CONTINUOUSWAVE

[On a 1976 OUTRAGE 19 boat] I re-powered with a [1999 Ocean Pro V6] 150-HP engine from a [1999] four-cylinder 130-HP engine While the horsepower increase is minimal, I still hope to get increased torque and top-end. Both motors have excellent compression and spark.

The Ocean Pro 150-HP is 25-inch-shaft model (as was the prior engine], and both were mounted on a CMC Manual 5-inch jack plate. But I believe the engine mounting height is still to low.

I've discovered that my biggest concern may be the difference in the lower unit gear ratio. Based on what I recently read, the 130 has a 2.25:1 ratio and the 150 has a 1.86:1.

When the boat was powered with the 130-HP engine an a 14.5 x 19 stainless steel propeller, the boat speed reached 37 to 39-MPH at an engine speed of 5,700-RPM.

With the same propeller and the 150-HP engine, the boat top speed was 35.5-MPH at an engine speed of 4,500-PRM.

Q1: can the 150-HP engine with a 1.86 gear ratio increase the torque and top-end ?

I realize there are several other factors to consider, but I thought I would start here. Also, the 130 weighs 405-lbs and the 150 weighs 370-lbs. Any advice and/or recommendations is greatly appreciated. I tested other propellers and will discuss the results in the future.

Thank you---EPJ

Something sounds off to me. That 150 doesn't seem like it is reaching full power.

Q: How deep is the in the water is the engine running ?

Even though [the 150-HP engine] is only 20-HP more [than the 130-HP engine], [the 150-HP engine] should be putting out way more torque, and should be able to handle that propeller.

I know it is a different motor but when I owned a Lowpro 19 with a Yamaha 150 2005 VMAX it would run 50-MPH or more. The propeller was 19-pitch.
Archie

Thanks Acassidy. I agree with you. With the motor obviously too low, I tried a 15.25 x 15 aluminum propeller. Boat speed was 37.2-MPH at 5200-RPM.

[A 15.25 x 15 aluminum propeller] clearly isn't the right propeller, but I wanted to see if I could get engine speed to increase.

In one day I will retest with additional vertical lift and with the stainless steel 14.5 x 19 prop. I'll report my findings.

The difference in gear ratio means that the load on the engine from a particular propeller will be greater on the 150-HP engine because its gear ratio has less reduction (1.86:1) than the 130-HP engine (2.25:1).

I think by your expression "top-end" you mean boat speed at full throttle.

The boat speed of a moderate planning hull boat is a function of power-to-weight ratio to the 0.5 exponent.

If you change to 150-HP from 130-HP and there were no change in weight, the boat speed would increase by a ratio of (150/130)0.5 or by a factor of 1.07--but that is if there were no weight change.

The 150-HP engine has added 35-lbs to the boat. I suspect the total boat weight is probably around 3,000-lbs, so we can figure the weight gain was 35/3000 = 0.01 or minimal. Adding that factor into the estimate for speed increase we get [(150/130)/1.012]0.5 or by a factor of 1.067--really no difference.

You report that with the 130-HP engine the boat could reach 39-MPH. With the 150-HP engine we should expect the boat to reach 39-MPH x 1.067 = 41.6.

The notion the boat speed could increase to over 50-MPH due to a change to 150-HP is not realistic.

Find a propeller that lets the new 150-HP engine accelerate into its optimum engine speed range. Usually for a carburetor V6 engine the optimum engine speed range is about 85-percent of maximum allowed engine speed.

I don't have any data on your particular engine, but to illustrate I will assume the maximum engine speed allowed is 6,000-RPM. The optimum engine speed is probably about 5,000 to 5,500-RPM.

With this in mind, we look at your outcome with using the 19-pitch on the 150-HP engine. The engine could only accelerate the 19-pitch to 4,500-RPM. In order to increase engine speed, the propeller load must be reduced. This is usually done by reducing pitch. We can make a guess that a 17-pitch propeller will let the engine accelerate to around 5,000-RPM. With that assumption we can predict the boat speed using a propeller calculator and input values:

RPM=5000
RATIO = 1.86
PITCH = 17
SLIP =10

The predicted speed is 38.9-MPH. Perhaps by raising the engine mounting height you can get some additional engine speed from reduced drag of the gear case through the water. Let's assume you can hit 5,300-RPM. The 17-pitch will then produce a boat speed of 41.3-MPH. That is about all you are going to get with the 150-HP engine.

Jim, thank you for your response. I admit that my expectations were a bit high. Also, unless I'm mistaken, the 1999 130 hp Johnson actually weighs about 30-35 lbs more than the 1999 150 motor. I'll have some data for you folks in a few hours. Again, thank you very much.

There are still too many details missing. Rigging and prop selection is mostly science with a bit of art.

What is the current engine mounting height on the setback bracket?
What is the height of the anti-cavitation plate above the keel using a straight edge?

What is the WOT rpm range of the new-to-you engine?
What is the lower unit gear ratio of the engine?
What is the brand and model of prop you are using?

Prop recommendations for the engine/boat combination include:

14-1/4" x 19" OMC SST
14" x 19" Mercury Laser II with newer hub style

It is recommended to change only one variable at a time when conduction propeller testing otherwise results are not definitive.

epj wrote:...the 1999 130 hp Johnson actually weighs about 30-35 lbs more than the 1999 150 motor..

Hah--very surprising that the V6 weighs less. But the predicted speed increase for 150-HP compared to 130-HP should be about the same, as the weight difference if very small.

Also note: the torque that turns a propeller is the torque at the propeller shaft. A gear reduction of 2.25:1 amplifies the engine's crankshaft torque more than a gear ratio of 1.86:1 does. The V6 150-HP might have more torque than the L4 130-HP engine at the crankshaft, but the 130-HP engine gets a more favorable gear ratio to turn the propeller shaft.

I would research that again. The looper 130 is a V^ OMC missing 2cyls, it is not heavier. There is something wrong with both of your setups as My 1976 Revenge 19' did 40 with a 115hp and over 50 with an OMC 175hp spinning a 21" SST an a Revenge is heavier. You should be running low 40's with the 130 and 50+ with the 150.