I am installing two mast exit plates for the main and jib halyards on my boat. I have the first hole cut six feet up from the base and would like to know where the second one should be relative to the first as they both exit on the same side. What concerns me is that I might be weakening the mast itself if they're too close together. Is this a problem?
Sue & Larry respond:
Your questions remind us of just how many times we’ve been faced with having to figure out various problems if we wanted to work on our boats ourselves without employing costly professionals. When we’re faced with a problem like the one you've got, we try to do a little research on our own, and then apply good old common sense.
Since every mast is engineered differently, there’s no specific amount of separation listed for halyard exit plates. There are, however, some general guidelines that you can follow in making your cutouts. You're absolutely right in not wanting to place the holes too close together because that would weaken the spar. Also, exit plates should not be mounted in a horizontal plane, but rather should be spread apart vertically. When cutting the holes for your exit plates, the corners of the holes should be rounded, not squared off. If the cut out is made with squared corners, cracks can occur more easily. We like to start the cut for each exit plate by drilling a hole in each corner. Next we connect the holes by cutting the remaining material out with a jigsaw fitted with a metal-cutting blade. The hole drilled in each corner ensures in advance that our corners are nicely rounded.
As there’s no hard-fast rule for determining exactly how much vertical spacing you need between exit plates, we’ll tell you how we’d proceed if it were our boat. First, we’d do some dock walking to identify similar sized boats with similar masts to yours. We’d note the amount of spacing on their exit plates. After building a consensus, we’d return to our boat and add a fudge factor of several inches just to be sure, and then we'd cut away. In general we think it’s a good idea to locate your exit plates high enough on the mast to allow a crew member to easily raise the halyard manually if desired.
If for any reason you’re not comfortable with your independent determination, you could hire a spar engineer to come out and examine your mast, and be told exactly where to place your exit plate. Other options include phoning your spar manufacturer assuming they’re still in business and talking to their engineers to get some advice. Lastly, you may try calling your local rigger for his/her advice.
For future projects like this, you might want to know about a good multi-purpose reference for working on your boat yourself, that's Nigel Calder's Boatowner’s Mechanical and Electrical Manual. Many cruising sailors we know simply refer to it as, "the bible." Best of luck with your project.