Questions about surface tension

Andrew Claughton

Andrew Claughton completely agrees with me, i quote:

"The wave lifts the stern, sinks the bow, so that a large Hull Yaw Moment is produced"

(end of quote)
(Max Michael Munk Moment)

Max Munk - Wikipedia https://en.m.wikipedia.org/wiki/Max_Munk

The bow of a heeled sailboat has the ability (by breaking symmetry) to create a huge Angle of Attack

(And on top of that, some have a huge centerboard/Keel with its Hydrodynamic center forward of the Center of Gravity of the Yacht)

 

(Thomas Harrison Butler)

We have to go back to the past (?) No. We have to understand the efforts of those who preceded us and admire the solutions they found, and following their Spirit recreate in a modern way the summit of the Classics.

 

So that boat, which looks quite unremarkable, is over 25% faster than the maxis designed in its time like Ticeronderoga? It's 25% faster than the vast cutter Satanita, which had a 93 foot waterline? That boat is 25% faster than something like a J/35, which is a good all-rounder and a dramatically faster yacht in all conditions?

Many of us have sailed boats that are dramatically faster all-round, in winds far higher than force 7, and yet not hit 20 knots in them. That is the experience of many people who are known to be meticulous and highly experienced navigators and sailors.

As the US government says about its own GPS system, "the speed accuracy of GPS depends on many factors." GPS units are well known to be utterly unreliable when it comes to measuring peak speeds, because they suffer severely from "spikes". That's why windsurfers, for example, only allow certain GPS units to be used for GPS speedsailing records, AND require all users to keep their files so that they can be examined for spikes.

None of us have trusted GPS for instant speeds for decades since we have years of experience to show that they are, as the creators of the system say, not dependable. And many yachties have noted similar issues;

Random spikes in GPS track - Cruisers & Sailing Forums https://www.cruisersforum.com/forums/f13/random-spikes-in-gps-track-190525.html

The speed is significant because there is no reliable evidence that it was obtained, and therefore no reliable evidence that the Beneteau in question was better than many other boats.

 

Everyone who has sailed well downwind knows that. It does not mean that the boats are as bad as you claim they are. Every boat has a series of tradeoffs and many of us don't have trouble driving "poorly balanced" boats, or others, downwind at high speed.

 

Surface tension or hydrophobicity are not significant factors when it comes to hydrodynamic drag. Intuitively, it seems that a hydrophobic coating should have lower skin friction. I doesn't seem to work out that way. At least that seemed to be the case 30 years ago. Things may be changing.

 

You constantly and consistently fail to understand what the Munk Moment is, and how is works.

A body needs to be fully immersed in a fluid for there to be a Munk Moment...a yacht...is not!

 

Were the above answers helpful to you, Michael?

It sounds, to me, like you are looking for a comparison of surface friction on a planing surface to that of a submerged surface. That comparison would involve an equal surface area, say a per square meter of contact area.

As you pointed out in your original post, there is a difference between the resistance of moving water mass aside for a displacement hull and the relatively minimal movement of water mass acceleration (changing direction or speed) for a planing hull. A surface bound displacement hull has to contend with not just overcoming the inertia of the surrounding water as the boat plows its way through it, but also with that of gravity as it tries to climb its own bow wake. A fully submerged boat does not have that gravitational acceleration to contend with. Submarines are generally more efficient below the surface than on the surface.

As for surfing versus planing. A boat climbing up or down an inclined surface should have a reoriented Normal force perpendicular to the wave face it is navigating, effectively making the boat a little lighter in the water. It may not be much, but I would expect a boat traveling up or down a wave face of about 30 degrees, to actually have less hull in the water, reducing wetted surface.

For surface tension and surface friction between a planing hull and the water versus the surface tension and surface friction between a displacement hull and the water, speed may be a significant factor as well.

I am not a NA, and I have only been introduced to these concepts through high school and university physics courses, as well as a life around boats, but one of the concepts I have learned about is the two different types of surface friction. There is static friction, the friction that allows your tires to drive your car down the road, and there is kinetic friction, the greatly reduced friction that occurred when you hit the breaks on a car that doesn't have ABS. Kinetic friction is significantly less than static friction. I have not read any mention of the difference in surface friction on the skin of a boat in contact with the water at different speeds, but I see no reason to believe the wetted surface of a boat moving at twenty knots across the surface of the water, would experience the same resistive forces per square meter as the wetted surface of a boat moving through the water at seven knots.

I doubt I have answered any part of your question with my uninformed and intuitive descriptions, but I hope I have, at least, helped to clarify your question and given you some useful concepts to mull over.

-Will