using spectra line for centreboard cable

Discussion in 'Sailboats' started by Mor22, Jun 27, 2013.

  1. Mor22
    Joined: Jun 2013
    Posts: 1
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: punta gorda Florida

    Mor22 Mor22

    Has anyone any experience with Spectra line. Our Morgan 22 has a centreboard with steel cable that needs to be replaced every couple of years. My understanding is that Spectra is much stronger and impervious to saltwater. But how would you secure it in this application? The steel cable is swaged to secure it. I would be a little leery of using a knot, not knowing the characteristics of the spectra.

    Any thoughts?
     
  2. Petros
    Joined: Oct 2007
    Posts: 2,936
    Likes: 139, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    I would give it a try, but you are correct in being concerned about a knot. When you bend any line in a tight radius you loose half its strength. I would whip the end as a loop, and use a large radius dowel or even a pulley sheave to wrap it around where it attaches at the end. You just want to avoid bending it in a tight radius, such as a knot might cause.

    Also, if it is exposed to sunlight it might break down. Most synthetics do not tolerate being exposed to sunlight as it causes it to break down fairly quickly. So if your application is down inside the cabin it would be okay, but it is out on deck it might not hold up very well as compared to a steel cable.
     
  3. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 471, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Spectra is a bit stretchier than the steel lanyard you previously had. I don't know why you needed to replace your Morgan lanyard this often, but I'll bet it was 304 grade 7/19 instead of 316, which makes a huge difference in brackish and salt water, possibly explaining things.

    I use Spectra on light boards, but prefer steel on ballasted or heavy ones. Spectra will slip or break with most typical knots, like a bow line or double half hitch over a rolling hitch. I'd recommend a double fisherman or the anchor bend, both having their tails seized, just to be sure.

    Most of the time I don't bother with a knot in the board, I just drill a significant hole with a perpendicular, of the line size, into it. I pass the end of the line through the small hole, coiling it in the larger one, then epoxy it flush with the board sides.

    Tieing to a becket or strap should be done with a thimble and seizing. 3/16" 7/19 stainless wire (304) is about the same strength (3,700 lbs.) as 3/16" Spectra (3,800 lbs.), so the strength difference has been considerably over estimated.

    If it was me, I'd use a 316L 7/19 wire and forget about it for a several years. Stretch is minimal and it attaches well, with little fuss and little profile in comparison.
     
  4. gggGuest
    Joined: Feb 2005
    Posts: 807
    Likes: 17, Points: 18, Legacy Rep: 76
    Location: UK

    gggGuest ...

    Wouldn't consider knotting a hi-tech rope: I'd splice it...
     
  5. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 471, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Spectra can be knotted, but the knot has to be considered. For example a bow line will break at about 30% of the line's strength, so more area and radius type knots are the way to go, like the anchor bend. I tend to agree, these lines should be mechanically secured, preferably around a thimble where applicable.
     
  6. jonr
    Joined: Sep 2008
    Posts: 721
    Likes: 11, Points: 0, Legacy Rep: 57
    Location: Great Lakes

    jonr Senior Member

    I've replaced cable with spectra. Works great, never rusts. I used only long bury/loop splices.
     

  7. bpw
    Joined: May 2012
    Posts: 290
    Likes: 4, Points: 18, Legacy Rep: 34
    Location: Cruising

    bpw Senior Member

    I doubt breaking strength will be an issue with anything but the tiniest of spectra lines. 3/16 amsteel could probably pick up the entire boat.

    Don't worry about knots, it is incredibly easy to splice.

    After replacing the rig on our boat with synthetics I doubt I will be using wire for much of anything ever again. The Synthetic is so much easier to work with and much nicer on hands.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.