CD 28 Hull Speed

[WaywardWind]

"exceed the theoretical hull speed"

In the world of physics there is no such thing as "theoretical hull speed", any more that in the world of astronomy there is any truth to astrology.

"Hull speed" is NOT a theory, therefore there can be no such thing as "theoretical hull speed".

A MAJOR problem in using the term "theoretical hull speed" is that ill-informed people think that use of the term "proves" its existence. Not the case, anymore than use of the term "astrology" proves its existence.

Yet, I once knew a woman who divorced her long term husband when she found out her and his "sun signs" and "moon signs" did "not match up".

[darmoose]

I ask which schools you guys got your BS in Physic from?

BTW, aeronautical engineers have known for 70 some years that free wheeling props have more drag than stopped props.

Damn! Who were those clowns who voted in those Laws of Physics?

Dear MR Wind,

It has been established on this very site, that if what you claim is true for airplanes and helicopters, it certainly doesn't apply to sailboat propellers.

Seems that more recent science than that of seventy or more years ago, proves that just the opposite is true (refer to the archives), and open-minded sailors, engineers, scientists and writers are revising their positions on this question daily.

There are those, however, that simply refuse to evolve and we will continue to work with them.

FWISF
Darrell

[John Vigor]

"Hull speed" is NOT a theory, therefore there can be no such thing as "theoretical hull speed".

Yet, I once knew a woman who divorced her long term husband when she found out her and his "sun signs" and "moon signs" did "not match up".

Dear Wayward Wind:

Mr Webster does not agree with you. Mr Webster's fine dictionary defines the word "theory" as:

"1. orig. a mental viewing; contemplation
"2. a speculative idea or plan as to how something might be done
"6. popularly, a mere conjecture, or guess"

Numbers 4 and 5 are apparently the kind of scientific theory you are talking about. But when we ill-informed sailors talk about the theory of maximum hull speed we (and Mr. Webster) may not be as dumb as you think.

And in case you want Europroof, Mr. Concise Oxford defines "theory" as:

"n. supposition or system of ideas explaining something, esp. one based on general principles independent of the facts, phenomena, etc. to be explained"

As for incompatible sun and moon signs -- heavens, man, I'm not surprised the lady wanted a divorce. Aaack! As a sun man, I can't imagine kissing a moon woman, never mind ... well you know what.

John V.

[WaywardWind]

John, please, I think very highly of your books. But please, please, please --IF-- we are going to talk science, let's use the scientists' working version of the term "theory", okay?

There is no scientific theory behind "hull speed". A hypothesis disproven by reality is not considered a theory. Hull speed, as a hypothesis, is disproven by nearly every sailboat designed in the last 60 years. Indeed, hull speed never even made it to the point of being a hypothesis, except in the popular literature. It always was a quick shot from the hip to quiet British Naval brass.

Again, I think very highly of your books.

[WaywardWind]

"Dear MR Wind,

It has been established on this very site, that if what you claim is true for airplanes and helicopters, it certainly doesn't apply to sailboat propellers.

Seems that more recent science than that of seventy or more years ago, proves that just the opposite is true (refer to the archives), and open-minded sailors, engineers, scientists and writers are revising their positions on this question daily.

There are those, however, that simply refuse to evolve and we will continue to work with them."

..............................................................................................

People are welcome to believe anything thing they wish, including -- believe it or not -- that this small user group site is the arbiter of all things scientific, or at least all things water related.

The physics of fluid dynamics has not changed in several millennia, and probably not in several mega giga-millennia.

However, let your prop freely spin if that is your wish, and tell yourself your boat is going faster because of it, also if that is your wish. It's a big world out there, with lots of room for variable thought.

[darmoose]

"
..............................................................................................

People are welcome to believe anything thing they wish, including -- believe it or not -- that this small user group site is the arbiter of all things scientific, or at least all things water related.

The physics of fluid dynamics has not changed in several millennia, and probably not in several mega giga-millennia.

However, let your prop freely spin if that is your wish, and tell yourself your boat is going faster because of it, also if that is your wish. It's a big world out there, with lots of room for variable thought.

Mr Wind,

Please forgive me, I apologize most profusely. You are absolutely right.

Had I known that you were merely expressing your version as "variable thought" I would never have dreamed to question the bigger world out there from my little perch here in this small user group.

Darrell

[chase]

Last fall while sailing upstream in the Pamlico River channel, we attained regular speeds of 7 kts. We were on a beam reach, flying all working canvas, the rail was not buried, and the wind was very consistent around 15 kts. I could not understand it, as the boat is typically a 6-6.5 kt boat save for current. I thought hull speed was a law.

The wind was not from astern, so no wind driven current, it was blowing across the river. Eddies? No way. There were no waves to slow the boat down either. I think in certain conditions the theoretical speed can be exceeded, but with my limited experience this has been only a few miles out of a thousand. Here's a photo from a few hours earlier on the sound, and yes I'm clueless about the finer points of sail trim...

[WaywardWind]

Actually, I was expressing the scientific version, but that's okay.

There are people who feel if God intended man to sail fiberglass boats He would have made fiberglass trees.

[Troy Scott]

Well, even if God didn't make fiberglass trees, I'll bet I could make one. Epoxy is wonderful stuff. And there are those who refer to trees as naturally occurring fiber reinforced plastic.

[darmoose]

Actually, I was expressing the scientific version, but that's okay.

There are people who feel if God intended man to sail fiberglass bo
ats He would have made fiberglass trees.

Mr Wind

Seems you think that the conclusion reached on our little board was not based in science or fact. I appreciate your opinion as a physics afficionado. Perhaps you would do us the kindness of refering to our archives to the thread "How sailboats sail", the latter pages (9, 10, 11, etc.), and explain how the Strathclyde Ocean Engineering Study, as well as the M.I.T. study got it wrong?

Darrell

[WaywardWind]

Every nice Sunday afternoon, Hobie cats -- by the thousands across the country -- regularly exceed some multiple of "hull speed".

This leaves those readers of popular literature in the unenviable position of INSISTING the extremely deep-vee hulls of Hobie cats are actually planing hulls. In the world of science, that is known as the "If-the-data-doesn't-match-the-theory, change-the-data" syndrome.

Some pop lit autodidacts claim that because the outboard side of Hobie hulls are flat that the Hobie does indeed "plane", which kinda ignores the observable fact that Nacra's -- with their symmetrical hulls -- are actually faster than Hobies.

In fact, such finely designed sailboats such as Catalina 22's, Grampion 26's and O'Day's of any size regularly exceed "hull speed", and there is no Hand of God pushing them up on plane. This thread alone has owners of heavy displacement, wine-glass shaped hulls of Cape Dory's reporting well exceeding "hull speed."

If "hull speed" did not have decimal places and and square roots in the mix, no one would have ever given the term the slightest notice.

[WaywardWind]

Back just after the turn of the 20th century (or perhaps even in the 1890's, I haven't checked the dates against my memory), a British individual built a (displacement) powerboat he tried to sell to the British navy. British naval brass insisted he was a fraud, because his 40 plus foot long, six foot wide boat could not possibly "exceed hull speed" as was his claim.

And, when he fired up his steam powered boat and literally ran circles around the best of warboats the British navy had at the time (and did it publicly in front of the British crown) he was threatened with arrest.

[kerlandsen]

and yes I'm clueless about the finer points of sail trim...

[/quote]


Who cares about the finer points of sail trim, looks to me like you were out there making it happen. Great picture and good times.
Kyle

[Troy Scott]

xxxxxxx

[Steve Darwin]

The question I have about "theoretical" hull speed is whether the formula was derived from calculations of physical properties such as wave resistance, wetted surface are, and hull friction, or if it is a speed estimation based on observations of certain types of hulls under certain sailing conditions. I suspect that hull speeds were measured and then a formula (water-line length times a constant) was found that more-or-less fit the data. If the formula was derived that way, then "theoretical" hull speed is really only "estimated" hull speed. Why should there be a correlation between water-line length and speed? That's a separate question, the answer to which would, indeed, be quite theoretical.

Steve