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Senior Smart Aleck
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Discussion Starter · #1 · (Edited)
My wife gave me permission to go sailing yesterday while she took my son to some soccer event. The forecast appeared ho-hum 5-10 kts. out of the S.W. Instead, there developed some higher extended gusts in the teens with widespread small whitecaps in relatively flat water on the Rappahannock River.

My Pearson 28 with a clean bottom and repaired rudder showed 7.9 kts. with smooth, stable sailing on a beam/broad reach, pause at 1:05 on this video for speedometer readout:


As you can see in the video, the Pearson is sailing faster than the developing waves, so it was not surfing. (This boat does not plane, but will surf a bit: the only other times I have exceeded hull speed were under spinnaker, riding down small waves.) This is on a 24 ft. designed water line; I keep the boat as light as possible. The hull speed should be around 6,8 knots. After the first hour, my GPS in these photo showed a top speed of 7.5 kts., with an average of 6 kts, which included 15 minutes motoring at 5 kts. from my slip to the river and heading into the wind to raise sails (I also took photos of the bow waves, which were pretty cool):

https://picasaweb.google.com/101935788163929897438/FastSailing90614?authuser=0&feat=directlink

I was concerned about the upwind leg so I dropped the genoa and still made 5+ kts. on main alone. The wind lessened a bit, and I was able to raise the genoa again to sail back:


One of the best sailing days in a long time. Ironically, I saw only 2 or 3 other keelboats sailing out on the river in the 3 hours I was out sailing.
 

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Looks like you had a lovely sail.
 

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You have to remember that "GPS" speed does not really tell you anything about boat or aircraft performance since it is telling you speed over the ground, not through the water or the air. If you are going to use GPS speed you need to take into consideration the movement of the water over the ground also. Then add or subtract as the case demands. However all of this is moot since it was obviously a great day to sail and you had fun.

Jerry
 

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I had a similar experience with my boat in similar conditions (strong winds and smooth water on a beam reach), and agree that it is exciting, but I think you're mistaken when you said, "This boat does not plane." When it was at 7.9 kts as measured by the knotmeter, I think it was on a plane.

The reason why hull speed is considered a limiting factor is because it is very difficult for a displacement hull to generate enough speed to drive it up and over the boat's own bow wave. If your boat was making 7.9 kts speed through the water, that means it must have driven over it's own bow wave, because that is what has to happen for a displacement hull to exceed hull speed. If you had looked over the side, I believe you would have seen that your bow wave had moved significantly aft. When it happened on my 35' boat, the bow wave moved aft almost to the winches. Instead of pushing the bow wave in front of it, my boat appeared to be surfing continuously down the front face of it's own bow wave at between 8-9 kts, and, because those conditions of strong winds, smooth water and a beam reach persisted for two hours, my boat maintained those speeds consistently for two hours. What a thrill!
 

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i was on a beam reach coming through portland head light, and hit 8.7 knots on the gps with an incoming tide....gotta love the tide...was doing 6-7 all day with light winds...alll in all a great day 9-5-14
 

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Yup gotta agree boat was planing. Glad you had so much fun. First I got my boat left Norfolk Va headed for R.I. Had 30-35 behind us. With Solent on pole and double reefed main stayed in double digits for three consecutive watches. Had another day like that with 4 h on plane coming back from Maine a few weeks back running down Buzzards Bay. Even non ultra lights will plane in the right setting. Find I can tell because the bow wave moves aft but also the boat seems to swat then settle down and level off a bit just like a motor boat's hole shot.
 

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Discussion Starter · #10 ·
You have to remember that "GPS" speed does not really tell you anything about boat or aircraft performance since it is telling you speed over the ground, not through the water or the air. If you are going to use GPS speed you need to take into consideration the movement of the water over the ground also. Then add or subtract as the case demands. However all of this is moot since it was obviously a great day to sail and you had fun.

Jerry
That is a thru-hull, paddle-wheel driven speedometer, not GPS, in the video. The paddlewheel speedometer measured 7.9 kts.

My GPS unit is in the photo measured a top speed of 7.5 kts.
 

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The hull speed should be around 6,8 knots. After the first hour, my GPS in these photo showed a top speed of 7.5 kts., with an average of 6 kts, which included 15 minutes motoring at 5 kts. from my slip to the river and heading into the wind to raise sails (I also took photos of the bow waves, which were pretty cool):
Hull speed isn't a "speed limit". When your boat moves through the water, the bow creates a standing wave (wave whose position doesn't not appear to move relative to your boat). As your boat moves faster, the wavelength of the this standing wave (bow wave) gets longer. This creates a kind of ripple effect in the resistance vs velocity curve, as the peaks and troughs of the bow wave get longer and interact with your hull's displacement to create more or less resistance:
File:Wave making resistance curve.svg - Wikimedia Commons

When the bow wave wavelength equals the boatlength (k=1 in the graph), the boat's essentially sits in a trough, and has to climb uphill to move forward. (top pic here)
http://rcspeedsailing.com/speed-graphic.jpg

Wavemaking drag does not go to infinity beyond this point. It is still possible to power through it without planing. But as the rear of the boat sinks further into the trough, the boat has to climb "uphill" more and more to move forward. (Bottom pic)

Planing is one way to (mostly) eliminate most wavemaking drag. Ships which are too heavy to plane adopt alternate solutions. If you've ever seen the bulbous nose of an oil tanker in drydock:
http://maritime-connector.com/ships...6-oil-chemical_tanker-port_-_dry_dock-871.jpg

The bulb moves the start of the bow wave forward, so that at hull speed the bow wave is shifted slightly forward from the ship's length. The bow of the ship sits further behind the peak of the bow wave, and the ship does not have to work as hard climbing "uphill" to move forward.
 

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Everyone here has missed the point and missed the point by a (nautical) mile:

ONLY SAILORS GET THIS EXCITED ABOUT GOING EIGHT KNOTS

(With the old boat, 5.5 was exciting)
Once you start racing you get excited about going tenths of knots faster with each tweak you make.:D
 

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Jim,

Its hard to believe her PHRF is 189. Wish I had raced her, as she outsails "faster" boats regularly. You have made a great boat even better over the last 3 years.
It was a great day on the Chesapeake yesterday too. I had novices onboard, so I furled the jib down and still hit 6.6 knots.
Joel
 

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I have to agree with James. This weekend was just plain perfect for sailing in the Rivah. Went out Sunday in Rappahannock and it was one of those beautiful days: nice steady wind, relatively flat water and very comfortable weather. Yet, hardly anyone was on the water. Strange, very strange. Anyway, we had a blast though I can't say that I set any speed records (I blame it on the dirty bottom and never on the skipper :)).
 

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Whoa ... something must be going on. Sunday, here on the left coast, we also had a super day of sailing. Lisa (my wife) and I went out in 16+ knots and just had a blast moving the boat through the water. Maybe it was the moon? Glad you had fun too!!
 
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