Myth: Hull Speed

[denverd0n]

Originally Posted by Randyonr3

The point I was making is that the Hull speed Formula was created many years ago and as I believe, was for a oil tanker...or a boat of Full Displacement where the waterline length comes into play.

No, we don't need a new hull speed formula. The one we have works perfectly well. The point is that many modern designs are able to plane. That's all.

By definition, the "hull speed" is the maximum speed that you can achieve while maintaining your full displacement in the water and pushing the water out of the way as you move through it. The ONLY way to exceed that speed is to climb on top of the bow wave, on top of the water (which effectively reduces your displacement at that instant), and ride on TOP of the water rather than THROUGH it.

In the past most sailboats were strictly displacement hulls. Powerboats have long spanned the continuum between displacement, semi-planing, and planing (and it is a continuum, not a black and white step from one to the next). Nowadays many sailboats are being built that fall into the semi-planing and planing categories.

[Randyonr3]

Originally Posted by denverd0n

No, we don't need a new hull speed formula. The one we have works perfectly well. The point is that many modern designs are able to plane. That's all.

Here again, you are try to explain how the formula works and the boat "MUST" be planing, or simi planing...
What has been said by not only myself but others as they come forward, that they have exceeded the numbers in a broad reach under working sails.. The bottom may be flat, but in a broad reach, your side is in the water and the side is not flat.. The waterline may infact be longer but not to the extent to offset the difference in speed gained..
Planing by deffinition is when a boat breaks lose from the waters surface and rides above the water as a powerboat does..
A modern sailboat is not planing when heeled at 12 degrees....

[gramos]

plenty of really good info here regarding hull speed calculations , however , there must be a seperate set of formulae for assessing a boats hull speed when it has 2x hulls linked by a bridgedeck ? how can we use the same formula for one or two hulls ? it cannot be the same ??.

[Oyvind]

Hull speed, per the popular formula, is not a set in stone figure for any boat, but does give a pretty good indication of max economic cruising speed.

There is a very good discussion on the subject here: Hull speed - Boat Design Forums

[GeoPowers]

I assume everyone is talking about speed through the water (not speed over ground)?

How many people have actually seen a displacement sailboat plane? If that is the reason for speed over "hull speed", then wouldn't we see it a lot in local races?

I'm another vote for one size doesn't fit all with that equation...even in our liveaboard, we've gone over theoretical hull speed before- waves in Puget Sound are usually 1-2 feet, so no surfing here!

[Randyonr3]

The whole idea of posting this thread was to shock some and inform others that the term "Hull Speed" and its formula falls somewhere in the general prospective of the 4 minute mile for a runner, or the land speed record of 300 mph...
At one time it was a rule of measurement, but as times change, so do the rules and who would have ever thought the America's Cup would be a play-off between two Mulit Hulls.
We've reached a point that the term "Hull Speed" has No Merrit............

[neelie]

Randy, it looks like you might be right about the obsolescence of the hull speed thing.

Quoting Wiki:

"The concept of hull speed is not used in modern naval architecture, where considerations of speed-length ratio and Froude number are considered more helpful. It is still used by amateurs in relation to traditional displacement hulls"

Hull speed - Wikipedia, the free encyclopedia

[GordMay]

Originally Posted by neelie

Quoting Wiki:
The concept of hull speed is not used in modern naval architecture, where considerations of speed-length ratio and Froude number are considered more helpful. It is still used by amateurs in relation to traditional displacement hulls"
Hull speed - Wikipedia, the free encyclopedia

Quoting Wiki is for amateurs.

Books on yacht design, like "Elements of Yach Design" by Norman L. Skeene, "Basic Naval Architecture" by Kenneth C. Barnaby, discuss how the wave making resistance increases at or around a Speed Length Ratio of 1.34.

It looks like the issue here is one of semantics, not one of naval architecture, engineering, or science.

[barnakiel]

Originally Posted by GordMay

Quoting Wiki is for amateurs.

Well, the Bible is apparently the most quoted book ever. Event though it is way out of date and we can't even trace the sources.

What ACTUALLY is wrong with quoting Wiki?

b.

[GordMay]

Originally Posted by barnakiel

... What ACTUALLY is wrong with quoting Wiki?

Wikipedia, is the free encyclopedia that anyone can edit.

Articles in Wikipedia may be well written and insightful, and may provide useful links, but they are not embedded in the world of scholarly discourse.

Without knowing who wrote the article, it is more difficult to judge whether the author's writing is worthy of consideration, or to critique his or her motivations or qualifications.

Without a known author, Wikipedia articles cannot be considered authoritative.

Religious treatises address one’s faith, not intellect.

[Starbuck]

Gord May, he say:
Quoting Wiki is for amateurs.

+1

barnakeil, he say:
Well, the Bible is apparently the most quoted book ever.

Considering its unparalleled impact on Western Civilization, I'm persuaded to accept that at face value.

Event[sic] though it is way out of date…

Some would use the term timeless.

…and we can't even trace the sources.(emphasis mine)

If you mean the times, places, occasions of the particular writings, then biblical scholarship demonstrates the opposite is usually the case; if, however, you mean identifying a specific individual as an author of a particular book, your statement is only semi-accurate, an is an over-statement.

Simple dismissal doesn't amount to a sound argument.
You can check it out on Wikipedia, if you'd like.

[44'cruisingcat]

Multihulls have been exceeding theoretical hull speed for decades. Without planing.

According to Edmund Bruce, it is all to do with waterline length/beam ratios. At high enough ratios, bow waves aren't big enough to cause the "hull speed" effect.

[Wotname]

Not sure about Wiki (and the other mention reference sources) but I find that quoting CF usually cuts the mustard

[FSMike]

And on the eighth day God created hull speed limitations.

[clockwork orange]

Originally Posted by Randyonr3

Thats the same attitude that I got from the guy who went out with us, as he started running the numbers and said it wasnt possible..
HiLite has just stated that he does 10 in a broad reach.. fast point of sail but the kite is still in the bag..
Our speeds are not abnormal and 10 to 12 is an everyday event in flat water with no current.. With the kite up, 14 to 16..
The point I was making is that the Hull speed Formula was created many years ago and as I believe, was for a oil tanker..or a boat of Full Displacement where the waterline length comes into play..
When new designs of underwater surface came, the formulas went out the window..

If this is the Frers design IOR hull then i call BS, the charter skipper of one that is used for day charter at a local resort worked with us last fall and we talked about the boat and he had never seen double digits(no spinnaker)and the owner who loves to fly the kite whenever possible in a breeze when using the boat personally had seen a max of about 12 if i remember correctly.Those boats do not have a hull shape that will plane or surf readily for that matter,of course anything will surf given a steep enough wave, 360 miles in a 24hr run ,no way,ever,sorry, i just watched a documentory on 100 years of the Transpac and when Merlin set the record that stood for 22yrs her fastest days run was about 360 miles surfing the big pacific swells,no way any Bene will match Merlin.
Steve.