Lead recommendation of small sailing canoe

Discussion in 'Boat Design' started by Sectumz, Jun 30, 2020 at 1:08 PM.

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  1. Sectumz
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    Sectumz Junior Member

    Hi,

    I've been working on a small sailing canoe with modyfied oppi dingy rigs for a little while now. However, build is to start in two weeks and I have not been able to pin down the placement of the centerboard yet, so therefore I turn to you guys here at this excellent forum.

    For reference have a look at the sailplan attached.

    The problem I keep coming back to is how much to account the mizzen sail for. E.g. Principals of Yacht design recommends 0.4 factor for rudder compensation, however, these are sails which not necessarily interfere on a reach for example. And the mizzen if of equal size to the main so it has a big impact.

    I will build the centerboard box a bit too long which will enable the centerboard placement to be reconfigured on the fly when sailing, mainly by tilting backwards, as well as pre-sail by setting it at another spot. But, the shorter it is the more weight and materials are spared.

    I expect it to sail quite flat since it is a dinghy (an optimist has virtually no lead as far as I can see on the few semicomplete plans I have found?). A working prototype linesplan is attached if it is any help.

    TL;DR:
    Given the attached images, how much lead would you recommend?
     

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  2. upchurchmr
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    upchurchmr Senior Member

    Lots of previous canoe sailors use a leeboard to determine the proper position.
    You could then add the centerboard or daggerboard.
     
  3. Sectumz
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    Sectumz Junior Member

    Hmm, that is not a bad idea. In my case I think I'm limited by the fact that the structural members needs to be in the front and back of the centerboardbox, and they need to go in almost first in the build.
     
  4. latestarter
    Joined: Jul 2010
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    latestarter Senior Member

    A couple of thoughts; that is a lot of sail area, this design adds up to 9.4 sq.m. a Laser which is more stable has 7.06.
    Michael Storer's Beth does have 7.9 sq. m. but is designed to be reefed for less sail area as the wind increases. Beth Sailing Canoe - Fyne Boat Kits https://www.fyneboatkits.co.uk/plans/sailing/beth/
    A typical size for a sailing canoe is 4 sq. m. and can be reefed by rolling around the mast. The Bermudan Rig http://www.solwaydory.co.uk/products/canoe-sailing-rigs/the-bermudan-rig/
    Also where will you be when tacking and gybing.
    P.S. I was not able to view the linesplan.
     
  5. Sectumz
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    Sectumz Junior Member

    Ahh, well, when writing sailing canoe I kind of mean the scandinavian-swedish sailing canoes like the C-class or the IC-10m2. The design displacement is about 300kg with two adults plus a little bit of extras. With than in mind the sailplan seems almost to have a little bit to little sail. But, that said, it it not a very stable design (about the same width as an optimist, but less stable) since it needs to be narrow to fit on a car top, so it might be tricky to sail. The top sails can be added for light weather or kept unhoisted for heavier. For the heaviest wind only the main can be used. I'm thinking about adding reef points in the oppi sails, but that will have to wait until next year.

    Regarding moving the sails from one side to another, it will be fun to see if my uncle will manage that gymnastics :D Jokes aside, it will not be the easiest, but there will be a slot between the main and the mizzen, and the main boom will be about 60-70 cm above the floor, which hopefully will be enough. In practice I suspect we will try this out at buildtime and set the boom height as low as possible for an adult that is almost "stiff as a fridge", as we would say in sweden, to still move under.

    Hmm, the linesplan should be viewable since it is a pdf, but I will convert it to an png when I get home today.

    Thanks for the input on other sailing canoes! Makes me want to add some more statiblity in the form even though it costs weight :(
     
  6. upchurchmr
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    upchurchmr Senior Member

    The water gets pretty cold in Sweden doesn't it?
    You might want even more stability/ width.
    IC-10m2 canoes are famous for giving the sailor a bath, and that doesn't take into account the conflict between two people.

    IMHO. Top sails are a waste of time and money. They won't be very efficient, they will be heavy at the wrong place, where do you store them, you don't need more complexity in controls on that tippy of a boat.
    A taller sail which you can twist off will be more useful.

    I'm confident that if you can design the boat and build it, you can figure out a way to retrofit a centerboard. Lots of boats have had very little more than a case attached to the keel line and a brace at the top. Large bulkheads at each end are not really necessary. And with two in the boat they might really be in the way.

    Have fun.
     
  7. Sectumz
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    Sectumz Junior Member

    Yeah, it can be, but the gulf stream and the long hours of sun does it's trick, so during the summer we have about 20 Celsius, and with the last years heat waves we've seen temperatures of upwards of 24. The inland small lakes will get warmer.

    I know the topsails aren't very effiecient (and neither is a ketch/schooner type rig), they do give a little bit of needed umph in light winds though. I don't expect the sail controls to be more complex, sure it will take a little bit more time to set up, but once they're up they are controlled together with the main or mizzen with the ordinary sheet. I also excpect the top to twist of as I have read that gaff rigs tend to do. The rig is built around the optimist rig, from which sails are readily available used or quite cheap new.

    I will have a crack at trying to increase the width a bit and see what the weight of the empty hull adds up to, but I will suspect I can't get up very far. The issue with the centerboard is that the construction will be a stitch and glue with polyester resin, since keeping the cost down is a high priority and longevity not super important. I excpect the boat to sail maybe 5-10 days a year and lay upside down on land the rest of the time. Therefore there will only be 4mm plywood of not the best quality, but boiling proof glue, and two layers of 300g glassfibre holding the centerboard box. And the centreboard I plan to build in the future will have a contrete bottom part, so it will weigh some kilos. So to combat this I plan on attaching the centerboardbox on two floors fore and aft of the box. These needs to go in the boat before floatation tanks are added and will benefit from being installed together with the longitudinal stringers for chemical bonding of the polyester.

    With this said, I will have a crack at trying to figure out how to maybe install them later and using a leeboard to find the correct balance. That relies on us being able to finish the jib though :D

    I attached the linesplan as an image before I attempt to widen it a little bit.
     

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  8. latestarter
    Joined: Jul 2010
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    latestarter Senior Member

    If it is 60-70 cm above the floor what will be the gap between the top of the centre board case and the boom? Not easy to duck under the boom and climb over the centre board case at the same time.
    There is another option, an offset board. There is a slight performance penalty but if you are not racing probably does not matter.
    It was discussed on this thread Offset Centerboards https://www.boatdesign.net/threads/offset-centerboards.35056/
     

  9. Sectumz
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    Sectumz Junior Member

    So I crunched the numbers and incresed the beam, and stability, by about 10%. Now there should be better reserve stability and therefore time to react when a puff comes along. The Centerboard/boom slot might not be very big (about 20-30 cm), I think we might feel like paper-Mario when we sail. The placement of the centerboard might partly end up in the slot between the sails, so that the aft person can step over and the fore person duck under the boom without the obstruction of the centerboard. Your comment on offcenter board made me think though. It might be the best idea to just forget about the centerboard altogether and just have leeboards for the first season at least (I don't particularly like the look of leaboards, however it will provide a much better cockpit area). That way there is some time to fiddle around with the balance and boom/centerboard letterbox slot, as well as the height of the centerboard box to make the boat partly self draining through the box, since there is a hole there. This leads to:

    Have you got an idea on how to fasten semi-temopary leaboards for experimental lead finding? I.e. so that they can be quickly adjusted for/aft. Maybe use the hull as some form of track on which to have a sled/cart on which to fasten the leaboards? I'm moslty concerned with the strenght of the leward board, because I think there will be enough stuff going on with the 3 sails to also have to lower and raise leaboards. Maybe I'll just make two daggerboards like the modern racing monohulls and make the slot really long. That way the boxes are not in the way, and the structure could be better incorporated in the floatation tanks. So kind of like inboard leabords maybe. Alot of thinking to be done still it seems...

    Should I make the leaboards/daggerboards half the size of the intended centerboard or slightly larger (area)?

    PS. Thank you so much for the input so far! I think it has proven invaluable with regards to proactivity. Also attached is an updated linesplan. DS
     

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