Upper and lower spar connection

I am considering making the joint for the yard and boom with good line threaded threw grommet in sail and holes in spars is this sufficent. Also have made wooden jaw out of 3/4 ply to hold the boom to mast will want to use smallest carriage bolt threw wood jaw and mast can i use a #10 or #12 bolt? I have no sailing experience so this is all new to me
dave

 

Dave,

I assume we're talking about a lateen sail here. Yes, it's possible to connect the yard and boom by lashing both to the tack grommet on the sail - as long as (1) it's a good grommet - which probably means at least a #2 spur grommet, not some sort of hardware store grommet and (2) as long as the sail has good corner reinforcement patches to keep the grommet from pulling out. This probably means a minimum of around four layers of fabric (sail panel plus 3 reinforcing layers) in that corner.

I'm not sure I understand the concept you mentioned of bolting the jaw to the mast, as they are generally attached to the boom, not the mast. In any case, often the best way to attach a jaw to a spar is to cut a shallow groove or trench in the spar (maybe 3/16"-1/4" deep) glue the jaw into the trench and then reinforce it with a couple fasteners (screws, bolts, rivets, etc.). The tight fitting slot and glue just help keep the jaw from twisting or wiggling around in use. There are, however, a lot of variations and other ways to do it.

 

Todd
this is a lateen rig, the sail corners are not reinforced so i will do something else i have your book to look at other options.
The wood jaw will be going on the boom i like your idea to mill slot on boom.how do i locate the jaws position on boom?
Thanks dave

 

There is a tremendous amount of variation from one lateen rig to the next in terms of both masthead height and just how much of the sail is sticking out in front of the mast. These factors will affect the jaw placement on the boom. In general, once the halyard is tied to the yard, you want to place the jaw or gooseneck in a spot that will yield a boom that is a bit higher at its aft end than it is at its forward end (typically maybe 6"-12" higher, but this also varies). The system seems to tolerate variation pretty well and as far as I know, there isn't one specific boom angle or mast height/placement that works hands-down better than all the others.

I've even done a few sails for customers where the jaw position was adjustable, like the one on the Baileys Harbor flyer, which can be run normal, reefed or cranked up aft and used with a jib - all with different gooseneck/jaw positions.

 

I will put it together and try it out. Still not sure how i want to attach the spars. I have seen where some have drilled 3/8" hole threw spars passing 3/16" line threw to lash these parts together. Will this work?

 

It will probably work fine, despite the fact that it seems rather low-tech. There isn't an awful lot of strain on that connection.