Mercruiser 3.0 opinions?

[snowthrower]

I just bought a 1991 bayliner capri with a 3.0L alpha one. To replace my 1967 seaswirl with a mercruiser 120.

Now I thought just the refinements in engine design and the 1/2 litre in displacment would make it pull better but it is a little slugish. It will pull me up on the wakeboard OK with the wife and two small kids but the old 120 would yank me right up. I want to be able to have freinds along but I'm not sure how it will pull.

I'm thinking a reprop would help but need advise.

The new boat with the 3.0 is running a 19" pitch prop at 4600 rpm @ WOT and acording to the speedo I'm at about 34-35mph.

The recomended WOT range is 4200-4600 according to the engine cover. I did note that the engine will rev into the 2900-3000 pretty quick on the hole shot.

Should I go to say a 21" three blade to bring the RPMs down and move more water or even a four blade 20"

I wish I could swap the 21" pitch off the old boat onto the new one for a test run but they use differant thrust washers ( ya I checked ).

Also is there any diameter, cupping, or ... ?? that I should concider? If it would help the prop on there does not appear to be the factory unit and all the paint is greyed/missing, could I be cavitating?


Any one else pulling wake boards with a 3.0 that can input?

 

[Bondo]

Re: Mercruiser 3.0 opinions?

but it is a little slugish.
pretty quick on the hole shot.

Which is it,..??...... It Can't be Both............

Going to a 21" will turn it into a Dog,........ It's at it's Peak Power now with the 19".........

 

[snowthrower]

Re: Mercruiser 3.0 opinions?

The whole quote should have been

"I did note that the engine will rev into the 2900-3000 pretty quick on the hole shot. "

I said that just trying to give all the info I could.

That does make cents but the thing that thows me off is that old mercruiser 120 has a 21 pitch and will out pull the 3.0 and it's 40 years old.

 

[Silvertip]

Re: Mercruiser 3.0 opinions?

This boat may be heavier than the old one or the engine may be in need of a tune up. Swapping props is the last thing that should be done to solve a performance problem. And just to confirm, increasing prop pitch would indeed make your situation worse.

 

[snowthrower]

Re: Mercruiser 3.0 opinions?

I understand.

I have already, done new points, cap, rotor, plugs, wire and set the timing.

It just seems this thing should have a little more.

 

[rogerwa]

Re: Mercruiser 3.0 opinions?

If low end grunt is your thing and towing is important, maybe trying a 17" may be better. You will suffer on top end and can overrev, but you will have more pulling power.

I had a 17' searay with the 3.0l and found the 19p to be the best all around, although I was able to approach 40 with smooth water and a light load. I think your numbers are pretty close to my experience.

It could be your previous boat planed easier due to its hull shape which allowed you to gain RPMs and thus gain speed quicker. I know my searay sat real low in the water and was difficult in the 15-20MPH range because it was in a semi plane state.

You may look at Smarttabs to help as well.

 

[snowthrower]

Re: Mercruiser 3.0 opinions?

I thought about tabs but the boat already had a doel fin on it... I know not as good but I would think it would do the trick.

My top end is about were I want it, would going to a 19" four blade help at all? I really don't want to be over reving the motor, it's not uncommon for use to run 15-20 miles up the lake at full tilt.

 

[tommays]

Re: Mercruiser 3.0 opinions?

You will never be happy with one prop


A 19" FOR running down the lake and a 17" for the wakeboard i have been trying for 12 years and there is NO all around prop that will make up for the lack of HP



Tommays

 

[rondi]

Re: Mercruiser 3.0 opinions?

You will never be happy with one prop


A 19" FOR running down the lake and a 17" for the wakeboard i have been trying for 12 years and there is NO all around prop that will make up for the lack of HP



Tommays

What about the Torque-Shift or the (overpriced) Aerostar?
Maybe even the Enertia?

 

[snowthrower]

Re: Mercruiser 3.0 opinions?

Man those are pricey !!

THe only one I did not find a price for was the torque-shift but I'm sure it's pricey.



I got a new problem, my wife decided to drift into the launch last nite then try to gun it away and destroy my prop so now I gotta get a new prop.

I have a very good condition 19p prop that came with my old boat but it did not fit that thrust washer and it's a 15 1/2" diameter and my old prop was a 14". Now I know how pitch will affect the boat but what about diameter?

 

[Crownie2]

Re: Mercruiser 3.0 opinions?

Your lower unit may have a very different ratio than your old one and that would explain the differences in the prop pitch.

As others have noted, if you are sure the motor and hull are in good shape you might try the Merc 18" four blade or possibly the 17" three blade if you really need more pulling power. Be careful - these may take your RPM's above the recommended range at top speed.

 

[pjrogers]

Re: Mercruiser 3.0 opinions?

Snothrower: Is your 3.0 an L or an LX? The L made 115 hp, the LX made 135 hp. It is possible that your newer boat is actually less powerful than the old. FWIW, in the '90s we owned a Spectrum 1750 aluminum bowrider with a 3.0 L. With two adults in the boat and a 17" prop it would pull me (170 lbs) out of a deep water slalom start. With a 19" 3 blade it could not. It could pull me up with a 19" high-five, though. So if you are into water sports you might be best off with a 17" three blade, or if you can afford it, a 19" stainless high-five.

 

[pjrogers]

Re: Mercruiser 3.0 opinions?

Oh, and take that fin off the A/V plate. Get a set of Smart Tabs instead. Best couple hundred you could possibly spend on your boat. Search Smart Tabs on the forum, and beleive everything you read - they truly are a wonderful addition to any planing hull.

 

[craze1cars]

Re: Mercruiser 3.0 opinions?

I know this post is getting old, but in the interest of helping others who are budget-bound to older 3.0 L runabouts, I thought I'd share my success story with my 18 ft 1992 Rinker 181 with a 3.0L Mercruiser (the wheezy 115 hp 4200 to 4600 RPM version)

My setup:

1. Turning point Hustler 14 1/2 x 17 pitch aluminum prop (first generation, has the exhaust ports...will buy second generation again soon due to great success with first, and some nicks are starting to build up)

2. Smart Tabs. ABSOLUTELY CRITICAL FOR ANY UNDERPOWERED BOAT. BEST investment I EVER made in this boat, bar-none.

3. Understand your trim adjustment and how/when to use it. I actively use trim with every ski run (and have trained all other drivers for when they pull me), depending on whether I'm taking off, trying to hold a speed, turning, etc. If you just set it and leave it, you're shorting yourself HP while using more fuel. Thumb on the rocker button...ALWAYS!!!

4. Always has a proper and current tune-up to stock specs, including new plugs, check timing, check carb adjust, arrestor cleaning, pull outdrive, change all fluids, check engine alignment, etc. I do all of above EVERY WINTER in my garage for around $100-ish. And I keep it all Mercruiser parts and fluids.

5. Clean bottom. Always trailered and therefore crust/algea-free. Boats left floating in slips with dirty bottoms are s-l-o-w.

This boat is used almost exclusively for water-skiing adults, with no 2-skiiers in our group. We all do deep-water slalom starts on competition to intermediate slalom skis (none of us has those big-daddy surf-board type skis to help get you out). Our lightest skier is 170 lbs, heaviest in our group is 215 lbs. It pulls each of us out of the water with very minimal drag time, with up to 4 of the same sized adults on board (5th on a ski) and a full tank of fuel. Very quick to plane with minimal bow rise, top speed is a consistent 34/35 mph GPS (maybe only 32 with 5 adults on board), and it is turning about 4,400 RPMS at WOT. The back of the boat gets dragged around a bit with the hard cuts, but since we rarely have much chance to run a course, it holds a straight enough line for an I/O used for open-water skiing.

We're in our 3rd trouble-free year of open-water skiing behind this underpowered machine, and I see no reason to invest in anything better for the moment. 'Tis consistent, quick, and functional. And when you consider it's a 15 year old 115 HP 3.0 L Mercruiser pushing a rather heavy full-fiberglass boat with a heavy load? It's frankly outstanding.

And if ANYONE owns ANY type or size of slightly underpowered boat that has a long plane time...and you haven't bought Smart Tabs yet? Man...you don't know what you're missing. I was a little skeptical until I put them on and took my first ride after install. Lemmetellya...those whale-tail hydrofoil things are not even close to being in the same ballpark as a properly installed set of Smart Tabs. They do pretty much everything but open my beer for me. And no, I have no affiliation with them whatsoever. Just an incredible, inexpensive, trouble-free, cure-all product.

Good luck!

 

[MikDee]

Re: Mercruiser 3.0 opinions?

IMO, I'd suggest an 18"- 4 blade to bring your power up, and keep your RPM's, and speed, in the proper range, you'll probably get less slippage, then your 19"-3blade also, even though a slight drag of the 4th blade will be there, you'll still be ahead of the game, that's why I don't recommend a 21"- 3blade, or a 20"- 4blade.

 

[rondi]

Re: Mercruiser 3.0 opinions?

I have just returned from a week out at Lake Mojave after purchasing a slightly used 19P Hustler "old style". What a difference.
With the Hustler and 40lb Smart Tabs the 175 is literally on plane instantly. There is never any bow-rise, as soon as I hit the throttle it is planing. We had the boat completely loaded with a full tank of gas, 4 adults, 3 kids, 2 ice chests, 2 EZ-ups and all the other junk with the load all in the rear section - boom . . . . jumped right on plane. Ive tried this same load before with the stock prop and no tabs and the bow pointed to the sky for 30 seconds. Also, there was a noticeable difference in how smooth this prop runs, no vibration all the way through the low to high RPM's.
My wife says the new prop was a big improvement pulling her up on the slalom ski. When going WOT I lost about 3 MPH although when testing I was running with the bimini up and there was a strong breeze. With the stock 21P Black Max my WOT RPM's were at 4600 and with the Hustler 19P it's now at 4750, so there is no worries of over revving.
The Hustler bites much better than the Black Max. We pulled 2 different tubes all week and never once had the prop blowout in a sharp turn.

The Hustler 19P will remain as my primary whacker and the Black Max will hang out under the jump seat as my backup. I will trade a slight loss of MPH for all the benefits that the Hustler gives any day of the week.
This 175 with the ST 40's and the 19P Hustler is a really big difference from stock and just may be as good as it could get without the high costs of a SS prop, especially for watersports usage.

 

[craze1cars]

Re: Mercruiser 3.0 opinions?

Glad to hear that someone else has found great success with a nearly identical setup to mine, and my findings were not just a fluke. I believe the combo of Smart Tabs along with the inexpensive Hustler aluminum prop is tough to beat for a 3.0 runabout. The combo will certainly beat the snot out of spending the same amount of money on ANY expensive stainless prop (without the Smart tabs).

Out of curiousity, what is your top speed before/after your changes? I actually switched from an old stainless prop to the Aluminum Hustler...gained notable accelleration, kept my identical top speed. And I presume you have the LX 135 hp version, correct?

 

[rondi]

Re: Mercruiser 3.0 opinions?

Out of curiousity, what is your top speed before/after your changes? I actually switched from an old stainless prop to the Aluminum Hustler...gained notable accelleration, kept my identical top speed. And I presume you have the LX 135 hp version, correct?

Actually, after the install of the Smart Tabs I was able to gain a few MPH up to 47 GPS (alone, 1/2 tank of fuel, winter cold and no bimini on glass). Now after going to the Hustler 19P I am back down to 44 MPH - but this was under different conditions (alone, 3/4 tank, summer warm, windy and bimini up) I really don't think I lost much if the conditions were the same. But even if I lost the whole 3 MPH - the new strong feeling of this prop would be worth it.

Yes, I have the 135 HP 3.0 Merc with an Alpha One 2.0 gearing.