Re: leaky rivot
Crazy,<br /><br />Without wanting to start a war, I beg to differ. <br /><br />Galvanic action takes place when two dissimilar metals are in proximity to each other while in the presence of an electrolyte. And here’s where many people get confused. THEY DON’T HAVE TO BE IN PHYSICAL CONTACT. In this case, the dissimilar metals are a stainless steel bolt and an aluminum hull. The thing that links them together is the electrolyte – the water they sit in. When they are in physical contact the corrosion is often more evident because it occurs mostly at the point of contact – ie. on the aluminum around the head of the bolt - which is no doubt why you advised, correctly, that the bolt and hull be isolated from each other.<br /><br />Fortunately the stainless bolt is small, and the aluminum hull is big by comparison, and also – hopefully – Karma has an anode fixed to his outboard leg. The size difference between the two metals, and the anode itself, will minimise corrosion, but will not stop it happening. Maybe you kept your anodes in good shape which is why you didn’t see any corrosion when you had your aluminum craft. <br /><br />Electrical current flows all the time a boat is in the water, and any two dissimilar metals are affected, with the least noble (see tables of noble metals, giving a run-down of corrosion susceptibilities) being ‘sacrificed’. That is why I said that any accessories, like swim ladders, can add to the potential corrosion in your expensive outboard leg even if there is no physical contact. Current flows from the leg to the swim ladder, and even if the swim ladder doesn’t suffer, the leg does – unless its anode is kept in good shape.<br /><br />Unfortunately, two things work against us here – first, the saltier or more brackish the water, the more sunshine it gets, and the more your boat moves through it, the greater the corrosive potential. Pity really, cos we all like warm water, sunshine and fast boats!<br /><br />And second, how many anodes do you see that are half eaten away or have whitish deposits? As the anode gets smaller its effectiveness decreases. The whitish deposits – oxides – act as a barrier to its sacrificial duties. Answer? Clean anodes frequently, with a file if necessary – and replace them when they’re half gone.<br /><br />You can see I’ve really got a thing about them!<br /><br />Ciao
