Mirage 33\35 Stemhead replacement FIX - SailNet Community
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Mirage 33\35 Stemhead replacement FIX

Hey everyone,

I thought I'd post some notes on the stemhead fix I just did to my new (to me) 1982 Mirage 33 Firefly. The Mirage 33\35 are solid boats, with one weakness- a cast aluminum stemhead. I found anecdotal evidence online about people having them fail suddenly and losing the whole rig. I never saw pictures but heard about "friends of friends" type scenarios. There was one account I found on an old message board from very long ago with a first hand mention from a guy about losing his rig to the failure. But not real follow up or "how to" fix it.

Essentially what happens is this... The stemhead is made of cast aluminum, and the eye where the headstay pin goes through eventually loses the battle against the stainless steel clevis pin. Over time it ovals out and eventually blows out. Because nothing is attached to the deck anymore there is nothing but the babystay to hold your mast up and that most likely wouldn't cut it. I've attached pictures below of my old stemhead and you can clearly see some cracking and ovalling (red arrows). What the pictures didn't pick up was that the metal at the "top" of the hole was also mushroomed out a bit. I am VERY glad I changed mine out...

I dug around online looking for SS fabricators to see if anyone had blueprints or something to go by to make me a new one. By dumb luck I was on a website from a company (I have no vested interest in) called Stainless Steel Outfitters in Barrie Ontario Canada. While I was filling out the "ask us a question" form I noticed my exact stemhead scroll by with a stainless one right beside it on the banner! After talking with one of the staff there (John) he confirmed he has a Mirage 35 and is aware of the stem issues.

They would normally have you send in your old stemhead and would copy it exactly. I however didn't want to spend the 2k it would cost to hire a crane to pluck my mast, not to mention wasting time with how depressingly short sailing season is up here in on the great lakes. So John agreed he can make the new stemhead and send it to me, I would just need to drill the holes myself since the hole patterns varied over different production runs. He matched the anchor roller up to the 25lbs mantus I purchase so it would fit perfectly.

Once it arrived it was time to get it installed, with only 1 day free to work on my boat the pressure was on.

Tools you need:
-drill press, it could be done with a hand drill, but I wouldn't recommend it
-titanium nitride coated drill bits, I used the "cheap" Canadian Tire ones and only burnt one down
-cutting fluid, can be bought anywhere, it's used to keep the drill bit and surface cool so it doesn't work harden
-new hardware most likely, all mine was corroded from dissimilar metal corrosion (SS against aluminum). I used 1\4" SS machine screws, locknuts, and washers, 15 total. Countersunk ones for the cleats.
-white out, yes the liquid kind in a bottle
-butyl tape or 4200, whichever you prefer for sealing


1) Run the spinnaker halyard and jib halyard forward to the toe rail, one per side, and winch them tight.

2) Begin loosening the standing rig to take the pressure off the headstay pin. As you loosen the rig do it a bit at each turnbuckle so the load is removed evenly, once you make it around all the turnbuckles sinch up any slack in the halyards to keep the mast supported.

3) Once the pressure is off the headstay remove the clevis pin and, using some line, lash the furler to the pulpit, if you don't have a furler it's easy just move the wire.

4) Remove all 15 bolts that hold the stemhead down (the amount may vary per boat). Mine needed a 12mm, and 13mm socket, 4 of the bow cleat bolts will be inside the chain locker, it's tight but even this gorilla fit in enough to get to them.

5) I had to tap most of the bolts up out of the stemhead by knocking them from underneath with a hammer.

6) Pop up the stemhead and it should come off ok. The original '82 butyl underneath was still gooey and sticky, great stuff!

7) Clean the surface as best you can with thinner.

8) Place the new stemhead onto the bow, clamp it in place however you like, and starting at the base pick a side and using the white out brush go up through the hole on the underside of the bow flange and paint the bottom of the stemhead plate. Carefully lift it after waiting a few seconds for it to dry and you should have a nice round white spot where you will drill the first hole.

9) Punch the middle of the hole, or steadily drill a starting spot centered up. I initially used 1\8th bits to start but bent one, I found the 5\32 was the best size to start on then finished the hole to 1\4" without issue. Use your cutting oil, and enough pressure so you don't force the bit but that it is still cutting. I set my press to 960-1000rpm and had zero issues.

10) Bring the stem back to the boat and put it on the bow, put the bolt through the hole you drilled and make sure everything looks good. With that bolt in place (but not bolted) mark your opposite hole with white out.

11) Drill that second hole and then refit the stemhead with both bolts in. They should act as a decent guide to keep it centered up. Now you can mark more than one, or all of them if you trust your skill, and drill the rest.

12) Clean up the plate with some degreaser (brake cleaner or similar) to remove the cutting oil and shavings. Fit it again and be sure all bolts fit. If any donít fit, but are very close, you can oversize\redrill the hole in the firberglass lip slightly. Donít remove too much, use your judgement here. The lip is solid glass (almost an inch or more) so thereís no core to expose.

13) In my case we went with machine screws of the same size\strength so we could screw them in for a tight fit and then put the nuts\washers on the bottom. The old carriage bolts were corroded, and would need to be tightly pulled into the SS to fit the square portion and I didnít want to crush any firberglass trying that.

14) Once youíre good to go put butyl or 4200 down around and on all the holes, and some on the plate bottom if you want. The lip ones, as I mentioned, have no core so they are fine either way, but the 4 inside holes on the bow cleats all pass through the deck and should be sealed nicely to prevent core issues. Donít forget to seal under the plate, then between the plate and the cleats, and then the screws and the cleats, yep 3 layers of sealant per cleat attachment.

15) Tighten everything down evenly and re-attach the headstay. Re-tension the rig but donít forget to let off on the halyards as you go since they are still carrying pressure.

Some youtube videos, nothing fancy

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Re: Mirage 33\35 Stemhead replacement FIX

Pictures didn't attach first time, trying again...
Attached Thumbnails
20180719_111646.jpg   20180719_111600.jpg   20180719_120901.jpg   20180719_134535.jpg   20180719_204838.jpg  

Some youtube videos, nothing fancy

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Last edited by Guyfromthenorth; 07-21-2018 at 03:54 PM.
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