Search For Understanding

Days on cruise:   282

No, this isn’t some sort of existential discussion of a spiritual quest to understand the meaning of Life. Rather, it’s a quest to understand the nature of props!

First: What’s wrong with this picture???

It’s not a good photo, so even a discerning eye might miss the point, but prop blades aren’t supposed to curl on the end like these do; all four of them!

Two days ago we hired Jamie, who lives here in the marina at Goodland, to clean our boat bottom, as we do every six weeks when in salt water. He dove down, cleaned off algae and some barnacles, inspected all the zincs, and obviously, inspected our props. Oh no!

For the life of us, we’re confused about when and how this happened and why we didn’t know it! Those of you who have followed our blog for some time will remember our October 29 post (LINK) describing going into an anchorage at Blue Bluffs on the Tennessee-Tombigbee Waterway where we hit an underwater obstacle despite being clearly right in the middle of the channel. We never saw what we hit, and the next day when we ran the boat up to 20 mph to check for vibration, the clue that indicates you have prop damage, there was none. Now, 1,000 miles later, we haven’t hit anything since, and we haven’t noted any vibration, though we run the engines up for 5 minutes every travel day to blow out the carbon in the turbochargers, since we travel at trawler speed the rest of the time. So how could we have such damaged props and not have noticeable vibration???

Today Jamie brought Matt to the boat to dive down and pull the damaged prop. He had a 65-foot air hose and air compressor, so didn’t need scuba tanks. He was here exactly 30 minutes from the time he arrived until the job was done and he left.

Note the size of that crescent wrench, with Cathryn’s foot in the lower right corner. He had all the right tools, including a strong line to tie to the prop in case he dropped it into the mud by mistake, so it wouldn’t sink out of sight.

We pressed for an explanation how we could have such damage and no vibration, and Jamie and Matt said if all 4 blades of the prop are bent equally, so there’s no “out of balance” situation, it won’t produce any vibration. It will, however, produce cavitation, which would explain the reduced idle speed and reduced fuel economy we’ve noted in the last some hundreds of miles. Guess we should have been more curious about the idle speed and fuel mileage reduction?

Jamie drove our prop to a prop tuning shop in Naples, FL and they promise it will be scanned (sort of like an MRI) and repaired by tomorrow morning at 10am. Unfortunately our health insurance won’t cover the cost. Jamie will pick it up and re-install it tomorrow mid-day and we’ll be good to go again. That’s service!

So, for those of you boaters who know more than we do about boats and props and such, and we know there are many of you, please feel free to wax eloquent in the Comments section of this post, or by email, or call us to explain this weird thing to us.

Jack and Sara: mostly we’re thrilled we discovered this before you have the boat hauled for the Sea Trial and Survey next month, as we’d have been SO horrified and embarrassed to discover it then!