Rigging plans

I've been studying the crab claw rig a bit, hoping that it will make sense by the time I launch.  It's very different from Western sail rigs, so a lot of my experience won't apply.  Here are a few of the things I've learned:

Weather Helm
When I learned to wind surf last month, I had some trouble sailing downwind until I understood the physics of it.  As you turn off the wind, you naturally end up with all of the sail on one side of the board, and this creates weather helm - the sail is levering the board around.  To correct on a windsurfer, you center the sail over the board.

Weather helm - the "x" marks
the sail's center of effort

Weather helm corrected.
Note the center of effort is in line
with the hull.

I think the crab claw rig will behave similarly.  If the mast is vertical, all that sail area to one side will tend to turn the boat hard, as shown in the diagram at right.  But if one uses the shrouds to change the mast angle, as shown on the right, the weather helm disappears.

The practical offshoot of this is that I need to be able to adjust the shrouds as I'm sailing, which means I ought to lead those lines aft to the helm.  I'm picturing blocks rigged to the forward outrigger pole, and the lines running from the mast, through those blocks, and back to cleats on the aft outrigger pole.  This is a minor departure from the plans, as Wharram recommends a simple toggle & deadeye arrangement.


Reefing
I mentioned last week that crab claw sails are reefed in an odd manner.  In Western sailing, the sail area is physically reduced by tying (or rolling) some of the sail along the spar or headstay.  The crab claw doesn't reduce sail area at all - instead, there are "spill lines" that bring the spars together and spill wind.

Full sail

"Reefed - the sail is allowed to curve excessively,
spilling wind and reducing the boat speed.

I plan to rig this system on my Melanesia even though it's not in the plans, because I want it to be as seaworthy as possible.  I'd like to be able to sail her in open ocean conditions, and even if I never do, I've had bad experiences right here in our little Colorado lakes with sudden storms blowing up.  Being able to reef in high winds is the difference between being windblown flotsam and a working sailboat.

Practically, this means that I should have four more blocks rigged - two blocks for each reefing line, and one reefing line for each side of the sail.  These lines, too, will be led aft to the helm, where I'll cleat them off.  If you need to reef, that's not a great time to have to abandon the helm station and walk around in the canoe.

Rigging for Load Variations
Because steering the Melanesia depends on the sharp bow holding the water, she's rumored to sail funny when there's no crew to hold the bow down.  Wharram even recommends carrying a 5-gallon water jug (40 lbs) to ballast the bow when sailing without crew!

I've heard of some Melanesia sailors being completely unable to work to windward because of this problem.  But I know that moving the center of effort forward can increase the bow's tendency to slide off the wind.  So being able to change the angle of the mast by adjusting the forestay will be helpful in handling the boat as load changes occur.

Light load, rig tilted forward:
this boat will not go to windward.
The rig should be brought aft to improve
windward performance (I think).

Normal load, rig too far aft:
This boat will tend to round up into the wind,
making it hard to sail in any direction.
The rig should be brought forward to balance the helm.
(I think...)

The practical implications here imply that I need to be able to adjust the forestay, but not necessarily that it needs to be led aft like the other lines.  The only situation I can imagine where I'd want to quickly change the angle of the mast would be if I lost my crew overboard and needed to sail to recover them.  But in that situation, it would probably be best to let the sail luff and paddle to the swimmer.  So here, I'll probably use a toggle and deadeye arrangement like the plans suggest.

Disclaimer
All of these diagrams and ideas are based on "book learnin'" rather than actual experience.  It may be that once I get my Melanesia launched, I find I've got some part of this totally backwards.  We'll see; for now, I think I understand the way the rig will behave, and these are my best guess at ways to improve the seaworthiness of my Melanesia.