The Crab Claw - Wharram style - Other style - Videos
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.
Please post pictures and/or videos!! We all love pictures and videos. A fast and dirty model can be very educational and illustrating.
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…
I believe in the schooner crab claw sail, especially with the spinnaclaw kind of easy shunting arrangement.
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.
I will test the sail a lot more when the weather permits. This was a first test of the basic concept, and i am very impressed by the Crab Claw sail.
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.
Please post anything and everything you want in this thread. A forum is/should be a collaborative development platform.
Thanks everyone for encouragement and kind comments on my last proa-model!
Cheers,
Johannes
OK. Here’s what I’ve been working on…
Basic concept here is a tall, narrow crabclaw with the yard seated rather close in. Reason: theoretically better windwardlyness—I think I invented that word, and quicker shunts because one need not move the yard so far.
A couple points. Shunting in Dierking’s method involves a rub-rail on the lee side, for the yard hangs down. Here, the mast is tall and the yard swings in an arc without scraping the deck. This will allow a lee pod or a safety ama. These are very important to me. A rig that won’t allow that is a deal breaker. In the open ocean, a capsize is not an option.
I tried using a boom, ala, “spinniclaw,” but that kicked out the bottom too far and kicked over the top of the yard in a shunt. No good. I can see what could happen in a big wind. Scary when the yard catches at the top of the mast and won’t budge due to wind pressure, necessitating dropping the whole show to sort it out. Meanwhile, big seas smash you from the side.
The huge disadvantage of this design comes from it’s advantage. It is tall. This gives you a better aspect ratio into the wind. But this also raises the CE. Not all that much, though. About the same as a genoa. While one could lower the yard and step it at the end of the boat, this makes the mast stick up high. Again, you have the problem of the yard catching the mast at the top. Reading Chris Grillabong’s review of the Dierking’s T2 persuaded me you really need the yard snug up high on the mast. This makes sense. You just can’t have the yard flopping around.
Well, this design works with the upright yard. Lower, I’d need to figure something else out.
Nevertheless, this is still a claw. The sail takes on that Rogallo wing shape, and with brailing lines, you can still dump power rather than reef. Now for some pix…
1. 18apr13_0315.jpg [EDIT: Got my photos mixed up. This is a shot of my layout for the five foot model. The “wasp wing.” I did not mean to upload this yet. Dang it!]
More to come…
Thought I reduced the file sizes enough, so I’ll have to do this in stages…
2. 18apr13_0338.jpg
Evidently, the bees like my sail! I consider that a good omen.
3. 18apr13_0324.jpg The problem of weather helm, downwind, solved. Q.E.D. A solution derived from a first person accounts of a walap in action run by people who knew how to sail him. I think I have drawn more inspiration from this boat than every other boat combined. http://homepages.paradise.net.nz/garyd/walap.html
OK. Worked out the file sizes. I had my export options set for higher resolution and sizes in Lightroom than I thought. A bit of work in Photoshop fixes that…
4. 18apr13_0338.jpg Couldn’t resist. That’s my Kiki. She thinks she’s a lion. See the look in her eyes? Quite the hunter, she is. Been bagging opossums lately.
5. 18apr13_0345.jpg Here you can really see the geometry. That’s my motorized bicycle in the background. Another hobby.
6. 19apr13_002 This is the MKII version. Lower boom. More power, down lower. CE just a touch aft of center. I did a better job on the tape this time around. Also I used carefully driven screws for jam cleats. That’s a carbon fiber mast, btw. A piece of a fly rod.
Rick,
Good models and some very logical thinking.
I don’t know if you have a copy (or can get one) of Marchaj’s Sail performance, theory and practice. The start of the famous chapter 11 compares the power of different rigs with the crab claw shining through. Later in the chapter many different aspects of the rig are tested. Two things jump out as important factors.
Firstly a range of angles of the rig is tested, sweep angle.
High, medium and low have the yard about 90, 60 and 30 degrees to the horizontal respectively. I will quote, ’ the sail set in a high position is inferior to the other two configurations, regardless of sailing heading angle’. The lowest sweep angle is superior and I would speculate why the traditional rigs rubbed along the vaka leeward gunwale .
A further test involves the curvature of the yard, a relatively curved yard is superior.
Tink
Unfortunately nobody has replicated his results.
Those using crabclaws on proa’s or cats have different findings and lower the rig and angle to depower it.
Ayrs says 60% angle. +-
A big part of the rig seems to be booms that have the ability to bend.
Too stiff and breakages happen.
Rick,
Good models and some very logical thinking.
Thanks much, and I appreciate the gift of knowledge. As we all know—or should—a theory is as good as it works.
Believe me, I am not at all sure I’m on a good track at all. I just know that properly built, cut, and sailed lateen sails are very close winded, so I looked at that shape as a point of departure. Then too, there are windsurfer sails. We KNOW those are very hot. You can see that pedigree in this design.
I don’t know if you have a copy (or can get one) of Marchaj’s Sail performance, theory and practice. The start of the famous chapter 11 compares the power of different rigs with the crab claw shining through. Later in the chapter many different aspects of the rig are tested. Two things jump out as important factors.
There’s a copy at the main library here. I checked it out several times, years ago. Thing is, to be honest, I can hardly remember much in it! Time to read it again, for sure.
Firstly a range of angles of the rig is tested, sweep angle.
High, medium and low have the yard about 90, 60 and 30 degrees to the horizontal respectively. I will quote, ’ the sail set in a high position is inferior to the other two configurations, regardless of sailing heading angle’. The lowest sweep angle is superior and I would speculate why the traditional rigs rubbed along the vaka leeward gunwale .
That’s a great quote, and it gives me pause indeed.
Now here’s the thing, Marchaj did not test a short boomed claw. That was one with a long boom. This would affect results, maybe radically. This is the very thing I’m exploring. I still want the wind to flow off the leech, not the foot. A classic claw, set high, has wind flowing off the foot, mainly, with some flowing off a rather floppy leech. That’s how the Wharram claws set, and I don’t like that. So I guess I’m working a little angle there that might get different results that Marchaj got.
Obviously, the thing to do is to make a classic claw for the same model and compare the results. This sail has a rather tight, hard, leech. I know I can easily control it. The boom in this config lends itself to some rather hard “vanging.” I can set the sail just about as flat as a steel plate. This little model, crude though it is, really taught me a lot.
Also, I’ve discovered that the vertical setup tends to some rather large compression loads on the mast. This makes for greater weight, up higher. Not good! It may be that the classic claw is better. If so, well, once again, I would bow to the ancient mariners and laugh at my hubris. So I have two options. 1. Maybe I’m on to something that might work, in which case I will have made a little contribution to our knowledge, or, 2. I learn that the ancients knew more than I thought, in which case I become a better person. Sounds like a win/win. 😊
A further test involves the curvature of the yard, a relatively curved yard is superior.
On that like “white” as they say, “on rice.” Further, I’ve figured out how to build spars that are progressively more bendy to the ends and progressively stiffer towards the tack.
Cheers,
Rick
“Not Craw, Craw!”
That’s a quote from an old Get Smart episode. The villain could not correctly pronounce any words that had what what they call “liquid L’s.” (Linguistically anomalous, he had no problem with liquid “R"s as in many English dialects.) He was trying to say “Claw.” That was his name. But Maxwell Smart heard “Craw.”
Making fun of an ethnicity whose native language does not include the liquids is bad taste. But making fun of yourself is OK. Thus, introducing the “Clabcraw!”
😊
In the interest of simplicity, I wondered what would happen if I just got rid of the mast and went with what in effect is a cross between a stayed windsurfer rig and a crabclaw. I doubt this is original. I know others have used windsurfer rigs on proas, but giving the rig that crabclaw boom and that ability to brail the sail changes the game. The staying and sheeting is gorgeous. Buckminister Fuller might say, “It is the least number of required tetrahedrons. There is nothing more to take away. You are done.”
I estimate that I’ve cut the weight by a third, and I’ve gained a total simplicity of fore and aft CE adjustment; plus, even snappier shunts, and, may I add, “Let the wind howl!”
Here’s some shots of the rig in light air mode. The CE is actually forward of center…
Rope stays on Wharrams smaller “ethnic” designs.
How would you shunt it tho?
If the aerodynamics are good, it’s pretty much ideal, that last one. Have you seen the brazilian Jangada?
http://i1.trekearth.com/photos/106940/jangada.jpg
Also, I’ll be trying out my scarily “high aspect ratio” crabclaw soon.
http://proa.me/wiki/doku.php?id=tdem_s_boat
-Thomas
I really like your mast-less Lateen/CC rig Rick.
If you can make it stable and controllable you will have very low windage and a lot of ways of tuning the sail for different conditions.
My next CC will be a high aspect schooner with short spinnaclaw shunting booms.
The CC will be the same 120 cm high but only 30 cm deep.
The leading edge spar will be the same wooden 12 mm round spar but the trailing edge spar will be thin preshaped plywood strips. I want a clean release of the airflow, and the aft spar should not bend inwards the sail area, only sideways.
I like your cat!!
Cheers
Johannes
maybe some videos would be interesting:
https://www.youtube.com/watch?v=zfZs9Yts5ug (here you can see P5, which is T2 in fact and Pjoa MKII, which is unique)
https://www.youtube.com/watch?NR=1&feature=endscreen&v=QS0nQNUM4x8 (Baltic breakers)
https://www.youtube.com/watch?v=EDR2g6Vq4kg (Pjoa MKI)
https://www.youtube.com/watch?v=CWF64ipSfhg
https://www.youtube.com/watch?v=QRSDO0U11Tg
and one technical top secret:
https://www.youtube.com/watch?v=nC4TKWAFrxU
ASP - Chinerunner - CC sail upwind
I tested the ASP+CC sail upwind in a soft breeze today. I’m amazed by its upwind capacity. I get it to somewhere around 30 degrees upwind?!? That is pretty amazing for a asymmetric AS hull with a Chinerunner and a polytarp CC sail!
The CC keeps on impressing me!!!
Cheers,
Johannes
Johannes
Looks like a lovely day, thanks for the video, very interesting. Could I ask a cheeky favour, could you put a tuft of wool or similar on the yard so us arm chair sailors can appreciate the apparent wind direction a little better
Thanks
TINK