To Don, 8.5 kn. with H27

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Olivier van Mierlo

I was pretty amazed myself I can tell you. However I am telling the truth. It was clocked on a normal log in stong wind (6 Bft.)and on a halfwind course. On GPS it was even more because I had the advantage of a downstream current. I don't know if it has anything to do by the fact that this happened on very salt water and gave the boat some lift, although that would cause the waterlinelength to decrease and that would mean decreasing the hull speed. Who can give the answer? Regards Oliver
 
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David Foster

Some questions & comments

Knotmeters have accuracy issues in the range of +- 1 to 2 knots. So I wonder what the difference between the knotmeter and GPS is with no current at 6 knots? A GPS is dead certain over a period that allows it to average out random noise (+-10 to 20 feet on Lake Erie more at higher latitudes) from the satellite measurements. Speed is calculated from the difference between two position measurements. So instantaneous GPS speed measurements often show wide variations in speeds. A GPS can avoid this problem by averaging speed measurements over several seconds. Ours is set with a 10 second filter factor, so we never see jumps in the GPS speed. We have logged sustained speeds over 7 knots in ideal conditions. The highest believable speed I have seen on the GPS is 7.5 knots. Currents in Lake Erie are tupically less than 0.5 knots. The hull speed of a displacement hull means that the wave on the hull becomes longer that the waterline. The depth of water at the bow and stern rapidly increase, making it harder (but certainly not impossible) to exceed hull speed. Finally, the Cheribini hull design overhangs on the bow and stern. As the boat heels, and as the hull wave grows. the waterline lengthens. For instance, a two foot longer waterline adds about 0.3 knots to the hull speed. What speed was your GPS reading during your spurt? Can you find out the filter time it uses? For me, I just love the feeling of a fast sail - especially if it can be sustained. David Lady Lillie
 
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Don Bodemann

If you say so Oliver

I might mention that I remember seeing numbers like that on my GPS with my 1980 H-27 and then realized my GPS was set at miles per hour instead of knots. Don
 
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