Well said. I was working on the same post when I read yours, and
you saved me a lot of time mulling over things that are obvious in
hindsight.
Which is not a criticism -- I think it's a great exercise to list
all the pros and cons together in order to come up with a conclusion
about weight location and moment of inertia on a proa. That's a lot
more useful than the usual lower-versus-higher argument, which never
seems to go anywhere.
- Mike
Dennis Cox wrote:
I've read that and heard that, but I don't think I've ever heard an explanation of why there is a concern.If I were to try to put an understanding on it from a purely engineering standpoint... you are most certainly correct. Moment of Inertia (I) would be incredibly higher for say an engine hanging off the transom versus at the keel with a shaft back. Taking two boats with with the same weight but with different distributions of weight and thus different (I), you could expect...Taking that concept further... the High (I) will tend to plow deeper into the trough of waves and would be that much slower to emerge back out. To compensate, you'd need more volume in the ends... which is more weight and the design spiral goes up again. Since we have less reserve buoyancy versus a big ocean going V-monohull, we need to be more concerned about where we put that anchor and engine.
- For an on coming wave... the High (I) would plow into it more. The Low (I) would ride up it more.
- Once clearing the wave... the High (I) would tend to continue in the up direction. The Low (I) would start heading down sooner.
- Thus High (I) is more dampened and comfortable (say like a Cadillac) versus the more responsive, Low (I) (like a mid-engined Ferrari).
Safety wise... If you were pushing it hard and going into a trough in a High (I) boat, it would bury deeper and tend be more likely to pitch pole. The Low (I) would be pushing up the bows sooner and from less depth.
At the risk of making people's eyes roll back into their head. From a dynamic standpoint if you have a higher (I) it will have a lower natural frequency. If the natural frequency is lowered enough, it might be getting closer to the frequency of the waves... and then you would get severely higher jumping up and deeper burying.
Dennis
From: Doug Haines <doha720@yahoo.co.uk>
To: harryproa@yahoogroups.com.au
Sent: Wed, June 1, 2011 8:45:51 PM
Subject: Re: [harryproa] Re: Schooner mast placement?
i don't think it would make much difference Gardner.
--- On Thu, 2/6/11, bjarthur123 <bjarthur123@yahoo.com> wrote:
From: bjarthur123 <bjarthur123@yahoo.com>
Subject: [harryproa] Re: Schooner mast placement?
To: harryproa@yahoogroups.com.au
Date: Thursday, 2 June, 2011, 5:31
i've seen people stress about weight in the ends of the boats before, farrier tris in particular. anchors up front and outboard engines in back. never understood why weight in the ends is worse than the same weight in the middle. the moment of inertia would be higher were it in the ends, no? and that should *decrease* pitching, no?? what am getting wrong???
ben
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