Morning all
Mast shroud tracks?
Looking around at various boats i see that these seem to be used on some of the Chapters but not much else.
Seems like a good idea to me so why doesnt everyone have them... is it just cost... or dont they work?
Cheers
Ian
It’s a marmite thing.
Some people like the idea of being able to let the shroud forward out of the way of the boom on the run without letting the tension off when it’s blowing.
Others argue how much use is a shroud under tension that’s not pulling in a useful direction and ask how many strings you want to pull when you go around a corner.
It’s your boat, your money and your choice.
If you’re going to do it don’t buy cheap cars or tracks.
Surely this addresses the age old 12 problem of how you can narrow the shroud base so that you can square off the boom offwind while maintaining forestay tension upwind?
I had shroud tracks on 3473 but have not had them since.
In the end it was cost benefit decision. It was an expensive way of getting a little bit more mast security (allegedly) when it was windy and being able to sail with the boom square in such conditions.
One other interesting benefit was in very light stuff to be able to change the shroud base and add rig tension so as to induce more mast bend and therefore flatten off the full mainsail that we were using. We would also pull the mast forward at deck level to help. Not much of an issue if you are a tiddler with flat sails anyway, but clearly of interest to the gentleman with a fuller figure. Not sure if it worked but I felt better.
Without the tracks now we still seek to pull the mast forward at deck level when the wind goes.
The other interesting thing was that pre shroud tracks most people had a 2:1 above deck purchase on their shrouds and frequently did not have enough throw in the system to square the boom. Shroud tracks enabled a lot of throw and Tom Stewart responded by rigging a 3:1 above deck purchase which had more throw and solved the problem at a substantially reduced cost. Many recent boats now do the same.
Quote from: 78...... Tom Stewart responded by rigging a 3:1 above deck purchase which had more throw.....
This isn't so. It is the distance from the anchor point in the boat (mast foot) to the deck that is the key driver. Adding purchase above the deck reduces the amount the shrouds can be let off. Once the blocks in the boat stop moving, the bits above the deck do too and if there are three parts rather than two, they move only two thirds the distance. Work it out on a piece of graph paper if you don't believe me.
Kevin
So i guess what we are saying is that they do work, but that the maginal increase in performance over a conventional shroud base doesn't warrant the aditonal cost and complexity involved!
Would that kinda sum it up.
Ian
In a nutshell.........................
Quote from: 165
This isn't so. It is the distance from the anchor point in the boat (mast foot) to the deck that is the key driver. Adding purchase above the deck reduces the amount the shrouds can be let off. Once the blocks in the boat stop moving, the bits above the deck do too and if there are three parts rather than two, they move only two thirds the distance. Work it out on a piece of graph paper if you don't believe me.
Kevin
At the risk of letting this get a trifle pedantic, I agree with you that it is not the 3:1 above the deck that gives the throw itself but rather the ability to rig the relevant blocks between the base of the mast and the deck to give sufficient throw in that part of the system whilst at the same time being able to (a) give sufficient purchase to be able to move the shrouds when it is required and (b) to use an economic amount of rope. You dont want to be pulling rope for too long when you go round corners, and you then only get it wrapped around your feet or pull the tails into the jib ratchet blocks! I simplified to 3:1 above deck - this is clearly not all the story! I believe that I have 5:1 below deck giving 15:1 in total compared to the 16:1 achieved with the 2:1 above deck.
Ian - I would disagree that the marginal increases in performance does not warrant the additional choice. It is like marmite as originally said. Sometimes you want it and sometimes you dont. You dont have to be consistent. That is why it is fun!
To be really pedantic but to try and clarify this issue . .
It's a basic rule of pulley systems, if you have 15:1 system, to move the load 1 cm, you have to move the other end of the system by 15 cm no matter how you arrange the pulleys and for a 16:1 system . . etc etc
However, as we set these systems up, the limiting factor is when you put in a cascade or even a partial cascade system which is
when you really run out of travel, and I agree with John, the limiting factor is the distance between the base of the mast and the turning block at the shroud plate.
If you take a typical 16:1 system with 2:1 above the deck and a 8:1 cascade to the mast base and assume there is 1000mm between the mast base and the turning block at the deck. The 8:1 has three blocks in the system but I can only pull 2000mm
of rope out until it becomes block to block, The last block below deck has only moved 250mm so the shroud has only moved 125 mm, which doesn't allow the boom to square off very much.
If I now put a 4:1 on the end of a 2:1 below deck with the 2:1 above (still 16:1), I can pull 4000mm of rope before it goes block to block which means that the shroud has now moved 250 mm. So I have double the movement at the shroud but at the expense of twice the amount of rope round my feet! Not a question of how much purchase there is above the deck but how it
is arranged below deck.
With a 5:1 below deck and a 3:1 above (=15:1) I can move the shroud 330mm but at the expense of 5m of rope
pulled but which probably gives you all the slack you would (ever) want.
So you would of thought that shroud tracks would have a distinct advantage, if only in the amount of rope to be shifted at the corners.
I've gone for a 5:1 and 3:1 system without using the full potential of travel but if I find I'm winding in arm fulls of rope at the bottom mark, I might go tracks yet.
If you have a cascade kicking strap system and find you're running out of travel, same principle applies, try replacing the last block of the cascade with a 4:1 instead of a 2:1 system
Phil clearly doesn't have enough to keep himself occupied at the moment!
My much anticipated and soon to be revealled Numinous has tracks, I can get 400mm of travel by pulling 800mm of rope - so in my view tracks are the way to go.
I think this illustrates one of the great joys in owning a 12, in that you can set things up just the way you like!
A classic N12 thread.
FWIW I went from tracks (on 3447) to coarse & fine (on 3484) back to single string as adjusted by Tom S (on 3514). We went back to the simple solution for the simple reason that it seemed quicker to pull in the extra rope than to put one down and pick the other up..... simple, strange and true. It is also, in my opinion, harder for a rope to get tangled with itself than with its neighbour! I never liked the tracks being adjusted out on the gunwhale, they were better on boats like 3473 where they were brought to the middle of the boat.
Antony
3348 (i can't even remember what it has, but it might include muscle boxes!)
Anyone got any pics of different arrangements?
The handbook to 1936-2000 has an excellent picture on page 171 of Bruce Johnson's 'Texas Flood' showing constant (but adjustable) tension tracked shrouds. (all in green string). I looked at doing it on my boat but once I priced up the parts, decided that for club racing with my daughter the money was better spent on beer, J2O and crisps!
Here are two photos of the P&B Dinghy Show Dead Cat Bounce. In the interior shot the shroud adjustment control line is white. The double block at the end is fixed to the end of the wire that forms the triple purchase.
Here is second photo
The the limiting factor is NOT necessarily the distance between the base of the mast and the turning block at the shroud plate. On my boat, N3503, there's no fordeck, just a low bow tank so I've been able to run the system forward to the stem via a turning block at the mast foot. Since the mast foot to stem dimension is bigger it gives me a bit more travel for the system. I copied the system off an old International 14. It might just be possible to see it in the photos of the boat on the database.
The other really important factor with pulley systems is to ensure that the rope stretches as little as possible. The implication of this is obvious: don't invest in expensive ball bearing blocks and then string them together with cheap stretchy rope, particularly in the high tension parts of the system!
Marcus, It would be great to see you and your shroud set-up at the Annandale N12 Open Meeting on 17 & 18 April. There should be at least one class measurer competing, though probably not enough time to measure your boat. (You could try contacting Brian Herring.)
I am really most impressed by your boat.
John
The ropework in picture 2 looks a bit of a bu**er's muddle! I hope it is simpler than it looks.......
Sorry to dig up an old thread, but having recently bought 3453 a carbon chapter I am now in a position to answer my own question.
Shroud tracks are great! Would I spend the money if i was rigging out a new boat, possibly, possibly not... all I know is that now I have them i use them.
Ian
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