Boxy Fisher Catamaran idea

Discussion in 'Boat Design' started by Fanie, Oct 28, 2007.

  1. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 174, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Latest hull shape of the boxy, some changes may still be implemented.

    I've always liked square decks. I've drawed the hulls top view out on the paving and I didn't like the sharp fore hulls. The wider shape foreward (and aft) has a lot of positive properties. The displacement proprties hasn't been changed.

    You can get right up front by just walking there, safely and it adds a lot of space.
    It would provide a lot of lift and buyancy if the hull gets burried.
    At speed it should foil the hull upwards before burroughing in a wave.
    It adds space to the inside of the small hulls (only 10m).
    It should veer water spray sidewards, could make for a somewhat drier deck.
    Unused extra space would become buyancy or storage.
    You can inspect the hulls 360 degrees.
    I think it is going to look cool.


    If you can think of any other changes I could implement, or any problems resulting because of this, please speak up !

    So far the only drawback is it is going to be more difficult to form... twice.
     

    Attached Files:

  2. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 174, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    This is what the cabin looks like so far. I want decent viewing all round (so you can see where the fish are :rolleyes:) and so one can have a proper lookout.
     

    Attached Files:

  3. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 174, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Ok, sorry some stuff happened since I last posted here, so there's some gaps.

    I since built a little trimaran to test the aft mast sail setup promoted by Brian Eiland since he's not helping with any information on it and also to get a feel for sailing. Power boating no problem.

    I haven't had time to put up a web page, but here are some basics

    http://www.boatdesign.net/forums/showthread.php?t=20371&highlight=sailing experience

    I must admit the little there was actually wind on our local dams me sailing, was quite enjoyable on such a small vessel. It's going to be ten times more satisfying on the boxy fisher !
     
  4. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 174, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Just to update some basics -

    Safety, comfort, functionality.

    Motorised sailer, two outboards and a sail setup.

    The boxy fisher is going to be 10m LOA, 8mBOA, GRP construction with sandwitched pollyethylene closed cell foam.
    Trailable on two trailers, hulls and beams on one trailer the cabin, decks etc. and holidaying stuff on the other trailer.

    The hull width is limited by the allowed width of a trailor, so the hulls are only 1m200 max. The vessel is assembled by launching the two hulls with a beam mounted to each thus preventing tipping over, tested and works well with the little tri's hulls. Drift apart and mount beams.

    Assembly time 3 hours or less and two persons must be able to do it (alone :D)

    There may be four main beams - for various reasons, but it may add to a few positive points.

    Planned a 15m mast and about 50m^2 sailing area, using the aft mast sailing setup, single main sail. Two aft stays and one forestay with a furling roller to control sail with.

    Berthing for four persons with a max of 8.
    All controls must be doable from inside the cabin.
     
  5. Richard Atkin
    Joined: Jul 2007
    Posts: 579
    Likes: 18, Points: 0, Legacy Rep: 219
    Location: Wellington, New Zealand

    Richard Atkin atn_atkin@hotmail.com

    Fanie, how fast do you want to drive your boat?
     
  6. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 174, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hi Richard, the hull ratio is around 11.8 so it's not going to win any world races. I suspect a faster is always a nicer.

    What have you in mind ?
     
  7. Richard Atkin
    Joined: Jul 2007
    Posts: 579
    Likes: 18, Points: 0, Legacy Rep: 219
    Location: Wellington, New Zealand

    Richard Atkin atn_atkin@hotmail.com

    Well...it's for fishing right? So I would make it slow...like 6 to 8 knots, and give it canoe sterns. You have lots of space...you don't need the wide stern. Canoe sterns will save fuel and will compliment the sail for slow speed sailing. You could throw on some monster engines and get the thing to plane....but planing puts much bigger loads on everything.
     
  8. deepsix
    Joined: Dec 2007
    Posts: 124
    Likes: 7, Points: 0, Legacy Rep: 94
    Location: SA

    deepsix Senior Member

    Apologies if this has already been discussed, I have not read the entire thread. How do you intend to load the cabin part? A fully fitted out cabin will be rather heavy.
     
  9. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 174, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    Hi Deepsix, I hate it when you guys ask stuff I don't know yet ! :D

    The cabin will not be fitted out fully, in fact it will only be the bare cabin. All accessories will ride loose and gets placed once the cabin is fitted. The accessories would probably account for quite a bit of weight. So if you want to take the gas stove with the stove and gass bottle would be placed in their space and connected up. Same with everything else.

    The cabin by itself will also be relative heavy. If we were as strong as ants it would not have been a problem :rolleyes: I have a few ideas to get it in place, but haven't decided on a specific method yet. It will be too heavy for two persons to lift in place, so I was thinking of using a winch(es) or maybe along the lines of a hydraulic lift to do the heavy work. The details are currently evading me.

    I could also make the cabin sides part of the hulls which will take some weight off the cabin, then lift it between the two hulls which might be easier to do, although this create another set of problems.

    If you have any ideas, lets hear them.
     
  10. doug kay
    Joined: Oct 2007
    Posts: 25
    Likes: 0, Points: 0, Legacy Rep: 3
    Location: Florada USA

    doug kay Junior Member

    I was thinking of doing the same thing with my Ground Effect since I have to transport the two hulls separately but on second thoughts I'm going to use a boatyard. I'm not fitting a cabin, in Florida it's not required and I will have a large deck area running fore/aft between the hulls. this will save considerable weight and building time. I've dispensed with the two rudders and keels replacing them with a centre keel " Cherokee " style and a centre rudder.

    The hulls were built of western red cedar glued with epoxy/wood flour and covered on one side with biaxial and the other with cloth. The rest of the boat was plywood, 1088 but rotted within 5 years and has been replaced with polystyrene covered with epoxy/cloth, very strong, light and rot proof, it also has great buoyancy of course and helps with the insulation, almost a perfect material. I would consider building a complete boat in it for fishing in coastal waters or lakes and make solid GRP obsolete. Don't use any resin other than epoxy.
     
  11. deepsix
    Joined: Dec 2007
    Posts: 124
    Likes: 7, Points: 0, Legacy Rep: 94
    Location: SA

    deepsix Senior Member

    The more I think about this the more compicated it becomes. I have a couple of ideas, but I need to understand how the mast will fit into the whole operation. What are your plans to raise it? If you use a crane/gantry to step the mast, just drop in the cabin at the same time, simple enough and safe.

    If you are planing on being self sufficient, using a canterlever or ginpole to raise the mast would be possible but is more risky. I prefer to do this while still on the trailer, so you must spread the hulls and attach the beams on the trailer. Then you can lift the cabin from the mast, you will need some kind of boom and a chain hoist. Then launch the whole thing.

    This sounds like a serious PITA, and will take at least an entire day to assemble. It might be worth compromising your accomodation and going with one of the simpler folding mechanisms discussed earlier, or you can assemble the cabin from flat pannels.
     
  12. Pericles
    Joined: Sep 2006
    Posts: 2,010
    Likes: 136, Points: 63, Legacy Rep: 1307
    Location: Heights of High Wycombe, not far from River Thames

    Pericles Senior Member

  13. Fanie
    Joined: Oct 2007
    Posts: 4,603
    Likes: 174, Points: 63, Legacy Rep: 2484
    Location: Colonial "Sick Africa"

    Fanie Fanie

    DOUG -
    Would be absolutely stunning ! If one can find a material to insulate the polystirene from GRP it would be equally nice to use. I intend to use a closed cell polyethilene foam, 30kg/m^3 and it bonds perfectly with GRP. Doesn't absorb water even over the long term, and this may be a problem with polystirene though.

    DEEPSIX -
    The mast is not an issue to raise or take down, using a canterlever or ginpole as you said. A simple winch that clips onto the fore beam front should do the trick. The mast would have two rear stays which gets tied up before the mast gets raised. One person would keep the mast from swinging either way while the other winches up. Once the cantelever end is past the ball of the mast it should go streight up. The ball would be attached to the beam and to prevent the mast foot to slip out a slot in the side of the foot that fits around the ball's neck should keep it in position.

    Using a temporary boom-like attachment to the mast and a winch is certainly an option. The cabin could have a hook to lift it up on, swing it over the hulls and drop in place. Just may be the way to go. Good idea !

    PERICLES -
    From experience I can tell you that polistirene absorbs some water over time. I do think the effect lessens if the boat doesn't sit in the water all the time and it gets time to dry out. Polistirene has only three drawbacks - 1 it does absorb some water over time, - 2 you have to insulate it from GPR or else and - 3 it is not UV (sun) resistant. Other than that it would be a very good material to use.
     
  14. Pericles
    Joined: Sep 2006
    Posts: 2,010
    Likes: 136, Points: 63, Legacy Rep: 1307
    Location: Heights of High Wycombe, not far from River Thames

    Pericles Senior Member

    Fanie,

    In effect, you mean that polystyrene is not a suitable product to be used as a foam core for big boat building. I heartily concur. :D :D

    Pericles
     

  15. Richard Atkin
    Joined: Jul 2007
    Posts: 579
    Likes: 18, Points: 0, Legacy Rep: 219
    Location: Wellington, New Zealand

    Richard Atkin atn_atkin@hotmail.com

    What is the strongest way to build a hull that uses fibreglass? In other words...what combination of materials and how are they applied?
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.