I bought the parts to upgrade my downhaul to the theoretical 16:1, but found after installation that I am limited to the length of the blue rope in the picture from the Murrays Catalog. The longer the rope, the less downhaul I get. I need the rope to be a certain distance to be able to hook it to the clew. I still have plenty of room between the clew and the blocks, but the limitation of the lenght of the blue rope runs me bullet block to pivoting exit block(block to block) Any solutions?
Murrays Downhaul Page

I'm not convinced that acts as 16:1. I'd bet if it was hooked up to a ruler, you'd only see 8:1 (Pull in 8", and see if sail comes down 1"). The blue line probably doesn't move in the center block as the two top ones on the sail come down evenly. You could add two jam cleats at the center or on the sides of the mast (typical H20 setup for a cascade 8:1 system), split the blue rope in two, then "preload" the blue ropes. As you note, you use up a lot of travel to get the thing hooked up. Other solution is ANOTHER rope to pull the sail down and hold it and then hook up the blue ropes. I'll try to post a sketch somewhere.

Chris

I agree with Chris, that is not a 16:1 downhaul, it is an 8:1 made by cascading a 4:1 with a 2:1.
Even in their description, Item "D" is called a 4:1 Downhaul block.
The second turning block is not needed. Like Chris said, most people use a clam cleat and preload the hell out of it.
Make the lines long enough to use the old Hobie 14/16 method of hold the end of the line and standing on it.
You may even have to redo it after the first race to keep it tight.
Most of us on the 18sqs used 8:1 downhaul. I and some others used a straight 8:1, while some used a cascaded 4:1, 2:1.
I even cascaded my 8:1 into a 16:1 for a while to see what it was like. It made adjusting very easy but I didn't use it very much.
How are you attaching the downhaul to the sail?
Some of the 18sqs used the big hooks. Some bolted double blocks to the clew plate.
I added an extra clew plate to the bottom of the sail with a single cheek air block on each side and I bolted a single cheek air block to each side of the standard clew plate and fed the line every time I rigged. The lower plate and blocks would pull the wrinkles out of the lower section of the sail. It wasn't very fast but it was clean and light.

This really is a 16 to 1 downhaul. I had one on my Tornado and it works great. To get more downhaul, you can do a couple things. The easiest: stretch the main luff rope by by downhauling to the max and then releasing it, and adjusting the blue downhaul rope to take up all the slack gained in the system. You want your downhaul initial setting to be at around the minimum downhaul setting for max depth on the sail.

The second: have a second grommet put in your sail up a little bit (six inches to a foot) from where your current grommet is. This will give you more room for downhaul adjustment. On my Tornado, there was over 2 feet between the bottom pulleys and the blocks on the sail after I had done an initital pull down on the luff of the main. I would occasionally get pretty close to max adjustment when the wind was honkin'.

I agree - that's a cascading 8:1 not 16:1.

Ooooo wait...no - they're right - it's 16:1 but in a weird way. Draw it out.

Hi Dave, That IS a 16 to 1 system. Because it is a doubled cascading 4 to 1 system it means that each section is 4 to 1 and that means you get equal amount of travel in each part of the system so that you quickly run ut of line in the blue part. A better approach is the 8 to 1 cascaded to a 2 to 1 system so that you can pull the 2 to 1 part really tight (stand on it with the mainsheet tight) to preload the system so that the 8 to 1 part starts out with the full amount of travel available. The blue line in your system has no easy way to adjust it so that it can easily be preloaded with the full amount of travel left to use. Therefore you use much of the available travel or line length just to get the system started. I looked at this system for a few minutes and cannot think of an easy way to make it adjustable. This is a poor system as it subtracts from travel length by the length of three blocks and a bowline knot. This would be much clearer if you had a photo to view of the popular 16 to 1 system I am describing. I do not have one or I would send it to you. I used it very effectively on my Mystere 6.0. It could really bend the mast - making a quite full sail become quite flat. We would lead the ends out to the shroud or the crew trapeeze so that it could be easily adjusted ("played") while trapezing so that in gusty winds it almost eliminated the need to play the mainsheet.

Mike

Dave,

My Nacra 6.0na has the downhaul Mike describes. I'll be at Pee Dee Friday night so you can see it there if you like. It's 16:1 and can bend that hearty 6.0 mast like it were a wet noodle.

Are they having an open class at Pee Dee? I thought it was straight Hobie.

Thanks for all the input. I revised my downhaul and used the small bullet blocks elsewhere, so no loss. I'll send pix when it stops raining long ebough for me to get to my boat!

David

The NOR doesn't say anything about whether or not there's an open class but I assumed there would be. I've got an email out to ask that question now.

I DID draw it out. If the red line has X tension, then each part of the red is at X, and the two top "red" blocks are each being pulled down at 2X. To counter act this load on each red block, the blue line must be at 2X tension, and it must be at 2X in each part. Since the top clew "blue" pulleys have a blue line around each one, each one sees 4X load, times 2 pulleys = 8X load on clew. What am I doing looking at that the rest of you aren't? All 4 bottom pulleys are fixed, right? I can email anyone my sketch, but don't know how to post it.
Chris

I think, with the way that you are explaining it, you're pulling both the red strings at the same time - not thinking of it as two sided.

If you look at the red system by itself its a simple 4:1 system just that you can pull either end of it right? Just like having a system with a double block at the top and a single block with becket at the bottom right. The bit that you tie on to the becket is essentially the end that goes through the other cleat.

Now if you look at the blue system then its exactly the same - just that the ends of the rope are blocked out up at the top block. So the blue system is a 4:1 system as well.

Now because you're only pulling one end of the red system at a time its essentially tacked on to the end of the blue 4:1 system making 16:1.

simple.... ish..... I think....

cheers,

The blue system is NOT is 4:1, since BOTH ends are being pulled down by the red pulleys. If one end was fixed to a non-moving surface, or if the bottom blue pulley was attached to the top red ones it would be 4:1, but right now, it is just a double-line 2:1 (if you run 2 lines through a single hanging block and pull down , you don't double the purchase, you just have a bigger diameter line). A line can't have more tension in one segment than in another, and every block being pulled down has a resisting force of twice the line tension pulling up. Doesn't matter if the red line is cleated at one end or being pulled at both; for the purpose of figuring loads the cleat is "pulling" the line. Again, the easy way to settle this is to have someone measure the distance each part moves...

OK, here's my drawing showing 8:1. 8X total loading at the top. Chris
[img]http://www.hobiefleet196.org/bigpictures.asp?ID=43[/img]

I perfomed a quick calculation on pull distances and it agrees with you - 3" of pull draws the sail down .125"...that's 8:1. I've tried every conceivable way to politely disprove what you've stated but keep coming up with your answer. Where I keep getting confused is that if you consider one of the blocks that terminates the blue line is free and not stationary - you might think that it adds to the tension on the blue line. I was considering that this effect was putting tension on the blue line equal to 4x (2x + 2x = 4x) because it was being pulled on either side by 2x but, as you stated, that isn't possible - if you split the system in the middle, the sum of the forces doesn't equal zero if you look at it that way. I'll drop a line to Murrays to let them know that they should probably re-examine that 16:1 description (althought they leave it a bit cloudy with the word "theoretical" thrown in there)

If you break the following diagram anywhere, your forces are not 20lbs in the middle but always 10lbs. i.e. the sumation of forces in a stationary system must equal zero no matter how you break it down.

10lbs <--------------->10lbs
10lbs <-----/10lbs (not 20 here).

I re-rigged and am pretty happy with what I've got now. Even though this old G-Cat weighs in @400 #s it quickly gets overpowered upwind single handed. Maybe now I can get the sq top a little flatter.

Thanks for all the information

David Mosley

Hey, you're the smart guy here :-) While we were arguing on the math, you went out and actually worked on the boat!
IMO 8:1 gets you all you need (especially when that adrenaline picks up in big air), but a 16:1 can be more easily moved by a weaker crew, and with very thin line for POSSIBLY some weight savings (more thin line and more blocks vs thicker line)

Chris

Jake, I worked on the system and I am pretty sure that I have figurated it out

The diagram showed in the Murray's does wourk out at 8:1. However, it is possible to re-arrange it to 16:1 but you will not be able to ajust it from both sides.


Another point, on my 8:1 system, you might argue that if two peoples pull with a 10lbs force, the total pull would be 20lbs. However, the rope tension is 10lbs and if one of the two person would pull with less than 10lbs, let's say 9lbs for example, he would not be able to hold the rope.
If the other sides is anchored by a cleat and something else, the anchor is actually pulling on the rope with an equal force