Fast cat hull speed and overpowering - SailNet Community
LinkBack Thread Tools
post #1 of 2 Old 06-23-2010 Thread Starter
Make it Happen
pwillems's Avatar
Join Date: Feb 2010
Location: Perth, Western Australia
Posts: 24
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
Question Fast cat hull speed and overpowering

Hi all,

Complete newB here just wondering if someone can clarify a couple things that have been on my mind. I'll not be doing my first sailing course for a couple more weeks, but have been doing heaps of reading on sailing theory as I would like to walk into the course comfortable with the classroom stuff so I can concentrate on the actual fun bit. I guess it's also 'cause I'm a bit of a nerd too .

Jeff_H put it very well in a post I came across explaining how the accumulated forces of a sail can be thought of as having three active components; Drive- which is the component of the force that acts in the forward direction of the boat, Drag which is a component that acts to reduce drive, and Heeling Forces which operate across the boat. He then goes on to say the following: "In an ideal sense the goal in sailing is to maximize drive while keeping the other two components under control".

Overpower a monohull and you'll end up with the rails in the water, simple to understand. But how does this work on a multihull? How does a multihull skipper know when he is getting overpowered as he can't rely on the heeling degree. Is it a bit of a seat of the pants thing that a multihull skipper just has to get a feel for?

Another thing that I'm trying to figure out is how some of the faster cats can travel way above hull speed. I'm talking about 40 footers cruising well above 15 knots in a good blow. Not surfing, just cruising. Are these vessels effectively planing or is there something else at play here?


“Noah was a brave man to sail in a wooden boat with two termites.”
pwillems is offline  
Quote Quick Reply Share with Facebook
Sponsored Links
post #2 of 2 Old 06-23-2010
Telstar 28
sailingdog's Avatar
Join Date: Mar 2006
Location: New England
Posts: 43,290
Thanks: 0
Thanked 18 Times in 14 Posts
Rep Power: 16
Red face

A multihull sailor has to take care not to get overpowered. This is one major reason multihulls reef for PEAK wind speeds rather than the average wind speeds. When a gust hits a monohull, it can often bleed ofb much of the excess force by heeling--something a multihull can't do. Some multihulls will have distinct warning signs of when they are getting ovepowered, others will not.

Many catamarans, especially those designed for the charter trade, are poor sailing craft and not much faster than monohulls. Others, like the Chris White-designed Atlantic series or the Melvin & Morelli designed Gunboat line, are very good and typically sail in the teens or higher.

I'd point out that these boats are not exceeding hull speed, but that their design requires a coefficient much higher than the 1.34 typically used for displacement monohulls.


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

Telstar 28
New England

You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

If you're new to the Sailnet Forums... please read this
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

sailingdog is offline  
Quote Quick Reply Share with Facebook

Quick Reply

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


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

Email Address:


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
Understanding Apparent Wind Steve Colgate Learning to Sail Articles 0 11-10-2002 07:00 PM
Understanding Apparent Wind Steve Colgate Seamanship Articles 0 11-10-2002 07:00 PM
Understanding Apparent Wind Steve Colgate Racing Articles 0 11-10-2002 07:00 PM

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