| No doubt Forespar's recommendations ARE very conservative. It is not in
their interest or yours to have a spinnaker or whisker pole fail. While
you may not intend to sail in strong winds, squalls, gusts, wind shifts,
and the like do happen.
The safe load on a long, slender column (eg, a whisker pole) is
proportional to
1/(L/d)**2
where L is the pole length and d is the pole diameter.
As an example, a Forespar LC13-24 line control whisker pole has a minimum
length of 161" and a maximum length of 271". The tubing diameters are
3.5" and 3.0". At maximum length the safe load is only about 35% of the
safe load at minimum length (assuming a constant 3.5" tubing diameter).
Decreasing tubing diameter makes a large difference. My 15' spinnaker
pole is 3.5" in diameter. The same length pole with 3.0" diameter tubing
would only be about 73% as strong.
Keep in mind, too, that the wind force on a sail is proportional to
A*(V**2)
where A is the sail area and V the wind speed. In a wind gust, the wind
speed typically is 40% higher than the average wind speed. That is, in a
gust, the wind force doubles. At a guess, the load on the pole will
double also.
So, it would appear that pole failure is most likely if you are using an
adjustable length whisker pole at or near maximum length with a genoa and a
strong wind gust occurs.
Failure could be shearing the inboard pole fitting off the mast or the
pole could buckle, both abrupt failures with no warning. If you happen
to be at the mast at the time, the result could be disastrous to you.
Assuming you use a pole length equal to 10.75*1.3 = 14', it appears that
the Forespar 8'-14' pole (2" tubing diameter) would be about 64% as
strong as the 10'-18' pole (2.5" tubing diameter). At a length of 18'
the 10'-18' pole has about the same safe working load as the 8'-14' pole
at a length of 14'.
I'm not sure that any of this really helps choose a pole, and I have no
idea what the margin of safety is. What it does indicate to me is that a
small diameter pole is likely too weak to be safe, especially given the
possible consequences of a failure.
Anyway, we opted to buy a fixed length spinnaker pole with a bayonet
inboard fitting (outrageously expensive but very strong) rather than an
adjustable length whisker pole. But, this was before Forespar developed
their line control poles. Today, I might buy a line control pole, but
then again I might not. Our 15' pole is hard enough to handle as it is.
Any additional weight would not be nice.
Alan
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| I have a line control pole, and it works very well. I like the ability
to adjust the length when sailing, then shorten it before I take it off
the sail.
Alan, I mounted my pole on a track on the front of the mast. No
lifting, better control, less foredeck dancing. The pole is rigged with
a topping lift and continuous downhaul, uphaul. To set the pole I just
release the bottom and pull the inboard end down. The best rig I have
seen was on Grant Saviers boat. (Oyster 42). Two downwind poles on
either side of the mast. Flying a spinnaker, we put out both poles, and
tacking was ho hum, just adjust the new guy.
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| re .2:
Ah, great minds thinking alike ..... I've rigged our spinnaker pole just
as you have, and this arrangement does work well for the most part.
Nonetheless, it can be a little problematic if conditions are at all
rough. I find handling the pole and the uphaul/downhaul requires two
hands as the outer end wants to bash into the liferaft and dorade vents
on our boat as the inboard end goes up the mast.
Were we to get a second pole, I'd get a shorter, lighter pole for using
in running downwind with the staysail and reefed main in heavy winds. We
were in one gale when this would have been really nice.
Alan
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