They both vary from brand to brand.
ABC and Octura use different alloys, but both look and feel more or less the same, I wouldn't like to say which is stronger. The no name Chinese BeCu props are much brighter almost like brass and are noticeably softer so I suspect there is a fair bit of tin in the alloy.
CNC props are available in several materials Tenshock are the best of the Aluminium alloy CNC props and are made from 7075T6 which feels a bout the same as an Octura or ABC from the bag, but 7075T6 is already hardened whereas you can still heat treat BeCu to further hardness if you have the ability and equipment (or can pay someone that does). The magnalium use in TP props is a little harder than BeCu, but more brittle. Most of the other CNC aluminium alloy props are made from 6061T6 which is much cheaper and easier to machine but also MUCH softer than even the no name Chinese BeCu. Doctorprops make CNC props in stainless steel and cobalt steel, both of which are MUCH harder than BeCu.
Octuras are horrible out of the box and need a lot of thinning and sharpening then balancing, ABC seem to be a little better, still needing sharpening and balancing but less thinning. All of the alloy CNC props I have seen have had acceptable balance out of the box, but all have been fairly blunt and needed sharpening and rebalancing after for optimal performance, the harder alloys can be thinned out a bit for the racing we do here too. Doctorprops CNC props come truly ready to run, and are much thinner and sharper than I could make a BeCu prop without it folding its blades on the first run.
Generally the CNC blade shapes are better than BeCu, some are direct copies of Octura's X series, but most companies offer something with less blade area than most that are available in BeCu, so the average CNC prop has lower amp draw for the same diameter compared to BeCu. I normally buy X series and cut them back past M series (which tend to have thicker blades, so a cut X requires less work than an M) to suit me. The low area TP props are copies of the Graupner carbon props and have the least blade area and amp draw for the prop size.
Not CNC or BeCu, but I should probably say that the Graupner carbon 2317/2317 series props are the most efficient props out there. The low area, very low lift blade shape works extremely well, and the blades are perfectly tapered from tip to root. They are so good that I know people that have made molds and cast them from alloy and stainless, and TP copied the shape for their CNC props. None give the same runtime as the originals though, the carbons can flex under load, and the most load is accelerating out of the hole, so under acceleration it has lower pitch reducing cavitation for better acceleration and lowering amp draw at the same time whilst at top speed there is less load on it and the pitch comes back so the top speed is the same (or higher if you can prop up), it is not something that is possible with metal as even if you could engineer the strength well enough to flex, fatigue would quickly kill the blades. On the down side they are pretty brittle and you only have to hit the smallest twig to lose a blade, and above about 45mm they are really not up to the torque of FE. Buying a bunch or carbon props and working up checking for temps and/or runtime is a great way to find what metal prop to put on your boat, but once you find the right carbon prop, pick a metal prop one size down, as it will draw more amps.
I do my own BeCu props with hand tools, which takes me about 4 hours and it makes my hands ache. I hate doing props, but love the satisfaction of having done it. I do not put monetary value on my hobby time, if I did and charged it at minimum wage (and there is no way I would do props commercially for minimum wage) I would be much better off buying a Doctorprops CNC prop.
Last edited by NativePaul; 03-04-2017 at 06:58 AM.
Paul Upton-Taylor, Greased Weasel Racing.
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