Shrouds, Spreaders, Angles, and Loads

Discussion in 'Boat Design' started by Kirk Jockell, Jan 20, 2018.

  1. Kirk Jockell
    Joined: Jan 2018
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    Location: Lake Lanier, Georgia

    Kirk Jockell New Member

    I will start by saying, "I am not a Naval Architect." That said, I've been around sailing boats my entire life, so I am quite confident and comfortable around them.

    A friend is looking to buy a larger sailboat. I was helping him look over an '83 O'Day 28. While not know for their excessive quality, the O'Day team produced boats of reasonable quality that had to compete within a certain price point. That said, I was surprise and taken aback when I realized somethind odd about the rig of this Keel stepped model.

    It is a simple, standard single spreader rig, with two lower shrouds fore and aft and an upper shroud that is swept and attached alongside the lower aft. While checking the turnbuckles and chainplate attachment points I looked up the rig and winced. The upper shroud is not in perfect alignment. It travels down to the spreader in near perfect alignment with the mast then takes a significant and noticeable turn back to the aft lower attachment point on the deck. In other words the spreaders are not swept back enough to keep the shroud and the compression loads in column.

    At first I thought it was just a mistake with this particular boat, but inspection of two more O'Day 28s confirmed the same. The rig was designed that way. In all my years of sailing, I have never seen a set up upper shrouds be configured in this manner and it seems of poor if not irresponsible design. Am I crazy and making a lot out of nothing?

    Comments....
     
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    I haven't seen one of these puppies in many years, but if the cap shroud (my assumption) is out of column, yeah you'll have an issue in bigger wind strengths. Can you post a picture, but what I think you're referring to is the cap shroud comes down to the spreader in line with the mast centerline, where after it angles aft to a chainplate. On most single spreader rigs, the spreader would angle aft to meet the shroud and permit it to fall at a modest sweep angle, offer some headstay tension, as well as side to side stiffness.

    My database shows the O'Day 28 with double lowers and a cap shroud, that does land on the aft lower chain plate but the spreader is rotated aft as well. This is the way it's supposed to be and this makes sense, as I'm sure you've realized too.
    [​IMG]
    The logical thing to do is find out way the cap shroud doesn't have a "fair" run, which is likely a corroded spreader socket fitting and of course fix it.
    [​IMG]
    This O'Day 28 shows a slight amount of spreader sweep, which may or may not be right, but there could be reasons for this, such as raking the mast to deal with weather helm, etc.

    From the few images I have, the spreader sweep seems to be relatively modest, but this isn't uncommon with a rig setup like this. The one above seems slightly less than average, but not much out of the range I have in my images. Some tuning should sort it out.

    Lastly, the O'Day 28 is a reasonable value for an entry level boat of this size. At her age, she'll likely have had most of her systems upgraded or will certainly need so. It's a sound design, being stable and capable, just not so well equipped from the factory as it could have been, which are all things that can be changed. I see these available ranging from $5,000 for a pretty rough one in need of love to well over priced version looking to recover some upgrade costs (my assumption). For $10,000, you can get a pretty good example and for a few grand for a pretty nice one. If looking at this yacht, try to find one built in the early 80's not the 70's, as model run changes made it a better boat at the end of her run.
     
  3. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    If the mast is raked too much, or the forward lowers too tight it would do that.
     
  4. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I suspected this Gonzo, as I have reports of some moderate lee helm associated with this design (depends on keel configuration), so they may have played with the rake to address it.
     
  5. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I think O'Days all had a socket for the spreader that didn't swivel.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    I've seen them with fixed and floating spreaders. The floaters commonly were a single pin through a stamped sheet steel bracket.
    [​IMG]
    There were two versions of spreader sockets, one for masthead and the other for fractional.
    [​IMG]
    Top one for fractional and it has some lateral movement available.
     
  7. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    I had an O'Day Daysailer with the swiveling type. I didn't know they used it in the larger sizes.
     
  8. Kirk Jockell
    Joined: Jan 2018
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    Location: Lake Lanier, Georgia

    Kirk Jockell New Member

    Thanks to everyone for their comments and input. I talked my buddy into moving on with his search. He liked the boat and the pricepoint, but asked if I'd have it. Simple answer: With that rig ... HELL No!
    I've gone back by the boat and took a picture of the swept back cap shroud and lateral spreader. It's just messed up. Keep in mind, I looked at two others that were the same. I have since looked at a fouth and it was the same only not as exagerated. To me, on this fourth one, the spreaders seem to be giving in to the loads and trying to correct themselves. It looks like a failure in the making. Thanks agian, everyone. Love this site. so much knowledge.
    Oday 82 Rig.jpg
     

  9. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    On the image you've just posted, it looks like the spreader socket may be mounted backwards. If mounted correctly, they'd permit the spreader to adopt the appropriate angle. It would be a simple fix, just by swapping port for starboard or maybe just flipping each.
     
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