To John on Seahorse, I'm always up for a question, fire away to tadroberts at shaw dot ca. Also I'll mention that any boat, no matter the size, shape, or ballast configuration, can be rolled over given the right size and shape of wave. Capsize tests in tanks have shown that any yacht can be rolled 180 degrees by a wave equal in height to 55 percent of her LOA. So a 30' wave taken beam on could roll the Skookum 53. In earlier postings on the Perfect Passagemaker project, a suggested requirement was positive stability to fairly high angles, one person suggested 105 degrees and another suggested nothing less than 140 degrees. I tried to explain that this was unlikely without major compromise. Being a curious type I decided to investigate for myself the stability of two well known modern Passagemakers. I created 3D computer models of a Nordhavn 55 and a Diesel Duck 462. I was able to do this from drawings offered by each builder on their respective websites. Nordhavn claim a half-load displacement for the 55 of 97,360 pounds, my model came in at about 99,000, so I left it floating at that. From pictures the DD462 seems to be floating quite a bit deeper than the DWL indicated on the lines, so I sunk her down 4", to about 75,000 pounds displacement. I also decided on a VCG of 18" above the waterline. This is about half topside height and would be typical for a steel vessel with limited deckhouse. For the Nordhavn I decided on a VCG of 3' above DWL, this is the height of the main deck (afterdeck) and she has two full stories of accommodation above this. Only the hulls and main decks were modeled, I did not include deckhouses as they are full of downflooding points. Maximum righting arm for the DD is about 30 degrees, this is where the deck edge goes under water and righting energy decreases. She runs out of positive stability at about 87 degrees. This will change with displacement changes (mainly liquids), and will be reduced with free-surface effect of the liquids in her tanks. The configuration of the N55 is unusual with her very high built-up foredeck. She exhibits an unusual righting arm curve with maximum righting arm at 65 degrees. But it then drops off quickly and goes to zero at about 85 degrees. There is a great deal of area under the curve (below zero) thus these boats, if they heeled to these angles, will be very reluctant to right themselves. An interesting result and I would be happy to send model pictures and data to anyone by email. All the best, Tad [demime 1.01d removed an attachment of type image/gif which had a name of image001.gif]

Tad, Your modeling is interesting. The N-55 is taller than the N-46. The 46 has a positive righting moment at all angles - this assumes the braced windows do not fail. I am very surprised at the analysis you show for the N-55. With the same assumption of no down flooding I can't image that there is not a HUGE righting moment from all that air. Do you assume the windows all fail ? John Harris World Odd @ Sea N-4657 -- I am using the free version of SPAMfighter. We are a community of 5.6 million users fighting spam. SPAMfighter has removed 427 of my spam emails to date. Get the free SPAMfighter here: http://www.spamfighter.com/len The Professional version does not have this message

Interesting but let's face it with the weather reporting available today, even with a 7 to 8 knot speed you can minimize the risk of capsize. Again in 75,000 miles of passaging I have never encountered more than 25' seas with a duration of around 10 seconds and that was east of the Straits if Lemaire. I do not minimize the possibilities of a rouge wave but can you really design the affordable boat that will endure all conditions? I hope I have learned the lesson of picking the right weather window and then enjoying the passage. God Bless - Ross on 10&2 On Wed, Nov 5, 2008 at 8:34 PM, Tad Roberts <tadroberts@shaw.ca> wrote: > To John on Seahorse, > > > > I'm always up for a question, fire away to tadroberts at shaw dot ca. > > > > Also I'll mention that any boat, no matter the size, shape, or ballast > configuration, can be rolled over given the right size and shape of wave. > Capsize tests in tanks have shown that any yacht can be rolled 180 degrees > by a wave equal in height to 55 percent of her LOA. So a 30' wave taken beam > on could roll the Skookum 53. > > > > In earlier postings on the Perfect Passagemaker project, a suggested > requirement was positive stability to fairly high angles, one person > suggested 105 degrees and another suggested nothing less than 140 degrees. > I tried to explain that this was unlikely without major compromise. > > > > Being a curious type I decided to investigate for myself the stability of > two well known modern Passagemakers. I created 3D computer models of a > Nordhavn 55 and a Diesel Duck 462. I was able to do this from drawings > offered by each builder on their respective websites. Nordhavn claim a > half-load displacement for the 55 of 97,360 pounds, my model came in at > about 99,000, so I left it floating at that. From pictures the DD462 seems > to be floating quite a bit deeper than the DWL indicated on the lines, so I > sunk her down 4", to about 75,000 pounds displacement. I also decided on a > VCG of 18" above the waterline. This is about half topside height and would > be typical for a steel vessel with limited deckhouse. For the Nordhavn I > decided on a VCG of 3' above DWL, this is the height of the main deck > (afterdeck) and she has two full stories of accommodation above this. Only > the hulls and main decks were modeled, I did not include deckhouses as they > are full of downflooding points. > > > > Maximum righting arm for the DD is about 30 degrees, this is where the deck > edge goes under water and righting energy decreases. She runs out of > positive stability at about 87 degrees. This will change with displacement > changes (mainly liquids), and will be reduced with free-surface effect of > the liquids in her tanks. > > > > The configuration of the N55 is unusual with her very high built-up > foredeck. She exhibits an unusual righting arm curve with maximum righting > arm at 65 degrees. But it then drops off quickly and goes to zero at about > 85 degrees. There is a great deal of area under the curve (below zero) thus > these boats, if they heeled to these angles, will be very reluctant to right > themselves. > > > > An interesting result and I would be happy to send model pictures and data > to anyone by email. > > > > All the best, Tad > > [demime 1.01d removed an attachment of type image/gif which had a name of image001.gif] > _______________________________________________ > http://lists.samurai.com/mailman/listinfo/passagemaking-under-power > > To unsubscribe send email to > passagemaking-under-power-request@lists.samurai.com with the word > UNSUBSCRIBE and nothing else in the subject or body of the message. > > Passagemaking Under Power and PUP are trademarks of Water World Productions, formerly known as Trawler World Productions.