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Mast Rake

Postby Russell on Mon Sep 27, 2004 2:00 pm

Having newly entered the class I am playing around with rake and step posn.
I noticed that someone said stepping the mast max aft is prob best , current step posn is 2670mm (so fairly close) and set up for approx 200mm rake (using c/board case as the horizontal)

Have plotted centroid of main and then transfered onto boat and this lines up with back edge of c/board case, ie indicates boat should genearate small degree of weather helm. So far so good.

However this set up looks all wrong looking back at other boats.(ie the fast ones) Boom end seems too high off transom. Approx 500mm .

Proof is in the sailing and time on the water as they say. But would apprec anyone's comments
Russell
 
Posts: 3
Joined: Thu Jun 17, 2004 2:07 pm

optimal mast rake

Postby fitzwarryne on Mon Sep 27, 2004 9:18 pm

There have been some good responses to this question in an early topic on this forum which should be required reading.

The consensus is that extreme forward or aft mast step position makes no difference as long as the rake used gives balance, the more forward the mast step the more rake is required.

If you are using rake measured in actual terms from the black band, it is critical to have the boat set up in the fore and aft sailing position- rather tedious. It is more practical to measure black band to transom. While it varies from dinghy to dinghy due to slight differences in shape, for an individual dinghy it is a precise measuring distance easily measured.

Having just acquired a Sabre, I tested out different mast step positions and adjusted the rack for balance in 8-10 knots of breeze. I used 266 and tested four sails, each had a different required rake for a mast step position. This was due to different sail shapes and mainsheet tensions to get the tuffs flowing.

To make life more interesting, there are of course numerous reasons why the optimal rake will vary. Just a few are fresh/salt water, weight of crew, flat/choppy or swell conditions, design of boat-mainly rocker etc..

My conclusion was that with more rake you could centre the boom marginally more in light-medium conditions, possibly a slight advantage. However, I ended up with the furthest aft position being better for me. The reason, I am tall, heavy, and old thus the more room to duck under the boom while tacking the better!

If the dinghy is balanced it will be potentially fast, the rest is cosmetic.
fitzwarryne
 
Posts: 58
Joined: Fri Jul 09, 2004 12:18 am
Location: St George, Bermuda

Postby Russell on Thu Sep 30, 2004 10:55 am

Thanks for response, one of the things that emerges is getting consistency in accurately measuring true rake.
Russell
 
Posts: 3
Joined: Thu Jun 17, 2004 2:07 pm


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