better laminar flow while boomless

Very useful post, thanks Daft. I really enjoyed the excellent article by Doug Peckover.

I think S-B-T-L explains why progress on starboard tack in this video is sparkling (for a Sport) but becomes plain dull immediately after a jibe (24 second mark in the video) to a broad reach on port tack. I had let the hummingbirds escape...

First, if you have an Island or similar boat with a reefing mainsail, you can eliminate a LOT of the mast turbulence by partially rotating the mast so the mainsail edge is outboard instead of in the center. The turbulence moves to the weather side which is better aerodynamically. Typically you will gain a half knot of speed. If you have a rotating mast, you achieve the same thing by rotating the mast so the leading edge is into the wind.

Downwind...that first set of graphics is dangerous sailing if you have a boom. Sailing with the wind coming from directly aft of the leach makes you vulnerable to abrupt gybes. On a boomed boat, someone may get hurt.

Downwind...except in extraordinary conditions, most sailors don't sail ddw. The mainsail is a foil and sailing ddw is stalling the foil so there is no lift. It is going back to the Egyptian days of letting the wind push the boat, that is, all you are doing is maximizing leeway instead of sailing.

Downwind...SBTL as depicted in the graphic where the wind is coming from aft and lee...the sail might work that way but it will be more efficient if you gybe back and forth normally. The sail is designed so the force forward (propelling the boat forward) is maximized (max camber placement) and located about 45% aft of the mast. I can see where the mast turbulence is eliminated, but again, you can minimize this by properly rotating your mast. Granted, I have sailed ddw and by the lee in special circumstances (current relief mostly or following a specific zephyr located in a narrow channel close to shore).

Taco shape...nothing wrong with taco shaped mainsail. Look at asymmetric spinnakers. You should be trying to make your mainsail mimic an asymspin when you only have the one boomless mainsail.

_________________
R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II

The mast prevents the mainsail luff from projecting windward like an asymspin being driven deep. In the video above, you can see that the boom helps keep the foot extended so all the camber is centered into a "U" shape between the two spars...very similar to the old Polynesian crab claw when heading off wind. When you don't have a boom or any headsails, you will be fastest to leeward keeping the apparent wind just aft of abeam. Use the telltales on the mainsail to trim the mainsheet--pay most attention to the outboard telltale, the inboard one will probably lift.

_________________
R/Thom
SeaRail 19
Triak
BMW C600
Formerly Getaway with Custom Spinnakers
Formerly raced F24 Mk II