Roached Mainsails!

[snowleopard]

Going back to the OP, I was told by a traditional sailmaker (he made the sails for the original Royallist) that 'roach' means a hollow leech and the correct term for a convex line was 'round'.

 

[bignick]

Small correction. It's not elliptical plan that's efficient. It's elliptical lift distribution which can be achieved in many ways but very difficult to do it with an elliptical sail as the sail has twist.

Spot on. A rectangular planform can easily be made to have an elliptic lift distribution.

 

[Seajet]

At a recent Drascombe Rally a friend of mine had a 'roached mainsail' (wider white area at the top of the sail supported by a batten as pictured). The sail can be used to good effect in light airs, although the usual way of 'harbour furling' the main, e.g. Rolling it up against the mast is hindered and reefing looks a bit nuts because you still have the large white area on top.

Question from a novice, I am totally wrong obviously but I would of thought the last thing you want is sail area on top of a sail as it will make the boat heel more. Why not have a larger area below, maybe as there is no boom!? To all those comics yes I know Drascombes will never be quick, they are not about being quick

For info, such sails below the boom ( dunno about rigging it on a Drascombe ) are / were known as ' Watercatchers ' - I would imagine pretty inefficient except maybe off the wind, but the obvious reason for their unpopularity is conflict with crew, seems like either one or the other...

 

[Boo2]

Yes

The thing with an anemometer head clearly visible below its tip? No idea. Maybe it's a bracket for an anemometer head, but that's just a guess.

Why is it so tall ?

Boo2

 

[JumbleDuck]

Why is it so tall ?

To keep it out the disturbed air, and especially the tip vortex, at the masthead, I imagine.

 

[bbg]

To keep it out the disturbed air, and especially the tip vortex, at the masthead, I imagine.

Your imagination is correct.

 

[Daydream believer]

very difficult to do it with an elliptical sail as the sail has twist.

So do most wings.( washout) It is just a lot less as the air speed is different

 

[Buck Turgidson]

So do most wings.( washout) It is just a lot less as the air speed is different

Which is why you don't see aircraft with elliptical planform wings these days except at airshows or historic ceremonies. The Spit had 2.5° of washout but this was to help move the initial stall inboard not for lift distribution.

 

[JumbleDuck]

Which is why you don't see aircraft with elliptical planform wings these days except at airshows or historic ceremonies.

And on gliders. The point of elliptical wings (or elliptical lift distribution) is to minimise induced drag, which is really only an issue at low speeds.

 

[Buck Turgidson]

And on gliders. The point of elliptical wings (or elliptical lift distribution) is to minimise induced drag, which is really only an issue at low speeds.

Firstly induced drag is an issue all the time. Secondly well done for finding an example of an elliptical wing. Finally, what about all the others which don' t use elliptical plan form but create elliptical lift distribution by the use of taper and twist (either aerodynamic or physical)? You don't see Boeing, Airbus, Embraer or Bombardier using elliptical plan form because it's probably the worst way to create elliptical lift distribution. They do however spend billions on reducing induced drag. Trust me, I know. ;-)

 

[JumbleDuck]

Firstly induced drag is an issue all the time. Secondly well done for finding an example of an elliptical wing. Finally, what about all the others which don' t use elliptical plan form but create elliptical lift distribution by the use of taper and twist (either aerodynamic or physical)? You don't see Boeing, Airbus, Embraer or Bombardier using elliptical plan form because it's probably the worst way to create elliptical lift distribution. They do however spend billions on reducing induced drag. Trust me, I know. ;-)

I trust you. However, induced drag is much more of a problem at low speed, and gliders spend an awful lot of time fairly near stalling speed, which is why glider designers work particularly hard to get rid of it. As Boeing et al know ... the use of winglets for drag reduction was pioneered by the German university Akafliegs on gliders.