Two or 3 blade prop for less prop-walk

[ruvane]

Hi all,

I have a 3-bladed prop on my 30' Moody and it's almost impossible to reverse to port. Best I can do is dead astern once she's actually moving backwards.

I need a new prop and was wondering whether it would improve with a 2-bladed prop. Not sure if it makes any difference that it's on a saildrive.

Thanks!

 

[Stemar]

I can't speak for your setup, but my Snapdragon got easier a little less difficult in astern when I went from 2 blades to 3.

My suspicion, with no supporting evidence, is that the bigger blade of the 2 blader pushed more water sideways at the bottom of its stroke, in more open water, than at the top where it's close to the shaft log.

 

[Bobc]

Can I suggest that your best bet would be a 3 blade Featherstream.

I had similar reversing characteristics om my boat and now it goes wherever I want it to.

 

[johnalison]

Any difference from a change of prop will not be large. I would not expect a lot of prop walk from a saildrive, though I get some on my 34. Your best policy would be to learn to live with it and use it to your advantage. When going astern, use the method of a large burst of throttle to get the boat moving and then knock it into neutral to give a balanced helm, and then engage gear when controlled movement is gained.

 

[Graham376]

Can I suggest that your best bet would be a 3 blade Featherstream.

I had similar reversing characteristics om my boat and now it goes wherever I want it to.

I found the same but with shaft drive. We had 2 blade fixed and lots of prop walk going astern but 3 blade Featherstream solved the problem.

 

[Tranona]

Hi all,

I have a 3-bladed prop on my 30' Moody and it's almost impossible to reverse to port. Best I can do is dead astern once she's actually moving backwards.

I need a new prop and was wondering whether it would improve with a 2-bladed prop. Not sure if it makes any difference that it's on a saildrive.

Thanks!

Generally speaking saildrives are better than shaft drives mostly because the props tend to be further away from the rudder so that any prop walk is reduced before it influences the rudder. A change from 3 to 2 blade unlikely to make any real difference and you will have to go up in diameter. while a Featherstream is a worthwhile addition because it reduces drag when sailing and often improves performance under motor not sure it will affect prop walk on a saildrive.

 

[pcatterall]

I could use a bit of prop walk sometimes!

 

[cmedsailor]

My previous boat had a shaft. Changed from 2 to 3 blade fixed prop and they both had the same prop effect (which I loved it to be honest; nice to have a stern thruster ).
Current boat has a saildrive and 3 blade fixed prop. You can hardly feel the prop effect.

 

[srm]

A previous boat had a two bladed prop, current boat three blade. Both with similar underwater profiles, keel hung rudder and prop in aperture, plus similar prop diameter. Also, as far as I can remember, similar prop walk. It was great for turning to stbd in little more than the boat's own length but forget about steering astern.

 

[sgr143]

Your best policy would be to learn to live with it and use it to your advantage.

If used "to advantage", as JohnAlison says, it can actually be quite helpful when mooring up or turning in tight spots.

When going astern, use the method of a large burst of throttle to get the boat moving and then knock it into neutral to give a balanced helm, and then engage gear when controlled movement is gained.

To me a while to cotton on to that... Obvious - when you see it.

 

[alan_d]

Generally speaking saildrives are better than shaft drives mostly because the props tend to be further away from the rudder so that any prop walk is reduced before it influences the rudder.

Might you be blurring the distinction between prop-walk and prop-wash? I have always understood prop-walk to be a force direct from the prop, nothing to do with the rudder.
I don't know if you are right about saildrives having less prop-walk effect than shaft drives but if so, might it not be because with a saildrive the prop is closer to the fore-and-aft centre of the boat so exerts a lesser turning moment?

 

[ruvane]

Thanks for all the input. Going to try the 2-bladed prop - don't think it can get much worse!

 

[johnalison]

Might you be blurring the distinction between prop-walk and prop-wash? I have always understood prop-walk to be a force direct from the prop, nothing to do with the rudder.
I don't know if you are right about saildrives having less prop-walk effect than shaft drives but if so, might it not be because with a saildrive the prop is closer to the fore-and-aft centre of the boat so exerts a lesser turning moment?

Also, the prop is deeper in the water and I presume the differential between top and bottom are less marked.

 

[Tranona]

Might you be blurring the distinction between prop-walk and prop-wash? I have always understood prop-walk to be a force direct from the prop, nothing to do with the rudder.
I don't know if you are right about saildrives having less prop-walk effect than shaft drives but if so, might it not be because with a saildrive the prop is closer to the fore-and-aft centre of the boat so exerts a lesser turning moment?

The 2 are connected. The closer the prop is to the rudder the greater the effect of propwalk if you try and correct. You are right about the fore and aft position and on many modern boats the drive is well forward but suspect on the OP's boat the drive is further aft and closer to the rudder than is usual now. A saildrive prop is also parallel to the waterline whereas a shaft drive is often as much as 10 degrees down, and even sometimes offset to the centreline.

 

[Tranona]

Thanks for all the input. Going to try the 2-bladed prop - don't think it can get much worse!

Think carefully and do the sums before you do that. A 2 blade is inherently less efficient when motoring than a 3 blade and if your engine power is marginal you may well find a drop in motoring performance. What engine do you have?

 

[Graham376]

We found effect of prop walk and no initial steering could be minimised by leaving a line on, engaging stern long enough to get water flow past the rudder and then casting off.

 

[V1701]

As well as bursts of throttle/neutral/steer it's a bit counter intuitive but also worth trying having the rudder half way (you can experiment with it) over rather than at "full lock", you might find that gives you some steerage - at "full lock" you're presenting a flatter surface to the water if that makes sense...

 

[Crazy-Diamond]

I had a Moody 30 with the original 2 bladed prop - I never had an issue with excessive prop walk - It went to SBD but not much

 

[LittleSister]

it's almost impossible to reverse to port.

You can go port or starboard if you get a long-keeler with the prop operating in a cut-out in the rudder. Which of the two ways it goes is always a surprise, mind!

And what is this 'going dead astern' of which you speak?

 

[Bobc]

Thanks for all the input. Going to try the 2-bladed prop - don't think it can get much worse!

I suspect that will give you even more propwalk relative to forward/backward drive.