Saturday, September 19, 2009

Ravn's keel, part one

Since deciding on Atkins' plan to build Ravn, there's been a lot of hand wringing over the keel. Both Valgerda and Kari 2 plans showed keels significantly deeper than the original Hardanger faerings. The designers added more than a foot to the traditional 4-inch keel of the boats they were designed after.

Atkins wrote: "Because of their lack of initial stability, I designed a new keel - the original boats had a long, shallow keel approximately 4 inches deep. When loaded, they had sufficient lateral plane to hold the little craft on the wind.... I prepared the rather shoal fin keel, fitted with lead ballast of approximately 106 pounds, because of her lack of initial stability and the unlikelihood of her carrying a cargo of fish."

On Kari 2, the designer wrote: "The hull is a close resemblance of the original but we have given her a deeper keel to enhance her windward performance."

I like good windward performance as much as the next guy, but I felt I needed shallow draft more. Neither Valgerda or Kari 2 are deep-draft vessels by any means, but even their modest 18-inch draft seemed too much.

In the end I decided to split the difference. I liked Atkins reasoning about faerings, being work boats, were made to carry loads. So I decided to add a 100-pound chunk of lead to the keel. My keel would be made of purple heart wood, which is denser and heavier than the oak specified by Atkins. It is commonly available and usually cheaper than white oak and glues well with epoxy. It is also rot proof, a very nice thing in a boat. I like to think that Atkins would have specified it had it been as common in the 1950s as it is now. I decided to lengthen the keel and carry it farther astern to increase the lateral resistance and directional stability.

I thought of Billy Atkin's advice:
"Now do not be tempted to pull the ends out, raise the sheer heights, swoop up the bow or stern, or do the many things a boat plan always impels one to do. Just put this... boat together and see how well she performs." I bowed my head and started ripping 12-foot purple heart planks into 2-inch wide lengths for the keel.

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