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Old 08-05-2018, 07:10   #1
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Boom Preventor

Has anyone designed a boom preventor on a 38 leopard 2010
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Old 08-05-2018, 08:22   #2
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Re: Boom Preventor

I'm not sure about your boat, but preventers do not have to be complicated.

Is there something specific about your cat that prevents the below?

1) Taking 1/4" dyneema (or stronger if you think you need it) and tying a Bowline around end of boom

2) Bring line forward and outside of lifelines (if you have a mid-ship cleat)

3) If you do not have a mid-ship cleat, bring forward to the bow

4) Run line through cleat, ensuring there is no way the line can detach

5) Run line back aft to cleat near stern

6) Adjust and cleat.


This has the advantage of being easy to rig and mostly out of the way while cruising.

Make sure you have the line outside of the lifelines, otherwise when under sail you will put pressure on your lifelines (obviously not good).

Disadvantages:

1) Need to re-run line each jibe

2) If you do accidentally jibe you risk bending a stanchion or causing damage where it mounts


I feel 2 is an acceptable trade-off, but you may not agree.
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Old 08-05-2018, 08:43   #3
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Re: Boom Preventor

On a cat his likelihood of burying the boom and breaking it is pretty low. Could probably rig something mid boom easier to manage.
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Old 08-05-2018, 08:56   #4
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Re: Boom Preventor

That's a great point.
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Old 08-05-2018, 09:44   #5
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Re: Boom Preventor

Ever thought of using a boom brake rather than a preventer?
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Old 08-05-2018, 10:03   #6
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Re: Boom Preventor

Quote:
Originally Posted by lokityler View Post
Has anyone designed a boom preventor on a 38 leopard 2010
First, a question... on a cat like yours sailing dead downwind is NEVER the fastest way to get straight downwind, so it should rarely be sailing at risk of a gybe. Point up a bit and reach, you'll get there faster...

But if you really need to sail downwind...

Dyneema would be a very poor choice for a preventer. A bit of stretch is a good thing in case the sail does get backwinded. (If it never gets backwinded, why bother with the preventer?)

The traditional way of rigging a preventer is to have a line or cable the length of the boom that is attached to the outboard end of the boom. The working end is stowed at the gooseneck. One each side of the boat there is a line that runs from the cockpit up to a block at the bow, and then back to be stowed, usually at the mast.

When sailing downwind, the line for the appropriate side is attached (shackled, or tied) to the boom cable and tensioned.

These lines need to run back to the cockpit because if you get caught backwinded, you NEED to have a way of gracefully easing the line to bring the boom across. It should be wrapped around a winch, not tied to a cleat so you can ease it with control. The loads on this line can be VERY high if backwinded in a strong breeze. Be sure that the block and it's attachment point are up to the task.

One of the reasons for attaching the preventer at the end of the boom is to reduce this load as much as possible. If your boom is not built for midboom sheeting, the shock loads in a sudden gybe can buckle the boom if the preventer is attached there.

Hope that makes sense...
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Old 08-05-2018, 11:07   #7
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Re: Boom Preventor

>> When sailing downwind, the line for the appropriate side is attached
>>(shackled, or tied) to the boom cable and tensioned.

If you use a block on the bow, why do you need to run two lines like this?
When lines goes from the end of the boom, to block on the bow, does it matter which side of the boat it is lead to the cockpit?
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Old 08-05-2018, 11:34   #8
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Re: Boom Preventor

Quote:
Originally Posted by pskudlarski View Post
>> When sailing downwind, the line for the appropriate side is attached
>>(shackled, or tied) to the boom cable and tensioned.

If you use a block on the bow, why do you need to run two lines like this?
When lines goes from the end of the boom, to block on the bow, does it matter which side of the boat it is lead to the cockpit?
You can use a single line... but the OP has a cat and the lead is (usually) better from the bow of the hull on the side the boom is on. Going straight forward reduces the load in the event of a gybe compared to an angled pull to the center of the boat.
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Old 08-05-2018, 12:02   #9
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Re: Boom Preventor

Quote:
Originally Posted by pskudlarski View Post
>> When sailing downwind, the line for the appropriate side is attached
>>(shackled, or tied) to the boom cable and tensioned.

If you use a block on the bow, why do you need to run two lines like this?
When lines goes from the end of the boom, to block on the bow, does it matter which side of the boat it is lead to the cockpit?
That's not the point. The point is that if you have one line, when you gybe you have to carry the line all the way forward, passing it around the stays, mast, and even the forestay depending on where the block is, and back down the other side. If you have two you simply haul the main in, detach one side then attach the other side, right in the cockpit even, complete the gybe and boom (pun intended) you're done.

This is how many preventers on offshore monohulls are rigged, and guard against the boom being broken if it gets buried in a wave as the boat rolls.
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Old 13-05-2018, 17:22   #10
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Re: Boom Preventor

The real answer is that every boat has special considerations that may prevent clean fairleads for controlling the boom: dodgers, rigging, stanchions, cabin tops, etc. and the best way to rig a preventer is to experiment with the most efficient method for YOUR boat. Stock formulas did not work on my boat and I had to experiment to get the best compromise . . . not necessarily the best solution. Loop an old halyard/sheet around your boom and see what works best. I hope this helps. In exodus mode . . . Rognvald
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Old 21-05-2018, 12:13   #11
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Re: Boom Preventor

You cannot really put a forward preventer on a L38/39. Take a block and tackle from the boom and haul it down onto the aft cleat of whichever side you want to have the boom. You must remember that the Leopard catamaran has no back stays and thus the shrouds are quite a bit aft of the mast. This means if your sail billows (boom kicks up a bit) whilst your boom is held out, your sail is going to chafe onto the shroud and your full length batons are going to break on the shroud. So, let your boom out so that a 2:1 or 3:1 block and tackle goes straight down to the aft cleat, haul it tight and away you go down wind. Use line with a bit of stretch and not one of the dyneema type lines. Remember, if you do break one of the batons, there are two spare full-length ones in the top edges of the stack-pack that can be used in an emergency.
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