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Go Back   SailNet Community > General Interest > General Discussion (sailing related)
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  #31  
Old 08-17-2006
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Jeff, thanks for the facts on the Scheels. Fluid dynamics, huh? Betcha there were at least a dozen computers in the entire US that could be leased to do that in the 70's and early 80's.

Now of course, all one has to do is be able to afford the software. (Still a bit steep for the home-doer, huh?)
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  #32  
Old 08-18-2006
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As a former great lakes towboat operator I can tell you that of the several boats i have pulled out of the sand off Toronto Island the most difficult by far was a wing keel that had motored on. It took two towboats at full throttle after a couple of hours of twisting and attempting to heel with the mast had zero effect.
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  #33  
Old 08-18-2006
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winging it

Quote:
Originally Posted by yotphix
As a former great lakes towboat operator I can tell you that of the several boats i have pulled out of the sand off Toronto Island the most difficult by far was a wing keel that had motored on. It took two towboats at full throttle after a couple of hours of twisting and attempting to heel with the mast had zero effect.
Once the boat is flat on the wing, it's a double whammy. When level, you've got the whole surface area of the wing to drag off. When it's already flat on the wing and you try to heel it, you're just digging one side in deeper.

As I said in a previous post, I'm more concerned about level grounding with the wing on our '88 Ericson 34 than grounding when heeled. It's about 13,000 lbs out of the factory. For that case I picked up some navy surplus fuel hose float bladders that I'm rigging up for lift bags. I have a high volume several psi 12vdc pump I can inflate them with once harnessed around the center of the vessel. I still need to pick up some durable tubing to go to each of the four bags. Fortunately they collapse to a tidy few inches thick so they can be stowed easily in the transom.

The level wing grounding is most likely to occur in either a motoring or downwind sailing configuration. When healed I have some warning and if quick enough I can reduce or neutralize sail and motor off. I have touched a wing tip a few times in light winds and been able to get back out with a quick tack.

After ten years sailing, grounding is a less likely event anyway as my experience and wisdom grows. I've skippered several bareboat trips in the Carribean and never grounded there, but then you can see the bottom condition pretty well anyway in the places that they allow the bareboats.
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  #34  
Old 08-18-2006
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wing profile

Someone mentioned wing lift. I've taken a good look at the profile of our Ericson 34 wing in between bottom coats over the winter. In this case they have the wing edges swept more forward than aft. Also when I view the profile from the side, the fatter portion is definitely on the bottom of the wing which would produce a negative lift. That in turn would be useful when heeled since it then has a lateral windward component. I can say that she does point very well. On the other hand, when she's going down wind, you've got the extra wetted surface of the wing doing nothing for you but producing drag. Also, the negative lift is still built in, so the extra wetted surface is producing useless lift force which is directly downward (lift downward ?, ok stay with me on this). The production of the negative lift costs some drag in addition to the wetted surface drag, without a purpose downwind.

At least from the looks of things they had the right idea to make it a functional wing in the upwind configuration. Who knows how well they pulled it all off.

Although she points well, I've noticed in light air combined with hobby horsing from power boat wakes that we stall easier upwind than the Ericson 32 did with a fin. I suppose that's from wagging that wing up and down in the water causes a lot of drag. To cmpound the problem when the wing slows down it produces less lift so now you don't point as well when hobby horsing. In heavy air it doesn't happen going upwind regardless of the waves I've seen up to four foot on the Chesapeake.

As I said before, if I was a racer I'd have the fin. But for gunkholing the wing suits my purposes as long as I tailor my gunkholing navigation to respect when the wing is more of a problem. Though not my first winged boat, this is my second year on this one and I am still learning the sailing envelope parameters.

Last edited by captnnero; 08-18-2006 at 07:33 PM.
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  #35  
Old 08-18-2006
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captnnero-

I'd have to say that I'd still avoid a wing keel... and a bulb keel can be made to give the same righting moment as a fin keel of the same mass. I never said that mass in the upper part of the bulb keel would have the same distribution as the fin keel.
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  #36  
Old 08-18-2006
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deja vue

Quote:
Originally Posted by sailingdog
captnnero-

I'd have to say that I'd still avoid a wing keel... and a bulb keel can be made to give the same righting moment as a fin keel of the same mass. I never said that mass in the upper part of the bulb keel would have the same distribution as the fin keel.
Sure you can get the righting moment but windward lift is another matter.

Last edited by captnnero; 08-18-2006 at 11:38 PM.
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  #37  
Old 08-19-2006
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Quote:
Originally Posted by captnnero
Sure you can get the righting moment but windward lift is another matter.
True... fin keels are far superior in terms of windward lift, but we were discussing problems with grounding, not windward lift. Overall, I would say that the fin keel is the best compromise of draft, stability, tracking and windward ability of the four types of keels—fin, full, bulb, wing.
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her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

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  #38  
Old 08-19-2006
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I do not have much sailing experience but my time is in aviation. There is a lot of correlation here since it is all fluid dynamics and the keel depth type etc discussion is a lot like a weight and balance problem. Remember the simple mathematical formula… weight X arm = moment. Where the depth (Length?) of the keel is the arm. Also whenever vortices are formed you also find drag. Just like whenever lift is formed you make drag. Just my 2 cents worth.

Jerry
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  #39  
Old 08-19-2006
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righting moment, windward lift

Quote:
Originally Posted by sailingdog
True... fin keels are far superior in terms of windward lift, but we were discussing problems with grounding, not windward lift. Overall, I would say that the fin keel is the best compromise of draft, stability, tracking and windward ability of the four types of keels—fin, full, bulb, wing.
SailingDog, besides grounding you also talked about how to use a shorter keel and achieve the same "righting moment". If you are concerned about righting moment then you are concerned about sailing performance. If righting moment is relevant then certainly windward lift is relevant.

If keel design is restricted to fin only and draft is constrained too much than you are going to end up with a really big, turbulent fin and sailing performance suffers. Hence a fin design sometimes ends up with a bulb or a wing.

I have a friend with a similar vessel who races with a 6'6" fin on the Chesapeake. Today he wants to visit our marina with his family. With my 4'11" wing I scouted our channel and found 6'6" near low tide. So he needs to traverse on half tide or more. I come and go whenever.
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  #40  
Old 08-19-2006
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With all due repect, Captnnero, as I read Sailingdog's quote, he mentions being concerned about righting moment, which may simply mean that he is concerned about stability, in other words safety without performance concerns. But if he were concerned about performance combined with shoal draft and safety, the current data seems to suggest that few, if any, of the production wing keels, so popular a few years back, offered any real performance advantages over a well shaped bulb, but those wings offered a serious grounding disadvantage over a bulb, which is why the more performance oriented coastal cruiser manufacturers have moved away from wings and are now predominantly using bulbs.

Jeff
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