18' Cat Ketch

Design Number 204

This design followed the 16' Sailing Tender by several years. During this interval, I'd had quite a bit of experience with the 16-footer as we looked after her for ten to eleven months a year. This experience with Conch Ad Libitum led to a number of thoughts and ideas on how she could be changed and/or improved.

The commission for the 18' Cat Ketch came from a client wanting to try out sailing a cat ketch on a smaller scale before owning a larger cruising boat with the same rig. He felt that this would give him useful experience and knowledge about how to sail a cat ketch and confirm his desire to own a larger one.

In creating her, we knew that she was to be sailed off a trailer. Reduced structural weights would make this easier to do, and make her more lively to sail. We also decided to increase her sail area, based on our experience with the 16-footer. We came to realize that most all the sailing of a small pleasure craft was in lighter wind conditions, rather than thrashing through heavy weather. More sail area would make her more fun to sail, and we've done that with the 18-footer

We've also given her a longer foredeck. This will provide shelter for bagged camping gear and a place for kids to hide from the weather. We've kept the cockpits more open, making more room for camping aboard. There is only one rowing position, well aft where the helmsman could row. Another position could be added forward, but this would mean adding another thwart, taking away from the open layout.

For a heavier duty version of this boat, I would suggest adding 1/8" to the plywood thickness of the hull and deck. This will add about 150 to 200 pounds to her structure. A heavier boat will carry her way better through some conditions, but I would not recommend doing this unless your usage calls for a very rugged boat.

The photos on this page show Dr. Jerry Limbers' 18' Cat Ketch built as preparation for the 34' Sailing Dory he now has under construction.

Length overall18'-0"5.49 m
Length datum waterline16'-0"4.88 m
Beam6'-0"1.83 m
Draft0'-8"/4'-6"0.20/1.37 m
Freeboard:Forward2'-6"0.76 m
Least1'-6"0.46 m
Aft2'-00.61 m
Estimated structural weight200 lbs.91 kg.
Displacement, to DWL800 lbs.364 kg.
Displacement-length ratio87 
Sail area155 sq. ft.14.4 m2
Sail area-displacement ratio28.78 
Prismatic coefficient.567 
Pounds per inch immersion280 
Entrance half-angle22 

Note: The displacement numbers are calculated to the arbitrarily chosen DWL.
The calculated ratios of displacement-length and sail area-displacement will vary widely depending on the loading of the vessel.

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