sail and boom design

Discussion in 'Boat Design' started by johnholland4, Jul 4, 2009.

  1. alan white
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    alan white Senior Member

    Johnholland, good luck with the boom. I'm off this thread, which has become a bit ugly.
     
  2. Paul B

    Paul B Previous Member


    Yes, it must be "ugly" when your nonsense is pointed out.
     
  3. tspeer
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    tspeer Senior Member

    The Searunner had the mast mounted in the center cockpit. The design philosophy of the boat was for operations to become increasingly concentrated at the cockpit as the wind strength increased, so the crew did not have to go forward when conditions were bad. There was no need to run lines along the top of the cabin. The same mast-oriented approach to sail-handling can be used with a more forward position of the mast.

    Do you mean 4 sheaves at the clew end (the tack end would be the gooseneck end), in addition to the sheaves at the gooseneck?

    The sheaves with cam cleats are for slab reefing lines. Each reefing line should be tied around the boom under the reef point, go up through the cringle on the leech and back down to a sheave on the end of the boom. Then it goes forward through the boom and out through the sheave and cam cleat at the gooseneck. This allows you to lower the mainsail and tighten the reefing line while you are at the mast. Three sets of sheaves are probably for three levels of reefing.

    The fourth sheave and cam cleat is probably for the outhaul at the clew. You may want to dead-end the outhaul at the end of the boom, then bring it forward through the clew and back to a sheave at the end of the boom, then forward through the boom to the sheave and cam cleat at the gooseneck. This will provide a 2:1 purchase (minus friction) to make it easier to tension the outhaul. The alternative is to simply go straight from the clew to the sheave at the end of the boom.

    The reefing lines take a lot of load, since they carry the whole leech tension from the mainsheet and vang, so use sturdy line.

    To reef, ease the mainsheet and pull down the mainsail until you can secure the tack at the next reef cringle. There may be a curved horn on each side of the gooseneck to which to secure the cringle. Tighten the main halyard. Then pull the reefing line down through the cam cleat at the gooseneck to bring the boom up to the reefing cringle on the leech. Sheet in, and you're done.

    You should not use the sheaves on the boom for halyards. If you want to run them back to the cockpit, they should be led to very strongly mounted turning bocks near the base of the mast, and back through an organizer (sheaves mounted flat to the deck) to the jammers & winches.
     
  4. Paul B

    Paul B Previous Member

    I think Tom is correct in his statements. I think there are a couple of places where there is a slightly better way:

    I would not tie the reeding line to the boom. It works much better if the line comes out of the sheave in the back of the boom, goes up through the reef point in the sail, then down around the bottom of the boom, and tied as a bowline to side along the part that is coming from the boom up to the reef point.


    I think it works better if you follow this sequence:

    Ease vang
    Ease mainsheet
    Pull aft reef line on(this pulls the boom end up into the air)
    Ease main halyard to pre-marked reef location and cleat
    Use a hook at the end of your tackle for the cunningham. Once the halyard is dropped you can simply unhook from the cunningham and hook into the reef point (the "new tack"). Tension the tackle.
    Pull on the main and re-set the vang.

    This should take less than a minute to do.
     
  5. johnholland4
    Joined: May 2009
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    johnholland4 Junior Member

    Now that we've all really sharpened our pencils I have two further questions: Does god exist? When did the Virgin Mary become a virgin?
     
  6. messabout
    Joined: Jan 2006
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    messabout Senior Member

    OK the last two questions are biggies, but they have no legitimate place within this forum. If you are serious, then go to this forum...Freeratio.org. Here you will get some real intelligent discussion.
     
  7. Stumble
    Joined: Oct 2008
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    Stumble Senior Member

    John,

    There has been a little disinformation and a lot of name calling in this thread so far, so I hesitate to jump in, but I think the information has been a little overly complexed so just to clarify...

    On a properly loosefooted or captive foot main there should be a shelf of material that runs along the boom. This shelf provides NO lateral support to the bottom of the sail, it simply acts to provide the bottom of the sail with a termination area. On a loosefitted main this will be done normally with a piece of spectra/kevlar/uberyarn sewn captivated by fabric. This allows the foot to be pulled tight to prevent flapping without distorting the sail shape particularly in light air or off the breeze.

    On a captive foot main it is basically the same except that the spectra line is replaced with a bolt rope that slides down a groove in the boom. However this actually makes it more difficult to cut a main properly since the shelf has to still exist to allow for easing the outhaul to indice more draft in the sail. Yat at the same time the bolt rope needs to pull tight when the outhaul is loaded to flatten the sail. In effect either system does the exact same thing but the engineering is actually easier with a loosefitted main since the shelf doesn't have to be cut on a camber to allow for the sail to be shapped properly on and off the breeze. The other problem with captive foot mains is that over time all boltropes shrink as they are exposed to heat/UV/cycle loading/whatever this shrinkage will reduce the ability to properly flatten the lower third of the sail and will require changing the bolt rope from time to time to keep it the proper length.

    As for boom selection, it really doesn't matter to be honest. Any boom that can handle a captive foot can also handle a loosefitted sail, and these days even carbon racing booms are made with a groove to handle a bolt rope. Not because they expect that it will be used for that purpose, but because it allows for slugs to be run into the track to attach reefing lines to. Note that this won't work in revers though, if you do happen to have a spar with no groove (I am not familure with any company that makes them like this but they may exist) then a captive foot obviously wouldn't fit.

    In short

    A loosefooted main:

    Advantages
    1) They are easier to rig & de-rig.
    2) The outhaul is easier to Trim - less friction.
    3) You can get a fuller roach shape (more draft) for light airs & downwind work.
    4) They suffer less chaffe since there is less to rub
    5) They are easier to reef since a strap can be run around the boom before the sail is lowered.
    6) like for like loosefooted mains are less expensive
    7) Eliminates the need for a flatening reef (almost always)

    Disadvantages
    1) may require replacing the bolt rope on an existing sail with a different shelf for a loosefitted main.
    2) Sometimes the spectra shelf rope can fluter being very annoying... fixable with bungee cord though

    Captive main
    Advantages
    1) they are traditional

    Disadvantages
    1) Induce more friction on the outhaul
    2) Won't trim as well since the bolt rope rarely runs free downwind
    3) Concerns over replacing the bolt rope due to shrinkage
    4) Harder to reef, rig and derig
    5) Make it impractical to


    I think it is clear that I prefer loosefitted for all aplications, since I really don't see any justification for a captive foot on a main. It was a reasonable step for sailmakers to make, but it is outdated, adds nothing to the sail, expensive, and makes the whole system more difficult to use. Heck the major sail makers actually now make all of their sails loosefooted unless you specifically order a fitted one.
     

  8. johnholland4
    Joined: May 2009
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    johnholland4 Junior Member

    I was mildly facetious with my short questions above thinking that we had in fact exhausted the question at hand; silly me. Now Tom's come in with a brilliant analysis of the boom which finally turned the light on. I see now that I was puzzled by the lines running through the boom because I was assuming they were for halyards. So thanks Tom. With regard to the preferable set-up - I'll have to print these suggestions and mull them over (am briefly in the marina right now then back on the boat). Will also follow further discussion on all this so please keep it coming (I'm out of touch for a week or so so lookforward to a mess of thoughts when I get back online. Just a thought on Capt Rubin's remarks: I look around the marina and EVERYONE has a main with a captive foot. Indeed the reason I originally asked the question was that this was the first time I had come across it on a large boat (I've owned about 20). Also: isn't it a lot harder to drop and furl a loose-footed sail? Without lazy jacks of course. Or is it taken for granted that one will have these? Thanks all. Kind breezes. Fierce winds. John.
     
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