1988 Merc 150 SR4 ELPTO Lower Unit

[j_martin]

Just tried to buy a prop for this engine, and the hub was too big. Seems it takes the props Mercury lists for 3-4 cylinder engines.

What gives? What would be my gear ratio?

John

[chris_lacey]

Sounds like you have the XR4, 4 1/4" gearcase. The ratio should be 1.78:1, I believe.

You are correct, you need the small hub props. Laserll, Trophy plus are available in that hub size as well as inline (small blade) choppers.

[j_martin]

It's a Bass Bote. It has a High Five 22" on it now. The original owner didn't have it set up right. Motor, on a manual jack plate, was way deep. Now that it's up an inch or so, boat handles better but goes over 6000 rpm with ease.

There's a High Five 24 available, or Trophy Plus at steeper pitches.

Bummer is I have to find or borrow a stainless prop to get set up numbers. There isn't a cheap aluminum prop available with a high enough pitch to load the motor.

Thanks for the help.

[M.CHAPMAN]

THe small hub LaserII is a pretty good all around prop for that gearcase on a bassboat. Maybe run a 22" or a 24" pitch. A 26" may even run good an keep it below 6000 RPM. Small hub Trophy will hold tighter turns and be a little more stable.

[j_martin]

Thanks, that's where I was headed.
My prop guy has a 24" high five I can try.

john

[Reese]

If top speed is your goal, you probably will not like the high five. I just tried one not that long ago and it is smooth as silk...for wakeboarding or skiing it's very nice. For good hole shot and top speed it's going to be hard to beat a small hub trophy plus.

[j_martin]

This is supposed to be a family boat. It is used for fishing and for water skiing. The smoothness of the high five is great, the hole shot is to die for, and I think I wouldn't mind giving up a little top end for it.

The problem I'm working on now is that the boat isn't even set up right. The jack plate was down to the bottom, and the boat plowed, porpoised, easily spun out, and otherwise behaved like it was possessed. I jacked the motor up some, and immediately got much improvement, but ran out of r's. got lots of wp left, and can't trim it out of the lake. The rooster tail is like fog. There's more improvement there to be had by raising the motor.

The motor is apparently not the average 150, as it seems to be a little strong, and it has the 4.25 inch lower unit on it. The smaller plow, and the higher gears probably both positively affect performance. Right now, I need something to put on it to load the motor so I can make up my mind what to buy for the main prop.

One goal is to get it into the power band for the motor. No need to overrev and wear it out for nothing. The other goal is to get the boat to behave like it should. It would be a bummer to have it suddenly chine walk or spin out and pitch my kid who's trying to drive it.

I suspect I'll need more pitch than I can get in a high five, and will go to a trophy plus.

The 22 in high five on it now would be ok for a spare.

thanks for all the help. This site is awesome.

john

[Reese]

Regardless of what type of boat you have you need to keep playing with the setup.

Start out low...gradually raising the jackplate maybe 1/2" at a time. An increase in speed is obviously the ultimate goal and you'll know when you have gone too far up because your rpms will increase but your speed won't. Each prop you try will probably need a slightly different setting. One more thing....adjust your trim to maximize speed....not rpm. Again if your rpms go up but speed doesn't you've gone too far.

BTW....there are lot of great folks on this site but you need to help yourself out by describing exactly where your lower unit is located in relation to the pad. For example....4" below the pad means the centerline of the propshaft is 4" below the pad or vee on the bottom of the boat.

[j_martin]

Thanks,
I'm sneaking up on it. Where it is now, I go 60 at 6000 rpm and 1.78 gears. It's not slipping yet, just going easier as I get some of the motor out of the lake.
I ran the numbers and it comes out about 14% slip. I'm using very crude instruments, the motor mounted speedometer, and the engine tachometer, so it could be spot on to off by 10% or so. That's backed up by how it feels. You can feel it when the prop loses grip, and see it relatively on the speedometer.

The motor is hanging out 6 inches behind the transom, which is behind the pad, so where the motor is in the lake depends on not only it's height above or below the pad, but also how high the bow is.
I think the goal is to get it to run quick, but in control. I've noticed that as I get it trimmed up it seems to go at lower than WOT speeds with a lot less throttle. I think that translates to less fuel. I like that.

I'm hoping my prop man comes up with something to mount today so I can throw it in the lake tomorrow and play with it.

john

[David]

If you want to try a prop, you can buy one, and then sell it if it doesn't work out. Props are fairly liquid.

There are some Lasers here: http://www.bassboatcentral.com/props4sale1.htm
I've never bought off that site.

Buying and selling has worked for me a couple of times. I have a small problem with accumulating propellers.

Just remember you want the even pitched Lasers (those are small hub) or the small hub Trophy.

[j_martin]

Thanks David, I got all the numbers for the laser II and Trophy Plus props off the mercury parts site. Trophy Plus is available in one inch increments in the small hub up to about 29 inches. I have a 25 inch aluminum 4 3/8 inch bore prop now, if you know where it would find a home. I think I'll take it up to lake Namakan (bottom structure is mostly motor parts) and sell it in the parking lot.

Reese, I just hung on the 24 inch high five, and I checked the motor height. The prop shaft is about 3 inches below the pad. I suspect it will be several inches deeper than that when it's running because it's set back on a jack plate. I'll hang my kid over the fantail tomorrow with a camera and see where it's riding. He's big enough to take care of himself, and smart enough to tie off.

Thanks for all the help.

[j_martin]

Went for a ride today, with a handful of wrenches. When I started with the 24 pitch high five, the shaft was 3 1/2 inches below the pad. It turned about 5500 and showed about 57 mph on the mercury speedometer.

I raised it up almost another inch, and made another run. At full trim, I started to lose water pressure, and the speedometer went wacky. Trimmed in just a bit, and turned about 5700 rpm. I don't know how fast I was going, but I damned near froze out at 39* air temp. I'm sure it was somewhere North of 60.

Did some slower running, and the boat handled like a dream at all speeds.

Setup is now 2 3/4 inches below the pad, trimmed out to about 1 " at WOT.

Kids took some long shot pictures from shore as I drove by. Looks good.

I'm gonna keep the prop. Fog it down, and wait for spring, unless I can find some excuse to haul it South for a bit.

Thanks for all the help.

john