would a three bladed prop give more speed

[johns]

i have a nicholson 30 with a volvo md1b it has a two bladed folding prop which looks origonal when motoring head on into heavy seas the boat was slowing to about 4 kts would a three bladed prop give more power

<hr width=100% size=1>

 

[claymore]

The short answer is yes in the conditions you describe. The disadvantage is that you would lose some speed when sailing as your folding prop will offer less resistance/cause less drag.
There's a lot to be said for making the conditions work to your advantage but obviously there comes the Sunday afternoon when you are downwind of your objective and have to plug into wind and sea to get back home
So simple really - which do you want? For me - 4 knots is OK, just set off a bit sooner - all boats slow when pounding into wind/seas. I'm not sure that a three bladed prop is going to offer you much above a knot in these conditions - stick with the folder!!

<hr width=100% size=1>regards
Claymore
/forums/images/icons/smile.gif

 

[Robin]

Almost certainly. Folding props are inefficient anyway and 3 blades are usually better than 2 in headwind/sea conditions and in reverse. Many years ago I had an Elizabethan 30 with a fixed 3 bladed prop, a friend had the same boat & engine (10hp Bukh) but with a 2 bladed prop. We could go backwards much better and in a headwind/sea we could keep going when his was cavitating & losing drive. In calm conditions the performance of both was similar. Under sail the extra drag of the 3 blade was not apparent, but the props were in an aperture in the skeg so unless the 2 blader was lined up vertically the blade areas exposed were probably the same.

Have you considered a self pitching/feathering prop like the Brunton? We have a 3 bladed Brunton Autoprop on our current boat which works very well, bit pricey though.



<hr width=100% size=1>

 

[charles_reed]

It certainly would give more power whilst motoring, far better control in reverse and a useful degree of propwalk for berthing.

You would lose some speed under sail, about 5 - 10%.

You have several alternative inprovements:-

1. Fit a 2-bladed fixed prop instead of the folding prop - you'll be amazed at how much more controllable the boat is in a marina. A properly chosen one will give little more drag than your folding prop and thye cost will be about £100. Sell the folding prop to some performance-obsessed muggins to cover the cost.
2. Replace your folding prop with a 3-bladed one - you'll certainly notice the added drag whilst sailing, but response to forward/reverse will be best. Coat about £300.
3. Fit a Brunton Autoprop - the most expensive but outstandingly the best solution giving you the ability to motorsail meaningfully at tickover, reverse as well as you can go forwards equally well, give less drag than the folding prop with about twice the effectiveness of the fixed props.

Having tried all three on the same boat, the least desirable is that which you have currently.

<hr width=100% size=1>

 

[vyv_cox]

I agree with Charles wholeheartedly. My Autoprop performs extremely well as he describes. One extra point: the Autoprop is a lot cheaper bought in Holland. No doubt there are hurdles put in place by the UK suppliers to prevent you from taking advantage of this, but these can be overcome.

<hr width=100% size=1>

 

[Evadne]

I too have been considering replacing my (fixed) 2-bladed with a 3-bladed for some time, and the consensus of other owners is that I should.
a) you get more usable power (especially in less than flat seas)
b) the prop walk in reverse isn't noticably increased - useful to know on a long-keeler.
It's just a matter of getting around to it, I'm generally happy with 3.5kts cruising speed under power, and if the seas is less than flat, it's quicker to sail.
Most folk reckon the extra drag is only noticable early in the season, if you're racing, and if you're in the habit of scrubbing the hull at least once per season after launching.

<hr width=100% size=1>

 

[Oldhand]

It would have to be a pretty small 3 bladed prop in order not to overload the MD1b. Would the reduced diameter likely to be necessary have too much blade area shielded by boat structure? Just somthing to consider.

<hr width=100% size=1>

 

[max_power]

A difficult decision that probably has no single right answer. But the Brunton , as our fellow shipmates have suggested seems a good option.

One thing that I think is worth mentioning is the addition of sail power when motoring. Apart from the odd occasion when in marina’s and narrow channels, I rarely have the engine going without at least one sail up, and not always the main.

Apart from anything else, I reckon, on average you save around 25% on fuel, have a much better ride in choppy weather, and make better time.

I have a medium long keel with deadwood that I can hide a two blade behind. In light weather I often go past much lighter yachts . Does your Nick have any deadwood ?

In a flat calm the best I can do is around 4 knots with tons of revs. If you have a small aperture like I have , you are always going to be struggling whatever prop you choose owing to the turbulence. MOdern hulls can probably make much better use of recent prop technology.


Best of luck with whatever you choose.





<hr width=100% size=1>

 

[charles_reed]

It is my impression

That most things are cheaper in continental Europe than in the UK - excepting PCs and parts for PCs.



<hr width=100% size=1>