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Old 07-28-2010, 06:48 PM   #1
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Fuel loading

I'm wondering what you guys thing about fuel loading and fuel burning. My Carver ACMY has 3 fuel tanks, 2 saddle and the aux tank located in the most aft section of the boat. Each tank holds 110 gallons.*It would seem most economical to not load fuel in the aux tank unless it was needed. Why carry around an extra 700 + lbs if it's not necessary. And doesn't that much weight that far back have an effect on the ability of the boat to come up on plane?

If fuel is in the aux tank, should it be burned first?

And here's a zinger, what about ValvTect as a fuel additive for diesel?

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Old 07-28-2010, 07:17 PM   #2
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Fuel loading

How much fuel you carry on board will depend on how far and how often you cruise. Our boat has five tanks, two saddle "cubes" on each side of the engine room that hold 85 gallons each and a 60 gallon day tank in the bilge in the engine room. This give us a total of 400 gallons.

The engines and generator normally pull from the day tank which we refill periodically by gravity from the saddle tanks. The engine's fuel return also is normally valved to go to the day tank. Our fuel management process is to drain an opposing pair of saddle tanks into the day tank which normally takes a couple of months or more depending on how often we're able to take the boat out. When the front or rear pair of saddle tanks is empty we leave them that way while we start pulling from the other pair of opposing saddle tanks. When this pair is about 1/3 full we then fill the empty pair and repeat the process.

If 220 gallons is sufficient for your typical useage than there is no point in carting around the additional 110 gallons. As you say, weight at the back (or front) of a boat can affect its trim with regard to performance unless that weight was intended to be there and the boat was designed accordingly.

What is important is that your fuel stay as fresh as possible. Better that you run through your fuel reasonably quickly and then refuel than have fuel that sits on the boat for months and months and months.

How is the fuel pulled from your auxilliary tank? Is it a gravity flow to the other tanks or to the engine fuel feeds from the lowest point in the tank or does it use a typical pickup tube? The ideal situation is to be able to pull off fuel from the lowest point in the tank which will get water and contaminants out. But if the tank has a pickup tube that leaves a few inches of fuel in the bottom of the tank un-picked up, that could provide a chance for water to accumulate in the tank over time as well as contaminants.

So if you don't need that fuel on a regular basis, and if there is no risk of buidling up water in the aux tank from moisture from condensation or any other source, then leaving it empty may be a smart idea.* Ideally the aux tank is accessible and has at least one inspection port that can be used to examine and clean out (if necessary) the tank.* If the tank is empty now, or when it becomes empty, you could pull the inspection port and make sure the inside, particularly the bottom, is water and contaminant-free.* At that point it should be able to sit empty for years if you have no need of its capacity.

Additives can help extend the viability of fuel but that is even a matter of debates as a search of this forum's archives will show.

We use two additives in our fuel at the recommendation of our diesel shop and friends in the marine diesel industry. We have debated the effectiveness and necessity of additives on this forum, but at this point we've elected to follow the advice we've been given by the people we know. So we use Hammond's Biobor, which is a bug-killer for diesel fuel, and Hammond's Select 3 which is a stabilizer and lubricity additive.

There are people who believe biocide, stability, and lubricity addives are a good idea, people who believe they are a bad idea, and people who believe they are unnecessary but don't hurt anything. What I know about additives and petro-chemistry wouldn't fit on the head of a pin so all I can do is make a judgement based on my take on the people who have given us advice.

I have no experience with ValvTect as it was not one of the additives that was recommended to us. I'm not trying to imply that it's good, bad, or indifferent. I simply don't know.

-- Edited by Marin on Wednesday 28th of July 2010 08:20:49 PM

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Old 07-28-2010, 09:59 PM   #3
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RE: Fuel loading

Sounds like a great idea not to use the aux tank or even to remove it. Ideally a boat should have most of her weight just aft of midships. To have it at either end or (heaven forbid) at both ends like a tandem canoe is folly. Put batteries, holding tanks, fuel tanks, engines ect as close to the center of the boat as possible. Most of our trawlers have one pointy end and a broad and rather flat stern. At speed a trawler runs best w her load close to but aft of ctr.*In following seas weight a bit further aft is desirable. If your boat is slim and very pointy fwd and wide and full aft you almost can't get weight too far aft. Weight too far fwd would be a handful or possibly even tragic. A boat that is full fwd AND aft is much more tolerant of casual weight distribution and over loading. The manufacturer can tell you where the design water line is. I've worked in boat building and all boats of this type are quite different as to what mechanical equipment is specified for an individual boat and also how much consideration is given to balance and trim. I have a 30' boat w 100 gal water tanks aft. Fortunately her stern is very full so I keep the tanks fairly full. Don't want to be caught in following seas w a light stern.

Eric Henning
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Old 07-30-2010, 05:41 AM   #4
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RE: Fuel loading

Thanks guys for your input. There was a recent article in Motor Boating magazine that advised to keep the fuel tanks as full as possible to prevent condensation. I know this has been a debatable issue for some time, similar to fuel additives, so who knows.

I started a thread on the sea ray forum: about Valvtect and fuel additives in general. Interesting reading. Be sure and check out this link: concerning an independent test on diesel fuel lubricity. I haven't put any fuel in my boat yet so am very interested.

I'm going to call Carver and ask them if they have any info or advise about weight distribution.
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