Why a sailing dinghy's hull is so much heavier than a windsurf board?

Discussion in 'Sailboats' started by xarax, May 4, 2009.

  1. ancient kayaker
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    ancient kayaker aka Terry Haines

    That's true, Chris, I should know better since I have a book full of them. Perhaps there is more of a linear progression from board to boat than I assumed. Quetzal is clearly one of them. I ws thinking of a more traditional dinghy.

    I did not know they could be built so light as the Bee: the designs in my book would be heavier. I have puzzled over the design I am adapting to make it as light as possible but I can't see how to get it below 60# / 27 kg finished, then there would be the board, rudder and rig on top. But I will be able to sail IN it, with the Missus: just barely! ;)
     
  2. xarax

    xarax Previous Member

    A novel steering device for a narrow dinghy.

    The (one hull /no keel) sailing boats have to be wider, thus heavier, than the sailboards, because (most) sailors cannot balance the rapidly varying forces induced by wind, water and gravity on narrow boats, as effectively as (most) windsurfers do.

    Contrary to what would seem be in accordance with conventional wisdom, windsurfers manage to keep their narrow hulls in an upright position easier than most dinghy sailors, because sailboard hulls are more sensitive to body movements – not because they are less sensitive and more stable. They can easier move and adjust the exact position of their body, because they use (the boom as) a steering device which also serves as a sufficiently firm handle – allowing them to swing their body weight as they wish to maintain balance, while steering with both hands. So, with the quick and precise movement of their body weight, the windsurfers can manage to balance the rapidly varying forces induced by wind and water easier than the dinghy sailors.
    To easier move on board and improve balance, the dinghy sailor has to overcome an obvious obstacle: most of the time, he can not use his hands to hold on and push and pull his body to maintain balance, as they are occupied holding the sensitive control mechanisms of the craft. Regarding balance, and considering the fact that keeping balance usually requires holding on somewhere and pushing and pulling one’s own body, the sailing dinghy sailor is essentially a no-hand man! This has to do with the fact that the design of the traditional steering mechanisms of the sailboats, the tiller and the mainsheet, is essentially unchanged for ages, basically a swinging bar and a rope that can only be pulled or released. The tiller and the mainsheet of a sailing dinghy do not offer the advantages of a firmly attached steering device which can be held by both hands, like a wheel in an automobile, a yoke in an aircraft or the boom in a sailboard.
    Can we improve on this?
    During the conversations on this thread, I have thought of a dinghy equipped with a balanced swing rig, so that the sailor can always turn the boom directly by pulling or pushing it, without need of any mechanical advantage offered by the pulley and rope system, and without much difficulty. In a dinghy the sailor should be able to position his body s centre of weight quite abaft the mast and also outside the hull (to achieve greater righting moment), so it is not possible to have a boom that will always be at arms length: We can not just hold the boom and turn it by our bare hands as the windsurfer does, we have to find another way. A suitable turning-the-boom-and-the-rudder-while-holding-on device could look like this : A pair ( at port and starboard) of two long rotating and reciprocating parallel shafts, both connected to two coaxial horizontal wheels: the first wheel is connected to the rudder, and the second wheel is connected (via a bicycle chain, for example) to the boom of a balanced swing rig. By rotating the shafts the helmsman can turn the rudder (he rotates each shaft around the shaft s longitudinal axis by rotating each of his forearms, while he is holding the shaft by his hand with the help of a d handle). By pushing and pulling the shafts the helmsman can turn the boom (he pushes the one shaft while he is holding it by the one hand and, simultaneously, he pulls the other shaft while he is holding it by the other hand).
    (To allow for an easier, stronger and safer grip at varying distances from the horizontal steering wheel(s), we can have telescopic shafts, shafts with many d handles, or even shafts with ladder-like multi handle extensions attached along them.).
    I am not a Zeus or a Jim Drake of course, so the design of a novel steering device for a single handed dinghy can not jump out of my head the way Athena or the windsurf did ! I would be glad if I had some critical responses on this matter from the so knowledgeable members of this forum.
     
  3. wet feet
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    wet feet Senior Member

    One point that has been overlooked in the previous post is that the sheet(s) can be cleated.Of course this requires a sufficiently strong,and thus weighty,structure to attach the cleats to.In addition,the hull structure has to resist the loads of the centreboard and rudder.If a good alternative to rudders existed it would probably have been introduced by now.
     
  4. dgkidder
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    dgkidder New Member

    A friend told me about this topic so I thought I'd chime in. I'm Doug, the Hoot guy. Yes, it is still progressing and yes it is way, way, way (I could keep going with that) behind schedule. But, to quote Monty Python "I'm not dead yet."

    A great deal of the driving motivation behind the Hoot was exactly that observation that windsurfers are a great deal lighter than dinghies. I really wanted a boat that I could sail like a dinghy but transport like a windsurfer. And I've got one. The tradeoff is that she's tricky to sail (but also really fast). If we made it more stable, it would be a whole lot heavier.

    But all of the comments in this thread about the much higher volume in the hull and the need for the hull to handle dramatically higher loads than a windsurfer are exactly on point. I really believe that, at 50 lbs bare, the Hoot hull is as light as you can get with modern materials (and a reasonable budget). The early Hoot hulls were as light as we thought practical -- and we broke them apart sailing. Generally we were ripping the wings off. The loads on this hull are shocking high. At one point we ripped the forestays out of a couple of boats. I calculated the minimum load to do that at around 1500 lbs. To this day, I have no idea how that much load can be applied to these forestays.

    The speed of the boat also adds to the weight as speed requires the hull to take the high loads from hiking. So it would be pretty easy to make a light, slow boat (anyone remember the Sea Snark) but don't even think about hiking hard.

    I read with interest the comments about the windsurfer rig on the Quetzal. We started with that rig as well. You do have to stiffen up the mast considerably in order to go upwind (anyone remember the MX-Ray), but in the end we moved away from the wishbone boom because it added too much weight too high up the mast. The stability difference from having the lower boom was quite noticeable. And those booms are relatively expensive.

    To everyone who has patiently waited for the Hoot and defended my slowness -- a sincere thanks.

    Doug
     
  5. xarax

    xarax Previous Member

    Thank you dgkidder,
    Have you ever tried to incorporate some kind of shock absorption mechanism to the forestays? It seems to me that these extremely high loads are generated by sudden abrupt movements only, and so they could be absorbed if the whole structure was momentarily less stiff and somewhat more flexible. I am eager to see a Hoot on a car top and on water! Go on !
     
  6. Doug Lord
    Joined: May 2009
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    Doug Lord Flight Ready

    aeroSKIFF

    This was my first monohull foiler-it was conceived of as a boat with the absolute minimum hull.
    I wasn't satisfied with the hull in short intercoastal chop and there were some other problems and I donated it to a sailing school(short rig picture):
     

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    Last edited: Jun 7, 2009
  7. Get Wet
    Joined: Oct 2009
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    Get Wet New Member

    The Sunfish and Topper may be the closest anyone has come to fitting your design brief and having it mass produced.

    Both have low aspect rigs, but I've seen footage of the sunfish planing in capable hands perhaps more easily than one could with a laser.

    Could a modern fiberglass/carbon sailboard could take the stress of a rigid mast without needing large and heavy structural reinforcements? A poly board might be strong enough though.

    For the cost and effort, a longboard sailboard dramatically betters both with a rigid, high aspect sail, can plane easily, plane upwind and has lower mass.

    Hiking wings would have to be added, and on such a narrow hull they would be real wave snaggers. Like the 49ers at the past Olympics, what a mess.

    Take away the wings and high aspect sail and in the end you're left with... a Sunfish.

    How about a 2-board planing catamaran?
     
  8. xarax

    xarax Previous Member

    If you count the weight of the supporting beams, it gets quite heavy, so it is no more cartopable, at least as a whole. The structure should also be stronger and heavier than that of a displacement catamaran, because the mast has now to withstand the up and down movements of each planing board on top of each next wave crest.
     
  9. bistros

    bistros Previous Member


    Although long delayed in volume production, how about the Hoot?

    It is certainly closer to the mark.

    --
    Bill
     
  10. Doug Lord
    Joined: May 2009
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    Location: Cocoa, Florida

    Doug Lord Flight Ready

    ---------------------
    Now that you mention it, this was a lot of fun:
     

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  11. Chris Ostlind

    Chris Ostlind Previous Member

    Groan.....
     
  12. ancient kayaker
    Joined: Aug 2006
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    Location: Alliston, Ontario, Canada

    ancient kayaker aka Terry Haines

    Seems to do best with a bit of ballast ...
     

  13. xarax

    xarax Previous Member

    When the mast is not fixed on the deck, we are closer to the windsurf sailboat, not the sailing dinghy...
     
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