How full to fill??!

[z1nonlyone]

Hey I am wondering how full should diesel tanks be filled on your trawler? I have a Kadey krogen 39 with two 350 gallon tanks that I just filled after 2 years of ownership. I filled them within 2 inches of the top, but then began to wonder if I should have left more airspace at the top..... My thoughts range from fuel expansion to stress on the tanks to sloshing out the vent in a rough sea.. Just trying to get different opinions.

chris

 

[Mako]

I would fill up to the 100% filled mark on your sight glass so you can track your usage accurately

 

[dhays]

I have 2 x 200 Gal tanks. I rarely fill them full unless I am planning an extended trip. I don't need to be hauling the extra weight.

For convenience, I will usually put in about 150gal of fuel when I am down to 100 total gal in the tanks.
It is easiest for me to transfer most of the fuel to the port tank then add fuel to the starboard tank. Often there is a discount for a certain amount of fuel an if so I may take on more or less depending.

Even with full tanks, a well designed system shouldn't spill fuel out the vents.

I don't worry about having partially full tanks over the winter. Despite the "dockside wisdom", I have never had water in my fuel due to condensation (or any other reason).

 

[z1nonlyone]

yes, weight is another thought. I noticed that my exhaust outlet is partially submerged now after filling which could allow marine growth. I have not experienced any water in my fuel either. I think I will take the boat out more and burn some fuel! Maybe save having full tanks till I plan a long trip..

 

[rwidman]

I would say it's your personal preference. One advantage to filling them completely is that you can keep a pretty accurate track of your fuel burn rate and you can predict when you will need to refuel by the number of hours you have run since the last fill up.

As for a sight glass, that's great if you have one, but you probably can't see it from where you are filling the tanks so unless you have a remote camera trained on it, that probably won't work.

 

[Choices]

I fill to the bottom of the fitting. I want as little air in the tank as possible.

We have extreme temperature swings here, and I have had condensation covering everything in the engine room, but only once.

A large heater solved that problem.

I figure all that fuel will keep the tank interior well lubricated.

 

[koliver]

My boat sits perfectly trimmed if all the tanks, fuel and water, are full.
When filling with water, overflow out the fill is acceptable.
When filling fuel, the noises generated by the flow of fuel into the tank give enough warning of complete filling so spilling doesn't occur. I have to trim side to side to maintain a level attitude with full tanks and with the dinghy hoisted on the davits, as the weight of the outboard can upset the side to side trim.
I have never experienced any issue related to the amount of fuel in the tanks.
Who has the agility or the time to check on sight glass levels (if fitted) while filling at the usually busy fuel barge?

 

[JDCAVE]

My boat sits perfectly trimmed if all the tanks, fuel and water, are full.

When filling with water, overflow out the fill is acceptable.

When filling fuel, the noises generated by the flow of fuel into the tank give enough warning of complete filling so spilling doesn't occur. I have to trim side to side to maintain a level attitude with full tanks and with the dinghy hoisted on the davits, as the weight of the outboard can upset the side to side trim.

I have never experienced any issue related to the amount of fuel in the tanks.

Who has the agility or the time to check on sight glass levels (if fitted) while filling at the usually busy fuel barge?

What he said. My KK42 rides better full. I don’t think a lighter boat necessarily has better fuel economy. I have 4 tanks. I generally try to keep the newest fuel in the aft tanks, so move the fuel in those tanks forward prior to filling.

Jim

 

[rwidman]

Some of us may have boats that hold 1,000 gallons of fuel, others (mine) may hold less than 100 gallons of fuel.

A single answer won't fit every situation.

 

[tiltrider1]

What I would not do is fill the tanks to he brim on a hot day and then park the boat. As the fuel warms up it expands and soon runs out the vents.

 

[Simi 60]

925 gallons a side on ours
I saw them close to full once with about 700 gallons a side.

 

[ksanders]

I always fill my tanks

Why???

Full tanks provide 3500 pounds of ballast weight at the bottom of the boat helping to smooth rolling in beamy seas.

Full tanks give me options. Options where to go to port. Options to stay at sea for an extended period of time if need be.

The ONLY benefit I see with not filling my tanks is if I am planning on a short trip up on plane. Any boat up on plane performs better the lighter it is.

 

[MYTraveler]

I like to leave a few inches for expansion, but carry enough fuel that range has never been a problem.

 

[rslifkin]

I usually fill mine unless I know I'm heading towards cheaper fuel. No reason to fuel up more often in my mind. We carry 420 gallons total.

At the same rpm, our slow cruise does get a couple tenths of a knot faster and makes the same or slightly less wake as we get lower on fuel, as our tanks are aft, so as we burn fuel, the stern comes up and we drag less transom through the water. Up on plane, there's no noticeable speed difference, just takes a bit less tab to reach best speed trim if we're light on fuel (and the boat climbs onto plane a hair faster).

 

[Lou_tribal]

Never more than 3/4 full for me (about 200L on each side). Reason is that I don't want fuel return to overfill any of the tank.

L

 

[FlyWright]

I top 'em off when I can and track the fuel flow. I have a sight gage, but as mentioned, it's hard to see while filling. I also have vent whistles that go silent the moment fuel enters the vent line, allowing for an early shutoff at FULL. I also have a Davis fuel recovery bottle to catch any vent overflow but find it unnecessary with the whistles.

I like that way my boat rides when full of fuel and water and with rising fuel prices, I figure it's a no-brainer for me to keep 'em full when possible.

 

[rwidman]

One problem I have had when filling my tanks is, diesel fuel seems to foam up as it's being pumped. Unless I have the nozzle on a very slow setting, by the time I hear the gurgling in the vent, even if I shut it off, the fuel still comes out of the fill opening and onto the deck.

 

[4fun1]

One problem I have had when filling my tanks is, diesel fuel seems to foam up as it's being pumped. Unless I have the nozzle on a very slow setting, by the time I hear the gurgling in the vent, even if I shut it off, the fuel still comes out of the fill opening and onto the deck.

Make sure your vent line doesn't have a droop in it that holds fuel. Mine did and i had the same problem. I had to fill real slow. The vent line is now sloped better and I can fill with the nozzle wide open.

 

[rwidman]

Make sure your vent line doesn't have a droop in it that holds fuel. Mine did and i had the same problem. I had to fill real slow. The vent line is now sloped better and I can fill with the nozzle wide open.

This is with both tanks (port and starboard) and I'm pretty sure there is no loop because the vent lines are very short. I will check though. Thanks.

 

[High Wire]

I also calculate the fuel needed to stop 2 inches from the top. My tanks fill at 5.3 gal per inch. If I need say 18" to get there, I will add 18X5 or 90 gallons per tank. That gives me a good margin to spill. Don't forget while filling one tank, if your cross-tie is open, with time the other tank is also very slowly filling. The second tank will take a gal or two less than the first tank. My backup is I always keep my ear within hearing distance of the vent so I can stop filling at the first sign of any gurgling sound. You have to watch out for high background noise. Needless to say putting diesel fuel in the water will ruin your day.

 

[jleonard]

I used to go to about 7/8 full. If I was a little less it did not matter at all. I had so much fuel for a single Lehman (360 gallons) that a few gallons meant nothing.

 

[koliver]

You have to watch out for high background noise.

I have noticed that fuel barges tend to locate next to float plane landing areas.

 

[Marco Flamingo]

On the first fill when I got the boat I marked the sight glass, put in 100 gallons, and went below to mark again. Did the same on both tanks, although I think they are identical. This was on the part of the tanks that is rectangular, not on the bottom @ 10 inches that is sloped to fit the hull. That gave me a "gallon per inch" or "liter per cm" calculation for future use. Only took a few seconds at the fuel dock. Then, I marked it several times before/after a few days. That gave me a inch or cm per hour burn rate when cruising. I average .206 inch per hour. I could compute that into gph, but I don't find that information too important on a boat. I want to know when to fill and how much.

I fill it up. Price and convenience in getting in and out of the fuel dock are the main issues. If the fuel dock is empty, I can see the attendant just standing there, no wind, cold beer, etc., that might outweigh fuel costs. But if like last week, I was passing a dock that had fuel $.58/gallon cheaper than most, that's where I'll stop in. I don't notice any change in performance when full. I do notice a change in peace of mind when full.

 

[Wdeertz]

I previously owned KK39-33 and always filled to the 325 gallon mark to allow sufficient room for expansion. 650 gallons was more than enough to cover almost any cruise except crossing the ocean. As I recall the sight glass first reading was at the 300 gallon level.

 

[Osprey69]

One problem I have had when filling my tanks is, diesel fuel seems to foam up as it's being pumped. Unless I have the nozzle on a very slow setting, by the time I hear the gurgling in the vent, even if I shut it off, the fuel still comes out of the fill opening and onto the deck.

I put a "whistle" in the vent line of my sailboat. When the whistle stops, stop pumping. Might that not be a solution for these situations?

Or are these flows so fast that it will not work.

 

[kapnd]

My tanks filler necks extend a (unknown) few inches into the tanks top, presumably to prevent overfilling, but has the unfortunate consequence of compressing, then suddenly expelling air and fuel when topped off. The fill line is 2”, the vent is 3/8”, so guess where the excess goes!
I’m looking for an internal pipe cutter…

 

[markpierce]

I stop fueling when I hear a particular higher sound pitch. (Have four fuel tanks.) It is too easy to overflow. Best to have absorbent cloths at hand.

 

[RonR]

We always try to keep them topped off. Fuel is only going up in cost, might as well buy it now. We pack 400x2 and use all of it!
It rides better with full tanks, it goes faster with empty ones !

We have a Davis No-spill catch can and it works.
Rumors are they do not make them anymore, but it would not be that difficult to fab up something.

 

[rwidman]

I put a "whistle" in the vent line of my sailboat. When the whistle stops, stop pumping. Might that not be a solution for these situations?

Or are these flows so fast that it will not work.

Different marinas have different pumps and nozzles. I had to cut the bead chain holding my fuel caps so I could get the larger nozzles into the deck fitting.

If the nozzle is small enough, air escapes around the nozzle and as long as I slow the fuel down when it's close to full I'm OK. If the nozzle just barely fits the nozzle barely fits into the deck fitting, I usually have foaming and spillage.

I try to keep an absorbent pad nearby when fueling.

 

[psneeld]

My experience is larger nozzles mean faster rate of delivery pumps. Small tanks can foam up no matter the vent size as it is the velocity that causes the foaming.


No science here..... just experience filling vessels from 26 feet to over 80.


Many places ask whether you can take fast or slow delivery... they will ask about vent size but that is about blowing the tank versus foaming.