I have made a short video which matches the description below and can be found at https://youtube.com/shorts/Kate8fJYANk?si=DEW4_bJyX6uq8SQ1. Hopefully pictures and video adds a bit more. I have not seen nor heard about any broken bolts. All the pictures I have seen, from people who have removed a bolt, has shown that they are good below the nut and washer; This good condition evidences the original high quality construction. My view is that the life limiting factor is not the state of the threads, but the state of the nuts and washers - all reliant on the condition of my bilge over many years!

Many thanks. As you point out, all the studs were fine below the nuts and washers - which gave me a lot of confidence about the original design. However, it was the state of the the nuts and washers that prompted me to change them. Firstly, the nuts: They seemed to be a mix of 32 to 34 AF against an ISO specification of 36AF for an M24 stud. In addition one of the studs had no threads emerging above the nuts. Once I got a nut off they appeared to be be very thin against a new nut - I was concerned that they had corroded away and therefore under specification. The nuts also appeared to have the remains of a flange that had corroded away. - similar to an ‘axle’ nut. The worst ones were under the heads floor. In my view, I was able to remove them with a socket before they had gone too far & I rounded the nut off. If that had happened, I would have had to cut a section out of the heads floor to slit the nuts and extract the stud. With the nut and stud combination out I was concerned about the gap between the stud and the nut, potentially indicating the threads had started to corrode see video https://youtube.com/shorts/B4rwsbv5c4A?si=tYPFRrscNaU-ENlw For the washers, in chipping the paint away, quite a bit of material flaked off. Having got the first one out, the washer had thinned towards the edge. It is the washer that transfers the loads of the keel to the hull hence there are 16 of them and oversized. I replaced them with slightly large ones in 316 stainless steel. Overall, it was the condition of the nuts and washers that I continued to find which prompted me to change them. My boat is a 1986 model - so probably about right after ~39 years! Of course, each boat will be different, depending on how well they have been looked after……

By way of update, I have now removed the panel under the port saloon settee at the forward end - the one that runs over the center line of 2 keel bolts. There is a short video at https://youtube.com/shorts/80nam4RXosA?si=R-p-ILvVdGs1gEfV. The panel is secured by screws from the inside and pins from the outside, but doesn’t appear to be glued. The screws, being brass were a struggle to get out having been there for 38 years! All 16 keel bolts now replaced! I’ll adjust the panel to fit the taller bolts and make it easier to remove in the future. Just the bilge to clean and repaint.

Hi Andreas, Many thanks & happy to share! Hopefully will help you get through my learning curve a bit faster along with gathering all the tools and materials! A few other tips: The impact wrench set up is at https://youtu.be/8GvdGMLWatQ?si=5XqIV0HritUdyNF6. Don’t use the impact wrench to tighten the nuts though, the torque that it can apply would probably crush the GRP hull, hence the 210nm by hand with a torque wrench. I used plenty of sikaflex to seal the stud in the hull thickness of the hole and under the washer. I also used a nickel grease to avoid the nut galling on either the stud or the washer. When removing one of the old studs by hand, I found that the nut came off leaving the stud behind. It was easier to dig out the old sealant around the stud with a small screw driver, and then put 2 x M24 half nuts on, locked together ( I used 2x36mmAF combination ring spanners) to turn the stud out. I was surprised at how much friction the sealant gave in fighting against the stud coming out! Once out and cleaned up I could turn it back in by hand. I did need to clean the threads on the stud though first with an M24x3.0 die nut - which takes a 52mm box spanner. An alternative method of removing the studs, particularly if the threads are bad at the top or under the nut is to use a roller cam type stud extractor. The only draw back is the clamping action does damage the threads - acceptable if they are being changed out. If the nuts were too far gone to take an impact socket, my plan was to slit the nut with the dremel and use the stud extractor. For one of the stud holes I had to use an M24x3.0 tap to help clear the threads. I made the new studs (16 of) slightly longer at 105mm to take a lock nut in future to turn it out - avoiding the stud extractor. The originals were only 3 1/4” ~83mm. The studs were made from M24 threaded bar in 316 stainless steel, which came in 1 meter lengths and cut down with an angle grinder using a metal/stainless slitting disc. With 2m of bar I made 18 studs with 2 spares! The ends had a chamfer applied with a de-burring/chamfer tool which fitted my cordless drill, although there was some final de-burring with a needle file to take the last of the sharp edges off. The only item I bought and didn’t use was a 36mm slogging spanner. Firstly, because it was too big for my original nuts and secondly, I couldn’t see how I could hit it with the lump hammer in the confines between the two hull ribs!! Rgds Simon

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