Thank you Vince for all the information, it is greatly needed and appreciated.The spreaders should project slightly upward, so as to bisect the angle formed as the shroud goes over the spreader tip. Alternate explanation is that the angle between the spreader and upper half of the shroud should be the same as the angle between the spreader and lower half of the shroud. So I think those spreader brackets are on the wrong side of the old mast.
We don't know if you're just trying to get a setup to go sailing, or if you are looking to race the boat, and therefore optimize it. The advice you'll find is aimed at optimizing things for racing.
For the past 20+ years the standard has been to use a spreader 'thru-bar' that you can see here, together with the plates that go over it. It's bent to give the desired sweep and upward angle: J/24 Spreader Thru-Bar Kit — Waterline Systems. Here's installation instructions that may also be helpful to you: Instruction Sheet - J/24 - Installing K-11867K Spreader Bar Kit
The North Sails Tuning guide J/24 Tuning Guide | North Sails gives a comprehensive explanation of how to set things up. If you're just going sailing, you don't need to stress about exact angles or dimensions, but for racing that setup has been the standard for a long time. They talk in there about their "Fathead Main". That's pretty much a regular main, similar to what Quantum or others would supply. If your spreaders are, or can be 760mm long, as recommended, you do want them to bear against the mast and not be simply held in place by the screws. You really want them to bear against the mast rather then try to shear off the screws.
When you rivet the plates in place, you should use an anti-corrosive paste, like tef-gel. Very important! Any place stainless steel and aluminum come together you'll have serious corrosion of the aluminum over time without it. A little syringe will last you a long time.
Lastly, the deck-stepped mast idea is totally non-standard, and I'd be suspicious that it could cause problems. The deck wasn't designed to take loads like that. It's a lot when the shrouds are cranked-up tight. Maybe it's ok, but we sure don't know.
-V
Will do. If the mast goes down, it's part out time.... Also, great explanation of why certain halyards exit where they do. I do think that the deck is set up for the way the mast is set up. Gonna set it up this week, take it to a yard and splash next week then 81 nautical mile sail / motor to the slip. Will take a couple days as there isn't much wind in Naples this time of year.You're welcome. Just keep in mind the advice about having the spreader push against the mast rather than the screws. If it should fail in a good breeze, you could lose your mast. That's expensive.
Jib and Spinnaker halyards exit on the starboard side because when racing it's normal that the marks are left to port. So coming into a windward mark you're on Starboard and ease the main as you round. The Stbd side of the boat is to windward and the boom is opposite, so there's room to work to raise the spinnaker and lower the jib if they're on starboard.
OK, OK.. I won't part it out. Ha. I should have realized that the one piece spreader bracket wasn't the actual size of the spreaders... I'm going to try and rig the mast and prepare it for stepping tomorrow and may have a question or two with photos to go along. I'm not planning to actually step the mast until I get to a boatyard next week. Just prepare. Also, I need to remove the the mast shaped piece that supported the deck stepped mast from the I rail (not sure if that's what it's called) in the bilge in the forward cabin (see pic). I think he took the newer mast he bought and cut it at the deck and fabricated aluminum to attach the now shorter mast to the deck. At least it wasn't unsupported. This is an old pic...Christian! Noo..ooo! You don't want to part it out after all your effort. I don't remember in detail how they were originally rigged, but yes, there were turning blocks 'foot blocks' on the deck to lead lines back to the cockpit. In 1978 it was all the rage to have everything led to the cockpit. With the halyards exiting on the starboard side of the mast as is the custom now, there is normally one cam cleat for the spin halyard which exits above head-high, for ease of hoisting (several big yanks downward does it). The jib/ genoa halyard exits lower... a couple feet above the boom, and has two cam cleats in series to handle the high halyard tension. Then goes through a ratchet turning block adjacent to the mast on the deck. So this one is pulled upward, finishing with your legs to get it very tight (when needed).
The spreaders slide over the tangs protruding from your brackets, of course. They (spreaders) ideally should be shaped at the inboard end with a file so that they match the curve of the mast and butt up tightly against it. Any slop you have then is just due to tolerances (poor fit) between the inside of the spreader and the tang on your bracket. Maybe those old-style ones aren't as close tolerance as the newer 'thru-bar' setup. The thru-bar that you see in this kit ...
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just provides something upon which to mount the spreaders. It's not the spreaders. You mount the spreaders onto the bar. They slide over it, as you do with your current bracket. I think the fit is reasonably tight, as I recall, but there's still a little slop. When you tighten the shrouds, all that slop will go away and the spreaders will be angled as far aft as the fittings will allow, if that all makes sense. If you buy new spreaders at ~$135 each, you need an end-piece too.
From Rigright.com:
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