Midboom Sheeting with low friction rings

estarzinger

Super Anarchist
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I might just comment on the original question that not all the blocks labeled "A" are in the same geometry.

Two of them (I have boxed in red) have 180 degree turns.  You most definitively don't want rings on those.

But three of them (boxed in green) are less than 90 degree bends - sure blocks would be less friction, but rings have been used in these places. I have seen several jeanneau's using german mainsheet system with rings (in the last two green spots).  It does work adequately.

I am not pushing rings here, simply pointing out that #1 those five "A" positions should really not all be lumped together, and #2 that rings have been used reasonably successfully on the front several lowe turn positions.

mainsheet.jpeg

 
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Zonker

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Canada
Yes but a German mainsheet typically has much line to pull in AND it almost always on a winch. You probably don't care about the extra friction because the winch just takes care of it.

This diagram has a 5:1 purchase on a 28' boat. On that size boat you're certainly only going to be using the winch in moderate to strong winds. In lighter winds you'll be pulling by hand. So you'll really notice the friction of rings.

Sometimes a boat builder does something not because it is better but because it is cheaper (rings) or trendy (hard chines, reverse bows) even if it doesn't make sense.

And except for the mid boom blocks with green markers, the one at the gooseneck and at at deck are close enough to 90 degrees that there is a significant deflection.

 

Rain Man

Super Anarchist
7,381
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Wet coast.
Yes but a German mainsheet typically has much line to pull in AND it almost always on a winch. You probably don't care about the extra friction because the winch just takes care of it.

This diagram has a 5:1 purchase on a 28' boat. On that size boat you're certainly only going to be using the winch in moderate to strong winds. In lighter winds you'll be pulling by hand. So you'll really notice the friction of rings.

Sometimes a boat builder does something not because it is better but because it is cheaper (rings) or trendy (hard chines, reverse bows) even if it doesn't make sense.

And except for the mid boom blocks with green markers, the one at the gooseneck and at at deck are close enough to 90 degrees that there is a significant deflection.
We just changed over our backstay cascade from low friction rings on the control line to ball-bearing blocks.  The two rings we eliminated changed the line direction a bit more than 90 degrees.  The reduction in friction in the system from removing those two rings is very noticeable.  Now that I have messed around with low friction rings on this system, and on our vang, I think blocks are a good idea whenever there is no winch being used on the control line.  

We will keep the low friction rings on the tweakers and on the first and second part of the backstay cascade - there they make sense.

 

Diarmuid

Super Anarchist
3,757
1,827
Laramie, WY, USA
I might just comment on the original question that not all the blocks labeled "A" are in the same geometry.

Two of them (I have boxed in red) have 180 degree turns.  You most definitively don't want rings on those.

But three of them (boxed in green) are less than 90 degree bends - sure blocks would be less friction, but rings have been used in these places. I have seen several jeanneau's using german mainsheet system with rings (in the last two green spots).  It does work adequately.

I am not pushing rings here, simply pointing out that #1 those five "A" positions should really not all be lumped together, and #2 that rings have been used reasonably successfully on the front several lowe turn positions.

View attachment 446615
Curious about the forces generated by that block nearest the gooseneck on those mainsheet-to-the-mast setups. Are they mostly just counteracting the spar compression/luff tension forces, or are we introducing a whole new bag of vectors?

 

Rain Man

Super Anarchist
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Wet coast.
Curious about the forces generated by that block nearest the gooseneck on those mainsheet-to-the-mast setups. Are they mostly just counteracting the spar compression/luff tension forces, or are we introducing a whole new bag of vectors?
The force vector from that block on its attachment will be directed downward and away from the mast at around a 45 degree angle.  The vertical component of that force will add to the compression forces on the mast.  The horizontal component will tend to pull the boom away from the mast.  When the boom is eased, there will also be a small horizontal component pulling the boom back toward the centreline.

 
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climenuts

Anarchist
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PNW
Yes but a German mainsheet typically has much line to pull in AND it almost always on a winch. You probably don't care about the extra friction because the winch just takes care of it.

This diagram has a 5:1 purchase on a 28' boat. On that size boat you're certainly only going to be using the winch in moderate to strong winds. In lighter winds you'll be pulling by hand. So you'll really notice the friction of rings.

Sometimes a boat builder does something not because it is better but because it is cheaper (rings) or trendy (hard chines, reverse bows) even if it doesn't make sense.

And except for the mid boom blocks with green markers, the one at the gooseneck and at at deck are close enough to 90 degrees that there is a significant deflection.
I've got 5:1 on my 29 and it's always been fine by hand for me but not for the admiral. Can be pretty tough to release in a gust. I get annoyed by the friction of the blocks for light air. Plan is to replace with 3:1/6:1 two-speed setup and move the 5:1 to the Vang.

 

Diarmuid

Super Anarchist
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Laramie, WY, USA
The force vector from that block on its attachment will be directed downward and away from the mast at around a 45 degree angle.  The vertical component of that force will add to the compression forces on the mast.  The horizontal component will tend to pull the boom away from the mast.  When the boom is eased, there will also be a small horizontal component pulling the boom back toward the centreline.
Thanks -- yeah, that's about what I had figured -- plus a vertical stretching of the boom section between the block and tack cringle (unless the block is stropped on?). It seems like a rather serious (and multiplied) resultant vector right at a hinge-y place where there's already some tricky loading. Mostly, it seems, for the purpose of keeping the mainsheet totally free of the cockpit?

 

12 metre

Super Anarchist
4,004
780
English Bay
Hands up for those people who prefer end boom sheeting.
Personally I prefer it, but best not to ask people with end boom sheeting who have gotten wrapped up in the mainsheet during a gybe.  Probably not an issue on tiller steered boats.

 
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European Bloke

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We all understand that the coachroof set up is a cruising compromise to keep the cockpit clear. The ones without a traveler are fucking horrible and those with a traveler just really bad because you can't get to the controls.

 

Rain Man

Super Anarchist
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Wet coast.
We all understand that the coachroof set up is a cruising compromise to keep the cockpit clear. The ones without a traveler are fucking horrible and those with a traveler just really bad because you can't get to the controls.
That it is tolerable at all is because these are cruising boats, and you are not making constant adjustments like a racing boat.  Trying to race a boat with this kind of setup would be very frustrating.

 

zenmasterfred

Super Anarchist
1,553
551
Lopez Island
My hands are raised for end boom sheeting.  Replaced a 5:1 w/ 3:1 Harken blocks to a 2 speed winch on my 42 footer, very nice, eliminated a lot of mainsheet.  Plenty of power.

 

blunted

Super Anarchist
1,517
366
Toronto
Hands up for those people who prefer end boom sheeting.
When racing I am 100% for end boom sheeting combined with a good traveller set up. If the helm cannot get out of the way of the sheet on a gybe, fuck 'em. I want leech tension and I want AOA control!  I don't want the boom bending and acting like some kind of aerodynamic shock absorber.

My bimini however on the Beneteau votes for mid boom sheeting. We have no traveller on that one so pointing sucks as a result. To correct for that I've put the two bottom blocks on either side of the companionway on snap shackles so on a long passage I can unclip one of the low blocks and using a thick line simply connect it to the windward docking cleat that happens to be abeam of the sheeting set up, this lets me sheet to centerline or above so I can actually make some VMG to weather. doesn't help the sheeting angle on the jib on the fat beast but it certainly gets me 5-7 degrees more point.

My most optimal sheet location of course is on the wing, and it's about a foot forward of the "clew". On that rig, it's really only a traveller equivilant that effects angle of attack.

 

tane

Anarchist
953
275
...since the appearance of the "low friction" rings I am wondering, if stainless thimbles would not be "lower friction" & at a fraction of the price (not to speak of the throat-angle of the retaining line...)

 




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