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Mast rake #150693
07/27/08 09:54 AM
07/27/08 09:54 AM
Joined: Sep 2005
Posts: 893
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waynemarlow Offline OP
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waynemarlow  Offline OP
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Joined: Sep 2005
Posts: 893
A question which I can't seem to find on a search of the net, how do you determine what mast rake you should have on your boat, I've tried quite varying degrees of rake and to be honest you have to move it a long way back before any sort of lee helm starts to appear. My guess is that there must be an optimum relationship between the balance of boards and rudders before things are not nuetral and the boat crabs up the pond.

Is there any sort of visual aid like the wake perhaps. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />

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Re: Mast rake [Re: waynemarlow] #150694
07/27/08 03:51 PM
07/27/08 03:51 PM
Joined: Sep 2007
Posts: 571
Hamburg
Smiths_Cat Offline
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Smiths_Cat  Offline
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Joined: Sep 2007
Posts: 571
Hamburg
Depends on the boat. On boats without boom like a Dart 18 it is very important. On boats with boom it is less important.
If I minimise the weatherhelm on upwind courses, my boat is very easy to fly on one hull, but on downwind legs with and without spi the leehelm is a bit strong. I balance between these two effects. I didn't measure the speed, but I don't feel a difference.

Cheers,

Klaus

Re: Mast rake [Re: waynemarlow] #150695
07/28/08 08:57 AM
07/28/08 08:57 AM
Joined: Jun 2001
Posts: 548
MERRITTISLAND, FL
Matt M Offline
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Matt M  Offline
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Joined: Jun 2001
Posts: 548
MERRITTISLAND, FL
Quote
A question which I can't seem to find on a search of the net, how do you determine what mast rake you should have on your boat, I've tried quite varying degrees of rake and to be honest you have to move it a long way back before any sort of lee helm starts to appear. My guess is that there must be an optimum relationship between the balance of boards and rudders before things are not nuetral and the boat crabs up the pond.

Is there any sort of visual aid like the wake perhaps. <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />


Unless you have a boat with a hugely misplaced front beam, the mast rake should be set to optimize the sail. Most sails, especially the newer big heads, work best when the leach is as close to vertical as possible. Boat ballance vs mast rake is one of those items that gets a lot of press time and the 2 have very little to do with each other.

The sail is your engine, set it up to work best. By moving the mast back and forth you move the center of effort and the center of gravity on the boat. It takes a huge adjustment (a lot more than is available on most boats) to move either of these more than a couple of inches. On a cat, even a heavy F18, the crews weight is so high compared to the boat that by moving your sailing position a couple of inches easily makes up more than any swing in the mast position. In a perfectly ballanced boat the center of resistance is located at the same place as the center of effort. Again, because you can move your ballast around, the center of resistance also is significantly more adjustable than the center of effort.

Talk to your sail maker about how much rake they recommend. Next spend some time making sure your crew position is correct and your sails are trimmed as they should be. Those 2 things are the main cause of the boat being out of ballance. IF you still have a ballance issue after all that, THEN look at adjusting your rudder rake. The Blade because of running 3 sail combinations, the hull length, boat weigh to power and very short tiller arms, is by far the most sensistive boat I have been on as far as trim. Sail weight and crew trim is critical to keeping the boat ballanced and going fast. It makes a difference in any boat, but is a lot more noticable on this platform.


M


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