75Hp Evinrude - New Prop 3 or 4 blade?

[samm835]

I am installing a 75 HP on my 24ft Pontoon in the next couple of months. Right now its in my garage getting a new paint job soon. My question is it currently it has the standard 3 blade prop on it, I have heard a 4 blade can push the boat better. Can anyone give me an idea of what to buy...here is what this will be used for.
1) 24 ft pontoon
2) some tubing (I don't need extreme quickness for the kids) its a toon not a ski boat
3) decent gas mileage
4) decent speed..again I know its a toon not a speed boat

What pitch and blades would be a decent all around prop to buy Thanks

 

[steelespike]

Re: 75Hp Evinrude - New Prop 3 or 4 blade?

There is no such thing as a standard prop.The prop size should be on the prop
Barrel or under the nut. _ _ X _ _ or a part number.
We also need year or model number of the motor.Only way to be accurate with a new prop ;we also need your present rpm and speed.True a 4 blade is generally used for heavy loads hard to push boats.If you need a tach check into the tinytach,reasonable and easy to install.Probably best to wait until you can test it out.

 

[samm835]

Re: 75Hp Evinrude - New Prop 3 or 4 blade?

Well I meant standard...by being it looks like what came with it. I don't have a tach on the boat or the motor hooked up at this point, I will get the numbers for you tonight and hopefully you can point me in the right ...rough direction. I am going to look into that tinytach...have you installed one before?
Thanks

 

[steelespike]

Re: 75Hp Evinrude - New Prop 3 or 4 blade?

I haven't installed one yet.But I believe it is direct induction from the plug wires. As I understand it it consists of wrapping the tach wires around the plug wires.Be sure to explain to them the details of your application as wires
cant be cut or spliced.I think on certain applications you need to do some math to get the numbers.ie:devide or multiply by 2?
I do intend to get one for my 65 Merc 500 when I get around to doing the final setup.

 

[Silvertip]

Re: 75Hp Evinrude - New Prop 3 or 4 blade?

A Tiny Tach has one inductive pickup wire so there is no # of cylinders selection. Two stroke engines fire once every revolution of the engine so make sure the one you buy is for that application. Four strokes fire once every other rev. Since you have a 75 HP motor, why not spend just a bit more money and get a "real" tachometer.

As for the prop, there are a number of specialty "pontoon" props that feature what are commonly called elephant ear blades. These props work well on pontoons because they have far more thrust in reverse than a conventional prop. They also provide a little better forward push but that all depends on lots of things. At this point it is all moot because you have no idea what prop you have now and what the wide open throttle rpm is with an average load. Until we have those numbers we can only guess what you need. When it comes to props, you don't want to guess as this process gets costly.

 

[samm835]

Re: 75Hp Evinrude - New Prop 3 or 4 blade?

Ok, so if I am understanding you both correctly...the best thing would to be put a tach on the boat first. Well I couldn't locate a "tiny tach", so lets go this route...since the boat is out of the water and the motor is getting a face lift.....how would I install a "real" tach. Is it a hard thing to do ...and is it expensive to do? Should I ask this on another forum?

 

[steelespike]

Re: 75Hp Evinrude - New Prop 3 or 4 blade?

I think you would get better tach results on the Evinrude/Johnson forum.
Probably does make more sense to get an OMC compatable tach.I don't think it is very complicated.You just need a tach that matches the OMC technology.

 

[Silvertip]

Re: 75Hp Evinrude - New Prop 3 or 4 blade?

Outboard tachometers are very generic and you can get them right here on iBoats, Cabela's, or Great Lakes Skipper for around 50 bucks. You cut the hole in the dash for the tach. There are four connections. 1) indicator light for night running. 2) ground, 3) +12 volts when the ignition key is on, and 4) the tach sense wire which connects to the charging system.. The instructions come with the tach.

Here is just one example and it even has a built in hour meter for $50:

http://www.greatlakesskipper.com/productdetail.cfm?CatID=7&SubCatID=25&ProductID=743