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Go Back   SailNet Community > General Interest > General Discussion (sailing related) > Keel type?
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Thread: Keel type? Reply to Thread
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Topic Review (Newest First)
09-18-2006 06:34 AM
Rockter If you ever get into issues with salvage with floatation bags (or any other issue), make it clear up front, with witnesses, or call the marina to witness it, that you are CONTRACTING the floatation bags to re-float you. You pay for the floatation, and they have no claim on the vesel.

The world is full of crooks.... be careful. At the first sign of reluctance on the part of the outfit rendering the service, you will know what they are up to, or may be.
09-17-2006 09:49 PM
SailorMitch
Breaking all the rules...

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.
Yotphix -- sounds like you and your pal spent two hours twisting and heeling that wing into the sand as though it were a screwpile for a lighthouse. Rule number one for a wing is to keep the boat level of course, so why twist and heel at all? I've always thought that if I ever do need help getting off the bottom with my wing, the best way is simply to pull the boat out backwards the way it went in. Plus, on my keel, the wings don't start until about the aft half of the keel. It's very possible that the wings won't be stuck at all.

Yes, folks, catching up with some old business before I DIE STUCK FOREVER ON SOME SHOAL BECAUSE OF THIS DAMNED WINGED KEEL ON MY PEARSON!!

Yes, that is my keel in my avatar.
08-22-2006 09:47 AM
sailingdog
Quote:
Originally Posted by captnnero
Regardless of the keel, in most cases if one can simply wait for high tide, towing will not be necessary. I once heard of a well known Chesapeake cruiser who runs aground frequently when exploring and gets out a book until high tide. The tow boats are for when you are unfortunate enough to ground at high tide or you just can't wait that long.
Very true.
08-22-2006 03:56 AM
captnnero
the same page

Quote:
Originally Posted by sailingdog
...
Captnero— I was speaking specifically, and only about stability and righting moment, and not the sailing performance of the boat. I'm not sure where you got the idea that I was speaking of sailing performance. Sailing performance of a boat is affected by much more than the shape of the keel, though the shape of the keel is an important factor to consider. I don't see any real advantages in a wing keel, when it comes to providing stability, over a bulb keel. However, the wing keels have serious disadvantages IMHO and experience, over bulb keels—so there is no reason to have one as far as I am concerned.
Selecting a keel type for a sailboat without considering windward lift is like picking sunglasses without considering UV rays.

SailingDog and Jeff_H - My concern is what SailingDog intended by not discussing windward lift while discussing shortened keel design. Without quoting Jotun's intial post of this thread (Keel type?), suffice to say that it defintely was not restricted to only stability and grounding effects of keels. Hence I interjected the relevance of windward lift as bulb configurations were discussed. If the relevance of windward lift is acknowledged then at least we're on the same page again. Of course sailing performance has other factors, but since the thread was about keel types I only wrote about sailing performance related to keel design.

I will relate two recent experiences I've had related to grounding near the South River and near the Choptank River. I hope that is sufficiently close to what one would consider to be Jotun's "Northern Chesapeake". About a year ago I saw someone with a shoal draft bulb keel quickly and hopelessly grounded in a deep heel. It took the professional tow boat an hour to pull it free. Then just this spring our engine quit due to a cracked filter screw while we were exiting a tight anchorage into the wind. We raised sail but were not able to get enough room so I resorted to Plan B and grounded our wing keel on a muddy shoal. Then as soon as we luffed and dropped sail, the wing leveled shallower and we just floated free. For those needing closure, we were then able to kedge into a better sailing position and sail out of the anchorage into the wind. If we had a bulb or fin of the same depth, we would have had to kedge off of that shoal first or perhaps I wouldn't have risked putting a heeled non-wing keel on a shoal at all.

If you go back to Australia II's successful use of a wing in 1983, it was a rule beater for racing vessels constrained by draft and was the first competitive America's cup challenger in many, many years and of course the first winner. From a performance standpoint the wing certainly was not a liability when compared to Liberty's equal draft non-wing. When Dennis Conner's team recaptured the Cup in 1987, Stars and Stripes was sporting a wing to beat the same rule and the defender. In the case of cruisers constrained by draft such as Jotun's Northern Chesapeake, the wing keel is a draft beater. Under sail it mostly behaves like a somewhat deeper keel with windward effects beyond a bulb, yet allows one into shallower anchorages.

Wing keels sprouted on production boats in the late 80's in high numbers. As a practical matter, if Jotun is considering 30 foot vessels of those heyday years, then eliminating wing keels from the mix will likely eliminate many otherwise acceptable vessels. In my own experience, such elimination is not necessary.

The real hazard for a wing is to motor quickly onto a shoal with a slight incline, while the fin or bulb is most vulnerable when deeply heeled. The width of the wing simply does not allow it to climb up a steeper incline, although you stop quickly. I've also found that when the wing is level it gives a little more warning when an uneven bottom is coming up, since it's width is more likely to touch the higher bumps than a fin or a bulb.

I was puzzled to hear that a professional tow boat in one of the posts would attempt to heel a wing off of a shoal. Also, two hours is a long time to be yanking on the boat's structure. I know that some tow boats carry flotation bags. That would seem to be a better strategy for a difficult grounding, but obviously I don't operate a tow boat. There is an issue about the use of lift bags triggering salvage rights. If that is the case it is unethical. That's part of why I now have my own lift bags.

Regardless of the keel, in most cases if one can simply wait for high tide, towing will not be necessary. I once heard of a well known Chesapeake cruiser who runs aground frequently when exploring and gets out a book until high tide. The tow boats are for when you are unfortunate enough to ground at high tide or you just can't wait that long.
08-19-2006 03:02 PM
sailingdog
Quote:
Originally Posted by jerryrlitton
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
Yes, but the weight of the arm must also be considered. The righting moment of a typical fin keel is the mass of the keel * X% of the length, which is determined by the center of mass of the keel. A bulb keel has a greater righting arm than a fin keel of the same draft and mass, as the mass of the keel is concentrated further out, in the bulb.

Captnero— I was speaking specifically, and only about stability and righting moment, and not the sailing performance of the boat. I'm not sure where you got the idea that I was speaking of sailing performance. Sailing performance of a boat is affected by much more than the shape of the keel, though the shape of the keel is an important factor to consider. I don't see any real advantages in a wing keel, when it comes to providing stability, over a bulb keel. However, the wing keels have serious disadvantages IMHO and experience, over bulb keels—so there is no reason to have one as far as I am concerned.
08-19-2006 02:38 PM
Jeff_H 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
08-19-2006 12:58 PM
captnnero
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.
08-19-2006 11:39 AM
jerryrlitton 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
08-19-2006 10:21 AM
sailingdog
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.
08-19-2006 12:29 AM
captnnero
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.
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