Ketch Gaff Conversion

Discussion in 'Sailboats' started by dreamketcher, Oct 19, 2009.

  1. dreamketcher
    Joined: Oct 2009
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    dreamketcher Capt. Mike

    I am new to the forum and just starting my next project. I have an Island Trader 37 Ketch, a very traditional full keel, bow sprit, heavy boat. It's a William Gardner design built in Taiwan in the late 70's. The masts are keel stepped. The original masts are wooden and rotten so I have to replace so I was thinking of redoing the sail plan and converting to a gaff rig to compliment the design of the boat. I'm not sure if that would require relocating the masts, I'm also assuming they will be shorter. I will probably use schedule 40 aluminum tube for the spars just need to design the sail plan. Any tips?
     
  2. alan white
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    alan white Senior Member

    The CE will drop aft a bit, meaning the masts would want to be a bit forward if changed to gaff. This wouldn't work, or would be nearly impossible to implement, so you need to find a way to get the CE back to where it should be without moving the masts.
    Unfortunately, you already have a sprit, otherwise you could afford some forward area more easily by adding one. Lengthening the existing sprit is dependant on what you have to start with. If it's a short sprit, then you might have some margin.
    None of it is cheap, since the rigging all has to be replaced or at least shortened. You really have to love gaffers to convert a perfectly set up bermudan rig, especially on a two-master. Consider a gaff main and a bermudan mizzen. It might be a lot easier to accomplish. You could, for example, take a bit of area from the mizzen by shortening the foot, moving the CE forward enough to compensate for the effect of the main's CE moving aft.
     
  3. dreamketcher
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    dreamketcher Capt. Mike

    The bowsprit is about 6 feet long or 1/6th the LOD. The displacement is 18,000 with only 567 sq ft of sail. Slow and heavy. The gaff rig should also increase sail area, I would think.

    Would conversion to a schooner help keep the CE close? Moving the current mizzen mast forward and possibly using a lug sail on the foremast. Most of the interior is gutted at this point so moving the aft mast forward might be easier. Chain plates would be an issue. The interior from the v-berth back to the saloon has been redone, the galley back is basically bare hull.
     
  4. alan white
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    alan white Senior Member

    You are talking about major changes and any analysis would require a lot of information and familiarity with the boat.
    You are not just dealing with the CE. That is the easy part. You could probably work out something with the masts where they are. Chainplates might or might not be a problem to relocate.
    You'll either need to pay a designer to do the redesign or commit yourself to an intensive crash course in boat design and rigging design as well. How well you do will depend on aptitude and experience.
    Not much can be done here except to say the usual thing---- it's impractical and so forth, which is really a subjective issue (you don't really need to sail at all in the first place, just like the rest of us).
    I think it can be done but a schooner would be difficult to balance as easily as a ketch. If you think you could move the main forward, that might be all you need to do. Then the structural issues involving the partners and the chainplates need to be addressed. Draw some pictures to scale and measure the centers and play around with different combinations. A high-peaked gaff sail is closer to a bermudan sail and might require the least structural work.
     
  5. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    Just a thought... The easiest way could be to dumb the mizzen totally and use a bit larger gaff main. This could maintain the CE and leave the mast in it's current place..
     
  6. Tad
    Joined: Mar 2002
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    Tad Boat Designer

    Google Island Trader 37 and you'll find lots of folks working on these boats. They are most definitely not a William Garden design, they are an illegal (and very badly done) knock-off of a Hugh Angleman Sea Witch design. Construction of these boats is generally poor, sailing performance is poor due to overweight, high vcg, short rig (low sail area) and poor hull/keel form. Hopefully you paid very little for the boat. Changing the main sail from Marconi to gaff head will do nothing to change the overall balance of the boat.
     
  7. alan white
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    alan white Senior Member

    If the keel is very long, balancing the rig is an easier task, since such keels tend to be more forgiving of the CE moving within limited boundries. My own gaffer is pretty tolerant of small changes.
    I think the Angleman Sea Witch was gaff mains'l and triangular mizzen. Changing the main to gaff would move the sail's CE aft a foot or two. Maybe that wouldn't effect the helm on this particular boat, but I'm sure it would effect some boats.
    What's the difference, Tad, between the Sea witch and the Island Trader? Is the hull the same? I know the Sea Witch had a sprit longer than 6 ft.
     
  8. BeauVrolyk
    Joined: Apr 2009
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    BeauVrolyk Sailor

    I'm with Teddy - toss the mizzen in the drink and put a nice long boom gaff headed mainsail on her. Be sure to make the mast tall enough to carry a good sized topsail.
     
  9. Tad
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    Tad Boat Designer

    Changing the theoretical CE of the central sail in a three sail array will move the overall CE a tiny amount. In a sensitive hull this could be a big deal, in this boat no one will notice.....sheeting and sail cut will make more diference.

    The Sea Witch and the Island Trader are completely different boats, but the IT is clearly a copy in the styling department. I have no idea if Charlie Davies (Angleman's partner) was involved or not, he was involved in a glass Mayflower (Islander 40) that was pretty awful as well. Bob Perry re-designed that boat into the Islander 41 which was better looking and fairly successful.

    The IT 37 is narrower, shorter on the WL, has a foot less draft, has less ballast and less sail area than the Sea Witch.
     

  10. kiwimariner
    Joined: Nov 2009
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    kiwimariner New Member

    Fitting a Yardarm to my Ketch rig

    Looking to fit a Yard to the main mast on my 42' Ketch has anyone seen it done ? .I have seen it done on a wishbone Schooner .
    Look forward to your input guys .

    Regards Sterling ..
     
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