28' sail cat

Discussion in 'Multihulls' started by mihari, Sep 4, 2009.

  1. jamez
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    jamez Senior Member

    You might like to check out the Kelsall website for info on foam/poly and his KSS construction system, Thomas Firth Jones for info on building economical safe ply multi's and a couple more examples of different styles of boat.
    http://www.members.optusnet.com.au/rhturner1/cc29.html
    http://www.wallerdesign.com.au/cc31.html



    ......
     
  2. mihari
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    mihari Junior Member

    Yes, I have been following the progress of masalai's build. He is doing great. I envy him. Anyway, I don't think that his hull section is far from being round. And I don't think that there will be no difference to performance between his hull section and this:
    http://www.ikarus342000.com/P86page2.htm
     
  3. boat fan
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    boat fan Senior Member

  4. mihari
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    mihari Junior Member

    James, thanx again for your thoughts.
    After reading a little bit more (not too much), I have come to realize that more people feel the same way with you about chined sections. Actually some think that when a chine is at aft of the boat might actually compliment the handling of a boat... I must reconsider.

    Is there any up to date information of double diagonal? It seems like a 60's way to go for non linear surfaces. Does anybody build in double diagonal plywood... today?
    If it red cedar is expensive there, then here it will probably only be found in museums of natural history... So strip planking in red cedar is out. The fact that fairing it would be of such difficulty, and weight adding, makes it even clearer to me that it is not the way to go.

    The jarcat is extremely interesting as far as layout goes that it has the mast splitting the cockpit from the saloon. That gives equally great area to both spaces. The downside is that the produced form seems really home made. That would be really bad for resale value. But still, I find that it has great advantages over conventional standard modern design. You have access to the mast and all the lines right from the cockpit. The resulting mainsail is a bit narrow because of the aft wards positioned mast, and the jib/genoa is shorter than usual (because it has to be above the saloon). Maybe the transoms need to be redesigned (look at the waves it is producing) http://www.members.optusnet.com.au/rhturner1/cc29.html
     
  5. sabahcat
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    sabahcat Senior Member

    Have a look at KIRI as a replacement to WRC.

    Also I had and built one of these from WRC, but in kiri, she would be lighter again, Simpson Ground Effect Catamaran.
    I think I will always regret selling this vessel, she was one of the best boats I have ever sailed on in her size range, not the fastest or the most comfortable, but in her size, she stacked up very favourably against any competition.

    The plans are available Here
     
  6. jamez
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    jamez Senior Member

    Sabahcat that is one nice boat. I reckon Roger Simpson really nailed it with the Backslash and Ground Effect. More boat than I need but I've always liked the GE. I've never found much in the way of photos or info on them. Any more pics you can post? particularly interested in interior/cockpit photo's. Now where did I put those study plans....
     
  7. jamez
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    jamez Senior Member

    I remember lots of boats being built in DD back in the 1970's when I was a kid. It fell out of favour after the introduction of strip composite. But if you can get a bunch of cheap ply why not? Its still a perfectly valid way of producing a round bilge hull. A lot of the Tennant GBE's here were built in 2 skins of 4mm ply over a mould that produced a strong, nearly clean hull inside. Other designers suggest doing the bilges in DD or strip and the flat topsides in ply (Woods / Simpson).

    There are lots of options and no one of them is 'right'.
    Gougeons book describes most methods, but so does a little known book by aussie designer Roger Simpson (the designer of Sabacats ground Effect) 'Simpson on Boatbuilding'. Difference is all the examples in this book are multi's and it covers things like building cross-beams, bridgedeck structures etc. etc. Its available from Boatcraft pacific in Aus.

    The Coral Coast (jarcat) 29 might look a bit caravanish but I think as a family cruising boat it has a lot going for it as you have identified. Its relatively light approx 1300kg with a 1 ton payload on top of that. There is a wing mast fractional rig option too. Seems like a lot of boat for the money, but I've never sailed on or seen one. There is a bit of wake in the photo but you'd expect some at 12 knots. Unlike many bridgedeck cats the skipper can actually see where they are going.
     
  8. sabahcat
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    sabahcat Senior Member

    Thank you very much, we liked her a lot and had many years of enjoyment over many years and won many bottles of rum with her before selling her off to a New Caledonian owner.

    We got to sail her across and have several weeks with her saying our goodbyes

    Have a flick through these pictures here. There are several shots of her amongst the pics.

    Heres one that was being built in England, he came out to see mine. http://www.themultihullzone.com/workshop.html
     
  9. mihari
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    mihari Junior Member

    Those are beautiful boats, beautifully built. They have my favourite section in the hulls. That knuckle is so sexy!!! I first saw it (and adorred it) in Shuttleworths designs. But I have to admit that it looks like a great deal of labour.

    Is kiri the same as Paulownia tomentosa? (Chinese - Japanese species)

    Has anyone (alive) tried to build in double diagonal plywood? In my simple mind, that seems like a little less work. I am only isnsisting in this matter because construction method is going to be a decisive factor of the overall design. Ofcourse, 2 layers of 4mm ply + epoxy inbetween is more pricey than 9mm ply. (I have to work out how much more expensive) It also seems a bit difficult to design the individual pieces of the ply to accommodate the curves of the hull. So, any experience in building/designing in double plywood would be appreciated.
     
  10. Richard Woods
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    Richard Woods Woods Designs

    Lots of people do still build in double diagonal ply.

    As a catamaran has long thin hulls the ply strips are almost parallel sided so are quick to fit, especially when using epoxy. It is on wide monohulls that you need to "spile" (plane curves on) the strips

    The big disadvantage over other systems is the space the stringers and frames take up inside - and they collect dirt and water etc.

    Also resale value is probably less. Also check insurance availability.

    Hope this helps

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  11. sabahcat
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    sabahcat Senior Member

    Why thank you sir

    Not realy, just gotta get the knuckle straight, spend a bit more time getting temporary frames (mould) right, which saves a lot of work later.

    The big white hulls (50ft) in the pictures hasn't even had a longboard yet and probably wont
    That it is.
     
  12. mihari
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    mihari Junior Member

    Since Japanese market absorbs 90% of world wide production, I assume that it will be really difficult to get around here, and if I could get it it would cost me leg and an arm. It is really light (~300 kg/m3, where okume is around 450kg/m3) and it looks like great stuff to work with.

    Now we have 2 alternatives for strip planking. Western red cedar and kiri. Are there any other alternatives to strip planking? I know that traditionally greek boatbuilders use pine. That will be readily available and very cheap. But I know that it is not the way to go...
     
  13. mihari
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    mihari Junior Member

    And I have another question, what does a machined strip's section (for planking) look like?
     
  14. sabahcat
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    sabahcat Senior Member

    Concave

    [​IMG]

    Tongue and groove
    [​IMG]
     

  15. jamez
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    jamez Senior Member

    Another alternative is to use horizontal foam strips although I think a better alternative for a round bilge hull in foam is to use vertical foam strip/panel such as the latest Farrier boats. Farrier's Study Site is well worth the 10 bucks to have a look around IMO. You can see a vertical strip build of a 28' racing cat here: http://www.bobfishermarine.com/page8.html

    Richard Woods now has a lot of study plan info available on his website. If you check out the build photos on the Strider design info you can see the difference between the same hull in sheet ply/DD vs strip plank. The strip hull interior is somewhat less cluttered.

    Full DD (from the sheer) can allow clean hulls inside, although there are some limitations on shape compared to strip. The attached photo shows the interior of a 28' Great Barrier Express hull. In the DD version the hulls are laminated over a mold in 2 or 3 skins and glassed on the outside. The only solid timber in the completed hulls are keel, gunwale stringers and a stem support. Frames to support crossbeams etc are fitted later. A number of Malcom Tennants designs have this construction method as an option. In the pic the lighter coloured planking in the bottom center right is a repair following a trip onto some rocks.
     

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