Why Carbon Props?

THE ANSWER

Upon further investigation we contacted Contur Propellers in Florida and asked if they could design and build some new propsfor the Mea Culpa. We were told that carbon fibre propellers would provide some significant benefits such as fuel savings when under way, less propeller noise, less vibration, much less weight and the ability to ‘get home’ in the event of striking a submerged object while under way. Just how true these claims were had yet to be seen.

Cavitation seemed to be the biggest detriment to the propellers. We had witnessed high-speed game boats doing 35–40 knots and having so much cavitation that the surface of the propeller could not withstand it. However, with a 130ft motor yacht that does 21 knots, cavitation was not an issue, as we were not planing.

During construction of the propellers, ABS witnessed the entire process of building the carbon propeller blades over titanium inserts that fit into the milled bronze hubs. Destructive testing was performed and AIR Technologies did a fantastic job with this process. The props were delivered in wood crates, and as we happened to be doing a shaft survey we therefore ‘blue-fitted’ the new props to the shafts. All went smoothly.On the first sea trial we noticed the following: across the board we had a 1-knot increase in speed at the same RPM, with the top speed now 22.5 under full load. Our McMullen & Wing yacht had experienced no vibration issues, no noise issues and the boat was fishing very well. On this sea trial, however, we found out that the new Contur Propellers had taken away the minute vibration and noise that is caused by turning two 50” (1,270mm) propellers with 52” (1,320mm) of pitch. Wow, what a difference; I couldn’t wait for the owner to experience the ‘new’ boat!

We saved a ton (literally) of weight, we increased our speed, increased our traveling range at 1,070rpm, and cut down propeller noise and vibration, thereby increasing our fish-ability. We also added safety to the vessel without even knowing it.

This brings me to a story that most captains don’t really want to tell: we had just completed a total refit paintjob at Rybovich in West Palm Beach using the new DuPont Marine Imron paint and were proceeding to a sea trial, when the unexpected happened. We hit a submerged object in the harbour while traveling at a slow speed. Immediately stopping the yacht after impact we then tested the propulsion and found that it worked. Our chief was standing in the cockpit and reported that no vibration and no noise could be felt when I went in and out of gear. I tested the maneuverability during the trip back to the shipyard and found that maneuverability was intact. We transited the channel, turned around and backed into our slip.

We then dove down to discover that about 5” (130mm) of all 10 blades were completely missing from the carbon props. Even though we had literally destroyed the tips of the blades, we were still able to maneuver the boat safely. Our props are deeper than the keel, stabilizers or rudders and therefore were the only thing that was struck.

Upon hauling out to observe the damage and put on a spare set of bronze props, we found no further damage. The rudders had not been touched; the stern tubes were perfect; the ‘A’ bracket showed no signs of any stress; the shafts were spun and tested with a micronometer and showed that they were still ‘true’ and the transmission and gearboxes again were in excellent condition. The only damage was that our propellers had been reduced in both diameter and pitch, yet were allowing me to operate the vessel with the same precision that I did when they were first installed.

While we were building Mea Culpa we made plans to travel to some remote areas in the world where charts were not always accurate in search of fish, beaches and adventure. Others can attest to the fact that had this same scenario occurred with the bronze props that again all 10 blades would have been mangled (but would have remained attached), and shaft, stern tube, perhaps gearbox and transmission would have sustained damage as well. For certain there would have been tremendous vibration and noise, and maneuverability would have been greatly reduced, if it were even possible to move under our own power.

The bronze hubs were sent back to the factory which built new blades and set up the props again for our reinstallation. I’m very proud to report that we have our Contur props back on and clocked 24.9 knots on sea trial under lightship conditions, again with no vibration or noise.

Our next trip is wahoo fishing in the Turks & Caicos Islands and we’re headed there with the knowledge that should an unplanned impact with a submerged object on the props we will be able to safely navigate and not be stranded. I cannot say enough good things about the benefits to a super yacht and challenge you to investigate the benefits for your own vessel.

The cost of these carbon propellers is similar to that of conventional bronze props. For a competitive bid or price indication anyone can contact Mel Katzen of Contur Propellers. If you mention this article, he will extend a $500 discount on an order. I can be reached at [email protected] if further comment or information is requested. Good sailing!

(We would rarely allow these previous sentences but since it is an unsolicited and enthusiastic testimonial and there is a potential deal for our readers it seems justified – Ed.)
Mike Hein
Images: Mike Hein and courtesy of DuPont Marine, Oscar Arellano, Juerg – Fotopress
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