Light floats

Discussion in 'Multihulls' started by bruceb, Dec 2, 2012.

  1. warwick
    Joined: Jan 2012
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    Location: papakura south auckland new zealand

    warwick Senior Member

    Some where on the forum there a section on building composite dead eyes for shrouds that may also be an idea as well. It may be possible to incorporate such an idea into a bulkhead. I cannot remember what the thread was called, but had read it before.
     
  2. outside the box

    outside the box Previous Member

    bruceb just for what it is worth, this shot is how one example of a plan built chain plate is done. Mr F does this as shown on the latest 22 that was built that can be seen going out on the trailer on his factory 22 progress updates page the carbon uni's section is made first, then well keyed and then bedded in 8084 glue to skins that have been cross linked inner and outer then glassed over, to our mind not to industry recognized standards with secondary bonding of a part but who are we to question one with so many in the water and all seem to work fine under what are extreme loads. On the weight front Buc 24' float quoted to be in 4mm ply 70 odd kgs the Mr F 22 float by the chap who's boat is in the photo mentioned above, home built hand lay to plan in epoxy, glass foam glass 60kgs. The chain plate method is in the production boats also. Hope this perhaps helps
     

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  3. bruceb
    Joined: Nov 2008
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    bruceb Senior Member

    Real details

    Thanks OTB, that is worth a lot. It is less material than I would have expected, but it is well tested. B
     
  4. Corley
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    Location: Melbourne, Australia

    Corley epoxy coated

  5. redreuben
    Joined: Jan 2009
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    Location: South Lake Western Australia

    redreuben redreuben

    Bruce, a middle ground alternative maybe to plank the floats in Paulownia and glass either side ?
    Density is 275kg compared to gaboons 430.
     
  6. outside the box

    outside the box Previous Member

    All good bb private message us or email from website contact us page if you wish to go that road and we can assist with the how to side of it in more detail for you. If you wish to go more conventional industry standard we will flick you a photo stream that will nail the how to for you, quite x y z once you have done the first one.
    On the Buc 24' new light float front, just for what it is worth when we get to the redesign, initially as it is prototyping we will do one off glass slipper hulls (schionning farther and son do this with their right way up build methods) the original under water section's of all three hulls will be removed the new underwater sections will be offered up including new bow/stern sections to the topsides and new bulkhead scarfed to originals and any new ones needed added at the same time, this way we get new underwater sections bows and stern sections tested in the platform for minimal cost.
     
  7. outside the box

    outside the box Previous Member

    bb
    We found this on Bernd Kohler K designs site, thought it is probably the easiest x y z explanation of it, to get ones head around the build with a simple photo stream.
     

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  8. Samnz
    Joined: Nov 2008
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    Samnz Senior Member

    The way I did it on my new boat was to Build a composite chainplate on the top of a bulkhead, then cove and tape the bulkhead into the hull.

    Bulkhead can be light foam and glass or 4mm ply, makes no difference. Cove and tape the bulkhead into the hull and then it spreads the load out over a massive area, it can never pull out.

    Trick is to spread the load as much as possible, remembering that the original chain plates are just bolted thru the 4mm hull with a very small wooden backing plate! I actually took mine off my Bucc and reinforced the whole area with Glass and Carbon before putting my rig canting blocks on.
     

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  9. outside the box

    outside the box Previous Member

    Great explanation Sam and the photo always better than those 1000 words, is hard to show someone when you have know idea of their skill apprehension level just how easy it is to do.
     
  10. bruceb
    Joined: Nov 2008
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    Location: atlanta,ga

    bruceb Senior Member

    more chainplates

    Do you cut the "slot" for the rigging attach point after you have installed everything? Also, is it necessary to leave some sort of protective sleeve through the carbon plate?
    Sam, I have added to the backing on my Buc also, it just didn't look like enough for a rig like mine.
    OTB, Bernd's way seems simple enough. I also like Sam's bulkhead system as it brings the chainplates inboard away from the edge of the hull. Maybe a little more crash protection.
     
  11. outside the box

    outside the box Previous Member

    bb yes and you can have a g10 extruded epoxy tube as a sleeve if you wished or make your own easy enough.
    The bulkhead system as Sam explained is superior in ways and more to industry standards, like Sam said the more spread the better.
     
  12. bruceb
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    bruceb Senior Member

    Float shapes

    Of course I have an opinion:rolleyes: I am not aware of any modern multis using V bottom floats, and I am sure there are lots of reasons not to,- but;) In very light air, I don't let any more than an inch or two of my leeward (or sometimes windward) float bottom touch- I think the V has less! wetted surface than a round bottom immersed that much. The Buc is really fast in light air. In more wind, using my "trial" a-boards, I can keep most of the float chines at about the surface level, and the water separates at the chine without climbing the float sides, also seemingly low drag and very fast.
    Just pointing out that the Buc's shape has some positives. A more modern tri would have less rocker in the main hull and floats, and have more top-end speed potential as a result, but the hard chines/v-bottom floats might not be so bad.
    The Buc's floats and main hull do need more volume aft, and that is the first area I would address. B
     
  13. bregalad
    Joined: Dec 2010
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    bregalad Senior Member

    @bruceb
    I'm ruminating over this in odd spare moments.
    Do you have any idea how much of the weight of each float is due to water absorbed over the years? Do you have access to a moisture meter?

    Going form 1/4" fir plywood to 4mm ply of a lighter species reduces the sq.ft. weight of those areas by about 1/2 before epoxy/glass/paint.

    Sitka Spruce for stringers.
    Alaska Yellow Cedar for the edging on frames.

    I think you could get the weight down ~ 125 -130 lbs. per float.

    My head get all fuzzy thinking about the decks. They need to be strong enough for someone to walk on. An oaf like me or a slinky type wearing, well, not high heels, but not boat shoes either.

    Amistad's decks flexed alarmingly underfoot. I built some absurdly light rowing boats in which you could only step here ...or there.
     
  14. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    The epoxy sheathed 4mm ply decks on my 25ft Gwahir catamaran have lasted 30 years so far (launched in 1982, I saw it last year). And they were wider than an outrigger deck. Hull topsides were also 4mm ply, but unsheathed

    Certainly stronger than the decks of our MandM designed 18sqm beach cat that we use as outriggers on our Strike 18 trimaran - which are VERY scary to walk on

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     

  15. oldsailor7
    Joined: May 2008
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    oldsailor7 Senior Member

    1.If the boat was built properly using the WEST system there should be little or no increase in weight due to water absorbtion.
    2. 4mm is about as thin as you would want to go. Don't get het up about the weight. Many B24s were made out of 6mm Fir and proved OK.
    2 & 3. Those woods would be just fine.
    4. As the decks are slightly convex they are very stiff and I had no problem with mine using 6mm light 3 ply luan mahogany.. Cabin top needs to be a bit thicker. See specs.
     
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