The Crab Claw - Wharram style - Other style - Videos
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….
I must say I’m impressed at the speed at which you work. Also, I agree with what you decided: to first get a feel for the basic design before you experiment more. I agree with that philosophy.
I am, however, violating that myself… a bit.
The problem is my spar-making procedure is probably overly elaborate. I have been laminating spars of fir. Only today will I be sheathing them in very thin fiberglass—the kind used on airplane models. This means it takes me four days to build a spar, for I have two, twenty-four hour waiting cycles between cutting, shaping, and finishing. The results are very pretty, to be sure, but it means I have to commit to certain designs and stick with them.
I wonder if I am just building elaborate failures.
I like the way you just try to eliminate every possible complication and go straight to the essence, Johannes. Good luck on your tests. I should mention that without a backstay, your yard may experience a bit more yard compression than the classic, Oceanic rig. This may affect the sail shape. On a small model, it probably won’t be noticeable?
@Alex, great link. I’ll read it tonight when I come in from work.
Cheers,
Rick
A bit more AYRS reading here
http://www.ayrs.org/Catalyst_N33_Jan_2009.pdf
http://www.ayrs.org/Catalyst_N31_Jul_2008.pdf
TINK
Thank you Tink, Alex and Rick!
That is very appreciated information. I have a lot of reading to do…
I just had a ruthless and brutal lession in the power of the Crab Claw sail…
I could not controll it at all! The proa wanted to fly. I had to hold it down to the ground with force. The mast and spars bended soo much i was surprised that they did not break. The wind snapped several cable-ties, so the rig just collapsed. One time the sail flew like a kite suspended from the haleyard.
I got it into the water once, and as long as the sail was stalling the proa just skidded downwind sideways. When a wave pushed the hull so that the wind got a 10 degree angle to the sail it just flipped upside down so fast i could not react at all.
I tried to hold the sail in my hand to get a feeling for the forces at play… I was mighty impressed. It is very very powerful!!!
It seams to have a very strong lift from about 25 degrees angle to the wind. At 45 degrees I had to let it go or else the spars would have snapped.
Its a beaufort 5 wind today, wih strong gust on top of that. I suppose that is hurricane force winds for a 4 foot proa.
The sail is 0,4 m2. The proa is 121 cms long and weights 2,4 kg. I believe that is scalable to a 40 foot proa with a weight of 2400 kg.
Cheers,
Johannes
The problem is my spar-making procedure is probably overly elaborate. I have been laminating spars of fir. Only today will I be sheathing them in very thin fiberglass—the kind used on airplane models. This means it takes me four days to build a spar, for I have two, twenty-four hour waiting cycles between cutting, shaping, and finishing. The results are very pretty, to be sure, but it means I have to commit to certain designs and stick with them.
I wanted overly strong and laminated spars today. Even if it takes time, all the work is a great way to learn and get a feeling for the materials.
The only wrong is NOT building anything.
I like the way you just try to eliminate every possible complication and go straight to the essence, Johannes. Good luck on your tests.
Thanks!
I like to keep things as simple as possible. 10 percent simplification = 50 percent higher probabilty it gets built and used.
Cheers,
Johannes
I have been playing with my Crab Claw Sail setup. I added a “spinnaclaw”-boom just to see how it played out.
I think the Spinnaclaw is great! It makes it easy to adjust CE, angle of attack of the leading edge of the sail, aspect ratio and the amount of upward lift of the bow. I have not test-sailed this yet. I hope there is better (less) wind tomorrow. I still need to build two new smaller crab claw sails with slightly higher aspect ratio.
I believe the schooner spinnaclaw could be a very versatile and powerful rig with lots of fine-grained control over many aspects of its function. It seems very fast to shunt (based on a semi-working beta model)
I hope I can post some more pics and/or videos tomorrow.
Cheers,
Johannes
Very cool! Maybe if you bring the fore/aft stays out to the ends of the hull, you’ll be able to bring the tack far enough to windward to reduce weather helm downwind…very interesting!
Great, looks like lots of control and if you accidentally let go of spini guy it would all flap down wind safely TINK
Wow, Johannes, those are some pretty exciting test results! I would consider them a success.
Frustrated by the slow pace of the large spars I’m making for my five foot model, and seeing how quickly you were working, I decided to cobble together a one-fifth scale mock-up of the rig, using a crude, roughly proa shaped, sheeting base, solid spars, and a clear, polyethylene sail. This, so I can test out the staying, sheeting, and shunting arrangement. I got it all built in a couple hours. It’s sitting on my desk in a pile now, for I need to re-tie everything. So thanks for the inspiration. Divide and conquer!
I expect to have a photo to upload by the end of the day.
Also, @Tink and Alex. I read all that stuff. Good info.
Cheers,
Rick
Hi Johannes
Great work, I just read about your tests with the crab claw. I’m working on the same concept for my proa, a schooner rig could be perfect for the crab claw on a cruising proa. As you mentioned the crab claw is very powerful, (I have actually flown a delta wing in the 90: s and it’s amazing how much weight they can lift)
that’s why it’s the beauty of having two sails, you can make them each smaller and easier to handle as I mentioned in one of my earlier posts…
Anyway, I can’t find many examples of a crab claw on a two masted schooner. My question (or rather thoughts) is, wouldn’t it be easier to shunt a crab claw on a two masted proa? This way one shouldn’t need to bring the sail all the way over to the other end. Instead one just need to swing two slightly smaller sails around each mast, the work is done at the wider part of the deck so no worry to loose balance and fall in the drink. I know the issue about the balance of the CE but when sailing with two sails one can easily adjust the sails, since we are not talking top speed I have no problem about reducing one of the sails.
I found another option that could be interesting, have a look at the tack tackle on my earlier posts…
http://proafile.com/forums/viewthread/261/
In this version the boom is very small and instead one has to adjust the tilt by means of the the tackles.
Matz
Oh Dear,
It seems that the extended post I wrote exceeds the 6,000 character limit of this forum. But it is all relevant, so I am starting a new thread…
Best, Rick.
[Never mind. It seems I cannot even post that. There is a global 6,000 character limit. Time to do a re-write. Sigh.]
Since I have done a whole lot of flying with a delta wing in the 90s and later on even flown paragliders where your life depends on knowing the behavior of the wind, (not least when going in for landing)…. I want to share an important aspect about the wind that you all perhaps already know.
The crab claw and wind gradient… (not to be confused with “gradient wind”)
You probably know where I’m going but imagine how the cc is designed. Compared to an Bermudan sail the cc is more like upside down and has its largest area up where the wind blows, Right down at water level, wind speed is effectively zero. The closer to the water, the slower the wind, this is the wind gradient, caused by friction between the wind and the water surface and its waves.
This is important not least when going downwind with the sail tilted up as the cc catches the wind up there even in very light winds. At the height of 6 meters the wind is approximately 4-5 times stronger than the wind at sea level.
Also when going windward, the apparent wind will differ along the mast. This is why the sail must twist, allowing its angle of attack to remain relatively constant to the apparent wind as that apparent wind frees off with increasing height above the water. With a cc this is one more reason to why the yards must be able to flex. (A Bermudan sail would just twist since its free to rotate up there).
If you have a look at the diagram below you will notice how the gradient increase fast up to about 3 m height and above that level it is rather modest.
Proa with simple Crab Claw Sail
I am extremly impressed by the Crab Claw Sail!!!
It is a very powerful rig. It seams very tolerant and powerful, and it want to sail upwind. There is some bow-down tendency but it is quite overpowered in this windstrenght, so with a more appropriate size of sail it should not be a problem.
Now I have to build a model of a schooner spinnaclaw version of this.
Cheers,
Johannes
Good videos - still doesn’t look very warm tho!!
Glad to see you’re not standing in the water anymore.
Be interesting to test the sail angled down more in those conditions.
I like this latest version of the ASP.
Great videos Johannes; it must be very rewarding to see the model sailing so well!
One of the real beauties of the crabclaw is that if you cant the whole thing aft by some amount (by moving the tack further forward, shortening the mast hoist, or some other method) the sail will create a more vertical thrust vector and actually try and lift the bow to help counteract the simple sharpie hull’s tendency to look down and trip over her toes! The Australian skiffs with spinnakers on extremely long bowsprits are an extreme example of this at work.
Great stuff, and congratulations on a little victory Johannes.
Thanks for the vids, Johannes. I love the way the claw just wants to find the wind and sail straight. Yeah, looks like lowering the rig might have helped in those conditions. Funny, how you thought the sail was too small at first. Not so, evidently. When I chugged the numbers for your model, I got a Bruce number of just over 1. Interesting. Very interesting.
Last night, I got frustrated trying to post. I discovered I had to do a re-write of an extended essay on sail design, but I was too tired to start over. Still, I do have pix of my new design—not a sailing model, just a way to play with the sail, sheeting, shunting operation, etc. I’ll try again tonight when I come in from work.
Again, Superb!
Cheers,
Rick