Spreader length

Discussion in 'Sailboats' started by jarcher, Mar 25, 2012.

  1. jarcher
    Joined: May 2011
    Posts: 30
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    Location: Smithfield, RI

    jarcher Junior Member

    Yes all three shrouds come to the same chain plate. I adjusted all six shrouds using a Loose gauge to about 13% breaking strength. The uppers and lowers are 1/4 inch, the intermediates 7/32 inch.

    Another thing I have to check is the rig tune under sail. In the 17 knot breeze, I think I saw the leeward lower sagging a bit, but didn't check carefully.

    I can see that loosening the lowers and intermediates would allow the mast to bend forward a bit, but then under sail, would this allow the mast to fall out of column?

    Thanks, yes inverting the mast has been my biggest concern. When going upwind, we tried to keep a lot of leech tension on the main that 17 knot night. We did fly the spinnaker downwind and that went very well.

    Don't the check stays add a risk of inverting? Without a baby stay, it seems they could pull the middle of the mast aft and have it break backwards?

    Really?! That's why I had been avoiding them, because of the extra aggravation when tacking. I was trying to figure out a way to use something like barber haulers to pull them inboard, then run the purchase to the toe rail.

    How would MORC style work?

    Hm, I'll have to review my notes. If I put an extra inch on I'll be pissed at myself, since its a major aggravation to fix that. The holes in the spreader bar need to be filled, and the spreaders and bar redrilled, and of course the countoring to the mast.

    My sailmaker is always around. He is a great guy, extremely knowledgeable and he has been a huge help. Once I get the next round of tweaks made and the check stays up, he'll be back on board.

    Thanks Paul!
  2. Paul B

    Paul B Previous Member

    Sounds to me like the intermediates have been cranked too much. Ints can seem to be too loose sitting at the dock compared to the uppers and lowers, but when sailing things are OK.

    FYI, in almost 40 years of racing keelboats I have tuned a lot of rigs on a lot of boats that won a lot of regattas. I never once considered the breaking strength of the rigging when setting things up. Most of the guys I know who are really good at setting up rigs would look cross-eyed at you if you asked them what precentage of the breaking strenght of the uppers they were tuned at.

    The FIRST thing you should do after stepping a new rig is to sight the aft edge of the mast when sailing loaded up. With the nice sail track there it makes it easy to see if you are in column. If you are sure your masthead is centered (this you can do at the dock) you can then start tensioning ints and lowers to get the mast in-column and bending the way you want.

    Your leeward uppers and lowers should not be sagging. Tighten them a couple of turns, then tack over and match the other side. Repeat until the rig is straight and the leeward rigging is firm. Then sight the rig and adjust ints (and maybe lowers) to get the rig in column and bending correctly.

    You want the rig to remain in column under sailing loads. But you can change things a bit, remain in-column, and get the result in shape that you want.

    If you want to get serious you might end up with settings for light air vs heavy air (example: 2 turns on lowers, one on uppers and ints for Heavy air).

    Yes. If you are sailing in 15 knots with the checks on and you let the backstay all the way off the rig could invert. So don't do that.

    I was once sailing on a masthead Two Tonner that lost the hydraulics in the backstay while sailing upwind in about 20 knots with the heavy #1 up. Runners and checkstays on tight. I could not believe the rig stayed in the boat. It had more bend inverted than I have ever seen on a mast in the normal direction. Don't do that!

    Masthead J29s originally ran the checks to a car on the genoa track, about 3 feet aft of the mast. Between the car and the stay they had a 4:1 (8:1?) purchase. So the checks were far enough to leeward that they could leave them on when sailing with the boom centered.

    Just don't have a need to sheet out and duck someone/something without thinking about this!

    Check out our posts from 03/27. I think you did the prudent thing.
  3. jarcher
    Joined: May 2011
    Posts: 30
    Likes: 1, Points: 0, Legacy Rep: 15
    Location: Smithfield, RI

    jarcher Junior Member

    Thanks again Paul, I'm heading out the door now and we'll at least check the mast being in column or out tonight. If I have time I'll adjust.

    I thought I needed at least the uppers at 13% or so of breaking strength to prevent the tip of the mast from falling off, thereby decreasing the angle of the upper shrouds to the mast and reducing the support as a result.

    But I guess this does not apply to the lowers and intermediates, so I'll adjust accordingly. Apparently the lowers will need a bit more tension since the leeward one was slack. I'll look to see where the middle of the mast is and adjust accordingly.

    On the check stays, if I anchor them to the genny track they will be a good bit outboard, pulling out as well as back. Is that okay?
  4. Paul B

    Paul B Previous Member

    The amount of tension is going to be directly related to the angle. On wider chainplates/wider spreader rigs the force required is less. On narrower rigs it can be a LOT more. So, to me, a number like 13% means nothing.

    Get the masthead centered in the boat and the rig approximately in column. Go out and load up. Tension the rig until the uppers remain taught on the leeward side. That should be about the right tension. Then adjust the ints and lowers to get the rig in-column and bending the way you want.

    When you are back at the dock double check to make sure the masthead is still in the center of the boat.

    It isn't optimal. It is trying to pull the rig out of column. But it is pretty lightly loaded (comparatively).

    I prefer to run a traveller track fore and aft on each side of the main hatch. Then you can attach a check to a car on each track. With a little 3:1 purchase you can pull the car back and it tensions the check. Releasing lets the check sag toward the mast.

    But this requires you to tend them every tack. It isn't a big deal, as the crew is going across anyway. The new windward one can come on mid tack, before releasing the old windward (new leeward) one. Very little loads.

    For daysailing you don't have to bother with any of this.
  5. jarcher
    Joined: May 2011
    Posts: 30
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    Location: Smithfield, RI

    jarcher Junior Member

    Okay, we got out good and early and as a bonus, the race committee was quite late. So we got lots of time to check out stuff. The wind was at about 11 knots true. At this wind speed, the mast stayed in column nicely. The lowers felt like they were under equal tension on both sides, on both tacks.

    So I'll have to try this again the next day we have 15 knots or so.

    Before we went out, I did take a close look at the pre-bend. As you said, I ran the main halyard down to the mast just above where it was furled on the book. A closer look indicated that it actually was pretty well bowed across its entire length, with an inch or two between the mast and the halyard at the deepest point. Much better than I thought.

    We then put the back stay on and got plenty of bend, probably well past 6 inches.

    I'll try to get some pics next trip down.

    That's a cool idea.

    I was thinking there are a few other options as well. The key info I was wondering is how much load there is on these, and you answered that, thanks!

    I suppose a simple option, just to get it going, is to bring the check stays aft to a purchase then just to the toe rail. That would let me see how well they work and if it helps get the head sail flatter, although at the risk of bringing the mast out of column.

    Then there are some fancier ideas. Here is a pic of my deck just forward of the companion way:


    I think I could put anchor points at the aft corners, just aft of and out board of the winches. When beating the boom is usually between these two points. I could bring the checks down from the mast to a 4 to 1 and anchor it with a quick disconnect shackle of some type. That keeps them out of the cockpit (I have a very small cockpit) and allows other crew members to adjust them and clear them when we turn down wind.

    Or, I could put a large anchor point in the center and shackle two blocks to it, with some cleats. A line with another block would go through those center blocks. The check could come down from the mast, through the block and then down to a 4 to 1 that connects to the toe rail. Kind of like a barbour hauler for a jib sheet, for lack of a better similar thing to cite.

    So now I can adjust how far inboard the check stay is pulled, and it can be eased when we turn down wind be extending the inboard hauler.

    The down side to these approaches is that they are fairly forward, so the angle down from the mast is shallow. That would require more force on them.
  6. jarcher
    Joined: May 2011
    Posts: 30
    Likes: 1, Points: 0, Legacy Rep: 15
    Location: Smithfield, RI

    jarcher Junior Member

    Oh, one other not so great thing, it looks like the AWA while beating was about 40 degrees on each tack, which is quite a bit lower than the 32 degrees I am used to and pretty low in general. Hopefully keeping the mast a bit straighter will help bring that up.
  7. Paul B

    Paul B Previous Member

    Sounds like you are in the ballpark.

    Compared to the shrouds the checks are pretty lightly loaded. But they aren't no-load. The first ones we did used the Harken tracks/cars of the time. After a few sails we were beating in a breeze, into big chop, and with a bang we had little Harken balls all over the place.

    We changed out to the Ronstan wheeled cars. I think those Harken cars had a SWL of about 800#, so the breaking load would have been 1600#. We exceeded that.

    Also, I know one J29 put a setup on the cabin top, adjacent to the hatch. They had to run tie rods down to a hard point inside the boat due to the checks trying to lift the deck.

    When I was talking about trimming them and said lightly loaded I was talking about the load on the 3:1 purchase for the cars. The vertical load on the check is actually pretty hefty. So if you use a purchase on the check and no car setup you will need a hefty system.

  8. Paul B

    Paul B Previous Member

    Something sounds wrong, and it's probably not the rig. An AWA of 40 would mean a TWA of about 55+, so you would have been tacking through more than 110 degrees.

    Better get your sailmaker out to have a look.
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