Trying to achieve my motors optimum RPM

[Sea Rider]

Re: Trying to achieve my motors optimum RPM

Some issues :

Are you experiencing back or over transom water splashes, ? If any will need to maximize engine/transom height, sorry this is not a math theorical issue, must be dialed under trial and error. If water splashes are sideways is the hull producing them and it's normal. So by having 2 less pitch you have gained 1200 rpm, that's 600 per pitch. This reading contrast against what have been stated nearly cast on stone 150/200, 200/300 rpm per +, - pitch. So you have jumped fron previous 4500 rpm with a 13 to 5700 with 11, right ?

Test same combo with you alone on a flat no wind condition waters, you should be around 6 K, if so, that's your prop, going one less pitch will take engine inevitably to the super over revving side assuming you will gain another 500/600 + revs per pitch change as before.

Happy Boating

 

[Keegan.MW]

Re: Trying to achieve my motors optimum RPM

I took the boat out again today with just myself and trimmed the motor both up and down with no increase in rpm or mph. I put it back to where it was originally and got the best results. Here is a picture of the motor/ cavitation plate and how it lines up with the bottom of the boat. Does this look good enough? Also is there anything else I could do to squeeze out another 100-200 rpm?

 

[MikDee]

Re: Trying to achieve my motors optimum RPM

You could jack your engine up an 1 inch, or 2, you're cav. plate is abit below the bottom. As long as you don't get prop bowout, due to the strakes on your bottom.

 

[Keegan.MW]

Re: Trying to achieve my motors optimum RPM

How much increase in rpm should I expect if I were to buy a stainless prop with the same pitch?

 

[dazk14]

Re: Trying to achieve my motors optimum RPM

How much increase in rpm should I expect if I were to buy a stainless prop with the same pitch?

you would probably add -200. Originally you wanted 5500. You got 5700 which is ideal, unless you plan to carry big loads. You hit a home run on the 1st pitch.

I have been trying to educate the iboats community about rpm increase when it's a high percentage and also when the motor is out of the powerband.

I would have predicted 3" pitch to do that. Mass produced props do have pitch variations.

I'm glad people are catching on and it's great that you posted your numbers, so I don't sound like a broken record. Most people get a new prop and never follow up.

We've fitted the SS Saturn's many times and usually drop 1" in pitch compared to a stock. Not much data on the New Saturn.

Since you have transom clamps, you're limited how high you can go. The prop will blow out anyhow.

Try raising it. just cut strips out of wood and try it. You may get 100+rpms. Pay close attention to that motor climbing up(and off) the transom.

What are you trying to accomplish changing props?

 

[Keegan.MW]

Re: Trying to achieve my motors optimum RPM

So youre saying a stainless prop will lower my rpm? The main reason I'm considering SS is because I do a lot of river fishing and the main river I fish gets pretty low late in the year and hitting logs is pretty unavoidable. So my plan was to buy cheap aluminum props until I found what pitch I needed and then pony up the cash for a SS instead of buying 2-3 aluminum each year. Also my testing weight for the boat I just did is on the extreme low side. I almost always have someone with me and 99% of the time I will have a big cooler, tackle and rods. Not to mention a trolling motor and 2 more batteries on board. So I would love to squeeze out that extra 200 or so rpm to get as close to 6000 if possible.

 

[Sea Rider]

Re: Trying to achieve my motors optimum RPM

You inquire what to do to take the best concentrated juice out of your combo, what you need to dial is best engine/transom height match to have engine fully delivering its 35 HP along a perfect prop pitch match for your boating application to achieve max or near max wot rpm stated for that engine.

It's not a matter of addding shims, chopping transom down, raising holes, playing with trim positions on tiller driven engines and not seeeing how's the party going on at back transom, your best sweet height match for your combo will be for water flow skimming right under small upper water deflector plate with boat riding paralell to water line when on plane and well ballanced boat as per guidelines. Once done under trrial and error, post end results, just for the record...

BTW, what's the round thing protuding at back transom ?

Happy Boating

 

[Keegan.MW]

Re: Trying to achieve my motors optimum RPM

That's a strainer/ filter for my inlet pump to the live well.

 

[dazk14]

Re: Trying to achieve my motors optimum RPM

So youre saying a stainless prop will lower my rpm? The main reason I'm considering SS is because I do a lot of river fishing and the main river I fish gets pretty low late in the year and hitting logs is pretty unavoidable. So my plan was to buy cheap aluminum props until I found what pitch I needed and then pony up the cash for a SS instead of buying 2-3 aluminum each year. Also my testing weight for the boat I just did is on the extreme low side. I almost always have someone with me and 99% of the time I will have a big cooler, tackle and rods. Not to mention a trolling motor and 2 more batteries on board. So I would love to squeeze out that extra 200 or so rpm to get as close to 6000 if possible.

Before you get ahead of yourself and make yourself crazy about a couple hundred rpm's, let's run it with some load. All boats respond differently and then we'll have the WOT as-built with a typical load. Bring along a couple buddies, whatever.

Can we also get some data raising the motor up a bit. I don't know what that prop has for cupping. If it'll run higher, it may miss an underwater strike, lessen bow rise on take-off, etc..