Changing pitch or diam?

[salar600]

Things are progressing testing is fun but I still have questions !

My 75hp E-Tec should be between 4500-5500 at wot. With the prop I'm using it goes to 5600 rpm when I fine tune the trim.

The prop is a BRP 13 3/4 x 15 - 3 blades.

Should I got to a larger prop same pitch or switch to a 17? In this case which diametre? same or smaller?

Thanks for your help.

Mart

 

[QC]

Re: Changing pitch or diam?

I wouldn't spend any time worrying about diameter. Do a search and some reading, but leave that alone for now.

Are you testing now with a load that will be the same as your normal use? People, stuff, gear, stuff, tools, beer, ice, stuff? If the answer is yes, then got to a 17. If the answer is no then maybe wait until you get data with an average or heavier load.

 

[junior1113]

Re: Changing pitch or diam?

i would'nt change anything just keep throttle at 5500 max.

 

[salar600]

Re: Changing pitch or diam?

Are you testing now with a load that will be the same as your normal use? People, stuff, gear, stuff, tools, beer, ice, stuff? If the answer is yes, then got to a 17. If the answer is no then maybe wait until you get data with an average or heavier load.

Same beer load but wasn't pulling a skiier, it's to cold for the now!

So keeping it for ski and having a back-up in 17 for riding could be smart?

 

[Yellow Yota]

Re: Changing pitch or diam?

Or a 15 pitch 4 blader.

 

[QC]

Re: Changing pitch or diam?

So keeping it for ski and having a back-up in 17 for riding could be smart?

Yeah, either that or the 15 four blade as mentioned. You need a spare anyway, so I'd go for it. If your hole shot is good as is, you might even get away with a four blade 17, but the 15 would probably be the best compromise and use the 3 blade as the spare.

 

[salar600]

Re: Changing pitch or diam?

Ok, I haven't change anything yet and now the ski season is on so I got more data.

Still with the same 13 3/4 x 15 - 3 blades, I can pull my skiier at 30-32 mph engin @ 3800-4000 RPM.

When I turn, RPM and speed go down to 3000rpm and 25-26mph.

Is there a way I could keep my speed up to 30+ mph with an other prop? Or is this cause by not being at WOT to pull the guy?

Before this motor I had an old 1977 Rude 70hp, prop 14 x13 and wot always at 26mph no mater if I was in strait lines or turns.

 

[Silvertip]

Re: Changing pitch or diam?

one hundred rpm over the recommended WOT rpm is not anything to worry about and certainly not worth changing props for IF that prop is what the vast majority of your boating activity is for. If loaded heavy or when towing water toys or skiing pulls the WOT rpm down well below 5500 then you may need two props. One for cruising and one for water sports.

 

[salar600]

Re: Changing pitch or diam?

The 13 3/4 x 15 I'm using is perfect for crusing. But...

I don't know what is WOT RPM went towing cause I'm not pushing the motor to WOT at that time. It's to fast for ski.

That is my concern if I do towing at 3800-4000rpm I probably don't get the 75hp out of the motor.

So for towing, what is the best solution to be abble to keep my speed during turns?

-13'' of pitch?

-4 blades prop?

-Is a Stealess prop could do better?

 

[steelespike]

Re: Changing pitch or diam?

I believe you will lose more speed turning left than right.Also your present prop may have more bow lift slowing the boat in turns.
Your 75 is 320 lbs,your 70 was 220 lbs that extra 100 lbs probably makes it want to fall off plane easier. You might try an extra person in the bow or less weight in the stern.A 4 blade prop will probably help as well.The Solas Amita seems to be really predictable.

 

[salar600]

Re: Changing pitch or diam?

Thanks for your input, that make sense.

Based on what I read, from a 3blades to a 4 blades, I should go down 1'' of pitch.

As I'm runing a BRP 13 3/4 x 15, is there a rule of thumb vs Solas Amita 4 blades?

This is what they have : 13 1/4 x 13 or 13 x 15.

Thanks

 

[trendsetter240]

Re: Changing pitch or diam?

Thanks for your input, that make sense.

Based on what I read, from a 3blades to a 4 blades, I should go down 1'' of pitch.

As I'm runing a BRP 13 3/4 x 15, is there a rule of thumb vs Solas Amita 4 blades?

This is what they have : 13 1/4 x 13 or 13 x 15.

Thanks

I have the exact same BRP 15p prop and I also have a Solas Amita 4 blade 13p prop. My motor is a 1995 70hp evinrude.

The 15p BRP is a great all around prop. I ended up buying a SS prop so I don't use mine any more but I would recomend you keep it for cruising.

I use the 13p 4 blade solas amita when I'm pulling wakeboarders and it works fantastic. You will need to watch the RPM at WOT because your motor will be able to overrev with it. Mine will hit 6600RPM at WOT with the 13p 4 blade and I get 5800RPM with the BRP 15p.

With the 13p you will have way more power pulling a skiier because instead of being at 4000RPM you will be up around 4600-4800RPM.

 

[salar600]

Re: Changing pitch or diam?

Thanks, that's a good benchmarck.

I think I'll try it and let you know about the results.