Hi Sigma 33 enthusiasts, I considering to buy a Sigma 33. During the first look it turned out, that the keel bolts have been changed about 6 years ago, but not the two most forward once. Therefore I would like to place a question about changing these particular keel bolts (blow the head compartment). Has somebody a rough idea about the effort to change the forward two keel bolts? These two bolts in the head area are looking quite rusty.
Greetings Amalphi.
Wow, Simon this is a „how to“ tutorial, many thanks for your very professional description.
Greetings Andreas
Hello Simon, thanks a lot for sharing your experience with me/us. Your detailed description gives me more confidence in that task.
Really appreciated.
Andreas
I am in the process of changing mine. I have completed the easy ones x 12 and pulled one from under the heads floor pan. I have uploaded a series of short videos showing the method https://youtube.com/shorts/B4rwsbv5c4A?si=vMpoluQRyBq7lnd_. I managed to get 3 out by hand but then got stuck. I ran out of purchase, even with a 750mm breaker bar - I couldn’t brace myself sufficiently to move the nut. The game changer was using a 3/4” impact wrench with a nominal rating of 700nm.
I made the access bigger in the heads floor using a 64mm hole saw. I didn’t want to cut a big section out of the floor pan as others have. The floor pan itself is bonded to the hull by resin under all the furniture in the heads!! The holes will be covered with 70mm internal pipe caps in white plastic.
The access was sufficient, although still awkward. I could then chip and clean the nut up with a dremel grind stone. I was fortunate in that there was enough of the nut left to be able to get an impact socket on. Although it did take 3-4 minutes of the impact wrench to get it out!! I would never have got it out by hand.
What prompted me changing them was the state of my nuts!! The original plan was to clean them back to bright metal and re-paint. However, once cleaned up I had a selection of what appeared to be 32mm AF to 34AF. The ISO standard for M24 stud is 36AF, a big difference. At 32AF that would indicate an M22 stud. Having got the first nut off it was M24 x 3.0, but the nut appeared to be an ‘axle’ or wheel nut with a flange at the bottom clamping face. In addition, there was quite a lot of thinning of the washers - hence changing the lot. There wasn’t any issue with the studs below the nut.
A previous owner had replaced 2 studs with stainless steel and I wanted to check what was going on below the nut - all good, no problems.
Be aware that the front 2 under the heads floor are drilled right through the keel flange and will therefore need sealing and fairing once done. The others are drilled and tapped into blind holes.
I replaced them all with A4/316 stainless steel studs, nuts and washers all torqued up to 210nm. The washers were slightly larger at 80mmx6mm instead of the original 2 1/2” x 1/8” ~ 63x3mm.
Hope this helps.
Simon
Interesting! I need to get started on the exact same project on my 1985 Sigma 36. Same set up, the forward keel bolt on the starboard side is under the shower pan.
Does anyone know the size and thread type of the bolts? The diameter seems to be 1 inch. But I'm in the US and always a little bit at a loss when it comes to British fastener sizes, so any leads are really appreciated.
Many thanks.
Hans
Hi Amalphi, I had all my keel bolts replaced earlier this year. The yard accessed the forward pair in the heads compartment by enlarging the inspection holes to enable sufficient space for their tools to get a purchase on the keel bolt nuts. You or your yard would probably need to remove the flaking rust with a wire brush and possibly, depending on the condition of the nut, weld a new nut to it which will then allow the bolt to be unscrewed. I glued a couple of white plastic discs over the enlarged inspection holes. The ‘33’ is a fantastic boat which has given me 40 years of unadulterated pleasure!! Hope you decide to go through with the purchase….Good luck ….Jeff (Workout GBR 4476)