Sailboat Racing Trim — Part 3

In Chapter 3 of his book Racing Trim, Bill Gladstone talks about general Trim Concepts & Definitions. The following post shows a short summary of that chapter.

A boat sails downwind because it is being pushed along by the wind.  However, it’s a bit different to sail up wind.  A boat is able to sail upwind because of lift.  If you look a the curved shape of a sail, one side is concave and the other convex.  The wind piles up on the concave side and travels slower.  However, it travels faster on the convex side.  This creates a sort of a vacuum.  So, the boat is pulled along.  Something similar happens in the way that the water travels along the keel.  Forces on the sails and the keel balance each other out to keep the boat upright.

The forces of wind on the jib and main sails combine to have an even bigger effect on the boat than you would get from the effect you would get from adding up the power provided by each individual sail.

SPEED FIRST, THEN POINT

The flow of air or water over the sail or keel creates the lift that moves the boat along.  In order to achieve that lift, air or water have to be moving.  For example, if a boat is sitting still, there won’t really be flow of water across the keel to provide lift.  So, the first step to sail is to get that water flowing across the keel.  In order for that to happen, the boat needs to be moving.  That leads to a much repeated phrase out on the water — Speed First, Then Point.  That means that you need to get the boat moving before you fine tune the trim of the sails.  It doesn’t matter how well your sails are trimmed if the boat’s not moving.

There are multiple factors that impact how efficiently the sails move the boat.  The angle of attack refers to the angle that the wind hits the front edge of the sail.  The draft, draft position, sail shape and twist also have a huge impact on sail performance.  In simple terms, you can think of this as whether the sail is baggy or tight, and how forces (e.g. lines) are pulling on the sail to control its shape in the wind.  There are many aspects to be understood here.  Let’s explore this more in future posts.

All aspects of sail trim come into play along with how the boat is driven (e.g. pinching and footing) to result in progress toward the mark or destination.  Velocity made good (VMG) is the best mix of speed and point.

 
Here’s a link to a sail trim game. It’s free, thought you might like to check it out.

This is the third in a series of posts based on Bill Gladstone’s book Racing TRIM from the North U. Series.  Periodically, I post about a chapter or two.  This will be my short summary of what I’ve read.  You can read the posts to get my abbreviated summary; or you could read through the books with me.  Your comments can help point out what you find most interesting, or even poke fun at what I do and don’t know.  If you are interested in getting this book, you can find it in the online store section of NorthU.com for $25.