I figured I'd share my recent experience with replacing the mast step on my H18. This post kind of a follow up to this thread..http://www.hobiecat.com/forums/viewtopic.php?f=13&t=42206
This weekend I planned on re-riveting my mast step. I had re-riveted it at the beginning of last season, but it loosened up again over the year (it had a considerable amount of fore & aft wiggle). When I removed the step, I found that the front crossbar had developed a crack between the dolphin striker post hole and one of the rivet holes. This old crossbar had been converted from a two rivet mast step to a four rivet step by a previous owner. It had some extra rivet holes drilled during the conversion. Also, some of the rivet holes as well as the top dolphin striker post hole were elongated.
Since I had acquired a spare crossbar last year, this wasn't a major catastrophe, but still a bit of a bummer and more work than I had planned on doing. My spare crossbar also had the old-style two rivet mast step installed. I drilled out and removed the rivets so I could install my four rivet step. Aside from being faded, the spare crossbar is in much better shape and doesn't look like it's seen much use.
I decided to try bedding the mast step to the crossbar using Marine Tex. With the mast step just sitting on the crossbar, there is about a 1/16" gap between the step casting and the crossbar extrusion. My hope is that by bedding the crossbar, this will both reduce the amount of wobble that can occur and also reduce the chance for point loading. Hopefully this will keep the rivets from loosening and prevent crossbar cracking (I have now had three front crossbars crack at the mast step over the years).
It's important to note that the aft rivet hole in the four rivet mast step is not in the same location as the aft hole in the two rivet step - it's 1/4" farther back. This presents a bit of a problem because if you just drill a new hole in the crossbar (as the previous owner of my old crossbar did), the new hole will be very close to the existing hole and the crossbar is likely to crack through. I decided to instead drill a new hole in the mast step so that it would align with the existing hole in the crossbar (the fewer holes in the crossbar, the better IMO). This isn't hard to do as long as you measure carefully and use a center punch so your drill doesn't wander.
I decided to use aluminum rivet washers inside the crossbar on the back side of the rivets. The washers should help to spread the load at the crossbar holes and also provide a buffer to minimize direct contact of the stainless rivet with the aluminum crossbar.
Figuring out how to hold the aluminum washers inside the crossbar took a little thought, but wasn't too difficult. I placed a small dab of 5 minute epoxy on the washer and then used a bent piece of clothes hanger wire to insert the washer through the bottom dolphin striker post hole and press the washer against the desired rivet hole. Once the washers were in place, I flipped the crossbar over, double checked their locations, and let the epoxy cure. Once the epoxy fully cured, I placed the mast step on the crossbar and verified that the rivets could be installed (and ran my 3/16" drill through the holes which were a little tight).
Before applying Marine Tex to the crossbar, I marked and masked off the mast step contact area on the front crossbar in order to keep things clean. I then waxed the front crossbar. The wax will act as a release agent for the M-Tex in the event that I ever need to remove the mast step in the future.
I mixed up the M-Tex and applied a thin coating to both the crossbar and the mast step casting. I used grey M-Tex because it supposedly has higher compressive strength than the white.
I placed the mast step onto the crossbar, inserted all four rivets, and pulled each rivet about half way to seat the mast step and squish out excess M-tex. Then I pulled off the masking tape and cleaned up any smears. Last, I gave the rivets their final pull until they popped and let the M-tex cure.
Right now the M-tex is cured rock hard and the step seems good and solid. Only time will tell if it stays that way. The next step is to re-install the dolphin striker bar. Then I have to remove the broken crossbar and install this one.