Blocks, Sheeting Angles and Headsails

I've been doing a lot of research lately on sheeting angles and fairlead positions to try and maximize the pointing and function of headsails on my AI. I know this won't interest everyone, but I find it all fascinating. Figured others may find interest too.

I came across what was for me an unfamiliar term "sheeting angle" in some reading I was doing. The more I looked into sheeting angles I realized that they hold secrets to getting the most out of our headsails whether its a jib or the Hobie spinnaker. I also learned how to best position your headsail block/fairlead to the boat.

Turns out, the sheeting angle is just the ideal angle of the headsail's bow attachment to, to the attachment point of the sails sheet to the boat. This angle should be 7-10 degrees off a line bisecting the boat to maximize your ability to point.

Next I found that if you take a point 40% up the luff and create a perpendicular line back to the hull, you can determine the best point to attach the sheet to the hull so that you maximize the ability to create the ideal tensions on the leech and foot of the sail when sheeting.

This is oversimplifying everything but if you do both of the above, it allows us to determine the best attachment point of the headsail sheet to our boats. Here is a nice article that goes into more detail and explains it better than I can.

http://www.sailmagazine.com/racing/rega ... -sheeting/

Next step was to take this new (to me) information and plot out the angles and points on an AI. Below is what I came up with. The orange dots represent where I have placed my leads or cleats.



The ideal sheeting points are for a 100% Jib and for the stock Hobie spinnaker (sailing upwind and pulled tight) if you use a 10 degree angle. Narrower angles down to 7% become problematic for the spinnaker because our boats don't have ideal attachment points for the spin cleat at that angle. A larger jib than 100% needs to be sheeted with blocks more aft on the hull. In an ideal world we would have adjustable lead blocks that moves the sheeting point forward and back or even devices like a jib travelers/inhaulers for lateral adjustments for certain angles into the wind. But these measurements make for a great place to start with stationary blocks on the AI.

So I made these changes on my AI and I noticed definite improvement in the ability to point higher and to get the ideal tensions on all sides of the headsail. I have not played with it enough to know if my pointing is any better than the main alone, but I suspect I'm close to having achieved that.

Here is how I am currently using a plastic Hobie clip to act as a fairlead on the front crossbar. I plan to add a pad eye or two along the top gunwale for different jibs that I use. The clip just gets moved from one attahment point to the next as jibs are changed out.



Finally, here are some nice articles on adjusting sail trim on headsails. I realize now that I tended to set my jib in accelerated trim and leave it. I should have trimmed it back into normal trim once up to speed. Learning as I go.

http://www.sailingworld.com/how-to/boat ... b-and-flow

http://sailingmagazine.net/article-17-s ... m-101.html

_________________
Greg

2016 AI - Spinn & Jib

“Out of sight of land the sailor feels safe. It is the beach that worries him.”
– Charles G. Davis