"I've spent a lot of time ogling classic moth designs, from the Gen II mistrals to the Gen I Mint, and I'm a bit smitten by the Farr 3.7 and the Contender (very different boats, I know). So I'm curious: among all the shapes swirling around in my head, some of them reportedly are much faster than others. And the moths in particular *look* fast but aren't nearly as fast as a laser, which nevertheless "sails like an aircraft carrier" in comparison.
"So my question: how do I evaluate a hull shape? What characteristics are associated with downwind vs. upwind performance, and what equates to overall speed? And why is a laser faster than a moth? Is it the sail? Is it the length? Is it the shape? What happens to a laser when you cut it down and put a moth sail on it (maser)? Does it slooooooow down?
The answer in a nutshell. A Laser is faster than the Classic Moth because it is longer (as several of the commenters to this thread noted - see "Chris249" comments for a more detailed hydrodynamic explanation). The Laser also has more sail area - the Classic Moth rig is more-or-less equivalent to the area of the Laser Radial. And No... making a Laser into a Maser doesn't make it faster than a Laser. (It does make it more fun in my opinion.)
I think the crux of "cmjns" question deals with hull shape and, specifically, why the flat Laser shape is so different from our fastest Classic Moth hull shape, the Mistral or Duflos designs which have low wetted area, narrow waterline beam, rocker forward, with a large amount of flare to the gunwhale. Does that mean the flat Laser shape is inherently "faster". Are the fastest Classic Moth hull shapes an anomaly?
First up is the Laser shape as put into computer format by PAR Design:
PAR Yacht Design - Boatdesign.net
For a comparison is the following four views of the Mistral hull shape as modeled by Andrew Stanislav. Not a flat area to be found. The transom is a very circular shape.
What gives? It turns out the characteristics of a Classic Moth Gen II fast hull (low wetted surface, narrow waterline beam, high flare to support hiking power) translates very well into a longer, very fast conventional hiking singlehander - in fact the fastest conventional hiking singlehander. It is the RS300 and it was designed by Mothist Clive Everest back in 1998. It is not length that gives the RS300 an advantage. (It is only slightly longer than the Laser - +.07 meter, giving the RS300 the same length as a Melges 14.) It is a hull with very little flats anywhere, where wetted surface is pared back ruthlessly, where the waterline beam is as narrow you can get away. The dirty little truth! For a design close to twenty years old the RS300 is faster than the latest, much ballyhooed RS Aero and the D Zero. Some RYA Portsmouth numbers:
- RS300 - 973
- RS Aero - 1024
- D Zero - 1029
- Farr 3.7 - 1039 (Yes, I know the Farr is a trapeze singlehander.)
- Laser - 1097
- Europe Dinghy - 1145 (I would expect our Classic Moth Mistrals to be slightly faster than this number.)
So our fast shapes in the Gen II Classic Moth fleet are not an anomaly. There are exactly the shapes you would design if you want the fastest hiking, non-trapeze, non-sliding seat, non-foiling singlehander. However, if you are trying to sell a lot of dinghies, you just might not find a large enough crowd that would enjoy all that wind-swimming.
From the Earwigoagin archives, you can find other RS300 posts.
A very well done RS300 promotional video: