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Old 28-07-2013, 19:14   #1
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3 Bladed Prop vs 2 Bladed

I recently purchased a Gulf 32 and having the transmission replaced. A bit of a shock! While she is out of the water I was considering changing her 2 bladed prop for a 3 bladed for better performance. Any thoughts?
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Old 28-07-2013, 20:02   #2
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Re: 3 bladed prop vs 2 bladed

There are general differences but the design of the prop, pitch and diameter can make the differences more or less significant. That being said

3 blade more power so faster start, stop. Better reverse, less prop walk. More drag.

2 bladed more or less the opposite of the above.
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Old 28-07-2013, 20:18   #3
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Re: 3 bladed prop vs 2 bladed

Thank you skipmac. I look forward to more replies and whether it's worth the expense. Do you have a recommended brand and model ?
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Old 28-07-2013, 20:30   #4
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Re: 3 bladed prop vs 2 bladed

Personally I'm going for a folding prop. Several brands, some better than others. My current plan is a Flex-o-Fold. A friend has a Seahawk and loves it.

There is a company whose name I can't recall at the moment that claims their fixed, three blade is more efficient, less prop walk etc. I think the name was Sailing or Cruising prop or something like that. Sure someone will come up with the name.
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Old 28-07-2013, 20:44   #5
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Re: 3 bladed prop vs 2 bladed

Campbell. A fantastic 3-blade prop if you want to go with a fixed prop. Less drag, less prop walk and more power.

Mark
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Old 28-07-2013, 21:01   #6
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Re: 3 bladed prop vs 2 bladed

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Originally Posted by colemj View Post
Campbell. A fantastic 3-blade prop if you want to go with a fixed prop. Less drag, less prop walk and more power.

Mark
That's the one I was trying to remember. The Campbell Sailor.

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Old 28-07-2013, 21:57   #7
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Re: 3 bladed prop vs 2 bladed

Volvo-Penta makes the lowest cost folding props, and they're very good. Been using one for the past 5 years. My only complaint is that the shaft models of 3-blade version don't have integrated zincs. So you need a shaft zinc. The sail drive versions do have it.

BTW - prop walk is your friend if you know how to use it to your advantage. There are times it's almost as good as having a bow thruster. I like it.
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Old 28-07-2013, 23:33   #8
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Re: 3 bladed prop vs 2 bladed

My heavyish 32 foot mon came with a 3 blade prop fitted, and 2 blade as a spare. When I did the first antifoul I swapped and put on the 2 blade.

While I didn't do any before and after testing, I didn't notice any difference in sailing performance. There probably was a bit, but not much. But I sure noticed the reduced grunt when punching into a steep chop. So I swapped back to the 3 blade.

I think it depends a lot on your preferences. For better sailing performance choose the 2 blade, but expect reduced thrust when under power.
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Old 28-07-2013, 23:52   #9
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Re: 3 bladed prop vs 2 bladed

Quote:
Originally Posted by skipmac View Post
There are general differences but the design of the prop, pitch and diameter can make the differences more or less significant. That being said

3 blade more power so faster start, stop. Better reverse, less prop walk. More drag.

2 bladed more or less the opposite of the above.
Ditto on all that. It pretty much covers it.

Quote:
Originally Posted by skipmac View Post
Personally I'm going for a folding prop. Several brands, some better than others. My current plan is a Flex-o-Fold. A friend has a Seahawk and loves it.

There is a company whose name I can't recall at the moment that claims their fixed, three blade is more efficient, less prop walk etc. I think the name was Sailing or Cruising prop or something like that. Sure someone will come up with the name.
I dunno...I think you should reconsider. They are damn expensive and I see a lot of fast wear on the Max prop here in the yard where I'm berthed. They also have difficulty feathering if growth is allowed to take hold. For the type of boats you and I have, what speed are we really gaining? Invest that money in creature comforts and enjoy the time it takes you in 24 hours to make up that extra 3 miles...
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Old 29-07-2013, 01:40   #10
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Re: 3 bladed prop vs 2 bladed

The gori do an amazing 3 bladed prop. It is very clever a fuel economy 2nd gear you could say. Very streamlined. I think a 2 bladed prop is everything as good as a 3 bladed prob going forward but if there is serious resistance 50 plus knots a 3 bladed would have more grunt once on full rev's. The most important aspect is getting the prop size and pitch to your boat and engine. This can only be worked out by computer.
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Old 29-07-2013, 02:34   #11
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Re: 3 bladed prop vs 2 bladed

Generally the choice between 2 blade and 3 blade props has to do with hull shape and aperture where the prop resides.
Based on engine power and transmission you select a 2 blade prop to fit. However, if the planned 2 blade is too large (diameter) for the hull shape and/or if you have a keel hung rudder with aperture, you switch to a 3 blade that will have shorter (smaller diameter) blades. Also your prop selection need to be about 25% of radius away from any hull surface above and below to reduce cavitation.
Another consideration is to chose a prop with enough blade diameter to "reach" out from the shadow of the keel in front of it to get clear flow water to bite into. All in all, there are a lot of compromises in the prop size / type selection.
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Old 29-07-2013, 06:56   #12
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Re: 3 bladed prop vs 2 bladed

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Originally Posted by Celestialsailor View Post
Ditto on all that. It pretty much covers it.


I dunno...I think you should reconsider. They are damn expensive and I see a lot of fast wear on the Max prop here in the yard where I'm berthed. They also have difficulty feathering if growth is allowed to take hold. For the type of boats you and I have, what speed are we really gaining? Invest that money in creature comforts and enjoy the time it takes you in 24 hours to make up that extra 3 miles...
Damn expensive is right. Not yet on the top of my list for where to put more of my vast quantities of disposable income.

Performance. Say you get an extra 1/4 kt which I think is in the ball park (real world experience from others very welcome on this subject). That would be an extra 6 miles/day. In a week long passage that's an extra 42 miles which is starting to sound almost worth while. If you got an extra 1/2 kt thats 84 miles/week.

I think at slower boat speeds the savings is more significant than when close to hull speed. This is when I would care most about the savings. Again, real world experience would be interesting.

However I have another motive for considering a folder; no prop spinning under sail. Transmission manual says its not a problem but there will be wear on the cutlass, the stuffing box and my nerves. The boat came with a shaft lock which is not working but could be repaired but it adds more junk it a very tight spot on my drive train due to the V-drive configuration.
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Old 29-07-2013, 07:14   #13
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Re: 3 bladed prop vs 2 bladed

You would not be dissatisfied with the Campbell 3 blade. Mainsail did a resistance test(sailboat forums) and I think the drag was about 13 lbs vs a standard 3 blade prop at 36lbs if I remember correctly. I also noticed that when I changed from a 2 to a 3, the vibration I had from the drive train disappeared.
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Old 29-07-2013, 08:03   #14
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Re: 3 bladed prop vs 2 bladed

There's more of an advantage to having a folding or feathering prop than just speed and distance covered; it also allows you to keep sailing in lighter winds than you would otherwise be able to manage without having to motor. When you're covering a lot of miles, that fact alone offsets the high cost of the props somewhat.

I have heard it said that the amount of drag produced by a fixed 3-blade prop is about the same as towing a bucket in the water. If you stop the prop from spinning to reduce wear, make it two buckets. I've had both a fixed and a feathering prop on the same boat and can testify that it does make a noticeable difference.
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Old 29-07-2013, 08:30   #15
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Re: 3 bladed prop vs 2 bladed

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Originally Posted by DefinitelyMe View Post

I have heard it said that the amount of drag produced by a fixed 3-blade prop is about the same as towing a bucket in the water. If you stop the prop from spinning to reduce wear, make it two buckets. I've had both a fixed and a feathering prop on the same boat and can testify that it does make a noticeable difference.
A study in Yachting Monthly showed a very clear difference between fixed and folding if the fixed were fixed (drag of 0.5 knot) but if allowed to spin the penalty was of the order of only 0.2 knots (figures at around boat speed of 5 knots)
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