Mainsail Cut On The Sparcraft Aftermarket Mast on the J/105

The original Hall spar on the J/105 bends primarily at the upper quarter when backstay is applied. That is a universal defect in the Hall spar, and why you commonly see permanent bend and stress cracks at the hounds, and increasingly breaks. It is more frequent in windier areas like San Francisco Bay, though it happens everywhere. And it happened to me a few years in the New York waters of Long Island Sound.

That is why I replaced the cracked Hall with a Sparcraft aftermarket mast. Though with my new mast, I became suspicious when my three-year old main (originally from the Hall mast) would put me on the podium while the new main landed me consistently at the back of the fleet.

Sparcraft Main - LauraBeaI learned it was because the stretch of the old main created extra mid-luff curve, which the Sparcraft needs because it bends evenly throughout its length -- like a bow. The Sparcraft  also is completely straight when no backstay is applied. That is why a new standard “Hall” main I purchased was too flat through nearly every backstay range, and could never power up. Fellow owner (loulou #334) and Doyle sailmaker Paul Beaudin worked with me on recuts, measurements and eventually a total redesign of the Doyle main for the latest Sparcraft model (which may be different than the old Sparcraft masts from 20 years ago on the French-built J/105s).

The result? The new Sparcraft main performance is promising. American Yacht Club Fall Series 2021 was our first regatta with the new main. We could’ve placed second, but some boat handling issues put us in third. Regardless, the improvement was instant and noticeable.

Of course, a new mast, rigging and mainsail mandated figuring out entirely new mast-tune settings. The backstay range is less on a Sparcraft, and the mainsail will invert sooner than with the Hall. So it is critical to be proactive in adjusting (especially) the caps for headstay tension when the breeze picks up or lowers. Many Sparcraft settings throughout the wind ranges are counterintuitive.

To my knowledge, Quantum and Doyle outright address the latest Sparcraft replacement mast with a special cut main. They each now market proactively their Sparcraft main cuts. My inquiries to other sailmakers resulted in no acknowledgment of need for a different cut for Sparcraft. Be careful of experts, because they can project expertise, and mean well, even if they don't really know the answer. You have to be your own expert!!!

I'm no expert, though I am an astute student. I’m happy to share my knowledge with any fellow J105 owners facing a Sparcraft replacement. A Sparcraft conversion can be a frustrating, penalizing experience on these "one-design-ish" boats. Though with a little finesse and knowledge from others who've been through the conversion, you can figure it out, too.

- Max Kalehoff, LauraBea, #249

Comments are closed.