The Crab Claw - Wharram style - Other style - Videos
Crab claw can have advantages, and most of this has not been reported before. There are radically different rigs being called crab claw, the wharram style and the ontong java style, replicated on wakataitea, for example, have little in common. Although I don’t mean to dismiss the other, which the owners are pleased with, I only refer here to the wharram style which has a number of aerodynamic and handling advantages over conventional rigs.
1. The sails have an airfoil shape no matter how they are cut, because the leading edge is more vertical and normal to the airflow than the boom. The closer to parrallel the flow is to the spar the flatter the sailcloth becomes in the direction of the flow. No other sail is shaped by its spars like this, but it requires the upsweeping boom. Putting a jib in front of the sail ruins this advantage because such a sail is more efficient with the draft in its middle.
2. Tilting the sail down not only lowers it but flattens it (as explained above), so the sheet load can be reduced, just when it becomes excessive. When the tilted sail is undersheeted it doesn’t become too full because it’s supported by the spars. This is effective depowering when close hauled. By adjusting the sheets and tack controls the sail can be quickly tilted up and down to the gusts. This technique is not for use off the wind.
3. All compression is on the stub mast and all bending is on the yard; a structural advantage.
4. Ketch rig makes real heaving to possible, which is the most powerful technique in all sailing. Ketch rig is also optimal for self steering to weather with the mizzen acting as a steering sail and the larger main set for power. Only crab claw balances the area of a low ketch or yawl mizzen with a top heavy main resulting in an even, close to elliptical, vertical sail area distribution of the entire rig. Other ketch rigs have the preponderance of sail area along the deck.
5. The sails automatically flatten in higher wind speeds because of their exceptionally bendy spars. Jibs inevitably work oppositely.
6. Drag producing halyards, shrouds and mast are all limited to the lower half of the rig reducing weight and windage aloft. The short masts also create much less windage and weight aloft in storm conditions at anchor and at sea under bare poles, also when motoring (doesn’t apply to me). The mast on the windward side of the sail puts its windage in an area of reduced and aft shifted airflow.
7. The aft leeward shroud can be untied, passed between the yard and mast, and retied aft of the sail so that the mizzen can set directly out to the side of the boat with no chaff. This eliminates the adverse affect a mizzen has on steering when the wind is abaft the beam making the mizzen an effective sail on these headings. It is easily done with the sail standing, which is impossible with any other rig. This is an advantage of the utmost importance in real sailing.
8. When the halyard is released the sail can not fail to instantly drop.
9. An effective new mainsail can be easily hand sewn out of polytarp for less than $100, because the spars support and shape the sails. The whole rig is unbelievably economical for the self-builder, the long bendy spars being the hardest part.
10. A runaway halyard can be reinstalled from on deck with a ten foot stick.
Vortex lift is not generated unless the leading edge of a foil is tilted back more than 45 degrees in the direction of the airflow which obviously doesn’t ever happen to crab claw. Ironically leading edge attached vortexes are probably generated by the gaff on a wing sail over the sail’s head.
Reefing can only be done when the sail is completly dropped so has no advantage. It is easier and quicker to put up a separate smaller sail and this will have better shape and smaller, lighter, optimal spars. This switch is easier than changing jibs, and with the short mast results in a better, cleaner reduced rig than any reefed rig, since it carries no bare masthead up at the top.
Nobody should try something really unusual like crab claw unless they are willing to devote their life to experimenting, failing, modifying and analysing it. Definately not for today’s consumer cruiser.From Glenn Tieman on Wharram builders and friends.
I know it’s a cat, but interesting none the less…..
Based on this quoted text from http://proafile.com/forums/viewthread/231/P30/ i think we must look into a ketch crab claw sail for any proa. That is very very interesting. A lot of the properties we are all looking for in a rig.
I hope we can move the crab claw discussion to this thread instead of the Junk rigged tacker - thread.
Cheers,
Johannes
I borrowed a picture from http://www.wharram.com to illustrate what the Wharram crab claw is.
I hope James Wharram likes some free unintended advertisement..
Cheers,
Johannes
I hope we can move the crab claw discussion to this thread instead of the Junk rigged tacker - thread.
Yes. Agreed. Didn’t mean to hijack the thread. Just got going on the topic. This is better. Thanks!
I made a simple mockup of the Spinnaclaw this morning.
Two Spinnaclaws could make a very nice rig for a cruising proa…
Its very easy to shunt and adjust. I have not tried it on a boat. Its to simple. I just wanted to play with it to get a feeling of the forces, how the spars bend and so forth..
Cheers,
Johannes
Is the bottom pole stationary, or does it swing like the original concept?
I really like this!
As a schooner it could be brilliant.
Is the bottom pole stationary, or does it swing like the original concept?
Yes, it swings like the original SpinnaClaw.
I will probably test something lik this soon on one of my models.
As a schooner it could be brilliant.
I believe so too. The text from Glenn Tieman is very interesting. I know it is not the same as the Spinnaclaw, but once i built the crabclaw sail, i had to test to add the shunting pole. It seems to work as advertised.
Cheers,
Johannes
Is your testing “tank” still frozen over?
Is your testing “tank” still frozen over?
No.. I hope to sail a new proa-model tomorrow. I am painting it today.
If everything works out like i hope it will there should be some new Youtube videos posted in a new thread tomorrow afternoon. I am slowly working on my 24 foot sharpie-proa. I don’t like using epoxy indoors when my family is at home, so that limits the time available..
Cheers,
Johannes
I made a simple mockup of the Spinnaclaw this morning.
Two Spinnaclaws could make a very nice rig for a cruising proa…
Its very easy to shunt and adjust. I have not tried it on a boat. Its to simple. I just wanted to play with it to get a feeling of the forces, how the spars bend and so forth.
Wow. I wish I could work that fast. Impressive.
I actually was not able to figure out how Michael’s draft of the spinnaclaw worked from the drawing or the description. You have the whole thing rotating around a single axis? I thought there was this boom thingy that somehow pushed it around.
I too am building a model of a crabclaw-ish idea, but the yard and boom are made of laminated fir, sheathed in fiberglass, so it’s a several day long cycle.
Cheers,
Rick
The pole on the bottom pushes it fwd (fwd on that shunt) to bring the c of e fwd I presume.
Would that be necessary with a schooner set up?
Then I got to thinking that the bottom pole isn’t necessary at all….....
As a schooner, you could reef the aft sail, to move the c of e fwd and gain the benefits mentioned by Glenn Tieman.
Well, I’m not keen on losing the variable aspect ratio capabilities of the traditional claw. Being able to step the end of the yard at different locations, move the top of the mast forward and aft, raise and lower the halyard to change the yard’s angle of attack, and dump power by releasing the sheet, are awesome characteristics.
The pole on the bottom pushes it fwd (fwd on that shunt) to bring the c of e fwd I presume.
Would that be necessary with a schooner set up?
I think that kind of control is very important for a cruising proa.
I like to have control over several aspects of the sails. CE, angle of attack, upward lift of the bow etc..
I think the Spinnaclaw is an easy, low stress, low cost viable option for a crab claw schooner proa.
I have bought 7,5 meter 8 mm thick round wooden spars and a 3 m2 polytarp. I’m way to tired today to make the rigs, so i will have to start early tomorrow morning.
Cheers,
Johannes
I really look forward to seeing the outcomes of your experiments, Johannes. If you have control over CE and aspect ratio, well, then. superb!
It’s morning here in California. I am ripping some fir on my tablesaw to make some spars. We are both chasing the sun.
http://tamamoana.blogspot.ie/2007/08/child-of-sea-ottilia-sailing-in.html
More on crabclaw experience/experiments.
I have built a small Crab Claw sail for my advanced sharpie proa. I hope I can test it tomorrow.
I have never built a crab claw sail before, so I hope i have made it correct.
I want to learn how to sail a simple crab claw before i start experimenting with schooner and spinnaclaw variations.
There is so much to learn….
Cheers,
Johannes