Prop number decode?

[canuckmark]

Hi everyone...

I'm trying to find info on the prop that came with my boat. Motor is a 77 Johnson/Javelin 85hp (so 13 spline). The only number I can find on the prop is M43426R - the M may be a N and the R may be a B (the characters are not stamped deep enough).

I picked up a OEM 13.25 x 17 as my new main prop (the original will be a spare) which is a bit larger than this one. Plus the original one is way heavier. I thought maybe SS but I have chewed the edges pretty good on it and thought SS doesn't do this that easily.

Any info would be awesome.

 

[steelespike]

Re: Prop number decode?

If its stainless it will attract a magnet. If its slightly larger than the 17 it may be less pitch.
What is the wot rpm and gps speed with the 17?

 

[canuckmark]

Re: Prop number decode?

Sorry, I don't know yet as I haven't gotten the new prop out on the water yet.

But the interesting thing is the old prop does take to a magnet, so I know it isn't aluminum. The thing I don't understand though is I thought SS itself is non-magnetic, so are current SS props actually some type of alloy? Also the old prop takes paint and has some rust on the inside passages, so could it be steel?

 

[steelespike]

Re: Prop number decode?

There are different grades of ss higher grades still attract a magnet but to a lesser degree.I think some ss props
are what I guess we could call basic stainless and may show some oxidation.

 

[etracer68]

Re: Prop number decode?

There are omc SST props that are SS, and are painted. The SS is a 400 series, and a magnet will stick. Depending on the boat that you have the Johnny on, and the RPM @ WOT trimmed, with a moderate load. The MPH should also be recorded with a GPS,(an auto GPS will do also). I run a 90HP on an 16ft glass boat, and run a 15 or 17 pitch. It depends on how many people, and what I will be doing with the boat that day. If Im correct, that motor is rated HP at 5500 RPM, but still can run 5800 to 6000 RPM without any problems. Running it @ WOT below 5000RPM will lug and, do more harm then good. I most times am running about 3700 RPM while not @ WOT, and just cruzing around.

 

[canuckmark]

Re: Prop number decode?

Great info, thanks guys. Been raining here so I still haven't gone out, but I'll make notes next time out.

 

[canuckmark]

Re: Prop number decode?

Finally got a chance to do some high(er) speed runs this weekend. The new prop (original OEM size/pitch that came with that motor new) is definitely a different pitch than the old one, or maybe it is the diameter difference? The boat was quite light (only me) and at 3000RPM was running 35KPH or so. With the old prop the same speed was about 3500-3700 and it sure did feel different. It seemed to use more gas with the old prop too, would that be about right?

Did a few short bursts of WOT, honestly I chickened out on that because it was a bit choppy and busy on the lake. Plus the boat isn't big so seems a bit nuts at that speed, so I gotta build up the experience and confidence a bit more first.

I know this isn't the speed some guys here like to achieve, but damn that was the most fun I've had it a long time!

 

[steelespike]

Re: Prop number decode?

On the water 35 km(21.75 mph)may seem really fast but its not; a 9.9 can manage 20 or 21 on a boat appropriate to its hp.
It is important to get a lightly loaded wot rpm and gps speed if possible.It's the only way to be sure the prop is right.
You'll probably end up at about 55 kmh (35 mph ) It will seem like you are flying but your perfectly safe as long as you proceed relative to the conditions. What size is your boat?
The 85 hp is rated at 5000 rpm and the wot rpm range is 4500 to 5500.
As you increase speed you should trim up to achieve the best wot rpm and speed.
probably do your test runs early in the morning before other boaters get out and its calmer and less crowded.
Once you establish your wot rpm you can boat at what ever speed seems safe for the conditions.
Let us know what you find

 

[canuckmark]

Re: Prop number decode?

The boat is a Grew 155 tri hull, basically a 15.5 foot. Honestly the motor is way more than we need (and possibly more than the boat needs too), but they were a package deal.

Trim is a bit of an issue right now. Currently it is "sinking" (not holding up) so if I adjust to a position it won't stay there long. That's the next thing to get fixed. I did add an extra stop bar one set of holes up that seems to be a good spot for the current tests.