Easy to handle sail plan for serious use with sit on top kayak - thoughts?

Discussion in 'Sailboats' started by Mariku, Jan 11, 2020.

  1. Mariku
    Joined: Jan 2020
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    Location: New Zealand

    Mariku Junior Member

    Wow Sharpii2, that's a lot of food for thought - thank you! I will digest your words for a while and get back to you here a bit later. Thanks heaps.
     
  2. Rumars
    Joined: Mar 2013
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    Location: Germany

    Rumars Senior Member

    Mariku, I should have been more clear, my bad. The pvc is not stiff enough, it will bend and deform under the sailing loads. Ask around, someone is bound to have an old rudder fitting from a dinghy or beach catamaran that you can use.
    Your straps should also be as wide as possible and as tight as you dare. The problem is strech, not strenght.
    I agree about the sail area, comparable sit-in kayaks have 3,2sqm as factory sails. Between 3 and 4sqm is what you want.
    Windsurf masts make good kayak masts should the present one be not satisfactory.
    To appreciate what expects you here a film with a sit-in under sail. The boat in the video is 4,5m long and 80cm wide with the full 3,2sqm of sail up.

     
  3. Tiny Turnip
    Joined: Mar 2008
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    Location: Huddersfield, UK

    Tiny Turnip Senior Member

    Thanks for the reassurance on sail area, Mariku. 2 square metres sounds reasonable. I was slightly concerned when you commented earlier about getting more sail area [higher up] with a rectangular sail, that you might be looking at an over ambitious amount of sail.
    Do have a look at the Solway Dory website; they make a range of very simple, light weight unstayed rigs and sails, including a 35sq ft expedition bermudan, and a 25 sq ft lug sail, which might provide some inspiration
    There's also a brief article on sailmaking. 'Canoe Rig' by Todd Bradshaw is reccomended.

    And yes, no typo! but I do have 200kg of buoyancy in each ama.

    Good luck!
     

  4. sharpii2
    Joined: May 2004
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    Location: Michigan, USA

    sharpii2 Senior Member

    After reading all your posts, I realized I had missed the requirement that there be no outriggers. While noticing that mistake, I also realized that the chilly bin will have far more buoyancy than it weighs. I calculate, based on one in my home, that it could have as much as 68 kg of buoyancy while weighing probably less than a third of that. What this means is that if it securely closed and securely attached to the kayak, it will probably keep the kayak from turtling if it capsizes.

    I also noticed that the seating in your kayak is somewhat lower than the deck, which means that if your upper-body is free to lean, the CG of you and your son can be calculated from the height of the seat instead of your actual vertical CGs. But keep in mind that this is only true if you and your son keep your upper-bodies dead upright at all times. If you lounge back in your seat backs, your effective CG ends up higher, as your upper- bodies will match the heel of the kayak.

    If this rule is followed to the letter, the range of stability and the initial stability may be enough to allow carrying sail without an outrigger float. The sail plan will have to be more modest than the rig I drew in a previous post. Its design would also have to be modified somewhat.

    (see thumbnail below)

    The first change is to eliminate the lower boom. By getting rid of it, I eliminate the need to sheet it somehow. I also reduce the SA, but in a place where such a reduction is least helpful. But it is somewhat helpful none the less.

    The second change is sure to get me into some hot water with other contributors to this thread.

    This change is to specify that this sail be flat-cut with no airfoil shape at all.

    The reason for this is to make it possible to feather the sail without it flogging. I have done this with a Super Snark (c) sailboat I once owned. I sailed it in winds of well over twenty kts without capsizing it. That was the fastest that boat ever sailed when I went downwind. The rudder created an actual rooster tail. Now getting back was a whole lot slower, but I did it. I had to make frequent stops to bail water out water that had slopped on board. I was able to do this without a single knockdown, with only myself on board, and while never taking down the sail. With a foil shaped sail, the flogging itself would have likely dragged the boat onto its side.

    Sa4kayak2.png

    I don't envision you intentionally taking such crazy risks. But I do envision you getting suddenly caught up in such conditions due to the considerable distances you like to travel. Keeping in mind that a flat-cut sail is about two-thirds as effective as a foil-cut one, I kept the SA as large as possible. This one-third loss in efficiency is most experienced while sailing upwind. Sailing across the wind, it makes far less difference. And sailing downwind, it makes no difference at all. So the roughly 2.9 sm shown on this new design is probably effectively a 2.0+ sm sail when sailing upwind. But, in my view, a 2.0 sm sail with a foil shape cut will be more dangerous, as it will either want to propel the kayak or flog itself to pieces.

    A third change I made was to fix the boom at its present height. Doing so allowed me to accomplish two goals:

    The first was to simplify the halyard arrangement (2). No more crazy halyard lasso at the top. Now, all the halyard does is hold the yard vertical.

    The second was to allow the lazy jacks (1) to be moved to that boom so that the upper part of the sail can be lowered while the lower part is still set. The lower part will not get you to windward, but it may be enough to keep the kayak pointed into the wind. It may also give you a far wider choice of downwind courses, and may even allow you some crosswind sailing.

    The lower portion of the sail can also be furled independently of the upper part. Its lower corner can be unhooked from the mast and the sail can be pulled up to the boom with a system of brails (3). These brails can be controlled by the forward paddler, as they will be hard to keep within reach of the aft one.

    A third advantage of the boom being at a fixed height is that it can now have a hold-down (D) to keep the end of the boom from cocking up.
     
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