A Photo & Discussion Forum for Wharram Design Enthusiasts
Hello all. Are there any Crab Claw sailors out there that have any feed back or design curio's about their rigs? If so,then out with it! I am setting up my Tangaroa mk4 with one and would like to know what others have done.
Yeah mate same here. I may do it with a Narai MK lV.
Well l've done one,just gotta see how she sails now. I know two previous owners of your boat btw.
check out wakataitea
hi -- i have had 3 wharrams (tiki 21, 26 and a tangaroa 36). i now have a jarcat 6 for simple trailering and more acommodations (age happens!). i intend to change the jarcat to a delta (flat crab claw) rig as it would be easier to put up and use. two prior wharram tiki 26 owners that i had known (both passed) experimented with crab claws and thought they worked reasonably well and then began researching the correct 'formula' for them. after their passing i continued that research and have deduced quite a few proportions and measurements for the delta design. the current research is very close to what my friends thought they should be for best overall useability and performance. a summary of my research follows.l
first, please read marchaj's work on rigs. he includes excellent info about crab claws and his drawings, while small are accurately scaled. i have also researched crab claws from other sites and books and scaled drawings from books on polynesian rigs. there is a huge diversity in crab claws but there does seem to be a consensus about the best size, shape and measurements. obviously some specific configuration may not be possible on some boats but if one keeps within reasonable parameters this should all work well. note that marchaj also discusses wing sails in the book. when hanneke and james were here in 2012 we discussed the size of the sock for their wing sail. it was believed that the size of the pocket should be about 3x the circumference of the mast. the bigger the sleeve the better for air flow.
marchaj indicates that a crab claw, on some points of sail can be up to 30% more efficient than a similar sized bermuda rig...hence, one might conclude that a 30% smaller crab claw will be equal to a much larger bermuda rig. subsequent research about delta shaped 'claws' (i.e., flat, no pocket) can add another 10% efficiency to that. pretty amazing!
i have also pondered how a wharram would work cat rigged using an unbattened sail and a wishbone boom. i have tried this on another multihull and it worked very well. similar to a nonsuch monohull.
on my jarcat i'll be using an A-frame rig, not a single pole. i believe this will produce less turbulence on one tack. it will also be easier to rig as it will be designed to fold down for low bridges, easy and quick trailering and stowage for anchoring (using a bimini) if needed. also, i have a 'tack track' (essentially a forward traveler) on the jarcat. that will allow me to move the sail in a wide arc and still keep it flat (taut) without much manipulation of the sheets.
here are my basic findings (all measurements would be 'as close as possible' to these). all machaj drawings match these numbers:
.approx distance of mast from bow and boat length. 1:3
.booms to hull length: 1:1 or possibly 1:1.2
.angle of lower boom off deck: 20 degrees (mine will have to be 25 degrees due to a cabin top on the jarcat)
.included angle of upper boom to lower boom: 30 degrees (note, my friends found that 45 degrees is too much!). machaj's and others drawings show 30 degrees.
.curvature in sail (pocket): many show a pocket but later research shows that a flat delta shape is better.
.the 'bend offset' of the booms to length of the booms: 1:20
.if using bridles to get the 'bend offset' in the booms the upper and lower halyards and sheets should be as close to 60 degrees off the deck as possible and hopefully in line with each other.
.i will be using aluminum sectional tube for the booms and am pre-bending them. hence no bamboo. if using bamboo there should be a taper in the bamboo from the bow to stearn about of about 3:1 but i have not researched this fully.
.on a wharram the base of the A-frame, if that is used instead of a single stick, will be wider than on my boat thereby enabling even better sail position for downwind sailing and a greater range of angles to the wind.
.a delta/claw horizontal position: the best overall placement of the claw is that 20 degrees off deck. you can increase speed by making that angle more by pulling the vertically up higher and can de-power by allowing the sail to go more horizontal (i.e., increasing the sail angle off the deck).
.i believe i can make all the sheeting controls from one single continuous line and that it will also allow reefing or lowering the sail without the need for adjustments as it is done.
that's it. it will probably be a year before i get to try this. i have the alum tubing (am using telescoping flag poles for the A-frame so it will be easier to stow when needed). but all the numbers are within reasonable parameters and all work together well.
if anyone has more or contradictory info and research, please post it.