Also, how do you cleat it ? Tie off on the aft cleats ?

I have been thinking about a new setup for a preventer on my 400e so this is a good chance to present it for some feedback.   

I'm thinking of installing two lines on either side of the boom (red lines on the drawing), attached to the aft end of the boom (F) and temporarily tied near the gooseneck (A) - maybe rivet two small horn cleats there.   These lines would have eye splices on the forward end.   To rig the preventer I would run a second (green line) that is tied to the eye on the red line, runs forward through the opening in the base of the forward mooring cleat(C), across to the second forward mooring cleat, back around the midship cleat (D) to the winch (E) (or aft mooring cleat).   To gybe I would untie the green line and run that (port) end of the green line aft, attaching the other (starboard) end of the green line to the second (starboard) red line.

A few key features:

- Can be rigged with boom fully out to leeward 

- Can be rigged from the mast (don't need to go forward of the mast)

- Can be secured to the windward winch unless I'm using my pole, in which case I can use the stern cleat

- One advantage of using the winch is that it can be quickly and easily released even under load

- Red lines make handy clothes lines when moored!

I've used a similar arrangement before but attached the preventer line to the forward cleat, which was not as convenient.

I think it may be ok to run the lines through the cleats with no blocks because they would not have to be tightened under load, just "snugged up" and again I can use the winch to overcome a little friction.

I do think you need to run the preventer line as far forward as possible to hold the boom forward, and am not so sure that attaching it to the midship cleat will work.

Anyway, before I experiment with this setup next month I thought I'd float the "thought experiment" on the forum for feedback...

Owen.

A couple of differences from your proposal:

I use just one line along the boom, your A line in the drawing. When we jibe, we just run it to the other side of the boom. It lives on the starboard side when at rest, tied off to a cleat on the mast, which also holds the B line when not in use. 

I keep a large soft shackle at the end of the A Line which facilitates a quick connection to the B line. 

The B line (Dyneema) is brought forward to the bow and is passed through a speed ring, that in turn is connected to two forward cleats by two Dyneema strops, each with generous loops spliced at the end. These loops are cow hitched to the cleats. This allows the B line to be centered mid ship just aft of the cleats, with the forces evenly distributed between the two forward cleats. I found that if this forward speed ring isn't centered, line B interferes with the lifelines. 

This forward speed ring is spliced into the Dyneema strops, so the whole package is quite secure. Takes just a moment to set it up between the bow cleats, which we do before we head offshore. 

The B line then runs aft through two additional speed rings connected to the midship starboard cleat, and then aft to the manual foreward winch. 

The system works well, though on my boat, the lower shrouds preclude the boom from being anything but fully eased or sheeted in maybe half way when the preventer is deployed. Otherwise the B line chafes against the shrouds - not good. 

Everything is done in Dyneema. The forces in a jibe would be enormous so I chose not to scrimp on materials. It's served me well and saved me more than once. I suppose you could use blocks but speed rings spliced to Dyneema seem the better choice. 

It is a bit fussy to jibe, but as you note everything can be done aft of the mast. 

Hope this helps. 

Possibly not a good idea if you are in the habit of dragging the boom end in the water at high speed with preventer on, but as a cruising sailor who reefs early I have had no problem with this. and you never need to leave the cockpit to apply or release.

One mod since the pictures, is to have a 1.5m length of rope (dyneema, like the ropes down the boom) with 2 snaplinks on it to connect the boom preventer line to the barber hauler line.  This makes it easier to set up and means, that in a tight situation, I can release the preventer and gybe the yacht without having to disconnect the preventer.    

I use an ordinary Super 8 with dynema 8mm line and low friction rings. It works very well. 

https://www.blackdiamondequipment.com/en_US/product/super-8-belay-rappel-device/" rel="nofollow - https://www.blackdiamondequipment.com/en_US/product/super-8-belay-rappel-device/

Total cost about 90 euro.

Could you sketch how you rig the line through that please; because I cannot see what stops the line jamming completely. So obviously I am missing how it works

The anchor point on the bottom of the ring to the fixing point on the boom is quite a long way. ie several inches. So does the boom swing from side to side a bit, even though the bottom of the ring is retained?

Other systems seem to be similarly fastened & it does make me wonder how the boom can be rigidly held.

Always strikes me that the preventer line should go right up to the underside of the boom. Not to a point some way below it.

thats right, you should not use this on bigger boats. I got the tip from one that using this on a X-yacht 382 and it works well on that boat to. The mainsail on that boat is also about 35 m².