Prop selection 20' MA 175 Mariner

[Bigshrimpin]

Originally Posted by Chaser

I have a couple of questions regarding the propeller on my Master Angler 20. I'm not a prop guy, know nothing about them, so pardon my ignorance. I'm just trying to get some info.

The boat is a MA 20 with a re-built 175 HP Mariner 2 stroke. I put the boat together two seasons ago, and its run great every step of the way. Its got excellent hole shot, and good top end speed, maxing out at about 38 knots with one person and minimal fuel. Cruises at 25 knots at about 4000 RPM using 10 GPH.

As I mentioned I know nothing about props, and I don't even know what is on there, since it came with the motor when I bought it re-built.

The only problem I have is the boat doesn't want to stay on plane with RPM's lower than about 3800-4k. At that RPM I'm doing about 22-25 knots, but any lower R's and it will slowly fall off plane and slow down. I'd like to be able to cruise a little slower for fuel economy. Like I said everything else about the boat/motor works great, and I'm very pleased.

Is it worth even considering a new prop, will I get any benefit in fuel economy? I don't mind sacrificing top end speed but would like to keep the acceleration I have.

Trim Tabs and 17P Mirage or Enertia. What year is that engine?

[WillyC]

Just for reference, I have a 20' SF with an old school carb'ed Yamaha 200 that weighs in right at 400 lbs. I'm running a Mercury Mirage Plus 19P (I suspect its actually been reworked to 21P as I get negative slip numbers running a prop calculator). Anyway, my minimum plane speed is around 20 mph at 2200-2300 rpm. I max out right at 50 mph at 5100 rpm (I'm pretty sure I need to raise the height of the motor and come down in pitch to a true 19P). I have a fuel management gauge and can get 3.5 miles/gallon at 3000 rpm. Keep an eye out on ebay for a mercury mirage plus 17P. Should be able to get a used one for 200 to 300.

[Blue_Heron]

Originally Posted by WillyC

Keep an eye out on ebay for a mercury mirage plus 17P. Should be able to get a used one for 200 to 300.

If you're very patient, and keep looking regularly, you'll be able to find one for under $150.

[Chaser]

Thanks for the info guys. The motor is a 1989.

I'll look for the mirage.

[jorgeinmiami]

Here's one on CL

http://miami.craigslist.org/mdc/boa/4179051025.html

[Blue_Heron]

Originally Posted by jorgeinmiami

Here's one on CL

http://miami.craigslist.org/mdc/boa/4179051025.html

It's LH rotation.

[eggsuckindog]

I have the same boat and something isn't quite right and as stated could be the prop design as the one that came with mine sucked- I have a Stilletto 19 and can only swing it more than 5400 with a 200 Merc but it runs 50+ with a T Top.

When I switched this prop everything was way better - cruise increased 3mph 28/29 @ 3400 - 5 mph more at WOT and the ride was greatly improved as it rides high up on the chines so made much dryer too?? Mine stays on plane at 2800/3000, it would be better if I had a 17 also, possibly even on top end by getting me up to 5800.

I would look around for a Stilletto 17 with a 175 should maybe find one for 150 or they are 280 new.

[Chaser]

Gonna go out and try the new Hustler 4 blade 14x19 today. It was a cheap way to try something new. We'll see how she goes.

[Chaser]

What a difference! Now the boat stays on plane at 2800 RPM, 1000 less than before, at nearly the same speed, using less fuel. Hole shot is better.

With the 14.5x19 3 blade (Merc): cruise 25 knots @ 4000 RPM @ 10 GPH. 5800 RPM WOT 38 knots.

With the 14x19 4 blade (Hustler): cruise 25 knots @ 3200 RPM @ 8 GPH. 5000 RPM WOT 40 knots.

Everything is better, except I'm not getting to the WOT RPM numbers suggested for the motor (5300-5800). I'm thinking the same prop in a 14x17 would get me there? With similar lower speed performance?

[FishStretcher]

You are heading in the right direction! A 14 x 17 is a good place to start. 10.5% less pitch means perhaps 10% more RPM. From 5000 to 5500, maybe. Other factors come in, like change in slip and such. But you can see which way the trend is going, and 14 x17 looks like the best next guess. And a prop shop can take a bit of cup out of a 17P and make it a 16P prop, if you like that one.

Bigshrimpin knows these engines well, I think. He actually already had a suggestion, and there probably wasn't much guessing on his end. Fr. Frank also helped me propping my 20MA.