speed of a Mac 25

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MArk

Heteroclinic Bifurcation (can I say that here?)

Dan, The more interesting part of the passage you sited is the next paragraph and associated graph. The graph shows an almost 3 knot increase in speed ( after initial 4 knot surge) when surfing a 2M wave. Gavity drives the boat down the face of a following wave, like a soap box derby car going down a hill. In this case the "hill" is more like a rug with a rolling pin under it. As the car goes down the hill, the hump chases the car keeping it falling but never reaching the bottom due to resistance (drag) pulling it back up the hill somewhat. Article linked below discusses other "interesting" effects of surfing a yacht such as capsizing, broaching and bow-diving. Happy sails *_/), MArk
 
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Dan McGuire

Downwind Performance Paper

I finally got a good chance to go through it all. It fully supports my position. I had some trouble with Figure 8. It appeared to be right, but it was difficult to detrmine which weay the force was, opposed to the boat or helping it. I then took another look at Figure 4. It is like MArk said. The gragh starts out with the stern at the wave crest. Then the boat immediately begins to accelerate and finally falls into position. Doing a rough calculation, the boat ends up on the forward side of the wave. Then go and look at Figure 8. The boats maximum help from the wave is when the boat is sitting on the crest with the stern about a tenth of a boat length back from the crest.
 
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Ramblin' Rod - Mac 26D - SeaQuell

Dan, Fig. 9 and Fig. 11....

...clearly show that the model doesn't reflect reality. These "scientists" declare wild deviations "acceptable". RR says, "It is attrociously erroneous to the extent the model is useless, even after throwing out 5% of the worst data." They then declare these errors don't matter because a 20 metre around the world racing boat is normally in waves with a period of greater than 40 metres in the southern ocean. RR says, "Cool, experimentation proves the model wrong so you just declare it irrelevant for your purposes and ignore it." Then they go on to declare that they really only have reasonable error in their model at wavelength/LWL = 1.5, and error to 35% at 1, because of flaws in basic assumptions (Froude-Krylov hypothesis). RR says, "Bravo! Start assuming Wave Modulation theory." Dan, I don't intend to debate the validity of this techical paper any further. It should suffice to say, the model and theory is flawed. I still eagerly await your explanation of how your wave particle contribution theory is supported by the illustration you submitted, with the hullform illustration I added, showing the net particle motion induced surface velocity to be negative? Hint: "Start thinking Wave Modulation theory!" ;-)
 
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Ramblin' Rod - Mac 26D - SeaQuell

Mark, interesting analogy...

But what about conditions where the wind wavelength is equal or close to LWL? In this scenario, there is negligible "slope" to soap box derby down? Hint: the answer is "Wave Modulation" theory. ;-) Note: I absolutely concur that a displacement hulled boat can surf like a surfboard on high, long-period waves. However, I disagree that this is the phenomenon frequently experienced is small sailboats, when they are driven above THS by relatively low, short-period waves.
 
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Dan McGuire

Tell It to the Judge

Every once in a while when I am deciding whether to do something, I try to decide how I would tell it to a third person such as a judge. In this case, it would go something like this. Judge. Dan tell me about this sailboat surfing. Dan. Judge. There are at least two theories: My Theory and one by Rod. Judge. That is a stupid name. Dan. Sorry Judge. That is the name my Moma gave me. Judge. I didn't mean your name. I was talking about "my theory." Tell me about "my theory". Dan. (Shows judge animation and diagrams). That is about it judge. Judge. That sounds simple enough. Does anyone else support this theory? Dan. Some scientists from Austrailia described some computer programs which tended to support my theory. Judge. Tell me about the other theory. Dan. The other theory is from Rod. He calls it "Wave Modulation". Judge. Great name. Describe the theory. Dan. I can't actually describe the theory. Rod has never described it to me. I think it is proprietary. Judge. Does anyone else support this "Wave Modulation" theory. Dan. I don't know. I don't think Rod has released it to anyone else. Judge. In light of there not being any evidence to the contrary, I rule in your favor. Stupid name though. Dan. Thank you Judge and I promise to come up with a better name.
 
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Ramblin' Rod

Closing Arguments For The Defense...

Judge: Do you have any question for witness Dan? RR: Do you recall my telling you that wave modulation means that hte waves combine to produce a higher net speed than the speed limiting bow and stern waves alone. Dan: Well ya. RR: Then I have explained the wave modulation theory haven't I. Dan: No. Well, that's my opinion anyway, because I don't want to hear or see anything that proves my theory wrong. RR: On many occasions I have asked you to explain how the illustration you posted, or the technical paper referenced, supports your theory of wave particle motion enabling a vessel to exceed THS. Have you? Dan: No RR: Why not Dan: I can't RR: The defense rests your honour. The prosecution continues to discredit the wave modulation theory, while having no other viable explanation for the phenomenon observed. Judge: In light of the facts before me, I have no choice but to rule in the favour of the defence. Case closed.
 
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Dan McGuire

reached the Silly Point

Rod I can't find any place you have described your theory. You did say something about combining and making a net wave. That is about as vague as your Wave Modulation theory. In addition, you have not provided any reference or link that that supports that position. I explained how the paper supported my position. Go ahead and rave on. I will again be unavailable for a few days.
 
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Ramblin' Rod - Mac 26D - SeaQuell

Dan, Serious Question Follows...

Dan, I have explained the "Wave Modulation" theory about 10 times now, during this and prior threads. Your turn. The illustration that you posted, and I placed a typical sailboat hullform on, shows that the the net water particle motion direction is zero or opposite the direction of the boat. OK, here's the question... HOW DOES THIS SUPPORT YOUR THEORY THAT IT IS THE PARTICLE MOTION WITHIN THE WIND WAVE THAT ENABLES THE BOAT TO EXCEED THE THS?
 
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Gary

Speed ?

You bought a sailboat. What differance does it make as to how fast it can go?
 
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gary

no difference anyway

Where ever you go in a sailboat is always directly UPWIND hence into the wave. Hence the question should be how much a wave slows the boat down.
 
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