1993 Evinrude 70hp Missing Prop, Seeking Recommendations

[petrowski53]

I have a 1993 Evinrude 70hp that I needs a prop. I bought the motor to replace a '97 50hp Evinrude on my underpowered 1997 Sunbird 150 Spirit (15'10"(L) and weighs in on the CAT scale at about 1900 pounds with motor, fuel & gear). I've spent the last year getting the 50hp in excellent running condition, but have came to the realization that it's just slightly underpowered for my boat. The 50hp performs marginally (at best) with anything more than 2 average people in the boat, even with the 13 x 11p prop currently have installed. With this prop, the 50hp can achieve about 24mph at 5900 WOT with just me in the boat, 20-21mph in the 5400rpm range with another person, and barely / fails to get on plane with 3.

Unfortunately, the 70hp I intend to rig did not come with a prop. I know both the 2-cy 50HP and 3-cyl 70hp use a 13 spline prop, but I believe the 70hp utilizes a slightly larger diameter prop (it has a larger gearcase). I currently have a 13 x 11p, 12.25 x 13P and 12.25 x 15P for the 50HP (all BRP/Solas aluminum), but I believe those all may be too small / low pitched for the 70hp.

Any recommendations for an aluminum prop for my setup with the 70hp? Getting on plane for comfortable cruising is my top priority vs. maximum speed. If i can comfortably hit 30mph, I would be happy. Anything more would be a bonus.

 

[jlh3rd]

When posting a question about propellers, you cannot get a reasonable answer unless you provide the following information in your post: Items 1-4 are essential for meaningful response to most questions.
1) Performance issue you are trying to correct.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
3) Current prop diameter and pitch (required).
4) Wide open throttle RPM and speed with an average load (very helpful)
5) Engine/drive make, model, year, and HP
6) Boat make model, year, length and weight

these are the guidlines to follow when propping a boat. Any other method becomes a guessing game and can be expensive unless you know a place that lends out props to try.
So, start with your props, know what your max engine rpm is, and go from there. See what the 12.25x15 does for a starting point.

 

[racerone]

Is your boat water logged ??----And is the motor in good condition ?-----Post the actual compression values here.-----A 17" pitch prop should do the trick.----But I think 1900 LBS is an issue here.

 

[Texasmark]

Is your boat water logged ??----And is the motor in good condition ?-----Post the actual compression values here.-----A 17" pitch prop should do the trick.----But I think 1900 LBS is an issue here.

Back when the family and friends spent a lot of time on the water, the 3 cylinder 60 and 65 HP OMC engines were running 15P props on their family's 15' lightweight fiberglass boats with pretty much non-veed transom area for boating and water skiing. I agree that totally shooting from the hip, if I were to ask myself that question, I would think that the 17P would be a good choice for the 70 hp.

 

[racerone]

The 93 model 3 cylinder is 56 cubic inches.----And prop rated power.----1900 LBS seems HEAVY to me.

 

[JimS123]

Obviously, you have no starting point data and you are flying blind. No sense for any of us to list what you need.

Get a prop catalog (Michigan wheel would be my choice....Solas?) and search for your motor and general boat size and go from there.

When you try the suggested prop, come back with rpm and speed data and we can direct you how to optimize your setup.

 

[jimmbo]

I agree with Racer, a 17" would be a pretty much what would be on a 70hp on a boat in the 16' range. I also think 1900lbs is a bit Heavy for that Hull.

 

[petrowski53]

The boat is not waterlogged, that is the weight, measured off of a CAT truck stop scale, with engine rigged, all my gear, full tank of fuel, batteries, etc. Empty weight of the boat per manufacturer brochure was around ~1200. The number was also caluclated by weighing my vehicle and then vehicel and trailer, so it may not be the most accurate.

Compression on the 70hp is ~130psi on all three cylinders per my gauge.

I understand that untill have a baseline to go off of with this engine rigged, it is somewhat of guessing game when it comes to correct pitch. I was mainly concered with correct prop diamter for the 70hp. As I said, I already own several props for my 50HP, but I was under sthe understanding that the 70HP may require a larger diamter and they would not be compatible.

 

[racerone]

13-1/4 or 14"---diameter for 70 hp.

 

[jimmbo]

There is an Easy way to get the Weight. Weigh the Boat and Trailer, unhooked from the Tow Vehicle(get it off the Scale), then go launch the Boat, return with the Empty Trailer and do the Solo Weight thing again for the Trailer.
Even 1200lbs for an 15-16 ft Hull seems a bit high
BTW, water is heavy, 10lbs per Imp Gallon(about 8 1/3 lbs US Gal)

I would be more concerned about the Diameter of the Propeller Hub, than the Blade Diameter.