Seat Pedestal

Discussion in 'Fiberglass and Composite Boat Building' started by Dillusion, Aug 9, 2022.

  1. Dillusion
    Joined: Aug 2022
    Posts: 4
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    Location: Hawaii

    Dillusion New Member

    First time with fiberglass for me so why not try it on something non structural.

    I have (2) 18 Gallon top side tanks under my rear seats. It makes my stern very heavy first thing in the morning to the point the scuppers are pretty much at the water line without anyone in the boat. Put someone in the rear and its wet. Also want to remove the rear seats (another project) later for more deck space.

    Plan is to build a box for under the seats and place the tanks under there. Box needs to be 16"H x 31"W x 16"D. Also want to keep one end open so I can pull the tank to fill up.

    I can easily get Divinycell locally.

    Was going to go with Poly resin since its cheaper and this is my first time. If I mess it up won't hurt my pocket as much. Already got some 1708 so guess I'm going with that as well.

    Should I go with 1/2" or 3/4" Divinycell and how much layers of glass? I was going to go with (2) then jump on the box and see if it can handle the pounding. I know the span is pretty wide without more support so I'm questioning the (2) layers.
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    I don't follow. You have tanks under the rear seats which make the stern heavy. However, you are going to add a box under the seats. Isn't that going to make the stern even heavier? Maybe some photos would help.
     
    fallguy likes this.
  3. Dillusion
    Joined: Aug 2022
    Posts: 4
    Likes: 0, Points: 1
    Location: Hawaii

    Dillusion New Member

    Sorry wasn't clear. Going to make a box for the front or midship (not sure what you would call them) seats. The are more towards the middle.

    This is the only pic I have on my phone right now I can take more when I get home.

    Also got a pic of my tanks and rear seat. Don't mind the mess.
     

    Attached Files:

  4. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    So, in a nutshell, you essentially want to move your 2 x 18 gallon tanks from under the seats in the stern, and put them in a new box under the midships seats?
    I can see a seat amidships in the side profile photo above, I guess they are going in this area?
    Can you supply some more photos of this area please?
    Re the dimensions you mention for the box, I calculate that this gives you a volume of 36 gallons - even if the dimensions are to the inside of the box, are you sure that the tanks will fit easily in it? You might want to add a little bit more to each dimension to give yourself some leeway?

    That is an impressive tuna that you caught! How heavy is it?
     
  5. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    Enclosing portable fuel tanks is a no-no. Gotta provide for the vent.

    Permanent tanks require access to them.

    You can build nice boxes with 12mm core and 1208 or 1708 glass and tab to the hull with same.
     
  6. Dillusion
    Joined: Aug 2022
    Posts: 4
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    Location: Hawaii

    Dillusion New Member

    Heres a pic. Plan to remove whats there now and replace with the box I make. Ill double check my measurements but I thought I gave an extra half inch all around.

    You pretty much guess correct on what i want to do. I know moving that much fuel can drastically change the weight distribution. I have a fish box which is always on the boat that I plan to move around to distribute as needed.

    Next plan is to cut out those stern seats so i have more deck space.

    Fish was 105 without the head obviously.


    Not planning on enclosing it. Going to leave the aft side open so i can also refuel easily.

    Which was my concern since its on less side that can bear the weight.

    12mm core is the 1/2” Divinycell that i can get. I have 1708 just wondering how much layers. I was thinking 2. I hate to be pounding around out there only to have it fail on me and be standing the rest of the way home.
     

    Attached Files:

  7. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Re your photo above, so you will be replacing the two seat pedestals in the photo with your new custom built box for the two fuel tanks?
    Re how the box is going to be 31" wide, this appears to be a bit less than the overall width (to the outboard sides) of the two 'boxes' currently supporting the seats - I am guessing that this might be about 4'?
    You will then have this box to step over each time when going fore and aft, but I suppose you will get used to doing that.
    Your box will have to be much stronger, relatively, than the two individual boxes shown, re supporting the seat bases - these are going to be imposing the most stresses on the structure, especially when you are underway in a rough sea with a 200 lb person sitting in the seat.
    Do you know, roughly, what sort of laminate schedule these existing boxes have?
    Your box will have a wider span - and also the aft side will be open, which again complicates things a bit.
     

  8. Dillusion
    Joined: Aug 2022
    Posts: 4
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    Location: Hawaii

    Dillusion New Member

    Yes replacing the 2 seat pedestals with my 2 custom boxes.

    I got 72” from port to starboard to work with so yes i will have less than a foot of space between.

    Stepping over the box is no issue i usually dont leave the wheel when fighting a fish so no much running back and forth.

    I took the hatch off before and the existing pedestal was about 3/16” thick no core material. Looks like is all glass and resin. So that would mean its 3 layers if 1708 was used?

    If i need 5+ layers im prolly gonna have to switch to a plan B. Maybe change to (4) 12 gallons tanks so i can have smaller boxes
     
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