Another prop question: 20' MA advice?

rkarran · #1 05-28-2012, 02:22 PM

Hi all. I've had my new-to-me 1979 20-0 Master Angler for just over 3 weeks now and am slowly working the kinks out. I keep adding stuff to the list, unfortunately.

I believe I am overpropped and wonder how to go about the analysis of the issue to correctly prop the boat.
The motor is a 1993 Evinrude 150hp Ocean Pro mounted at correct height on the transom currently turning a 15 x 17 SS cupped 3-bladed prop. Single, maybe double cup.

The Evinrude book says this motor should turn 5000 but I'm only getting 4500-4600 at WOT when trimmed way out, one person, full fuel.

I guess I should record speed at various rpms using this prop as a benchmark? My ultimate goal is an economical cruise speed. I'd like to hope that I could find some other props to try (I'm in the Tampa Bay area) in order to find the right size. Cost is a primary concern to me so i can't spend a lot on experimentation.

I don't want to reinvent the wheel, but rather learn from the experience of you SC guys that have been there - done that.

I have searched the archives but I always find a different variable that doesn't apply to my case. Any advice, suggestions, comments are appreciated!!

Bushwacker · #2 05-28-2012, 04:43 PM

At first glance it does appear that you're way overpropped, but before you start trying different props make sure your tach is reading accurately, as analog tachs can be very inaccurate. Also make sure motor height is correct. Top of the Anti Ventilation plate should be above the water when you're up on plane. I'd also make sure motor is up to snuff (correct timing, good compression, spark/throttle linkage correctly adjusted) If you don't have a factory manual, get one. It'll be the best money you ever spent!

I suspect the optimum rpm for your motor would be closer to 5500. It's 5400-5500 for the 150 E-Tec which is the same basic block. I think GFS and 76Red18 have similar motors and may be able to advise you on that.

rkarran · #3 05-28-2012, 05:02 PM

Thanks for all that, Bushwacker!! All very valid checks before acting. Yes, all that was just done, since at first I thought a motor issue. Tach is very close, height is right, compression good, timing, spark and throttle adj. is good. This is what finally led us to the propping......when all the rest checked out okay.

I do not have a factory manual, but saw one where stated 5000rpm is right. It did not indicate a range. This factory manual covered only a couple hp engines of this vintage, which included the 150hp. My model is E150EXETG.

Thanks for covering these items.......I should've mentioned steps I'd already taken to get to the idea of the prop being the cause.

Bushwacker · #4 05-28-2012, 05:18 PM

Sounds like you've done your homework on the motor and tach! Your motor will live much longer and burn less gas and oil if it's propped to turn optimum RPM at WOT. Just make sure you do any testing with the load you typically plan to carry. I thought my 14x20 4B prop was about right till one day I had 6 divers on the boat and could only turn about 4600 WOT!

My 15x15 4B will turn 5400-5500 pretty much regardless of load, and gets on plane MUCH quicker. These 2-strokes have all needle bearings and very short strokes, so high rev's won't hurt 'em. Better to over-rev a bit than to lug 'em down with too big a prop!

gofastsandman · #5 05-28-2012, 06:56 PM

Quote:

Originally Posted by Bushwacker

Sounds like you've done your homework on the motor and tach! Your motor will live much longer and burn less gas and oil if it's propped to turn optimum RPM at WOT. Just make sure you do any testing with the load you typically plan to carry. I thought my 14x20 4B prop was about right till one day I had 6 divers on the boat and could only turn about 4600 WOT!

My 15x15 4B will turn 5400-5500 pretty much regardless of load, and gets on plane MUCH quicker. These 2-strokes have all needle bearings and very short strokes, so high rev's won't hurt 'em. Better to over-rev a bit than to lug 'em down with too big a prop!

This is everything I have ever been told, taught, and believed. I have revvved the piss out of dirt bikes and RD`s. A friend had a Kawi 500 triple with a turbo. He was a sick man.

Four techs from BRP have told me that motor makes 150 @ 5K, and after that you are just over spinning the motor. I asked if they were afraid of us jumping our hulls and overrreving.

They said no. I do not believe that answer. Maybe they are correct, but it goes against my thinking and history.

It does have a sweet spot around 3700 and that is where I run her.

I run an old sst 15 x 16. Not bad, but the PT and Apollo were smoother through the boat and controls. Just can`t spin them. I`m looking for an Apollo 4 bl 15p.

The Mirage plus is also a sweet prop. Have not tried a Stilleto yet.

eggsuckindog · #6 05-29-2012, 04:54 PM

Sandy what is WOT for you with that prop??? yours is about as close to his as you can get -

Stilletto's are hard to swing, they have something called progressive pitch - you would prolly have to drop down to 15 with one - from experience. My old 19 and the Stilletto were 300 RPM different - raised it up and got 200 back.

gofastsandman · #7 05-29-2012, 07:04 PM

I found more bozo suprizes, so I won`t really know until I do another lync n sync.

I could pull 5000 with BW`s powertec 15x15 4 bl. I feel there is more in the motor, as I can turn 5200 with the sst 15x16.

My motor is a `96 150 rude.

Search Dunk`s decarb and do that. Call the FD and let them know your house isn`t on fire.

Or go to a quiet ramp. Do not run e10 in these motors. Use stabil marine or startron.

Run the motor often. Drop the leg once a year if for no other reason than to keep the main shaft greased for easy removal. Water pumps are cheap insurance. Pull the t stats and you will get a good idea of the condition of your cooling passages. New o rings and vaseline.

You MUST run Champion plugs or risk blowing P Packs and ois sensors. Run under 4k and you may get reasonable mpg for a boat.

Cheers,
GFS

Many of the ole rude runners use pennzoil semi synth and pre mix 50-1.

eggsuckindog · #8 05-29-2012, 07:19 PM

we've done all that just wanted to know what it turned with the 15x16

gofastsandman · #9 05-29-2012, 07:29 PM

Quote:

Originally Posted by eggsuckindog

we've done all that just wanted to know what it turned with the 15x16

Find your glasses Mr Dog.

76Red18 · #10 05-29-2012, 07:56 PM

rkarran I would say too much prop. I run an old style sst 15 x 15 most of the time on my 18 with a 150 about like yours. 39 - 41mph @ 5400 trimmed with a heavy load. Planes very easy and runs well when it gets a little rough.

Sounds like your motor is well tuned. You ever check compression? Mine is 103 - 106 with about 300 hours.