Outboard Props

Hurricane

Hurricane

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Recently, JFM suggested that I should try changing the prop on my Waker Bay / Yahama 40 to give a little more power for water skiing.

I think he suggested going down a couple of sizes.
The current prop is 11 1/8 x 13 G
I assume that the 11 1/8 is the shaft size, and the 13 is the pitch - not sure what the G stands for.
So, I think I would be looking for 11 1/8 x 11 G

Does that make sense?

If so - any good places to buy them?
 
No...!

USUALLY the prop size only gives 2 numbers - in your case I would guess at the 8 x 13 bit (8" dia x 13" pitch), dunno about G.

Could be 11 1/8" dia I suppose, but unusual to have the 1/8" bit on the end... Can you measure it and see if its 8" dia or 11 1/8" dia?

Also depends on what he means by going down a couple of sizes - is this pitch, dia or both?

Thought to ask JFM? ;)
 
11 1/8 is the prop diameter and 13 is the pitch. To improve acceleration decrease the pitch to an 11 or 12, but it will reduce top speed and possibly allow the engine to over rev.

IMHO I would stay with the same pitch and prop size but increase number of blades to 4, this should give more ' grip' and give a better pull out of the water for a skier.
 
Sorry - by 11 1/8 - I mean 11 and one eighth - I assume thats 11 1/8"

So, thanks for the above link
It quite clearly shows the prop that I already have.

Where do I get either a smaller pitch or a 4 bladed prop?
 
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Yup as others have said your current prop is 11.125 inch dia, 13inch pitch. Dunno what the G means but no worries. What I meant was reduce pitch to 11 inch. This a bit like dropping from 5th to 4th gear in car - slightly more force but slightly less top speed. Top speed is of course hardly any problem with the WB3.4 and Yam 40 because it is mentally fast, so you can afford to sacrifice a bit. The lower pitch however will help because when pulling a skier you cannot get the engine into its high power band with the 13inch prop. These 4 strokes just don't develop the same power low down the rev range as 2 strokes.

As these props are so cheap I would just buy an original from a Yam dealer
 
landlockedpirate said:
11 1/8 is the prop diameter and 13 is the pitch. To improve acceleration decrease the pitch to an 11 or 12, but it will reduce top speed and possibly allow the engine to over rev.

IMHO I would stay with the same pitch and prop size but increase number of blades to 4, this should give more ' grip' and give a better pull out of the water for a skier.
Click to expand...

Mark
I had the same boat/motor as Hurricane so know it well. It's not a lack of grip that's the problem. It's that the drag of the not-yet-skiing skier means the engine never gets above 2500rpm so never develops more than 20hp or so (4 strokes have less torque at low rpm than 2 strokes) and so cannot pull an inexperienced skier up onto the plane (or at least it struggles hard and it takes a while). It would be better if it had less grip if anything, like slipping the clutch. Imho it needs to change down a gear, ie 2inches off the pitch
 
jfm said:
Mark
I had the same boat/motor as Hurricane so know it well. It's not a lack of grip that's the problem. It's that the drag of the not-yet-skiing skier means the engine never gets above 2500rpm so never develops more than 20hp or so (4 strokes have less torque at low rpm than 2 strokes) and so cannot pull an inexperienced skier up onto the plane (or at least it struggles hard and it takes a while). It would be better if it had less grip if anything, like slipping the clutch. Imho it needs to change down a gear, ie 2inches off the pitch
Click to expand...

Sorry typed the 1st reply on my phone I should have wrote reduce to 10 or 11 pitch.

Ah, understand a little better now. It sounds like it could do with a vented prop. I have used quicksilver ones with 'PVS' (Just a few holes round the hub), you can alter the amount of slip by altering the size of hole with a plug. Leaving the holes fully open allows exhaust gases to bubble round the prop inducing slip and gives fantastic acceleration 0-15kts.

Not sure if you can get them for Yam 4 strokes, but you could buy a cheap prop and have a go at the hub with a black and decker ;)
 
Thanks JFM

I wasn't exactly sure what you said at the time.
It (sort of) made sense to me but now I can see exactly what you are saying.

As you said, its good as a spare anyway so I think I'll just get an 11" pitch prop and give it a whirl.

Thanks
 
landlockedpirate said:
Sorry typed the 1st reply on my phone I should have wrote reduce to 10 or 11 pitch.

Ah, understand a little better now. It sounds like it could do with a vented prop. I have used quicksilver ones with 'PVS' (Just a few holes round the hub), you can alter the amount of slip by altering the size of hole with a plug. Leaving the holes fully open allows exhaust gases to bubble round the prop inducing slip and gives fantastic acceleration 0-15kts.

Not sure if you can get them for Yam 4 strokes, but you could buy a cheap prop and have a go at the hub with a black and decker ;)
Click to expand...

Hadn't thought of that Mark but yes black-and-deckering the hub with a load of 5mm holes might well do it. Would be interesting to try, as you would have the benefit of the 13p once up and running. Probably easier to buy an 11incher though! I wish we could all just buy 2 strokes still
 
Just got back from nearly a month away.

Fitted the 11 inch prop (original was 13 inch)

Being a fat git, the old prop wouldnt lift me out of the water when I was skiing.
Big success
The smaller pitch one does

The boat seemed a little faster as well.

Other guys at the marina recon that I should go with a 12 inch stainless prop now but why mend something that isnt broken

Anyway - job done - I now have a dinghy that a fat man can ski behind.

Just got to perfect the wake boarding now without putting my back out!!
 
Hurricane said:
Other guys at the marina recon that I should go with a 12 inch stainless prop
Click to expand...
Weird suggestion indeed.
If the 11" alu prop runs fine, as a rule of thumb when you swap it for a s/s prop you should rather use a shorter one, not longer (AOTBE, of course).

Btw, it's perfectly possible that the shorter prop gives you more top speed, if the engine reaches a higher rpm.
Do you have a tacho on the rib? If you know the rpm difference at wot, it's easy to check the math.
Though any mobile gps can give you the SOG, of course.
 
MapisM said:
Weird suggestion indeed.
If the 11" alu prop runs fine, as a rule of thumb when you swap it for a s/s prop you should rather use a shorter one, not longer (AOTBE, of course).

Btw, it's perfectly possible that the shorter prop gives you more top speed, if the engine reaches a higher rpm.
Do you have a tacho on the rib? If you know the rpm difference at wot, it's easy to check the math.
Though any mobile gps can give you the SOG, of course.
Click to expand...

I'm not sure about the stainless thing but the explanation is that the stainless prop is completely different profile - stronger material etc..

Top end speed
It only felt faster - I'm not that concerned so wont go to the bother of swopping props etc to find out.
All I know is that at lower speeds, I now have enough power to get a fat man skiing.

Thanks for your comments anyway.
 
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