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Old 10-04-2010, 15:17   #1
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Preventer - C-Cleat Size and Load Rating

I'm building a custom preventer that runs forward to block, then aft and held fast by C-cleat at deck level just outside cockpit.
The Ronstan RF5020 Carbon C-Cleat (large) has a working load rating of 230kg and breaking of 460kg.
Do you think this is enough or is a more substantial retainer needed ?
Boat - Beneteau Oceanis 40'
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Old 10-04-2010, 15:30   #2
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I used a rope clutch instead and selected one which, in combination with the double-braid diameter used, will slip before something gets damaged but holds on again as soon as the load decreases to normal level again.
No matter what you choose, you must engineer a weak point which is not the boom. Better break a cleat if something has to go, but I find the rope clutch the best option.

ciao!
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Old 10-04-2010, 15:35   #3
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230kg == 507lbs. Seems like this isn't enough. I used a Lewmar D2 rope clutch - SWL 2,650lbs. As Jedi said, you need to work through the whole system and see where the breaking point will be.

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Old 10-04-2010, 18:33   #4
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I would think the working load is not enough and the cleat will get damaged at a point.

As for the 'weakest point' per Jedi - a load-sensitive cleat can be used too or part of the line (probably the outer end) can be made of lighter material as a fuse of sorts, optionally nylon or bungee can be used to introduce some give.

b.
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Old 10-04-2010, 19:02   #5
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planning on having a single line that runs down each side - at any one time one end is connected bo boom by quick release - the other in a cleat - hence the cleated end will have a QR shackle on it - thus need some sort of open clear that I can pull rope up and out.
Anything stronger than that Ronstan (large) cleat that will do this?

Also - not sure you want to let the boom wander - physics says that holding a still item against a forces requires X load capacity, but if the item has started moving the load requirement is multiples of X.
On the other hand - you do want some sort of hint of where the rig/boom is at or wants to go, and if it is all tensioned up you may not sense this for a bit longer than otherwise.
Hmm.
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Old 10-04-2010, 21:43   #6
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You need the weak point for when the end of the boom meets a wave. Something is gonna give in that situation, you have no choice.

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Old 10-04-2010, 23:28   #7
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I have a bit of 8mm line from the boom at the sheets down around the amidships mooring cleat as a turning block and then back to the aft mooring cleat.

On the boom I have a loop of 2mm line doubled over that I tie the 8mm line to. Thats my weak point.
The reason I want a weak point is that is gybed and the boat is pinned down aback the boat will be held down till released or a mainsheet block breaks. In a squall the angle of the boom and main may quite have the boat on its ear... dangerously so.

My way any uncontrolled gybe would be safe and then the thin line breaks.

Needless to say in such heavy weather as to make all preventers dangerous the mainsail should have been dropped anyway! Remember, a Beneteau 411 will run under bare poles in 30 kts at nealry 5 knots. With a scrap of Genny out even more.

Its not like you are in an old style heavy boat, or racing boat, where sails must be left up all the time. Just the hull of our boats are good downwind sails!

Total set up cost: A bit of 8mm line and a scrap.

Mark
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Old 11-04-2010, 18:34   #8
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My way any uncontrolled gybe would be safe and then the thin line breaks.

Mark
G'DAy All,

Somehow, this statement seems self-contradictory. If the thin line breaks in an accidental gybe, the boom comes crashing across just as if not prevented at all... maybe even more vigorously, it having been delayed slightly and thus with even more wind behind it.

But, the point about being able to release the preventer under severe load is a good one. And the cam cleat is a poor choice for that reason: once loaded up they are very difficult to release. I once experienced an accidental gybe just under the Golden Gate Bridge with just that sort of setup and was held down, spinnaker and spreaders awash, for what seemed like a week or two. Eventually a lull allowed me to uncleat the line and she popped back up, but I was **** scared for a while (this in a single-handed race, sailing a Yankee-30).

On Insatiable II we have permanent vang/preventers rigged. They cosist of three part tackles led from about mid-boom to a point just aft of the chainplates, and thence to the cockpit where they pass through a rope clutch and thence to a secondary winch. They act as quite powerful vangs, and we use them whenever the sheets are eased a bit. When we gybe (on purpose) we use the wraps on the winch to ease the sail across, giving good control. The risk of burying the boom and thus breaking it is real, but pretty small IMO and in our fairly long experience. When conditions are severe enough to cause such a big roll, we will likely have one or more reefs set. We had the reef cringles set so that the boom is kicked up quite a bit, reducing the odds even more. To me, the risk of boom breakage is less important than the risk of injury in an unplanned gybe.

Cheers,

Jim and Ann s/v Insatiable II lying Lake Macquarie, NSW, Oz
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Old 11-04-2010, 19:38   #9
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If you use end-boom preventing 1/4 inch double-braid nylon will work like a rubber band. The physics explains that with great stretch the jibe energy is absorbed by the nylon instead of shocking and transmitting a huge load directly to the gear holding the preventer. As such, 400kg rated gear will work as long as you get on top of fixing the jibe before too many huge waves broach the boat.

As the diameter of the nylon increases you will need higher rated SWL gear to handle the lack of stretch. As the nylon stretches the load integrated over the distance results in a dissipation of energy not absorbed by the gear.
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Old 12-04-2010, 02:43   #10
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Here is my logic thus far. My main purpose is to prevent accidental gybe in light airs running downwind - especially with family on board and on deck enjoying the sun. It is in these conditions the wind can get flukey. In this mode likelihood is greater, and exposure of people to the risk more likely. In this condition I feel a 400kg cleat should do the job.
As soon as the wind picks up, main is reefed, angles are taken to hold the wind away from the stern, people are off deck and the helmsman is much more alert. I am less concerned about creating the preventer for this mode.
Another advantage with a 430kg c-cleat is this will fail (I'm assuming the cam will break or release?) at that load rather than the boom or gooseneck taking the break.

On the idea of cam-cleats lockingup - I though that a vertical pull on the loose end would make an easy release ever under high load?
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Old 12-04-2010, 07:35   #11
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On the idea of cam-cleats lockingup - I though that a vertical pull on the loose end would make an easy release ever under high load?
30 knots at night the boat gybes, the boat is lying on is side, as Jim says spreaders in the water, you stagger up from below horozontally, you go to relese the line that hasent broken and find the preasure of the line on the cleat means is jammed fast.


There must be some alternatives that will work better for you.


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Old 12-04-2010, 08:52   #12
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It was said before: a Lewmar rope clutch will slip without releasing the rope when the load gets too high, holding on again as soon as load drops. I do not know a better system.

What is the gooseneck? (making sure my English is up to date... ;-)

cheers,
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Old 12-04-2010, 09:06   #13
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What is the gooseneck?


Nick.
The fitting between the boom and the mast.

Otherwise known as the blekentrufnespielendriftntrckased.
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Old 12-04-2010, 09:26   #14
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i use a piece of line and a winch and a cleat or a grabrail..lol--isnt necessary to use expensive items for a rarely used device....just donot create a blockage or a trip factor for going forward....
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Old 12-04-2010, 18:34   #15
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Here is my logic thus far. My main purpose is to prevent accidental gybe in light airs running downwind - especially with family on board and on deck enjoying the sun. It is in these conditions the wind can get flukey. In this mode likelihood is greater, and exposure of people to the risk more likely. In this condition I feel a 400kg cleat should do the job.
As soon as the wind picks up, main is reefed, angles are taken to hold the wind away from the stern, people are off deck and the helmsman is much more alert. I am less concerned about creating the preventer for this mode.
...
On a cruising boat there is a fair amount of risk when the wind and waves pick up significantly while sailing downwind and an autopilot or wind vane is engaged. This is true even if you are not sailing very deep. Sizing your preventer for light air doesn't make a lot of sense to me.

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