Best floor for a sailing dinghy

Discussion in 'Boat Design' started by jdonahu, Jun 3, 2013.

  1. jdonahu
    Joined: Jun 2013
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    jdonahu New Member

    Hello,

    I am "re-conditioning" (sounds like less work than re-building) a fiberglass penguin dinghy. While I finish the centerboard (the old centerboard was abandoned as a centerboard and used as a dagger board purposely splitting the centerboard cap), swing rudder, and standing rigging (5mm low stretch polyester coated synthetic line), am thinking about the next project.

    What is the best floor for a sailing dinghy. As I wrote, my dinghy is a penguin, so it is NOT self rescuing (yet!). My requirements are that it is comfortable on the knees, light, not too expensive (less than $500), and can add ~150lbs of bouyancy if possible (I could just add buoyancy bags, but then the buoyancy will be higher and make any type of self bailing transom contraptions less useful).

    I am sceptical that I can build an air-tight false floor (per the 75 year old designs for self rescue) and which don't leak and do not add significant weight to the boat. It's only 140 lbs now, and I beach launch it off of a driftwood filled Pacific NW beach, so weight matters.

    I have been reading about pool noodles used for flotation under decks. I was thinking about using them as the actual floor in the dinghy. I think I can get 150 lbs of flotation out of 100 feet of noodles (~20 noodles).
    I extrapolated from this thread - http://forums.iboats.com/boat-restoration-building-hull-repair/truth-about-noodles-387186.html

    I could strap them down with nylon webbing and have a cheap, easy, flotatious, comfortable dinghy floor.

    My boat is outside, upside down on driftwood in the summer, and covered in tarp during the winter (and I would remove the noodles in the winter). Assuming I, and my crew of 5, 8, or 10 year old are barefoot, why is this a terrible idea?
     
  2. alan white
    Joined: Mar 2007
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    alan white Senior Member

    The proper place for flotation that will assist righting the boat when capsized is higher up where it will do some good upside down.
    The places that make most sense would be along the gunwales and anywhere else as high up as possible that would be submerged upon capsize. Your idea of using the space under the sole means the flotation wouldn't even be submerged during a capsize but would stand clear of the water, doing essentially nothing. Only when the boat is upright but full of water would it contribute anything.
    It's nice to have unsinkability but even nicer to see your boat right itself so that you can bail and sail.
     
  3. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I have sailed and raced Penguins extensively. The two locations where you can add flotation that works well is on the stern and bow. Bags are light and easy to install. Also, what do you mean by "self -rescuing"? Pool noodles will make a tripping hazard. I am not clear on what you mean by "comfortable in the knees". This are small cramped boats and the narrow gunwale is not easy on the thighs when you hike out.
     
  4. Petros
    Joined: Oct 2007
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    Petros Senior Member

    treat the floatation for self rescue separately since positioning becomes critical. I would cover the floor with EVA foam. You can buy it in sheets and glue it together with contact cement. You can hold it in place with glue down Velcro type fasteners strips.

    You can also get large irregular scraps for free from those that use EVA foam in their products, the scraps fill up their dumpsters. You just jig-saw puzzle together the peices to get the size you want, more work but saves cost.

    If you want to make the surface of the EVA more durable you can glue down heavy synthetic fabric to it for a tough non-slippery surface.

    Good luck
     
  5. jdonahu
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    jdonahu New Member

    Thanks for the input. The big thing I learned is that adding buoyancy can be done for two different reasons: 1) to float the boat higher when it is swamped and 2) to float the boat higher and help with righting the boat when capsized. Buoyancy low in the boat (under floor) will help with #1 (raising the boat when swamped so that scuppers could self drain), but degrade #2 (making it harder to submerge the bottom of the hull when trying to right the boat); and Buoyancy high towards the gunnels will help with #2 (pushing the submerged gunnel upward), but not help with #1.

    I decided to put in cedar plan floors - 3/4 in the rear and 5/8ths in the front. This adds approximately 2 square feet (100 lbs netting out the cedar) in buoyancy to help when swamped.

    Another new bit of data is that did exist styrofoam below the two thwarts (maybe 1.5 square feet total, or 90 lbs disregarding the weight of the foam). So that should help with righting the boat.

    To additionally help with righting the boat, I plan on adding a buoyancy bag in the forepeak (need to build a cap as that is open deck right now) and either 1 across the inside of the transom, or 1 each quarter.

    Then I will test capsizing and swamping and adjust. I could then glue closed cell foam to the bottom of the cedar floors if I needed more anti-swamping help.

    Thanks everyone for your help!!

    Joe
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Don't worry about anti swamping, as the water level really doesn't matter, so long as the rails are still above water, with the crew aboard, which is the physical requirement, for this type of floatation. So, position the floatation under the thwart, bow and stern. It's not like a freighter is going to come by and overwhelm you, in one fell swoop. Boarding water can be handled as it comes, even if it's a big wave, so a foam sole is unnecessary and could make righting the boat very difficult. Even if the Golly Green Giant suddenly appeared and dumped a huge can of green bean juice into your boat, completely swamping it, well arranged bow, stern and under thwart floatation, will keep you from sinking and provide a place (a wet one) to bail from, which again is the whole point. In the event of a capsize, she will not float too high and will not tend to prefer being inverted either.
     
  7. jdonahu
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    jdonahu New Member

    Thanks PAR, that makes sense - focus on enough buoyancy to manage a swamping, and not try to use scuppers to reduce my bailing to a few inches (which was my original goal).

    I will say, that in my Penguin, a fiber glass model with wide gunnels which make it easy on Gonzo's thighs, shipping a lot of water quickly is way to do.

    On my first day I took my Mom out and as she was boarding in about 2 ft of water, the boat heeled and she grabbed onto the first thing she could reach and tried to pull herself back into the boat. Unfortunately she pulled on the boom and heeled the boat more and she was swamped before I knew it. The boat that is, Mom was dry above her knees standing in a swamped Penguin.

    Maybe I am overreacting to swamping on the beach, but that is where she is "moored":

    [​IMG]
     

  8. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Yes, I think you are overreacting to a novice's boarding approach. A fully swamped boat can't sail fast enough to self bail. Hell, you'll just be lucky to keep it upright as you manually bail. The Anderson bailer (and similar) will easily suck out several gallons of water, after a wave or a rough slosh to windward, but forget about it trying to drain a few hundred gallons in a swamped boat. 1 gallon milk jugs, with the top cut away, but leaving the handle is a great hand bailer. A few of these aboard and two scared crew, can empty a boat like this, in just a few minutes, at least enough so an Anderson bailer can evacuate the rest, underway. Lastly, if you do put in wide side decks, then place foam under them and down the hull sides, as well as in the bow and stern.
     
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