Cruisers Forum
 


Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on Cruisers Forums. Advertise Here
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 12-03-2010, 09:41   #31
Registered User
 
denverd0n's Avatar

Join Date: Jun 2008
Location: Tampa, FL
Posts: 5,009
Images: 6
Quote:
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.
denverd0n is offline   Reply With Quote
Old 12-03-2010, 10:01   #32
Registered User
 
Randyonr3's Avatar

Join Date: Nov 2007
Boat: Beneteau FIRST 42
Posts: 1,836
Quote:
Originally Posted by denverd0n View Post
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....
Randyonr3 is offline   Reply With Quote
Old 13-03-2010, 05:16   #33
Registered User

Join Date: Jun 2007
Location: kefalonia ,ionian islands
Boat: Solaris Sunstar 38, Wild Honey
Posts: 150
Images: 1
planing catamarans ...

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 ??.
gramos is offline   Reply With Quote
Old 13-03-2010, 06:27   #34
Registered User

Join Date: Jun 2008
Posts: 25
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
Oyvind is offline   Reply With Quote
Old 13-03-2010, 08:23   #35
Registered User
 
GeoPowers's Avatar

Join Date: Dec 2008
Location: Gulfport, MS
Boat: Beneteau 393
Posts: 954
Images: 27
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!
GeoPowers is offline   Reply With Quote
Old 13-03-2010, 08:27   #36
Registered User
 
Randyonr3's Avatar

Join Date: Nov 2007
Boat: Beneteau FIRST 42
Posts: 1,836
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............
Randyonr3 is offline   Reply With Quote
Old 13-03-2010, 08:48   #37
Registered User
 
neelie's Avatar

Join Date: Oct 2007
Location: On the boat
Boat: Valiant 50
Posts: 509
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
__________________
The light at the end of the tunnel are no longer the headlights of the oncoming train......yippee
neelie is offline   Reply With Quote
Old 13-03-2010, 11:17   #38
Senior Cruiser
 
GordMay's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 49,139
Images: 241
Quote:
Originally Posted by neelie View Post
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.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 13-03-2010, 13:36   #39
Registered User

Join Date: Aug 2009
Location: between the devil and the deep blue sea
Boat: a sailing boat
Posts: 20,420
quoting Gord ;-)

Quote:
Originally Posted by GordMay View Post
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.
barnakiel is offline   Reply With Quote
Old 13-03-2010, 14:25   #40
Senior Cruiser
 
GordMay's Avatar

Cruisers Forum Supporter

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 49,139
Images: 241
Quote:
Originally Posted by barnakiel View Post
... 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.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 13-03-2010, 15:02   #41
Registered User
 
Starbuck's Avatar

Join Date: May 2005
Location: Long Beach, CA
Posts: 863
Skimming Over the Surface

Quote:
Gord May, he say:
Quoting Wiki is for amateurs.
+1

Quote:
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.
Quote:
Event[sic] though it is way out of date…
Some would use the term timeless.
Quote:
…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.
__________________
s/y Elizabeth— Catalina 34 MkII
"Man must have just enough faith in himself to have adventures, and just enough doubt of himself to enjoy them." — G. K. Chesterfield
Starbuck is offline   Reply With Quote
Old 13-03-2010, 15:35   #42
Registered User
 
44'cruisingcat's Avatar

Join Date: Sep 2006
Posts: 9,398
Images: 69
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.
44'cruisingcat is offline   Reply With Quote
Old 13-03-2010, 15:44   #43
Moderator and Certifiable Refitter
 
Wotname's Avatar

Join Date: Jan 2008
Location: South of 43 S, Australia
Boat: C.L.O.D.
Posts: 20,301
Not sure about Wiki (and the other mention reference sources) but I find that quoting CF usually cuts the mustard
__________________
All men dream: but not equally. Those who dream by night in the dusty recesses of their minds wake in the day to find it was vanity: but the dreamers of the day are dangereous men, for they may act their dreams with open eyes, to make it possible. T.E. Lawrence
Wotname is offline   Reply With Quote
Old 13-03-2010, 16:07   #44
Registered User
 
FSMike's Avatar

Join Date: Aug 2009
Location: Bahamas/Florida
Boat: Solaris Sunstar 36' catamaran
Posts: 2,686
Images: 5
And on the eighth day God created hull speed limitations.
__________________
Sail Fast Live Slow
FSMike is offline   Reply With Quote
Old 13-03-2010, 21:18   #45
Registered User

Join Date: Dec 2007
Location: Duluth,Minnesota
Boat: Lindenberg 26 & Aloha 8.2
Posts: 1,280
Quote:
Originally Posted by Randyonr3 View Post
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.
clockwork orange is offline   Reply With Quote
Reply

Tags
hull speed

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Speed Statistics of Mono vs Twin Hull Cruisers VikingCat Multihull Sailboats 44 02-10-2009 03:03
Ensenada Cheap Bottom Jobs Are a Myth! mrcottonsparrot Construction, Maintenance & Refit 1 23-09-2009 14:49
Log Speed vs GPS [SOG] Speed? Sandyh Navigation 57 07-06-2009 22:22
maximum hull speed for cat Nauti Cat Seamanship & Boat Handling 6 30-09-2008 15:31
Catamaran Hull Speed JusDreaming Multihull Sailboats 6 15-08-2007 19:17

Advertise Here


All times are GMT -7. The time now is 10:32.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.