Bare poles

[snowleopard]

Coming back from the Yealm to Plymouth this afternoon there was a fresh Easterly so, feeling lazy, I decided not to bother hoisting sail. Half way along it blew up a bit so I stopped the engines and the speed went up - to 8 knots through the water.

BTW the area of the mast is 10 sq m, about 15% of the total sail plan.

I can't have a wind instrument so I had to estimate from sea state. The Inshore forecast was 3-4 increasing 5-6 but I would have said it was the top end of 4.

Perhaps I won't bother hauling on all those bits of string in the future /forums/images/graemlins/smile.gif

 

[Richard10002]

I may be missing something, but that is some big mast. Mine is 15m high, and maybe a foot from front to back, so less than 5sq.m

 

[photodog]

I was on the Solent last June with Ellen Mcarthur on her extreme 40... it was on that very stormy monday with all the floods right after Glastonbury.... anyways... the boat was going downwind at 12-15 knots with no sail up in around 30-35 knots of wind....

 

[jimi]

Going downwind the spray hood has a fair bit of windage.

 

[Sybarite]

You're forgetting about the other side...

 

[Clyde_Wanderer]

[ QUOTE ]
You're forgetting about the other side...

[/ QUOTE ]

Would it not be so that the area of only one side would count as a wind catcher at any one given wind direction?
C_W

 

[Richard10002]

I think he was joking, (I hope /forums/images/graemlins/smile.gif )

 

[Sgeir]

If there was only one side it wouldn't get any lift from the flow of air. Needs two sides.

 

[pyrojames]

Not so. Change in rotational momentum of air on a surface will induce lift simply from the curvature of the surface. Consider a dome tent on a wind swept mountain side.

 

[Jeannius]

Perhaps the engine revs you had set was less than the prop revs that you got once you stopped the engine and engaged neutral. Drag might have decreased once the props rotated freely.

If I want to slow my cat down the easiest way is to lock the props. Knocks about 10% off boat speed immediately.

 

[boatmike]

Calculating the area of the mast only gives you part of the answer. It's the total windage area of the boat that needs to be calculated. If you do that calc relative to total area of boat plus sail you will be surprised, especially if you have a wheelhouse, dodger, or sprayhood. I sailed a big Aussie cat in the Caribbean once and reduced sail to zero with about 40 knots of wind up my tail feathers. She actually sailed faster off the wind than dead downwind just like with sails up due I think to the large slab sided hull area.....

 

[Sgeir]

It was in the manner of Sybarite's post. Next time I'll use the smiley. /forums/images/graemlins/smile.gif

Sorry.

 

[snowleopard]

The spar is 15m long, the chord varies from 40 cm at the top to 1m at the base. It is aerofoil section and I rotated it to provide maximum lift with the wind about 40 deg off the beam. There was a fair bit of drive from the windage of the cabin and hard top but most comes from the mast. I can get quite high speeds with the wind on the beam when the windage effect is nil.

 

[whipper_snapper]

Bloody hell! How do you reef the mast when it really blows up!?

 

[boatmike]

I assume you can in fact rotate it to "feather"?

 

[pyrojames]

/forums/images/graemlins/smile.gif Not entirely switched on last night.

 

[snowleopard]

Exactly. By altering the angle of the mast I can go from zero to fully powered up. It rotates 360 deg. Boats that have lage wing masts that are stayed and therefore can't be feathered are, IMHO, dangerous. Tony Bullimore had masts like that on Exide Challenger and he reported that they were a menace.

 

[Richard10002]

Have you got a picture?

 

[boatmike]

Thought so. Of course I could comment that TB is a menace himself but that would not be polite would it? /forums/images/graemlins/smile.gif

 

[snowleopard]

Go to http://www.freewingmasts.co.uk/ and click on 'photographs'