I just found your site and was quite intrigued by the variety of information available!…I was particularly happy about the comment on mainsails, in which the mast sits in a sleeve about 2′. The idea is that this should reduce wind shadow around the mast, particularly important when the mast is fairly “fat” as in a cat-ketch.
I am considering building a 30′ wood strip-epoxy boat, and thought of 2 rigs using free-standing rotating masts, both cat-ketch with sleeved sails, one option being a big-roach fully-battened (possible conflict with the sleeves…) and the other gaffs (!), which I think merit consideration for shape control.
For the gaffs, I thought of using struts attached to the mast, parallel to the boom, which would keep the gaffs in alignment with the booms, reducing sail twist.
I worry about upwind performance on a cat-ketch: Any views on this? Would the mainsail interfere very much with the mizzen? Would a jib work well in this arrangement?
I look forward to looking through your site again! Thank you! Tom Kottmeier
Hi Tom: Last question first–we are fond of cat ketches. Our Beowulf is designed to sail bareheaded, and does so very efficiently. The small jib (25% of total area) is the first sail off the boat when we’re shortening down. This is a fractional sail, and we carry a large masthead reacher, tacked to an articulating bowsprit as well off the wind.
Efficiency-wise, you cannot do better than freestanding or semi-freestanding rotating wing spars. My guess is that you’ll get a 20% or greater improvement in usable power. Of course this comes at a large penalty in cost!
The sleeve around the spar is difficult to execute properly, and creates a lot of friction going up and down. But if you get it right, it can be very fast too, at much lower cost.
The big roached sails are of course very efficient. You can get most of the way towards these sails with a conventional rig, if you allow the roach past the backstay (this is covered in detail in our Offshore Cruising Encyclopedia). Or, go to swept spreaders and dispense with permanent backstays (which we’ve done on many of our designs).
In the end, however, I think that 30′ is too small for the cost and complexity of a ketch rig. I’d stay with a single stick, and go with a big main, small jib, and huge reacher.–Steve