[C320-list] Downwind Preventer - was Whisker Pole Length
Allan S. Field
allan.field at verizon.net
Mon Dec 15 18:50:14 PST 2008
I pulled this out of Wikipedia:
"A preventer, or jibe-guard, is a mechanical device on a sailing vessel
which limits the boom's ability to swing dangerously across the boat during
an accidental jibe.
The uncontrolled jibe (or gybe) is feared by all sensible yachtsmen. The
heavy boom can potentially inflict severe head injuries or dispatch crew
members over board; even the mainsheet or traveller can also inflict serious
injury. Uncontrolled jibes may also damage the boat itself.
Rigging a preventer on a yacht's mainsail is often performed when the wind
is behind the beam (i.e. when it's coming from more than 90° off the bow).
It can also be useful at other times when there is more swell than wind, a
situation when the wind may not have the strength to keep the boom in place
as the boat dips and rolls.
On any boat that is sailing downwind without a preventer, strict
'heads-down' procedures must be enforced anywhere within the boom's arc.
Certain areas of the side-decks and maybe the cockpit also have to be
strictly 'no-go' to all crew depending on what the boom and mainsheet could
do in unchecked full swing.
The preventer with the most mechanical advantage is a line, from the end of
the boom, led outside of the shrouds and a long way forward - perhaps right
up to the bow - through a block, back to the cockpit and secured within
reach of the mainsheet.
Many cruising sailors prefer to rig two tackles (port and starboard) that
run from the midpoint of the boom to blocks on a track such as the
headsail-sheet-block track. These tackles are typically a 2 - 4 part tackles
for greater purchase. This rig can also be used as a boom vang without
taking up space under the mast that may be essential to the cruising sailor
for dinghy stowage and other uses. There is a possibility of breaking the
main boom with a preventer rig such as this, but many modern yachts are
considered to have short enough booms and be beamy enough to overlook this
possibility in normal use. For example, while running with the preventer
cleated, a large swell could roll the boat, dipping the boom end into the
water, snapping the boom in half.
Care should be taken when selecting the rope which is used for preventer
lines. To reduce the shock loads on the tackles, for example in an
unexpected jibe, three-strand nylon line may be preferred over of braided
cored line."
Allan S. Field
Sea Shadow - #808
Columbia, MD
-----Original Message-----
From: c320-list-bounces at lists.catalina320.com
[mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of
Orlando.Duran at AveryDennison.com
Sent: Monday, December 15, 2008 11:18 AM
To: C320-List at Catalina320.com
Cc: C320-List at Catalina320.com; c320-list-bounces at lists.catalina320.com
Subject: Re: [C320-list] Downwind Preventer - was Whisker Pole Length
I can only say what I read on his site and what several riggers I spoke to
at the time I was getting ready to do this...mine was set up that way, it
worked on the 320 and I set it up on the 440 the same way, although what I
did there is to run it to snatch blocks that I placed on the aluminum
toe-rail...
The mainsheet attached to the end of the boom is for up-and-down pull
where the mid-boom placement for a preventer is for side loads
Scott Thompson
<sthompson at toad.
net> To
Sent by: C320-List at Catalina320.com
c320-list-bounce cc
s at lists.catalina
320.com Subject
Re: [C320-list] Downwind Preventer
- was Whisker Pole Length
12/14/2008 11:08
PM
Please respond
to
C320-List at Catali
na320.com
I think you have this backwards, Orlando. If the strain becomes less
and the leverage greater as we move the attachment point towards the
gooseneck then why don't we attach the preventer near the gooseneck?
It's because there is less load on the preventer and boom in an
accidental jibe when the preventer is rigged towards the outboard end.
This is the same principle by which boats designed more for racing
typically have the mainsheet attached close to the end of the boom, with
a traveller running through the cockpit, or sometimes aft of it.
Also, I haven't followed Brion Toss's "SparTalk" forum for some time,
but I'm pretty sure I recall him at one point recommending a setup very
similar to Warren's, using a pennant running to the outboard end of the
boom.
Scott Thompson
Orlando.Duran at AveryDennison.com wrote:
> Quick reminder, you get more leverage and less strain on the boom by
doing mid boom or 3/4, never go to the end of the boom to rig a preventer
on (my caveat here) most boats....Brian Toss mentioned that on his website
> ----------------------------------
> Regards,
> OD
>
> Sent from my BlackBerry Wireless Handheld
>
>
> ----- Original Message -----
> From: "Allan S. Field" [allan.field at verizon.net]
> Sent: 12/13/2008 01:29 PM EST
> To: <C320-List at Catalina320.com>
> Subject: [C320-list] Downwind Preventer - was Whisker Pole Length
>
>
>
> Sea Shadow is rigged for downwind sailing differently than is War De Mar
and
> I will try to describe what we did. Note that the idea for this came
from
> Orlando Duran - I give him credit the first 2 times I share this then
the
> idea is all mine!
>
> The boom sheet on our boats runs thru 2 blocks. On the aft most block,
I
> hung a long shackle from the bail that the block attaches to. This
shackle
> is probably 3 inches long. From each of the forward deck cleats, I hung
> long shackles probably about 4 inches long and hung a single block off
each
> one of them. The reason for the long shackles here is to leave room for
> mooring lines. Moving aft, I hung a single block on the base of each
> stanchion port and starboard sides.
>
> At the base of the forward part of each side of the aft
> wraparound-stanchion, I attached a block with cam cleat.
>
> Now for the rigging. I have 2 preventer lines, one for port, the other
for
> starboard (red line for port, green for starboard). I went to West
Marine's
> rigger and had him splice on the end of each preventer line a heavy duty
> snap shackle, the kinds with the spring loaded snaps. These 2 shackles
are
> then attached to the long shackle on the mast bail previously installed
(see
> above). The preventer lines then run forward to the blocks on the
forward
> cleats then back through the blocks at the base of the stanchions and
> through the block with a cam cleat. Once set-up, I can control the boom
> 100% from the cockpit.
>
> I am a bit uncomfortable with the preventer lines coming back only to
the
> aft-most boom bail. I would much prefer that they come all the way back
> like Warren has done. That will be a winter project to figure out how
to do
> this better but without interfering with the dodger.
>
> Unlike Warren, I was hesitant to use the anchor roller for any of this.
> Worst case scenario on Sea Shadow is that the boom breaks/bends mid-boom
or
> a deck cleat pulls out. Worst case scenario on War De Mar is the anchor
> plate gives way, the forestay breaks and the mast comes down. (NOTE: I
hung
> a block off the anchor bail and run the spinnaker tack line through the
> block and up to the ATN Tacker. A rigger saw this and cautioned me that
> this puts a tremendous amount of pressure on the anchor base and there
is a
> danger of it pulling out. But the maximum apparent wind I will fly the
> spinnaker is 12 knots; gets any higher, the spinnaker comes down. And
yes,
> I fully expect to take some list-grief over this!)
>
> Our downwind pole is mounted to the mast on a track so is fairly easy to
> handle, much easier than when deck and/or stanchion mounted.
>
> With this set-up, I have no hesitation about going DDW (dead downwind)
under
> any conditions.
>
> Hope this helps.
>
> Allan S. Field
> Sea Shadow - #808
> Columbia, MD
>
> -----Original Message-----
> From: c320-list-bounces at lists.catalina320.com
> [mailto:c320-list-bounces at lists.catalina320.com] On Behalf Of warren
updike
> Sent: Friday, December 12, 2008 4:12 PM
> To: C320-List at Catalina320.com
> Subject: Re: [C320-list] Whisker Pole Length
>
> No photos, sorry. She's under wraps now. Preventer is used for the main.
>
> Since it is not recommended attaching a preventer mid-boom, I followed
> mfgr.'s recommendation and attached a pendant of twisted nylon to the
end of
> the mast with a thimble spliced into the working end. The length is
enough
> to bring the thimble over the deck when the boom is well overboard. I
use a
> bungee attached to the main sheet thingy to secure the pendant when not
in
> use. This makes it quite easy underway with the boom outboard to unhook
the
> pendant attach the preventer line and secure the preventer.
>
> I accept the risk of starting a whole thread on how to attach/run the
> preventer as I've not yet found the ideal method. Typically, I use a
block
> attached to the anchor roller to turn the preventer bringing it back to
the
> cockpit. It's faster and safer if you can control it from the cockpit.
Yet,
> I welcome any and all ideas on how to do it better. When not in use, the
> block is pulled out of the way with a bit of light bungee tied to a
vertical
> on the pulpit. I don't bother to untie this, just slide it down the
pulpit
> to free the block for use. Yes, it is necessary to unhook the preventer
> line and run around the mast when after gybing. What price safety?
>
> My pole is two part telescopic with 2" aluminum tubing. It's an old dude
I
> bought off the internet when I had a C25. It was a major reason for
> upgrading to the C320. I had to protect my investment in the pole, all
$150
> of it. Don't think I could manage a fixed pole of 10 or 12'
>
> Warren & Pattie Updike
> Catalina 320, #62, "Warr De Mar"
> Middle River, Chesapeake Bay
>
>
>
>
> -----Original Message-----
> From: Bruce Stanley [mailto:brucestanley36 at gmail.com]
> Sent: Thursday, December 11, 2008 11:19 PM
> To: C320-List at catalina320.com
> Subject: Re: [C320-list] Whisker Pole Length
>
> Thanks Warren
> do you have any photos of the preventer?
> is it a preventer for the Main or Genoa?
> is your Whisker Pole a fixed length, or telescopic one?
>
> Bruce Stanley C320 #1084 "Fantastic Lady"
> Sydney Australia
> ========================
> On Fri, Dec 12, 2008 at 10:44 AM, warren updike <wupdike at hotmail.com>
wrote:
>
>> I have a 12' pole I use with a 150% jib. I rarely use all 12 feet.
>>
>> I'm using the pole mostly on downwind runs while wing'n'wing. It holds
the
>> jib out nicely and is easy to deploy and retireve. I also rig a
preventer
>> on
>> the main as a precaution. I've had days where I've run N or S on the
>> Chesapeake Bay for hours with this rig. Well worth the investment.
>>
>> Warren & Pattie Updike
>> Catalina 320, #62, "Warr De Mar"
>> Middle River, Chesapeake Bay
>>
>>
>>
>> -----Original Message-----
>> From: Bruce Stanley [mailto:brucestanley36 at gmail.com]
>> Sent: Thursday, December 11, 2008 4:09 AM
>> To: C320-List
>> Subject: [C320-list] Whisker Pole Length
>>
>> The Whisker Pole Length is given as the J measurement.
>> This is stated as 12'4".
>> stupid question but I am trying to Measure Twice before I cut ...
>>
>>
>>
>
>
>
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