Max Prop Easy correct pitch?
Hello all. I own Zeevogel, a Swan 1971 43' hull 49 out of Vancouver, Canada and I've just bought a new Max Prop Easy 18". I have a Perkins 4-108 with the Borg Warner transmission with a 2:1 ratio - has anyone had good experience with setting the correct pitch to gain hull speed (approx. 7.4 kts) between 2200-2400 RPM. Perkins told me that's the best RPM range to run that engine at and Max Prop (PYI Inc) has recommended a 11" pitch (18 degree set screw on the Easy prop)- the next degree/pitch up from there is 12.4" which is a 22 degree set screw.
The new Easy props can be set underwater which I could do but I would like to get it right if possible before I drop her back into the water. Wisdom welcomed.

Dear Don,

it is true that you can set the pitch underwater, in theory, as you do not have to completely dismantle the prop as in the old models, but consider that you have two screws, one of which is very small, and it is unlikely you can get them out without letting them drop as you are swimming and not completely still, so, absolutely better you find the right pitch before going back into the water.

I am sure Lars will give you the perfect answer!

Fair winds

matteo (47/069 Vanessa)

Dear Don
Some more information would be appreciated for calculations.
How many blades, and what is the exact diameter? One inch is too coarse.
The records suggest that the reduction gear was AS3-70CR with reduction ratio 2.10 to 1, pls confirm.
Kind regards
Lars

Dear Don Some more information would be appreciated for calculations. How many blades, and what is the exact diameter? One inch is too coarse. The records suggest that the reduction gear was AS3-70CR with reduction ratio 2.10 to 1, pls confirm. Kind regards Lars

Lars
The prop is a Max Prop Easy 3 blade 18"
The engine is a Perkins 4-108 with the Borg Warner trans - I do not have any records of the ratio for that trans but what I can find online is 1.19:1 but I'm not sure that's correct at all. The boat has run with a Max Prop 2 blade 18" for the last 20+ years and I cruise at approx. 2600/2700 RPM and push about 6 knots on a calm day - between 4.5 and 5.5 most of the time. My Perkins supplier in Vancouver was correct that the engine is happy around 2200-2400 RPM so that's my goal to get that RPM range and get close to hull speed. The engine has been completely overhauled and runs beautifully and there's no issue in getting full RPM range.
My concern with a higher pitch is what speeds would I get with low RPMs i.e. would I have to much trust for docking etc.
Regarding diving to change the pitch - my first career when I was young and crazy was a commercial diver so I'm very good with things underwater so in the worst case I could change things in the water...but then again I'm older now :)

PYI's pitch chart

Dear Don
Thank you for the information.
A pitch recommendation can not be given without reliable data.
For sailing yachts the 4-108 rating is 37 hp/3000 rpm, this means that at 2200 rpm 15 hp is used, and at 2400 rpm 19 hp.
19 hp produces about 7 knots, and you aimed at 7.4, for this higher rpms are required, about 2700, using 27 hp.
This is the same rpm you used before for cruising at lower speeds, it is obvious that the 2-bladed Max-Prop had too little pitch.
The minimum speed is related to the pitch as you assume.
It is suggested that you read the Forum thread dated 8 May 2010 about propellers.
Kind regards
Lars

Dear Don
Any progress with the pitch question?
It is also possible to evaluate the situation based on measured rpm/speed numbers, the full throttle numbers are of particular interest.
Kind regards
Lars

Dear Don Any progress with the pitch question? It is also possible to evaluate the situation based on measured rpm/speed numbers, the full throttle numbers are of particular interest. Kind regards Lars

Lars
Sorry to get back so late on this. I've had great success with 11" pitch with the 3 Bladed Max Prop Easy. I'm getting 6.5kts at 2200RPM and just over 7 kts at 2400 RPM. At 2600 I'm getting full hull speed even in a 1.5 current. It's a very smooth prop / no vibrations overall and with my new Isoflex engine mounts I'm very happy and would recommend those mounts to anyone with a Perkins.

Thanks for your comments and help.
Cheers

Dear Don
Good to hear that the performance is per expectations.
The reduction ratio appears to be the original 2.10:1.
The newer Swans have a speed-consumption-range-diagram in their Owner's Manual. If you would like to have such a diagram made also for Zeevogel six rpm/speed readings are required, about equally spaced, one of them full throttle.
Kind regards
Lars