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post #98 of Old 03-17-2012
Jeff_H
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Re: Full or fin keel?

Marchaj's book was a seminal work when it was written. Like Tony Marchaj's other books it did a great job of gathering existing testing, studies and performing targeted testing and explaining the principles in ways that a moderately technically savy amatuer could understand. For us normal sailors Tony's book really progressed the understanding of the factors involved in producing a seaworthy boat.

But the book was written 30 years ago. The research data was based on the testing available at the time. Most of the basic principles remain 100% valid, but many of the conclusions relate to the specific hull forms, keels, rigs and so on that existed at the time, and did not have the advantage of the ongoing testing which has occured in the 30years since.

In the countervening 30 years, designers, using much more sophisticated testing and design tools, have considered the basic principles that were identified in 'Seaworthiness' and designed boats which purposefully address these issues.

I would respectfully suggest that that Pvajko is mistaken when he says:
"The most important reason is that a full keel with its bigger surface area damps the rolling motion better."
"While a fin keel performs much better in ideal conditions (flat water), stormy weather with big seas is a whole different story. "

I would suggest that, in the first quote, Pvajko is in part misinterpreting what was being said, but in both cases, these conclusions were based on the type-forms and limited testing available at the time that the book was written.

Today, seaworthiness is no longer forgotten. Designers have long since learned how to design around the concerns raised in 'Seaworthiness' and have the tools to make both of the quoted statements inaccurate.


Jeff


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