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-   -   reducing keel/adding fin? (http://www.sailnet.com/forums/gear-maintenance/6772-reducing-keel-adding-fin.html)

abacosol 04-20-2003 03:42 AM

reducing keel/adding fin?
 
Does anyone know about the possiblities/cost effectivness/ and difficulties in reducing a bolt on led filled keel and adding a fin to compensate?

GordMay 04-20-2003 06:31 AM

reducing keel/adding fin?
 
Take a look @

http://www.marsmetal.com/html/keel_products.htm
Keel Products

Regards,
Gord

Jeff_H 04-21-2003 04:18 AM

reducing keel/adding fin?
 
Your question is a little vague so I am not sure precisely whether 1) you have a keel that is long fore and aft and you want to improve performance by going to a fin keel or 2) you have a keel that you would like to make shallower and by ''fin'' you mean wings.

In the first case you are somewhat limited in what you can do. Depending on the specifics of the boat''s design, a fin keel requires very different structural support than would be found on a long keeled boat. Obviously adapting the boat to a new fin would be complex, and expensive, and hard to do so that the resultant boat actually sailed well.

The second case is a little simpler but it too has its ''issues''. To begin with, simply shortening a keel can really have a major negative impact on sailing performance. When a shoal draft version of any particular boat is designed, the foil portion of keel of the shoal draft version is typically substantially larger in area because a disproportionately large proportion of the resistance to leeway comes from the leading edge of the keel. Normally this means increasing the fore and aft length of the keel significantly in proportion to the amount of keel span that is reduced. As a result the whole internal structure of the boat needs to get altered to support this longer length keel.

The loss of leading edge length can be partially offset with an end plate that prevents water from being able to slip off of the bottom of the keel. Designing a properly shaped set of keel wings is an extremely difficult process without the nearly unlimited budget of an America''s Cup campaign. As a result, on most so called wing keel cruising boats, in terms of leeway reduction the ''wings'' act as little more than a high drag endplate. An end plate is generally thought to allow the leading edge span to be reduced by 10% to 15% of its length without resulting in a significant increase in leeway but that assumes equal keel area. Remember that the span of your keel on a 5 foot draft boat is probably no more than 3 to 3 1/2 feet so you are talking a span of no more than maybe 6" and when you add back the thickness of the bulb you are probably back to where you started.

An endplate does little to offset the lost stability from the portion of the keel that is cut off so a bulb is generally needed to offset that loss. Bulbs vary in shape but they need to weigh significantly more than the weight of the keel that has been cut off. As a result they add a lot of drag due to the increased frontal area and wetted surface of the bulb. Properly shaped, a bulb will serve as an endplate. A Scheel keel type of bulb is especially shaped to maximize the end plate effect and minimize drag.

Which brings us to the practicality of cutting down a keel. Traditionally keel bolts were installed in long holes that went almost full length through the keel and had a big nut and washer at each end. Cutting off a traditional keel meant removing the keel and keel bolts, cutting off the keel bottom, shortening the keel bolts and threading the cut of end of the bolt and making new bolts pockets. All in all, it is not all that bad. BUT keel bolts in modern keels are generally ''J'' shaped and are cast into the lead. They often come quite close to the bottom of the keel so that in cutting off as much of the bottom of the keel as you are proposing you run the risk of cutting through quite a few keel bolts. I understand that there is a way to tell where the keel bolts are in the keel, but I can''t really what that method is.

Lastly there is the issue of motion comfort. Even if you can live with the increased leeway, and possible increased weather helm, there will be a pretty noticeable affect on rolling. The keel depth, and area goes a long towards dampening roll. When you reduce the area and depth of the keel, you will end up with a boat that rolls faster, and through a wider roll angle, and which also continues to roll longer than your original keel. This would be a significant discomfort in the rolly anchorages that you are likely to encounter in your chosen sailing venue.

If your boat was adaptable to adding a new keel or a bulb, the hot ticket is Mars Metals bith for expertise and price. They offer a number of stock bulb kits which come in tow halves and that can be bolted on through the bottom of your keel. They also make new keels. Bulbs are pretty cheap, but new keels, especially if you are modifying the internal structure of yoour boat can easily cost 25% to 50% of the value of your boat.

So in conclusion my suggestion is DON''T DO IT! If you were dealing with a deep draft fin keel where the fixes are simpler, the answer might be different, but you are not.

jvarkevi 05-03-2006 12:58 PM

Adding a bulb to a shortened fin keel
 
Have a look at the CS site. A CS 30 owner has done exactly what you're asking about.

* The eGroups web site is: http://groups.yahoo.com/group/CSOA
> ** SEARCHABLE ARCHIVES at: http://www.closereach.com/csoa/archives.html

sailingdog 05-03-2006 08:19 PM

There are some other implications with what you want to do...and it may make the boat unseaworthy, so I would consult with a marine architect or engineer regarding such a major change to the boat's design.

Bucks Flyer 05-03-2006 08:50 PM

I shortened my Peterson 34 keel by 1 foot. It was a fin keel covered in fiberglass.
Everything I read said to get an expert to do all the calculations.
I looked around the yard, saw what other keel fins looked like and decided to just copy the design. So I got out the electric chainsaw and sliced off the bottom off the keel. Then sliced and sliced and sliced until I could haul the 1200lbs of brick sized peices home, plus lots of lead shaving.
I contacted Mars, they surprised me with a many month lead time and didn't want the old lead. So I rented a large barbecue, bought a big steel pot, and melted the lead myself (in my driveway). I molded the old keel into 12 pointed 2x4 by about 18" ingots. I made the molds from 2x4 aluminum construction studs as . Then drilled holes all the way through each ingot. I stacked the 6 ingots on both sided of the existing keel with a slight offset between each, and through bolted with 6 1/2" stainless steel threaded rods. In between each piece I used plenty of 5200. I filled in the gaps and faired, then re-fiberlassed the whole bottom of the keel. There were lots of curious onlookers and many critics. The boat was fast before, and placed second in the next race she competed in on Lake Winnipesauke, NH. She also had less weather helm after.
Maybe I was just lucky, but it worked out great and that nagging rock at the entrance of our harbor no longer posed a threat.

Faster 05-03-2006 08:51 PM

Jeff H - I sincerely hope eveyone on this site appreciates the technically excellent responses that you regularily dispense - there's usually not much more to say after you've had yours! Thanks.

sailingfool 05-03-2006 10:26 PM

Bucks Flyer,
I really suspect you're pulling the boardmembers collective legs with your keel butchering story - its really a well done tale. Sort of like, not really, couldn't be, but then maybe...
Going on the remote possibility that you really did what you say then my comment on "Maybe I was just lucky, but it worked out great" is you won't know the rest of this story until you go to sell this boat and you find out the full cost of your project, reflected in the loss of value.

But you are kidding us, right...

santana30 07-01-2007 08:03 PM

I have cracks on my santana 30 keel , I graind the fiverglass and the cracs are in the lead also 2 foot from the botom a horizontal crack a foot long and another one 3 foot up and forward.
it is an encapsulated lead keel, anyone knows if the bolts on this boat are J shaped, some mayor work is coming , but i'll wil not give up.
I have think if the case is that the bolta are j shaped, to cut windows on it and replaced them. it is a 1974 old racer probably it had suffer alot of strss on his life, but the fiverglass still holding up good, with no blisters.

sailingdog 07-01-2007 09:32 PM

Santana30-

You really shouldn't be hi-jacking and reviving a dead thread... for something that you've already posted a separate thread on...


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