Shock Cord

I found, on a sailplan drawing, a thing called "spinnaker pole shock cord retrieve", and it was placed on the boom.. Can anyone explain me what is it for? The boat was an IOR half/ton

 

It could be a length of shock cord extending from the aft end of the boom to the pole at the mast. Used to automatically retrive the pole to the boom for stowage once the pole is taken off the mast. Similar ideas are used on dinghies such as 505's etc. Gybing is done by retrivieng the pole and then reseting after the gybe. I have seen this with port & starboard poles permantly attached to the sheets with a "leader line"(like a barber hauler). The whole setup takes pulling on one line to launch.

 

Thanks BrettM, but I can't understand very well how it works, do you know where I could find some drawings or picture of that?
and what is the advantage of such a system, I've never seen it..

 

I had a twin pole system on my Merlin Rocket that I raced on the Thames River. (the Merlin is a British national restricted class 14 ft dinghy.) It really works well for dinghies.

Here's how the strings go:
- The pole toping lift is fixed in length, and supports the pole as it dangles alongside the boom when stowed.
- The spinnaker sheet/guy runs through a ring attached to a line, like a Barber hauler, that goes from the ring to the end of the pole, to the mast. The length between ring and mast is exactly the same as the length of the pole.
- A pole control line goes from the mast end of the pole to the mast, down to the deck, and emerges at a cam cleat just under the aft edge of the foredeck.
- The mysterious shock cord runs from the mast end of the pole aft to a block on the boom and then forward inside the boom so as to have as much length of shock cord as possible.
- Finally, bands of velcro (pile side) are glued to the poles, with the hook side glued to the boom to keep the poles from flopping around too much. I've also seen large plastic rings (say, 4" - 6" in diameter) attached to the boom on each side through which the pole passed to do the same thing.
- Not unique to twin pole rigs, but the tail of the spinnaker halyard runs back forward under the foredeck, out through the spin launcher hole in front of the forestay, and up to the belly of the spinnaker to form the retrieval line.

To set the spinnaker, the crew pulls on the windward pole control line while the skipper hoists the chute. The pole control line pulls the pole forward and holds the butt end at the mast. As the pole goes out, the ring gets sucked in to the end of the pole, bringing the guy with it. So with one motion, the pole is out and the guy attached, and the crew then turns to setting the guy and manning the sheet.

To jibe, the crew simply releases the pole control line from the cleat under the foredeck. The shock cord zips the pole back along the boom. The crew ducks under the jibing boom and pulls the opposite pole control line to set the new pole. Back on guy and sheet, and the jibe is done. Crew never has to actually lay hands on a pole.

To dowse the spin, just release pole control line, and the pole self-stows along the boom. Crew pulls in on the retrieval line while the skipper eases the halyard, and the spin disappears into the launcher. Crew stuffs the spin up on top of the bow buoyancy tank and gives the pole a quick slap to stick the velcro to the boom. Weight back out to windward and feet in the straps as the skipper rounds the mark and heads up the beat.

Now, how that all works for an IOR half ton must be something to see!

 

Just a quick sketch to help you out. hope I remembered it correctly. It was on a 505 I crewed on a few years back. I sail lasers now and you don't get much of this stuff on them. Yes you do need twin poles and as tom said, I'd like to see it on a half tonner. The guy that has the job of setting it must be huge!