Chainplate location

Discussion in 'Sailboats' started by Overdraft, Mar 29, 2004.

  1. Overdraft
    Joined: Mar 2004
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    Location: Frozen North (Canada)

    Overdraft Junior Member

    I'm relocating my chainplates (long story, don't ask) and I'm wondering what the usual practice is for locating them fore and aft... Directly under the spreader tips (swept spreaders) or aft of the spreader tips so the stays are (apparently when viewed from the side) in line from the mast to the deck? Thanks for your input.
    Last edited: Mar 30, 2004
  2. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Without a fine study of the rig you have in place (old chain plate locations) you'll be hard pressed for a good return on the relocation of your chain plates. I'm reasonably sure I don't want to know about the mishap that is causing you to move about rather important hardware, but if the mishap is substantial enough to force this move, you should be consulting your insurance guy a surveyor or a broker.

    The "usual" location is dependant on the rig in question. The locations you don't want to talk about will be real close to the usual location (I'll bet) and another location will be placing undo stresses and strains in areas not intended for the additional loading. You may figure moving them a few inches aft should be okay, but the mast tangs, not being designed for the extra side loading pull out from the stick and the rig comes tumbling down while you're trying to propose to your girlfriend on a pretty sunset cruise. I don't want to be responsible for her drowning you after you unbury her from the doused canvas.
  3. SuperPiper
    Joined: Jan 2003
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    Location: North Of Lake Ontario

    SuperPiper Men With Little Boats . .


    I sail a stubby little pocket-cruiser. With the genoa sheeted outside the shrouds, the pointing ability was limited by the shrouds. So, I had to decide whether to move the shrouds inboard or otherwise. Moving inboard would increase the mast compression - not good. Moving them aft and outboard would accommodate inboard sheeting of the genoa.

    Did it. Like it.

    Did the shrouds interfere with the mainsail when running dead downwind? Who the %@#& ever gets to sail dead downwind?
  4. DaveB
    Joined: Dec 2003
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    DaveB Senior Member

    what's the structure like

    It'd be good to know what the structure's like that the chainplates tie into. Is there a transverse bulkhead?

    Are there any longitudinals?

    How about some dimensions of your boat (length, displ, beam, sail area, rig height & type)

    This is an interesting problem...

  5. Overdraft
    Joined: Mar 2004
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    Location: Frozen North (Canada)

    Overdraft Junior Member

    Thanks for the input. Apparently I'll have to provide the back-story now which will mean that everyone will tell me that what I'm doing is silly rather than answering my question, but here goes! The boat is a 22 footer that I will characterize as an 'old school' sport boat (ie. lots of canvas, deep keel, flat bottom, beamy, but heavier than a current sport boat, no bulb on the keel... think, say, Martin 242 for comparison). It currently has inline spreaders and no runners. The problems I am having are not enough forestay tension (jib sags to leeward a lot) and not enough room to fit a larger jib. Therefore I am changing to swept back spreaders. I am installing a new bulkhead to take the new chainplates and all I'm trying to determine is, when designing the chainplate location for swept spreaders what's the current practice? Thanks in advance for your thoughts!
  6. Overdraft
    Joined: Mar 2004
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    Location: Frozen North (Canada)

    Overdraft Junior Member

    Here's the question graphically: [​IMG]
  7. SailDesign
    Joined: Jan 2003
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    SailDesign Old Phart! Stay upwind..

  8. Paul B

    Paul B Previous Member

    I know your boat, it is one of the old Mull designed Pocket Rocket 22s. I built a rig for one of the original boats. You must have the later "Rocket" version with the big rig. Have you considered leaving the chainplates where they are and adding jumpers to the mast? Jumpers allow the backstay to tension the headstay.

    Do not do "B". When the mast bends, the middle of the mast will move forward as the top of the mast moves back and you'll be trying to pull the shrouds out of the spreader tips.

    You shold do something more like "A", and it is actually better to have some "poke" on the spreader. That is, the drop of the V1 should not be vertical, it should be loading into the spreader tip a bit (chainplate slightly forward and inboard of the spreader tip).

  9. Overdraft
    Joined: Mar 2004
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    Location: Frozen North (Canada)

    Overdraft Junior Member

    Thanks Paul! I'm amazed that you know of the boat... only 14 or so built I think. Actually mine is one of the original series not the 'Rocket' version which was a lighter build with a bulb keel and an articulated sprit. The one I have was ordered with a taller mast by a customer for reasons unknown. I'm happy with the configuration. I'd sooner have a bigger main that I can depower at will and a small non-overlapping jib than the original deal where (knowing my luck) I'd always guess the wrong genoa. I've lived with runners on my previous boat (Kirby 25) and am not anxious to return to them. I've often thought that jumpers (or what used to be called a jack-strut) would be the way to go if you could make them adjustable. Toyed with the idea of a ram but the thought of hydraulic oil dripping down inside the mast with the halyards didn't appeal to me! In any event, your explanation was very helpful as I totally forgot to think in terms of mast bend. I was all set up for A but then I started doubting myself, so this gets me back on track! I've got 20° of sweep on 30" spreaders so even with a vertical drop I'd have to displace the mast forward say, 11" before the stay would straighten out, so I feel there's a comfortable margin there.
    Thanks again!
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