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Thread: Aux aluminum fuel tank on a transom extension

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    Member Maast's Avatar
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    Default Aux aluminum fuel tank on a transom extension

    An earlier comment about me only having a 110 gal tank got me to thinking about where to put an aux 40 gallon (or so) tank.

    The only place I can think of is to put a diamond plate tank on the transom extension. Something along the lines of 12 inches tall by 12 inches deep by 66 inches wide (40 gals, 248 lbs)

    The motor is a Suzuki DF250 which weighs 580 lbs, the extension is rated for 950 lbs.

    I've seen propane bottles on a transom extension (good idea) but never noticed a aux fuel tank.
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    Member TWB's Avatar
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    Quote Originally Posted by Maast View Post
    An earlier comment about me only having a 110 gal tank got me to thinking about where to put an aux 40 gallon (or so) tank.

    The only place I can think of is to put a diamond plate tank on the transom extension. Something along the lines of 12 inches tall by 12 inches deep by 66 inches wide (40 gals, 248 lbs)

    The motor is a Suzuki DF250 which weighs 580 lbs, the extension is rated for 950 lbs.

    I've seen propane bottles on a transom extension (good idea) but never noticed a aux fuel tank.
    Not to distract but those DF250's are f'n SWEET!
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  3. #3

    Thumbs up Motor Trim

    I'd make sure it wouldn't interfere with triming the motor up, but if you can put a cooler back there, I wouldn't know why you couln't put a fuel tank. It'd be easy to hook up and fill too.
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    Moderator Paul H's Avatar
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    It depends on how your boat is currently balanced. An extra ~250#'s at the transom will definately be noticeable in how the boat handles.

    I'd opt for gunnel side tanks if you have room. Quite of few makers offer 18-25 gallon saddle tanks, and you could position them closer to the boats balance point for less affect on your boats trim. The downside is additional fuel line plumbing.

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    Member Maast's Avatar
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    I thought of interior saddle tanks, but I dont want to clutter up the rear deck with yet more stuff that I'll trip over or bang into.

    I'd love to do an underfloor tank, but its already taken up with fishboxes and the main tank, I'm a little leery of putting in a fuel tank under the floor inside the cabin area.
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    Member kaisersosei's Avatar
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    I would think twice adding that much weight to the extended transom. If you have a self-bailing deck, that would lower the water-line dangerously especially if you had a load of fish in the back and heavy seas. Even if you did not have a self-bailing deck, I would think that it would alter the handling of the boat and lower the back-end in big water which could be dangerous too. If you have been in over 6 foot seas or confused seas that resulted in you only maintaining hull-speed, it would be scary. Calm water, on-plane, not so much...

    I had a 20x20x20 (approx) aluminum cube built and fastened to the bulkhead on my Fish-rite with a filler toward the rear corner and put a marine grade pad on it for a seat and it worked out well. It was then plumbed to the main tank with a valve. I think I got something like 38 gallons out of it. Silverstreak did the work and it looked good too as I had it painted to match the boat. It was also handy to step on to get on the gunwale to go out front. I had mine removable so I would only take it on an extended cruise. Worked out well for not much money.

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    Member Rod in Wasilla's Avatar
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    You can always load up your transom extension with 250 pounds of sand in cotton bags to try it out. If things start looking a little overloaded, you can cut the bags or dump 'em off and you would be no worse for trying.
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    Member hoose35's Avatar
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    I agree that you should try putting some weight on your transom and trying it out, I think you would probably be ok. Also, I have my tank mounted under the floor and most of it is inside my cabin, I have had the boat for nearly 5 years and have never ran into any problems with it being located there, and without a doubt, the best place to place a large tank is directly in the center of the boat as low as possible.

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    I suspect that my comment in one of your other posts got you thinking. I carry close to 400 gallons when all three tanks are full. I only fill the front tank when I am going on an extended trip like we tend to do when chasing spring bears. Two of my tanks are directly below the cabin and one under the cockpit floor. All three have access hatches above the fittings. I have never had any vapors in the cabin. My old 24 foot hewescraft had a 160 gallon tank. Half of it was below the cabin. No problems. Run it as is for the 1st season. You might find that you have plenty of range with the given fuel supply for your needs. Have fun outfitting her!
    Spending my kids' inheritance with them, one adventure at a time.

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    Member Gerberman's Avatar
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    Default 3 tanks

    I have three fuel tanks on my boat and two 250 Suzuki's I always run the rear tank down on the way out to the fishing grounds to avoid the self baling deck problem, if you keep the fuel on the stern of the boat it will become a problem as the fish box fills up. It never hurts to have extra fuel available, Just use up the unbalanced fuel first. Gerberman

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    Member Gundog's Avatar
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    The Raider has no reverse chine to help with roll you would not want that much weight that high changing your center of gravity that is why fuel tanks are in the bottom of the boat to keep the center of gravity low.

    I suspect there would be room to add more tanks under the floor in the center of the boat under the floor in the cabin keeping the weight low and balanced. You may want to just run it and get some fuel consumption numbers that 250 is pretty good on fuel. Many of the guys carrying 400 gallons have a much higher burn rate and need the extra storage.

    Mike

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    I have two big insolated fish holds that I end up using to store gear. The reason for this is that a cooler is easier to clean the the fish holds, so I use a cooler in the cockpit on on the transom to store fish and really don't use the fish holds. The reason I mention this is if I needed more fuel, I would consider putting a tank in one of the fish holds since this is out of the way and not raise the center of gravity of the boat.
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    Member bhollis's Avatar
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    I would not only be concerned about the added weight on the stern, and how that might affect your boat's fore and aft trim, but also the possibility that the free surface effect of the fuel in the tank could have a significant effect on your boat's roll stability.

    You might want to do some reading up on free surface effect.

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    Member Maast's Avatar
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    Thanks for all the advice. This is exactly the kind of feedback I was hoping to get.

    You've got 400 gallon capacity in your boat Spoiled One?! Good lord - I'm gonna start calling you Mr Tanker! I'm thinking you must have had it built with inside passage travel in mind.

    Good info on free surface effect (positive feedback side-side sloshing), the tanks will need to have baffles.

    Maybe two tanks on either side, in the form of 3-tread stairs up to the gunnels....
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    Member Mort's Avatar
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    Don't worry, Maast will never have that big a load of fish on board!!!

  16. #16

    Default Fiberglass/inboard view point

    I have a big cooler mounted on the swim step of my Sea Sport. I have a inboard, so the weight is well centered compared to outboards on an extension so my opinion may very well be irrelevant. We fill the cooler with water, snow, and shrimp, even stand on it to get into kayaks or the dinghy, seems to be a non-issue with the handling of the boat. But, the big issue would be how it all does in a critical situation. From what I have witnessed when it comes to weight-issue modifications, knowing how it all reacts when testing the limits of the vessel during rough seas is important. Ex: The lake ferry that had a modified sun cover added, it worked well until a little wave hit the same time everyone slid to one side and it flipped.

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    Member Maast's Avatar
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    Hah! Hey Mort - now that I have a decent fishing platform to fish from, and that'll give me the range to get farther out I should be a lot more productive. Not that I did all that bad before....

    Really looking forward to fishing out of Ninilchik and Homer
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    Member Gundog's Avatar
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    You might look into a fuel bladder if you need extra capacity you could put the bladder in one of the fish holds and use the fuel in the bladder first then you will have the fish hold empty when you need it.

  19. #19
    Member Mort's Avatar
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    Make sure you can run that boat real well before you do the tractor launch at Ninilchik. Launching is a piece of cake, but recovering can be very sporty!

    Glad you have such a jumbo ride! Better than a rewiring job, eh? Congrats, can't wait to see it.

    I have no doubt you'll be laying in some flatfish and filling that freezer like a banshee!

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