prop question for 3.0 mercruiser

jran · Aug 10, 2013

I have a 3.0 1989 mercruiser in a 17' sea ray boat. I have a 19 inch aluminum prop on it and can pull two tubers at one time with 5 college kids in boat at the same time at speeds right around 25 to 30 mph. I'm wondering how to get more top end speed (obviously with no college kids)...With just myself and wife in boat i hit about 3500 to 4000 rpm's and can get about 35 to almost 40 mph.I just want a couple more mph's if possible. What size prop is gonna give me a few more mph's ????

Genjem · Aug 10, 2013

Re: prop question for 3.0 mercruiser

It sounds to me like you are over propped now. If you can't hit more than 4000 rpm. I would say to try a 17 pitch. That is assuming the motor is in good tune. The smaller pitch will give you more rpm but maybe no more speed. I would say 40 mph is pretty good.

scott8058 · Aug 10, 2013

Re: prop question for 3.0 mercruiser

I agree jus the 2 of u should be able to spin that more than 4000 I would agree w the 17, how we'll do u plane w the 2 tubers and 5 people? If your only topping at 25 to 30 I would think that it's hard to plane w a load. In that case a 4 blade may benefit but what do I know!

jestor68 · Aug 10, 2013

Re: prop question for 3.0 mercruiser

The full throttle rpm range for your motor is 4400-4800 rpm.

But you gotta run it wide open to find out where you are.

Mule Laker · Aug 11, 2013

Re: prop question for 3.0 mercruiser

jran said:
With just myself and wife in boat i hit about 3500 to 4000 rpm's and can get about 35 to almost 40 mph.

That doesn't sound right.

steelespike · Aug 11, 2013

Re: prop question for 3.0 mercruiser

I suspect your tach is not accurate.40 is pretty typical of a 3.0 speed at about 4800 rpm.If your doing water sports with
5 young adults aboard you are doing well with a 19" prop. The only way to be sure of your speed is with a gps.
Confirming your speed will help tell if the tach is accurate.Some cells have a gps app.
Are you trimming up for the best wot rpm and speed?
Depending on your actual rpm a prop change may give you slightly more speed

jran · Aug 12, 2013

Re: prop question for 3.0 mercruiser

I had my 3.0 rebuilt last season and that's why I don't really tach over 4000 rpms... Chicken I guess.. Lol... I guess I can stop baby'n my boat as the motor now has about 50 to 60 hours on it... So do I go down to 17" pitch or a 21" pitch for a couple more mph's.... I will be checking my speed with my gps also....any other ideas???

jran · Aug 12, 2013

Re: prop question for 3.0 mercruiser

The boat planes great with 2 or 4 people aboard. Had it rebuilt last season and I baby the boat big time I'm a putzer.. Lol... Engine has over 50 hours on it and really runs great... Just lookin for a couple more mph's and not sure if I go up or down in prop pitch...

Genjem · Aug 12, 2013

Re: prop question for 3.0 mercruiser

In theory you go up in prop pitch to gain speed. But, if your 19p won't get you to 4800 rpm you don't want to pitch up because you will lose rpm and speed. Don't think I would want a 21p in a 19ft boat with that motor. I would go for the 17p first, find you wot engine rpm.

Mule Laker · Aug 12, 2013

Re: prop question for 3.0 mercruiser

So now you're telling us you just don't want to rev it past 4000rpm and you're "wondering how to get more top end speed"? How's about putting the hammer down?

steelespike · Aug 12, 2013

Re: prop question for 3.0 mercruiser

We really can't tell where your at without a wot rpm and gps speed. Its ok if it over revs briefly to get the figures.
We can't tell if a prop change would work or what size might work.
When I run my outboard a I seldom go over 4000 to 4500 rpm.
Of course I run it wot occasionally, its 25 years old and going strong.
If you're like some guys and pound it wot from here to there every time
it won't be long a rebuild will come along.

fishrdan · Aug 12, 2013

Re: prop question for 3.0 mercruiser

jran said:
I had my 3.0 rebuilt last season and that's why I don't really tach over 4000 rpms... Chicken I guess.. Lol...

HAMMER DOWN Captain!!! (We need good numbers to recommend a prop.)

I pick up 5-6 MPH from 4000 RPM to WOT and normally open it up once a trip (for a few seconds) to see how things are doing, but I usually cruise at 3500. Cruise at 25MPH, tops out at 35/36MPH

scott8058 · Aug 13, 2013

Re: prop question for 3.0 mercruiser

Yeah, what does it do when u drop the hammer? I would def say u want a 17 over a 21 w a 3.0 my 5.7 only over rev'd about 600 rpm w a 21.

eavega · Aug 13, 2013

Re: prop question for 3.0 mercruiser

Have you thought about changing out to a Stainless Steel prop? I run a 20 SST on my 176 Stingray (17 1/2' bowrider, 3.0 L Mercruiser) and get right at 4400 WOT RPM with a full load of fuel, two kids, two adults, plus gear. I get almost the exact same performance (I can rev up to about 4600, with no difference in top speed) with a 17" aluminum I have as my spare prop.

Rgds

Eric

jran · Aug 13, 2013

Re: prop question for 3.0 mercruiser

Lol..... Hammer down Captain!!!!!!!...... You are right about that. The boat wot can hit 4500 to about 4800 rpm's.....35 to 40mph... It just screams tho...... I get a little Leary.... Like I said before I'm a putzer and I'm looking for a few more mph's without going camando like ...... And I love this quote....Hammer Down Captain.......( I'm gonna use this quote.. Lol)....... Thanks guys

steelespike · Aug 14, 2013

Re: prop question for 3.0 mercruiser

If you want us to help select select a prop we need accurate information 4500-4800 is too vague,35-40 is too vague.
Sure it varies do to conditions but run it at speed and give it a chance to settle you'll realize the number.
A early morning run before wind and boaters rough up the water will get it done.

steelespike · May 31, 2015

Welcome.You need to start your own thread.There is a tab near the top of the prop forum.
We need your prop size(near the base of the blades or under the prop nut.
We need the make and year.We need a lightly loaded, wot(wide open throttle) rpm and gps speed.
An induction tach will work and most phones have a gps app.
We're not trying to be difficult but it is important the motor is able to rev freely within its rpm range.
We can't get you there without the information. and for best performance and motor health.

prop question for 3.0 mercruiser

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