Sizing an anchor riding sail?

[Tim Good]

Questions:

Is there a formula for calculating the area of an anchor riding sail?

Should the sail size decrease as the wind increases? …. or is the windage in the hull and rig, such that the sail wants to remain the same size to counter the additional forces regardless of wind strength?

Background:

I don’t want to talk about the merits of an anchor riding sail, as I already know they work extremely well for our boat, which in extreme conditions yaws around and snatches at the anchor. The same for most boats when it blows 45kts +.

After making a DIY anchor go riding sail and witnessing the amazing results during a 50kts + storm, I was committed to the idea of having one professionally made.

The picture is the result from SKB in Falmouth. The quality is excellent but I am a little concerned it is too small. I did specifically ask them to make it on the smaller side since I want it for extreme conditions rather than just a general blow. Basically I said I don’t want it to be too big so that when the shit really hits the fan and it’s blowing 50 kts, I get worried is it just too much sail up! Even if it is an anchor sail.

Equally, if it blows like hell and it’s soo small to keep us perfectly aligned to the wind, then that’s a waste of good money spent.

Boat is 43ft, 16tonnes displacement with deck saloon and a tall semi classic bow. Photo attached.

Thoughts?

 

[wallacebob]

I have seen a figure of 4% of working sail area, or rough guides/guesses of 40-50% of LOA = area of riding sail(!?)
The delta wing kind are small. Sailrite do a DIY version, don’t know if they give a size calculator.
I’m interested!

 

[Mudisox]

Is it not the wrong way round, luff to the fore?

 

[[70521]]

@Tim Good I have some notes from a very old post on here on a PC, I'm currently in Brittany and will fire up the machine later. The sail I have notes on is much simpler that the one you have pictured, based on two triangles and a pole, boat hook, keeping triangles apart.

In theory the sail cannot be to big as you are head to wind and the two triangles are keeping the boat steady. Your third 'face' might cause the sail to drive the boat.

Hope you and all in the OCC are well.

 

[wallacebob]

This is the FinDelta:

 

[wonkywinch]

I like the idea of these after reading this website .. FinDelta #2 "Classic" Anchor Riding Sail for Boats 33 to 46 Feet

Sail maker in Hamble quoted me £300 to make one up.

 

[[70521]]

PM sent.

 

[RobbieW]

Check out this post...
PIOTASKIPPER ALBUMS
and read the link to v riding sail.

 

[oldmanofthehills]

I have seen a figure of 4% of working sail area, or rough guides/guesses of 40-50% of LOA = area of riding sail(!?)
The delta wing kind are small. Sailrite do a DIY version, don’t know if they give a size calculator.
I’m interested!

Sailrites one is not a delta, and my experience with our (ex) ketch showed that the single surface was not completely effective in stopping swing. However it does indicate how that old trisail stowed forever under the bunk could be hoisted on the back stay to get better stabilisation than none at all.

 

[Poignard]

V-Twin Riding Sail

 

[NormanS]

Mine, on a 36ft deck saloon ketch, consists of two triangles with a common luff with slides to fit the mizzen mast.
Luff 3.25m. Foot 1.83m. Leach 3.9m. Each clew is sheeted to its corner of the taffrail, and are also kept apart with a modified boathook. I've used it in winds of 60+ knots without any problem, but of course it's better to rig it before the wind gets up to that. It does everything that I hoped it would. To the OP, what dimensions are you proposing?