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.