How much "flex" is okay in a GRP hull?

Discussion in 'Sailboats' started by souljour2000, Dec 30, 2009.

  1. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    Since you are going to go to some trougbles doing this you can just as well do it well.

    Par is right. You use epoxy with wood unless you plan to do it over in a short while. Polyester doesn't work well with wood. The other advantage epoxy has is the cure time. Polyester is going to land you in all sorts of troubles with poor end results.
     
  2. Fanie
    Joined: Oct 2007
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    Location: Colonial "Sick Africa"

    Fanie Fanie

    I would suggest that everything you put back in you test before you do. Small things make big differences, like a seat's height, the back's angle or the space your feet has to fit in. Couple of drawings later...
     
  3. souljour2000
    Joined: Aug 2009
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    Location: SW Florida

    souljour2000 Senior Member

    Well I am trying to get a hold of some epoxy used for lining bad pipes..the stuff should be pretty good..it is two-part and I'm trying to get a sample since I do residential plumbing and my new company uses this pipe re-lining process that blows glassfiber and epoxy into old pipes. If it seem to bond well to bi-axial I will try and use it and posssibly save over any stuff with the word "marine" attached to it...I just can't afford the stuff at the marine stores for my boating hobby at present. Your right though...Epoxy is the way to go...in a money crunch one would certainly want to use it with the roof at least where strength and good water-resistance is a premium...PAR I was only half-kidding about chopping the mast....that would be a last desperate measure if I really screw this up..hopefully I can get by with ballast..I use 1 gallon heavy plastic tropicana and cranberry juice bottles for my water supply and auxiliary ballast.I have at least 30 of these bottles and I fill them all and stash them around on long camping trips...the boat has tons of crannies where I can stash these for trim and especially in that lazarette by the keel bolts..there's room for 8-10 there alone....that 80-100 pounds down fairly low right there..though fairly low is a relative term on a fairly flat-bottomed boat like the H20..
     
  4. CDK
    Joined: Aug 2007
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    Location: Adriatic sea

    CDK retired engineer

    When I contacted the Norwegian manufacturer of my Draco Twincab many years ago to ask where to support the boat for transport by truck, the answer was that this was the sturdiest product in its class and could stand indefinitely on a small wooden block under the center of gravity if that was what I wanted.

    Yet when a couple of years ago some lowlife stole my GPS, signaling pistol and some other stuff, I designed, built and installed a laser based burglar alarm with a transmitter, so I would be warned while sitting in my living room.

    On the first windy evening it became clear that this would never work. Even small waves (1 ft or so) were enough to flex the hull and move the beam to a point above, below, left or right of the little mirror that should reflect it to the sensor. The hull is 1/2" thick near the flange with the deck and nearly 3" in the keel area, yet it flexes. Not quite like the 747 wingtips, but enough to ruin my little project.
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Okay, lets see if we can dispel some myths. Your boat was only built for a few years. It's 1,700 lbs. displacement, with a 23% ballast ratio (400 lbs.), it's D/L is 203.8, capsize screen is 2.5 and SA/D is 19.1.

    The SA/D being 19 is what gives it it's light air ability, even though it's kind of heavy considering it's 15' 6" LWL boat (not overly so). Placing extra weight in the blige will not improve this, it will decrease it's light air ability.

    Lets say you had a 150 pounds worth of pop top and other stuff you removed and you over building efforts cause you to add 450 pounds (an easy number to hit judging by you techniques) that's over a 20% increase in the weight of the boat dude and something that should be avoided.

    Production boats move, as I mentioned in my first post on this thread.

    Don't try to fix this, there's nothing wrong.

    The epoxy used for lining pipes is usually coal tar epoxy, which isn't something you want to use. It's designed to go down in thick coatings to seal pipes, and other industrial applications. Typical coating thicknesses would be 30 to 40 mils in one coat, making it way to viscous for the work you're trying to do. Contact www.bateau.com or www.fgci.com and see if their prices are acceptable for you. These are real marine laminating resins.

    You could skip the plywood aspect of this job completely if you used foam and fabric. Of course you'll need lots more epoxy and fabric, but you don't have to worry about encapsulating wood or rot. This could help considerably on your weight issue, but does increase your "goo factor" a good bit.
     
  6. souljour2000
    Joined: Aug 2009
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    souljour2000 Senior Member

    Happy New Year everyone!!!...May you find yourself upon the waves...taking in the sights and bays....far from large-wake powerboats and knaves....okay..we'll stop there...Happy New Year!

    Fanie...your earlier comment about testingout new seats, etc and so forth before installing is critical...I sometimes wonder if some of these designers ever really laid down in one of the so-called quarterberths or sat in a mock-up of their designs or really actually tried to squeeze into that aft dinette seat...20-foot and under sailboats is a different world though...

    THIEVES,LASERS,and FLEXIBILTY of GRP HULLS

    What a cool topic CDK...your story about the ,thieves,lasers and flexibilty of GRP hulls was really interesting ......backstay and rigging tension is a huge consideration that I hadn't factored into my addled brain as yet ....doing re-models are probably at least or more stressful than ground-up design and engineering..I am feeling drained by it all when I am not enthralled by the times when spurts of progress occur....... PAR...thanks for the specs info..that is really helpful....I am slowly getting a better feel for those engineer spec ratios and numbers..math was always a struggle...well-explained examples like you provided are gold to me... info about the coal tar epoxy...that's cheating isn't it though I guess they squeeze oil from it so it's the same thing as more commonly re-fined black gold...I have some research to do in that whole epoxy dept...bateau I will check for sure though....as for foam core instead of ply for the roof...I will give it some real thought...rot issues in a wood core cabin roof are probably only second to transom or floor rot I would guess in terms of frequency...probably second to none when I think about it...thanks for the informative comments folks...
     
  7. messabout
    Joined: Jan 2006
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    messabout Senior Member

    Check out Fiberglass Products in St. Pete. They have everything you might need for your project including numerous epoxy types. I have used them as a source for years, price, service, and quality have been good.
     

  8. souljour2000
    Joined: Aug 2009
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    Location: SW Florida

    souljour2000 Senior Member

    Thanks messabout..I actually was on their website this morning...It is not as easy to use as US composites website but their prices seem excellent and they are nearby. I was not sure how much catalyst to buy with a gallon of resin...US composites sells them together..I think US composites sells a gallon of resin and an almost half gallon of hardener sells for $71.00 or almost a gallon and a half for that price including 2-3 day shipping in Florida It's nice to have options if I want to just run and get some that is also fairly cheap so i will check them..wait..are they FGCI like Par mentioned or a diffeent ST Pete company?.
     
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