2 or 3 bladed prop

[thegasmannick]

just asking to see if people prefer 2 or 3 bladed prop as im about to remove a 2 bladed prop and fitting a 3 bladed prop as performance was poor on a 2 bladed prop i know ill loose a little on sailing performance but not alot and if under engine want a better engine performance for marina`s and no wind condition`s

comment`s please

 

[langstonelayabout]

3 blades = a real drag.

If you want motoring and sailing performance, fit a folding or feathering propeller. In the past I've fitted Flexofold and Gori props, but my favourite was the Flexofold.

I'm sure there will be others along soon with their favourites.

 

[lw395]

Why can you not get OK performance with a two blade prop?
A fixed 3 blade prop defines your boat as one where people don't really care about sailing.

 

[oldharry]

Why can you not get OK performance with a two blade prop?
A fixed 3 blade prop defines your boat as one where people don't really care about sailing.

I replaced a 2 blade with a 3 blade after it was damaged. It resulted in around 25% fuel saving, but made no noticeable difference under sail. I don't race so that extra ,1 of a knot that everyone tells me I must have lost makes no difference. My boat is quite sensitive to extra drag like a bit of fouling and loses speed quite quickly. The 2 props were correctly matched to the boat when checked by different calculators, and I had expected a drop in sailing speed, as that is conventional wisdom, The gain in extra thrust under power in adverse conditions is noticeable though from the bigger blade area. So for me it was a win win change.

 

[vyv_cox]

Why can you not get OK performance with a two blade prop?
A fixed 3 blade prop defines your boat as one where people don't really care about sailing.

Yes. My 2-blade Autoprop has given excellent motoring performance fo years and of course feathers when sailing. At the time I bought it I was advised that 2 blades would be perfectly adequate and so it has proved.

 

[NormanS]

Many years ago I built a Folkboat, and with a Volvo MD1, fitted a two bladed prop. I marked the shaft so that when sailing, the propeller blades were stopped in line with the stern post. Speed under engine was fine when it was flat calm, but trying to motor against any wind and sea was pretty hopeless. I changed to a three blade prop, and the difference under power was quite dramatic. It probably cost me a fraction of a knot when sailing. Nowadays, I would be looking at some kind of feathering or folding prop. On a different (bigger) boat I now have a Bruntons Autoprop, which is excellent, but very expensive.

 

[[70521]]

My current 2 bladed prop pushes the boat along at 6+ knots. Looking forward to fitting the flexofold next summer to see if I get a bit of peace and quiet.

 

[Tranona]

just asking to see if people prefer 2 or 3 bladed prop as im about to remove a 2 bladed prop and fitting a 3 bladed prop as performance was poor on a 2 bladed prop i know ill loose a little on sailing performance but not alot and if under engine want a better engine performance for marina`s and no wind condition`s

comment`s please

In principle you are correct although not all 2 blade props are the same as some have very small blade area. The loss of sailing speed between the two is mostly overstated for most cruising boats - and on balance the improvement in motoring performance is often worth it. Normally a 3 blade is smaller diameter than a 2 blade and this can be a big advantage in some boats where diameter is constrained by clearance to the hull.

So it is not a simple good/bad decision. You need to have the details of the boat and engine/gearbox then feed them into a propeller calculation programme which will give you the optimum size for 2 or 3 blade and expected speed. However it won't reveal the clear advantage a 3 blade gives in adverse conditions or stopping power. Nor, of course will it give you the marginal loss in sailing speed because there are so many other variables that influence it.

 

[Laysula]

I swopped my 2 bladed fixed prop for a second had Kiwi prop I then had it serviced and set up for my boat total cost about £450. Well pleased. It sails better, motors better and manouvres better in Marinas.

 

[PCUK]

I went from a two blade flex-o-fold to a three blade Volvo folder and achieved a 25% increase in speed for the same revs.

 

[jwilson]

When I bought our present 35 ft Jeanneau with a 27 hp Yanmar and the standard fixed two-bladed fixed prop I expected it to lack thrust, having had three-bladed on previous boat. In fact it works very well indeed. With clean bottom and prop a genuine 7.8 to 8 knots at full throttle, and gets up to that from stationary in maybe five/seven seconds. If the prop gets damaged I may replace it with a feathering one, but I'm not rushing to do that.

 

[Daydream believer]

When I bought my 2 bladed Brunton Autoprop for my saildrive, Bruntons did give me the option of 2 or 3 blade. When I queried this, It was suggested that 3 blades gives a smoother run than a 2 blade. Cannot say that I have noticed excessive vibration, but only ever having had 2 blade on the boat I could not comment.( other than it is a poor prop for motoring in choppy, or rough, sea)

 

[dom]

When I bought my 2 bladed Brunton Autoprop for my saildrive, Bruntons did give me the option of 2 or 3 blade. When I queried this, It was suggested that 3 blades gives a smoother run than a 2 blade. Cannot say that I have noticed excessive vibration, but only ever having had 2 blade on the boat I could not comment.( other than it is a poor prop for motoring in choppy, or rough, sea)

I have a 3-blade folding prop; excellent performance up to the same sea state limits you suggest when motoring into the waves. I'm not sure modern hulls are great at that to be honest motoring to windward in big seas, much better sailing.

 

[thegasmannick]

thought this might cause a debate but i just had to get peoples views as i was in the view that a 3bladed prop is better to against tide and in rough sea`s and close work in marina`s as well as it bite`s better think ill go with 3 bladed and if it fail`s to perform i will inform forum of my finding`s

thank`s for all replie`s all very helpful and informative

 

[Daydream believer]

I have a 3-blade folding prop; excellent performance up to the same sea state limits you suggest when motoring into the waves. I'm not sure modern hulls are great at that to be honest motoring to windward in big seas, much better sailing.

My old fixed blade prop was considerably better than the auto prop for general motoring & in port maneuvering & fuel consumption. The autoprop is better for less drag & for motor sailing