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Tuning Issues

Started by jeremyf, 11 Jun 2009, 12:58

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jeremyf

I have now started to re assemble Grimalkin and am thinking about issues like mast heel position / jib sheet angle etc etc.
I have read the 'tuning guide' with interest and will use that as my bible but can anyone start me off with some 'proven' settings for a Cheshire Cat ?
In particular :-
Mast heel position say measured from inside transom
Spreader height above s/l, width and depth.
Rake
jib fairlead position from centre line and transom or bulkhead
 
I hope a reasonable start point may avoid 'gruyere cheese' syndrome at a later date !

Antony (Guest)

Jeremy,
The core tuning guide that almost all people start with is the article by Dave Peacock (even though it was for his Bagggy), perhaps with the added benefit of the P&B Design 8 'numbers'.  Where these are applicable i suggest that you use them as a starting point as you will not be too far wrong.
Antony

jeremyf

Thanks for that.
Sounds sensible.
jeremy

Derek

Jeremy / ANthony,
 
Just one comment about Dave's numbers.
Baggy, in a particular Dave's and Rob's were built with a very short shroud base to allow the boom to swing further with the rig tension still on. If you take a line from the back of the mast to a line between the shroud points, this was just 10" for these boats. They were such a step in speed that most subsequent boats had a fairly short shroud base as a consequence. Earlier boats, like the Cat will have had 12 - 14" as a shroud base and so the spreader dimensions in particular will need a bit of adjustment to reflect this. As a suggestion for a starting point, put he mast in the boat without the spreaders connected and set the rake and tension as desired. Then mark up the spreaders to give you perhaps 1½" outward and ½" forward deflection of the shroud. I seem to remeber these numbers being about right for a proctor "C" or a Kappa. Then put it on the water in fully powered up conditions and see how the boat points and how it bends and make adjustments from there. I am sure someone else will offer updated advice if I am wildly wrong.
Good luck
 
Derek
 

jeremyf

Thanks for that Derek, I will give that a try.
Jeremy