Seeking advicable: Prop pitch for 41-17
I'm looking for help with prop problem.
I have replaced my Perkins with Yanmar 4Jh4E. I would appreciate your tips on way forward with the propeller.

Current propeller:
Maxprop,
16inch
2 blade

Legth of boat water line: 9,22m
Boat weight: 10800kg
beam: 3,64m
draft: 2,1m

engine:
Yanmar 4JH4E, 55hp / 3000rpm

Gear box:
KM35P
reduction: 2.36

Dear 41-17
Thank you for stating the technical particulars, this enables an analysis of the situation.
Regrettably, even with the Max-Prop set to the maximum pitch 30 degrees it absorbs only about 70% of the engine power.
The recommendation is to change to a 3-bladed propeller with the maximum diameter that can be fitted. It is likely to be over 17" with some clearance left.
If the shaft diameter is the original 30 mm the safety factor in the shaft will be lower than usual with the changed propeller, but assuming that you seldom use full power this should not be a problem.
Kind regards
Lars

hello 41-17
i have same situation.
changing old perkins out of a swan 411-02
new engine is a yanmar 4jh5e with same gearbox, but 2,61 ratio.

would be nice, to get in touch with you, about engine bed and other questions.
i have the 2 blade folding prop.
what you did with your shaft?
my is 38,2 mm diameter.
want to reduce to 30mm and using also a flex coupling R&D Flexible Coupling 910-002 for 4" Yanmar Couplings
how do you did the job?

regards, stefan

engine room

Hi Lars

Thank you very much for your advice. This really helps me. :)


Regards,
V-V

Stefan,

I wish I could giive details on that matter. The job was done by guys in Caribbean (St Vincent), and also my boat is still in those waters.

I'll look through what kind of part list I would have from that, but unfortunately not much photos.
Could you be more specific about your question and also if you need specific photos? I could ask if my friend would be able to take some photos while he is there.

hi V-V,
thanks for reply
i'm on grenada, secret harbour.

pictures would be nice, but part list too.
so i dont forget to buy this.
i will do this job by my self.

whow, nice forum ;-)

regards, stefan

V-V
If you need help with choosing a propeller pls let me know


Stefan
Pls note that the engine installations on the 41 and the 411 are not identical. Even if it was the same Perkins engine the 41 had the reduction ratio 2.1:1 and a 17" propeller, while the 41 had 2.91:1 and a 21" propeller.
Also now you have a bigger reduction ratio, and together with the bigger propeller this requires the shaft diameter to be bigger.
If you have the original 21" folding propeller it does not fit the new engine and reduction, you will be even worse off than 41-17.
Pls check if the propeller diameter, pitch, and handing are stamped on the hub.

Kind regards
Lars

HI Lars

I would really be delighted about having help from you in selecting right kind of prop.
I have my eyes set on feathering props. Right now I don't have exact measurements on the clearing for the prop. If I recall right, 17inch is the biggest one can fit?
I have been offered 17inch, 4blade Featherstream prop. Any knowledge of those?

Dear V-V
18" diameter should fit the Swan 41 while leaving about 40 mm clearance against the hull, and this can be increased slightly by moving the propeller aft so there is 30 mm distance between the hub and the strut. One shaft diameter is the maximum recommended distance here.

You asked about 4 blades, therefore I did some calculations for your case to demonstrate the differences caused by changing the number of blades while retaining the same diameter. Speed range is between 6 and 7 knots.
The diagram shows the difference in horsepower absorbed by propellers with varying number of blades producing the same thrust. 3 blades is used as reference here.
It can be seen that up to 6.5 knots the 2-bladed uses the least power, but suddenly the power requirement goes up, and this is caused by the propeller becoming overloaded due to lack of blade area.
For good performance over 6.5 knots 3 blades are required, and near maximum speed 4 blades give the best performance, but on the other hand consumes more power in the normal cruising speed range.
The final choice can be based on your priorities.

Recommended propeller reading can be found on the Forum thread 08 May 2010
Kind regards
Lars

Dear V-V
You asked about Featherstream, here some comments.
It appears this propeller was originally developed and patented in Sweden in 1974 by Järnförädling Ab. Later the manufacture moved to Germany under the name Boy-Prop, and now there is a British manufacturer and the present name. Originally it was all bronze, but now Darglow make them with stainless blades, and has added an external pitch adjuster.
The hub is rather big, and even if this increases resistance there is likely to be plenty of strength in the gears. There is a zinc anode on the hub for protecting the bronze in contact with the stainless shaft and blades.
Have you decided on the number of blades? For calculation of the pitch angle it would be helpful to get the corresponding Blade Area Ratio from the manufacturer.
As your reduction gear has different ratios in forward and reverse the recommendation is to set the reverse pitch so the performance is the same as in forward gear, would this be acceptable?
Kind regards
Lars

HI Lars

Thank you for the very good explanation on the propeller blade difference. That table graph is very informative.
Please find enclosed the data what the prop supplie provided on Featherstream.
They said that 17" with 4 blades would be close to boat's requirements, but not ideal. That is the reason why I need to look into what size of prop could be fitted.

My other options would be kiwiprop, Maxprop or Autoprop. I would be very delighted about views on which way to go.

V-V

Lars,

41-017 is starting up circumnavigation, so it gives a picture on what kind of waters she is facing. Currently 41-017 is located in Caribbean waters.

Dear V-V
Can agree with Featherstream, a bigger diameter would provide better performance in your case, but can not be fitted without changes to the shaft installation. Suggest you check if 18" can be accommodated.
Referring to propeller comparisons it is suggested that you study this test report
http://old.segeln-magazin.de/SVABerichtNr.3492.pdf
and particularly the summary in Table 6.
If you have difficulty with the language pls let me know.
Kind regards
Lars

Dear V-V
You asked about Kiwiprop, Max-Prop and Autoprop.
The first two have flat blades like Featherstream, and behave in the same way. Autoprop is very different and unlike any other.
The mentioned SVA report compares Max-Prop and Autoprop, both have 2 blades, here a summary with comments.
Kind regards
Lars

Bollard pull forward:
Max-Prop 2187 rpm, pull 1632 N, 10.5 kW. next lowest pull after Autoprop
Autoprop 3200 rpm, pull 1546 N, 6.5 kW. Allows full engine rpm, but uses only half of the power, the lowest pull of all the tested propellers

Bollard pull in reverse:
Max-Prop 2491 rpm, pull 1847 N, 12.2 kW. Smaller pitch than in fwd as rpm higher?
Autoprop 3200 rpm, pull 1599 N, 6.7 kW. Allows full engine rpm, but uses only half of the power, low pull, but some others are even lower in reverse

Cruising speed 6.4 knots, required thrust 548 N:
Max-Prop 2040 rpm, used 4.0 kW,
Autoprop 1670 rpm, used 3.0 kW (best propeller used 2.6 kW)

Full forward 7.6 knots, required thrust 1630 N:
Max-Prop 2950 rpm, used 13.3 kW.
Autoprop 2880 rpm, used 12.7 kW (best propeller used 10.6 kW)

Propeller resistance at 6 knots under sail:
Max-Prop 2.0 N
Autoprop 20.0 N