[Public-List] Spreader Lengths

[Bill Wallace]

According to Brion Toss in the Complete Riggers Apprentice, the shroud angle should be at least 12 degrees, and the spreaders no shorter than 40% and no longer than 50% of the boat beam at the chainplates.   He also suggests the need be to less than vertical in order to prevent snagging things alongside (eg a raft up, being tied up at low tide to a concrete wall etc).

The beam at the chainplates is about 8', so spreaders no longer than 48" and no shorter than 38 1/2".  The spreader height is about 19' above deck, 17' below the mast head if I remember correctly, and that gives an angle for a 40" spreader of about 12 degrees.  The 36 3/4" spreaders give an angle of about 11 degrees - a bit small, but definitely workable.

The angle of the shrouds from the chainplate is about 2 degrees for the 40" spreaders and 3 degrees for the shorter spreaders.  The longer spreaders will increase the load in the lowers, and will increase the chance of losing the mast of the lowers let go. However, they decrease the tension in the spreaders and decrease the vertical compression of the mast.  The mast will probably be a bit stiffer and you will point just a bit higher.

Overall - if you aren't taking your boat out on longer blue water trips and don't tend to sail during strong storms, it sounds like a good choice.  If you are cruising long distances far from help, then perhaps the shorter spreaders would be better, or else perhaps consider slightly stronger lowers (perhaps 1/4" lowers - also convenient for having only 1 size to manage.)

If you get Brion's book, the formulas etc are all in there to figure out spreader loads, mast compression loads etc - it isn't that hard to draw up a diagram for a simple boat like the Alberg 30, and then figure out for what you are doing what setup you want.

Bill


----- Original Message ----
From: Michael Taylor <m_tayau at yahoo.com.au>
To: public-list at lists.alberg30.org
Sent: Mon, March 29, 2010 5:24:33 PM
Subject: [Public-List] Spreader Lengths

I am ordering new aluminum spreaders from Klacko spars in Toronto.   Danny makes them up as an aerofoil design 40" long.  My old wooden spreaders are 36 3/4" as are others I discovered in the archive.  I was always of the belief that the combined two spreaders, mast, spreader base widths should be equal to the distance between the two lower shroud chain plates so that the shroud runs vertically down from the spreader tip to the chain plate.  

Does anyone agree with this or is there something that I have not taken into account?  I have just emailed Danny also but I have not given him time for a response.  

Thanks

Mick



      
_______________________________________________
These businesses support your Association:
http://www.alberg30.org/store/A30supporters.html
Please support them.
_______________________________________________
Public-List mailing list
Public-List at lists.alberg30.org
http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org



      __________________________________________________________________
Make your browsing faster, safer, and easier with the new Internet Explorer® 8. Optimized for Yahoo! Get it Now for Free! at http://downloads.yahoo.com/ca/internetexplorer/

 1269903670.0