Monday, January 09, 2012

What I've learned about sailboat propellers

After warning me that my propeller needed to be replaced while scraping the coral reef from the bottom of the Starwind, our diver returned Saturday morning with more tools to pull the prop.

Starwind Prop

The prop was much smaller than I expected. It was a 12" diameter with a 10" pitch and a 1" shaft. It also turns right-handed. I learned this is all stamped on propellers and usually denoted with something like RH 12 x 10.

Obviously the diver was correct. The prop needed to be serviced. It's already missing chunks. But how could he know (aside from feeling that hole) in the murky water with almost zero visibility?

Apparently the quick and easy way to tell if a propeller is still good is to tap it with a wrench or something metal. If it rings like a bell, you have good metal. If it makes a dull "tink" sound, the metal has become porous and full of fractures.

My original plan was to get the diver to pull the prop, hand it off to me while I found something comparable at the Kemah resale shop down the street, and then have him put the replacement on as soon as I got back. I'd only have to pay for one dive and a smoke break. Unfortunately, the closest thing I could find was a RH 13 x 14. That's a 13" diameter with a 14" pitch. It was not only a larger propeller, but it also pushed a great deal more water.

The diver got it seated, and I fired up the Kubota. It really vibrated at idle, so I throttled up to see what would happen ... but the engine speed never went up. Instead, my exhaust turned black.

I was over-propped.

My diver suited back up and pulled the RH 13 x 14 back off, so I could go return it. I think he was secretly happy that I'd have to pay him to come out for yet a third weekend once I found a correct replacement, but he hid it well.

I did find a RH 12 x 10 on eBay, which I procured for only $101 including shipping -- not a bad deal. Now there's nothing to do but wait for it to arrive and hope it does the trick.
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