factory prop size

[1990 Fourwinns 220H]

Hi guys sorry if this has been beatin to death. I have a 1990 fourwins horizon 220 5.7 omc cobra (21:16 ratio). The prop looks to be original. Its beat up and is a 15x15. I looked everywhere trying to find out if this is the factory size but cant seem to find any info on my boat. Does a 15x15 sound right? If not what do you guys recommend? I do mostly tubing and cruising. Thanks!

 

[jimmbo]

The WOT range for your engine is 4200 - 4600. What is the current prop getting? The spec sheet shows a gear ratio of 1.41:1, which is not 21:16(1.31:1).

 

[porscheguy]

Top speed and rpm? I’m of the opinion that the factory prop is irrelevant since they can get it wrong. What’s relevant is your WOT rpm and top speed with a given prop. My belief is that you increase pitch until you can no longer hit redline on a lightly loaded boat. That is your cruising prop. For watersports, come down 2 inches in pitch, possibly even 3.

 

[jimmbo]

The Factory prop can be relevant, they are usually close. Where it can be very important is it can show that an engine is not performing well, and someone sticks a lower pitch prop to hide the poor performance so the engine will again get to the WOT range speced, but not producing it's rated power

I guess that could be countered that the factory prop would be overloaded by a waterlogged boat and be unable to attain its rpm range because it is now overloaded

 

[1990 Fourwinns 220H]

Sorry yes my drive is a 1.41 ratio my upper gear ratio is 21:16 (I only know this because i just replaced my upper drive gears) Well, i believe my factory tach is inaccurate. I see my engine range is indeed 4200-4600. At WOT according to my factory tach is 4800. Im new to boats and this is my first boat. It seems everywhere i looked most people were running a 15x17. 15x19, or 15x21. Ive never seen anyone running my 15x15. I was just wondering if it was an odd ball prop the previous owner just threw on.

 

[Sea Rider]

Boaters going for new engines or second hand ones delivered with a prop should re prop their engines for their specific boating requirements soon after break end period has ended and immediately after second hand boats are put on water for engines to rev at least middle to max wot rpm range factory stated to take the max out of their horses powering their combos.

Happy Boating