Hull Speed? - SailNet Community
 4Likes
Reply
 
LinkBack Thread Tools
post #1 of 23 Old 10-16-2011 Thread Starter
Senior Member
 
NewportNewbie's Avatar
 
Join Date: Jul 2011
Location: Newport Beach
Posts: 529
Thanks: 0
Thanked 1 Time in 1 Post
Rep Power: 5
 
Hull Speed?

I am curious as to how accurate this is at determining your max sailing speed. My hull speed from the manufacturers states 6.5 knots...I can get to that pretty easily, I would have thought that it wouldn't be that easy to get to the max speed. This was actually close hauled into the wind...I know you can get way above that downwind and surfing the waves. This speed was from my GPS and that was averaged over 3 minutes so it wasn't just a spike at that 6.5 speed...it was an averaged speed. With some tweaks to sail trim and a very clean bottom I'd think I can get to 7.5. Where some manufacturers more conservative with rating the hull seed? Or is it maybe modern sails and rigging make it actually possible to sail above hull speed? Or am I thinking too much and just enjoy that I can get the boat moving like that!

S/V Cuajota - 1975 WD Schock Santana 30

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
NewportNewbie is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
Advertisement
 
post #2 of 23 Old 10-16-2011
Senior Member
 
celenoglu's Avatar
 
Join Date: Dec 2008
Posts: 672
Thanks: 0
Thanked 14 Times in 13 Posts
Rep Power: 7
 
Hull speed is a theorotical value. The constant varies from one boat to the other. As the stern f the boat gets wider the boat travels faster. With good sails and good wind, hull speed can easily be beaten.
celenoglu is offline  
Quote Quick Reply Share with Facebook
post #3 of 23 Old 10-16-2011
Senior Member
 
jackdale's Avatar
 
Join Date: Dec 2008
Location: Calgary, AB, Canada
Posts: 9,041
Thanks: 27
Thanked 59 Times in 56 Posts
Rep Power: 7
 
Theoretical hull speed of a displacement hull= 1.34 X sqrt LWL


Other factors -

1) planing will take you above theoretical hull speed, usually downwind with a chute of some sort.

2) fouled bottom will slow you down.

You need a knotmeter, not a GPS when dealing with hull speed as it is through the water not over the ground. In addition you want a momentary speed not an average.
Faster and dhays like this.

__________________
ISPA Yachtmaster Offshore Instructor Evaluator
Sail Canada Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
ASA 201, 203, 204, 205, 206, 214
As I sail, I praise God, and care not. (Luke Foxe)
jackdale is offline  
Quote Quick Reply Share with Facebook
post #4 of 23 Old 10-16-2011
Just another Moderator
 
Faster's Avatar
 
Join Date: Sep 2005
Location: New Westminster, BC
Posts: 16,546
Thanks: 105
Thanked 314 Times in 301 Posts
Rep Power: 10
     
As Jack said, the GPS is speed over ground (SOG) including effects of any current that might be there (aiding or hurting) A knotmeter is the better tool for 'boat speed', esp as a result of changes in sailtrim. Having both allows you to quantify the current and approx direction.

You'll get up to 'hull speed' sooner, typically, while beating because your apparent wind is the highest it can be for the wind speed... a clean boat will get there quite easily, as you've observed. Without a lot of breeze or swells truly exceeding hull speed is quite difficult.

Also some boats are said to 'extend' their waterline while sailing (as flat overhanging stern counters become submerged by the rising stern wave) therefore theoretically creating a longer LWL at that moment, perhaps 'skewing' the calculation.

Anyhow, I wouldn't get 'hung up' on the number.. find out what is comfortable for your boat (heel angle and apparent wind angle,)and use that number , whatever it is, as a target and steer for that when trying to optimize your VMG to windward. Polar diagrams may be available for your boat that would tell you what that optimum speed/angle would be. But even with that data you'd need to be certain your instruments are accurate.. not always easy to do.

Ron

1984 Fast/Nicholson 345 "FastForward"

".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
Faster is online now  
Quote Quick Reply Share with Facebook
post #5 of 23 Old 10-16-2011
Senior Member
 
Join Date: Jan 2001
Posts: 158
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 15
 
Hull speed as determined by the 1.34 x square rt of the LWL is not a hard number, just an approximation or rough guideline.

Below is a portion of an in interview with Gary Mull:



He was casually asked whether the maximum speed of his intriguing new boat design was 1.34 times the square root of the waterline length.
"I wish people would quit saying that," he retorted with intensity. "There's no such thing as a maximum speed under sail. There's a point at which the speed-versus-resistance curve begins to get very, very steep. At low speeds, a certain increase in horsepower gets you a fairly good increase in speed - but at high speeds, doubling the horsepower only gets you a very slight increase in speed. Usually somewhere around 1.34 times the square root of the waterline length - the sailing waterline, not the static waterline - that speed/ resistance curve starts to get very steep. But there's no absolute limit."

"But," he was asked, "doesn't the quarter wave start to build up higher than the cabintop?""No! That's not so!" he exclaimed. "I've never seen such a thing. That's all magazine talk. That's not naval architecture. I'm continually seeing this 'maximum speed under sail' or 'maximum speed-length ratio' or whatever-the-hell, and it's totally meaningless to naval architecture, as an absolute maximum. It does have meaning, because the speed-resistance curve does get very, very steep, as I say; but it seldom gets absolutely vertically asymptotic."
BigZ is offline  
Quote Quick Reply Share with Facebook
post #6 of 23 Old 10-16-2011
Senior Member
 
blt2ski's Avatar
 
Join Date: May 2005
Posts: 6,884
Thanks: 0
Thanked 30 Times in 29 Posts
Rep Power: 12
   
Not sure if it has been mentioned, but "SOME" sailboat hulls do not follow the rule of the 1.34 time sqrt of WL. many of the newer planing hull designs are like power boats, you CAN go faster than the formula. On the otherhand, take a boat like the Pinta, Santa Maria, old ironsides etc, those will be lucky to hit the formula, and if they do go over, some designs DO sink into the water and eventually sink! I would SWAG that most boats built in the last 30 or so years, some as far back at 50-60 have the ability to go over the theoretical hull speed.

marty

She drives me boat,
I drives me dinghy!
blt2ski is offline  
Quote Quick Reply Share with Facebook
post #7 of 23 Old 10-16-2011
PCP
Senior Member
 
PCP's Avatar
 
Join Date: Dec 2004
Location: Portugal, West Coast
Posts: 16,214
Thanks: 21
Thanked 105 Times in 88 Posts
Rep Power: 11
 
Quote:
Originally Posted by jackdale View Post
..

Other factors -

1) planing will take you above theoretical hull speed, usually downwind with a chute of some sort.

..
On a light cruising boat you don't need a spinnaker. Enough wind will do the job even without a spinnaker

pogo 10.50 cocody - YouTube

Regards Paulo
PCP is offline  
Quote Quick Reply Share with Facebook
post #8 of 23 Old 10-16-2011
Both ends are pointy.
 
junkrig's Avatar
 
Join Date: Jun 2011
Location: Missouri
Posts: 228
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 5
 
Everybody knows, as well, that multihulls blow the hull speed numbers out of the water. And, naval architect Dave Gerr, director of the Westlawn school of naval architecture, says that relatively long skinny hulls are not bound by the theoretical hull speed number. OTOH, people who sail older designs like my Lyle Hess-designed Nor'Sea 27 do much better to expect no more than the theoretical hull speed and just be happy with it.
Jeff


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

S/V Seablossom Nor'Sea 27 with modern junk rig.
Just because I like it.
junkrig is offline  
Quote Quick Reply Share with Facebook
post #9 of 23 Old 10-16-2011
Senior Member
 
jackdale's Avatar
 
Join Date: Dec 2008
Location: Calgary, AB, Canada
Posts: 9,041
Thanks: 27
Thanked 59 Times in 56 Posts
Rep Power: 7
 
Quote:
Originally Posted by junkrig View Post
Everybody knows, as well, that multihulls blow the hull speed numbers out of the water.
Jeff
I believe the multi's plane. Theoretical hull speed applies only to displacement hulls.

__________________
ISPA Yachtmaster Offshore Instructor Evaluator
Sail Canada Advanced Cruising Instructor
IYT Yachtmaster Coastal Instructor
ASA 201, 203, 204, 205, 206, 214
As I sail, I praise God, and care not. (Luke Foxe)
jackdale is offline  
Quote Quick Reply Share with Facebook
post #10 of 23 Old 10-16-2011
Both ends are pointy.
 
junkrig's Avatar
 
Join Date: Jun 2011
Location: Missouri
Posts: 228
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 5
 
Quote:
Originally Posted by jackdale View Post
I believe the multi's plane. Theoretical hull speed applies only to displacement hulls.
I didnt know for sure if they planed, but I knew for sure they're fast.


To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.



To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

S/V Seablossom Nor'Sea 27 with modern junk rig.
Just because I like it.
junkrig is offline  
Quote Quick Reply Share with Facebook
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Similar Threads
Thread Thread Starter Forum Replies Last Post
C&C 24 hull speed? PaulinVictoria General Discussion (sailing related) 7 06-17-2010 11:41 AM
Hull Speed? PalmettoSailor General Discussion (sailing related) 38 08-10-2007 04:14 AM
Hull Speed timangiel General Discussion (sailing related) 35 07-24-2007 09:08 PM
LWL and Hull Speed flicker General Discussion (sailing related) 2 12-03-2003 07:41 PM
Hull Speed Sailormon6 General Discussion (sailing related) 11 08-03-2002 08:16 AM

Posting Rules  
You may post new threads
You may 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 On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome