In addition to stainless steel, what other materials make suitable backing plates for winches, cleats; etc.? Ideally, something like G10 or material that does not decay in salt water and which can be worked with typical home shop tools can replace SS. My boat has had significant water intrusion and some of the backing plates were aluminum; they fell apart at my touch! With luck and work, the water intrusion will be gone.
Dear Chris
Thank you for the information
Would suggest that falling apart at the touch is not typical behavior for sea water reistant aluminum. Considering the extreme stringer modifications it comes to mind that aircraft grade magnesium alloy may have been used for the backing plates. The original owners were aircraft pilots, keen racers, and knew that magnesium is lighter, and where to get it. This material corrodes badly in a marine environment.
G10 would be a good alternative, is corrosion free, and the recommendation is to increase the thickness 1.6 times compared to aluminum or 2.5 times compared to steel for equal bending stiffness.
Kind regards
Lars
I was unaware of the difference among the various grades of aluminum. G10 was a suggestion on my part; if you were to choose the correct aluminum or G10, would you have a preference? As you know, working with aluminum is also easy so I am indifferent. I wonder about the cost.
Dear Chris
Would recommend G10, as it can be easily glued to the deck, and the screw threads do not freeze by corrosion. Aluminum offers the opposite.
Suggest you compare cost, I do not have information.
Kind regards
Lars
Thank you for your reply; I was away or I would have written sooner.
Your comment about aluminum has me worried since I am having a new quadrant and sheaves fabricated at two machine shops and they may not be aware of the proper type of aluminum to use. Can you specify the appropriate aluminum so I can pass this information along?
Dear Chris
The sea water resistant grades are in the 5000 and 6000 series.
Most plate and sheet is made from the alloys 5083, 5086, or 5454.
Most extrusions made from the alloys 6063 or 6061.
Kind regards
Lars
The aluminum of choice for one shop, and I believe the other too but need to confirm, is 6061. He also mentioned 5052. I see that 6061 is on your list so I'll go with that unless you advise differently.
I recommend you take the Professor's advice over mine, but just to give you some confirmation, all of the aluminum
fabrication we have done on Hatha has been 6061.
This includes new toe rails, mast collar, turning blocks cheeks, and their pads.
I learned the hard way that for anything you want to clear anodize after welding, your welder must know to use the correct rod, otherwise your welds can turn black. I checked my notes and have written down #4043 or 4047 rod for the 6061 aluminum, but don't take my word for it, you would be wise to confirm. Perhaps the Professor can explain.
Imagine getting my new toe rails back from anodizing, after all the hard work to get to that point, and having black welds at the spinnaker block tabs! We ground them out and re welded, stripped and re anodized, paid twice, and all is fine now. Not the first time we've done something twice on the project!
Dear Tony
The welding rods you mention are formulated for 6061 giving smooth welds by the addition of silicon, but it is the high silicon content that makes the weld turn black after anodizing.
The recommended welding rod for clear anodizing is 5356.
Kind regards
Lars
I forgot to mention that in addition to the quadrant and sheaves I am also having a new gooseneck fabricated. Seems like the 6061 would be a good choice for that. Do you agree?
Dear Chris
There are also other aspects than corrosion resistance.
The gooseneck will probably be welded together, and the effect of this must be considered.
6061 is not suitable for high loads when welded, much of its strength is lost unless properly heat treated afterwards, has the shop experience of this?
5083 would be the recommendation for this application, as it retains most of the strength when welded.
Kind regards
Lars
Thank you. I have passed along this information to the machine shop. I have seen his work and it appears to be exceptional; I need to ask about the technique. If the quadrant for the trim tab were to break, I would be okay. The gooseneck is a different story. I had that happen during a race - very dangerous.
