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S&S Swan General - 4 Blade feathering prop for a Swan 47
14 June 2019 - 07:03
#1
Join Date: 14 June 2019
Posts: 5

4 Blade feathering prop for a Swan 47

Hello there Swanners,

I am currently researching to replace the original 20" 2 blade feathering Max Prop with a 4 blade feathering prop for my Swan 47.  

Has anyone already done this?  I am very keen to know other owners experiences, what props they settled on and what the improvements were.  

Currently, in flat water Crackerjack will nicely cruise at 7.2 knots (on the GPS) at about 2,200rpm with the Perkins 4154 on a 2.97:1 borg warner transmission. 

However, driving into a breeze with a good Port Phillip steep chop, it will knock her back to between 4 and 5 knots.  Its not the engine, as its not even noticing the work, but I expect that the blade surface area is a bit light on for the 16 tonnes it has to drive.  

I am considering a 4 blade Variprop, they suggest a 22 inch diameter.  I was also considering a 4 blade kiwi prop, again they suggest 22", but I am not convinced that the kiwi prop would be the best option.  

Any thoughts on the above would be very greatly welcomed.  

Thanks,

Philip.

14 June 2019 - 09:26
#2
Join Date: 29 January 2007
Posts: 728

Dear Philip,

Lars is very experienced on this matter, and will give you a proper answer, anyway I can tell you I had a 21" 4B Max Prop on 47/069 Vanessa and I am trying a new Bruntons Autoprop 3B, H6-534, 21", which I have just installed, I am going to test  this one over the next week end.

My engine is a (too powerful for my taste, but the one I found already installed when I bought the boat) Yanmar 4JH3 HTE, with a Kanzaki KM4A ratio 2,63.

With a Max Prop, in flat water, no wind, performances are:

@2,000 RPM, 6,5 kn
@2,200 RPM, 7 kn
@2,400 RPM,  7,4 kn
@2,600 RPM, 7,6 kn
@2,800 RPM, 7,8 kn
@3,000 RPM, 8 kn
@3,200 RPM, 8 kn

The stern starts to sink @ 2,200/2,300. I will post comments concerning the Bruntons after the week end.

Fair winds

matteo (47/069 Vanessa)

14 June 2019 - 11:34
#3
Join Date: 14 June 2019
Posts: 5

Thanks for that Matteo,

That's great to know, how did it fair in rough water, did the previous prop keep her pushing through in big waves?

Yes, anything past 7.5knots is destroyer mode and the back end is right under, even over the exhaust outlet on crackerjack.   

I think most of the props will get to just past waterline length quite reasonably, but keeping the boat at speed in adverse conditions is probably the telling part.  

Looking forward to any comments on the Bruntons.  

Kind Regards,

Philip.  

14 June 2019 - 12:14
#4
Join Date: 02 January 2008
Posts: 1338

Dear Philip

Your conclusion is correct, with 20" and 2 blades there is too little blade area when the going gets heavy. The 2-blade prop works well when cruising at 2200 rpm, and then absorbs about 20 hp.
There is a good thread on propellers here
 
4 blades and 22" have been suggested, calculation shows that 3 blades and 21" would provide practically the same performance at full power, and be slightly better for cruising. This is therefore the recommendation here, and would also reduce the cost a little.
Further questions?
 
Matteo, your engine has a nominal max rpm of 3800, and Yanmar would not approve the present pitch setting limiting the rpm to 3200. But it is assumed there is no engine warranty any more, and that you normally use around 2200 rpm, then you can use this pitch setting.
If you ever use full throttle keep an eye on the engine cooling water temperature, it may rise above the allowed limit.
Kind regards
Lars

14 June 2019 - 14:28
#5
Join Date: 29 January 2007
Posts: 728

Dear Lars,

you are correct, my engine is 19 years old so warranty expired.

I am usually cruising at 2,2400/2,600 RPM, I hope to be able to cruise at 2,000/2,200 with the new Bruntons, in order to keep consumption and noise at a lower level, anyway I am going to post result of my test on Monday!

Fair winds!

matteo (47/069 Vanessa)

17 June 2019 - 11:43
#6
Join Date: 14 June 2019
Posts: 5

Hi Lars,

 

Thanks for that, greatly appreciated.  

The main reason for the change in Prop is to set the boat up for having to motor into wind and waves, which is fairly common in Melbourne.  We get a regular sea breeze from the SW, 20-30 knots and a good fetch of 40km, so by the time waves are getting to the top of the bay, which is also fairly shallow, we typically have 2m short and steep waves, which are probably the worst wave period to punch into and the boat hasn't got the run between waves to get back some speed.  

Does this scenario change your recommendation?  

17 June 2019 - 14:59
#7
Join Date: 02 January 2008
Posts: 1338

Dear Philip

Thank you for describing the conditions of most concern.
Assuming a speed of 5 knots in a strong headwind, and 75% engine output (max continuous achieved at around 2600 rpm):
1- changing from the present 20" 2-blade to 21" 3-blade will increase the propeller thrust by 21%. 
2- changing instead to 21" 4-blade increases thrust from 21 to 22%, 
3- changing to 4-blade 22" increases thrust from 21 to 28%.
 
Is this sufficient information for making a decision?
Kind regards
Lars

17 June 2019 - 15:01
#8
Join Date: 29 January 2007
Posts: 728

Dear Philip,

in the meantime I tested a the 3B Bruntons. I am not positive.

The speed is not exactly as it was supposed to be (similar to the 4B MaxProp one), but what does not make me happy at all is it is very noisy.

In reverse it is a very good propeller and does not vibrate at all.

...but I usually use the boat in fwd gear! Up to 1,800 RPM, no noise/vibrations, above 1,800 RPM it start to vibrate (quite a lot) and be noisy. I called Bruntons and they assured me the blades have been properly calibrated, so this is not the problem and a technician from Bruntons is coming omnboard next week end , but I will get back my Max Prop, maybe I will swap it with a 3B next season!

More and detailed info after next week end!

Fair winds

matteo (47/069 Vanessa)

17 June 2019 - 20:20
#9
Join Date: 01 March 2007
Posts: 123

Dear Philip,

i experimented with new propellers when I put a new engine, gearbox in Sarabande in 2010. I was replacing a 3 blade max prop and had heard good reviews about Brunton propellers and had one installed. It was not a success. It pulled the boat to port, sucked the stern into the water and was too clumsy and aggressive. I changed back to a new 3 blade max prop and have not looked back !

Rob

Sarabande 47/029

18 June 2019 - 05:53
#10
Join Date: 29 January 2007
Posts: 728

Dear Rob,

is it a 21" and do yo remember the setted pitch?

Fair winds!

matteo (47/069 Vanessa)

18 June 2019 - 07:08
#11
Join Date: 14 June 2019
Posts: 5

Hi Lars,

Thats incredibly useful and greatly appreciated!!

Thanks very much.  

18 June 2019 - 07:15
#12
Join Date: 14 June 2019
Posts: 5

Thats great information Rob, very useful.  This is all helping to narrow down the field of choice.  

Does your current prop provide you with the required amount of drive in a swell?  What engine and hp is it driven by?  

18 June 2019 - 09:25
#13
Join Date: 01 March 2007
Posts: 123

Thats great information Rob, very useful.  This is all helping to narrow down the field of choice.  

Does your current prop provide you with the required amount of drive in a swell?  What engine and hp is it driven by?  

Dear Philip,

I have sent an email to you with some notes from trialling a Bruntons Varifold in 2011.

We installed the Yanmar 75 in 2011. At 2200 in flat sea she will motor at about 6.6 -6.9kts, my preference is 2000 in flat conditions. Max motoring speed is about 7.4, but I rarely go there.

Matteo, regret no set up info as Im onboard and away from home, but it is 21" 3 blade.

Best

Rob

Sarabande 47/029

18 June 2019 - 09:36
#14
Join Date: 29 January 2007
Posts: 728

Thanks a lot dear Rob!

Enjoy Sarabande and Greece!!!

Fair winds

matteo (47/069 Vanessa)

18 June 2019 - 10:26
#15
Join Date: 02 January 2008
Posts: 1338

PS

Philip
I also checked the thrust with 22" diameter and 3 blades at 5 knots, it increases nearly as much as with 4 blades, to almost 28%. Because your engine power is rather modest, 4 blades bring only a minor increase.
 
Matteo
The vibration and noise problem is likely to be caused by the blades swinging forward and coming too close to the shaft strut or the hull. 
 
Referring to your wish to cruise at 7.5 knots/2100 rpm, the 4-blade Max-Prop should be set to 24 degrees for this. The max achievable rpm will then drop further from 3200. Full throttle must be avoided with this pitch setting, as pointed out above.
 
Kind regards
Lars

18 June 2019 - 10:30
#16
Join Date: 29 January 2007
Posts: 728

Dear Lars,

attached is a pic while they were installing it!

Fair winds

matteo (47/069 Vanessa)

06 July 2019 - 07:07
#17
Join Date: 29 January 2007
Posts: 728

Dear Philip and Friends,

after a non satisfactory test with the Brunton, I decided to overhaul my “old” 4B 21” MaxProp and install it back on Vanessa, which I will do next week. As it was in the factory to be overhauled I decided to slightly modify the pitch, which is now c. 19,35 degrees. That, in theory, should give me about 100/150 more RPM at full throttle and allow the engine to be a bit less “charged”, in order to decrease its smocking (difficult task with a Yanmar...!).

I am going to post test results after July 14th.

Wish you all a good sailing week end!

Fair winds

matteo (47/069 Vanessa)

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