Yamaha Propellor

robanfield

New member
Joined
24 Jun 2010
Messages
22
Hi To All,
Can anybody help me with the correct prop for Yamaha f50 4stroke on Shetland Suntrip 535, 2 / 3 people fishing very heavy battery stored in bow. Honda 5hp auxilliary engine.
I have emailed Shetland but no joy.
Many thanks to anybody who has the time to reply.
Regards,Rob
 

robanfield

New member
Joined
24 Jun 2010
Messages
22
Hi wipeout, No issues just a new engine and my other Yamaha f50 carb model was never taken above about 4300 revs, I am not interested in speed, more economy but I felt that engine was close to wot.
Company has asked which prop I req, Yamaha tech has told me to ask Shetland, which I have done but no reply.
Thanks,Rob
 

Spi D

...
Joined
25 Jul 2011
Messages
2,253
Location
Denmark
The right way to go about this is by power/weight ratio, then factor in gear ratio and the recommended rpm range at wot.

Rule of thumb is, that one inch less in pitch will give 200 rpm more on the engine (and vice versa).
If your old f50 had a prop pitch of say 15" and reached 4000 rpm you'd be looking for 5" less to reach 5000 rpm. Everything else alike.

The best possible economy (and engine longevity) is reached when the recommended rpm range can be reached (as this indicates a correct load on the engine).
 

wipe_out

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23 Feb 2013
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1,396
Location
Bournemouth
Hi wipeout, No issues just a new engine and my other Yamaha f50 carb model was never taken above about 4300 revs, I am not interested in speed, more economy but I felt that engine was close to wot.
Company has asked which prop I req, Yamaha tech has told me to ask Shetland, which I have done but no reply.
Thanks,Rob

The new engine you are looking at has a WOT range of 5000-6000 rpm and specs say 50hp @ 5500rpm..

So if you were only getting 4300rpm WOT on the old engine/prop combination it sounds like you would be very over proped using the same pitch which suggests that you want to go down in pitch quite a bit to get up to around 5500rpm under normal load conditions.. Just how much is really hard to say and I went through 3 props on my boat before I got it right..

Unfortunately unless you can find a really nice shop they won't let you return the prop after your have tested it if it's the wrong one..

Sorry I can't me much more help than that..
 

robanfield

New member
Joined
24 Jun 2010
Messages
22
Thanks again wipeout and the others who have helped.
The prop on my existing engine is 11 1/8 x 13 - G.
I dont know if this would help anybody pass a second opinion.
Thanks again all.
 

dan from bhg

Member
Joined
6 Nov 2014
Messages
49
Location
Lymington
Thanks again wipeout and the others who have helped.
The prop on my existing engine is 11 1/8 x 13 - G.
I dont know if this would help anybody pass a second opinion.
Thanks again all.

It doesn't sound too far wrong in my opinion. I wouldn't have thought it would need any lower than an 11 really. Is the control cable set up correctly? Is it pulling WOT? Or is the boat trimmed right?
 
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