Wing-drive

[sharpii2]

Originally Posted by kjell

Kjell Dahlberg Wing-Drive is a wind propulsion system. A safety simple sailing system for Catamarans.
http://www.youtube.com/user/wingdrive#p/u

Checked out your videos.

I really liked the flapper drive.

It may be a good substitute for a propeller on a sail boat.

I can imagine it causes far less drag when its not being used then a typical fixed bladed propeller of the same propulsion capability. It may not be as efficient, but perhaps its other virtues make up for that.

When I think of a motor sailor, I think of a boat with about 1.0 hp per ton or less. The engine is to reduce the size of the rig and to get through calms. On good sailing days, it is to be turned off.

1.0 hp/ton will not get you anywhere near hull speed. But I don't see that as an issue, as it takes considerable energy, maybe 4 times as much as it does to go half hull speed.

For my concept to work, I need a low drag propeller. There are only three options available:

1.) a relatively inefficient small fixed blade propeller, driven at high rpm,

2.) a folding blade propeller that can be larger, but is more expensive and more likely to fail to open, and

3.) a feathering propeller, which may cost as much as the engine.

Generally, I would go with three. Sometimes spending money on the more expensive option is the better bargain over the long run.

Your flapper drive opens up a fourth option. One that you might consider yourself when it comes to your wing sail design.

It looks handy but seems a little poor in sail area.

I know it's supposed to be three times as efficient as a conventional sail. But what does that mean?

Does that mean it proved three times as much lift? Or does that mean it proved three times as much lift per given amount of drag?

The two sound deceptively similar, but they are different.

My dad's Cessna 150 flew at about 100 kts at about three quarter power.

To land, flaps were deployed, to slow the flying speed down to make it safer to land. The flying speed dropped to about 45 kts, but required nearly full power for the plane to stay up in the air.

Except for going up wind, a sailboat is in the second situation. The amount of actual lift is more important than the lift drag ratio. So if a larger sail is one third as 'efficient', it may still sail past a wing sail with one third the area.

Your rig does not seem all that fast, especially for a multihull, but may be a good rig for a motor sailor.

It seems a whole lot handier than most sail rigs.

Have you ever had it out in really blustery conditions?

[kjell]

It is possible to have desmountable wings.

[sharpii2]

Originally Posted by kjell

It is possible to have desmountable wings.

I see.

But they are extremely vulnerable to wave damage that way. And even though they reduce the capsizing moment quite a bit, they are still sticking up in the air.

Just that they are low aspect ratio now instead of high aspect ratio.

All that area can not be feathered except by pointing the bow into the wind.

IMHO, best to leave them up and find a way to make them self feather.

Another possible solution is a clever idea I saw in "WoodenBoat".

Basically the wing sails were really soft sails with the wing ribs acting internal battens. A very powerful halyard was needed to stretch the sail cloth tight.

Furling happened the usual way. The halyard was slacked and the sail cloth and ribs bunched up at the bottom.

[kjell]

Inflatable wings are one solution.