Shape of a chainplate that might spread load better?

Discussion in 'Multihulls' started by perry2222, Jun 26, 2021.

  1. perry2222
    Joined: Sep 2019
    Posts: 15
    Likes: 0, Points: 1
    Location: Sydney Australia

    perry2222 Junior Member

    the Standing Rigging on my 10m cat was altered by the previous owner, from a running back stay rig to a 3 part standing rigging - forestay and sweptback shrouds (is this what they are called, shrouds?). There seems to be some issue with getting enough tension on the forestay it appears t be sagging excessively. PO says it cant be tensioned enough.
    The chainplates for the shrouds are a conventional strap, but overall the installation could be improved eg the reinforcing on the bulkhead could be beefed up.
    More forestay tension probably needs the shroud chainplates to be a bit bigger to spread the load over the bulkhead, certainly for my peace of mind. I am leaning toward a sort of a triangular shape that might do this, the bulkhead is reasonably thick, 1.5cm , but thought I might ask about for anyone else's knowledge/ experience.
     
  2. redreuben
    Joined: Jan 2009
    Posts: 1,813
    Likes: 136, Points: 63, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

  3. bajansailor
    Joined: Oct 2007
    Posts: 2,182
    Likes: 738, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Perry, can you post some photos of your catamaran please?
    Hopefully the photos will show how swept back the shrouds are.
    Some photos of your existing chainplates would be useful as well.
     
    Will Gilmore likes this.
  4. kapnD
    Joined: Jan 2003
    Posts: 898
    Likes: 157, Points: 43, Legacy Rep: 40
    Location: hawaii, usa

    kapnD Senior Member

    Spreading the load can be stronger, but the particular circumstances of the situation are unknown here.
    Wider chain plate base may require wider backing.
     
  5. perry2222
    Joined: Sep 2019
    Posts: 15
    Likes: 0, Points: 1
    Location: Sydney Australia

    perry2222 Junior Member

    OK A few images. Best I have to show the position of the 'Shrouds'. PO set up tackle to pull the shroud to leeward.
    Between that and the image here of the sagging forestay I wonder if the rig is tensioned enough.
    And yes, the A Frame is a bit disreputable.
    The Chainplate as it's installed is a bit... 'creative, entering through the deck and in the inside of the hull. I suspect to get around the hull deck joint and the buffer. It has been reinforced, but I feel it needs attention. Another job. There are quite a few.

    slack fstay?.jpg small at slip.jpg
     

    Attached Files:

  6. Will Gilmore
    Joined: Aug 2017
    Posts: 549
    Likes: 230, Points: 43
    Location: Littleton, nh

    Will Gilmore Senior Member

    Perry,
    I can't say what the appropriate load limit is on your chain plates, they look adequate, if a bit home made. Chain plates through the deck and attached inside the hull are not unusual, only those exposed hex-head bolts lack aesthetic appeal.

    My immediate reaction to your rig is it doesn't look like you have the rake right. I can't be sure from your photos, but it looks like your mast has a forward lean. You may get better luck tensioning the forestay with about six or eight inches of rake aft.

    As far as the terminology goes, I would call those stabilizing stays simply, 'diagonals'. You have the #1 reverse diagonals from the mast foot to the first set of spreaders, then the #1 diagonals from the first spreaders to the mast at the second set of spreaders, then the #2 reverse diagonals and #2 diagonals going down and up from the second set of spreaders.

    I also can't tell what's going on with the back stay. It looks like the only line that comes off the masthead is your topping lift. Is that an adjustable back stay that attaches to the mast at the same level as your forestay? How does that work? How high does your sail raise?
     
    Last edited: Jun 27, 2021
    bajansailor likes this.
  7. bajansailor
    Joined: Oct 2007
    Posts: 2,182
    Likes: 738, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    How much 'sag' do you have in your forestay?
    There does not appear to be much in that first photo of the A Frame and the furler?
    There appears to be some 'pre-bend' in the mast, which is to be expected on a fractional rig, even though it is only very slightly (about 9/10?) fractional.
    If you do need to get the forestay tighter, is it possible to put any more tension on the cap shrouds?
    Or even fit a pair of running backstays again?
     
  8. perry2222
    Joined: Sep 2019
    Posts: 15
    Likes: 0, Points: 1
    Location: Sydney Australia

    perry2222 Junior Member

    thanks for your input. I didnt notice a

    Thanks for this Will.
    Theres no back stay. Its reasonably common I think to have a 3 part standing rigging on cats these days, its so you can carry a big roach. I was unsure what they were called and have since chatted with a mate who has one and is also a surveyor he didnt know what they were called either.
    You could be right about the rake, I didn't notice it at the time I was there and haven't seen it in the flesh for over a year. Its not something I am stressing over as I plan to replace the 3 stays. Whatever they're called.
     
  9. perry2222
    Joined: Sep 2019
    Posts: 15
    Likes: 0, Points: 1
    Location: Sydney Australia

    perry2222 Junior Member

    Thanks for this Bajan. Re forestay sag, the photo is as much as I can tell you as I havent sailed it yet. Its still on the hard. I thought it looked a bit excessive, as I said in combo with the tension on the 'cap shrouds' - makes me suspicious.
    I think the 'prebend' is a product of phone camera distortion, it didnt look so bad in the flesh. But (OK we going to call them cap shrouds? fine with me) getting more tension is why I was asking about chainplate shapes. I dont like the installation and pretty sure It can be improved. Particularly unhappy with the reinforcing of the hulls/bulkheads on the existing ones. thanks again.
     
  10. Will Gilmore
    Joined: Aug 2017
    Posts: 549
    Likes: 230, Points: 43
    Location: Littleton, nh

    Will Gilmore Senior Member

  11. bajansailor
    Joined: Oct 2007
    Posts: 2,182
    Likes: 738, Points: 113, Legacy Rep: 37
    Location: Barbados

    bajansailor Marine Surveyor

    Re how the chainplates are only bolted through the hull (as shown in the last two photos) - I would be happier if there were long backing plates (at least the same size as the chainplates on the inside) in way of the securing bolts, rather than just having large washers under the nuts.

    Can you elaborate some more re how you are unhappy with the reinforcing of the hulls / bulkheads currently? Maybe add some more photos?
     
  12. perry2222
    Joined: Sep 2019
    Posts: 15
    Likes: 0, Points: 1
    Location: Sydney Australia

    perry2222 Junior Member

    >>> the inside of the hull shows that the chainplates have some fibreglass additions, but god they're messy. Just strips. These pics aren't that clear, but best I have and enough to make me unhappy.
    I'm of the opinion that the straps should be wider/ larger/ a different shape and preferably on the outside, while the inside I reckon needs to have a substantial piece of material glassed on of a similar size at least.
    My feeling is that the whole arrangement needs to be larger to spread the load if I need to put more tension on the stay.
    I am also inclined to suspect that the position of these shrouds might have been placed a little further aft.
    Despite my unhappiness with the job done, however, the boat has an Atlantic circuit to its credit and so I guess it works. I just don't have a lot of confidence in the work that has been done on the boat, the cumulative extent of which makes me uneasy about the quality of all of these jobs and this in particular. Ah. For example PO told me he had redone the mast step by bolting it tapped through the top of the X beam. and that 'in his experience' the corrosion would hold the bolts tight. No Tef Gel. If he had through bolted it I think I might have let the whole idea of buying it go. It was the PO's to do what he wanted, now its mine. An old story.
    Thanks for your input Bajan.
     

    Attached Files:

  13. perry2222
    Joined: Sep 2019
    Posts: 15
    Likes: 0, Points: 1
    Location: Sydney Australia

    perry2222 Junior Member


  14. Blueknarr
    Joined: Aug 2017
    Posts: 1,204
    Likes: 273, Points: 83
    Location: Colorado

    Blueknarr Senior Member

    Perry
    Swept back shrouds need much greater tension to tighten the forstay than a backstay or running backs would.
    Play the vang like it is an adjustable backstay.
     
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.