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post #1 of 8 Old 07-10-2007 Thread Starter
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ratio of keel weight to total weight

I'm curious about how the keel to boat weight ratio affects boat handling, performance, comfort and safety in cruising boats. At some point, the keel is going to be so light that the boat will capsize or so heavy it will sink. If the keel is only 30% of the total weight, for instance, is that too 'tippy'? What is the range of keel to total weight ratio within which most cruising boats fall? Is there a certain 'best' ratio? What are the trade offs between more or less keel weight?
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post #2 of 8 Old 07-10-2007
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The ratio of ballast to displacement is an indicator of stability, but it is not a very accurate one. This is because this ratio does not differentiate between bulb ballast at the bottom of the keel and ballast in the fin keel or hull or of the hull shape of the boat.

Two boats can have the same ballast ratios with very different righting moments. If the hulls are the same, boat A with all it's ballast in a bulb at the bottom of the keel will be stiffer then boat B with a long shoal draft keel even though they may have the same BR. Since the location of the ballast is not taken into consideration only boats with similar ballast arrangements should be compared.

The average value is between 0.35 and 0.45 for cruising boats.

Although a high ballast ratio may make for a more stable boat, one that is very high is said to make a boat extremely stiff, resulting in supposedly uncomfortable “quick motion.”

Last edited by CapnHand; 07-10-2007 at 03:00 AM.
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post #3 of 8 Old 07-10-2007
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The tendency of a boat to capsize or not is affected by a lot of factors, including sail plan, hull shape, keel design and mass, etc. There are boats out there that have relatively high percentage of their mass in their keel, but aren't really seaworthy... and there are boats out there will relatively low percentage of their mass in their keel or no keel at all in the case of a multihull, that are very seaworthy.

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post #4 of 8 Old 07-11-2007 Thread Starter
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thanks for your replies

Appreciate your taking the time to answer my question. So many grains of knowledge to scrape together. life is long but there is so little time......
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post #5 of 8 Old 07-11-2007
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Try here for the answers your looking for.


Sailboat Design and Stability

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post #6 of 8 Old 07-11-2007
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My Morgan 25 (full keel) is .365 Charlie designed it as a Racing/Cruiser back on the late 60's.
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post #7 of 8 Old 07-11-2007
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My little V-21 is .337 and seems to do fine.
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post #8 of 8 Old 07-11-2007
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My Gramp 26 is right at 46% (.46)

Diaplacement 5600# (nominal) Ballest 2600# cast iron

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