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Re: Other: On measuring rocker
By:ChrisO
Date: 12/6/2003, 2:46 pm
In Response To: Other: On measuring rocker (Mike Scarborough)

> ... Can the BBS community come up with a standardized way to
: measure rocker? A method that is quick and easy and repeatable so that we
: can all talk about rocker and be describing the same attribute of a kayak.

Mike,

Unfortunately, that's one of the tough ones to describe and there's no real concensus, even among naval architects.

One of the problems of measuring rocker from a hull while it is sitting on a hard surface is that it doesn't reflect the relationship of the hull to the water when the boat is sitting on her lines in the water. Gravity pulls at the hull according to the shape of the hull and the respective weight of each end. When in the water, gravity is doing the same thing except that the buoyancy of each end of the boat will resist the pull in a different fashion than will the air. If the lowest point of the boat's draft is forward of the center of gravity than the bow will be high when sitting on the ground.

One description I got from a well regarded naval architect who has done a few canoes and sea kayaks is as follows: Create a line that is parallel to the waterline of the boat that just touches the lowest point of the hull. (Assuming you know where the waterline of your boat is located, I would do this by resting the hull on the floor of a shop and trimming the boat fore and aft till the waterline is parallel to the floor) Drop a plumb bob from the farthest forward point of the bow to the floor and measure back ten inches from the pumb line. The distance from the floor to your hull is the rocker of the bow.

Repeat for the stern and you have the complete picture of the rocker of the entire hull.

Since others may measure their hulls diferently than this method, it makes this procedure relevant only to your measurements of boats in your quiver or ones to which you have access. When you know how the others may handle in the water, then the relationships between the differing rocker measurements start to have some value.

I don't have an answer for the standardization thing about which you asked. There are some decently large egos involved in the potential process and they would have to reach a concensus for the term to have value as a norm.

Chris

Messages In This Thread

Other: On measuring rocker
Mike Scarborough -- 12/6/2003, 10:41 am
Re: Other: On measuring rocker
Jay Doorly -- 12/10/2003, 3:10 am
beautiful mystery
Water Pixie -- 12/10/2003, 4:08 am
Re: Other: On measuring rocker
Jay Doorly -- 12/7/2003, 1:25 am
rocking rockers
mike allen -- 12/7/2003, 2:26 am
Re: Other: On measuring rocker
ChrisO -- 12/6/2003, 2:46 pm
Re: Other: On measuring rocker
Roger Turgeon -- 12/6/2003, 5:21 pm
Re: Other: On measuring rocker
Nick Schade - Guillemot K, ats -- 12/7/2003, 9:07 am
Re: Other: On measuring rocker
mike allen -- 12/8/2003, 3:12 pm
Re: Other: On measuring rocker
Tom Yost -- 12/6/2003, 6:32 pm
Re: Other: On measuring rocker
Pete Roszyk -- 12/6/2003, 11:41 am
Re: Other: On measuring rocker
LeeG -- 12/8/2003, 3:54 pm