"noexpert" wrote in
:
Hello,
need to get some data on load figures on masts for sail boats.
Various pulling forces from forestay, halyards,shrouds , backstays etc
plus pushing forces from spreaders
act on the mast.
Need some real numbers in lbs for standing rigging as well as under
sail for variable conditions.
Of course each boat and size have different value ranges.
Have looked into various books but real data are scant.
Can somebody help with links or bits of wisdom? Just assume and make
references to boat length , mast heights etc.
help is much appreciated
thanks mik
First thing is the 'tuned' values fro the standing rigging. What seems
to be an industry 'rule of thumb' for tuning for 15-20knt winds is as
follows.
12% of breaking strength for shrouds(some set the back ones at slightly
less) 15% for the fore and aft stays.
The actual lbs will vary according to the cable diameter.
A good source ofr the breaking strength etc of cable is from Loos & Co,
who also produce and sell a relatively cheap gauge that is easy to use.
But if you do not own one then (on NEW or nearly new cable only) you can
do the following
sounds a lot trickier and involved than it really is.)
First find out the amount of stretch that your cable goes to at breaking
load. This will be given in percentage. Also the actual load breaking
strength, these are correlated.
Begin with the fore and aft stays, then the lower shrouds and work
upwards symetrically from side to side.
Take a ruler (metric) and mark exactly 1 meter on the cable using a
magic marker or such. one mark begininng and one end. Place these
where the top one is as far up as you can comfortably reach. Now from
the lower(0) mark going upwards toward the 1 meter mark, place marks at
each mm for at least 20 mm. This is done with the cable just barely
taught, just a tad beyond sag.
Now start tightening the turnbuckles, Every few turns measur the two
OUTSIDE marks the start and the beginning you will notices that at
exactly one meter on your tape that the two marks are actually reading
LESS. In fact each mm shorter equals 1% of stretch. At about the one
half of desired load move to the opposite side and bring that cable up
equal to the first. Also check EACH time for the correct mast
alighnment so you don't get any bows in the mast.
Just keep doing this until you are finished.
Now back to your load on the mast question. Add all these individual
cable loads up and that is your static load. The working loads will be
this amount plus those placed by the sails...which of course depends
upon wind strength etc. Lots of places to find wind load information,
just remember that the force of the wind QUADRUPLES when the speed
doubles.
It's late, I re-read this and seems okay, but for christs sake double
check it.
g'Luk