Conversion to gaff rig

Discussion in 'Boat Design' started by Kaaro, Aug 16, 2022.

  1. Kaaro
    Joined: Aug 2022
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    Location: Sweden

    Kaaro Junior Member

    Hi, I want to convert my 16 foot centerboard sailboat from bermudan to a gaff rig, mainly as a fun project. I am aware that the mast may need to be moved in respect to the planned bowsprit and the shape of the sails. I have so far gathered that it's practically impossible to predict the balance of a boat, and that testing of the boats helm is required. So I am thinking of adding another centerboard behind the first one to gain the possibility to more the C.L.R. more aft? Would that work?

    My other concern was regarding the sail area, I am thinking a 45 degree gaff, forestaysail, flying jib and possibly toppsail. Should I try to keep the same sail area as before, or could i increase it?
     
  2. tlouth7
    Joined: Jun 2013
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    tlouth7 Senior Member

    I suspect it would be much easier to move the rig around than to add another underwater foil + trunk etc. Does your boat have a centreboard or a daggerboard? If the former then you have quite a lot of opportunity to move the CLR with the existing board.

    How is the mast currently stepped? Is it stayed? These will affect how easy it is to adjust the foot position and/or rake.
     
  3. Kaaro
    Joined: Aug 2022
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    Kaaro Junior Member

    I have a daggerboard, so I can't adjust my CE that way. The mast goes through a hole in the deck into a fitted metal ring, it has a forestay and shrouds (but these can be moved). The goal was to build a tabernacle, so I'll have to remove/modify the current mast setup anyways.

    Another thing: Should the CE allign with the CLR or should it be ahead of it? In Skeenes elements of yaht design, he states that the CE preferably is 15- to 19% of the designed water line ahead of the CLR (for sloops). What am I missing?
     

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  4. tlouth7
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    tlouth7 Senior Member

    I don't think you are missing anything, a small amount of lead (CE ahead of CLR) is the standard. When the boat heels the forward thrust from the sails is offset to leeward which will tend to make the boat round up (weather helm). Lead reduces this effect.
     
  5. Kaaro
    Joined: Aug 2022
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    Kaaro Junior Member

    Ok, that makes a lot of sense, thanks. Any idea on how much sail area is sensible on this kind of craft? The current mast is about 6 meter tall.
     
  6. tlouth7
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    tlouth7 Senior Member

    How much sail area has the boat currently got? How over or underpowered does she seem?
     
  7. Kaaro
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    Kaaro Junior Member

    I think about 10 square meters, I would like more. Would 15 be too much?
     
  8. Kaaro
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    Kaaro Junior Member

    Nevermind, the Haven 12 1/2 is almost 16 feet, gaff rigged and has a sail area of 12.4 sqm. I'll just do something similar to that :)
     
  9. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    @Kaaro can you post a few photos of your boat please?
    And perhaps a sketch or two showing your proposed rig conversion?
    I think that these would help us to understand what you want to do.
     
  10. Kaaro
    Joined: Aug 2022
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    Kaaro Junior Member

    @bajansailor Yeah sure, I don't have a sketch of the full rig yet, but I hope it's goog enough. The first picture depicts the mast, with mainsail and toppsail (and the two forestays). The second, more cluttered picture depicts the bowsprit and how the two forestays are drawn, the plan is to have a jib and flying jib on the two stays.
     

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  11. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    How well does the boat sail with her current rig - can she easily reach 'hull speed'?
    If you have the capability of reefing the mainsail, what is the maximum wind strength that you can currently sail in with full sail, approximately, before you have to reduce sail?
    You will have to buy a new suit of sails if you convert her to gaff rig, and extra rigging and a bow sprit, and the cost of all this will add up significantly, compared to the value of the boat as she currently is, but the new sails will not necessarily improve her value by much.
    And the odds are that you will probably be able to sail closer to the wind with your current bermudan rig, when compared against a gaff rig.
     
  12. Kaaro
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    Kaaro Junior Member

    The current rigg can't be reefed, and it can be sailed quite comfortably in wind speeds at 8 (10), after that things become complicated. Don't know about her hull speed, nor do I have a logger installed.

    I have the financials figured out, and the goal is more to have a newfangled rig and a fun project than to improve the sailing capabilities.
     
  13. messabout
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    messabout Senior Member

    Bajansailor is being polite and gentle while quietly advising against converting the rig. I will be a little more direct. Converting the rig as you have drawn it will cause some unwelcome helm balance issues. Adding the bow sprit, flying jibs, and topsails will move the center of effort of the sails a distance that is likely to make the boat handle poorly or even dangerously. The rig that you have proposed will require more hardware. more lines, and at least one other crew member who knows a bit about tending such a rig. A lot of strings to pull.

    Is your reason for making these changes only because you imagine the new rig is more salty, more cool? Is appearance the only motivating factor?
     
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  14. Tinkersail
    Joined: Mar 2020
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    Location: Europe

    Tinkersail New Member

    I have a similar project to convert my enterprise to boomless shroudless sprit rig. The reasons are many, but mainly: increased stability, and much shorter spars for ease of handling. I believe that aspect ratio thing is much overhyped, and that the sprit will perform as well as a bermuda. In any case, I can't handle the present tall rig in our often blustery conditions and it's such a pain to setup. So I perfectly understand what you're up to and wish you success! To help me with the design I made a small programme to sketch the sail plan and calculate all the important parameters like spar lengths, centre of effort, sail areas. Can handle also lug, gaff, leg o mutton, bermuda and lateen, with or without bow sprit. Now all I hope for is some spare time and some sail cloth to try out my new sail plan. screen shot attached.

    upload_2022-9-10_12-43-41.png
     

  15. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    You are reducing sail area. It would be simpler to cut the existing mast just above the shrouds attachment point and re-fit the mainsail.
     
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