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Old 14-07-2012, 11:14   #1
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Propeller Advice If You Please !

I just repowered my 44.7 Roberts ketch with a Yanmar 4JH4TE 75hp engine with the 2.70 gear transmission. The old propeller was a three blade 20 X 14 LH and the Yanmar requires a RH propeller. Yanmar suggests a 20 X 14 RH or better yet, a 20 X 13 RH to achieve 3200 rpm.

Max Prop is suggesting a 20 X 15 RH prop.

I am confused! To make matters more interesting, I would consider a two blade prop as well.

I am told to add an inch of pitch for a two blade and subtract two for a four blade.

If it helps, the boat has about 39 feet of waterline and weighs about 28,000 pounds.

Your thoughts?!?!?

THX!
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Old 14-07-2012, 12:53   #2
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Re: propeller advice if you please!

I plugged your data into boatdiesel's prop calculator. It gave a 20x15.6" 3 blade prop. I would buy a MaxProp and start with 20x15 and go from there.

How did your 20x14 LH prop perform with the old engine and what was its hp?

If you buy a fixed prop then ask the supplier to give his recommendation. That will be the most accurate probably and most shops will repitch for free if needed.

David
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Old 14-07-2012, 14:08   #3
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Re: propeller advice if you please!

I would highly recommend an autostream instead of the Max-Prop. One of the nice features is you can change the pitch without taking it off the boat, it just takes a wrench and a quick dive.

Having owned both the Max and now the Auto, the auto has much better performance.
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Old 14-07-2012, 15:41   #4
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Re: propeller advice if you please!

David,

It was a Ford/Lehman 80hp and it pushed the boat along nicely at seven knots...
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Old 14-07-2012, 16:12   #5
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Re: propeller advice if you please!

I repowered Boracay with a 85hp John Deere and had the prop cut down to 21" dia and 13.5" pitch.

The boat was still overpitched as I only got 2250rpm. (max revs is 2500).

I had the prop coated with Propspeed last time I hauled and now get the full 2500rpm (just).

I've been cruising offshore with wind, wave and current coming into play, but I've seen over 8 kts on the GPS at 2200rpm.
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Old 14-07-2012, 20:02   #6
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Re: propeller advice if you please!

I'd go with what Yanmar recommends. They know their engine performance better. If you want to go with the 14 pitch you can always have it repitched next haulout if your engine overheats while trying to reach 80% max rpm.

There is a reason why you are confused. It's because even the pros have a hard time getting it right the first time all the time.

kind regards,
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Old 27-07-2012, 22:13   #7
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Quote:
Originally Posted by Stumble
I would highly recommend an autostream instead of the Max-Prop. One of the nice features is you can change the pitch without taking it off the boat, it just takes a wrench and a quick dive.

Having owned both the Max and now the Auto, the auto has much better performance.
FYI, the new Maxprop Easy Blade has external adjustable pitch. It can be performed under the water. Even the whole prop can be easily assembled or disassembled under the water, so no haul outs are required!!. Way different than the original (now called 3 blade "classic") and just around $400 more expensive. They also have a new automatic adjustable pitch prop, just like the Autoprop called Eco Wind. the price is also at the same level!!!
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Old 27-07-2012, 22:16   #8
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Stumble, BTW, how hard is to install the Autostream?? Is it possible to be assembled on the water?? Wasn't able to find online instructions....
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Old 28-07-2012, 05:37   #9
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Re: propeller advice if you please!

Quote:
Originally Posted by Maxs View Post
Stumble, BTW, how hard is to install the Autostream?? Is it possible to be assembled on the water?? Wasn't able to find online instructions....
Autostream Instructions ➥ Low-Drag, Feathering & Folding Propellers for Sailing Yachts & Sailboats made in Australia by Seahawk

Shaft ➥ http://www.seahawk.com.au/images/models/S1.pdf

Saildrivehttp://www.seahawk.com.au/images/models/S1.pdf
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Old 28-07-2012, 13:55   #10
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Thanks a lot GordMay!!
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Old 02-08-2012, 08:55   #11
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Re: propeller advice if you please!

I've no experience of the Autostream, but I've had both the Maxprop and Autoprop on my boat and would go for a self-pitching rather than feathering prop every time. The Autoprop was, incidentally, substantially cheaper than the equivalent Maxprop for my boat (on Oyster 435). See my report at the end of the Autoprop? thread in this forum.
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Old 13-08-2012, 15:21   #12
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Re: propeller advice if you please!

a BIG thanks to all who replied. I am going to put a 20 X 14 (middle ground) three blade fixed back on and repitch if needed.

will post a follow up!
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Old 12-09-2012, 08:45   #13
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Re: Propeller Advice If You Please !

I have a Flex a Fold folding propellor for sale that may be the perfect prop for you. Best folding prop on the market.

20" diameter, 15 pitch 1.25" shaft. In great shape. Fresh water use only.

Call if interested 269-426-4202.
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