Prop recommendations please: 20' Seafari w/ 150 Johnson OB...

[JUST JOHN]

Hello everyone, as stated, looking (in a panic) for recommendations on a propeller, as I may likely have spun my hub on Sunday. I lost power all of a sudden, and had to troll back the remainder of our journey at 1500 rpm max... above that just "reved" with no forward thrust. I thought this was a gas, bad fuel or clogged filter problem, but after talking to my a local marina on the phone, where the 2-stroke 2004 transom-mounted (stock height) motor was purchased; he keyed me into this possibility. I want to be prepared with some information and brands before heading in to see him tomorrow so I make an educated decision. I'm removing the prop first thing when I get home within the hour, and will update the thread accordingly.

Turns out I have a spare three blade, white-painted prop (aluminum?), I believe I can probably run, but know nothing about it, and really want this boat running again by this weekend! ... and a quick education if you will.

Full recommended throttle operating range is 4500-5500 RPM. The existing prop is a 3-blade right-hand stainless steel unit, with worn black paint; I'll update the diameter and pitch when I get it off the existing one. I always assumed that when we repowered in 2004 that this was the same prop from the original 1978 Evenrude 175hp. I understand that the correct prop puts the engine in the recommended rpm range, and needs to be tested for such, but I'd love a starting point. I rarely open her up, usually cruise at 3500-4500 rpms, rarely over. I don't have trim tabs, and don't really have issues getting on plane.

There's a marine consignment store a block away from my work w/ shelves and shelves of props... bad idea buying used??

Three blade / four blade?

Pitch recommendations?

Brand recoomendation?

Replace with what I have already?

What should I expect to pay?

What not to buy?

TIA

watching this now...
https://www.youtube.com/watch?v=Sp0MdKzXaSw

...and reading through Bushwacker's prop sizing thread:
Propping Correctly and how to test props
Unfortunately I do NOT know whether my tach is accurate!

[JUST JOHN]

old prop is a 15 x 17 pitch Johnson Evinrude 387518.
spare one I have is a 14-1/2 x 19 OMC/Johnson/Evinrude 39120.

[Fr. Frank]

John, you didn't say what your performance was with the old prop.

Were you able to reach the maximum rpm (5500) of the maximum recommended rpm range (4500-5500) with the boat at maximum loading? This is called propping for Max of Max at Max. This is the ideal all-purpose prop performance goal.

Many, myself included, keep more than one prop for different situations. But in no case should you ever use a prop that will not let you reach the Max of Max with a light load. If it's just you and a full load of fuel in the boat, you should always be able to reach that 5500 rpm mark. If you cannot, you are over-propped.

In that scenario, if you take on a little water, put a couple of extra people on board, or find yourself in dangerous seas and now you may no longer have adequate applied torque to perhaps get you and your passengers home safely.

Similarly, an over-propped boat is significantly less maneuverable, is much slower to plane, and puts a great deal more stress on all reciprocating or engaging parts.

On the other hand, a slightly over-propped motor can slightly increase your fuel economy and sometimes (but not often) increase your cruising speed. I never use an over-pitched prop when going offshore just for safety precaution.

I run a BRP 15x17 Viper on my Etec 90 25" on the back of my 18' Seacraft. I can reach Max of Max at Max with this prop.

I also have a BRP Cyclone 14.5x15 that drops my max rpm by about 200 rpm, but I can cruise 4-5 mph faster and get 7.4 mpg at cruise instead of 6.9 mpg. It's a bit slower out of the hole, but I can also trim it significantly higher which is helpful in the shallow water through which I often run inshore.

And I have a plain older 14.8x17 aluminum Michigan prop as a spare/emergency prop that I carry offshore, just in case.

[JUST JOHN]

Unfortunately I don't know the performance with the old prop because the boat's been set up that way forever... I believe the old prop was likely correctly sized however. I will be trying the 14.5x19p aluminum prop this weekend, and likely buy another 15x17p if the RPM's are lower than they should be.

I'm curious Frank, wouldn't your 14.5x15 prop increase the RPMs over the 14.8x17? Is it the diameter difference that accounts for this instead of the decrease in pitch?

I did go to the Marina yesterday... he wanted $350 for a used Viper 17p and 550+ for a new OEM ss prop. Also went to the marine consignment shop and although there was only one close one (same diam and pitch, but had fairly aggressively cupped edges), or a prop that need a separate hub which he didn't have in stock... I passed on all options. Also checked FB marketplace, ebay, and craigslist. Might buy something locally...

[Bushwacker]

Frank’s smaller pitch Cyclone prop is a 4B prop with heavily cupped blades, so it’s a totally different animal with much more blade area than the 3B Viper. The Viper is BRP’s “speed” prop which may provide the highest top speed, but it doesn’t have a lot of stern lift, so it won’t hang on plane at low speed as well as a 4B in my experience. Not all props are created equal either, so you have to consider the prop’s design intent . . . some have small blades with lots of cup that are designed to run at high speeds very close to the surface, while others are designed with large blades for heavy loads at lower speeds. BRP’s Rebel is a 3B prop, but it has very large blades with lot’s of cup, so it typically acts like it has a couple inches more pitch than advertised! A dealer told me the Rebel was so hard to turn on a boat like the Seafari that it was not normally used on the small block 60 degree V-6 2.7L motors like the 150/175/200 E-TECs; it’s typically used on the larger 3.3L 225/250/275 hp motors.

Since you currently have so many unknowns (tach accuracy, WOT speed with current prop, motor height, min planing speed with current prop), I would stick to an inexpensive aluminum prop that can be easily repitched if you later find it produces too much or too little max rpm. Once you have decided what performance characteristics are most important to you (max stern lift/cruise fuel economy and minimum planing speed or strong hole shot for water skiing OR max WOT speed) then you can select a prop design that best meets your requirements. I tested a lot of props on my Seafari with a 150 E-TEC/bracket and found that a 4B 14.5x15 Cyclone was the best, but I had to raise the motor about 4” with a jack plate before it would reach max rated rpm. That prop was harder to turn than a 4B 15x15 Michigan Apollo with the same blade area because of the heavy cup on the Cyclone blades. In general, I found that the 4B props provided much more stern lift that helped me to hang on plane at lower speeds than the 3B props, and that is a very significant benefit!

[Fr. Frank]

Denny is right on. I bought the Cyclone just for long range efficiency at cruise and maneuverability. If I'm planning on running out to the Edge, 30 nm offshore, or out 90 miles from Cedar Key to the Florida Middle Grounds, then I put on the Cyclone. (I've only had this boat out to the Middle Grounds once)

For the 18' SeaCraft, largely because of the way I have my boat set up, I'm better off with the Viper for general purpose use.

I have a new copy of the original 49 gallon fuel tank, two Group 27 batteries under the center console, and two Group 31 batteries up in the forward below-deck compartment, and a Minn-Kota Riptide Fortrexx 80lb 62" trolling motor on the bow. So with my weight distribution, I'm not as concerned with stern lift. This is why I'm good with the Viper, which is more of a bow-lifting prop.

[JUST JOHN]

Thank you for all your input!

So we went out Saturday with the spare aluminum 14-1/2 x 19 39120 prop installed. Two people, medium load, 3/4 tank of fuel. Unfortunately, my tach took a dump and wouldn't read above 1500 rpm! The thing can be temperamental sometimes. Last time out my fuel gauge didn't work, which I have since fixed...but there's always something broken on an old boat! Ugh. I'll troubleshoot that tonight.

It was choppy on our 3 mile trip over to Fire Island, southeast wind, so it got smoother as we reached our destination; the barrier island blocking the wind. Still too choppy to run full throttle. As expected, the prop seems to take a bit longer to get on plane, a little less hole-shot punch, which I don't like, but not terrible. I wouldn't say we had any issues getting-on, or maintaining plane. This is an old prop, but was in new unused condition. The Great South Bay is mostly sand, but somehow I managed to put a ding in one blade's edge. -A vote against buying aluminum. I do typically raise the motor substantially and run in shallow waters regularly, to drop passengers and gear. Regardless, it's not a new prop any more... We kissed some paint bye bye LOL.

On our trip back, the wind had died down and it was a very smooth ride, and the prop performed really well! Unfortunately with the tack being in-op, I have no "data" to reference. I may pick up a new aluminum Michigan Vortex 15x17 (992003) from a seller locally and order the appropriate XHS 200 hub Kit. It will all be under $100 if I go this route. The size and profile of the blades looks similar to what we had been running for all these years...

[Bushwacker]

The Michigan Vortex is a good aluminum 4B prop and the 15x17 size should be about right for a 150 motor on your boat, depending on how much load you carry. Their 2-piece hub system is also quite robust and similar to the BRP props. If you get an accurate digital tach and find out that you’re a couple hundred rpm over or under the 5500 target, it can be repitched lower to get more rpm or cupped to reduce rpm.

I selected a 15x20 version of the Vortex that I later had repitched to 15x18, because I made the same mistake that most folks do, ie. not testing with max weight! Once I started testing with a full live well (~15 gallons) and a couple of 60-70 qt coolers full of sea water to simulate the load I typically carried with several divers or on a long cruise, I realized that I was over propped! I ended up with a SS 4B PowerTech ELE4 which used the Michigan hub system and worked very well. I had an awesome hole shot and allowed me to easily run at any speed between a min planing speed of 12-13 mph and a max cruise of 30-35 mph at about 4500. Optimum cruise was about 3750 and 27-28 mph and about 3.7-3.8 mpg on the 150 E-TEC. I ran it for several years until I tested the Cyclone and discovered I could run it higher with a jack plate and pick up 2-3 mph at WOT and get a solid 4.0 mpg at cruise!

[JUST JOHN]

Thanks for the info Denny! I'm going to pick up that brand new Vortex for $40 today and order the hub thereafter. I'll figure out the tach problem... didn't get to it last night. If anything this will become my backup prop if I find I need a different size/pitch, but price is right. Inevitably, I will likely need a stainless prop... The original SS is pretty worn down without major damage, whereas the aluminum resulted in a dent just by looking at it crooked!

Funny you mention the SS PowerTech props... I was in contact with another local who has a new-condition 14-1/2 x 17p SS prop for sale (RAS3R17PMS275)... The blades look narrower, and it was on a 225hp Mercury... so I believe I'd need to buy a new hub to even try it on my Johnson, at a significantly higher asking price for the prop.

I also read good things about the BRP Rebel, but that it acts like a prop two-pitches-higher, so go down in pitch... Any experience with that?

The Marine Consignment shop around the block also has a 14-1/2 x 17p SS Mercury Vengeance prop I'm considering. I might go take a second look at. I'd need to source the 835265Q02 hub.

[JUST JOHN]

So I read that an aluminum prop should be sized one pitch up than an SS prop, and vise versa... This changes everything. I should stop reading!!
This must be why the 19p aluminum seemed OK getting on plane and cruising... or at least somewhat comparable to the 17p SS.
I held off on buying the aluminum vortex wheel...