Howdy-
I had to jump in here on this topic as I have used both the Performance Prop( synthetic) and two metal props on my 30ft 10,000 lb Hunter with Advanced Marine 2K 24v motor.
The results were pretty heavy. When I first dropped the boat in the water for testing and trial results I had the synthetic prop on the shaft. Many times it felt as if the prop was flexing or bowing from the torque and RPM load. It actually WAS bending and flexing. I started to look at numbers vs. knots. I wasn't getting the instant power I needed and going in reverse was nearly impossible, even just backing out of the slip was an event. Absolutely no direction no matter how hard the keel was turned. I must mention I had just finished a 42 mile journey back to my slip (the maiden voyage) from the boat yard with silent and confident motoring, even though I was only getting half of hull speed most of the time (3 knots) in the Inner coastal.
After a month of wondering why my boat wasn't getting the numbers and efficiency the motor deserved, I ordered a 3 blade aluminum 12 x 11 (after many discussions with prop shops) to see if that would do the trick. In the time it took to receive my prop order the synthetic prop had turned into a barnacle muffin. Completely round and free of any blade definition. didn't think the synthetic would foul in the same fashion than the usual brass.
Tried the aluminum, kept us in the lighter load zone but still wasn't pushing the boat quite right nor was it giving my any better results in reverse.
NOW finally went back to the original 13x10 that was on my original Yanmar YSM 12... control of reverse was instant and on spot. Actually had to use half the RPMs. Switched into forward, again half the RPMs out of the slip. I could finally feel the thrust and torque of a solid prop. Brass and original size. I know cruise along with half the effort and all the efficiency I was hoping to achieve.
My lesson- use the prop made for your boat FIRST and then TRY variables. There is a reason.
I know we are all trying to get the best results with our E Boats and there is obviously still a lot to be learned and understood in the process. Everyone has their opinions and specific wants and needs for their vessels. I read something that was posted on here when I first joined... we are Sailors on Sailboats...
AND try your original prop first.
DEJ
--- In electricboats@
>
> Our Ericson 27 had an Atomic Four, but we never tested with the original two blade 12x6 prop when the 2kw 1000rpm brushless motor was installed. The first, an 11 x 11 three blade, was too steep, especially with a fouled bottom and low motor power. The 12 x 8.2 self-feathering two blade from MaxProp was noisy and cavitated at low speeds, but worked efficiently while under way. It did go flat to near zero resistance while under sail. Nice, but motoring is more interesting. We re-pitched the three blade to 11x9 and freshened the bottom. Now she slips along at 4.5 knots using 1.3kw in still conditions. More testing needs to be done under wind and tide conditions to get the full results.
> A Catalina 30 with a larger 5kw motor, 1850 rpm no-load, was installed with the original prop, pitch unknown, for a base-line. The old 22hp Universal Diesel drove the prop through a 2:1 gearbox. Although the boat moves well with the new direct drive, using 2.4kw at about 4 knots, the motor is being lugged. WOT is a mere 950rpm while under way. The Prop Shop will consider the numbers and provide a solution next week A Rawson 30 with a full keel is also using the original prop in a 5kw install. The old 20hp Palmer was direct drive. That boat pulls the full 5kw to hit 5 knots. I have not measured the motor speed, but the tach is in the truck now.
> I can say from the experience so far: A matched prop will produce the best results, but nearly any prop will be able to move a boat. A bad case is the first boat I converted. It's 30ft on the water with a 10ft beam, and has a very large steep prop. The motor current limits at 560rpm, but the boat has been in constant use since 2008, moored on a buoy, with a 100ah 24v battery pack charged only by solar and wind. Paul uses the motor as it was designed, for mooring and an occasional "power jib". If he were to consider a beat up the coast from Mexico, however, the system would never fly. A fresh, very low-speed motor, 740rpm no-load, is nearly ready.
> The worst case so far was a 40ft trimaran, re-powered (not my work) with a 72v brushed fork-lift motor connected in direct drive to the prop shaft. They had tried to wire the system at 24v, but without any controller, just massive voltage stepping contactors. The prop was also very, very big. The motor pulled 100a at just 12v, emitting a spray of sparks from the brushes. They headed for LA from San Francisco with a full bank of 8GCs and a Honda on the deck. I donated a Charles 12v50a charger, and told them to take plenty of fresh water. They never made it out the Golden Gate the first try. Later, my cousin towed them out the Gate with an outboard. They were later pulled in by the Coasties when I explained there was an ignition hazard in the bilge. They had stalled off Santa Cruz, and were being faced with a rescue tow bill. The brushes made for a "dangerous condition", and the Coast Guard's charter then allowed for a tow.
> That boat then got a Beta Marine re-power back at port.
>
> Safe Boating All,
> Arby
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> ____________
> From: gramplarry <pfister.l@.
> To: electricboats@
> Sent: Sat, March 6, 2010 9:59:45 AM
> Subject: [Electric Boats] Re: propellers
>
>
> Yes the extendo is still being made. However check your prop space if all you need is a 15 inch prop my data base shows that some of the hunters at that age had variants and a 15 inch prop will fit on a few.
> FYI I have a web page that helps in determining the max diameter prop for a boat.
> http://mysite. verizon.net/ resqp86c/ performanceprope llers/id41. html
> It also has a bit on the extendo and how it fits into the propeller sizing issues.
>
> Just a note about propeller sizing for sailboats. At one time 80% of the sailboats being manufactured in the USA had an atomic four gas engine. This engine was used in boats up to 40 ft in length. The boats of that period were designed for that engine and a 12 inch diameter propeller. That is why nearly everyone repowering an older boat with electric or diesel has a prop sizing problem. The atomic four was rated at 30HP at 3000 rpm and has a direct drive. slower props require a larger diameter.
>
> --- In electricboats@ yahoogroups. com, "aweekdaysailor" <aweekdaysailor@ ...> wrote:
> >
> > I've been eyeing the "extendo" prop for a while as it in theory allows me to get to my ideal prop size of 15". This is still being made? This is for a 1978 Hunter 30, 5ton with 6HP motor (which I generally run at about 2.75HP for cruising @4kts). Hunters have struts and a skeg-mounted rudder, so not a lot of room, but I think i could swing it.
> >
> > --- In electricboats@ yahoogroups. com, "gramplarry" <pfister.l@> wrote:
> > >
> > > CDI stopped making the both the 2 blade and 3 blade feathering propellers about 15 years ago...
> >
>
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