prop question 2005 202 gs with a 5.0 IO

nedgorski

hello 
 what is the preferred prop size for a 2005 202 gs
 i just recently purchased one.  it has a new prop and a rebuilt out drive .. i'm guessing its the wrong size seeing as i was able to bring the boat close to 6000 rpms ..  

nquirk

Two measures to the prop.  Diameter, which I'll assume is most likely fine.

The other is pitch.  If you know the maximum RPMs at WOT then you can adjust the prop accordingly.

Each inch of pitch is worth about 200 rpm. Lowering the pitch will increase rpm and vice versa. For example, if your engine is rated at 5400RPMs and you're currently at 6000RPMs, you need to adjust your pitch to reduce 600RPMs.

If its currently a 17P prop, then you'd want to increase it to 20P.

Alternatively, you can get a rough estimate to validate the above math here.

https://www.mercurymarine.com/en/ca/propellers/selector/?utm_term=en&utm_medium=us+&utm_source=Overlay_IP=ca&utm_campaign=Region+Redirection#/step-one

This will get you close.

skibum

If memory serves me right you should be turning no more than 4800 rpm if a mercruiser or Volvo penta engines. Keep it up at 6k and it will get expensive very quickly, because you WILL be replacing the engine.

nedgorski

thanks for the info .. i forgot to mention when i did test the boat and i hit 6k i was by myself. I know the boat is rated for 10 people.  I have  always been a 2 stroke out board guy .. i'm assuming the mercury i/o don't have a over rev like the 2 strokes do  ...
should i test the max rev when the boat is fully loaded?  or empty  to determine the prop size??
 thanks again for the info 
 Regards Ned 

nquirk

Here is one link I found regarding your engine.  Note the max RPMs.  This is what you need to use as your spec depending on it being carbed or EFI.

@skibum was correct in the assessment of 4800RPMs.  You need to get it down or you'll very quickly create issues.

https://www.perfprotech.com/blog/tech-specs/mercruiser-50l-marine-engines-specifications

ccrobin

nedgorski said:

hello 
 what is the preferred prop size for a 2005 202 gs
 i just recently purchased one.  it has a new prop and a rebuilt out drive .. i'm guessing its the wrong size seeing as i was able to bring the boat close to 6000 rpms ..  

What did you finally land on? I have the same boat and am looking for a new prop now. Appreciate any response or info!

thurricane

I would suggest using the mercruiser prop selector. https://www.mercurymarine.com/en/us/propellers/selector/