Prop Parts and what should I be using

[clockdaddy]

I've got an '85 Evinrude 120 VRO. On that particular year (for some unkown reason!!) there was a 150 hp lower unit put on by the manufacturer. I've verified this and, sure enough, props for the 150 lower unit work perfect.
Right now, there's a "Composite" prop on the engine. I have never had a composite before and know absolutely NOTHING about them. This prop is made in sections so that a (as in 1) blade can be taken off if it gets damaged and replaced with another blade. On one hand it's nice because it helps protect the lower unit, but the prop will break quite readily and I don't know where to get replacement parts. This is a four blade power prop and the only markings I can find are"1418A-4". Can anyone fill me in on where this can be replaced?

What size of speed prop should I get for the engine. The power prop is great when I have my kids out skiing, but a speed prop is better for my fishing trips. Should I go with another composite or should I bite the bullet and get S.S. or go the middle line and get an aluminum?

 

[Silvertip]

Re: Prop Parts and what should I be using

For starters, you need to provide some current performance data. What is the maximum engine RPM and maximum speed at wide open throttle with an average load. Then you need to determine what the current pitch is. Going by the number you posted I would think its an 18 pitch. The problem here is that composite props have a great deal of blade flex so although its an 18 pitch, it may actually be performing like a 17 or 16. Regardless, without accurate RPM and speed numbers you have no idea if the composite is even correct for the engine. At wide open throttle, you want the engine RPM to be at the top of the recommended maximum RPM band for the engine. This will be about 5500 - 5800 RPM for your engine. If the engine does not reach that RPM range you need less pitch. If it exceeds that RPM range you can use more pitch.

 

[clockdaddy]

Re: Prop Parts and what should I be using

Unfortunately, I just got the boat a couple of months ago. It has primarily been in storage 99% of its lifetime and due to the lack of use, the carbs are in need of a severe cleaning. I've only had it out once and experienced significant starting and idling problems. I really didn't realize everything that was needed to properly size the prop to the engine. I guess I'm getting the cart before the horse...better get the engine running top notch first!!
Now, at least, I know what to consider and check for when I get it on the water again. Thanks!

 

[Silvertip]

Re: Prop Parts and what should I be using

While you are in the process of getting the engine performing properly, determine what the lower unit gear ratio is. That will be a number like 2.0:1 or 1.86:1 which means the engine must turn 2 turns to make the prop turn once, or 1.86 times to make the prop turn once. You can then use any of the on-line "prop calculators" to play with those numbers to determine the starting point for prop selection. Entering engine rpm, gear ratio, prop pitch and speed you can determine prop slip. Or entering any four values you can find the fifth. The ideal prop will put engine RPM at or slightly above the maximum recommended WOT rpm.

 

[WillyBWright]

Re: Prop Parts and what should I be using

What you have is a Piranha Prop. Google it and I'm sure you'll find their website. There's probably a dealer locator function. Besides being able to replace damaged blades, you can also repitch by replacing all four with another spec set.

It's probably not a 150 gearcase, just the same housing with different gearring. That's a very strong 120 and it performs very well with the V-6 size gearcase.

As to which kind of prop is best, it depends on where you run the boat. If it's deep water and you want performance, stainless is the best option. If you run rivers where water can be difficult to predict, the safety offered by composites is best. Aluminums are good all-around props and a good compromise.

Besides protecting the gearcase, composites also flex which can aid in holeshot (accelerating to plane), acting sort of like a variable ratio transmission. Stainless flexes very little and you get the opposite effect, however most have ventilation holes that allow exhaust bubbles to cushion the thrust and accomplish prettty much the same effect as the composite flex.

Being new to boating, I would discourage stainless. If you hit bottom, you can destroy the gears inside. Aluminum or composite is best for beginners. Props are a fraction of the cost of a gearset and shafts.

Next to a reliable motor on a sound boat, the most important thing to have is a map of the body of water you'll be operating on. That way you have a really good idea where the shallow water is. A lot of renters and newcomers assume that if there's water with nothing sticking out of it, you can drive a boat there. But trouble lurks under the surface if you don't know how deep the water is in any particular spot. There can be shallow water right in the middle and deep water right along the edge.

 

[clockdaddy]

Re: Prop Parts and what should I be using

Hey guys, ya'll have given me a lot to look at!!! But that's great!!! When I learn all this "stuff" I can help others, too.

I appreciate the tip on the pirana props. I'll check it out and let ya know what I find.

Thnak you, thank you , thank you!!!!!!!

 

[clockdaddy]

Re: Prop Parts and what should I be using

Hey guys, ya'll have given me a lot to look at!!! But that's great!!! When I learn all this "stuff" I can help others, too.

I appreciate the tip on the pirana props. I'll check it out and let ya know what I find.

Thank you, thank you , thank you!!!!!!!

OOpps ! I mispelled the name of the prop....oh well!!!

 

[clockdaddy]

Re: Prop Parts and what should I be using

Manufacturer: Evinrude
Model: "V-4 Engine with V-6 Gearcase"
Year: 1985
Horsepower: 120.0
Cylinders: 4
Type: 2 stroke
Gear Ratio: 2.25:1
Min WOT RPM: 4500
Max WOT RPM: 5500
Spline Count: 15
Drive Type:

I've checked out the Piranha site and the information above is the OEM setup. This will help me a lot! The props are sold retail at 95.00, but if it saves my lower unit just once, it's paid for itself for the next 5 years!!!

 

[clockdaddy]

Re: Prop Parts and what should I be using

Well....I checked out the piranha site a little better and the price I said before is just for the hub assembly!!! The entire 4 blade prop (which mine is) is 189.00 ea. and 22.50 a blade to replace any damaged blades. Kinda steep...