Propping a F70LA Yamaha

[Jim Hawkins]

I had planned to take the prop off my old 90HP 2 stroke Yamaha and use it as a test to see if I wanted to adjust diameter and pitch on my new 70 4 stroke.

It doesn't fit. It just barely hits the motors zinc trim tab as shown in the first picture. Even though all the prop selector tools show it should fit, it doesn't and I don't know if it's possibly something I'm doing wrong or the prop. Prop is an Apollo 13 3/8 X 15 Stainless. See photos



And, what the heck are those things in the last pic? They were on the shaft as shipped. I assumed they were just something to protect the splines since they look to be cheap steel.

As always, advice appreciated.

 

[Jim Hawkins]

Or, if you have a recommendation for a good prop for this motor I'd be glad to hear.

The boat is a 18' Nautico by Seagull. The motor is considered under-powered for this boat but I am not a "go fast" kind of boater. The hull I believe is around 1000 lbs and with passengers etc. probably 2000 lbs. I am looking for economy first and fast hole shots least. My best guess is to stay with a 15" pitch but maybe go down to 13"diameter.

 

[Jim Hawkins]

Or, the prop charts show I can go has high as 14" diameter which I suppose would fit but only if the pitch were less, drawing the blades back away from the trim tab. I think. But prop expert I am not.

I did however just see that the 2 items I did not know in the picture above are a spacer and a washer. For what I don't know.

 

[Jim Hawkins]

I found an old thread with this posted by the forums very own Bondo, on the subject of another merc prop,

Re: Hustler prop hits trim tab - Mercruiser Alpha
Ayuh,........
There are Atleast 3 different Anodes that fit there,......
A Large 1,..... I'm Guessing that's what Your's is,.....
A Small 1,.....
And the Flat Plate that Willy mentions.......
You can either Change it,....
Or as Willy says,..... File it to Fit.......
1/4" Clearence is Plenty.......

so, looking at the trim tab options...

 

[Sea Rider]

Is the new 4 stroke 70 HP a Yam model ? Need to dial a prop that revs OB between min to max wot rpm range factory stated and as usually loaded on calm flat water cond. But middle to max wot rpm range is preferred to achieve faster hole shot or slight more top end speed.

Will need to pick whatever suits your boating needs as can't have both scenarios in a single prop at same time.Yam has a large variety of OEM props to choose from. OB must count with a healthy tach to play safe while testing props on wot runs.

Happy Boating

 

[Jim Hawkins]

Hello Sea Rider,

By Yam, do you mean Yamaha? This is a 2016 Yamaha 4 stroke 70HP.

I removed my trim tab temporarily so I could use a prop I have, a 13 3/8 X 15 stainless 3 blade. I will use this prop for the break in period for the new motor at low rpm's and then see how it performs as I get closer to WOT.

My guess is for a under-powered catamaran I will choose a 4 blade prop and somewhere around 13.5 X 13 but that may be altered depending on what the trial prop does.

Checking tach and other gauges is on tap for today before I splash tomorrow.

 

[Sea Rider]

Is the SS Apollo 13 3/8 X 15 prop made by Yamaha or it's from other fabricator ?

Assuming that the new 4 strokesYamaha 70 HP-OB comes with a factory delivered prop, you should test that combo with it and once break end period has ended perform a wot test and check if OB revs middle to max wot rpm range. From there can fine tune the OB for better hole shot or better top end speed playing with pitches, you decide.

If you think that swapping a 90 HP prop will make your 70 HP to perform better, the answer is no if happens to be different diam sizes. Removing the trim tab for the prop to fit comfy on lower leg is an indication that the 90HP prop is bigger.

Happy Boating

 

[Jim Hawkins]

Is the SS Apollo 13 3/8 X 15 prop made by Yamaha or it's from other fabricator ?

Assuming that the new 4 strokesYamaha 70 HP-OB comes with a factory delivered prop, you should test that combo with it and once break end period has ended perform a wot test and check if OB revs middle to max wot rpm range. From there can fine tune the OB for better hole shot or better top end speed playing with pitches, you decide.

If you think that swapping a 90 HP prop will make your 70 HP to perform better, the answer is no if happens to be different diam sizes. Removing the trim tab for the prop to fit comfy on lower leg is an indication that the 90HP prop is bigger.

Happy Boating

I probably rambled too much and wasn't clear.

I don't believe Apollo is a Yamaha prop, I think it is made by Michigan Wheel.

The new motor did not come with a factory prop, nor was it supposed to. I bought the motor new in a crate.

The Yamaha prop selector shows my motor can take props as big as 13 5/8 diameter and pitches from 10 to 16

I do not expect the prop from my old 90 to work well, I only want to use it as a starting point to see where the motor is rpm wise so I can calculate a best guess for diameter and pitch.

 

[Sea Rider]

Info is clear now LOL!! Can use a Yam prop/boat selector if there's one available to buy a starter prop and then go from there maximizing the prop that best suits your boating needs. You'll be extremely lucky to nail the prefect prop for your application on firts attempt, usually it's achieved on second one and sometimes on third one. Good Luck.

Just for the record post whichever wot rpm was achieved with the Apollo prop and at which min-max wot rpm range the engine was revving at.

Happy Boating