Friday, May 30, 2008

Time for new exhaust riser

I often wonder what people do who are not obsessively fastidious about maintenance. Seems you either think about every possible chink in the armor all the time, create and follow an incredibly detailed checklist of items, or suffer the consequences of stuff breaking at predictably inopportune times. I've always been in the first bunch myself: too compulsive to neglect things, too lazy to create the list, and too attached to health and happiness to risk inaction.

Being of this first type, some mysterious but undeniable voice in my mind recently said: "Hey, it's been a few months since you last checked your exhaust riser for rust, don't you think it's about time to check it again before you head to Barkley Sound?" So not being one who likes to ignore those voices and then have the double guilt of it failing and knowing you could have prevented it, I set about to check the little devil.

Getting to this on the Gulf is not too tough. At least it is not buried deep back into a crawl space as I've seen on many other sailboats. On the Gulf 32 you just have to remove the floorboards and there she is. Earlier this year I had treated the riser with a rust stop spray to see what that would do. As far as I know, and I'm pretty sure about this, this riser is the original one to the boat and so has endured use since 1988. That's a long time for an exhaust riser, and this one only lasted this long because the boat was lightly used and did most of it's work in fresh water on the Columbia River.

Well when I checked it, I noticed quite a bit of rust and the unmistakable surface buckling of rust having gotten under the surface of the metal and gone deep. As I started to chip away at the rust, I went deeper and deeper, until I began to worry I was going to break through to the inside. Although this never happened, I did go might deep before reaching something solid. Something odd though, is that some of the material I removed had the chalky feel and grey appearance of graphite, even though it was by all accounts just rusted metal. Anyway, I knew right away that I had to replace this riser as I couldn't trust it any longer with that much metal removed. Sure enough, when I started the motor, a very small amount of water seeped out of the spot where I had dug out metal.

So I've ordered the replacement part from Gallery Marine here in Seattle. It is a 1.25 inch Universal exhaust riser with a 2 inch exhaust hose end. When I get the new one installed, I'll add a picture and tell the story of whether it was straightforward, or not.

1 comment:

Dandy said...

The graphite like stuff you found actually was graphite, cast iron contains lots of carbon flakes (2-3% by weight for gray cast iron, as opposed to <.3% for mild steel, and lower still for low carbon alloys), they give it its desirable thermal properties (especially shrinkage for castings) at the expense of total strength. Silicon is added to prevent the carbon from forming iron carbides that would reduce the amount of graphite in the iron.

As the metal corrodes the iron forms iron oxide but since graphite is really noble it just sits in the middle of the oxide mush without changing form.