Pics of my '83 Californian 42 LRC mast.
- Tabernacle shows the hinged mast "step". It is located on the aft cabin top immediately aft of the aft saloon windows.
- Mast mount shows a pair of angles, one aluminum and welded to the aluminum mast. The other stainless and bolted to the aluminum angle. The bolts with wing nuts go into the receiver.
- Receiver. Accepts the bolts with wing nuts. It is mounted on the saloon cabin top.
- Stay attachment point. There are 3. One each port and starboard about 31" from the mast. One forward close to the fly bridge seating about 5 ft from the mast.
The Californian owner's manual has nothing to say about the mast. In my opinion it would be good for 300 lbs. Maybe 400 lbs. I have lifted about 200 lbs with mine.
If you have one or are having one built and you want to lift more than 300 lbs I advise you to get a naval engineer to calculate safe working loads. I think the vertical component of the load is pretty good because the tabernacle base is almost on top of the bulkhead separating the aft cabin from the saloon. All of that will be in compression and quite strong. The problem comes when lifting something from over the side with the boom. You will be relying upon the relatively weak stays and mast mount + receiver. Their weak point is they are surface mounted with screws to aging fiberglass covered plywood. Not through bolted with backing plates.
Though it has nothing to do with the mast and boom on a 42 LRC this little story will serve to illustrate the change in working load with boom position. A boat I used to run had a hella stout crane. With the boom vertical the safe working load was 11,000 lbs. Boom at 45 degress 2,500 lbs. Boom horizontal 1,600 lbs. Boom below horizontal 800 lbs.