Usable Fuel GW 335

[capeman]

I have a 2019 GW 335 with 290g main tank. Wondering what amount of that 290g is actually usable. I can estimate, but wondering if anyone has real world knowledge.

 

[seasick]

It depends on where you stand
If you and your friends stand aft, the tank will have a greater angle and the gas will pool towards the aft end of the boat, in effect making the effective level higher. You will have the greatest angle when getting on plane but not there. Now if you and your passengers decide to move forward, the effective gas level will lessen and you may starve the engines.
Seriously though, if you are planning on running to the last drop, you are going to eventually run out of gas

 

[Beyond A Wake]

Always calculate to leave at least 10% or 30G when refueling. ANother good question is how do you know when the tank is full? On my 2019 335 it is so hard to get any reasonable flow when fueling that the blowback can confuse you about tank being full when it is not.

How good is your fuel gauge as that is my greatest issue (only one) with the boat right now.

My CL7 shows either FULL or -- -- -- and when boat bow rises it shows full even if about 30G is used. Connection to Raymarine fuel manager is iffy at best.

H

 

[seasick]

I don't take long trips and honestly I can't remember the last time I filled the tanks in either of my two boats!
I do keep records and logs of things like gas added and the fuel gauge readings before and after fueling. I can estimate fairly well how much gas I have and how much I expect to use for a specific trip.
One of my boats has just the fuel gauge bar display but the other have a level display as well as estimate of gallons remaining, GPH consumption and gallons used since last reset.
I have a pretty good idea of how many gallons per hour I consume at cruise speed ( and at WOT in rare cases). If I am going cruising for 4 hours, I estimate what I will burn and make sure I have enough gas.

There are reasons I don't fill my tanks; The first is that it is a waste of money to haul an extra several hundred pounds of gas that I am not going to need. Secondly, I don't like to have the fill and possible vent hoses full of gas.

In your situation something is messed up with your gauge readings. Regardless, fuel level gauges on boats are inaccurate by the nature of the beast. It is much more accurate to have some sort of working fuel management system that measures consumption.
Finally, the rule for gas is 1/3 for the trip out, 1/3 for the trip back, and 1/3 spare gas. If you expect to use 25 gallons for a trip out, you should have at least 75 gallons in the tank.

 

[Beyond A Wake]

That is all correct and yes something is afoul with my stuff now. Anyway I do monitor the use and the GPH and MPG are pretty well shown. Under normal conditions I just calculate with 1 NMPG slow or cruise doesnt really matter and I again tend to keep my tanks over 1/2 as I usually fill up with less than 100G to full.
The remaining fuel on CL7 doesn't show anything except full or just lines. I have not manually calibrated it but used the default way by indicating when it is Full.
I live with it for now and try to get it going every time I fill up.

 

[capeman]

Thanks for the information and feedback. I have been for long trip planning assuming a 10% or 30g reduction in usable fuel. It would seem that is likely a reasonable assumption.

As far as filling up the tank near 100% it is indeed challenging but I do believe I've been able to fill it to the whatever the max might be. Its very slow going for the last 10g with many starts and stops.

 

[seasick]

If you are not going to use 200 gallons or so on a trip, why fill the tank? As mentioned your MPG will suffer due to the added weight and you won't have to fight that last 10 gallons.
As an aside, I have read several messages from folks with later model year boats that have the mandatory vapor recovery canister for the fuel tank. They seem to frequently have issues gassing up due to the fill nozzle constantly tripping.

 

[Beyond A Wake]

My reason for full(er) tank is less condensate water risk and if u need it it's there. But yes drawback is u do haul some extra weight. I also keep water tank and diesel tank full plus anchor and cleaning supplies etc.etc that all are seldom needed under way so in the long run burning a little more fuel is not that big a deal.
AND yes the new reg fuel fill vent is a real p i a . And no way to reach the Canister either.

H

 

[capeman]

If you are not going to use 200 gallons or so on a trip, why fill the tank? As mentioned your MPG will suffer due to the added weight and you won't have to fight that last 10 gallons.
As an aside, I have read several messages from folks with later model year boats that have the mandatory vapor recovery canister for the fuel tank. They seem to frequently have issues gassing up due to the fill nozzle constantly tripping.

I burn 130-150g on a typical fishing trip offshore. I feel that leaving the dock at full fuel provides me the option to go a bit further and provides me a solid safety margin. When I visit the NE Canyons I am full fuel plus 120g gas bladder. Knowing my actual useable fuel is most important on such a long trip where I burn minimum 250g. However, I agree with your point and often run less than full when staying close to home.

 

[Beyond A Wake]

How do you use the bladder? DO you have a transfer pump or do you have a direct connection/valve to fuel supply line?
h

 

[seasick]

My reason for full(er) tank is less condensate water risk and if u need it it's there. But yes drawback is u do haul some extra weight. I also keep water tank and diesel tank full plus anchor and cleaning supplies etc.etc that all are seldom needed under way so in the long run burning a little more fuel is not that big a deal.
AND yes the new reg fuel fill vent is a real p i a . And no way to reach the Canister either.

H

Here is an interesting view on filling the tank or not.
The argument is that a full tank will be subject to less condensation and I suppose that is true. How much condensation is a tough question to answer. The physics is complicated. Condensation will only occur during cycles of temperature so if you store or dock your boat where the temp and humidity doesn't change much ( like at night), the amount of condensation will be less.
I am assuming that ethanol gas is used. E10 will absorb about 1/2% water by volume. In a 200 gallon tank, that is 1 gallon of water. After that amount, water will fall to the bottom of the tank.
The water absorbed will be burn off in the motors. It is logical to assume that if a tank goes through multiple cycles of condensation, eventually water will start to buildup in the bottom of the tank. If enough builds up, you will suck more and more water into the motors and they don't run very well on water alone (wouldn't that be nice if they did).
So the argument is that if you are going to take multiple short trips, you should add only as much gas as you will need and do that before the trip. That way ,hopefully, you add fresh gas that can absorb new moisture.
I boat in the north east and we usually do not have the same temp extremes as the south nor the same constant high humidity and I can honestly say that in all my years of boating and my experience at my club, 90$ or more of water in the gas problems were due to water intrusion or a load of bad gas and not condensation.
There are issues with corrosion due to water in gas and those are typically worse with alcohol blends but that is another story.

 

[capeman]

How do you use the bladder? DO you have a transfer pump or do you have a direct connection/valve to fuel supply line?
h

I actually siphon the bladder into the main tank via the deck fill tube. I did consider direct connection and fuel pump. The direct connection would require modifications to the fuel supply lines which would not be straight forward given the routing of the lines. Not to mention dealing with gas lines and the related safety concerns - I am handy, but don't consider this something I should tackle. On the pump side, you can purchase a pump that transfers ~70g/hr. I can transfer ~60g/hr via siphon (1/2" hose). The pump also requires it to be plugged in and will hold some amount of residual gas once used. The additional complexity of the pump and associated safety risks doesn't buy me a much quicker fill time. I only visit the canyons 2-3x per year, so it makes more sense to keep the transfer of fuel as simple as possible in my opinion - so I just siphon it.

 

[capeman]

Here is an interesting view on filling the tank or not.
The argument is that a full tank will be subject to less condensation and I suppose that is true. How much condensation is a tough question to answer. The physics is complicated. Condensation will only occur during cycles of temperature so if you store or dock your boat where the temp and humidity doesn't change much ( like at night), the amount of condensation will be less.
I am assuming that ethanol gas is used. E10 will absorb about 1/2% water by volume. In a 200 gallon tank, that is 1 gallon of water. After that amount, water will fall to the bottom of the tank.
The water absorbed will be burn off in the motors. It is logical to assume that if a tank goes through multiple cycles of condensation, eventually water will start to buildup in the bottom of the tank. If enough builds up, you will suck more and more water into the motors and they don't run very well on water alone (wouldn't that be nice if they did).
So the argument is that if you are going to take multiple short trips, you should add only as much gas as you will need and do that before the trip. That way ,hopefully, you add fresh gas that can absorb new moisture.
I boat in the north east and we usually do not have the same temp extremes as the south nor the same constant high humidity and I can honestly say that in all my years of boating and my experience at my club, 90$ or more of water in the gas problems were due to water intrusion or a load of bad gas and not condensation.
There are issues with corrosion due to water in gas and those are typically worse with alcohol blends but that is another story.

My marina only sells non-ethanol fuel - no E10. So that is a plus. As far as water in fuel I have inline fuel/water separators one for each engine. In theory, no water should find its way to the engine. Filters are replaced annually and inspected for water. If water found, then efforts made to determine where water is entering tank. Right or wrong, I was told by the dealer to try to keep the tank full to minimize the occurrence of condensation. I am in Cape Cod and we have fairly large temp/humidity swings at times. I've never had any issues with water in the fuel.. knocking on wood.

 

[Beyond A Wake]

Right about condensation issues. I wake up in the morning with all house windows covered in condensate on the outside as the indoor temp is so low compared to outdoor and dew point. AC vents are blowing towards windows as well!!!
On the boat yes no E10 around marina either and temp variations are "small" as boat is kept in vented covered storage with same humidity and temp as outside. Summer to winter yes some difference but it comes gradually and boat is used all year round so not really a big issue, but keeping tanks at high level anyway.

Siphoning is a fairly fast way of transfer but deck fill is fairly high up so how deep do you drop the 1/2 in and how do you prime it?
I have one of those check valve hoses that can be used as a primer if possible to shake it in the bladder but then the opening has to enable it. Is that how you do it?

h

 

[seasick]

My marina only sells non-ethanol fuel - no E10. So that is a plus. As far as water in fuel I have inline fuel/water separators one for each engine. In theory, no water should find its way to the engine. Filters are replaced annually and inspected for water. If water found, then efforts made to determine where water is entering tank. Right or wrong, I was told by the dealer to try to keep the tank full to minimize the occurrence of condensation. I am in Cape Cod and we have fairly large temp/humidity swings at times. I've never had any issues with water in the fuel.. knocking on wood.

If your pickup is sucking water from the bottom of the tank, your water separator will fill with water. The water has to go somewhere.

 

[capeman]

Right about condensation issues. I wake up in the morning with all house windows covered in condensate on the outside as the indoor temp is so low compared to outdoor and dew point. AC vents are blowing towards windows as well!!!
On the boat yes no E10 around marina either and temp variations are "small" as boat is kept in vented covered storage with same humidity and temp as outside. Summer to winter yes some difference but it comes gradually and boat is used all year round so not really a big issue, but keeping tanks at high level anyway.

Siphoning is a fairly fast way of transfer but deck fill is fairly high up so how deep do you drop the 1/2 in and how do you prime it?
I have one of those check valve hoses that can be used as a primer if possible to shake it in the bladder but then the opening has to enable it. Is that how you do it?

h

I initially had a 1/2" hose out of bladder to a 3/8" primer bulb & hose. I've upgraded to a 5/8" primer bulb and hose, but still come out of bladder via 1/2" hose. I place the bladder (120g, 48"x48"x12") mid-cockpit which is raised 8-12" above main tank and run hose down fill tube for about 3.5' - so is likely right before 90 degree fitting into the main tank. I've tried from the rear deck, but the height from bladder to main tank is much too small (3-4") to keep a siphon running.

 

[capeman]

If your pickup is sucking water from the bottom of the tank, your water separator will fill with water. The water has to go somewhere.

Yup.. the purpose of the filter is to catch that water. If water is excessive.. check for other sources of intrusion.

 

[Gulffisher]

Right about condensation issues. I wake up in the morning with all house windows covered in condensate on the outside as the indoor temp is so low compared to outdoor and dew point. AC vents are blowing towards windows as well!!!
On the boat yes no E10 around marina either and temp variations are "small" as boat is kept in vented covered storage with same humidity and temp as outside. Summer to winter yes some difference but it comes gradually and boat is used all year round so not really a big issue, but keeping tanks at high level anyway.

Siphoning is a fairly fast way of transfer but deck fill is fairly high up so how deep do you drop the 1/2 in and how do you prime it?
I have one of those check valve hoses that can be used as a primer if possible to shake it in the bladder but then the opening has to enable it. Is that how you do it?

h

I haven't bothered doing the thermodynamics calculations, even thinking about it makes my head hurt, but I think the "air" space in a tank above the fuel surface is mostly fuel vapor and not air and therefore not water from said air. So while condensation is real, I just don't think condensation alone will account for fuel/ water seperators repeatedly filling with water. If you repeatedly have water in your fuel, FIND another source than condensation.

Now to the real question. If I am going to fish near shore (less than 75 miles), I will FILL my main tank every time I go. I have a known 190 gallon starting point and I reset my fuel used meter so I can keep track. I have only once ran the main tank dry but when I did I recall it yielded around 190 gallons, more or less. If I am fishing more than 75 miles, I will also fill the auxiliary tank giving me another 150 gallons. I always empty the auxiliary tank first, and it always runs dry at 150 gallons more or less. I would be surprised if fuel tank yields in other GW models were significantly different from mine.

I fill the tanks for two primary reasons, one of which has already been stated above, to allow me to go "just another 10 miles" when I can't find a good show closer in and for emergency. Over the years, I have more than once run as much as 40 miles, usually in a direction I don't really want to go, dodging thunderstorms. Yes I carry a heavier load than I may need. Yes I may average 32 gallons per hour for the first 150 miles instead of 30 gallons per hour. But I don't have to worry about going around heavy rain, frequent lightning, 30 knot wind and 6 foot seas and instead plow straight through such nastiness because I'm worried I will run out of fuel.