WOT speed on a '83 20' SF w/200

Blue_Heron · #1 10-30-2006, 05:51 PM

I've got an '83 20' SF with a 99 Merc 200. I've been playing with props and setup and can't get it to go more than about 46 mph gps. Shouldn't this be a 50+ mph boat?
Thanks,
Dave

ocuyler · #2 10-30-2006, 07:07 PM

The appropriate prop needs to be installed to acquire 100% of the maximum rpm as specified by the motors OEM with a light load. That said, yes, it should be a 50 MPH boat. There are a number of factors that could slow her down (excessive weight, t-top, poor tune-up, hull condition, etc.), but the prop thing is a given.

fvmako17 · #3 10-30-2006, 08:56 PM

should have got a yamaha 200, you could have a 50+ boat with a 175 and a clean hull.

Blue_Heron · #4 10-30-2006, 10:12 PM

Quote:

should have got a yamaha 200, you could have a 50+ boat with a 175 and a clean hull.

Yamaha makes a good dependable outboard. So does Mercury.

The boat came with the Merc already on it. If I were starting from scratch, I might go with a Yami. If top speed were my only consideration, I'd stick with the Merc. All that being said, a 175 Yami ain't gonna be faster than a 200 2-stroke of any make. Horsepower is horsepower, it don't matter what color the engine is.

Ikan Besar · #5 10-30-2006, 10:15 PM

Quote:

should have got a yamaha 200

...ah, welcome to the site.

eggsuckindog · #6 10-30-2006, 10:26 PM

I would think so too, I have a 20 MA with a T Top and 200 Merc and I can get to 49 with the top and really and standard marginal Merc prop. Seems like you should but who knows maybe not just have fun with it.

Thanks for your good input FVMAKO17 it was helpful stop back in when we need more help

Blue_Heron · #7 10-30-2006, 10:45 PM

Quote:

Seems like you should but who knows maybe not just have fun with it.

I'm really just trying to get the best efficiency out of the setup. To some extent, that translates to top end speed. Besides, for me, part of the fun is tinkering with it.

I have the '83 post-Potter 20SF made by Seacraft Industries. I know it's 8" longer than a Potter 20SF, and maybe a little heavier, but I don't know if performance is similar. I've read here that the potter 20s are stern heavy. Mine seems to balance more toward the bow, at least at higher speeds. I couldn't get mine to porpoise at WOT to save my life, though it will under 4,000 rpm if it's trimmed up enough.

Bigshrimpin · #8 10-31-2006, 02:31 AM

mercury mirage plus 19" prop, hydraulic jack plate, and trim tabs will give you 50+mph.

Lighten the boat up as much as possible by removing any excess gear and get the engine up as high as possible (cavitation plate will be about 3" above the bottom of the hull). You're motor might be too high already if you can't get the bow to porpoise w/ full trim.

Blue_Heron · #9 10-31-2006, 07:58 AM

Quote:

mercury mirage plus 19" prop, hydraulic jack plate, and trim tabs will give you 50+mph.

You're motor might be too high already if you can't get the bow to porpoise w/ full trim.

Not too high, if anything, too low. The prop doesn't break loose until it's trimmed up almost all the way. I've got the cavitation plate about 1" above the bottom of the hull and it's covered with white water when running. Holds real good in turns, too.

I was thinking of raising the motor up one hole. Don't want to spring the $$ for a jack plate. I'm running a Mirage 21 and the rpms are lower than I'd like, closer to 5000 than 5500 at WOT. Maybe I should try a Mirage 19. My wife may throw me out if I add another one to my prop collection. It's getting pretty impressive.

lost2a6 · #10 10-31-2006, 08:53 AM

FWIW, I had a 1977 20ft Sceptre with a 200 Yamaha and it would run 53-54 @ 5400 RPM and has hit 55 with a light load. I was running a 21 pitch Lazer II Merc prop. It seems that the SeaCraft Industries boats are heavier than the Potter boats. I have owned both.