Re: Mast Rake and Bend

David Kautz (
Mon, 08 Feb 1999 12:01:23 -0800

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West Wight Potter Website at URL
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On the placement of shrouds, the text I looked through recently
(_Understanding Rigs and Rigging_) indicated that the minimum angle for
place placing shrouds aft of the mast in a "3 wire" setup is 5 degrees
when viewed from the side. This is half the minimum value used for
shrouds when viewed from the bow. The use of spreaders is recommended
when mast height or narrow beam does not allow the 10 degree min. angle
to be maintained. I know that on the P-15 the shrouds are placed
adequately aft to ensure in excess of 5 degress, is this not the case on
the P-19?

Remember too, that when the boat is sailing downwind it is best aligned
with the force vector that is driving it, the boat makes the least
amount of resistance and the apparent wind is lowest. When travelling
into the wind the force vector generated by the sails and carried by the
rigging must be quite large since only a small component of it is
useful, the rest of it going to heel and leeway.

I agree that when going dead downwind with a three wire setup the
compression loads on the mast and the structure below it will be very
ugly due to the small angle the shrouds make with the mast. The tension
on the shrouds, though, is shared between the two, rather than carried
by one with a backstay (this is assuming the backstay is carrying the
load and the shrouds are somewhat slack).

If the point of sail is to have the wind coming over the aft quarter,
rather than directly over the transom, the load moves more to the
windward shroud, but as it does,fortunately, the angle of support
becomes more favorable. A pretty slick system, really.....

Having said all this, let me qualify it by saying that it is all
textbook stuff. As Judy correctly pointed out, I have _zero_ experience
rigging or sailing the P-19 and will quickly defer to those that do. My
earlier post was directed more at exercising caution when tensioning a
backstay to induce mast bend or to prevent forestay sag when reaching or
pointing. I am more comfortable with the added backstay idea if it is
used, as Jerry describes, to support the mast when sailing downwind.

Ain't physics wonderful?

Dave Kautz
P-15 #1632 "Tilly Lucy"
Palo Alto, CA

______________________________ Reply Separator
_________________________________ Subject: Re: Mast Rake and Mast Bend -
Part 1 (WAS potter 19 backst
Author: Non-HP-Magico1 ( at hp-boise,mimegw7 Date:
2/7/99 11:40 PM

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West Wight Potter Website at URL
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I will have to agree with Judy on this issue,(i seem to agree with her
alot). A Potter sailing downwind without a backstay is putting a serious
load on the compression post. The farther foreward the shrouds are
placed, the more pressure is put on the post. On the P. 15 the shrouds
are placed further aft, and this works just fine. I don't recomend using
a backstay adjuster with the lighter mast because it might put a
permanent bend in it. However my friend had a 4 to 1 purchase adjuster
on his P.19 and it seemed to help in strong winds. My conclusion is that
adding a backstay on a P.19 REDUCES pressures on shrouds, turnbuckles,
and on the compression post.
Jerry Barrilleaux HMS 18 # 48 & P. 14
# 564