prop sizes
Submitted by petermac on Thu, 2014-11-27 20:32
how do prop sizes work , my 80 hp yamy revs out to nearly 7000rpm with a 13x17 prop on it I was advised to go to a 13x19 prop I haven't put the new prop on yet but it is a physically smaller prop than than the 13x17 prop how does that work?????
z00m
Posts: 1086
Date Joined: 10/05/14
13 describes the diameter so
13 describes the diameter so that should be consistent.
The pitch (17 or 19 in your case) describes how many inches the prop screws through the water per revolution (think of how far you can screw a screw per revolution to get the idea)
If your 13 is smaller than your 13 it could be due to some rounding of the figures 12.8 is still considered a 13 etc.
How different are the diameters?
petermac
Posts: 2946
Date Joined: 03/03/10
the 19 is
the 19 is 10mm smaller than the 17 when measuring blade to blade tip
Marineboy
Posts: 842
Date Joined: 14/03/14
Prop size
down in kardinya there is a propellor mob max ogrady the guy there Steve was very good and honest with me.
My spots are so secret even the fish don't know about them !
D_DOUSH
Posts: 497
Date Joined: 23/12/07
I think you will find that
I think you will find that is because the pitch increased there is more curve in your blades! The surface area of each blade should be the same
petermac
Posts: 2946
Date Joined: 03/03/10
that sounds right
that sounds right the blade sizes look the same but the diameter is smaller on the 19
sarcasm0
Posts: 1396
Date Joined: 25/06/09
a few things
The above about diametre and pitch are correct, but a rule of thumb is that every +-1" in pitch is approx +-200rpm. So to get your prop back to 5500-5800rpmWOT Loaded (manufacture recommended) by pitch alone you would need to be at a 13 x 24 which is unavailable because the angle of attack of the blade is too steep for water as a medium.
See here for props for F80 yammies : http://yamahaoutboards.com/sites/default/files/pdfs/Four-Stroke-F115-T50.pdf
Guide to selecting Yammie props: http://yamahaoutboards.com/propellers/picking-a-propeller
Edit: the guide above says +-1" = +-50-100rpm eg a 13x31!
Pics? Motor to high? Prop bush spun?
Bryan
Vinesh87
Posts: 2751
Date Joined: 02/04/11
7000RPM. Damn that's high. I
7000RPM. Damn that's high. I aussume its running the stock yammy prop ? Like Bryan said maybe there is something wrong ? Dodgy tacko ?
Deleted
Posts: 6265
Date Joined: 26/04/14
7000rpm yewwww that bad boy
7000rpm yewwww that bad boy is hurting if that is true?
Marineboy
Posts: 842
Date Joined: 14/03/14
7000 rpm
i thought yammy governed their motors to a max of about 6300-6400rpm
i would check dodgy tacho too.
My spots are so secret even the fish don't know about them !