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Go Back   SailNet Community > Skills and Seamanship > Seamanship & Navigation
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Seamanship & Navigation Forum devoted to seamanship and navigation topics, including paper and electronic charting tools.


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  #11  
Old 09-11-2009
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Quote:
Originally Posted by Jeff_H View Post
John Shasteen,
At least from the research that I have encountered, conversations with designers, and from conversations with towboat operators, while wings may complicate getting a boat unstuck, bulbs at the bottom of keels apparently tend to make getting unstuck easier than a simple fin and should not add to the stress on the keel bolts 'as you wiggle out of the muck'. As noted above, bulbs do add to the sailing loads to the bolts, rig and surrounding supporting structure.
Respectfully,
Jeff
Jeff, I wouldn't disagree that a bulb might get you out of the muck easier and yes, they can more readily damage the boat. The boat yards I've been on the hard in over the past 50-years of sailing (from Burr Bros in Marion MA all the way down to the Port Isabel TX Yacht Repair just north of the Rio Grande), more recently (past 10-15 years) almost all of boats I see on the hard for keel repairs are bolted-on fin keel and the most severly damaged keels are those with bulb or wing - with wings being the worst. They run about even on bent rudder posts.
The only damaged keel repairs I've seen to encapsulated ballast, modified fin or full keel, has been big nicks in the fiberglas from banging into something. And of course, the only keels that seem to fall off are bolt-on fins, i.e. the s/v Cynthia Wood.
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Last edited by johnshasteen; 09-12-2009 at 08:52 PM.
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  #12  
Old 09-11-2009
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That's very good to know. I was curious about the roll rate characteristics. The boat in question has a new keel constructed out of the existing alumnium so there are no keel bolts per se, rather a newly molded keel integral with the hull.

Jon
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Old 09-12-2009
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IF the overall weight and CG remain the same, then the loading on the bolts and hull will be the same. Performance change is a trade off depending on boat and sea's, wind condition. If you live in an area that requires a shoal keel, then it is a condition that is required and you must live with the performance trade offs. Its better than not sailing....
The Cal 9.2 R model 5'7" draft keel was designed to be able to add 300lbs of lead to a hollow window at the base of the keel . It was produced with a foam plug that was faired, easily modified by design for the hardcore racers.
I don't know of other boats with this option.
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Old 09-12-2009
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Mars Metals

Mars Metals, who is perhaps the largest keel manufacturer in North America, does LOTS of bulb conversions and they do use an N.A .when doing the design and calculations.

Mars Keel (LINK)

Personally I would not do it but I do know a few who have. One guy, a local Ericson owner, even consulted Bruce King the boats designer and Bruce promptly told him to sell the boat and buy one designed with shoal draft and to NOT modify his design.

The guy contacted Mars and did it anyway. He then hit bottom and ripped the bulbs clean off because they are only through bolted onto the keel then faired over.
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Last edited by Maine Sail; 09-12-2009 at 07:27 PM.
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Old 09-12-2009
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Maine Sail - thanks, that validates my theory that wings and bulbs are not as fabulous as many dream that they must be.
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