I want to raise my boom where it connects to the mast so the boom clears the bimini. The main sail can be hoisted up the mast a further 6" before it meets the mast top main hoisting block. I plan to go up 4".
There is a plate that connects to the mast at the boom connection. It is attached with 4 pop rivets. I plan to drill it out and re connect it 4" up with another set of 4 holes.
Boom needs to be approx 4" higher to clear bimini.
Photo of plate I plan to drill out and reconnect 4" higher up the mast.
Any one else had this done. Problems. Comments please.
I haven't raised my boom, but I can't see any mechanical or "engineering" reason your method wouldn't work. The only thing I could imagine is that you might have to reef a 'skosh sooner - and you should be reefing sooner anyways, in a Mac.
There is one "problem" I have encountered, that you might face with a higher boom - the halliard splice tail jamming into the masthead block. This became an issue with my new KH C2000 main, which was a little taller than the old original Doyle main. I couldn't haul my sail up taut, and it got these lubberly "scallops" between the sail-slugs.
My solution was simple and old-fashioned; in fact, it harks back to the days before metal shackles on halliards. I cut off the long-tailed splice and tied a double bowline directly into the headboard.
Explanation: A regular bowline starts with one bight in the standing part of the line; for a "double" bowline, you start with two bights. This is more trouble and harder to untie, but it's very secure and it's significantly stronger. A regular bowline will hold up to about 55% of the breaking strength of the rope, but a double bowline is good to 75% - nearly as strong as that long-tailed eye splice. If you're concerned about its security, you can tie the bowline around your old headboard shackle, then use some sail thread to stitch down the running end to the bowline loop - that won't come loose on you!
PS: The proper name of that plate is the "gooseneck connector." You will need 3/16" stainless-steel rivets to reinstall it. For all and sundry, those rivets may work loose over time - they have on Bossa Nova. It's not hard to drill them out one by one and re-rivet the connector; it would be a lot harder to rig something to do its job, if it broke while you were doing some hard sailing.
If you want to avoid the trouble of raising the boom, I'm pretty sure you could adjust the straps of the bimini so that the forward edge fits below the boom.
Seems like it would work OK. I'd recommend going to Bluewater and ordering a new gooseneck mast assembly to mount higher, leaving the original in place just in case things didn't work as well as you'd like. Looks like part number 3408-1V0, which is under $17.
Do you have a Topping Lift ? It should have 2 hooks one for sailing without the biminy up and one about 5" up to miss the biminy. Our boat sails OK with the shorter topping lift but I figure were not sailing in much breeze if the biminy in open and a baggier sail in light air is perfered.
I just drilled out the loose & floppy stainless-steel rivets that secured my gooseneck, and replaced them with new 3/16" stainless-steel rivets from Fastenal. It is a bear to get those SS rivets to pop!!!
Don't even consider this with a Home Depot grade rivet-tool. I bought a "heavy-duty" rivet puller for the job, and it took about 20 minutes wrestling per rivet - I finally scored and weakened the inner shaft of the last one I set, and that one "snapped" after five minutes of hard work.
Annapolis Performance Sailing has a tool in their catalog that's supposed to be able to pull 3/16" SS rivets, for about $45 - wish I'd gotten one of those, but the job's done now.
If I were to do it all over again, I'd probably take the boat to a rigger who has a REAL heavy-duty rivet puller.
...................clearance on the bimini. The bad news was that the rivets drilled out so easy that I thought they were aluminum and replaced them with aluminum ones. They ......................
............failed out on Priest Lake in Utah. I had to jury rig a fix out there (picture above). It held, but I improved on the repair before we went back out on Lake Powell. The repair has worked, but I'll probably put in stainless ones before we go back out.
I have replaced the rivets for the goosneck fitting for the fourth time now. They just get loose on me every year. I've vinally had it; so I doubled the number of holes and went from the 3/16" rivet to #14 screws (8 total.) Hopefully, I won't have to replace again. I raised the fitting about one inch. I had no issues with the bimini but would occasionally graze the dodger. My sail goes almost to the very top, so to save some space up there, I used a short shackle and a fisherman's bend knot vs bowline, which is supposedly stronger, but more importantly, takes up less space.
Rick,
I didn't know that a single bowline is only good for 55% of the rope's breaking load. Once, I snapped a 5/16" line (nearly 3000 lb breaking load) but the bowline was intact. Another time I broke a SS shackle off the spinnaker halyard. The metal sheared while my bowline was intact. Turned out I used the wrong shackle (non-swiveling) which caused the failure. A few mechanical items failed on me in the past, but never a bowline knot. Just seems like those things are bullet-proof.
You probably did better using SS screws than I did using rivets. (Hearing your story left me wondering if you might have used aluminum rivets; but eight #14 screws will out-hold four rivets, regardless.)
Maybe I'll get that $45 rivet-puller, and "be prepared" to replace them again. I'm sure I'll find other uses for a heavy-duty rivet-puller.
The bowline is indeed "bulletproof," but it can still come loose - especially if it's flogging, as with a jib sheet. The extra round turn of the standing part makes the knot a lot more secure, with the price of it being harder to tie and untie. I'm not sure how the source I read came up with a "55% of rope strength" figure, either, but the double bowline gives up very little strength to a "proper" eye splice - plus, it won't jam in a block. It simply won't even pretend to try to go through.
Seems that SS screws are the prefered solution for reattaching the boom gooseneck fitting to the mast. Reason being, easy to fit compared to SS rivets & perhaps longer lasting (time yet to confirm).
Another thought to raise the boom height... Maybe the goosneck fitting on the aft of the boom could be turned upside down to gain 1" or so height of the boom to clear the bimini.
(Hearing your story left me wondering if you might have used aluminum rivets
Never aluminum. Always 3/16" SS rivets. I don't have a rivet puller so I had to drill them out every time... Major PITA Installing the new ones isn't too hard with a Home Depot rivet gun. It does take a good amount of physical effort but doable for most. So far, I can say that rivets will come loose over time. Never had one fail on me completely though. I think screws (maybe a size or two larger) would be a better solution than rivets. If my 8 #14s don't hold up, I may have bigger problems
I would have had two extensions welded onto the V on the mast goose neck brkt so as it would extend out to the midsection of the mast like the mast hounds then drill a 3/8" hole through the mast in the center possition & install a 3/8 "x 4"SS bolt
for the same reason 
Installing the new ones isn't too hard with a Home Depot rivet gun. It does take a good amount of physical effort but doable for most. So far, I can say that rivets will come loose over time. Never had one fail on me completely though. I think screws (maybe a size or two larger) would be a better solution than rivets. If my 8 #14s don't hold up, I may have bigger problems 
