Author Topic: Self Tacker track shapes  (Read 38962 times)

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Offline Tom K

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Self Tacker track shapes
« on: January 14, 2008, 05:29:30 PM »
As I put in a reply to Dave on the mailing list I am currently looking at adding a self tacking jib system based on a 'W' shaped track to Beans. Enabling me to keep the same sheeting points that are longitudinally just behind the mast foot.

As my sheeting point is already pretty close to the deck I would like to avoid raising the track off it to try keep sheeting angles similar to as they are now. I suppose I could get a longer clew board put on the jib and adjust the hole i use to compensate.

This arrangement above would involve bending the track in 3D, has anyone done that? Ide guess it would be best to drill the attachment holes after bending to try keep the car running smooth?

Also, what are peoples opinions of sheeting a self tacker. The two options I am aware of are either taking the sheet from the clew, through a block on the track car and towards the bow where is loops back and goes to a cleat in the cockpit, or tied at one end of the track, through the first of two blocks on the track car, through a block on the clew and back down through the other block on the car and then to a block or cleat at the other end of the track. The seconds system seems good as it involves less clutter near the kite system, but does mean the sheet comes out on one the side deck on one side of the boat. Thoughts?



Offline Phil Alderson

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Re: Self Tacker track shapes
« Reply #1 on: January 14, 2008, 05:48:45 PM »

I use the system tied at one end of the track with the purchace running up the port side of the foredeck, with no problems. It puts less pull on the jib towards the center of the track when the sheet is pulled tight so you can get away with a larger radius for the curvature of the end of the track,

Having the track curve down at the ends might make the car want to migrate up the slope and inboard under the load for the jib.
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Offline Will_Lee

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Re: Self Tacker track shapes
« Reply #2 on: January 18, 2008, 08:21:48 PM »
I've been doing some thinking about this. Here are some methods:

1) Classic: Bend it in a circle around the perpendicular to the forestay. This definitely works.  :) Used on many boats and known to work.
2) Atum Bom: Bend it in a circle around the perpendicular to the forestay, only make the radius bigger.  :) Used on Atum Bom and works.
3) Flat: Bend it in a circle but keep it flat on the deck. :) Ronin and Spanish Inquistion have this and it works.
4) Modified classic: Just like 1 only the middle section is flat. More like this ] than like this ). :) This is How the Pasta Frenzy's is, and works. Allows the clew to be further back.
5) W: Like 4, only more so. :) Seems to work on that i14.
6) Smilie: Like 3, only instead of being flat vertically, is flat horizontally.  :-\ Dont' know whether this will work or not.
7) Completely straight: I suspect this may work, but only with sheeting system B, below.  :-\ .

Sheeting systems:

A - sheet goes via central block way forward on the foredeck somewhere.
B - sheet goes from one end of the track, through the car, then the clew, then the car again and then to the other end of the track. This has the advantage that the sheet is not pulling it to the middle of the boat.

Kevin had his track prebent by Ronstan before he drilled the holes. This is the only way I would recommend.

Offline phil_kirk

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Re: Self Tacker track shapes
« Reply #3 on: January 25, 2008, 01:03:12 PM »
slippery's track came with the boat although not cut to size or fitted.  It is an option four being slightly flat in the middle.  The same track is used on RS800's but of course is slightly the wrong radius for Slippery.  The track is aligned perpendicular to the forestay.  The sheet lead through the foredeck is slightly off set to miss structure underneath.  We have packed the track on the port side to give us the same sheet tension on each tack. We also moved the 2:1 purchase to between the track car and the clew to reduce the effect further.

The helm often ends up easing the sheet because the crew can't cleat it.  (Cleat lead problem not a crew problem). The crew is often far too stressed about the kite anyway to care about the jib. :-)

Offline Phil Alderson

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Re: Self Tacker track shapes
« Reply #4 on: January 26, 2008, 05:31:21 PM »
When I was setting up Primal Woofy described the technique to setup the radius of the track.

Get a peice of rope and tie it to the forestay point, thread a block through and take the other end through the forward turning block for the jib sheet. Adjust the length so the block is where you want the outboard end of the track to be (depends on the foot of the jib)

As you swing the block across the boat it will describe an arc where the jib sheet tension will be neutral i.e. it will not pull the jib up to the centerline with extra tension. This arc tends to be tighter radius outboard and flatter towards the center.
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patrick_cunningham

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Re: Self Tacker track shapes
« Reply #5 on: January 29, 2008, 09:42:37 AM »
LRN has had 6) for the three seasons it was used; which is curved to the radius of the average of the radii of the forestay right angle and the radius of the track/block to the turning block. the bend track was then mounted horizontally and attached on the CLine and the ends.

"6)Smilie: Like 3, only instead of being flat vertically, is flat horizontally.   Dont' know whether this will work or not."

Patrick
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mathew_harris

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Re: Self Tacker track shapes
« Reply #6 on: January 29, 2008, 02:20:46 PM »
B - sheet goes from one end of the track, through the car, then the clew, then the car again and then to the other end of the track. This has the advantage that the sheet is not pulling it to the middle of the boat.

How do you go about sheeting in with this system, i've been thinking it through and can't quite understand it.  I even drew it on a piece of paper but thought that rather than keep drawing it and messing about would be easier to ask.

Offline Phil Alderson

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Re: Self Tacker track shapes
« Reply #7 on: January 29, 2008, 04:56:40 PM »
If you look carefully at this picture you might be able to work out the system,

The car has two blocks on it and the sheet is lead from one end of the jib track through the first block on the car through the block on the jib clew and back down to the second block on the car and out to the other end of the track. As the car moves from side to side the sheet runs through the blocks and the length does not change*.

To sheet in and out you simply adjust the length of the string. this is normally done by having a block at one end of the track and then leading from that to a purchase if necessary and back to the cleat. One advantage is that you can keep the sheet lead to the side of the boat so that when the crew is in front of the mast in light winds there is less to trip over.

On Ronin I think the kept everything over to one side and have the cleat on the stbd side. On Primal I route the sheet through blocks back to the centreline underneath the mini foredeck so still out of the way

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Offline Will_Lee

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Re: Self Tacker track shapes
« Reply #8 on: January 29, 2008, 08:46:46 PM »
Some sums done for Dave Ching just now:

Distance from left to right of the track = 900mm
Radius of current track = 1430mm
Radius of circle on deck centred on bow fitting = 1800mm
Min radius that Harken will do the track to = 1070mm

Q1: How far in front of the mast is the end of the jib track if the back of the track is against the mast?
A1: 72.6mm

Q2: What would that distance be if the end of the jib track was at the same angle, but the radius was 1070mm, and the two curved bits were joined by a straight bit?
A2: 54.4mm

Q3: What would that distance be if the end of jib track was at the same angle, but the track was W shaped, with the min radius of 1070mm throughout?
A3: 51.4mm

I did this geometrically in Rhino, and can't v readily see how to make a general purpose spreadsheet to do it.

Offline Stuberry

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Re: Self Tacker track shapes
« Reply #9 on: January 30, 2008, 06:18:55 AM »
So even if the track is W-shaped it's very difficult to have the clew of the jib behind or even level with the mast?

So to approach this from a different direction... Can Rhino tell you:

What radius of the middle bit of the "W" would be required to give a distance in front of the mast  less than or equal to 0?

Offline Will_Lee

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Re: Self Tacker track shapes
« Reply #10 on: January 30, 2008, 08:40:11 AM »
Possibly, but it would be different for each boat, and it cannot be done on Shiny if you keep the angle at the ends of the track the same.

W

Offline gav_sims

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Re: Self Tacker track shapes
« Reply #11 on: January 30, 2008, 08:52:57 AM »
Fizzy Shark has a 'W' track thats been fitted since before 2002 (I think) nationals at Pembrokeshire YC.  It is quite narrow (600mm side to side) and manages to get the track behind the mast either side.  I think it is Fredriksen.  You can just about see it here ( http://www.sailingsource.com/cherub/test/lib/exe/fetch.php/boats/2662-200107xx.jpg?cache= ) hmmm, although the picture makes it look quite straight.

I used a harken track (the micro version) on Mango and found it very flimsy.  Originally I had it supported at either end and the centre (as the holt track I fitted to strawberry was) but that snapped during the second outing at the grand slam.  I then ended up glueing a reinforced wooden batten to the desired radius to the existing supports on the foredeck and screwing/bolting through every hole in the track to the batten. 

Offline Will_Lee

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Re: Self Tacker track shapes
« Reply #12 on: January 30, 2008, 08:59:05 AM »
This is me trying to make the picture come out.


mathew_harris

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Re: Self Tacker track shapes
« Reply #13 on: January 30, 2008, 12:29:32 PM »
My friend has a flying dutchman which has a self tacking (ish) traveller for the mainsheet.  It works on the principle whereby when the pressure is not on it can slide.  I'm not 100% sure of the exact way it achieves this but i'm sure other people will have seen it, my thought is would this be possible on the jib to have some form of cleat for the jib (sheeting without a traveller) were when you pull the opposite sheets post tack it automatically uncleats the then windward cleat?  I know that in dreams this would at least save the crew having to uncleat then sheet in on the new side, and i think i'm going to struggle to get a self tacker in without having a tiny jib.
« Last Edit: January 30, 2008, 12:44:36 PM by Matt Harris »

Offline Will_Lee

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Re: Self Tacker track shapes
« Reply #14 on: January 30, 2008, 01:06:18 PM »
This is quite easy to think of but quite difficult to do:

1) Plastic ring around one jib sheet.
2) Bit of string going from the rig through an unspecified number of blocks to...
3) One or both of the jaws on the jib cleat on the other side. (You can drill and attach string to the jaws such that a pull on it will open the cleat - but it won't work if the jib is very heavily tensioned)

W