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Main Sheet block position

Postby GuestMember on Wed Jun 07, 2006 3:39 pm

Do I notice on the photo on the front page of the website that Andy McIntre in "Rocket Science" is sheeting from the boom? I also see a photo in the photo gallery of a main sheet block on the thwart. What is the most preferred position for a mainshhet block?
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Postby andymac on Thu Jun 08, 2006 9:12 pm

A lot of Sabre sailors seem to sheet directly off the boom downwind to get a more direct response when pumping. Only recently I was shown the trick of reversing the mainsheet so that the purchase is virtually eliminated and the response even more direct. Sheeting like this requires more vang as the mainsheet is just controlling boom position rather than twist.

Unlike a lot of the Bethwaite design skiffs that have eliminated the cockpit mainsheet block altogether, the Sabre sheeting system I'm most familiar with still incorporates a floor mounted block. I don't know if this is a rule or just a trend...but it feels more comfortable upwind to be sheeting off a more stable point.

Andy Mac
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Postby ronny_f73 on Fri Jun 09, 2006 11:08 am

Andy
can you please explain the trick of reversing the mainsheet ... or do you mean having the rachet block on the boom not down low??
thanks
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Postby matt westland on Sun Jun 11, 2006 10:37 am

I tried the off boom sheeting upwind in 25knots (accidently as ratchet block shackle failed). It turned out to be real slow as the boom is pulled in too close to the centreline without enough leech pressure. Unlike Sabres , skiffs have very powerful vangs which hold all the leech tension.
Down wind is a different proposition as less vang is needed and off boom sheeting will work on a Sabre. Just depends on preference.

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Main sheet block position

Postby Alan Riley on Tue Jun 13, 2006 3:05 pm

The Sabre rules require the last block of the mainsheet system to be to the floor of the boat behind the centreboard case. You can't put it on the thwart! However, there is no rule on how you can control the mainsheet ie. although the last block is attached to the floor, there is no rule saying you have to use it! Thus you can use off the boom sheeting if you like it.

I used off the boom sheeting for most of the 2003/04 season, including the Blairgowrie nationals (coming 3rd overall - in fact, I only used a 2 to 1 mainsheet system that year!). For me, it's the most comfortable way to sail. I certainly didn't have the problem in heavy winds Matt mentions - I could always get enough leech tension by using the vang. Where I did have an issue was in lighter winds where you want leech tension without using the vang. The problem was, most of the time when pulling on the sheet the boom came in towards the centre, rather than tensioning the leech.

These days, I compromise. My last mainsheet block comes off the floor of the boat using a bit of electrical conduit to get it up to toe-strap height. From there, I use a piece of rope about 20-25 cm long to get the block up to about the height of the traveller. It works and feels fairly similar to off the boom sheeting, but allows you to sweat down on the mainsheet to get more leech tension if needed with the added advantage that it holds you up a bit when hiking - thus helping the thighs and stomach muscles on windy days!

Downwind I always use off the boom sheeting with as few purchases as possible since the vang controls the leech so you get a much better "in-out" response off the boom.

Alan Riley
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Postby matt westland on Wed Jun 14, 2006 9:46 pm

Good point Alan. I always enjoy your posts as you are consise and informative. I suspect that I wasn't using enough vang tension to control the leech. I have since upped the ratio to the 6:1 allowed with vectran lines for better control.
To explain to Andy re "reversing the mainsheet" the trick is to hold the main sheet from the first pulley off the boom which will give you quick response and 2:1 ratio. When going upwind again you can grab the sheet from the ratchet block to get 4:1 purchase again.

Cheers
matt
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Vang

Postby Alan Riley on Thu Jun 15, 2006 10:30 am

Matt,

I think you are probably right, you need to use more vang tension to control the leech. However, you can use up to 8:1, not just 6:1. I find 8:1 more than enough to control the sail shape successfully. In heavy winds, even if I am using a 4:1 mainsheet system, it is only used to control in-out movement of the boom since the vang is doing all the work in these conditions.

The other thing you can try when going downwind is using 1:1 sheeting. Let the mainsheet all the way out to it's end knot, then grab the two "strands" running from the floor block to the boom block, and the boom block to the traveller block. You have to hold both "strands" so that the mainsheet does not run through the boom block - giving you 1:1 sheeting! You can only do this in light/medium winds (unless you are built like Mr Universe), but I find it the most effective sheeting method for downwind and particularly efffective for pumping.

Regards,

Alan Riley
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"Pumping"

Postby Eliza C on Thu Jun 15, 2006 4:45 pm

Hi Alan,

Thanks for all your informative feedback.

Would you please explain "pumping" as I thought this was illegal. What do you actually do and how does it help boat speed?

Thanks

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Postby matt westland on Thu Jun 15, 2006 11:07 pm

Thanks for the clarification Alan. I had meant 8:1 vang. I have tried the 1:1 on the main downwind and kept getting into trouble with one rope slipping . I have since discovered washing up gloves which give outstanding grip so I should try it again.
Just as an aside I had rigged my boat with the vang lead routed via the centrecase onto the side deck. I have recently removed this and just have cam cleats on the bulkhead. This has been a great improvement-more space in light winds, less accidental uncleating and easier to give it a good yank as needed.

Cheers
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Pumping

Postby Alan Riley on Fri Jun 16, 2006 12:01 am

Hi Shane,

Pumping is covered under Rule 42, which covers Propulsion. Rule 42.2(a) defines pumping as "repeated fanning of any sail either by pulling in and releasing the sail or by vertical or athwartships body movement". When you "pump" a sail, it gives you a momentary "kick" in boatspeed. Therefore, if you repeatedly do it, you can propell your boat faster than just using the wind and waves alone.

However, under Rule 42 pumping is illegal except as allowed by Rule 42.3(c), which states "Except on a beat to windward, when surfing (rapidly accelerating down the leeward side of a wave) or planing is possible, the boat's crew may pull the sheet and the guy controlling any sail in order to initiate surfing or planing, but only once for each wave or gust of wind". In other words, when going downwind you can pump ONCE for each wave or gust of wind to make the boat surf or plane. It's a good skill to acquire (and I mean skill - you have to time the pump just right to help you catch a wave) since catching waves makes you go heaps faster. However, you do have to be very careful when doing this, because if you fail to get your boat surfing or planing you are in the "yellow light" zone and in danger of being disqualified for illegal propulsion.

Check out http://www.sailing.org/rrs2005/42interp ... ns2005.pdf for a fuller discussion of Rule 42.

Hope this helps! :wink:

Regards,

Alan
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