UK-Cherub Forum

Cherub Chat => Tech Chat => Topic started by: JP233 on February 24, 2015, 11:19:01 AM

Title: Tack line tension.
Post by: JP233 on February 24, 2015, 11:19:01 AM
Does anyone strong the fitting needs to be that hold the tack line (Rope that come out the pole) too the hull when the kite is up at full chat?

Shiny's pole launch rope is then her tack line, I want to change this for variouse reasons.

If the forces on the fitting aren't that high I belive I have two options;
1. Tie new tack line around the king post, job done.
2. Bolt deck eye in to carbon plate, plexus plate to hull infront of king post.

Would appreciate anyone ideas and or worrys with this.
Title: Re: Tack line tension.
Post by: dave_ching on February 24, 2015, 12:57:49 PM
Is the king post far enough back?
Title: Re: Tack line tension.
Post by: JP233 on February 24, 2015, 03:26:02 PM
Good question. Will have a hunt through the rules later.
Title: Re: Tack line tension.
Post by: pratn0 on February 24, 2015, 03:50:12 PM
On shiny the pole comes back past eh king post when it's retracted so you may find you can't get the tack in the kite bag with tack line tight being held byt he pole.

on madge i had a two to one adjustment on a standard v cleat.
Title: Re: Tack line tension.
Post by: JP233 on February 24, 2015, 04:12:16 PM
Depending how much poll we can have out the front of the hull my plan could work. Failing that, I move the unattached fitting aft.
Title: Re: Tack line tension.
Post by: simon_jones on February 24, 2015, 04:39:14 PM
Ours is tied off at the back of the sock, on the saddle that holds the block for the downhaul.
Title: Re: Tack line tension.
Post by: JimC on February 24, 2015, 05:00:12 PM
The amount the pole bends should give you some clues about the load on the tack line. Its certainly not trivial. Probably the same sort of order of magnitude as the kite halyard cleat.
Title: Re: Tack line tension.
Post by: Neil C. on February 24, 2015, 05:44:37 PM
We used to have it tied round the base of the main sheet post, but I guess that's not a very useful tip these days.
Title: Re: Tack line tension.
Post by: JP233 on February 24, 2015, 07:06:39 PM
Nick, i plan on abandoning trying to get the poll thought the hole in the bulkhead so should (by my reakoning) work

Jim, pole is usually stiff as...


Rules say '4.2.3 Bowsprit
The bowsprit, if fitted, shall be retractable to within 4300mm of the transom. The outer end of
the bowsprit shall be solid or capped. No sail other than a spinnaker may be set from the
bowsprit. '

This simpleton guesses it means the 4300mm is measured from the transom to the tip of the pole?
Title: Re: Tack line tension.
Post by: Neil C. on February 24, 2015, 08:18:53 PM
The boat is 3.7m long from transom to stem. You are allowed another 30cm of length for the snout. When retracted, you are allowed up to 30cm of bowsprit sticking out the front of the snout. Or, if you had no snout at all, up to 60cm of bowsprit sticking out the front of the boat.

The vague bit of the rule is the definition of "retractable." It has been argued that you might get away with a fixed bowsprit with spreaders and stays, which is retractable once you have finished sailing with the aid of a shackle key and a screwdriver. But that's not the spirit in which the rule was intended. Somebody suggested at an AGM some years ago that it should be changed to "retractable whilst under way" but it never actually got amended.
Title: Re: Tack line tension.
Post by: JP233 on February 24, 2015, 08:30:35 PM
wonderful, thanks neil!
am a real fan of asking before acting.

will measure up and see what i can do this weekend!
Title: Re: Tack line tension.
Post by: roland_trim on February 24, 2015, 10:39:30 PM
Jealous - I want to be by a boat that can be taken sailing this weekend :-)
Title: Re: Tack line tension.
Post by: JimC on February 24, 2015, 11:03:38 PM
The vague bit of the rule is the definition of "retractable."
I have a dim memory going round my head that we wanted to make sure that folk couldn't get protested by a particularly [redacted] M****n sailor because the bowsprit hadn't come all the way back in and so we were staying well clear of using phrasing like "shall retract". Back in those days there was a lot of funny thinking about sprits, with rumours of some clubs even talking about introducing bans.
Title: Re: Tack line tension.
Post by: simon_jones on February 25, 2015, 09:13:04 AM
You will be Ro, just not near any water!!
Title: Re: Tack line tension.
Post by: andy_peters on February 25, 2015, 01:44:31 PM
Not sure why you would want to separate?  We have one rope which works perfectly in launching/recovery and holding the tack nice and tight.  Very little friction and just pulling up/down the halyard sets or drops the whole kite and pole caboodle.
Title: Re: Tack line tension.
Post by: JP233 on February 25, 2015, 11:17:35 PM
Currently the pole comes back though the bulkhead in a tube (drainpipe)
The pole comes all the way back as can been seen, meaning when the crew does a viciouse drop the pole cracks them on the knee.

So, I want to stop the pole coming too far back. I couldn't do it when I played with the stopper knot so I think the 2 string way is the way forward.
By all means correct me if I'm wrong.

http://www.uk-cherub.org/forum/index.php?action=dlattach;topic=1859.0;attach=3100;image
Title: Re: Tack line tension.
Post by: dave_ching on February 26, 2015, 06:45:02 AM
Hi,
Pole never used to come that far back.
It used to come just through the balk head.
How does the drain pipe work with the return bungees and the tack line through the pole?
Alternatively knee pads
Title: Re: Tack line tension.
Post by: Tom K on February 26, 2015, 09:16:08 AM
Would it not be easier to train the crew not to stand in the way?

Less pole out front = reduced pitching moment = faster
Title: Re: Tack line tension.
Post by: JP233 on February 26, 2015, 10:04:50 AM
She has complained, therefor I shall change it.
I'm replacing the tack line anyway so if I want to change how it works, now is the time to do.

Also more crew space would be nice.
Title: Re: Tack line tension.
Post by: phil_kirk on March 02, 2015, 10:44:17 PM
As on Elenor E number's tack line is tied to a saddle bolted to a 8cm diameter 2mm thick disc of carbon or glass which is bonded to the deck.  the kite down haul line is also tied to the same saddle.  I would estimate the loads at 40kg but shock loads from a kite filling could be greater.
Why not use the same tack line arrangement and stretch some bungee over the end of the drain pipe to catch the pole. Equally pre load the pole on the bungee like a cross bow for the hoist.  ;D
Title: Re: Tack line tension.
Post by: JP233 on March 11, 2015, 01:36:29 PM
Might be having a brain fart moment,
When sailing does the end of the poll have to sit 300mm or less from the snout or have the ability to?
Title: Re: Tack line tension.
Post by: dave_ching on March 11, 2015, 04:12:41 PM
ability to