SJ23 Tech Tip F08, (Updated 2023-06-09) Art Brown, Bob Schimmel

Index

Boom Jibe Preventer.
Index - Jibe Preventer, Boom Brake
Banana Split, is equipped with a jibe preventer which is a line tied to the boom to prevent it from swinging across the cockpit, uncontrolled.  This is an excellent description of an accidental jibe!  Sorry, but shit happens sometimes, even with the best of crew.  One can only hope that a head doesn't get bashed in.  That swinging boom is a perfect recipe for a headache, to say the least.  With this design it might even be possible to eliminate the vang, although it couldn't swing with the boom.  In the absence of a boom brake the prescribed technique for jibing is to pull the boom to mid cockpit, jibe the boat, and release the mainsheet after the boat falls on the new heading.

Operation - Banana Split has two control lines, one to either side.  Each is equipped with a cam cleat for quick release.  By pulling one or both lines tight, and then securing them into their respective cam cleat, they keep the boom stationary.  I think the best value is that they prevent an accidental jibe.  Next, they can be used to keep the boom hard out on a downwind run.  While moored or under power I frequently set each in their cleat to keep the boom stationary. 

Does it work well? - Yes, it is very effective in keeping the boom from swinging about when you want it to be steady, like in light air or when I find myself in the wake of some "smoke-pot"!

Is it easy to use? - They are very easy to set.  Just call to the "First Mate" to set the preventer and if you are in her good graces she will pull the lines tight and set them into their cam cleats.  On the other hand, you can do it yourself!

Is it a hindrance in any way? - Having the preventer on the boat also means there are two additional lines on the side decks to trip over.  On occasion, I forget to release them when I want the boom to swing.  To quote The Art and Science of Sails, "Setting a preventer has its drawbacks too, some of which can be serious."  If a preventer is set when a broach occurs, the main will back fill on the wrong side.  This can pin the boat down, even if the spinnaker is let go.  However, the danger of not sailing with a preventer should be obvious and can be deadly.  In an accidental jibe, someone might get hit by an uncontrolled boom as it makes its terrifying arc across the cockpit."  Art Brown.

Fig 1 - The angled lines from the middle of the boom over the cabin to the side decks are the preventer  lines.


 

Fig 2 - Preventer lines attached to the bottom of the boom.


 

Fig 3 - Below are the details for attaching a preventer line to the toe rail.

 
 

Fig 4 - Detail on the deck.


 


 

COMMENTS

A preventer stabilizes the whole rig off the wind and if you fall or something and the boat jibes then nobody gets hurt and the main is small enough that you don't broach afterward.  You can even operate the preventer from the cockpit as an emergency brake when reaching or beating.  So much for the sailing part.  The best reasons are when the boat is not sailing:

  • The first thing you do is set the boom off centerline so you don't bash your head every time you go in or out of the cabin.
  • You can tether the dinghy to the end of the boom away from the big boat so it doesn't bash the hull all night.  Use the boom topping lift.  The boom can also be another stabilizing point when boarding from the dinghy. 
  • You can also set the boom way out and hang stabilizing buckets, anchors, or kids who misbehave, to make the boat slop around less.  If the kids still misbehave, you can ease the topping lift! 
  • Extra bonus is tying the mast down at the spreaders to keep it from twisting and bouncing when the boat is trailered.  My tackle is mainsheet sized which gives easy travel and hand feel, but 5/16" line would probably never fail.  You really want a cleat on both sides! 
  • Sail hard.  Gleno

"I find that a single block on each toe rail is the best set up.  I've talked to people who sailed the Vic-Maui race, which is bigger water than I sail on, and they want a line that is small enough so it can break in a hard knock down.  This is on >35' boat with serious sail area.  200 ft2 of main, or more, and over 25 knots of wind.  I have found a 1/4" or 5/16" line is fine for the Puget Sound waters and the Strait of Juan de Fuca.  Last time I crossed the Strait, I had 15 knots of wind and 7' waves on my starboard quarter and could just barely steer with a wheel in my SJ34.  If I found myself in those conditions in a SJ23, I would run for cover and wait until it calmed.  Use a block on each toe rail and put the line on a winch so you can ease it in a controlled manner.  A boom is so expensive.  Your money is better spent on strong spirits that can embellish the story when you get to the dock!"  Gene Adams
 

BOOM BRAKE by MeriMarine - A simple and effective version of a boom brake to prevent an inadverted jibe.  It works with friction and even has a setting for high winds.  Seems easy to adjust with one control line, although you could release or set either end of the control line.  Click on the link for the details https://dreamgreen.org/boom-brake
 

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