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Re: Skin-on-Frame: How much Rocker?
By:Paul G. Jacobson
Date: 12/4/2003, 12:44 am
In Response To: Skin-on-Frame: How much Rocker? (Bryan)

: I'm at the point in my skin-on-frame West Greenland kayak were I'm lashing on
: the chine stringers, and I needed space in my shop to start cutting forms
: for a new boat, so I put the kayak on the floor. It seems to me that there
: is a lot of rocker in my kayak. How much rocker should I be looking for?
: Is there any good way to measure this so I could tell if I have too much.

: Thank you,
: Bryan

Generally, if you want a longer boat to turn easier you need more rocker. OIf you want a shorter boat to track better you want less rocker. The exact amount will vary by design, and by the weight of the load.

With many Skin-on-frmae boats the frame is fairly flexible. While you could measure the built-in rocker on your frame with a ruler and an assistant to hold the boat in place on a flat surface, this would not give you useful data. Once you get the boat in the water, you will sit in the middle of it, and create even more rocker as the frame flexes!

If you can find a very shallow area of calm water near a soft beach, launch the boat and edge towards progressively shallower water until you land on the bottom. Mark the spot, and have a friend measure where(if at all) the bow and stern come out of the water. If they stay in the water, then measure how far down they go. Then measure the depth of the water where your bottom met the ground.

this tells you the draft of your boat at the deepest point (probably in the 4 to 7 inch range). Then, by comparing that to the draft for the bow and stern you can see how much higher those parts are floating. The difference is your actual rocker. Some "banana" boats hae extreme rocker of 12 inches or more at the bow and at the stern. They can also turn very easily, but you might not want them for long distance cruising.

Interesting sideline here. If you compare the handling of a flexible s-o-f boat with that of a rigid stripper, plastic or plywood boat you'll see that having the same rocker does NOT give the same handling. Since the s-o-f boat flexes, you'll almost certainly have the full waterline of the boat submerged, giving you a long waterline for good tracking, and stillhae a nie rocker shape for easy trning. While a rigid boat with great rocker might have parts of the boat in the air.

Whatever works for you is what is "right". Lots of people try one boat and then compare it to another and eventually find a style and shape that they are most comfortable with. A boat with lots of rocker may be great for some trips, but on others you'll want one with less roker and more speed. BUILD MORE THAN ONE BOAT!

PGJ

Messages In This Thread

Skin-on-Frame: How much Rocker?
Bryan -- 12/3/2003, 8:32 pm
Re: Skin-on-Frame: How much Rocker? *Pic*
Tom Yost -- 12/4/2003, 1:39 pm
Re: Skin-on-Frame: How much Rocker? *Pic*
Tom Yost -- 12/4/2003, 12:19 pm
Re: Skin-on-Frame: How much Rocker?
Bryan -- 12/5/2003, 7:03 pm
Re: Skin-on-Frame: How much Rocker?
Brian Nystrom -- 12/8/2003, 12:53 pm
Re: Skin-on-Frame: How much Rocker?
Bryan -- 12/8/2003, 6:45 pm
Re: Skin-on-Frame: How much Rocker?
Brian Nystrom -- 12/9/2003, 12:55 pm
Re: Skin-on-Frame: How much Rocker?
West -- 12/4/2003, 1:01 am
Re: Skin-on-Frame: How much Rocker?
Paul G. Jacobson -- 12/4/2003, 12:44 am
Re: Skin-on-Frame: How much Rocker?
Petewp -- 12/3/2003, 9:48 pm
That sounds like Peter Strand's storm kayak *NM*
Brian Nystrom -- 12/4/2003, 1:14 pm