20 hp Props

[dgilchrist]

So I'm shopping 20 hp props for a new boat build and have looked at Mercury, Yamaha, Suzuki and Tohatsu. All great 4 stroke, EFI motors that I'm sure I'd be happy with. I've seen some threads about how manufactures may share components between hp classes like Suzuki 15 and 20 models. Considering that, is the key power measurement the rated KW of each motor? I know prop size and pitch plays a big factor, trim while running, etc..... Just trying to compare apples to apples on power output of the engine. 

[fishinwrench]

I've been an outboard tech for 25 years, but you're asking questions that are over my head.  1 SAE horsepower is .0412 stronger than 1 Metric horsepower.   So if you wanna compare one brand against the other I guess you need to know what standard of measurement each is using.   

Or.....you could just throw one beer (or handful of ice) out of the boat cooler and call it a push. 🤣

[snagged in outlet 3]

If it’s the same power head and one is rated 15  hp and the other is 20 hp wouldn’t the 20 give you more umph?  

[Basfis]

I’m no boat mechanic....

HP or KW are two ways of measuring power. Nowadays outboard power is typically at the prop shaft. Many power classes share parts, especially as computers control so much. The allowed ratings are expected to be within a percentage of label. For example +/- 10%. 
 

some are indeed “stronger” but within a range. Yes, the prop along with the power band and gear ratio of said engine create the feel of more or less “umph”.

so, KW and gear ratio are your comparative points combined with operating range. 

[fishinwrench]

50 minutes ago, snagged in outlet 3 said:

If it’s the same power head and one is rated 15  hp and the other is 20 hp wouldn’t the 20 give you more umph?  

Doubtful that a 15 and a 20 share the same powerhead, but with the newer "4-stroke EFI's" that he has his heart set on, I really don't know, nor do I care since nobody will ever be overhauling/rebuilding one.   They are designed to be clean running and disposable.  

 

[snagged in outlet 3]

3 minutes ago, fishinwrench said:

Doubtful that a 15 and a 20 share the same powerhead, but with the newer "4-stroke EFI's" that he has his heart set on, I really don't know, nor do I care since nobody will ever be overhauling/rebuilding one.   They are designed to be clean running and disposable.  

 

I didn’t look at those models but Evinrude has a couple different hp sizes based on the same power head.  I just assumed the others did the same thing.  

[fishinwrench]

3 minutes ago, snagged in outlet 3 said:

Evinrude has a couple different hp sizes based on the same power head

Which ones?   I wanna look up some parts on them.

[snagged in outlet 3]

The 90, 75 and 60 ho look like the same power head.  I’m no mechanic though.  

https://www.evinrude.com/en-US/e-tec/e-tec-full-specs.html#tab=6

[fishinwrench]

Yep, sure'nuff.  75 and 90 are the same part #, 60/65 is different.    The 15 and 25 share the same cylinder block also.  I don't exactly understand the agenda there.  I'll ask at my next opportunity.  

[Basfis]

Any time you can use the same casting across pn’s it saves a ton of $. Often allows same machining fixtures, shared tools and such. At the scale of evinrude, easy to imagine the cash savings being in excess of $1m on a single share starting at the foundry thru inventory.