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S&S Swan Maintenance - Forestay Tension 38
28 August 2008 - 18:07
#1
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billyon
Join Date: 12 June 2007
Posts: 39

Forestay Tension 38
Help please - Have One ton Rig 38 experiencing too much weather helm in 15Kn +.
Using fully battened main and 140% Genoa.
I feel forestay is too loose. Have been told mast should have 10" rake with no backstay on. Currently it is vertical with some prebend.
my opinion is that to rake the mast will give more weatherhelm , and that firstly I should make the forestay tight - but will that still allow me to use hydraulic backstay to blade main + blunt genoa entry in 18+ knots wind ?
original settings/opinions welcome.
Thanks
Alasdair
Billyon
30 August 2008 - 18:01
#2
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The Professor
Join Date: 02 January 2008
Posts: 1547

Dear Alasdair

Would suggest that sail shape has more influence on weather helm than mast rake, and flattening of the sails is very important for keeping weather helm within limits. Consult your sailmaker, or let him show how it is done. You mention a hydraulic backstay tensioner, what loads do you use?

You are right that 10" rake is given on the sail plan, can you achieve that without backstay on?

Kind regards

Lars
31 August 2008 - 16:51
#3
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billyon
Join Date: 12 June 2007
Posts: 39

Dear Alasdair

Would suggest that sail shape has more influence on weather helm than mast rake, and flattening of the sails is very important for keeping weather helm within limits. Consult your sailmaker, or let him show how it is done. You mention a hydraulic backstay tensioner, what loads do you use?

You are right that 10" rake is given on the sail plan, can you achieve that without backstay on?

Kind regards

Lars

Hi Lars
Thankyou for that.
Sailmaker says genoa cut for tight forestay, suggests I talk to rigger. Hydraulic backstay has no guage on it . I have about 1 cm adjustment at mast base so think I will rake it back to whatever that gives, and set up with tight forestay then try to apply bend with backstay to see what can be achieved, before sail trials - what you think ?
Alasdair
31 August 2008 - 19:52
#4
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The Professor
Join Date: 02 January 2008
Posts: 1547

01 September 2008 - 11:44
#5
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The Professor
Join Date: 02 January 2008
Posts: 1547

Alasdair

My reply text disappeared into cyberspace...

The maximum recommended backstay tension is 4200 lbs, but with the long topmast it is recommended that the backstay is slacked off when a spinnaker is hoisted. Could a pressure gauge be added to the tensioner? Without one you do not know the tension.

Lars
01 September 2008 - 15:50
#6
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danielefua
Join Date: 30 January 2007
Posts: 462

Friends,
I do not consider myself an authority on the subject, but I like to quote a paragraph from the immensely helpful Swan Owner´s Booklet for 411´s which you may find in the Manuals Section of this site:

Chapter 8 (Rigging), Mast Rake:
With the backstay slack the mast should stand vertically. With maximum tension applied (see preceding paragraph) the top of the mast should rake aft as given in the sailplan. etc etc

This was a an interesting thing I did not know and learnt only few months ago: according to the original designers, no backstay tension, no rake.

Regards
Daniel, 411-004
03 September 2008 - 12:10
#7
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The Professor
Join Date: 02 January 2008
Posts: 1547

Daniel

Would like to comment that things have changed with the time - today most designers specify rake with the backstay slack. This has to do with aesthetics, a vertical mast appears to lean forward.

For the same reason the mizzen mast needs to have more rake than the main mast

Lars
04 September 2008 - 15:07
#8
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billyon
Join Date: 12 June 2007
Posts: 39

Thanks Guys
Am going to try shortening backstay, lengthen forestay, tighten both up and go for a trial. Next step will be to move mast heel forewards. Am not convinced 10" untensioned rig rake is answer to weather helm
Alasdair
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