Should I change prop pitch/ go to stainless.

[Gbakman53]

I am going to be adding a jackplate with 6 inches of setback to my setup. My current setup is a 15-foot v haul, with a 115 merc tower of power, 19 pitch aluminum prop. Currently turning around 5000 rpm. This is a bit low right now, but that should come up with the jackplate height. Currently experiencing some chine walk at 50mph, im worried the jackplate will make this worse. Im wondering if a prop change might help, or maybe trim tabs are the way to go. I know its going to be hard to give advice withought me having any feedback yet with how the jackplate handles. But thanks in advance.

I am not sure if I could make any difference in speed or performance maybe even fuel efficiency but I would like the members comments and feedback on my boat prop? I have a 1979 StarCraft Fishmaster 160 with a 1985 Johnson 70 hp J70ELCOS outboard motor. The boat has been completely rehabbed and I would put my best guess at 700-800 lbs without the motor. The motor weighs about 250 lbs. so total weight without fishing gear and passengers it’s about 1000 lbs. Give or take! I currently have a 13-1/4” x 17 prop on it. I also have a 13-3/4” x 15, steel prop not stainless steel because it is magnetic attaching. Usually 3 or 4 adults will be on the boat. My question is should I stay with the 13-1/4” or change it to the other one? I forgot to mention that I have a Stingray Senior classic 2 series fin on the motor above the prop and I have a Hydro-Shield fin located underneath the prop. Picture posted

 

[jbcurt00]

Best to ask questions about your setup in a topic of your own.

The topic you posted to was about an unidentified boat w a Merc 115, completely different then your setup.

Moved

 

[jimmbo]

First of all, do you have any info regarding what you maximum Rpm is with the 17 inch prop? Also do you have the rpm without all that Garbage bolted to the Gearcase?

I have Never heard of a Steel Prop for that Engine, only AL and SS. Not all SS is non-magnetic

 

[racerone]

Why would you say that the 15"prop is not stainless?----Some stainless is indeed magnetic.

 

[Gbakman53]

First of all, do you have any info regarding what you maximum Rpm is with the 17 inch prop? Also do you have the rpm without all that Garbage bolted to the Gearcase?

I have Never heard of a Steel Prop for that Engine, only AL and SS. Not all SS is non-magnetic

To answer your questions about RPMs, NO! I have never had the boat in the water. I have never had the motor in the water. As for the “Garbage”
well the top fin was standard on that motor when it was built! And the hydro-shield, I bought it and installed it, it is supposed to do two things, one protect the prop from underwater debris damage and second, it is supposed to help the boat get on plane faster. Now, I have two props, one is painted black, 13-1/4” x 17 and the other is silver metal, 13-3/4” x 17.
I would ask does anyone know or have any experience or knowledge about
which prop would be the best for my boat? I am looking for someone who can give me some advice as to which prop would best suit my boat. I am not looking for a boat that will run like a bat out of hell! Just looking for a good handling, good performance, fuel efficiency and reliability! Anyone who may have an honest opinion, please share it. For those who don’t
have a worthwhile opinion, feel free to keep your opinions to yourself!

 

[jimmbo]

That big white piece of Garbage bolted to the AV Plate is Not Standard on any OMC Motor. Whatever that thing bolted to the Skeg is, is certainly going to slow you Down,
I suspect the 15" is gonna be close to what you need to run. WOT Range for your Motor is 4500 - 5500. That Motor is making about 1.4hp per cubic Inch, and is best to prop it to run in the Upper Half of the WOT Range, at WOT. Try the 15" first. However, if you don't have a Tachometer, get one, and make sure it is set correctly for the Engine.

 

[aspeck]

Is the Stainless prop a 15” or a 17” pitch. You mentioned both. If it is 15” I would start there since you want to run with 4 adults. I will say that at one point having a 16 ft bass boat with a 75hp Johnson, 4 adults will be tight and tough to get a good hole shot. As mentioned, make sure your tach is accurate because you really want to keep the RPMs in the proper power range.

 

[Gbakman53]

That big white piece of Garbage bolted to the AV Plate is Not Standard on any OMC Motor. Whatever that thing bolted to the Skeg is, is certainly going to slow you Down,
I suspect the 15" is gonna be close to what you need to run. WOT Range for your Motor is 4500 - 5500. That Motor is making about 1.4hp per cubic Inch, and is best to prop it to run in the Upper Half of the WOT Range, at WOT. Try the 15" first. However, if you don't have a Tachometer, get one, and make sure it is set correctly for the Engine.

I have one ordered and it will be here Thursday.

 

[Gbakman53]

I just want to provide some information about the ”garbage I have on my motor. It has a 4 out of 5 rating with retailers that sell it. I believe a person who is looking for better overall performance from their boat would appreciate the facts about this equipment. Those who wish to not have this information or prefer to down someone else’s choices should really consider to keep their negative opinions to themselves rather than make themselves look very foolish and IMHO IGNORANT! I think I have said enough about this topic!

 

[jimmbo]

It is your Motor and you are free to downgrade your Boat's Performance with that stuff.

 

[redneck joe]

take it off and see what happens to your performance. Put one or the other back on and measure. Since you have not had in the water yet, this is a perfect time.

I've never seen the one on the bottom (assuming it has the same goal as the upper) and as stated it was neither was a standard from any boat motor manufacturer. There are things that they help with like getting on plane or staying on plane at low speeds, of course moving bodys around can have the same effect.

here is your catalogue if interested:

https://starcraftmarine.com/wp-content/uploads/StarCraftFishBoats1979_web.pdf

 

[Pmt133]

I'll be the first to admit I've used doel fins (the davis ones as the others just never worked well) on and off forever. On very underpowered and heavy hulls they have their place. My 3.0l in a 19' is a perfect example of severely under powered.

But adequate power, proper propping or trim tabs usually negated them, and for less of a penalty. I won't say they don't have their place, but if you can get equal performance without them, I personally don't run them.

If anyone is curious, below is a speed comparison between using and not using a doel fin... While I didn't do a statistical analysis... I've had this engine in the hull for 3 years, I can say for certain the orange line is always what it ran with the doel fin and the blue line is always what it ran without it. That is an across the board improvement and rpm pickup near the top which means it is creating a significant amount of extra load on both the drive and engine... Worth trying both ways in my opinion.

 

[aspeck]

I used the fin and removed the fin. Yes, it gave a better hole shot and helped the boat plane faster ... your 70 on that 16 footer will probably appreciate the help in planing. But it will be at the expense of top end speed. It also adds drag and therefore lowers the fuel economy at on plane speeds (it will save fuel getting on plane faster, but you will have to run the engine harder to go the same speed, thereby reducing fuel efficiency). But if you don't care about top end speed and are only looking to cruise around at lower speeds, the fin can be your ticket. I never saw one of those bottom skeg contraptions, so I can't comment on them.

But back to the prop ... the reason for this thread anyway ... it will be a trial and error to get the correct pitch for your setup. Be prepared to try different props and check them by their feel or performance against the tach. You want the best performance you can feel in the specified rpm range. You don't want to over rev your motor and do damage to it or under rev and be constantly putting a strain on it. As I said before, the 15" pitch is a good place to start, but be prepared to go up or down as needed.

 

[Gbakman53]

After reading several articles about prop size and pitch. Even though the original prop that was on the motor when I purchased it, as well as the “so called garbage “. The Stingray Senior Classic Series 2 hydrofoil which I was told by the previous owner to be factory installed, was actually dealer installed at time of original owner purchased the motor with the boat package they purchased. But I will go ahead with it and see if it performs as advertised and as well as other purchaser’s opinions. I will also go with the Hydro-Shield which I purchased and installed as I will be using my boat on the local Trent River and my go a bit north to the TAR River. Both have some floating debris that is very hard to see and can do major damage to the boat and motor. I believe in being an Active Person and not a reactive person, the Marine Corps taught me that, so if my garbage can help save my boat and motor, I will be happy with my garbage. I removed the black 3 blade, 13-1/4” x 17, that I have read was a standard prop for this boat. I cleaned up the other prop, 13-3/4” x 15, and as I suspected it is in fact, a Stainless Steel prop! Did some other work today, ran a gray wire from my center console back to the motor and tapped into the gray wire for my tachometer gauge, which came in but it is not the correct one so reordered and it will be in on Monday. But I have the hole drilled and the wires ready for it so I’ll have it working pretty quickly. I appreciate all the help from members that provided honest constructive comments and advice. For those that feel they are the “Know it all on the forum “ well I have said my thoughts on you! Posted a pic of my fuse panel probably not the quality that most people would have used but I am happy with it. It is located on the port side of the center console in a small electrical box, I believe that if it gets wet, well the boat is probably going to need a complete overhaul and repair because it was sunk!

 

[jimmbo]

The pic of 15" shows it to be a Stainless. As for the 17" being Standard. It is the Pitch that is shipped with the Engine. It was picked by the Manufacturer, as being suitable for the expected Boats the Engine most likely to be installed on. In the Evinrude-Johnson Engine Brochures, it was stated that the Prop shipped with the Engine could be swapped for one more Suitable for the Boat and intended usage. Mercury solved the "Standard Prop" misconception by not shipping the Motors above 20hp with a Prop many decades ago.
As for protecting the gearcase, avoid Shallow areas, especially if they are Rocky, as nothing bolted on is going to save the Skeg or in most cases the Prop. A SS Prop while resisting Minor Damage itself better than AL, becomes a Liability as it will transfer more of the Impact Energy to the Drivetrain. AL Props will pretty much break apart absorbing said Energy. Many Propshafts are bent when SS Props hit things. Been there, done that.
Good Luck with your Adventure

 

[redneck joe]

i run way upstream most every trip. I just budget a cheap aluminum prop every year.

 

[dingbat]

As for protecting the gearcase, avoid Shallow areas, especially if they are Rocky, as nothing bolted on is going to save the Skeg or in most cases the Prop.

Can’t get any shallower or rockier than the Potomac River above the fall line.

Standard equipment for River Runners

 

[jimmbo]

ROTFLMAO!!!

My experience with Rocks and SS Props. Bent the Propshaft too. Impact occurred at about 21mph

 

[Pmt133]

I want to run the middle/upper Delaware... and then I see the rocks and boulders that are in the channels during low flow from land when I'm out to dinner and I decide not to. I'll take my coastal plains and ending up on a sand bar over a gearcase.

 

[aspeck]

In most cases a SS prop will improve performance, but not all cases. I changed to a SS on my current boat and it didn't do anything for upper end performance, which surprised me. However it greatly aided low speed manuevering. That surprised me greatly, but I was happy because my current boat is a sled at slow speeds. A pontoon boat handles better at slow speeds than my 19' dual console.