Do I really need all my chambers filled with flotation foam

Discussion in 'Boatbuilding' started by Steve Quate, Jul 16, 2022.

  1. Steve Quate
    Joined: Jun 2022
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    Location: Keller, Texas

    Steve Quate Junior Member

    Good hot afternoon everyone
    I am building a catamaran style shallow water scooter boat hull design all put together and taped up and 1st coat of resin applied, just to harden up everything so I can get ready to apply 3 layers of fiberglass(woven 10%). My question is this:
    Each hull side(catamaran style), side will hv 9 cavities, total of 18 both sides, front and rear very small, because of angles needed to get the style of sponson I wanted. Money is limited right now, my question is: should I fill every compartment with flotation foam or just every other one, or just one compartment at each corner of boat & 1 in center. Less than 550lbs total on boat batteries, trolling motor and myself, poles lures stuff like that. I will hv 3 layers of woven fiberglass, and 2 layers of gel coat all are name brand products. I’m looking at about 35.approx 1 1/2cubic squares per chamber cept for front and very back. Thinking maybe 3 per side, not over thinking this cause won’t hv very long less than a year and will give it away. The kayak I want rigged out is over 5 grand plus electronics. Saving fir down payment for another boat thanks for any Input, please no smart alkecs comments thank you fir your time great boating everyone
     
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  2. Will Gilmore
    Joined: Aug 2017
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    Will Gilmore Senior Member

    Sounds like you get to do whatever makes you comfortable. You aren't planning to carry paying passengers, right?

    I'd be incline to do the ends where a collision might hole the bow or stern, then just a couple of inches against the underside of the deck. But you're a catamaran, so she won't right herself, no need to keep the flotation high like that.
     
  3. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Are you allowed to not have any foam filled compartments at all?
    If so, and noting that you will have 9 compartments in each hull, I would be inclined to just build them well, and keep them as watertight void spaces.
    You will still have a much better chance of staying afloat if a compartment (or even a few) is holed, compared to the average 'small' yacht which has no watertight bulkheads, apart from maybe a collision bulkhead in the bow.

    How big is your cat scooter?
    It sounds like you are building it with plywood(?) and then sheathing it with fibreglass? If so, are you using polyester or epoxy resin? I presume polyester, as you mention finishing with gelcoat (?)
    Can you post some photos please of your progress so far?
    We always love to see construction photos of projects underway.
     
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  4. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Are the compartments sealed or open lockers?

    Foam open lockers to just above dwl, otherwise, a closed chamber is fine for a private boat.
     
  5. wet feet
    Joined: Nov 2004
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    Location: East Anglia,England

    wet feet Senior Member

    A point that you might give some consideration to is how you will drain any leakage from the hulls.It isn't the simplest of tasks to create that many totally watertight chambers and in regions that have large temperature fluctuations you may need to also ease pressure variations.Putting a boat in to cool water after it has been on a trailer in the sun may well encourage the entry of a little water through screw holes and you will need to drain it.18 drain plugs on the outside of the hulls would look messy.
     
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  6. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

  7. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    I would NOT limber the watertights at the bottom. If they are indeed intended to be watertight, I'd either install submersible vents at the top or just a breather hole. Others have also used a piece of hose. One issue with the watertights I see is water vapor, even in a submersible vent, can build inside them, so they probably need occasional drying out. Edit (also, if plywood inside, better plan for water)

    McMaster-Carr https://www.mcmaster.com/4505N11/

    McMaster-Carr https://www.mcmaster.com/vents/
     
    Last edited: Jul 17, 2022
  8. Ike
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    Ike Senior Member

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  9. rnlock
    Joined: Aug 2016
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    Location: Massachusetts

    rnlock Senior Member

    Some time ago, I was helping with work on a small, portable, sealed medical gadget. It had membrane switches on the front. When ascending in an airplane, the pressure difference would pop off, or at least unseal, the membrane switches. The solution was a little Gore Tex patch that would pass gases and vapors, but not liquids. I don't know which flavor of Gore Tex; they have a bunch, but it might be an easy solution. Of course, it's a good idea to ventilate the chambers from time to time.
     
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  10. DogCavalry
    Joined: Sep 2019
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    DogCavalry Senior Member

    I use Gore Tex breather valves on my watertight bulkheads.
     
  11. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    I could use some snap in Gore Tex vents. Where do you get them?
    My Googlefoo didn't find any in stock.
     
  12. DogCavalry
    Joined: Sep 2019
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    DogCavalry Senior Member

    Search gore tex breather valve
     
  13. Milehog
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    Milehog Clever Quip

    Thanks, I tried that but no retailers with anything in stock came up.
    I'll keep trying.
     
  14. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Mcmaster carr submersible vents. I can link if u need. Too tired now.
     

  15. Milehog
    Joined: Aug 2006
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    Milehog Clever Quip

    Thank you.
     
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