock.

It may well be that our marinas charge more than the one you're using and our trucks charge less. Another advantage of truck is speed at which it pumps. Disadvantage is you have to schedule it.

Quantities are a big factor in delivery pricing. For instance a typical structure today might be something like $2.65 if under 200 gallons, $2.45 from 200 to 1000, $2.40 from 1000 to 5000, $2.35 over 5000. Plus prices often vary on method of payment.

I know the USCG and your insurance company would frown on this but, it would be nice to have a small drain at the bottom of the tank, to check for water.

BandB said:

In our area, Anchor, Luk, Peterson, Admiral, and Shoreline are a few. Peterson even delivers by barge. We've used Anchor and Peterson. Use Anchor since they are Valvtech. Palm Beach delivers north of us. We use AnchorIn your area, I'm familiar with Mobil and River and then Dockside delivers to your dock.

It may well be that our marinas charge more than the one you're using and our trucks charge less. Another advantage of truck is speed at which it pumps. Disadvantage is you have to schedule it.

Quantities are a big factor in delivery pricing. For instance a typical structure today might be something like $2.65 if under 200 gallons, $2.45 from 200 to 1000, $2.40 from 1000 to 5000, $2.35 over 5000. Plus prices often vary on method of payment.

Click to expand...

Wow, those prices aren't any bargains, but delivery could have some advantages. The lowest I'm getting for delivery is $2.65 and my marina, 1/2 mile away is $2.50. I could only put on perhaps 230 gallons at the most, but choose to fill for the mission and gonna haul it for some new transducers in the next few months, so I'll keep it light.

Also, I get nervous with those big gas trucks driving on my pavers, and then hauling the hose 150ft thru the yard. Not enough upside, yet.

But thx for the price comparison.

Seevee said:

Also, I get nervous with those big gas trucks driving on my pavers, and then hauling the hose 150ft thru the yard. Not enough upside, yet.

But thx for the price comparison.

Click to expand...

You and the USCG get nervous too.

OldDan1943 said:

I know the USCG and your insurance company would frown on this but, it would be nice to have a small drain at the bottom of the tank, to check for water.

Click to expand...

Still legal for diesel, very likely. There are standards for the valves, not sure this system passes on that regard.

diver dave said:

Still legal for diesel, very likely. There are standards for the valves, not sure this system passes on that regard.

Click to expand...

It doesn't pass the rust test either.

I think many boat fuel tanks are flat on the bottom and sit on a flat surface. Mine do and to provide for a sump like in the photo they would have had to reduce the capacity by quite a bit.

Seevee said:

Wow, those prices aren't any bargains, but delivery could have some advantages. The lowest I'm getting for delivery is $2.65 and my marina, 1/2 mile away is $2.50. I could only put on perhaps 230 gallons at the most, but choose to fill for the mission and gonna haul it for some new transducers in the next few months, so I'll keep it light.

Also, I get nervous with those big gas trucks driving on my pavers, and then hauling the hose 150ft thru the yard. Not enough upside, yet.

But thx for the price comparison.

Click to expand...

But there we have the difference. In our area here are some marina diesel prices.

Bahia Mar $3.20
Pier 66 $3.35
Sails $3.26
LHP $3.09
Harbourtowne $2.92

So, for 5000 gallons it can be $3000-5000 difference. It's also for the convenience factor and speed and known quality.

As to parking on pavers and dragging hose, we get filled most of the time at a marina with parking access immediately outside and within 50' of the boat. At home, we can get delivery by barge or we can park the fuel truck on the street and distance will be 120' and only across pavers, no grass, or take the truck on the drive to within 20' of the boat.

Obviously with the amount of cruising we do a very small percentage of our fuel purchasing is done at home. No more than 15-20%.

I kinda like the catch bowl but it would leave some water on the bottom of the tank as boats tip this way and that. Especially if the tank was'nt perfectly flat.

What I like is a port and valve in the lowest corner of the tank achieved by installation/design or by accident. My tanks are low fwd slightly and inbd too so my tanks almost always have any water in the inbd fwd corner of the tank.
I rig up a small pump, fix a hose to it and a 1/8" copper tube that is easily bent to whatever shape I want. I bend it kinda like a base cleff and carefully insert it through a pipe plug hole in the top of the aft/inbd corner of the tank. I think I get every drop of water up and in the plastic (semi clear) one gallon water jug. I can then see even the smallest drops of water. I'm due to do that.

OldDan1943 said:

You and the USCG get nervous too.

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WAY out of the jurisdiction of the USCG......

BandB said:

But there we have the difference. In our area here are some marina diesel prices.

Bahia Mar $3.20
Pier 66 $3.35
Sails $3.26
LHP $3.09
Harbourtowne $2.92

So, for 5000 gallons it can be $3000-5000 difference. It's also for the convenience factor and speed and known quality.

As to parking on pavers and dragging hose, we get filled most of the time at a marina with parking access immediately outside and within 50' of the boat. At home, we can get delivery by barge or we can park the fuel truck on the street and distance will be 120' and only across pavers, no grass, or take the truck on the drive to within 20' of the boat.

Obviously with the amount of cruising we do a very small percentage of our fuel purchasing is done at home. No more than 15-20%.

Click to expand...

Wow, those prices are brutal! And with that I'd be sure to patronize the delivery options.

Seevee said:

WAY out of the jurisdiction of the USCG......

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You just think so.
My brother's friend took a whiz over the side of his boat. The USCG sent him a ticket along with the photo.