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Thread: masthead fitting

  1. #1
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    Default masthead fitting

    I'd love feedback on this design, in case I'm making a rookie mistake.

    Boat is a 36' strip-planked staysail schooner (atkin "Erin"). Originally junk-rigged, but stays and shrouds were added in the 1970s. The masts are short and stout -- weight aloft is not my main concern. Everything else about the boat is overbuilt and heavy, so want to follow through on that theme.

    I have the masts out for repairs and painting, and decided I didn't like the 2-piece bands that the rig was attached to so I plan to replace those with a stainless welded cap like this (working on the mainmast only for now):
    wayward_mastCap_180709c_800x.jpg


    drawing shows eye-jaw toggles on shrouds, but would be actually be double-jaw toggles with 1/2" pins.

    pipe has 1/8"+ walls, the rest is 1/4" plate, or 3/8" plate for the shroud tangs. wires are all 5/32". Running backstays attach on a separate fitting lower on the mast, so the forestay and "triatic" are just going to pull on this fitting with no direct opposing force besides the mast itself. Mast is douglas fir, solid at the top, hollow with 1.5" walls (!) farther down. 5.25" diameter at the masthead.

  2. #2
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    Default Re: masthead fitting

    Mine is almost identical. I made a mold and had it cast.

  3. #3
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    Default Re: masthead fitting

    ...weight aloft is not my main concern...
    Not to be obnoxious, but if performance is in any way of any interest to you, then weight aloft should be a concern. And if your standing rigging is 5/32", that is a seriously meaty cap.

    That said, it looks like it probably won't break.

    From a manufacturing standpoint, the horizontal plate, with all those notches for the tangs, looks like it might be an awful lot of fussy (expensive) machining. If it's to be welded, would it make more sense to have the tangs simply butt against the underside of the plate?

    Those double suspension point tangs: Are you certain that whatever is shackled to the upper point will lead fair, or might it hang low enough to interfere with whatever is shackled to the lower point, or even chafe on the lower point itself? Bash up the upper block on the lower tang when she's slatting about in a calm or even sitting at a mooring?

    How long are your clevis pins? Do you have enough room between the tangs to be certain the clevis pins for the toggles will have enough room to be inserted or removed? How about the cotter pins to secure the clevis pins? Will you be able to get a wrench or a shackle pin key on the shackles for all the blocks?

    Alex

  4. #4
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    Default Re: masthead fitting

    important question-- how tight of a fit do I need between this and the wood? I'm hoping +/-1/8" is ok if I bed the whole thing in 5200. The mast isn't especially round and I'd very much prefer to not have to shave it to fit (and thus repaint).

    Quote Originally Posted by Pitsligo View Post
    Those double suspension point tangs: Are you certain that whatever is shackled to the upper point will lead fair...
    those are for halyards and topping lifts, and no I'm not thrilled about how those are laid out. Earlier design had 1"x1" tabs along the top, 1-hole each, but that only left about 1" between them and I was worried that didn't leave room for welding. This is more than I need for current sails, but I believe in leaving a few extras!.

    welders assure me that letting the notches into the top plate will be far stronger than butt joints. Also makes assembly easier and more certain. Will be cut on a water jet so the complexity is no problem.

  5. #5
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    Default Re: masthead fitting

    Without doing any calculations..... my gut reaction is that this device is far more complex and heavy than is needed. For starters, I wouldn't extend the top plate to the outside of the tangs. The tangs don't need that much contact. And, actually, I'd have the tangs taper toward the top so that they'd blend into the top. Simple fillet welds of the tang to pipe are sufficient.

    There's a lot going on with this device in a rather small area. I do a lot of welding but I'm not a welder, just a guy who knows a little bit. Part of that is knowing that heat wrecks havoc on the shape of steel, especially stainless steel. Seek out a very competent welder for advice. Be aware that the welder probably won't care a whit about the aesthetics.

    I'd mock the device up in wood, paint it silver, and stand back and have a good look before committing this to steel.

    As Alex said, 5/32" standing rigging doesn't seem to need this.

    Jeff

  6. #6
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    Default Re: masthead fitting

    I would make the mechanical fit as snug as possible. The unit will be taking strain from a number of directions for years. any chance of a wobbly fit will tent to strain and loosen the mechanical fastenings, and introduce the possibility of rot in the wood in way of those penetrations. My mast head fittings are essentially the same, and appear to be well fitted, no sign of breakdown after 30 + years.

  7. #7
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    Default Re: masthead fitting

    I would make it 1/8" smaller diameter than the mast, and shave the wood to fit. You really don't want it rocking around on each tack. Your sheet/leech tension does oppose the headstay when closehauled. How far down are the runners? Within 18" or so you are probably fine, I would get nervous if its much over 30 inches.

    Will your modelling program tell you the weight? It could probably get shorter to reduce weight, a bit less height than the mast diameter perhaps.

  8. #8
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    Default Re: masthead fitting

    I agree that it is more cumbersome than is needed. In additon to the weight aloft it offers more windage than a traditional, flat tang set up will. in addition, consider the use of bronze plate as it is less prone to fracture than is stainless steel. One of Pete Langly's cast bronze fittings would be faster to obtain and probably less expensive. Pete Owns the Port Townsend Foundry. You can see a bit of their line on their site.
    Jay
    http://www.porttownsendfoundry.com/

  9. #9
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    Default Re: masthead fitting

    Regarding the weight aloft, if it's a fairly heavy cruiser I don't think it'll make much of a difference other than slowing the role. In my case the new mast was thinner and lighter, so it was somewhat of a trade off. The cap on the original mast was double the weight. The new system works quite well .

  10. #10
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    Default Re: masthead fitting

    9/32, haha, just testing.

    heavy cruiser is an understatement. In SA/D and many other measures, the chart looks approximately like this:
    racer|<-------------------------------|Westsail 32|------->|Me.

  11. #11
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    Default Re: masthead fitting

    next important question -- do I need something to prevent twisting? Part of the design goal here was no fasteners into the wood, so I'd do something like weld a plate across the top of the pipe (vertically) and cut a slot in the mast to accept it.

  12. #12
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    Default Re: masthead fitting

    ...weld a plate across the top of the pipe (vertically) and cut a slot in the mast to accept it.
    How does that weaken the mast less than a bolt?

    Alex

  13. #13
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    Default Re: masthead fitting

    Quote Originally Posted by miles archer View Post
    next important question -- do I need something to prevent twisting? Part of the design goal here was no fasteners into the wood, so I'd do something like weld a plate across the top of the pipe (vertically) and cut a slot in the mast to accept it.

    That slot sounds like a really good place to start a rot pocket.

    Jeff

  14. #14
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    Default Re: masthead fitting

    Make the part hexagonal or even octagonal if you want to stop twist. I would make it slightly tapered so it fit tight.

  15. #15
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    Default Re: masthead fitting

    Quote Originally Posted by miles archer View Post
    important question-- how tight of a fit do I need between this and the wood? I'm hoping +/-1/8" is ok if I bed the whole thing in 5200. The mast isn't especially round and I'd very much prefer to not have to shave it to fit (and thus repaint).
    If the gaps are completely filled with 5200 the joint will be extremely stiff because the elastomer is constrained by the rigid surfaces that it is bonded to. The hard part will be filling the joint without coating the entire shipyard.
    next important question -- do I need something to prevent twisting?
    If you glue that bad boy on there with 5200, the only way it is coming off is with a saw.

    There are some narrow spaces between the tangs that might be very difficult to weld. Then again, it sounds like the welders have already looked at it.

    The stainless should be a low carbon grade like 316L or 304L for welding. While the carbon content is lower than it used to be these days, it doesn't hurt to use the welding grades.

    I would like to see more information about Jay's concern about fracture. It may be related to dissimilar metals like galvanized fittings. You do need to passivate or at least grit blast with clean, fine blast media after welding. The more polished the surface the better with stainless. If duplex 2205 stainless is available, it is 2x stronger and more corrosion resistant, but if McMaster is any guide, also twice the price.
    Management is the art of counting beans. Leadership is the art of making every being count. --Joe Finch

  16. #16
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    Default Re: masthead fitting

    "If you glue that bad boy on there with 5200, the only way it is coming off is with a saw"

    I have mentioned this in the past, but if you heat up the metal part with a torch (A relatively small tip on an Oxy-acetyline torch) it will come off with about as much difficulty as if you had used chocolate...

  17. #17
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    Default Re: masthead fitting

    Mine fit very tight. I had to hammer it on. The inside of a casting is pretty rough. That locks it on just fine.
    Mine had a tang for the forestay, one off to the side for another pulley. (Spinnaker?). One for each cap shroud. And one larger one that accepted the backstay and spring stay.
    Last edited by mariner2k; 07-15-2018 at 09:33 AM.

  18. #18
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    Default Re: masthead fitting

    Quote Originally Posted by Pitsligo View Post
    How does that weaken the mast less than a bolt?
    not for strength reasons, but to avoid a fastener and a way for water to get in.

  19. #19
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    Default Re: masthead fitting

    Quote Originally Posted by MN Dave View Post
    There are some narrow spaces between the tangs that might be very difficult to weld. Then again, it sounds like the welders have already looked at it.
    the box for the forestay and triatic will be a bit of a challenge. The one welder said the trick is to taper the surface out to the outside, so you can basically weld the whole surface without access to the inside of the box. He says he'll discuss with a stainless expert, too.

    structurally, the welds from tang to pipe aren't as critical. The tangs hang off the top plate and the welds there should have more than ample strength. In effect, this is more like a set of bands over the top than a cranse iron.


    Thanks for all the thoughts, everyone!

  20. #20
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    Default Re: masthead fitting

    Quote Originally Posted by Canoeyawl View Post
    "If you glue that bad boy on there with 5200, the only way it is coming off is with a saw"

    I have mentioned this in the past, but if you heat up the metal part with a torch (A relatively small tip on an Oxy-acetyline torch) it will come off with about as much difficulty as if you had used chocolate...
    My point was that removal will not be a trivial exercise, and having the thing twist is not going to be a problem. It doesn't sound like a hollow mast where anyone will have to pop it off to access anything anyway.

    Good advice about using heat to soften 3M 5200 on smaller parts, but that part will need a large heat source like a propane weed burner torch to evenly heat the the entire part without overheating a small area. 3M says not to use it if the temperature will exceed 190F, but that is not going to soften it enough to do this job. (I would not paint it black though.) With all the surface area and the fact that you will have to break the vacuum as well as break down the adhesive, it is going to take a lot of heat and force.

    EDIT: Canoeyawl, it is not a small part.
    5.25" [mast] diameter at the masthead
    so maybe 8" top diameter and 6" long 15lb of steel and 300 square inches outside surface to radiate heat plus the end of the mast is a heat sink. 300 series stainless has a very low thermal conductivity. 1/3 that of carbon steel and 10% that of bronze.
    Last edited by MN Dave; 07-15-2018 at 09:11 PM.
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  21. #21
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    Default Re: masthead fitting

    I have used a lot of both Sika and 5200, and my experience in removing metal fittings is to concentrate a small, hot flame (not a weed burner, but a welding torch) directly on the metal away from the edges and the metal will conduct enough heat to get well over 4-500 degrees without damaging even the surrounding varnish.
    I have done this many times even on items as small as a 2" cleat. It really does just lift off like warmed up chocolate. It takes about 700+ to char the wood, as it is a great insulator. If you overdo it, the varnish in contact with the part will soften of course, but never have I done any real damage.

  22. #22
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    Default Re: masthead fitting

    I like your design.

    - Weight is function of material thickness so picture may be misleading. // weight up high will dampen a snap roll and thus may keep you from being rolled by beam sea?
    - Fit: My inclination is snug fit // treat wood with some preservative ( copper napthalate / ethylene glycol / etc etc ), any end grain that could wick moisture should be allowed to saturate with a bit of poison // dried out and bedded with 3M 4200 or 5200 type stuff
    - To pin or not to pin: could weld small cross bar to underside of top that then keys to a notch/slot in top of spar so no hole for moisture to intrude and cap can not twist
    - Bronze vs Stainless: Brnz has advantages but sourcing and welding may be bit harder // 316 CRS is considered easily available VERY weldable.

    I like your design.
    Last edited by George Ray; 07-15-2018 at 03:05 PM. Reason: weight aloft comment
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  23. #23
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    Default Re: masthead fitting

    my first thoughts are why do you have toggles at the mast head? extra weight and no advantage that I can see.

  24. #24
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    Default Re: masthead fitting

    Here is a masthead mast that I designed for a racing boat. Note that the shieve box has been drilled and lightened. All bolts have had their heads milled out a bit concave and their shafts drilled for further lightness. The blocks and shieves are also as light as possible without sacrificing strength. Windage is also considered by using a cap made up of strap material and retaining nuts are made of bar stock and have a beveled and slotted head for a locking pin. The principal halyards run inside of this mast through pvc tubing. Every effort was made for both strength and lightness. This hollow spruce mast minus the wire rigging is 44' in length and weighs less than 200 lbs. Every ounce added to a masthead increases its leverage and creates less ability to carry sail.
    Jay
    Last edited by Jay Greer; 07-15-2018 at 03:19 PM.

  25. #25
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    Default Re: masthead fitting

    Quote Originally Posted by MW Jones View Post
    my first thoughts are why do you have toggles at the mast head? extra weight and no advantage that I can see.
    Because they're simple 1-hole tangs, I'd have to put forks on the wire ends. I was told that that's a no-no because every unfair load will try to pry the jaws open, and so they tend to break. With a toggle, everything can twist so the tang takes the unfair load, not the fork. The drawing shows eye-jaw toggles because I was being lazy, but they'd be jaw-jaw toggles.


    Quote Originally Posted by MN Dave View Post
    that part will need a large heat source
    I think if I ever need to get this thing off, I'll try the saw method first, and only resort to a weedburner if plan A fails.
    Last edited by miles archer; 07-15-2018 at 08:03 PM.

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