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post #545 of Old 10-16-2012
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Re: Full or fin keel?

Originally Posted by PCP View Post
40class racer is massively more stiff [B]and by your reasoning, since both boats share the same kind of hull, the Class40 should be less of a rough water boat.
Originally Posted by PCP View Post
Probably means that there is a big chance to be or it is a way not to say exactly that it is
I asked a number of times that you post the stability diagrams for the two boats so you might immediately see otherwise. I wanted to see specifically the boats you were comparing. Obviously, one boat is a very specific boat (Oceanis). The racer represents a whole class of boats with varying RM diagrams.

However, I wil post the representative RM diagrams to see if what you say makes sense.

The red plot is the RM diagram for the oceanis. The blue diagram is the RM of the racer. As we see, the racer has a much larger RM value that the Oceanis sooner in the RM diagram. And as you say, the RM has similar amplitude.

Now as we all know, stiffness is the derivative of the RM diagram. So at the top, I show Where each boat has the higer derivative. The Oceanis clearly has a higher stiffness over more of the RM diagram that the racer.

Usually a cruiser is more stiff near zero. The racer is more stiff at some heeling angle above a few degrees up to probably about 30 to 40 degrees. Afterwards, the oceanis is more stiff. Clearly these break points are different depending on who designed the racer.

Such RM differences are typical for racers and crusier. But again I ask, why would anyone think a racer is a rough water boat??

So remind me again.. which boat is more stiff? Better yet.. Massively more stiff???
Attached Images
File Type: jpg StiffnessOceanisRacer.jpg (27.2 KB, 12 views)

Last edited by BryceGTX; 10-16-2012 at 08:29 PM.
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