Pulled out my 95 17' Alumacraft from storage recently and found several small pinholes in the bottom of hull. They had white powder circles about the size of a quarter around each one. Scaping the powder away revealed a small pin hole I could push the tip of my pocket knife through. Called a boat repair shop and he said he has seen that before with that brand. He found it was caused by small bits of metal left over from the manufacturer process that were laying on the hull and were dissimilar metal and caused corrosion... Possibly rivet pins.....WTF! Got to be kidding me! Anyone else heard of this, does it seem plausible? I used JB Weld to repair them for this summer, will pull the floor this winter and make permanent repairs. Glad I bought it cheap and rest is in great condition or it wouldn't be worth the effort.......
Pinholes in aluminum hull
White powder is aluminum rust, just like reddish powder is iron rust.
Galvanic corrosion (aka electrolysis) is a likely culprit, as mentioned. The cause is up for further investigation on your part. Corrosion spots in the middle of the hull that not near a joint or rivet would make me suspicious.
The corrosion can occur from either dissimilar metals, or from stray voltage, or a combination of the two (combo would be a worst-case scenario in that stray voltage accelerates galvanic corrosion that occurs from dissimilar metals).
Could be extraordinarily difficult to diagnose your cause...unless you have an easily found bare wire, supplying voltage to the general area (that normally should blow a fuse, but for some reason does not). Good luck.
I seriously doubt that is your issue after 22 years. I would be more willing to believe you have a chaffed or loose wire in your boat that is causing the issue. How are the anodes on the motor?
This is extremely possible. Galvanic corrosion (what you are seeing) is on every engineers mind when designing anything. The further apart two materials on the corrosion chart the faster the corrosion will happen. Very important to "isolate" different materials when assembling anything. Nylon/rubber washers when running steel bolts thru aluminum. Paint is a suitable barrier but tends to wear away after time.
Any dissimilar metals coming in contact with each other will cause an electralsis reaction that can cause this problem. One of the most common culprits is green treated lumber in an aluminum boat, green treated lumber is treated with copper and can actually melt holes in the aluminum.