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New Props Fixed Our Shaft Vibration Problem.

Bollard pull test

This week, I experienced an event akin to watching BBC's Dr Who as a child. I feared the outcome but was glued to the drama, hiding behind the sofa for protection (for the uninitiated, Daleks are scared of sofas).

Monday was the day we tested our new Bruntons Varifold propellers. Somehow, we had to cure the vibration problems that became evident with the Autoprop installation. 

Changes made by Bruntons Propellers

For previous discussions and investigations of this, see the Blog below. Bruntons Propellers, the manufacturer, visited to understand what was happening and proposed a solution: to use their Varifold sail drive propellers. We would retain the ability to run on a single engine efficiently and alleviate the vibration issues that had become evident. The proposed solution was to:

  • lock the propeller pitch (but retain the folding ability)

  • reduce the blade loading by increasing the disc area ratio (4 blades, not 3)

  • increase the hull to hull/prop tip clearance

  • relieve the tip pitch on the blades, (reducing the load in that specific location where vibration may initiate.

Bruntons Varifold Propellers

We wanted to test this solution immediately; leaving Antalya depends upon a good result!

Bollard Pull Test

We arranged for a static bollard pull test at the commercial berth in Antalya. It is a concrete dock mooring with significant attachments for the mooring lines. Many marinas dislike bollard pull tests. They can destroy the dock cleats or wash the floats out from underneath the decking, but not in this location. It is good enough for a 300T fancy yacht, which will be good for our small offering operated by a bunch of old blokes!

Bollard Pull test results

Our test used the Port engine initially. We secured all available Port rail fenders and broke out the foul weather mooring ropes, doubling up on our spring lines. Two crew members were on the helm, one in the engine room and one at the stern, with plenty of eyes and ears and a clear shutdown protocol. The engine operated from 750 RPM, idle to full fuelling, which correlated to 2050 RPM. Full shaft speed is designed at 2300 RPM, though, for a bollard pull, it's typical to expect that changed flow water conditions will result in a higher load for a given RPM. We will confirm this during sea trials. (Data was recorded quickly and before the system stabilized after each load increment hurriedly; forgive the scatter.)

Test Results

The outcome is as per the enclosed photographs and without vibration. The water depth on the pier is just over 5.0m, effectively clean water unaffected by the surrounding structures. We managed to stir up some benthic sediment near full load, but the dock remained unscathed otherwise! I am still nervous about our drive train, an emotion more resulting from unfamiliarity than science. However, problems with rope cutters and vibrating propeller blades are now receding astern of our adventure.

Further Work

We need our drives to be rock solid, dependable, and efficient. In one respect, we should have paid more attention to how they were assembled and tested during the build. No one can fix the past, and we have a work package to improve the fit and performance beyond a typical shipyard standard— a feat fairly easily achieved now but not later.

Thanks to Bruntons Propellers for their first-class support and advice during this time. We got there in the end.

Chris Leigh-Jones

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