The following letter was written by Wayne, owner of Mobius in answer to a question of fitting either a Controllable Pitch Propeller or a self pitching Autoprop type design to an LRC58.
Mobius is single engine & rudder design fitted with a 160 BHP Gardener engine. In either case, the condition to avoid is high BMEP (Brake Mean Effective Pressure) and reduced engine revs. This is the operating envelope where the incidence of bore polishing increases. A typical example would be beam trawlers when nets are deployed greatly increasing the hull drag and lowering the speed.
Anyhow, over to Wayne ……
“Re your questions on AutoProp, short answer is that I am a big fan of them and seriously considered one for Möbius. I had them do a similar set of graphs for us and they were appealing.
Yacht Propeller Test
I considered choosing the AutoProp for Möbius but in the end as you know, we decide rightly or wrongly (we’ll see) to go with the Nogva CPP. While I think the AutoProp would have worked well and is arguably more simple way of getting some variable pitch in a very “automatic” way, it is our belief that the CPP will give us even better performance in terms of being able to optimize the Gardner’s power and torque. The big deal for me with CPP is the ability to dial in the pitch for ANY set of conditions we encounter. No matter what speed we want to be cruising at we can adjust the pitch to put the loads on the engine to be in the “sweet spot” of the fuel map where we have the just right amount of load, EGT (exhaust gas temp), RPMs, etc. This is ideal for both maximum lifespan on the engine with the right loads and RPM as well as the best possible fuel burn rates for that situation.
Surprisingly, when you go through a full cost analysis, a CPP is pretty much the same cost as a fixed prop or an AutoProp assuming you are comparing like to like quality of components wise. The unit we got from Nogva was exceptionally complete including not only the 4 blade CPP prop and servo/gearbox, but also the AL prop log tube which made it very easy to weld in the surrounding prop shaft tube into the hull during the initial hotworks of the build and then used Chock Fast to set the Nogva tube into that. Also included the Tides Marine “no drip” shaft seal system which works very well in my experience.
So when I took into account the full list of items you need for both a fixed prop system and the AutoProp system, and kept all those components top quality materials and companies, the cost was close to the same for both.NOT trying to sell you or the LRC58 client on CPP, just giving you some of the background on our decision.
Back to the AutoProp, it worked very well for us on Learnativity. It is basically a “install it and forget it” kind of unit and all I ever did was grease and service it every few years. Never had any problems with it in +50k nautical miles over 10 years and only extra expense was that I did replace the bearings after about 6 years but that was because I had left them out under the boat when I had taken it all apart and the bearing races got a bit of rust and pitting on them so I decided to replace them all and all the seals. Worked flawlessly until we sold it in NZ at the end of 2016 and we stay in touch with that couple and the AutoProp continues to work very well for them.
AutoProp Yacht Propeller Benefits
Key benefits of the AutoProp as I see it are:
“install it and forget it” propeller that gives you “automatic” variable pitch.
Reverse is as strong as forward which can come in handy when you get stuck and really need thrust (ask me how I know?!!)
Super simple design and build and the only thing more simple would be a fixed prop I guess.
I can’t give you direct comparison numbers between the AutoProp on Learnativity and the fixed prop it originally came with as I replaced it with the AutoProp right away. But I would say that it definitely was more efficient in putting more power/thrust into the water and increasing the fuel efficiency. My best seat of the pants guess would be about 15% improvements.
As for the LRC, I think an AutoProp could be a very good choice for all the reasons above; more efficient, automatic VPP, very low maintenance, etc.
CPP Yacht Propeller
If I had it all to do over again, I would still opt for a full CPP system and I have been very pleased with the quality of the Nogva so would go with them again as well. FYI, Nogva also sells full propulsion “packages” with everything from the diesel engine (choices of JD, Sania, etc.) all the way back to the prop so this might be a great way to go so have the full propulsion system coming as a complete package.
Wayne Hodgins, mobius.world.
Credit to Bruntons Autoprop and Mobius.world for use of their video, Nogva for the cover image.
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