West Wight Potter Owners Home Port _______________________________________________________________________________________________ |
| Technical Information Using a GPS and Wind Gauge to Test P-15 Sail Trim and Sailing Skills by Bruce Hood |
My friend Peter Allison and I went sailing a few days ago out at Black Butte Lake near Orland,
California. Black Butte, is a reservoir lake created by the Army Corps of Engineers surrounded by
rolling grassy hills, and some seven miles long, with a striking black basalt Butte looming
over the shore near the Eagle Pass launch ramp.
As we launched “Eilidh” my 1996 P-15, we took along Pete’s Magellan hand held GPS, and my
simple plastic “pitot tube” wind gauge. Our main goal was to have a fun afternoon of sailing,
but as a secondary goal we wanted to get more familiar with how to use all the “Bells and
Whistles” on the GPS.
We soon were away from the shore, running downwind with a very nice steady breeze from the
Northwest, tweaking the main and jib halyards, checking luff tension on the mainsail, and in
general, making sure that everything was in order. As we were cruising around, we turned
on the hand held GPS and set it in the cabin where it was easy to glance at, set the boat speed
function to read in Knots, and got out the wind gauge.
To our delight, as the day progressed the wind on the lake, which we had measured at the dock as
8 knots gusting gently to 10 and back again to 8, remained remarkably consistent over the next
four or five hours. It seemed to be one of those “Perfect Wind” days.
We were able to bear off on a very long beam reach with the main let out just short of luffing, and
the lapper jib let out rather full and just short of a luff. Pete and I took turns at the helm, and would
watch the GPS and call out boat speed from the reading… “3.8… 3.8… 4.1.. 4.2, 4.5,” etc. We
found that we were able to very precisely see the difference small variations in sail trim would
make.
Now, all small boat sailors, develop a very good “seat of the pants” feel for speed and trim as
they gain experience. What we were finding on this day from the electronic instrument, was
confirmation of when we were doing things “exactly right”, and when we were making mistakes. It
was very clear when we were “over sheeting” or tightening things down a tiny bit too much, or
trying to “pinch” upwind a little too much… and this was often when “the seat of the pants” was not
telling us soon enough.
We also were learning about apparent wind vs. true wind. Under sail, the wind guage was
reading a very steady 13 knots most of the time… and on occasion we were getting readings as
high as 5.1, to 5.3 knots on the GPS... by subtracting the 5kn from 13kn we get 8 knots... Which
seems to confirm that both the wind guage and the GPS speeds were pretty accurate.
We went on sailing for four or five hours, enjoyed a superb sailing day, and the fun of learning
more about the “gadgets”. At days end, Pete, who is an, exceptional Mechanic and Sailor, Olive
Grower, and Micro-Brewery owner, brought out some of his best Ale, for a toast to learning to
sail better!
Bruce Hood
California. Black Butte, is a reservoir lake created by the Army Corps of Engineers surrounded by
rolling grassy hills, and some seven miles long, with a striking black basalt Butte looming
over the shore near the Eagle Pass launch ramp.
As we launched “Eilidh” my 1996 P-15, we took along Pete’s Magellan hand held GPS, and my
simple plastic “pitot tube” wind gauge. Our main goal was to have a fun afternoon of sailing,
but as a secondary goal we wanted to get more familiar with how to use all the “Bells and
Whistles” on the GPS.
We soon were away from the shore, running downwind with a very nice steady breeze from the
Northwest, tweaking the main and jib halyards, checking luff tension on the mainsail, and in
general, making sure that everything was in order. As we were cruising around, we turned
on the hand held GPS and set it in the cabin where it was easy to glance at, set the boat speed
function to read in Knots, and got out the wind gauge.
To our delight, as the day progressed the wind on the lake, which we had measured at the dock as
8 knots gusting gently to 10 and back again to 8, remained remarkably consistent over the next
four or five hours. It seemed to be one of those “Perfect Wind” days.
We were able to bear off on a very long beam reach with the main let out just short of luffing, and
the lapper jib let out rather full and just short of a luff. Pete and I took turns at the helm, and would
watch the GPS and call out boat speed from the reading… “3.8… 3.8… 4.1.. 4.2, 4.5,” etc. We
found that we were able to very precisely see the difference small variations in sail trim would
make.
Now, all small boat sailors, develop a very good “seat of the pants” feel for speed and trim as
they gain experience. What we were finding on this day from the electronic instrument, was
confirmation of when we were doing things “exactly right”, and when we were making mistakes. It
was very clear when we were “over sheeting” or tightening things down a tiny bit too much, or
trying to “pinch” upwind a little too much… and this was often when “the seat of the pants” was not
telling us soon enough.
We also were learning about apparent wind vs. true wind. Under sail, the wind guage was
reading a very steady 13 knots most of the time… and on occasion we were getting readings as
high as 5.1, to 5.3 knots on the GPS... by subtracting the 5kn from 13kn we get 8 knots... Which
seems to confirm that both the wind guage and the GPS speeds were pretty accurate.
We went on sailing for four or five hours, enjoyed a superb sailing day, and the fun of learning
more about the “gadgets”. At days end, Pete, who is an, exceptional Mechanic and Sailor, Olive
Grower, and Micro-Brewery owner, brought out some of his best Ale, for a toast to learning to
sail better!
Bruce Hood