flat vs convex surfaces

[lucdekeyser]

Fair enough. Thank you for your patience and insight.

 

[BlueBell]

I'm a little late to the party but the
elimination of "pounding" is exchanged for rapid decelerations
experienced by the crew on such wave piercing hulls.
Testimonials regarding the severity of such "piercings" were telling.
Extreme fatigue resulted from such decelerations.

So, sure, eliminate the pounding at the cost of extreme decelerations.
But no pounding...

 

[lucdekeyser]

eliminate the pounding at the cost of extreme decelerations

Thank you. I was not aware of that compromise. If the impact on the human body is exponential with the speed of change of position then this would be way more bearable in the speed ranges of sailing multihulls as these are about half of those for fast crew ships where strapping in motion dampening seats is required.
I guess decelerations lead less to seasickness than pounding as the horizon is more stable. With two hulls though, preventing corkscrewing would be the next concern Here the proa seems also to be at an advantage when the waves hit the bows at an angle more simultaneously going upwind.

 

[BlueBell]

You're welcome.

I wish I could remember the video where the crew member was talking about the intensity of the decelerations.
It was in EarthRace or some other similar stabilized monohull.
He made reference that it was just redirected slamming.

I could have worded it better.
Slamming is an "extreme deceleration" but piercing slows the boat more over a slightly longer time period.
Resulting in higher forces on the crew... but no slamming.

 

[lucdekeyser]

Are there any systematic studies of the different types of change in motion on human stress outside of spaceflight where the latter is probably more concentrated on G forces during lift off, longer term weightlessness and accidental spinning.

Probably the analogy does not hold, but in airplanes sudden drops in air turbulence are much more noticeable than when entering a rain cloud. The speed of a multihull cruiser is about 40-80 times less than that of an airliner and water is about 800 times more dense than air, and even more at altitude

But this leads us further away from flat vs convex.

 

[cavalier mk2]

The US Navy has done quite a few motion studies, I imagine most major navies have.

 

[BlueBell]

Terrific graphics.
From a "flat vs convex" perspective,
the Horton speaks for itself.
Enjoy.

 

[gonzo]

I wonder how well it does in heavy seas?

 

[BlueBell]

I wonder how well it does in heavy seas?

Great, so long as you don't touch down.
It was more about flat stealth tech vs compound curved surfaces.

 

[Iridian]

My previous thinking on negative rocker ended up as a triscarph, which did the job, but had poor weight carrying. Didn't matter because it foiled.
It might be time to revisit it. Easy enough to add triangular ends to one hull of the water taxi or the catamaran fishing canoe the students are currently building. Then tow test it and use the yaw to determine the relative drags. Won't happen before Xmas, but a fun project next year.
Luc, a facetted C50 windward hull which we drew as an exercise. Was more work to build than the channel mould so we didn't pursue it. It looks a lot more angular than it actually is.View attachment 198686

Something like this could be good for an alu cat. Might substantially cut down on work required.

 

[garydierking]

All of Jim Brown's Searunner trimarans were built with compounded sheet ply. This was not difficult to do and added significant panel stiffness.

 

[lucdekeyser]

added significant panel stiffness

Do you have an idea how much?

 

[baeckmo]

Do you have an idea how much?

Before you speculate further regarding strenght issues, I recommend that you study the dimensioning principles in modern scantling rules. There you will find that the panel camber (expressed as the curvature height/span) has a major influence on the strength of the structure. For example, in the ISO 12215 standard, the skin thickness has to be doubled when going from a camber value of 0,18 to zero, all else equal. Those rules are based on first principles of physics.

 

[lucdekeyser]

ISO 12215 standard, the skin thickness has to be doubled when going from a camber value of 0,18 to zero, all else equal

Thank you for the reference. 124 pages of the normalized applied physics behind the ballpark figures, or, a convincing exhibit of why one needs an NA. Excellent.

 

[TANSL]

In reality, you wouldn't need an NA for that, you would just need to get the standard and read it carefully. But yes, in general I agree with you, it is good to have the help of an NA, we must leave aside the idea that anyone can design a boat, which is an idea that, unfortunately, is becoming very widespread since the existence of cheap rendering programs.