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Old 02-04-2012, 13:21   #16
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Re: Adding a Mast Cleat

About the threads.. I think a normal thread is most used, not a fine thread but also not a (often special order) course thread. My Forespar masts and booms all have regular thread. The only riveted parts are the doubler reinforcements inside boom and masts (like where the vang attaches or where the masts have joiners). High load parts like boom-to-mast and vang-to-mast use epoxy + tapped screws.

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Originally Posted by sy_gilana View Post
Just a question, reading this whole thread I could not find how you would trim your halyard tension?
Here I'm in trouble with English In Dutch, for small boats, we have what we call "hanekam beslag" which is a piece of hardware that is fastened to the mast with a row of hooks that point down (like the thing that a rooster has on his head ) You winch the halyard tight, which brings the eye in the end near one of the hooks so you can decide which one to use. Then you crank a bit more so you can push the loop over the hook and while pulling the temporary 2nd half out of the way, you release tension on the winch so the hook takes over.

For big yachts a piece of track with a car is used. The half-halyard loop is fastened to the car (around a pin). Now you can use any system for moving the car much like on a traveler) to control tension.

ciao!
Nick.
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Old 02-04-2012, 14:01   #17
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Re: Adding a Mast Cleat

Some may disagree but as a Machinist I use fine threads for a couple of reasons.
First, because one can get the screw tighter due to the pitch/leverage of the thread. Which, if you don't have a flat surface, will draw the two surfaces together much closer/tighter.

Second, with this in mind, it's common knowledge that once something starts to move (at sea) it continues to move, getting worse over time. And you still have the same amount of contact area between the threads whether it be 4 shallow threads or 2-1/2 deep threads.

And if the threads pull out, then you didn't have enough material thickness to start with.

Ya'll can stick with your method and I'll stick with mine.
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Old 02-04-2012, 14:14   #18
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Re: Adding a Mast Cleat

Quote:
Originally Posted by sy_gilana View Post
Just a question, reading this whole thread I could not find how you would trim your halyard tension?
Good question, on the jib, it is hanked to the forestay, so tight is good...right.

If I do this to the main the down haul or cunningham can keep it tight, as long as you dont have far to go.
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Old 02-04-2012, 18:26   #19
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Quote:
Originally Posted by capn_billl

Good question, on the jib, it is hanked to the forestay, so tight is good...right.

If I do this to the main the down haul or cunningham can keep it tight, as long as you dont have far to go.
A turning block at the base of the mast and bumping the halyard should be sufficient. On a furler I don't need the halyard like a harp strring. I know there are foils that are tight but mine is smooth all the way to the top.

If that doesn't work I have seen a cam cleat just below where the halyard exits the mast. The sail is winched up, temporarily held by the cam cleat while the halyard is secured on the cleat. That way the cam cleat is not taking the full tension of the genny.

My motivation for this is simply to free up a piano clutch. The two candiates for banishment are the genny halyard and the boom topper.
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Old 02-04-2012, 19:32   #20
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Re: Adding a Mast Cleat

In most terms, coarse are "normal" threads. The millwrights i worked with for years insist on coarse threads in aluminum. In the us anyway. For instance, a 1/4 bolt may have a 16 tpi or 20 (fine) tpi. I know of no "medium" thread system commonly used in the inch system.
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Old 02-04-2012, 19:55   #21
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Re: Adding a Mast Cleat

Easiest way to find out if your mast wall thickness can support a machine screw is to remove some access hatch or cover plate so you can see the actual thickness of the mast wall. Then put a 1/4-20 NC machine screw up against the mast wall and see if you will have more than 3 threads within the limits of the wall thickness.

If not and you don't want to use pop-rivets, then I would suggest stainless steel sheet metal screws which have a thread that cuts deeply into the aluminum to get a good grip. But for heavy loads such as a cleat or clutch machine screws are better and the use of a doubler plate makes more sense.
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Old 02-04-2012, 20:31   #22
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Quote:
Originally Posted by osirissail
Easiest way to find out if your mast wall thickness can support a machine screw is to remove some access hatch or cover plate so you can see the actual thickness of the mast wall. Then put a 1/4-20 NC machine screw up against the mast wall and see if you will have more than 3 threads within the limits of the wall thickness.

If not and you don't want to use pop-rivets, then I would suggest stainless steel sheet metal screws which have a thread that cuts deeply into the aluminum to get a good grip. But for heavy loads such as a cleat or clutch machine screws are better and the use of a doubler plate makes more sense.
Yeah. For a cleat I am not a fan of sheet metal screws.

I have always heard and applied the rule of thumb for machine threads of using fine threads for hard materials (steel) and standard threads for softer materials like aluminum. The threads are deeper on standard threads and the soft material will deform so the deeper threads give better purchase. But machine threads on thin wall is the risk here.

I am still contemplating rivnuts. Plenty of shank, plenty of threads, cleat, nut, mast all in compression and secure. Because the rivnut would not be flush (pretty sure I dont have the wall thickness to use countersunk) I could slightly counterbore the backside of the cleat for clearance so it sits flush on the mast.

Aluminum rivnuts, aluminum mast no corrosion concern. Monel screws or stainless?
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Old 02-04-2012, 21:10   #23
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Re: Adding a Mast Cleat

Assuming you have a rather thin mast wall section, IMHO, rivnuts or machine screws, etc. would be problematical, especially considering that the cleat has normally only 2 fastening holes for screws, etc.

A thicker aluminum plate shaped to the mast surface curvature and pop-riveted in place - and - then drill and install rivnut or tap and thread for machine screws through both plate and mast wall.

My personal worry about rivnuts is that they will move/wiggle and enlarge their mast hole until they fall out. Or maybe even set up a stress point where they pass through the mast wall and foster spider cracks radiating from the rivnut hole.
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Old 02-04-2012, 21:20   #24
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Re: Adding a Mast Cleat

Quote:
Originally Posted by Cheechako View Post
In most terms, coarse are "normal" threads. The millwrights i worked with for years insist on coarse threads in aluminum. In the us anyway. For instance, a 1/4 bolt may have a 16 tpi or 20 (fine) tpi. I know of no "medium" thread system commonly used in the inch system.
Well, from memory, 1/4" NC is 1/4-20 and 1/4" NF is 1/4-28. Those are the standard available threads IIRC. Many other pitches for special applications, but please, never use them on MY boat!

And for the OP, using a doubler plate seems like a good idea here. Another approach is to use epoxy to bond the doubler to the mast as well as a few rivets.

Cheers,

Jim
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