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Sam.Spoons View Drop Down
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    Posted: 05 Jan 17 at 10:36pm
That looks very neat Dave but just to be pedantic, it's actually 3:1 (two at the back plus one from the boom). Do you find sheet loads are lighter when it's run throughout the turning block or is that just to increase the grip on the ratchet (It shouldn't make any difference to loads as you have the 3:1 regardless)?
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Posts: 23 		Post Options Post Options   Quote Glitcher7 Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jan 17 at 11:35pm
I think I may try the Supernova arrangement on the Punt. Will be interesting to see if it works for trapeze-helming (I don't see why it shouldn't). I find that the mainsheet rubs against the bridle if it comes from a block on the floor and I'm getting really far forward upwind. This alternative arrangement should avoid that.

I'll stick it on the 3.7 too if I like it. 
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Posts: 1312 		Post Options Post Options   Quote Do Different Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jan 17 at 8:03am
This is the best thread topic for ages. A proper bar room subject, everyone can have a different idea all with merits and nobody is wrong  Thumbs Up

Still thinking about DaveB 2:1 vs SS 3:1, I'm reckoning more like 2.5:1 at the boom end due to lost leverage by coming off halfway down the boom. Beer
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Posts: 8956 		Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jan 17 at 8:10am
Does the change of direction add a purchase? If I have a pulley in the ceiling to lift a weight off the floor, I'm still lifting the whole weight. Aren't I?
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Posts: 3 		Post Options Post Options   Quote rich4rd Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jan 17 at 9:02am
It does if you place the pulley on top of the weight and secure the rope to the ceiling. The rope passes through the pulley and must now pulled upwards to raise the load. This rope now bears the entire load. As it is anchored at 2 ends (one end to the ceiling, and one end in your hand) each anchor point only bears half the total load, thus the load felt in your hand is now only half the total load.
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Posts: 382 		Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jan 17 at 9:03am
You are right that changing the direction by having an additional block does not in itself increase the purchase but it may.
The best way to look at it is what loads are being applied to the boom by the blocks attached to it. Puting a final block on the floor will not dierctly affect the load applied to the boom but it may affect the direction of the load that is seen by the final block on the boom. If the angle that the sheet goes round the final block on the boom changes, the load on the boom will change, being low if the angle between the 2parts of the sheet is eg 90 deg and higher if the block has a full wrap of the sheet and the angle is 180deg. So a final block in the bottom of the boat will change the warp on the last block on the boom and thus will also affect the purchase of the system.
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Posts: 822 		Post Options Post Options   Quote PeterG Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jan 17 at 9:10am
So a final block in the bottom of the boat will change the warp on the last block on the boom and thus will also affect the purchase of the system.

It may have some (probably small) impact on frictional losses on the last block on the boom as the degree of wrap changes - but it won't have any effect on the purchase of the system.
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Sam.Spoons View Drop Down
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Posts: 3401 		Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jan 17 at 9:23am
Originally posted by Do Different

This is the best thread topic for ages. A proper bar room subject, everyone can have a different idea all with merits and nobody is wrong  Thumbs Up

Still thinking about DaveB 2:1 vs SS 3:1, I'm reckoning more like 2.5:1 at the boom end due to lost leverage by coming off halfway down the boom. Beer

I love it, Clap that's exactly what I thought but decided to not complicate matters further, of course the x.? depends exactly where on the boom the ratchet is. On the Blaze it's around 2.3:1 with it coming off the kicker take off webbing :)
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jan 17 at 9:29am
Originally posted by Dave.B

On my Farr I use a rear bridle, run the mainsheet along inside the boom to a Ronstan pivoting ratchet block. 

That's cool. I've only ever seen universal joint blocks used on the boom here. The pivoting block only moves in one direction, does that cover all your sheeting angles? It certainly gets the block closer to the boom, which gives more head room. 
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jan 17 at 9:50am
Originally posted by Cirrus

But, it doesn't look like they are taking the main off the boom in either photo or diagram. So they're not really 'clearing the cockpit'.

The point I am making is different - IF you go for rear sheeting THEN you can also run the mainsheet along the boom and have the ratchet directly attached either in front of the helm or opposite them..   The result is a totally clear cockpit and  the crew can move around without restriction.  If you like think of something like a Laser BUT with the ratchet directly attached to the boom (But I'm pretty sure the die-hard laserists would of course ban such a radical 'innovation' as being 'not invented here' etc) LOL

Sorry, I thought you had mistaken what was being shown the pictures. 

Plenty of people sheet off the boom in lasers and other boats (I do it in the 200). I tend to do it in light winds downwind, to remove the extra friction, and allow me to sit further forward (as the lasers do). 

However, off the boom sheeting isn't the utopia you describe! And I don't think it's because people are 'against innovation' as you seem to imply, but because it's not always the best solution.

First of all, you change the direction the final purchase in the your system is pulling at as you move around the boat. (you have a 2:1 purchase at the rear bridle, and a fractional purchase coming off the boom). If you have a block on the deck / thwart it keeps that final purchase consistent. (i.e. main sheets pulls more down on the boom as the boom approaches the center, which helps create leech tension when you're hard on the wind). 

For instance in skiffs when the crew has the main, when they move extremely far forward this purchase (from the boom to them) stops pulling any leech tension, and instead they start pulling the boom in to the mast, actually bending the mast and opening up the leech.

Secondly, having off the boom sheeting really depends on the size of the boat and other people in it. Trapeze boats, or wide boats (i.e most fast boats) will need longer tiller extensions for their length. This means even if they have off the boom sheeting, they will struggle to get eh tiller through the tacks without hitting the crew (or mast in the case of the moth).  The answer to this problem is either to run twin tillers (like many skiffs). Or have a central sheeting system, with no rear bridle, and pass the tiller around the back. 






Edited by mozzy - 06 Jan 17 at 10:06am
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