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

    Hi everyone,

    first post, I'll jump right in, hope that is ok - if I should be using these forums differently in any way, please don't hesitate to let me know! Thank you very much for providing them.

    I hope a sailing kayak will be taken seriously by some people here who know more about sail design than me - I could use some help with brainstorming for that part of our current project, and would really appreciate any input you might have for us.

    My eleven year old son and I are using a triple seater sit on top kayak as a platform for dolphin watching, snorkeling, free diving for paua, fishing, and more; generally along the coast, but not infrequently in somewhat remote places and / or places where landing is out of the question, and on occasion a good mile or so off shore. As I am writing this I am shaking my head again in disbelief, not for the first time, about how lucky we are to be living in such a place...

    Just in case you wonder, I humbly believe that we do know what we are doing, and importantly where our limits are. I have a background in white water kayaking, swift water rescue, scuba diving, as well as sea kayaking, and in addition to knowledge and skills we are very well equipped, including but not limited to warm wet suits and VHF radios and a 406 MHz beacon carried securely in / on our life vests. We also let reliable friends know before we go out what our plans are and when we intend to report back with them. We are both very comfortable on the water, in the water, and under water - when dolphins came up to our boat for the first time in early 2019, about a mile off shore, my son instantly jumped into the water, in about a metre and a half of swell... one of the reasons we chose a sit on top, getting back in is easy! We are also meticulously picky about weather, wind, and sea state forcast when doing our trips. Our priority number one is to come back in one piece, always. So while we have never seen any other a sit on top kayak in some places that we go, and not many closed kayaks either, we are playing it very safe nonetheless.

    We are currently in full swing of kitting the boat out for sailing - and I don't just mean downwind, I mean actual sailing. Our goal is not more speed, but a bit more reach than the seven to ten miles that we usually do on our day trips; and to have more physical energy available both for our activities at our destinations, as well as as backup energy in case something doesn't go to plan with a trip.

    My son wanted to do this as a learning project, partly for the design and build process, partly because he wants to learn some basics of sailing, and partly because he wants to have more adventures on the water - and I have happily embraced his suggestion.

    So after a few weeks of chipping away on this with our brains and hands, the pictures below show where we are right now.

    We have chosen an unstayed mast in a rather hefty mast foot in order to minimize any standing rigging. Less is better on such a small boat; we often have snorkeling and other gear with us as well, plus the chilly bin for fish and paua, and we move into the water and back into the boat often, so space to move around without getting tangled in lines too easily is important.

    After some thinking we are currently leaning towards a junk rig inspired sail plan. Some of our reasons for that are quick and easy reefing so the sail area can easily be adjusted to the wide range of wind speeds that we can encounter here within a single day; and relatively easy design and fabrication of the sail itself. We are also leaning towards cambered panels, maybe with the exception of the topmost one or two.

    One difference to typical junk rigs would have to be that the sail can not extend more than maybe five or ten centimetres at most in front of the mast, simply because that is where the front person sits - the back rest of the front seat leans pretty much directly against the wooden mast food that we have built, and which is ratched strapped to the boat (we did not want to drill any holes that weren't already there, and have succeeded in that so far).

    We may or may not add a jib of some description later on; but are likely not to use it (often) when sailing the boat with two people in it, simply because it probably gets in the way of the front person too much. So we need to maximize the propulsion that we can get out of our main sail, while still keeping things as simple to make and to use as possible.

    The relatively long leeboards swivel and thus allow to adjust the centre of lateral resistance fore and aft to some extent, which should help to balance the boat, and allows for some flexibility with the exact shape of the main sail. We have positioned the leeboards with sailing with only the main sail in mind.

    As you can see, we have devised a rudder control system that allows the rudder to be controlled from either the rear or the front seat, and by either hand or foot. We are also intending to make the running rigging accessible from either seat. The idea behind this is flexibility - either of us will be able to control the entire boat, for example if the other person is fishing, navigating, or whatever else. It also allows my son to stop the boat (reef) and to either sail or paddle it back to me should I ever fall over board unintentionally. And if one of us should get injured, the other one can still sail the boat, regardless which seat each of us is sitting in.

    So... that's as much as I can think of telling you right now. Maybe more information than you need to know, but I thought some background of what we're trying to achieve may be useful, and potentially interesting for some.

    My question is simply: What are your thoughts on the design of the sail? Which of my thoughts make sense, which don't in your opinion, what suggestions do you have?

    I would hugely appreciate if you can share any ideas that you may have, so that we can soon add wind power to our coastal adventures - down here in New Zealand, it's summer right now!

    Thank you for reading, looking forward to hear what others think!




    This is an overview of what we have so far. Don't confuse the ducting on the side of the house with the thinner and taller aluminium mast! There is a bit more than a metre between the mast and the nose of the rear person. The mast extends approximately 220 cm above the chilly bin. The boat is just under four metres long. See following photos for some more details and explanations.


    The mast doesn't go anywhere, it is rock solid. There will be a second ratchet strap approximately where the carrying handles on the side of the boat can be seen. Additional triangular bracing will be added from the mast foot "wall" to the rear, along the side of the chilly bin. I am considering to add a traveller aft of the chilly bin - seeing that the bin limits how low the boom can be, there won't be a lot of space above the chilly bin for a boom vang, which therefore might not be all that effective.


    The leeboards are only at this shallow angle here because we are on land in this photo. The white pipe along the side of the boat is our rudder control.


    Since the rudder control pipe only runs along one side of the boat, we steer with one foot - pushing and pulling on a "pedal" that covers the bottom and the top of the foot at the same time.


    This is our rudder. Since wood and some flat 4mm thick PVC was what was in the garage, that's what we made a lot of our parts from. Wood is an awesome material, and PVC is a beautiful material to work with as well - warm it up with a heat gun, and you can form it into nearly any shape you want. Together with the dark wood I personally think it doesn't even look half bad.
  2. Mariku
    Joined: Jan 2020
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    Location: New Zealand

    Mariku Junior Member

    Given the space that we have available for the sail - which is basically limited to aft of the mast, and limited to some extent by the position of the rear person - we are also somewhat interested in crab claw or lateen type sail designs. However I am not sure yet how such a design can be made so that it can be reefed easily, which we will definitely need to adjust to a relatively wide range of wind speeds.
  3. Mariku
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    Mariku Junior Member

    Hm, this doesn't sound promising for a junk rig for a kayak:

    "The junk rig is not renowned for its upwind performance. The rig described here functions perfectly well with the wind on the beam, but that is the limit for useful progress."

    Source: Junk sail on a Klepper kayak http://www.padfield.org/tim/kyk/sail/junksail_01.htm

    We do need to be able to sail upwind. Without being able to do that to a degree that is of actual practical use, I would not consider this sailing conversion of our kayak successful or very useful for us.

    Can you see anything from the photo in that article that the author might have done wrong to not be able to sail upwind, and that we could do better?

    If a junk rig should not work for our kayak, what other ways to rig our boat would you suggest?
  4. Mariku
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    Mariku Junior Member

    Would a junk rig with a cambered sail make any significant difference to this?
  5. gggGuest
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    gggGuest ...

    The classic decked canoe cruising rig was actually two unstayed masts, one up in the bows and one behind the crew. That does impose quite a torsional load on the boat though, I'm not sure how good your style of boat is in that respect. You might find it interesting to browse the Decked Canoe Archives. Although much of the material is 100 years or more old, it may provide ideas. Its on the International Canoe website, start here: The Decked Canoe Archive - Index http://www.intcanoe.org/en/dca_index.php. Although the actual modern International Canoe is an extreme craft with not much to inform you, the legacy material covers much of the territory you are considering, and may well provide ideas on rigs, reefing and the rest worth considering. After all the sea hasn't changed in the intervening time!

    Just as a small point, centreboard and rig placement. Folk here get enormously excited about centres of effort, balance, weather helm, lee helm etc, to an extent my own experience suggests is over-rated when it comes to small boats. your leeboard position is very far forward though, I wouldn't be altogether surprised if you do find that the boat needs a bit of offset on the rudder to get her to sail straight. If this is the case, before deciding to completely redesign everything, I would simply try a bigger rudder blade.

    The very simplest and easiest rig you could consider is a very basic unstayed bermudan rig with no battens and a triangular sail. While not highly efficient (but probably as good as most alternatives), this has the huge advantage that it can easily and efficiently be reefed by wrapping the sail around the mast. Also, unlike other rigs, there are no gaffs or other spars up in the air that come down on you when trying to reef. If you look up the Topper Sailing Dinghy https://www.sailboats.co.uk/media/datasheets/topper_rigging_guide.pdf and try and ignore some of the racing complexities you'll see a basically simple rig that's easy to reef. You just unhook the kicking strap, roll the sail round the mast, and hook it up again. The kicking strap stops the sail from unrolling.

    Just a thought, bearing in mind the lunch box position gives you issues with kicking strap and general access to halyards and the like, have you thought of having it in front of the mast instead?
  6. Mariku
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    Mariku Junior Member

    Hi gggGuest, thanks heaps for your thoughts, some very good food for thought, I really appreciate it!

    I will definitely explore the Decked Canoe Archive for inspiration, thank you for pointing me in that direction.

    You are right, we do need to be mindful of torsional load, since we do intend to stay in our seats rather than use our body weight as a counter weight in any kind of excessive way.

    I agree that, at least for our application, while balancing the boat half well would be nice, balancing it perfectly is not crucial. And thank you for the idea with the larger rudder - we have made it reasonably large already, or at least we think that, as well as the leeboards, exactly to have more authority if that should be needed. We can always experiment with smaller ones later on if the boat should turn out not to need them this big.

    Are you sure the leeboard position is really that far forward? It was dictated to an extent by the hefty square chunk of wood that the ratchet strap holds down on the boat, and which was the most logical point to attach them to. However so far I was hoping that, expecting to have the leeboards angled back at about 45 degrees or thereabouts, the leeboards' centre of lateral resistance might be roughly where the centre of force on the sail would be. We made them long not least because with this length we won't have to put them down vertically, at least that was part of the plan. Also, the hull itself has more lateral resistance near the stern than near the bow.

    I must say the bermudan rig that you describe is also on our shortlist of options. So far we are shying away from that still simply because it would put significantly less sail area into the air than a sail shape that is closer to rectangular; as due to the distance between the mast and my (the rear person's) nose the boom is limited in length to about a metre. The other challenge is that a bermudan sail would make designing the panels to form a proper foil a lot more complex I think. I would need to spend time on working with Sailcut CAD or similar, for a start. Not impossible, but we want to use this this summer still... hm.

    That's some good lateral thinking to place the chilly bin in front of the mast! However that would only leave about 65 centimeters at most for the length of the boom - if the boom is supposed to pass through between the mast and my face. Or would you suggest to angle the boom upwards enough that I can duck through underneath it, and extend it to maybe somewhere near where the rear seat rest is? The kicking strap is an issue, but I think maybe a simple traveller might do double duty in its place.
  7. gggGuest
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    gggGuest ...

    Well, all you can do is to draw things and explore options. Everything is going to depend on everything else if you know what I mean. I imagine it will take a fair bit of trial and error to get things right, so experiment with cheaper materials, and don't expend too much mental energy on getting changeable things "right" first time, 'cos you won't!
  8. philSweet
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    philSweet Senior Member

    As mentioned by gggGuest, the usual arrangement is two leg-o-mutton sails, one at each end. An easy way to do this is to cut in two round deck plates at the mast step locations, reinforce the edge of the top hole, stick a mast receiver base in the bottom of the hull and buy an extra lid for each. Mount the mast receiver sleeve to the second lid so that it pins into the mast base. When you want to sail, unscrew the regular lids, install the mast receiver lids, and drop the mast tubes in. The fore mast should be taller for visibility, so if you want to keep all the tubes small and manageable, consider a gunter rig on the foremast. That would keep all the tubes at about 7' or so. Use a decent deckplate with big, strong threads, $20, not $7.

    And do refine the leeboard and rudder foils. Put a NACA section on them, such as 0012, and leave the cheeks flat if you don't have enough thickness. In other words get the front and back of the foils to conform to a 0012 profile. Switch the steering to a quadrant and run the lines in the hull.
  9. Rumars
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    Rumars Senior Member

    Craig O'D's Cheap Pages/The Index http://web.archive.org/web/20040124074626/http://www.friend.ly.net/~dadadata/
    A good collection of resources, mainly older.
    Open Canoe Sailing Group | Sailing Adventures http://www.ocsg.org.uk
    The modern inspiration.
    Outrigger Sailing Canoes http://outriggersailingcanoes.blogspot.com
    The local resource.

    As you will see by browsing those links you have a lot of rig options, from batwing to mast furling.

    As beautiful as your rudder instalation is I am afraid PVC is not strong enough. Use it as a model for one made from aluminium plate or composite.
    Leeboad placement will depend on the final sailplan, there is no way around that.
  10. Tiny Turnip
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    Tiny Turnip Senior Member

    Definitely as gggGuest and Phil Sweet say cat ketch and reef by rolling round the mast. You don't need or want a ton of sail area. Check out the Solway Dory website. My 16ft canoe tri makes 12knots on less than 80 sq ft of sail. Bear in mind I have outriggers and can hike out a bit.
    bajansailor likes this.
  11. Mariku
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    Mariku Junior Member

    gggGuest, "everything depends on everything else", so true. It is an iterative process very much to arrive at a good combination of all parts of the whole.

    And very good advice not to try to get it right first time, because you are right, we won't.
  12. Mariku
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    Mariku Junior Member

    philSweet, I understand, however due to how we use our kayak, we are limited to one mast, in the location the mast foot is now. I would also not want to have to deal with two sets of rigging while using the boat as a platform for fishing, snorkeling, and more...

    Everything we have built so far I expect to alter and improve over time, we just want to get something on the water for now. So yes, we will eventually reshape the leeboards and rudder, no doubt.

    I am quite happy with the steering mechanism as it is right now, we'll see how it works. We definitely don't want to run lines or anything else through the hull, we are determined not to drill any holes that are not already there. It is just a preference we have.
  13. Mariku
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    Mariku Junior Member

    Rumars, thank you for the links, they have led us to a lot more information!

    I accept your challenge to find out whether our PVC rudder design is strong enough! In my experience many people underestimate PVC as a material for anything other than plumbing, but it can perform really well, when the design is tailored to the properties of this material - which we have done to quite some extent. I have some experience with this material, so I have reason to believe this may work reasonably well.

    However we will do very thorough shakedown tests of everything before we trust anything we have built with trips to more remote places or further off shore.

    And I will happily report back truthfully if the PVC fell apart - it's all learning...
  14. Mariku
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    Mariku Junior Member

    TinyTurnip, I understand what you are saying. However as explained further up in this comment, we have reasons not to want more than one mast and one set of rigging.

    We can not use outriggers of any kind simply because we play far too much between the rocks for that to be practical. Our activities are often very amphibious, navigating through tight gaps between rocks, going on and off shore, taking the boat out of the water and putting it back in etc. That is the main reason we have chosen a kayak and not a bigger boat.

    80 square feet? Is that a typo? That would come to about 7.5 square meters, which seems like a wild amount of sail area for a 16 ft canoe!

    We think we will go for somewhere near 2 square metres of sail area for very low winds, however it has to be a design that can easily be reefed to half that or less and still work well - which is one reason why we are considering a crossover between a batwing and a junk sail.

    For reference, kayaksailor.com is around 1.6 square metres, and sit on top kayaks seem to do very well with that amount.

  15. sharpii2
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    sharpii2 Senior Member

    I've read your posts and seen your pictures.

    It looks like you have come a long way in developing your rig.

    Junk rigs can sail to windward reasonably well but not well enough to win races. But the main objection I would have to such a rig is the weight of the many Boomlets (often called “Battens” but IMHO are not. Battens stiffen a sail panel; Boomlets support it). And each of these needs to be attached to the mast somehow. You can probably get away without Sheetlets, but I think you are probably getting my drift. The two main problems would be top hamper and possibly set up time. Top hamper would be the biggest problem.

    As for the crab claw, the Center of Effort (CE) would end up being too high. Also, the geometry of such a sail with your existing mast would limit your Sail Area (SA) to something short of 2.0 sm and maybe far short of it. I'm assuming that the all-up weight of your kayak, loaded with your son and your provisions is somewhere in the order of 180 kg. I estimate that you need a minimum of 2.5 sm of sail to be worth your trouble. Due to both the limited initial stability and very limited ultimate stability of your craft, I think the upper limit in SA is around 4.0 sm. (more on stability issues later)

    For some time, I have been toying with ideas for the most practical sail for a tiny boat. The biggest problem of such a sail is reefing it. Tiny boats usually have just one sail, and shortening this sail can be a bigger problem than most people realize. First, there is the problem of getting to the sail without upsetting the trim of the boat. The second problem is having to lower the entire sail to tie in the reef points. Roller-reefing is an excellent solution to these problems, but it often comes with some unwanted complexities such as the need of heavily loaded bearings or swivels. And often after reefing, the sail does not set so well. Expensive roller-furling systems do a better job.

    The system I came up with shares two similarities with the junk rig (Chinese Lug) (CL). First, is it too will have Boomlets. Second, reefing will be done by lowering one Boomlet on top of another. The two differences are that one, there will be no Sheetlets, and two, there will be much fewer Boomlets. The one I am building for my own boat will have just two, a top one and a bottom one. By lowering the top one onto the bottom one, the SA will be reduced by nearly half. So if it suddenly breezes up, I can quickly reduce the SA by that much without stopping. Just slack the halyard until the top Boomlet rests on top of the bottom one, then pull on a line which will hold the two together. After that is done, the halyard can be tensioned to lift the sail off the lazy jacks. The beauty I see in this system is that it can be built with relatively crude materials and work quite well. It also doesn't need any carefully machined parts, so can probably be repaired in the field. If I were going to use this sail on a much larger boat, I would put at least one tied reef point between the two Boomlets. This way, I could quickly cut the SA in half, tie in the tied reef point then raise the sail again, having once again completed the task while staying under sail the whole time.

    Below, I have sketched a version of this type of sail for your kayak. I have followed all the rules mentioned in your earlier posts. I believe the SA will be sufficient when the wind becomes noticeable. If it really breezes up, the upper Boomlet can be lowered onto the lower one to reef the sail. Or the lower one can be raised up to the higher one, if you don't want to duck under the longer Boomlet. This will cause a much higher CE, but will be more convenient. If you go this route,the upper Boomlet will need the lazy jack. If it were my kayak, I would lower the top one onto the bottom one and put up with ducking under the lowered top Boomlet. This is why I sketched it as I did.

    In my sketch, the halyard (2) is attached to a loop which holds the yard to the mast This loop is really a lasso with a stop-knot, so once the top Boomlet (C) is lowered down to the bottom one (D), the Yard (B) can be folded down to furl the sail.

    I really worry the stability of your kayak with the added sail. I know it by nature has a high Center of Gravity (CG). The mast and other spars will only add to this. The question is that will it have enough initial stability to stay upright under sail without anyone hiking out. My suspicion is that it won't. If it doesn't, it could quickly flip over on its side or even completely turtle, dumping your self and your son into the sea, along with anything else that is not lashed in place.

    I hate to say it, but I think you need some kind of double outrigger system with low-buoyancy floats. Such could accomplish two objectives:

    1.) It can provide greater initial stability for sailing power, and
    2.) It can provide a much greater range of stability (maybe up to 80 degrees or more).

    The reason for this is that, when the leeward float is pushed completely under, its buoyancy still provides some righting moment, so that, once the capsizing force is removed, the kayak will spring back upright. I think this is a major safety issue you should consider. You can probably get away with just one cross-beam and maybe as little as 10.0 L total volume for each float.

    What ever you decide to do, I wish you the best of luck. And I hope you will keep us posted on your progress.

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