I Love to Eat Crab Claws - Here's Another Reason to Love them

[Will Gilmore]

I play around with designs for my ultimate cruising boat and so have been looking at rig options. The Bermuda rig seems like a no brainer, but a staysail rig is so simple and easy to work. There is some leading edge improvement on efficiency but the consensus is that the Bermuda rig is still a more efficient rig overall. Then, I stumbled upon the crab claw discussions online.
Here's a quote from this Website [ https://www.boatdesign.net/threads/what-about-the-crab-claw-rig.19156/ ]:
" The crab claw rig has been tested in a wind tunnel by the famed aerodynamicist C. A. Marchaj:

"Even more startling is the extraordinary performance of the crab claw sail… which demonstrates its superiority to a Bermuda mainsail right from the close-hauled condition. Its superiority increases when the boat bears away, and on reaching, with the heading angle 90 degrees, the driving force coefficient of the crab claw rig is about 1.7, whereas that of the Bermuda rig is about 0.9. That is, the crab claw delivers about 90 per cent more driving power than the Bermudan rig." "
And, for those who have the need to sail when your favorite lake is frozen over [ https://proafile.com/multihull-boats/article/crab-claws-on-ice ]

- Will (Dragonfly)

 

[capta]

Isn't that just a modern lateen rig, which has been around for some eons, now? The Polynesians used a very similar rig, as well.

 

[Will Gilmore]

Isn't that just a modern lateen rig, which has been around for some eons, now? The Polynesians used a very similar rig, as well.

Yes to Polynesian, not exactly, to lateen rig, but close. Lateens are free footed.

- Will (Dragonfly)

 

[rgranger]

I've been researching the crab claw for years. I also am intrigued by the idea.

Here are some links and pics to wet your imagination.

Check this link first

http://www.workingsail.com/sails/crabclaw/index.html

This guy has his crab claw sail on a T-post mast. Instead of reefing, you can simply raise the T and make the sail more horizontal. The effect is less heel but you still get lift... so the boat becomes effectively lighter and sails faster. I like the idea and lot and hope to play with the design some day.

Here are some more just for fun.

http://www.rclandsailing.com/catamaran/index.html


and if you PM me an email address I can share an excel file that shows performance calculations. It is not mine and I forget who gave it to me (sorry guy).

I also have the lofting instructions for the cat and sails in this pic.

 

[Will Gilmore]

The effect is less heel but you still get lift... so the boat becomes effectively lighter and sails faster.

I have been envisioning that exact idea. Tacking is just a matter of flipping the sail over the mast top. Jibing might be hard on the rig, but amazing.

- Will (Dragonfly)

 

[rgranger]

We should compare notes.... Here is a design I've been imagining for control of the "angle of attack" but I'm calling it an aspect angle (reefing) since it is not exactly an angle of attack or an aspect ratio idea but something in between. The crab claw yards would be strung out between the ends at the top of the "T". On a light wind day, you would let the T rest at 90-deg. I imagine a weight in the bottom of the T so it will have some tendency to want to stand up naturally. As the wind picks up, you can pull in on the reef line and tip the "T" post up and lessen the aspect angle. If the wind gets to stiff, then it is time to collapse the sail. I'm also wondering if you could not use "full battens" on a crab claw that could be sewn in with a "pocket that allows the battens to be tied to the T-post so as to become a spar and you could have a true reef by stringing out he sail on one of the battens instead of the true spar....and lessen sail area that way as well.

 

[Will Gilmore]

Again, your ideas seem to mirror some of mine.
I picture the spars almost accordianing up from either side to reef, but I haven't spent that much time thinking about that aspect. I picture something like a hang-glider connected to the top of the mast. As you pointed out earlier, there would be the ability to generate upward lift as well as driving force. Another idea I was thinking about was making it a lateen rig but setup just this way. The full battens are also an idea I'm considering. Sort of like a chinese fan.
If I get some time, I'll sketch out my ideas and send them along.
It should be noted, I am considering this idea for my ultimate cruiser at about 50' LOA.

-Will (Dragonfly)

 

[rgranger]

It should be noted, I am considering this idea for my ultimate cruiser at about 50' LOA.

-Will (Dragonfly)

you and I have similar fantasies. I have a notebook full of sketches of something I 'm calling my "Cargo Cat". And I have a few computer generated sketches of a sharpie design I've been playing with.

 

[Brian M H23]

I'm confused, how is this different from a sunfish?

 

[Will Gilmore]

I'm confused, how is this different from a sunfish?

If you are referring to the rig style, it isn't. That is a crab claw rig.

- Will (Dragonfly)

 

[Will Gilmore]

I have a few computer generated sketches of a sharpie design I've been playing with.

How interesting that you mention sharper, because that is part of the foundation concept for my idea. The other is a north sea trawler with deck house set aft and bulworks.

- Will (Dragonfly)

 

[rgranger]

Wow

Well you probably already know this book but if you don't... you will devour it. It is a fantastic read

https://www.amazon.com/Sharpie-Book-Reuel-B-Parker/dp/0071580131

r

 

[rgranger]

I also enjoyed this book a lot

https://www.amazon.com/Chinese-Sail...sr=1-2-fkmr0&keywords=How+to+build+a+junk+rig

 

[Will Gilmore]

I haven't read either. Glad to have the suggestions. I'll check them out.

- Will (Dragonfly)

 

[rgranger]

Enjoy

 

[Will Gilmore]

Apparently, there is a new startup company trying to supplement commercial shipping powerplants with sail power. They are designing around the crab claw rig.
https://proafile.com/multihull-boats/article/the-crab-claw-comeback

- Will (Dragonfly)

 

[Will Gilmore]

This is an interesting cruising sharpie around 44'. I'm interested in steel construction, much wider hull and a shallow 'V' bow. I also like the look of a fantail stern, just because. However, I think there may be some performance benefits to the softer exit shape for the stern wake too. That's just a sense that I have. The rigs I'm interested in are: a tall Marconi katch, a katch staysail, or a katch crab claw that flips over the top of the mast (maybe a modified lateen idea I'm developing that works in a similar way). The more I read about the crab claw, the more I like it. Simplicity of handling is about equal with performance, maybe even a little more important. Heavy weather performance and handling is also a big consideration.

- Will (Dragonfly)

 

[rgranger]

I like the rounded sterns of the original oyster sharpies. I think they simply look nice.

 

[Will Gilmore]

The crab claw Ice boat in action:

Here's that flip 'T' crab claw in use:

- Will (Dragonfly)

 

[MisterR6]

Love the soundtrack for the iceboat video. Always was a personal favorite!