Bootstrap Cat

Discussion in 'Boat Design' started by anothernutter, Mar 25, 2015.

  1. anothernutter
    Joined: Mar 2015
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    Location: South Africa

    anothernutter Junior Member

    Hi,

    I am looking for a simple catamaran design. about 45 feet, minimum complexity and hassle to build; solid spars,(masts and beams),gaff or lanteen rigged,strip planked, flat bottomed(hull is floor) in cabins. wide hulls The boat is to be used mainly for thin water tropical cruising,(sand banks, reefs and beaches) so a really shallow draft is needed. That said our South African coast can quickly become nasty to sail. The boat is envisaged as a holiday boat, one that can also be used to take youngsters cruising(backpackers) on the cheap, so its the usual kayaks wind surfers, boards etc that it needs to carry

    This is not to be a fast cat but one that is actually designed to carry the 'stuff ' we move on board over the years.Just about every cruising cat I see visiting our shores here in South Africa has its butt dragging and is way over designed load. So we might as well just design a heavy cruiser in the first place.

    The boat should ideally be demountable so as to be able to be moved from one location to another, I will also be building quite far inland from the coast.

    Looking at 2 X 3 to 3,5meter flexi-space cabins per hull plus a large above waterline shower cubicle in one hull and toilet in the other. Partially enclosed kitchen and nav station fore bridgedeck(that one can 'look through' from the tiller and big cockpit aft that can be covered and enclosed in bad weather. Cabins to ideally have "pop tops" to open up in the hot weather and shut down in bad weather so full headroom not a must in hulls.

    I am not keen on going the ply/epoxy route as it is just too expensive, and I hate working with epoxy. Wharrams are too poky for my liking, his designs too expensive and I don't like those sterns.

    We have Eucalyptus cloeziana available locally for about 300 US$ a cubic meter, so it would appear that strip planking is the way to go for me, using good old resorcinol and finishing the hull rustic and clear:) see for info

    http://www.woodsolutions.com.au/Wood-Species/gympie-messmate

    they use this timber untreated in harbors in Holland and reckon they will get a 50 year life out of it. it is also resistant to marine borer.

    Does anybody have any ideas of designs around I could look at, or adapt.

    Or is this to be another pure faith amateur design and build job;) ?
     
  2. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    At the risk of being harried by the resident catamaran expert, I would say this timber could make for a boat this is.......heavy ! You learn something every day, and I was not aware that the power pole outside my house is probably that timber, Gympie Messmate, according to the website link given above. These poles are copper and arsenic treated though, which would be toxic to work with.
     
  3. FAST FRED
    Joined: Oct 2002
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    FAST FRED Senior Member

    The best glue is resoursanol if you don't like epoxy , the problem is the fit musty be perfect!

    Epoxy will fill small gaps and is used by folks that find perfection hard to do.
     
  4. anothernutter
    Joined: Mar 2015
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    Location: South Africa

    anothernutter Junior Member

    Hi Mr Efficiency,

    Yeah generally put at about 900 kg's per cube, but about 750 to 800 kg's around here. The sawmills locally will cut to any size i want. The problem is the drying of the timber as it must be stacked and air dried over winter,(our dry season)

    I just see so many overloaded boats, i was wondering why we don't just say sod it and build a heavy cat. Saw a 46 Tiki, the guy sheepishly admitted to me that he figured on about 13 to 14 tons that she was carrying!!

    I think that there is a big gap in the understanding of designed loads between designers and the lifestyle of beer swilling cruisers.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    Obviously that is a plantation timber, wouldyou be wanting heartwood only ? A lot of the Eucalypt timbers have durable heartwood, but the sapwood not so good. I had an old uncle who was in the milling business for 50 years or more who would have known about the durability of that timber, and its uses, (mill not that far from Gympie, actually) but he has recently gone to God. I would imagine there would be timber trawler builders who would know, but I think you would want solid confirmation it is indeed suitable for planking a boat.
     
  6. anothernutter
    Joined: Mar 2015
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    anothernutter Junior Member

    Fred,
    "The best glue is resoursanol if you don't like epoxy , the problem is the fit musty be perfect!

    Epoxy will fill small gaps and is used by folks that find perfection hard to do."

    I haven't experimented much with epoxy, but up to about 2mm gaps are still fine with resorcinol, so its not a very difficult tolerance to work with.
     
  7. anothernutter
    Joined: Mar 2015
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    anothernutter Junior Member

    Mr Efficiency,

    The heartwood is as hard as the hobs of hell, the sawmills here apparently hate this stuff. A guy in the know says that they use the sapwood for untreated decking. I must say the timber looks quite good and with 2mm :) glue lines, the hull painted clear might look good.
     
  8. snowbirder

    snowbirder Previous Member

    Flat bottom? All this weight?

    What is wrong with just using a barge? I'm not trying to insult, but it may be quite a bit easier.
     
  9. waikikin
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    waikikin Senior Member

    Good idea, something like this...http://www.boatdesign.net/forums/sailboats/new-zealand-scow-28735.html

    would be more suitable in that material for carrying a good load, caulked with oakum.
    If epoxy is out & a clear finish- ie no sheathing? that hardwood may give some issues of collective shrinkage/ in topsides area if edge glued.

    Jeff
     
  10. anothernutter
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    anothernutter Junior Member

    Waikikin,

    Re shrinkage. The shrinkage of this stuff is very much the same as western red cedar, do you think it can be a problem?
     
  11. anothernutter
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    anothernutter Junior Member

    I don't think a cat such as this will be all that much heavier than an average 43 - 45 foot cruising cat. Which is what ?? a lightship displacement of 6, or 6500 to 7500kg's ??

    The problem comes when 8 or 10 guys get on the boat for a 2 to 3 week trip away from shops and bang....you can add 3 to 4000 kg's.

    So why not just build a minimum hassle 8,5 ton cat that can take a 5 ton payload?
     
  12. WestVanHan
    Joined: Aug 2009
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    WestVanHan Not a Senior Member

    A few years ago I looked into a strip planked 45' power cat,using balsa cored glassed strips and it was 4200 hours for the shell to be done and another 600-700 to get the interior,electrics,plumbing etc,fitted out.
    And the interior was mostly bare fiberglass..... so I gave up on that idea.
    Perhaps the times may be similar..or less? I don't know.

    You also have to count your time.
    If you spend say 4000 hours building it,but you took time off work/business to build it..have to count that.
    Figure out what that cost is,plus all the supplies,moving it,rigging, hired help, plus a couple trips to the hospital and perhaps a divorce (not kidding-happened to a guy who posted on here,and others I'm sure) and add 25%.

    It'll likely work out cheaper to buy,lots of cheap ones on yachtworld.
     
  13. Richard Woods
    Joined: Jun 2006
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    Richard Woods Woods Designs

    I'd agree with Westvanhan, look at used boats in your area. You can get one for the price of materials for a new one. So it makes no sense building a cheap, not well designed boat if you are going to spend that money. After all a sheet of ply, a roll of fibreglass etc costs the same whatever design it goes on. So get a good quality design

    Flat bottomed multihull hulls tend to pound in a seaway more than monohulls because they are so shallow drafted. I think only Derek Kelsall designed big flat bottomed catamarans, and he stopped doing that years ago. My largest flat bottomed boat is the 28ft Gypsy, even then it is V'eed forwards

    My Meander, Ondina and Rhea may be of interest, much more room than on a Wharram for the same length. If you think epoxy is expensive then you should go for a smaller boat, one you can afford. How many people do you plan to have on board 6? 12? more? Remember that you will need to comply with charter boat rules

    I doubt if a 1000sqft lateen sail is any cheaper than a regular sail - if you know for sure that it is, please explain

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  14. snowbirder

    snowbirder Previous Member

    Adding to what the last two posters said...

    Chris White once told me exactly what Richard Woods just said: " It costs the same and takes the same amount of time to build any boat of a given size. Might as well build a good one."

    And WestVanHan is right on with is numbers... and facts regarding cost.
     

  15. sharpii2
    Joined: May 2004
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    sharpii2 Senior Member

    You could probably build your two hulls plank on frame, if you're not after super light weight (like modern multihulls).

    The Polynesian voyaging canoes were not all that light weight. They were made out of hollowed out tree trunks, with topside planks sewn on.

    I'd forget the flat bottoms and go with "V" bottoms instead, and add healthy skegs to them, for lee way resistance. Yeah, you get more draft, but little or no pounding.

    This vessel, since it will likely have a D/L of a more typical mono, will also have similar performance. It might do slightly better than displacement speed. But otherwise would have all the advantages of a multi.

    1.) low heeling angles,
    2.) wide decks, and
    3.) relatively shallow sailing draft.

    Some very heavy cats were built during the late 30's to the early 60's, which were two to three times the displacement of more modern cats of the same dimensions (L+B).
     
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