What are regarded as sound principles regarding the rigging of a safe
preventer so far as blocks, shackles and line ?

Am I overlooking anything here ?

Appreciatively,
Courtney
--
s/v Mutiny
Rhodes Bounty II
lying Oriental, NC
WDB5619

Courtney:

Well, I can give you an example of what is too small.

Sailing wing on wing with one reef in the main and the genoa rolled up a bit
in 25-30 kts of wind with 8' seas of the stern in a Saga 43, the preventer
was challenged by a big sea and let go. It was 5/15" dacron reeved with two
parts from the aft of the boom to the toe rail. The block on the boom was a
light weight component, probably good for only 3/8" line or smaller and it
let go and allowed an uncontrolled jibe.

We then rigged a preventer from the aft of the boom direct to the bow
fitting with one part of 5/16" dacron. Another heavy sea started a jibe that
stretched the dacron by several feet and allowed a somewhat controlled-
uncontrolled jibe. We subsequently saw that the stresses had destroyed the
roller wheel on the bow chock.

So, the point is that preventers need to be stout, but maybe not so stout.
At some point of wind and sail you are going to break the boom, particularly
if the preventer is only rigged to one point.

Probably the best scheme would be to rig the preventer from the toe rail to
the boom in multiple parts at two points- midboom and at the end. With this
rig you have several parts so you can use reasonable sized line and blocks
and the stress on the boom is spread out along its length.

Any others have thoughts?

David

"David&Joan" wrote in message
news:fhHTd.158434$6u.147000@fed1read02...
(clip)
So, the point is that preventers need to be stout, but maybe not so stout.
At some point of wind and sail you are going to break the boom,
particularly
if the preventer is only rigged to one point.

Probably the best scheme would be to rig the preventer from the toe rail
to
the boom in multiple parts at two points- midboom and at the end. With
this
rig you have several parts so you can use reasonable sized line and blocks
and the stress on the boom is spread out along its length.

Any others have thoughts?

David



On our boat, and many others, I'm sure, the boom sheet is at the end of the
boom.

While I'm sure there must be failures in the records, I don't know of any
booms sheeted this way which have failed due to overload. If that's where
the sheets can take all the stress, it ought to be the stoutest part of the
boom. Ergo, that's where I have my preventer.

Now, whether or not the places I put the other end, or the tackle used, is
going to be strong enough to manage a forceful attempted uncontrolled jibe,
I've not yet tested. Generally, unless it's not working for the geometry at
the time, I put it on the genoa track shackle loop which I can slide
anywhere up to where the genny block is at the time. Otherwise I carry it
forward to a stanchion base (never having had it out far enough to warrant
taking it to the bow). I also use this method to provide a three-point
system, giving me downhaul control even well out.

The tackle appears to be a prior vang. The way our cockpit is set up, the
only way a vang could work is if there were no bimini - and there *is* a
bail on the boom in the location where a vang would make sense. Of course,
I could put the preventer there - but I don't like the thought of a bent
boom in the case of violence :{))

L8R

Skip and Lydia


--
Morgan 461 #2
SV Flying Pig
http://tinyurl.com/384p2

"Twenty years from now you will be more disappointed by the things you
didn't do than by the ones you did do. So throw off the bowlines. Sail
away from the safe harbor. Catch the trade winds in your sails. Explore.
Dream. Discover." - Mark Twain

Courtney Thomas wrote:
What are regarded as sound principles regarding the rigging of a safe
preventer so far as blocks, shackles and line ?

Am I overlooking anything here ?

Appreciatively,
Courtney

Hi Courtney,

Lots of ways of doing this, and some good comments posted already.

Only things I would add:

If you rig a preventer, be sure to give it a "weak link" that will part
if you should broach and the boom drags. Maybe a couple loops of 1/8"
dacron or similar, just enough to keep the boom from an accidental jybe
but not enough so the boom will break.

Perhaps even better than a preventer is a "boom brake". I know of
several single handers' that swear by them, and although I've never used
one I like the idea: slows the boom in the event of an accidental jybe,
but still allows the boom to move in the event of a broach.

Hope this helps.

--

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David&Joan wrote:
Courtney:

Well, I can give you an example of what is too small.

Sailing wing on wing with one reef in the main and the genoa rolled up a bit
in 25-30 kts of wind with 8' seas of the stern in a Saga 43, the preventer
was challenged by a big sea and let go. It was 5/15" dacron reeved with two
parts from the aft of the boom to the toe rail. The block on the boom was a
light weight component, probably good for only 3/8" line or smaller and it
let go and allowed an uncontrolled jibe.

We then rigged a preventer from the aft of the boom direct to the bow
fitting with one part of 5/16" dacron. Another heavy sea started a jibe that
stretched the dacron by several feet and allowed a somewhat controlled-
uncontrolled jibe. We subsequently saw that the stresses had destroyed the
roller wheel on the bow chock.

So, the point is that preventers need to be stout, but maybe not so stout.
At some point of wind and sail you are going to break the boom, particularly
if the preventer is only rigged to one point.

Probably the best scheme would be to rig the preventer from the toe rail to
the boom in multiple parts at two points- midboom and at the end. With this
rig you have several parts so you can use reasonable sized line and blocks
and the stress on the boom is spread out along its length.

Any others have thoughts?

David



If you build it, and rig the rest of the boat, so strongly that
nothing will ever break, it won't float.

My preventer is a snap shackle on one of the vang tackle block
parts, which gets clipped onto a stanction base if a run is to be
very long. It's normally a six part vang, three seperate blocks at
the mast base, with two parts to the gunwhale, and I have used it
for circling and heaving to while swimming under sail, but not in
high winds, and someone who can sail must stay on the boat. The vang
attachment on the boom must be well out from the gooseneck, or the
leverage could break any gear. One third of the boom length seems
safe enough so far.

The stanction bases are backed up with metal plates.

The boom end is too far overboard for a preventer on a run, that's
why if needs to be inboard of the boom part where it crosses the
gunwhale while wung out.

A seperate boom end line to the bow, P&S is too much bother to rig,
or leave loose on deck, or dragging over the side.

When sailing, you are supposed to be paying attention while on a
run, and anticipating gybes, and steering to prevent them. In heavy
weather, you shouldn't be trusting a preventer. A preventer is
really to stop slopping around in some conditions, it is not a
normal sail trim thing, though it can stretch out a nice run by the
lee. It dipping the boom is going to be a problem, maybe you should
be paying attention to conditions, reefing, gybing and rigging for
heavy weather, not a good time to be trusting the rig to a
convenience feature.

Terry K