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  Topic Review (Newest First)
26 Minutes Ago 08:16 AM
SanderO
Re: 2 blade or 3 blade propeller

I have had a fixed 2 blade prop on Shiva since I got her 32 years ago. I have no basis for comparison. But it would be interesting to try a season with a 3 blade or even a folding or feathering prop... since I am quite familiar with performance on this boat with a 2 blade fixed.

I don't race... fractions of a knot are usually of no interest to me... I know this can add up on a long passage to actual time. But really... does it matter? I sail to escape the constraints of time and the clock and appointments and so on... I sail to enjoy the boat, the motion, the wind, the waves... the solitude... the wonder and so on.

The two blade pushes the hull at hull speed, backs well... and seems to not have noticeable drag. It's simple. The prop seems to align itself in a vertical position when sailing.... I don't know why... maybe the orientation has the least drag???


I am not motivated to spend thousands for an advanced prop.
40 Minutes Ago 08:02 AM
Minnewaska
Re: 2 blade or 3 blade propeller

75% of max rated rpm is usually a rough sweet spot. You need to know what your motors max rated rpm is.

However, I don't think RPM is the cause of your vibration. Even if more seems to smooth it out, you should still figure out why its vibrating so much. You said you aligned your shaft, which is the first thing I would do. Were the engine mounts in good shape or could they be changing after you started the motor.
8 Hours Ago 11:51 PM
Captin G
Re: 2 blade or 3 blade propeller

How about RPM's verses changing prop. I have two issues. I can not seem to correct the vibration of my two blade. I removed and balanced. Then Aligned shaft. Still can't keep my cutlass bearing from loosening. The screws back out. I tried a little epoxy on a new cutlass and screws. lasted a few months. I thought a three blade may have less vibration.
Also, with a little head wind and current on the nose I can only get 2 or 2.5 knots motoring. I have a 35 hp perkins 3 cylinder parama M35 in a Heritage West Indies 36 (17500 displacement). I have a manual and have asked around however I can't seem to get a straight answer on RPM's. I try not to go over 2000, 2100 max. I would like more speed and less vibration. Can I rev her up to 2500 rpms? Anyone?
10-11-2012 09:00 PM
HMoll
Re: 2 blade or 3 blade propeller

I'll tel you what's dragging: this thread! For cruising in heavy currents, on a small boat: 3 blade-folding. I went from feathering 2-blade maxprop to 3-blade folding flexofold. Gained a full knot motoring and maybe lost .2kts sailing, which is unmeasureable, 'cause I probably "lose" more than that just chillin' and enjoying the ride! Get 3 blades. No brainer.
10-11-2012 08:27 PM
sailingfool
Re: 2 blade or 3 blade propeller

Quote:
Originally Posted by Capesailor View Post
Hello,

I'm a new member. I'm buying a new Marshall Sanderling and am deciding on a two blade vs three blade prop for the 10 hp Nanni 2.10 diesel. Is there more drag with the 3 blade? Is the three blade quieter with less vibration? I am interested in getting max thrust in a tidal outlet to the Atlantic.

Capesailor
That's a small diesel, it certainly will work fine with a suitable size 2 blade. I would doubt they make a 3 blade to deliver so little thrust...
10-11-2012 04:11 PM
Gene T
Re: 2 blade or 3 blade propeller

Generally better to start a new thread than use one 8 years old. 3 will have more drag with lower vibration probably only felt on the tiller. Drag with a 3 blade is so significant most sailors will go with a folding or feathering 3 blade, and pay the difference.

Gene
10-11-2012 03:30 PM
Capesailor
Re: 2 blade or 3 blade propeller

Hello,

I'm a new member. I'm buying a new Marshall Sanderling and am deciding on a two blade vs three blade prop for the 10 hp Nanni 2.10 diesel. Is there more drag with the 3 blade? Is the three blade quieter with less vibration? I am interested in getting max thrust in a tidal outlet to the Atlantic.

Capesailor
12-29-2004 07:12 PM
dougyoung
2 blade or 3 blade propeller

I looked into this same switch. A local prop shop shop said to go with the same dia w/ 2" less pitch. Think about it, 150% of the thrust area of a 2 blade, reducing the pitch takes the strain off the engine at the same rpm. The big difference that was explanied to me was with a 3 blade, two blades were always thrusting in less distrubed water from the keel, with a 2 blade there is only one.
11-11-2004 11:17 AM
JohnDrake
2 blade or 3 blade propeller

OK, just got an email from Mich Wheel. Sent them all my specs and asked for a quote. They recommend a 3 blade fixed....17x11.

Interesting, Campbell also said 17x11 at first blush but then changed that to 16x9 when I sent them my trans specs later on.

Hmmmm......Jeff????? Jack??? Anyone?

I am going to write campbell back and ask them to recheck. I can see 16", not a big deal. But going from 12" pitch to 9"?

J
11-11-2004 11:05 AM
JohnDrake
2 blade or 3 blade propeller

Thanks Jack. I will have to look up Gerr''s books. I like his writing and if Nigel recommended them....all the more. Nigel is a great guy. He really likes Hood 38''s too, so...that colors my opinion.

I am trying to ''ground truth'' the prop specs recommendation from Campbell by using some net resources (though would really like real world examples still). I have written Michigan wheel to get their recommendation...they have a similar "sailor" prop. A 3 blade with thinner blades for less drag. They said about 10 days to get back to me. Whew.

If your plans include more Med sailing this coming summer, check out La Maddelena. One of my favorite places and the one I''d like to get back to most.

Best

John
s/v Invictus
Hood 38
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