Styrofoam for emergency buoyancy?

Discussion in 'Metal Boat Building' started by mosk22rte, Feb 20, 2009.

  1. mosk22rte
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    mosk22rte Junior Member

    As I mentioned in my previous post, I am doing some repair work to a new-to-me 1983 12' Klamath aluminum V-boat. I'm new to boats but not new to fabrication.

    Tonight I removed the old rotting wooden bench covers in preparation for their replacement and discovered that the benches, which are hollow, were packed with chunks of styrofoam.

    It's a 12' boat and there are three benches, and each bench is ~13" wide and the width of the ship at the point of attachment. I haven't calculated the exact interior volume of the benches, but by my rough calculations the total interior bench volume represents something like 30% of the interior volume of the boat.

    A few questions:

    1) I realize the styrofoam is there to help prevent the boat from sinking like a stone, but is this enough styrofoam to really help keep the boat afloat?

    2) If the styrofoam is necessary, should I replace it with something newer or better? Does styrofoam lose its buoyancy after 26 years?

    3) Would I be a fool to remove some or all of the styrofoam and convert the interior bench space into storage? How much, if any, could I safely convert?

    Thanks in advance,

    Jeff
     
    Last edited: Feb 20, 2009
  2. ned L
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    ned L Junior Member

    Yes, In small aluminum boats it has been pretty common practice for decades to fill the locations beneath the seats with Styrofoam for floatation. Unless it is all broken down from oil soaking or something similar it should be just fine to reuse. If it were me, I wouldn't reduce the amount of foam, there is enough to keep the gunwales above water but not too much more, without it the boat will sink like a rock if swamped or overturned. --- When I was growing up, one of the boats in our family was a 12' aluminum 'john boat' that we used for knocking around. One of the things we would do in the summer was to take that dinghy out & swamp it, roll it over, & use it as a 'play thing'. That activity was actually a good learning experience as it is surprising how one of those things behaves when full of water. Not a whole lot of reserve buoyancy, easy to roll over if not careful (really need to sit in the bilge & not on the seats if you want it to stay upright), and when you are righting it from upside down it is quite easy to 'overshoot' the target and have it go right over again. ---- In short, keep all the buoyancy you can.
     
  3. Lt. Holden
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    Lt. Holden Senior Member

    mosk22rtem,

    Yes, as Ned pointed out this is a very common setup. I redid a 1960 Mirro Craft last summer and it was the same. For some reason in my seats the foam was about 3" below the top edge of the seat box. I replaced the styrofoam with 2" thick blue insulation foam and heat sealed it in plastic bags. The reason for this is Masschusetts now requires that the foam be sealed so if the boat capsizes there won't be bits of styrofoam floating around everywhere. You may want to check California regulations. Can you post pics of your boat?
     
    Last edited: Feb 20, 2009
  4. marshmat
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    marshmat Senior Member

    Hi Jeff (mosk22rte),

    The usual requirement for small open craft is that they must remain floating, and roughly level, when fully swamped.

    An easy way to figure how much foam you need under the seats is to take the weight of the boat (including a typical amount of gear and the biggest outboard it can handle), and note that one cubic foot of foam will support 55 to 60 pounds (ie, the density of water minus the weight of the foam itself). It never hurts to use a bit extra. Make sure to put more of it toward the stern, to support the engine weight- you want a flooded boat to float roughly level, not stern-down.

    I'd avoid using EPS foam (the white, granular stuff), it breaks down and makes a mess. The extruded variety, known as XPS, is commonly sold as insulation- those pink or blue rigid sheets- and is much more durable and waterproof, not to mention it won't fill your bilges with little foam pellets. Docks built using this stuff as flotation regularly survive for 20 years or more. Cut a few sheets of it to size and glue them together, it's cheap and it works. If the old foam is in good shape you can just re-use it.
     
  5. mosk22rte
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    mosk22rte Junior Member

    Great advice, guys - thanks! I haven't been documenting this project all that thoroughly, but here's a few pictures of the boat as I bought it.

    [​IMG]

    [​IMG]

    I'll post a few pics with the innards exposed sometime this weekend.

    -Jeff
     
  6. rasorinc
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    rasorinc Senior Member

    stryofoam never adsorbs water. I have it under a floating dock for over 30 years. I cubic foot of stryofoam will float 55 lbs.
     
  7. Lt. Holden
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    Lt. Holden Senior Member

    mosk22rte,

    Nice looking boat! Is the hull all welded or a combination of welding/rivets? In your other post about flooring are you referring to the casting deck or the after cockpit at the helm? Is that a home-made tiller control?
     
  8. mosk22rte
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    mosk22rte Junior Member

    Nice looking boat!

    Thanks :)

    Is the hull all welded or a combination of welding/rivets?

    The hull is fully welded, which was one of my requirements when I went looking for an aluminum boat.

    In your other post about flooring are you referring to the casting deck or the after cockpit at the helm?

    Both, actually. I want to re-do the casting deck, but I also want to add some floors. My local metal supply carries expanded aluminum, so after looking at the various options suggested in the other thread, I think carpet covered expanded aluminum is the way I'm going to go.

    Is that a home-made tiller control?

    Yeah -- good eye! The previous owner broke the stock handle, and this was his repair. Luckily (?) it didn't use a twist-style throttle control, so it was easy to bolt some flat stock to the stub of the old tiller, and affix the shifter-style throttle mechanism to it. Actually, I already have a newer, more powerful 15 hp Nissan, so the outboard in the photos is going up on Craigslist very soon.

    Thanks again, everyone, for helping this newbie get his 12' fishing boat back in the water!
     
  9. drmiller100
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    drmiller100 Junior Member

    i've sure seen it waterlogged and really really heavy.
     
  10. apex1

    apex1 Guest

    1 m³ of 30kg (raw density) expanded Polystyrol or Styrofoam can absorb a maximum of 2-3 ltr. water, but a max. of 40 ltr. of vapour! :!: If exposed to UV light, the surface gets brittle, the structure gets loose and it can ( and will ) absorb water like a sponge!

    Regards
    Richard
     
  11. rasorinc
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    rasorinc Senior Member

    My dock is still floating hi and dry after 30 years. It is covered from sunlight.
     
  12. apex1

    apex1 Guest

    You see?
     
  13. drmiller100
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    drmiller100 Junior Member

    i have seen quite a few 10 year or older aluminum boats with several hundred pounds of waterlogged foam under the floors, benches, and seats.
     
  14. rasorinc
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    rasorinc Senior Member

    Thanks for informing me of the UV deterioration of stryofoam, I have put lots of blocks of it in boats but they were all sealed in so no UV and no absorbsion.
    If you have a copy of an article on that, I would greatly appreciate it if you would post it. Thanks much, Stan Years back I put a piece of stryofoam in a bucket of fresh water and sunk it with 2 bricks and left it for about a month. When I lifted the bricks it popped to the survace and felt totally dry in about 10 minutes. BUCKET WAS IN MY GARAGE.......................NO UV
    I've never trusted FOAM.
     

  15. apex1

    apex1 Guest

    Welcome mate,
    UV deterioration needs month to years to weaken the stuff, so, your bucket test would have shown the same result, if executed in bright sunshine.
    Unfortunately I cannot provide a link. My statement was based on knowledge and a old datasheet about insulation material "Styropor" , published by "BASF" about 20 years ago. The 30kg m³ referred to that.

    drmiller
    No contradiction, see post #10 ...vapour...

    Regards
    Richard
     
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