Marine bedding compounds generally do an excellent job of sealing deck fittings. However, they can be expensive and messy and tend to cure in the tube when stored for a long time.
When I was refitting my ketch, Silverheels, a professional yacht repairman told me he’d been using rope caulk bedding above the waterline for years and had never had any leaks. I bought some that day, was delighted at how user-friendly it is, and have used it ever since to bed and seal everything from stanchion bases to padeyes to portholes to my anchor windlass. After six years, nothing I’ve bedded with it has ever leaked a drop.
Rope caulk is a gray putty that comes in a stranded roll, making it easy to peel off a bit and lay a bead as thin or as wide as needed. You can also mush it together and roll or mold it by hand to suit the job. It doesn’t run or stick to your fingers, and unless it’s exposed to the weather and sunlight for a long time, it never hardens. Fittings bedded with rope caulk can be taken up years later and the caulk will still be fresh and malleable enough to scrape up with a putty knife and reuse. Its shelf life seems to be limitless. It’s sold in most hardware stores, and a few dollars’ worth can meet a typical boat’s bedding needs for years. It’s great stuff to have on board.