for the speed freeks

Birdseye

Birdseye

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worth watching https://www.youtube.com/watch?v=QP_9rFbvY_Q

thats sailing at 6 or 7 times what an ordinarly family boat will do. Or to put it another way, its as if a Ferrari sports car would travel at 700 mph. I wonder why there is a far bigger difference in capability between the average sailing boat and the really fast than the equivalent on the road.
 
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I'd guess that a large part of the difference can be put down to resistance. Cars have two forms of resistance, friction and air, common to them all. Boats have air resistance and resistance through the water. Water resistance is by far the greater, it's viscosity being much greater than air. When most of the hull is lifted out of the water, the resistance drops dramatically. This is just a guess based on general reading. No doubt someone more knowledgable will be along soon.
 
StormNorm said:
I'd guess that a large part of the difference can be put down to resistance. Cars have two forms of resistance, friction and air, common to them all. Boats have air resistance and resistance through the water. Water resistance is by far the greater, it's viscosity being much greater than air. When most of the hull is lifted out of the water, the resistance drops dramatically. This is just a guess based on general reading. No doubt someone more knowledgable will be along soon.
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That won't do at all. Your answer is far too logical to be correct. The only possible explanation must be an AWB manufacturers' conspiracy. No idea why, though mumble mumble.......
 
StormNorm said:
I'd guess that a large part of the difference can be put down to resistance. Cars have two forms of resistance, friction and air, common to them all. Boats have air resistance and resistance through the water. Water resistance is by far the greater, it's viscosity being much greater than air. When most of the hull is lifted out of the water, the resistance drops dramatically. This is just a guess based on general reading. No doubt someone more knowledgable will be along soon.
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I think I heard him say that there were two square metres underwater when sailing at speed.
 
StormNorm said:
I'd guess that a large part of the difference can be put down to resistance. Cars have two forms of resistance, friction and air, common to them all. Boats have air resistance and resistance through the water. Water resistance is by far the greater, it's viscosity being much greater than air. When most of the hull is lifted out of the water, the resistance drops dramatically. This is just a guess based on general reading. No doubt someone more knowledgable will be along soon.
Click to expand...

That's a big part of the story. At any significant speed you can ignore friction and other losses on a car: aero drag is everything. On a boat that planes (either on it's hull or on foils) it's different. The frontal area is divided between air and water. As the boat climbs on to the plane a lot of frontal area is transferred from water to air. Drag is proportional to the density of the fluid, and water is hundreds of times more dense than air, so QED.

In addition boats in displacement mode (just about all cruising yachts) are further restricted by hull speed. That creates another difference between "mundane" boats and "racy" boats. It's a difference with no equivalent in cars.
 
Just watched the video with SWMBO. We are setting off across the Atlantic this week.
2.5 days? We'll be delighted with 2.5 weeks!! I think we prefer our accommodation and bathroom facilities though. Does this mean I'm getting old? Should I be posting in the lounge? (whatever that is)
 
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