Jammer for Main Outhaul and 3rd Reef

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thinwater
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Jammer for Main Outhaul and 3rd Reef

Postby thinwater » Tue Jan 24, 2017 11:56 am

For years I've struggled with an undersized cleat on the side of the mast. I finally fixed it properly, replacing it with a double jammer, which also serves to secure a 3rd reef. Actually, the motivator was using the 3rd reef a few weeks ago and being annoyed that there was no good way to adjust the outhaul tension.

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http://sail-delmarva.blogspot.com/

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Re: Jammer for Main Outhaul and 3rd Reef

Postby Phenix » Sat Feb 04, 2017 2:46 pm

Nice. Did you do this without a backing washer or plate? What's on the inside of the boom?
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Re: Jammer for Main Outhaul and 3rd Reef

Postby thinwater » Sat Feb 04, 2017 4:30 pm

No backing plate, just threads. Previously, the cleat had been secured by just 2 x #8 screws, and it is now 4 x #12.

In fact, the force on the reefing line is not that great. The sheet load is about 600 pounds max (I've measured this as part of an article on jibe tamers), and this line holds a little less than 1/2 of that, perhaps 400 pounds in a bad jib when in very tight. A #12 screw should be able to hold ~ 700 pounds in shear, and 4 are sharing the load. As for up-lift, the leverage reduces that by ~ 5:1 and it is shared by 2 screws. Thus, the pull-out force is about 40 pounds, far less than the pre-tension applied when tightening the screw (859 pounds by ANSI standard, though it would be slightly less in high-strength aluminum).

So no backing is required. In fact, backing plates are very seldom needed for jammers in relatively thick-walled aluminum spars. The leverage limits the load. I would put nuts on it if I could reach them, which is quite impossible.

Cut clean threads and use an anti-seize (grease, Tefgel).

As for what is on the inside of the boom, look in the end. There is a block and tackle for the internal reefs, but there is clearance on the side. The screws were carefully calibrated in length and do not stick in more than 1/8-inch.

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Re: Jammer for Main Outhaul and 3rd Reef

Postby Phenix » Sat Feb 04, 2017 4:49 pm

Thanks for the additional detail on the screws. Interesting. I always feel that I am accomplishing something then I have a tap tool in my hand. 8)

You talk about the load on the reefing line, but in your pic, it appears that this is the outhaul. I assume the reefing line somehow goes through the upper clutch?

My outhaul comes out at the mast-end of the boom, not at the side of the boom like yours does. I have 32 hull #7, none of my halyards, reef lines, outhaul, etc. run aft to the cockpit.

As for my question "what's on the inside of the boom?", it was referring to your jammer, as in "is there anything on the inside of the boom providing backing support for your jammer?"
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Re: Jammer for Main Outhaul and 3rd Reef

Postby thinwater » Sat Feb 04, 2017 5:55 pm

The first 2 reefs are internal and the jammers are inside the boom, on the underside near the boom. This is for the 3rd reef.

No, there is no additional internal support. The load is not that great, never more than 100 pounds.

All reefing lines go around the boom, up to the reef cringle, down to a pulley near the boom end, and forward. Internal reefs are internal, but this line runs down the side of the boom.

Your outhaul must go forward to somewhere. Even on dinghies, they don't end at the end of the boom.

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Next time I go out I will take some pictures and post them. I simply have not been out in that much wind lately. I try to avoid it!

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Re: Jammer for Main Outhaul and 3rd Reef

Postby Phenix » Sat Feb 04, 2017 7:42 pm

thinwater wrote:Your outhaul must go forward to somewhere. Even on dinghies, they don't end at the end of the boom.


Yes, my outhaul line comes out of the front of the boom then goes through a jammer right there. The reefing lines also come out of the front of the boom then go down to blocks at the base of the mast, then back up to spinlocks on the side of the mast.
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