Results 1 to 11 of 11

Thread: Fuel Tanks

  1. #1
    New member
    Join Date
    Apr 2006
    Location
    Sitka, AK
    Posts
    142

    Default Fuel Tanks

    So, I bought a 28' bowpicker last year. The boat used to have twin 350's in it and it was converted to a single diesel engine. The boat has two fuel tanks, but during the re-power, the front tank was disconnected... I believe it was around 1999 or 2000. Since then, only the rear tank has been used.

    I removed the reel, and levelwind for more deck space and I noticed I threw the weight balance WAY off by doing so. The boat is pretty heavy in the stern now, so I'm looking at shifting my 100 gallons to the forward tank.

    In order to do this, I have to re route the fuel line from the tank and plumb a return line either back to the tank, or use a t-fitting and pipe it back into the supply line. That's the easy part.

    My question is basically, what are your experiences with older fuel tanks. The boat was built in 90, the tank was last used for gasoline, and hasn't been used at all for about 7 years. How did you clean the tank, or did you? Anything that you ran into in the past doing a project like this? Tips or anything else to consider are very appreciated.

    Thanks

  2. #2
    Moderator Paul H's Avatar
    Join Date
    Apr 2006
    Location
    Anchorage
    Posts
    5,594

    Default

    Sounds like the tank will definately require a cleanout. The tough part is what to do with the stuff you get out of the tank. You can put methanol in the tank which will suck up moisture, but then you need to get it out of there.

  3. #3
    Moderator Daveinthebush's Avatar
    Join Date
    Jul 2003
    Location
    Valdez, Alaska
    Posts
    4,402

    Default Carefull inspection

    I'd do a careful inspection. You did not say what the tanks were made of. Aluminum does corrode so in time any saltwater tank is subject to fail. A friend has to have his replaced and it involves pulling the engine or cutting the deck out.

    Diesel is less dangerous but I would still use caution.

    Vietnam - June 70 - Feb. 72
    Cancer from Agent Orange - Aug. 25th 2012
    Cancer Survivor - Dec. 14th 2012

  4. #4
    New member
    Join Date
    Apr 2006
    Location
    Sitka, AK
    Posts
    142

    Default

    They are aluminum tanks below deck and directly in front of the fishhold bulkhead. I could actually remove the tank by cutting through the front of the fish hold, but I wouldn't be very excited about cutting a bulkhead and having to do a bunch of fiberglass work.

  5. #5
    Member
    Join Date
    Jun 2007
    Location
    FAI
    Posts
    2,294

    Default visual inspect and pressure test

    First of all be careful about gasoline vapors. The longer you can air the tank, the better. If you still are not sure about vapors, find a buddy with a multi gas detector and place a sniffer in the tank. It will read in % of LEL (lower explosive level) and/or ppm of volatiles.
    Can you conduct an internal and external visual inspection? Is there a built in method to drain the tank? If so, depending on the design and accessibility, I might flush with H2O. If not, be sure to ground and bond any system (intrinsically safe) that you use to attempt to remove fuel. Ie a shop vac would not be a grand idea unless you are looking for an insurance payoff.
    Pressure testing would be a good idea. Certified tanks require a pressure test at approx 3-6psi. Be careful in the the larger the tank, the more area of volume you end up with. The test will require a low pressure, low volume regulator and gauge.
    Last but not least, keep an eye on the system and plan for recurring inspections until you are sure there are no leaks either in the tank or adjoining system.

  6. #6
    Sponsor potbuilder's Avatar
    Join Date
    Apr 2006
    Location
    Palmer
    Posts
    4,229

    Default

    If your going to remove the tank just cut out the deck on top of it. Then all you have to do is screw a inside plywood flange around the cutout, set the piece of deck back in, a bit of bondo and some mat for tape and stick'er down. Done.
    You mentioned something about balance, well just put some drums with water in them over the empty tank and go for a ride and see what happens. I bet you won't notice a big differance. My bowpicker,28'buffalo w/41P volvo, goes about the same with 100gals of fuel or with 30 gals of fuel. Use your trim tabs & drive trim to balance the boat out. Unless you need the extra fuel why push the weight around, with bp's the lighter the better. That 41 you have in the boat will last a lot longer if your not pushing extra weight around.

    little28.jpg

    Alaska Shrimp Pots

    Rigid & Folding Shrimp & Crab Pots
    Electra Dyne Pot Haulers
    Ropes, Buoys, Bait
    alaskashrimppots.com
    akshrimppots@mtaonline.net
    907 775 1692

  7. #7
    Member
    Join Date
    Jun 2007
    Location
    FAI
    Posts
    2,294

    Default I concur

    with Potbuilder. I assumed you had done weight and balance already. Keep it simple and start there. He is right on the money. Might save a bunch of time and effort.

  8. #8
    New member
    Join Date
    Apr 2006
    Location
    Sitka, AK
    Posts
    142

    Default

    I checked the balance already. With two drums of fuel in the bow and my old 4D gel battery up front for additional weight, I ran around at 21-23 knots with A4 props at 3450 RPM's... when I unloaded the fuel in the bow, I dropped back to about 19 knots at the same RPM's. I'm having to use my trim tabs pretty much maxxed out just to keep the bow pushed over.

    With the reel, power roller, net, and ice the boat cruised at 19.5 knots at 3450 RPM's with A3 props. Removing all gear slowed the boat to 16.5 knots at 3450 RPM's with the A3's, so I jumped up to A4's and still hit 26 knots at 4000 RPM's (WOT). Being able to prop up was nice, but my weight is so far in the stern that I'm having to really max out my trim tabs to keep the bow down.... which is why I wanted to shift the 700 pounds of fuel forward about 8 feet. The difference between the old and new waterline is pretty significant. I'd say I'm an additional 6 inches higher in the bow and 3-4" lower in the stern just by removing all the gear.

    I'm leery about using this tank, because it hasn't been used at all in 6-7 years.... We'll see how things go once I get the tank cleaned out. I'm able to access most of the tank's exterior, but I have no way of looking inside. It's not glassed in, but mounted in a way that makes it very difficult to inspect and getting inside the tank isn't even an option.

    I planned on draining the tank (whatever might be in there) and adding about 10 gallons of diesel. I figure if I can get it sloshing around for a while, I'll be able to pump it out and burn it in an old stove before adding fresh diesel, filtering it and running it through my Racors.

  9. #9
    Sponsor potbuilder's Avatar
    Join Date
    Apr 2006
    Location
    Palmer
    Posts
    4,229

    Default

    Does the tank have a fuel gauge sender on top of it?? if it does you might be able to take it off, usually just some screws, and look down into the tank even if you have to use a mirror and a light. OR if you want to cut a small inspection opening in the tank just fill it full of water and your fume problems will go 99% away. Cut the hole see what it looks like inside and make a cover for it out of another piece of aluminum and screw it down with a rubber gasket under it. If its a older 41,A or B series, you should be propped for 3600 WOT so you might want to try a pair of A-5's on it or go to stainless C-4's. I put stainless on mine 5 years ago and have never regretted it. If its a newer 41 like a P series you want 38-3900WOT. One thing seems funny to me and thats i've never seen a boat go slower with less weight on it.

    Alaska Shrimp Pots

    Rigid & Folding Shrimp & Crab Pots
    Electra Dyne Pot Haulers
    Ropes, Buoys, Bait
    alaskashrimppots.com
    akshrimppots@mtaonline.net
    907 775 1692

  10. #10
    New member
    Join Date
    Apr 2006
    Location
    Sitka, AK
    Posts
    142

    Default

    Yeah, me either, I normally see boats get faster with the lighter weight.... go figure. I'm running my tilt at -1 to 0 where I can't hear or feel the U-joints rumbling... trying to make them last as long as possible.

    It is a 41P with 2100 hrs on it. The service bulletin spec'd 3850-4100 RPM's at WOT. Right now it's running 3900-4000 RPM's at WOT, depending on gear and water conditions.

    My rear tank has a sending unit on top, but not the front. I don't have a lot of access to the top, only one small inspection plate in the deck, but it's enough to get to the pickup tube. I'll take another look at it.

    Thanks,
    James

  11. #11
    Sponsor potbuilder's Avatar
    Join Date
    Apr 2006
    Location
    Palmer
    Posts
    4,229

    Default

    James,
    Are they the original u-joints? if they are you need to change them. I get about 800-100 hours out of mine and i'm towing on my gear all the time. The new style volvo u-joints are pretty bombproof but i still change them at 800-1000 hours. I run my boat at -1 to all the way down but my rams are bypassing fluid so it always creeps down and i just trim it up. If thats your rpm's its propped about right better to let it spin a bit than to lug down. You might be able to see something thru the tube hole but if it were me i'd cut a hole on top and take a look.

    Alaska Shrimp Pots

    Rigid & Folding Shrimp & Crab Pots
    Electra Dyne Pot Haulers
    Ropes, Buoys, Bait
    alaskashrimppots.com
    akshrimppots@mtaonline.net
    907 775 1692

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •