Rowboat->sailboat conversion

Discussion in 'Sailboats' started by Henriko, Sep 26, 2022.

  1. Henriko
    Joined: Sep 2022
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    Henriko Junior Member

    Hello folks,
    Just a simple question, I have a standard sized small rowboat and have built myself a sailing kit, with rudder, leeboards, mast and sail.
    Tested it today, sails like a dream, but of course, the upwind capability could be better - it slows down considerably=extremely slow. Of course it HAS upwind capability, but as we all know the wind needs to be strong enough to give the forward kick and if I'm not careful, pressing too much upwind, the wear and tear on the leeboards, sail and mast is considerably violent.
    Does not bother me though as 180 degrees sailing is a dream as long as the wind is in your back.
    So - I know the perfect alignment and position of the sailing components is: sail CE and the boat CLR and the leeboards are lined up vertically under eachother, preferably with the CE a bit forward in order to compensate the sail shape transformations by the wind. But if this perfect alignment of all three is impossible due to the mast location for example, what is better - to have the leeboards lined up with CE (means leeboards are way forward from CLR quite close to the mast, as the mast is located closer to the bow) or the leeboards lined up with CLR (means leeboards are way aft from the sail around mid-boat where the CLR is located)?
    Anyone else here who has created an own sailing kit for a standard glassfibre rowboat (ca.3,8m)?
    Appreciate any thoughts regarding this fundamental question when designing sailing kit.
     
  2. gggGuest
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    gggGuest ...

    The importance of CE position is way overrated for small boats. Its just not critical. The lateral resistance is balanced between board and rudder, and just steering the boat in a straight line deals with it. Unless you are having to hold the tiller well off the centreline to maintain a straight course you are better off not worrying about it, so just have the boards somewhere in the middle and leave it at that.

    The fundamental requirement for sailing upwind well is a good lift to drag ratio from both underwater foils and rig. So if you want to sail upwind better you need to consider where drag is coming from, and how to minimise it. I'd start with looking at fore and aft trim. Are you sitting too far aft? Will moving forwards a bit help the boat slip through the water better? Leeboards are never going to be anything like as good as a centreboard, but you have to go with what is practical, but what does the water flow look like round them? Are they flat or aerofoil shaped? Would a bit of gentle shaping be possible? Same applies to the rudder. And could the sail be trimmed better? But you know, it is a row boat, and its never going to be an upwind demon. Maybe taking the mast down and rowing is going to be the best option and there's nothing wrong with that!
     
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  3. Henriko
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    Henriko Junior Member

    Thanks a lot, appreciated!
     
  4. messabout
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    messabout Senior Member

    Henriko, keep the faith. A little rowboat can be persuaded to sail upwind with some degree of adequacy. Your sails themselves can be a contributing factor. If they are cut too full the windward ability is likely to be compromised. How you trim the sails is also a rather delicate skill or learning proposition.

    Do continue to tinker with the sail to board balance. As mentioned above, the lee boards are less efficient than centerboards or daggerboards. That has something to do with surface ventilation.... or whatever. Be that as it may, making the lee boards bigger can have a positive effect on how much lee drift the boat is forced to endure.

    Part of the fun, or satisfaction for conquering the problems, whatever they happen to be, is finding the most favorable compromises. First suspect your sail shape. Then contemplate the way you are attempting to persuade the sail and the boat. Pay close attention to minor wind shifts, do not wiggle the tiller unless it is necessary....and a few other bits of wisdom that will come to you with time on the water......downhaul, outhaul, vang pressure, sheet tension and all that jazz.
     
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  5. Henriko
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    Henriko Junior Member

    I do appreciate all your answers, but kindly, just to remind you, I'm a serious conversion builder and want the optimum performance according to science; thus I was asking for the correct relations and placements of CE (sail center of effort) and CLR (boat center of lateral resistance) with the leeboards - their correct positioning. I'm sure there are boat designers and builders who know the answer. Regardless of sail, leeboard or rudder shape. Thanks again!
     
  6. Flotation
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    Flotation Senior Member

    Traditionally most boats making use of leeboards have a way to adjust their longitudinal position in an easy way. Even on a well tuned boat it can make sense to adjust them on the fly depending on weather and sea conditions, point of sail, variations in weight distribution and sails that are set.

    The simplest ones just hook over the side of a boat with a L (upside down) shaped piece of material, that way they can be placed over a wide range. They are kept in place by lateral forces.

    You could look at some of the Bolger designs with leeboards for more inspiration on how to make them movable.
     
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  7. Henriko
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    Henriko Junior Member

    Really appreciate your answer, and yes, I am aware of adjustments on the fly for example only one leeboard on either side according to upwind tacking which improves performance. As you all know, my problem is the conventional flat full fat rowing boat without a keel (only 10 cm) so of course this is a challenge. What I look for is exactly what Bolger favored - simplicity over complexity. My sailing kit is easier to use on/off than most kit designs and much easier to use than a conventional sail boat (according to my studies). I simply have a portable rudder, two leeboards for each side, and the mast with sail installed ready (rolled as wrapped around, can be rolled in/out). The leeboard and mast attachments are permanent part of the boat (self built). My core question here was actually not about fine tuning but about the different components positioning; should the leeboards be close to the mast (syncing with C.E.) or rather exactly on the point of C.L.R. (the point of the boat that is center of force, when you move it from this point it will not rotate). If the latter is true, then - and this is the interesting question - how does it affect the upwind tacking performance? Which solution is better?
    One significant tendency I noted last time sailing was: it sails like a dream in 180 degrees spectrum (downwind), tiller keeps straight without need to force it at all, but it can get "stuck" completely, if you turn the bow into the wind, pointing straight into the eye of the wind. The only solution is to use oars to force it out of this lock.
     
  8. Henriko
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    Henriko Junior Member

    Another important note here is, that I don't use a boom. This is because of practical reasons as well as safety reasons: once the wind gusts increased so much I had to jump up rapidly taking the sails down or it would have ended in catastrophe. The possibility to quicky suffocate the sails and take the down is important - with a boom it would also practically be much more difficult to set up/take down. I'm aware of tacking upwind sail shape and can keep the shape with hand power.
    I have only a main sail, boat length ca. 3,5 m so the mast fits inside the boat, sail shape is triangular but not as high and narrow as they recommend, but I think it functions better in weak winds (have no experience of narrower sail performing better tacking although I have many years been test sailing this kit).
    I sit in the boat ca. 1 m from the aft on a comfortable pillow, quite low, which as you also mentioned improves the balance and sailing performance.
    Provided a picture of my prototype.
     

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  9. sharpii2
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    sharpii2 Senior Member

    It looks to me like your lee boards are too small.

    From your picture, I can't tell how deep they go.

    Do you have both down at the same time?

    When I was 17, I made a 4 man vinyl raft into a sailboat. It had two lee boards that were fixed and a large canoe paddle for a rudder.

    With two people on board, it sailed upwind surprisingly well. With just one on board, it behaved like you say your boat does. It rounded straight up into the wind and refused steer out of it.

    The lee boards on this raft were long and shallow rather than narrow and deep, like yours appear to be. My theory was that, with two people aboard, they were deeper in the water than with one person on board.

    I considered making them deeper, but got an opportunity to get a real boat, so gave up on the raft.

    The canoe paddle would have been replaced too, had I kept the raft. It was horribly inefficient, and now I think it had insufficient area.

    This could be another part of your problem. Your rudder may be too small.

    You may be sitting too far aft as well. If you sit too far aft, the boat trims down by the stern. This creates a lot of extra drag. But this drag would tend to make the boat turn downwind instead of upwind.

    But, when the boat trims aft (especially when it trims aft a great amount), the mast effectively rakes aft too. This aft rake moves the sail's CE aft. And this aft movement of the CE may make a far bigger difference than the added drag aft.

    If this is the case, your boat will round straight up into the wind and stay there (just like my raft did).

    Before changing anything, I suggest you sit further forward in your boat. That may solve the problem by itself.

    If sitting further forward is impractical, I'd go with a bigger rudder. I'd try making it longer rather than deeper to get the added area. Deeper rudders are more efficient, it's true. But they stall a lot easier too. And that's not what you want in this situation.

    Finally, you might consider increasing the area of your lee boards. Lower aspect ratio may well be better than high aspect ratio, in this situation, for the same reason as with the rudder. So consider making them longer rather than deeper.

    I would try making all of these changes before changing the fore and aft placement of the lee boards. They really need to be at the widest part of the boat-especially if both are to be down at the same time.
     
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  10. gggGuest
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    gggGuest ...

    It seems to me that you've got fixated on a minor feature and assigned it a significance out of all proportion. The precise positioning of your leeboards is going to have at best a marginal effect on the upwind performance. Position them in a sensible place - anywhere between the two extremes you mention and forget about it. It just isn't very important. If you want to go upwind well there are far more important design considerations to work on, but be aware its entirely possible that other design features that are important to you will preclude any kind of sparkling upwind performance. Nothing wrong with that: every boat is a compromise. I'm currently mulling over how to put a sail on an inflatable canoe to explore the rivers around where I live, but I already know that any sailing rig I put on will be strictly cross/downwind only because the compromises and complications required to get it to go upwind won't be acceptable to me.
     
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  11. Rumars
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    Rumars Senior Member

    There are plenty of threads on the proper "lead", but they mostly relate to initial design. For a flat bottom boat most people say there should be no lead, CE should be over CLR. Where CE and CLR are depends on the sail and board+rudder shape.

    For a conversion the reality looks like this: the mast is more or less fixed in place, the leeboards are not. Get the boat sailing to windward as high as you can, then move the leeboard fore-n-aft until you have a neutral rudder or very slight weather helm. Since your body weight will affect immersed surface trough healing, this condition should be achieved in the most probable crew position.
    If you observe to much leeway, increase the size of the leeboards and try again. If your rudder doesn't seem to do much, increase the size. After a few rounds you achieve optimum pointing performance for your given sail.

    You should always keep in mind that a 3.8m long boat is not going to be fast, theoretical hull speed is 3.x knots, just a little faster then the average human walking speed.
     
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  12. Henriko
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    Henriko Junior Member

    veikkoset.fi

    Here is a local inventor, I have also carefully analysed - my set up corresponds 99% to his. I forgot to mention about the picture: my leeboards have moved forward, as close to the mast, as you see in his invention on small boats. This means, the leeboards are not on the widest part and CLR of the boat anymore. Test sailing this set up couple of days ago, it seemed to act a lot more better upwind than before, when the leeboards were close to CLR and widest hull part (as you see in my picture the old set up). My leeboards are ca. 30 cm long under water and reaches ca. 60-70 cm depth (recommended under keel). This is a prototype set up so it looks ugly (except mast and sails are ready). I prefer to use a slight angle on the leeboards ca. 10-20% as to create a lift effect, but I have noticed, that even using 45 degrees angle on the board gives well enough stability (no drift) and even less drag (in gentle side wind extremely good sailing capability).
    Unfortunately I cannot sit more in to the boat as this means sitting under the sail which would not be practical in sail control anymore.
    Very good points & highly appreciated!
     
  13. Tops
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    Tops Senior Member



    Video from the website. Once of the boats with the letters on the sail has an interesting mast mount, sort of an A-frame going from mast to gunnels/leeboards and stepped on top of a seat. It shows up clearly in the next video played by YouTube.

    tops_bdf_finnish_mastsep.png
     
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  14. Henriko
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    Henriko Junior Member

    Yes it's a good idea and invention, with the beautiful message of environment friendly boating which I respect highly, but the mast rig is rather short sighted, ugly and impractical, as that metal chunk cannot be removed and will be a hindrance when you move to or from the bow inside the boat. Even if you take it off it will be a major pain to store in the boat. My mast is attached to a thick wooden (beautiful too) plate securely fixed permanently in place in the front bench glassfibre and it is not in the way. Note the positioning of the leeboards: they are way front aligned with sail C.E. far away from C.L.R., this was the reason why I asked.
     

  15. Dolfiman
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    Dolfiman Senior Member

    My approach for a dinghy with one mainsail :
    - compute the CE of the mainsail with assuming the flexure of the mast (when in upwind sailing) and center of effort at 30% of the chord,
    - compute the CLR of the daggerboard with center of effort at 25% of the chord
    - you can neglect the hull and the rudder effects : the CLR of the hull is quite forward (due to a kind of Munk moment), the rudder CLR is backward, the two in some way compensate,
    - put the daggerboard CLR about 5% to 6% Lwl back to the sail CE
    ( daggerboard area being at least 3% of the sail area)

    That works very well with the 12' dinghy Velocette. That does not prevent you to have a margin of adjustement for your mast foot around this value, but at least you have a method of comparison with your feelings,
    Velocette : a nesting dinghy for fun sailing https://www.boatdesign.net/threads/velocette-a-nesting-dinghy-for-fun-sailing.67078/
     
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