mast rake

Moderator: GreenLake

mast rake

Postby jdoorly » Fri Jun 17, 2011 10:50 pm

I was bothered by excessive weather helm last year; it was a problem for my auto pilot which needs a balanced helm. I started by adjusting the mast straight up (0 degrees rake) and was shocked, shocked I say at the high amount of lee helm the boat now exhibited. I simply could not point the boat at any upwind coarse.

Then I read a discussion on this forum about rake and vectored over to North Sails Daysailer tuning hints. I tried my best to convert their DS1 data (distance from band 3 to transom 25.0', and from mast base to transom 11'1/2") into DS2 data but really can't be accurate with out more data... (not to mention my mast is only 20' 1/2" instead of 20'6"). But I plugged in some fudge factors and conjectured that a mast should rake aft about 6.5 degrees. I wasn't able to implement 6.5 degrees, but only 5.75 degrees due to the shroud turnbuckles bottoming out and the boom coming in contact with my boom gallows. However, I was very pleased with upwind performance in 8-10 kn breeze. In light air conditions there was lee helm upwind and when a 25kn gust caught me with the UPS up on a close reach she rounded up smartly and I was glad of it.

Now I plan on putting a 1 to 2 inch spacer under the mast base so the boom won't touch the gallows and I can have some adjustment in the turnbuckles and will then try to fine tune it.

When I look at the mast rake it looks like it's raked too much- like the schooner America! But so far so good...

Anybody know what is optimum for a DS2?
DS2 #6408 "Desperado"
jdoorly
 
Posts: 379
Joined: Mon May 17, 2010 2:24 pm
Location: CT

Postby K.C. Walker » Sat Jun 18, 2011 10:35 am

I would guess that each boat is somewhat unique because of all of the variations. I think your approach is right on. That is, get in the ballpark and then fine-tune it. With everything set "normal" for close hauled and keeping the boat fairly flat you should have a very slight weather helm at 8-10 kn actual. Under the same circumstances if you have a fair amount of heel you would have weather helm.
KC Walker, DS 1 #7002
K.C. Walker
 
Posts: 1335
Joined: Sun Jul 06, 2008 10:50 pm
Location: North Stonington, Connecticut


Return to Rigging

Who is online

Users browsing this forum: No registered users and 1 guest