Preventers

[Metalicmike]

When I bought my boat, like most sailors I checked the control systems and realised that there were no preventers. That is not to say that the previous owner never rigged something up but It was something that I had to consider. There are various methods of laying out control lines and devices that use friction to stop the boom accelerating violently. After a lot of thought I rejected all the pre described systems focussing on what I wanted to achieve which was to safely get the boom into a position where I could control it with the mainsheet and mainsheet traveller. I achieve this by setting a block on the gunwale further aft with control lines running from the boom to the cockpit This allows the boom to move freely for about 30 to 45deg before it is held by the restrictor and at this point it is under very little load as the wind has not yet caught the sail. In this position I can now take control with the mainsheet and Traveller. My Preventers live most of their life hung on the guard rails ready to be clipped on when needed.

 

[Laser310]

i'm a little confused...

do you have one on each side?

I don't see how, when the boom is all the way out, this system stops the boom swinging across.

 

[Metalicmike]

Yes I have one on each side so if the boom is on port side I clip on the portside restrictor. they are anchored via a block on the toe rail. Also having the block set further back reduces the stress on the lines.

 

[Boathook]

I have a preventer a bit like you described but rig as required. When in use on a "run" there is no slack, as if the wind gets behind my main it goes over and I would expect to see a fitting broken if the preventer allows the boom to start moving.

 

[Laser310]

when you say "preventer", do you mean something to prevent an accidental gybe, or something to control the boom in a gybe?

i confess that i don't really see how this system does either...

 

[Fr J Hackett]

There are two distinct things:

A boom brake. Designed to slow down and control the booms transition from one side of the boat to the other. Attached to the underside of the boom usually just after the vang with lines lead to port and starboard to a convenient point inline with the preventer and then lead back to the cockpit where they can be tensioned according to point of sail. Very useful for a single hander.

A Preventer. Designed to prevent the boom from moving unintentionally. This is attached to the out end of the boom and usually lead to a block at the bow and then back to the cockpit where it is tensioned. Commonly there is a fixed line on the boom with a quick release shackle that can be quickly transferred between the preventer lines after the gybe and clipped to the vang fitting when not in use. There are two lines one port one starboard, it can be difficult to control the boom when gybing using just the preventer which is why they are often used in conjunction with a boom brake as they both do different jobs. The point of attachment is important because if attached to the middle of the boom with an unintended gybe the forces can snap the boom.

 

[Metalicmike]

I am very happy with the setup as it is only there to keep things under control during an accidental jibe. You may believe that that the boom should be held firm against the mainsheet which is the standard approach. I do not believe that is necessary and as long as the boom cannot swing across the cockpit building up inertia then the system will work. Less lines on deck and safer sailing is what we all aspire too.

 

[dunedin]

Yes I have one on each side so if the boom is on port side I clip on the portside restrictor. they are anchored via a block on the toe rail. Also having the block set further back reduces the stress on the lines.

I take our preventer to the bow mooring cleats - threaded through and back to a winch or rear mooring cleat.
To my mind leading the rope forward reduced the stress on the lines (the opposite of your thinking) when the boom is let out - and never use a preventer if boom is not let out.
One big advantage of a preventer led forward and kept under tension against the mainsheet is that it stops the boom slatting back and forward in waves when the wind is not strong enough to keep the mainsheet rigid.

 

[Metalicmike]

There are two distinct things:

A boom brake. Designed to slow down and control the booms transition from one side of the boat to the other. Attached to the underside of the boom usually just after the vang with lines lead to port and starboard to a convenient point inline with the preventer and then lead back to the cockpit where they can be tensioned according to point of sail. Very useful for a single hander.

A Preventer. Designed to prevent the boom from moving unintentionally. This is attached to the out end of the boom and usually lead to a block at the bow and then back to the cockpit where it is tensioned. Commonly there is a fixed line on the boom with a quick release shackle that can be quickly transferred between the preventer lines after the gybe and clipped to the vang fitting when not in use. There are two lines one port one starboard, it can be difficult to control the boom when gybing using just the preventer which is why they are often used in conjunction with a boom brake as they both do different jobs. The point of attachment is important because if attached to the middle of the boom with an unintended gybe the forces can snap the boom.

You are absolutely right in what you write, however the forces at play multiply as the boom swings across the cockpit and the initial forces are very low therefore there is very little risk to the rig if the boom is managed before the forces build. Everyone will do what they are happy with, for me it gives me more time to haul in the mainsheet while i have control with my restrictor.

 

[NormanS]

I am very happy with the setup as it is only there to keep things under control during an accidental jibe. You may believe that that the boom should be held firm against the mainsheet which is the standard approach. I do not believe that is necessary and as long as the boom cannot swing across the cockpit building up inertia then the system will work. Less lines on deck and safer sailing is what we all aspire too.

"...building up inertia..."?

 

[Fr J Hackett]

You are absolutely right in what you write, however the forces at play multiply as the boom swings across the cockpit and the initial forces are very low therefore there is very little risk to the rig if the boom is managed before the forces build. Everyone will do what they are happy with, for me it gives me more time to haul in the mainsheet while i have control with my restrictor.

Accidental gybes happen very quickly.

 

[Metalicmike]

I take our preventer to the bow mooring cleats - threaded through and back to a winch or rear mooring cleat.
To my mind leading the rope forward reduced the stress on the lines (the opposite of your thinking) when the boom is let out - and never use a preventer if boom is not let out.
One big advantage of a preventer led forward and kept under tension against the mainsheet is that it stops the boom slatting back and forward in waves when the wind is not strong enough to keep the mainsheet rigid.

That is true but that's when I launch my spinnaker and haul in the mainsheet.

 

[Laser310]

Preventers are often required equipment on ocean races these days.

They inspect for them in some races.., and mostly what they want to see, is a preventer led to the bow.

There was a fatality in New Zealand a few years ago in which a preventer fixed amidships was implicated - i think it failed.

the most common setup for racing is two dyneema lines led from a bail at the end of the boom to the gooseneck - one on each side - with eye splices at the end.

then another line leads from a cockpit winch, through a clutch, to a block or low friction ring at the bow, and then back to the mast. It has a shackle, and can easliy be attached/unattached from either of the dyneema lines.

Gybing requires taking the forward line off of the old leeward dyneema line and putting it on the new leeward dyneema line - so someone has to go to the mast, which is not an issue on a race boat. there is often someone there anyway for the gybe to handle the spinnaker.

 

[Metalicmike]

Accidental gybes happen very quickly.

True but the damage happens on the windward side after the boom has crossed the cockpit

 

[Metalicmike]

I am not saying that my way is the best or the right way, I have spent most of my life making improvements, the number of times I have heard people say that a particular method will never change, every one does things this way. If not for people like myself who like to think outside the box we would still be driving horse and carts.

 

[Metalicmike]

Accidental gybes happen very quickly.

Very quick on a Dinghy I use to sail a laser.

 

[Sea Change]

I'm not sure I fully understand the OP's description of his setup.

One aspect of preventers in which there is room for discussion is whether to have any elasticity or not.
One way of doing things treats the preventer like an extension of the standing rig, holding the boom rigidly in position.
The second way is to deliberately have some 'give' in the preventer to absorb the shock load.

I'm in the first camp. When the main is first backwinded, there isn't actually much force on it, and the boat can pivot with it as you gybe.
The second way seems to risk letting the main build up momentum and if the preventer stretches enough, the line will contact the shrouds and put a load on them for which they are not designed. Ibl think it also increases the risk of the preventer failing and allowing the boom to sweep the cockpit, which is precisely what we are trying to avoid.

 

[Laser310]

I'm not sure I fully understand the OP's description of his setup.

i don't understand it either.

maybe a diagram or photo would help

 

[Laser310]

I'm in the first camp. When the main is first backwinded, there isn't actually much force on it, and the boat can pivot with it as you gybe.

i agree with this.

i have been on a boat with a preventer rigged, without slack, to the bow.., and an accidental gybe was not all that dramatic.

the main was fully aback for a while, but eventually, the boom ended up pointing downwind, with very little load.

it was more of a problem dealing with the headsail - a genoa on spinnaker pole, as we were wing on wing - i think we just blew the sheet

 

[Sandy]

You may want to take a look at

and

If you really want to scare yourself about preventors. It has certainly given me some food for thought how I rig mine.