3-blade vs 2-blade (FIXED)

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cmedsailor

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A 3-blade FIXED propeller is much more efficient when motoring against rough seas as well as better for manoeuvres in comparison to a 2-blade FIXED propeller.
However, when sailing a 2-blade propeller has less resistance thus better performance.
So, what is the best compromise for a ‘usual’ 36ft (5.5-6 tonnes with an engine of around 30HP) sailing boat?
 
Get yourself a proper feathering 3 blader. We bought a Kiwiprop for Tigger and it has been amazing. We used to have a fixed double blader and the difference is really remarkable.

It is one of the most cost effective options too: Ideal for a boat of your specification. THe UK distributors, Vecta marine, are brilliant. It is run by an enthusiastic sailor who is there to help.

Needless to say, my only connection is that of a very satisfied customer: you'll hear more of us on here in due course.
 
The price differential you would pay for either a 2 or 3 bladed fixed prop is so close to getting a decent folding or feathering 3 blade prop that I would not even consider going down the fixed prop route - as long as my boat was a 'sailing' boat - not talking motor-sailor - I think that they should have a 'proper' fixed bladed prop.

You may have to pay a few hundred pounds extra over the cost of a fixed blade taking into consideration machining of shafts etc, but when fitted, you will then get the best of both worlds.

When sailing you will instantly notice an increase in acceleration and speed. This will always be there and is not a one-off. When motoring, modern folding or feathering props will give as good performance at both slow revs for manueovering (sp?) as at cruising revs.

I changed from a fixed two blade prop on my Moody 346 to a two bladed Gori folder. I now would not consider having in the future a sailing boat with a fixed prop.

3-blade vs 2-blade (FIXED) - Don't do it - you will always be dissapointed.

Donald
 
If you absolutely insist on a fixed prop then get a 2 bladed one. Sailing with a three blade prop is akin to dragging a bucket behind you at all times.

But as everyone else has said, get a proper folding/feathering prop and enjoy sailing your boat.
 
Definately agree that a folding/feathering prop is by far better.
It was more a "theoretical" question especially on the effect when sailing rather than motoring.
 
The only time I've sailed a boat with a three blade prop I'd spent all morning trying to work out why I couldn't seem to make it go. Then the owner fired up the engine with an "oh well, at least I've got a big engine and a three blade prop to get me home". That explained that!

Another thing that's not often mentioned is that a fixed prop just in front of the rudder really disrupts the flow, resulting in much less grip by the rudder. When my dad fitted a folding prop to his boat the biggest difference (other than the speed under sail) was that the rudder had loads more bite, and the boat was much more controllable downwind in the strong stuff.
 
[ QUOTE ]
A 3-blade FIXED propeller is much more efficient when motoring against rough seas as well as better for manoeuvres in comparison to a 2-blade FIXED propeller.
However, when sailing a 2-blade propeller has less resistance thus better performance.
So, what is the best compromise for a ‘usual’ 36ft (5.5-6 tonnes with an engine of around 30HP) sailing boat?

[/ QUOTE ]

Surely for equivalent 'grip' a 2 blade is going to have a larger diameter and therefore similar drag as a 3 blade? We have a fixed 2 blade prop. I'm told some people will mark the shaft so that they can align the prop with the rudder and reduce drag. Never tried it myself.

As a fiscally challenged sailor I'm reluctant to fork out for a folding prop since from what I read on these pages you need to replace (expensive) anodes annually and I tend to lift every 2 years. I don't even have a shaft anode on our Moody and as far as I can see she's never had one fitted. Our prop is presumably original and has the odd pink tinge here and there. Probably need replacing in 5 years but at £150 a go I'm not too bothered /forums/images/graemlins/smile.gif
 
I just took a folding prop off my boat - it had only done twenty years and could easily be shimmed up to do another twenty. Changed it 'cause I wanted to try a shorter pitch. The only folders I've heard off which rot are the ones on Volvo saildrives, they are electrically insulated from the anode, so they are quickly eaten by electrolysis against their own S/S hinge pins!
 
To give you an idea - RYA PYR handicap scheme suggests against the same boat with no prop, a feathering/folding = 1% slower, two blader fixed 2% and they suggest an allowance of 4% for a three bladed fixed.

However, friends that have switched from fixed to feathering have suggested a 1/5 improvement in speed. I am currently changing over to a feathering prop.... can I suggest you have a read of the materials on the darglow site?

http://www.darglow.co.uk/html/products/props.htm

No commercial connection, but I have been really impressed with their assistance with my re-propping.
 
[ QUOTE ]
As a fiscally challenged sailor I'm reluctant to fork out for a folding prop since from what I read on these pages you need to replace (expensive) anodes annually and I tend to lift every 2 years. I don't even have a shaft anode on our Moody and as far as I can see she's never had one fitted. Our prop is presumably original and has the odd pink tinge here and there. Probably need replacing in 5 years but at £150 a go I'm not too bothered /forums/images/graemlins/smile.gif

[/ QUOTE ] Rob thats our thought as well, particularly as we can reach hull speed under sail without to much trouble.

Pete
 
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