Message-Id: <199804161640.MAA31071@mailhost.capecod.net>
From: "billow" <billow@capecod.net>
To: <baidarka@lists.intelenet.net>
Subject: Re: [baidarka] baidarka cockpit placement
Date: Thu, 16 Apr 1998 12:40:21 -0400
This is a normal problem if you are building boats for different sized
people or are changing the design. What I have done is to determine the
actual CG for a particular person. A method is to put a thick board about
6' -8' long on a dowel. Sit on the board and move back and forth until you
and the board balance with the center of the board at the balance point.
That way the weight of the board does not enter into the equation. Notice
the point of balance on your body. That will tell you where your CG is in
relation to say your back rest.
The shape of the hull is very important in this procedure. If you are
building to a set of plans and feel that the designer had the CG correct
for a particular weight and you want to alter the cockpit position to
compensate you can use a fixed position such as the backrest and adjust for
the CG you just measured. Recheck with someone of the weight the boat was
designed for. I have found that for most people in the 160# - 180# region
the CG is about 4" forward of the lower pelvic bones in the butt.
As Kirk pointed out an adjustable seat is a big help but only if the
cockpit is mounted aft enough to allow you to move to the rear. Most of the
time I find the cockpit is mounted to far forward and there is not enough
room to move back. The other problem is that the cockpit must be large
enough to allow you move in either direction.
After you have determined all this and start building the boat you must
retain the same hull shape. If you should shortchange the hull volume in
the stern then the boat will sit lower in the water toward the stern and
have the effect of moving the CG toward the rear.
I have redesigned a number of boats and made the calculations to adjust for
the weight. It is still a crap shoot because of all the variables. I have
had to go in and readjust on occasion. The other solution is to throw in a
little weight to correct the CG. It depends on how much of a purist you
are.
Bill
----------
> From: William D Duarte <duarte@value.net>
> To: baidarka@lists.intelenet.net
> Subject: Re: [baidarka] baidarka cockpit placement
> Date: Thursday, April 16, 1998 10:20 AM
>
> Rick,
>
> I'm at the same point you are at building my "Brinck" boat. Same
> problem, but I'm 6'2'' tall and 185 lbs. I plan on leaving the plans as
> is and inserting an adjustable seat as Kirk mentioned. I'd be
> interested as well to find out how everyone else fronted this problem.
>
> William