Main Sail Runner (or not)

[Alan Mighty]

Originally Posted by Rustic Charm

What are the springy things right on the bottom attached to the deck called?

A 'stand-up' or a 'stand-up block' or a 'stand-up block base'. Term first used in print in 1980 according to my records. Likely used in oral English for some years before 1980.

Function is to keep the block up-standing when tension in the sheet is low (i.e. the stand-up stops the block from flopping over and whacking the deck in an impolite gesture).

Al

[Alan Mighty]

Originally Posted by cwyckham

This is a very odd set-up. It seems equivalent to a centerline sheet to me. As you point out, the problem with this is that you can't both have the boom on center and the leach twisted off at the same time. With dual sheets this is quite easy without messing with topping lifts (can't imagine that works too well).

I've no problem with dual sheeting of the main, but I take issue with the idea that a double-ended mainsheet (1) is an odd set-up and (2) cannot control leech tension when the boom is on or near the centreline.

On #1, note that double-ended mainsheets have been in use since before 1922 and were quite common in the 1950s and 1960s (when horses were common and just before travellers became popular). Admittedly, these days double-ended mainsheets are regarded as 'traditional' and boats carrying them tend to be called 'classics' or 'classic rigs'. But that's not the same as 'odd'.

Led Myne has a double-ended mainsheet with a 4:1 mechanical advantage, reeved through a double block at the boom end, a fixed single block on her taff rail at the centreline, and single blocks at the starboard and port ends of the taff rail with cam cleats at each of those final two blocks.

On #2, when the boom is within the arc defined by the starboard and port blocks, the mainsheet controls both angle of the boom and leech tension. When the boom is outside that arc, the vang controls leech tension.

When within that arc, including at or near the centreline, easing both ends of the main simultaneously reduces leech tension and trimming both ends simultaneously reduces twist.

Al

[bmz]

"You can "vang sheet" (which I've been known to do) where you use the vang upwind, but whether that's a good idea depends a bit on your boom design. If you vang sheet, then you're using the vang for sail shape all the time, and you can then use the main sheet for sail position. It sounds like this is what you do.
However, if you want to get the boom on center, you're still going to need to move the traveler up or else the sheet will close the leech."

IMO a traveler is a relic from an earlier period; that is why a number of manufacturers have eliminated them. When you center the boom for upwind sailing, you want to close the leech.

[Ex-Calif]

Originally Posted by bmz

<snip>

Ex-Cal: " The vang and the traveler are completely different controls and do completely different things." What do you do with a traveler that you can't do with a vang?

Originally Posted by cwyckham

The vang controls sail shape off the wind. The sheet controls sail shape on the wind. The traveler controls sail position.

<snip>

However, if you want to get the boom on center, you're still going to need to move the traveler up or else the sheet will close the leech.

What he said...

Originally Posted by Garrettw

<snip>

I have to resist this using more topping lift if I am wanting to twist off the sail. While this mostly does the trick, it puts tremendous forces on the lines, fittings and boom.

This is an interesting idea but as you note it would put tremendous loads on the boom.

If the sheet is attached mid boom and the topping lift is end of boom the bending load would scare the crap out of me...

[savoir]

Originally Posted by Rustic Charm

I didn't realise the topping lift was used on a regular basis. I thought it was just used to hold the boom from falling on the deck?

An adjustable topping lift is a useful sail trimming device for any boat that has an all rope boom vang. You tighten it to take the load off the leech of the main. This is not an issue on any boat with a rod vang provided the spring is correctly adjusted.

[cwyckham]

Originally Posted by bmz

"You can "vang sheet" (which I've been known to do) where you use the vang upwind, but whether that's a good idea depends a bit on your boom design. If you vang sheet, then you're using the vang for sail shape all the time, and you can then use the main sheet for sail position. It sounds like this is what you do.
However, if you want to get the boom on center, you're still going to need to move the traveler up or else the sheet will close the leech."

IMO a traveler is a relic from an earlier period; that is why a number of manufacturers have eliminated them. When you center the boom for upwind sailing, you want to close the leech.

I disagree. I want sail angle of attack and sail shape to be independent. This is very important to main sail trim.

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[bmz]

cwyckham: if you use your vang for sail shape and your main sheet for angle of attack, they are independent; except for close hauled sailing when tightening the main tightens the leech--which is what you want it to do.

[cwyckham]

Originally Posted by bmz

cwyckham: if you use your vang for sail shape and your main sheet for angle of attack, they are independent; except for close hauled sailing when tightening the main tightens the leech--which is what you want it to do.

When I am close hauled I only sometimes want to tighten my leech. I want my boom on centerline for light and moderate winds. I want my top batten to be parallel to the boom at the leech, which means that the sail has a moderate twist to it.

In light winds, there will not be enough wind pressure to twist off the sail with the sail on centerline if I have a centerline sheet. In fact, it's technically impossible to get the boom on centerline with a centerline sheet since I would need infinite tension (in the real world, I guess I can get close, but still need really large tension).

As the wind builds, I want to twist the main off more with the boom still on center. This depowers the top of the sail, reducing heeling. As it builds more, I will drop the sail a little bit. Finally, I will reef and bring the sail up to center again with the top batten parallel.

As the wind builds further, I will repeat all of the above until I have to put in another reef, etc.

It is absolutely fundamental that I be able to control angle if attack and sail shape independently. A vang and a centerline sheet don't allow that when I'm close hauled, only when I'm reaching.

I do vang sheet sometimes, but I don't have a centerline sheet. I have two independent sheets in an inverted V, so I can still place the boom on center. I can then control the shape either with the second sheet or with the vang.

[Garrettw]

Originally Posted by Ex-Calif

This is an interesting idea but as you note it would put tremendous loads on the boom.

If the sheet is attached mid boom and the topping lift is end of boom the bending load would scare the crap out of me...

Exactly; not an ideal setup. My main sheet attaches in several places with the last one being about 70% out so it's not terrible but I still have to use common sense and realize that I'm not going to get completely to centerline with an open leech. My past boats have had a traveller so my point of comparison is to have mutually exclusive sheeting angle and sail twist. Hard to get there with my setup hence my cautious use of the topping lift.


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[Garrettw]

Originally Posted by savoir

An adjustable topping lift is a useful sail trimming device for any boat that has an all rope boom vang. You tighten it to take the load off the leech of the main. This is not an issue on any boat with a rod vang provided the spring is correctly adjusted.

Is this something that can be adjusted in common mass market vangs? I don't have any documentation on mine so I have no idea how I would go about it (but would love to know, if it's possible).


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[savoir]

What are you asking ?

Are you saying that you have a rod vang and don't know how to adjust the spring ?

[Garrettw]

Originally Posted by savoir

What are you asking ?

Are you saying that you have a rod vang and don't know how to adjust the spring ?

I'll try to use less syllables I guess. Yes, I have a spring loaded rod vang. I was not aware that the spring was adjustable in a vang strut. I was asking if that was a common feature.


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[savoir]

I have never seen one that wasn't adjustable. Even the old hydraulic vangs used a bicycle pump for upwards adjustment. The idea is to keep the weight of the boom off the leech in light air so that it doesn't haul the leech to windward and strangle the sail.

Forespar is a mass market brand so this might help.

http://www.forespar.com/pdf/techTips...s-tech-tip.pdf

[Garrettw]

Originally Posted by savoir

I have never seen one that wasn't adjustable. Even the old hydraulic vangs used a bicycle pump for upwards adjustment. The idea is to keep the weight of the boom off the leech in light air so that it doesn't haul the leech to windward and strangle the sail.

Forespar is a mass market brand so this might help.

http://www.forespar.com/pdf/techTips...s-tech-tip.pdf

Thanks for the link. My Z-Spar strut doesn't have anything quite so obvious as to what Forespar shows there, but it gives me an idea of what to look for.


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[savoir]

Look for a slot on the top of the rod with some kind of sliding lock nut thingy inside. The pins used by Forespar are only coarse trim.