Yes, that's right....
I'm looking for your Aluminum Galvanic Corrosion Remedies.
The cat is a 2010 Goodall C2 F18 that was previously based on the Chesapeake.
Upon close inspection, especially of the fore cross beam, there is galvanic corrosion pitting around the perimeter of the larger stainless steel parts, such as the beam/hull M10 bolts, Dolphin Striker flat-bar, mast step reinforcement plate, and the spi-pole attachment plate. The smaller-mass, riveted line and block attachment SS eyes don't seem to have any visible signs of corrosion.
It appears that everything was bedded with Duralac (the older formulation) and the larger bits have possibly some insulating thin material (tape?).
I don't know if it would be worth it to drill-out all the rivets on the bigger SS fittings, prep the Aluminum with a chromate conversion coating such as Alodine, then reinstall with the newer 'green' Duralac, insulating pad, and new 316 SS rivets. The 316 rivets are at least 4x as dear as 18-8 (304) SS rivets, and so far I've found that only McMaster-Carr carries the smaller quantities that I could purchase in 316 SS.
Another little problem...
The very end of the starboard side front beam has two rivets on top that attach a vertical aluminum web that the lateral-most hull bolt also clamps to from the bottom of the beam. One of those rivets (about 3/4" from the end of the beam) created a slight, transverse crack in the top of the beam that is roughly 1.5" long. Beam aluminum thickness is 0.090". I'm currently thinking about TIG welding it with R5356 filler rod. I've done some practice on 6061-T6 pipe that is only 0.060" thick by grinding a very narrow slot, much like I would have to with the crack, and start the welding from the end furthest from the beam end, and progress to the beam-end. The result on my first practice attempt was very good, especially considering that the pipe material is much thinner and of far less thermal mass. I'd likely grind/sand/polish the weld to match the exterior and interior surfaces, and then chromate the affected areas. The practice repair after polishing looks like nothing ever was done to the pipe. However, the HAZ (heat affected zone) likely has weakened the base material where the rivets would be replaced. Anybody familiar and experienced with welding these cat beams?
The beam/hull bolt threads were full of galvanic-generated powder, so I'm guessing someone who assembled the boat didn't lube the bolts very well with anti-seize. After cleaning and blowing-dry, the aluminum threads of the hull plates don't look fresh -- a slight wiggling of the bolts fitted dry and not quite bottomed-out with about 24mm (rear beam) and 28mm (front beam) of maximum screw-in depth. I'm thinking of installing some 30mm deep Helicoil inserts and longer bolts along with some proper anti-seize goop.
So, anybody have any suggestions and/or comments?
Thanks!
There’s a better place to get rivets that I found-Maybe Hanson rivet supply?.. I’ve not heard of anyone welding masts nor crossbeams, though suspect it’s been done. It would certainly ruin the temper in that area, but might still be strong enough. From what I see what you’re planning to do it’s more than most would do.
Hence the problem with the molded aluminum plate. I had similar problems with the 18-2 where a few of the bolts stripped out. I used a Timesert insert to "repair/rebuild" the threads. I had used a corrosion inhibitor on the bolts but when I went to remove them a few weeks ago, they did not budge. I haven't had the beam off in 8+/- years in a heavy saltwater environment. I may dig in this winter and get them out. The downside is I'm going to destroy something getting them out. I think the better long-term solution is to install an inspection port and thru-bolt them.
I don’t see much in those photos that would be cause for concern. Put it back together using Tefgel or whatever your favorite corrosion-inhibiting paste happens to be.
The best thing you can do, IMO, is to rinse the boat off with fresh water whenever possible during the season. And in the off-season, if possible, dissassemble the crossbars from the hulls and store them indoors in a dry location. Galvanic corrosion will be halted anytime the aluminum parts are dry.
sm
I agree with @dogboy
If you have reason to take a fitting off, you can sandwich in a layer of plastic between the steel and aluminum, even clear packing tape.
That is how the mast fittings were protected on the Hobie 18.
@dogboy I try to rinse mine every time but at the beach, I use Salt be gone when fresh water isn't available.
Thanks for all the good replies.
Hence the problem with the molded aluminum plate. I had similar problems with the 18-2 where a few of the bolts stripped out. I used a Timesert insert to "repair/rebuild" the threads. I had used a corrosion inhibitor on the bolts but when I went to remove them a few weeks ago, they did not budge. I haven't had the beam off in 8+/- years in a heavy saltwater environment. I may dig in this winter and get them out. The downside is I'm going to destroy something getting them out. I think the better long-term solution is to install an inspection port and thru-bolt them.
Yes Texastuma, I saw your vid on your time-sert installation while perusing your YT channel after seeing your description of your installation in another thread. Thanks!
Did you use steel or SS time-serts?
What kind of corrosion inhibitor did you use on the bolt threads?
My bolts came undone very easily, surprisingly, though with some aluminum oxide powder on the bolt threads.
I have no idea how the aluminum hull plates are situated.... the bolt holes are blind and roughly 32mm deep. If I was the engineer designing the C2 hull structure, I'd position the aluminum plates in a transverse (vertical) plane below each beam, affixed to composite bulkheads, with the bolt holes drilled into the edge of the plates, the plates being thick enough to allow for enough material around the bolt. With some soundings along the hull sides, it appears that the bulkheads may be something like that described. I could drill some small-diameter (1/16") exploratory holes on either side of the bolt holes through the beam pads to get a better idea of the plate geometry. I should fish a go-pro camera through the hulls to get a better idea of their construction details.
I don’t see much in those photos that would be cause for concern. Put it back together using Tefgel or whatever your favorite corrosion-inhibiting paste happens to be.
The best thing you can do, IMO, is to rinse the boat off with fresh water whenever possible during the season. And in the off-season, if possible, dissassemble the crossbars from the hulls and store them indoors in a dry location. Galvanic corrosion will be halted anytime the aluminum parts are dry.
sm
Right!
The worst corrosion is on the bottom side of each beam at the outer-most bolt holes, where moisture can accumulate and remain wet.
The mast and beam hardware was isolated with plastic film and bedded with what appears like the older Duralac formulation.That has kept the corrosion on the beam aluminum extrusion to only the perimeter of the larger SS hardware. The mast was replaced at some point due to a lightning strike, and there is no observable corrosion on any parts of the stick.
I agree with @dogboy
If you have reason to take a fitting off, you can sandwich in a layer of plastic between the steel and aluminum, even clear packing tape.
That is how the mast fittings were protected on the Hobie 18.
Yes!
Initially I was thinking of using Anodine chromate conversion on the beam at the hull pads to help protect the aluminum from further corrosion where moisture is constant. I have also been toying with the idea of having the beams re-anodized. There's supposedly Charlotte Spars in Charlotte that re-anodizes masts. They're two hours away from me, but Sparcraft (Wichard) bought them out a few years ago, so they may not be in business now. Perhaps overkill.
Thanks for the comments and suggestions.
I just called Wichard/Sparcraft in Charlotte,NC.
Nope. They no longer do anodizing. They farm it out. But my contact, Kurt, indicated that he'd find someplace close that could do it. Good guys there.
At least that might be one possible option. We'll see.