200hp outboard. Is one like the other?

[Chapap]

Strictly performance related, shouldn’t they all be the same? For cars, the engine’s behavior through the entire rpm ranger matters. Boats just sit at a one rpm the whole time. Shouldn’t 200hp be 200hp no matter how they get there?

I was snooping around a Bass Pro salesman touting this supercharged outboard. It took me a while to figure out why I wasn’t impressed. Then I asked how this $15k supercharged 200hp was better than the $10k NA next to it. He continued to the next customer.

 

[JOLENE_THE_RANGER]

Horsepower is a byproduct of torque and rpm. Boats are different than cars in that you can’t always use all the rpm. If a motor doesn’t have enough torque to spin the prop and push the boat it’ll stop at a certain rpm where as others with more torque will let you get into higher rpm’s and thus use all the Hp.
the supercharged motor probably has a better torque output and curve so that you can spin a higher pitch prop (you can go faster) regardless of HP.

 

[fastpakr]

If they're geared to spin at the same RPM and both are spinning at the engine speed where they make 200hp, then the torque measured at the prop should be identical.

 

[bobbywalter]

Yeah......no.....maybe.

 

[Chapap]

Well that makes sense. Partial throttle performance may vary. Is that why 2 strokes are pretty much gone?

 

[bobbywalter]

Super charged 200 hp vs n/a 200 hp....

N/A for reliability.

 

[scotts90ranger]

2 strokes are gone for emissions reasons, there's a bunch of bodies of water that won't allow 2 stroke engines at all...

Since HP=(torque*rpm)/5252 it all depends on what rpm it's rated for... there's a lot of variables and what kinda marketing is involved...

 

[JOLENE_THE_RANGER]

We’re the two engines of the same make? Or were you comparing a Mercury to a lesser manufacturer.

 

[Chapap]

We’re the two engines of the same make? Or were you comparing a Mercury to a lesser manufacturer.

No idea. We were comparing literally the stickers because everyone involved was clueless (a safe assumption I think). One was "200" and the other was "200 supercharged."

I guess for a boat, you want to pick the prop characteristics you want then find an engine that'll match it. I know prop selection is a massively important and sometimes finicky operation. Power curves just seem less important for a boat cause you can pick any RPM you want at any time... And all engines of the same power range have basically the same max RPM. But I suppose you don't want to get stuck with a finely tuned 2 stroke that makes 5hp from 100-4900rpm then 200hp at 5000rpm.

edit: I reread this post and I'm confused again. If the engine is spinning at x RPM, so is the prop. It doesn't matter what the daggum tq and hp are... but it must matter. This just doesn't seem to cross over between land and water.

another edit: Think I got it. If you floor it at a stand still, the engine won't spin to redline. you have to get to speed first. It's like having a really slippy torque converter. I think I feel better.

 

[RonD]

Yes, you have a fluid drive, called a propeller in this case, but it can never actually "lock" because it has to keep pushing fluid passed, lol

 

[scotts90ranger]

Say the engine is rated for 200hp at 6k rpm which is likely, if you put a prop on it that stops the engine at 5k rpm it is no longer able to make 200hp with that setup while if you put a prop on it that lets the engine spin up to 6k it will make 200hp... it's complicated and means dang near nothing but hp is related to speed so if you have a prop that lets the engine get to it's rated rpm you are pushing more HP so you can make more speed... but it also combines into drivability too, in the jetboat world they like to run lower rpm because you can't blow out the impellers as easy so the off the line speed is faster but it suffers a little in top speed... no offense intended but the Canadians like to push this to extremes, we rate our engine at around 5k rpm, they seem to have it in their mind that you shouldn't run a V8 engine over 4k rpm for whatever reason, they'll see that the engine is rated to say 400hp, put an impeller in that holds the engine back to 4krpm or less then look at an impeller curve and complain that their 400hp engine isn't making it to where it says 400hp on the impeller curve...