Mercury vs evinrude

[merc 18xd]

And I'm currently thinking about upgrading my merc 18xd (18hp) with a 35hp evinrude. The outboard will be use on a 14ft x 6ft wide jonboat with decking. The boat weight about 500lbs with TM ands battery and 800 lbs with me and fishing gears ands stuffs. The max speed is 22 mph with a 13" prop.

Here's the thing thats bugging me. Mercury outboard use a larger pitch prop than evinrude for the same class of hp ex: 25hp merc = 13 evinrude 10-11". With a higher pitch the merc should be faster?

So will this upgrade make me go any faster and which prop do you recommend.

My main focus is top speed.

Thank you all in advance.

 

[Silvertip]

Re: Mercury vs evinrude

It isn't only the prop pitch that determines speed. The lower unit gear ratio determines the speed of the prop at any given engine rpm. If both engines turn 5000 rpm, they both have the same gear ratio and use the same diameter and pitch prop, then they would (theoretically) run at the same speed. Without a tach you have no idea how fast your Merc is running so you have no idea whether the prop you have is correct. I don't know the ratios offhand nor do we know what year engines you refer to. As an example, 40 and 50 HP carbed Mercs use 1.83:1 gear sets and typically run 13P props. 40 and 50 HP Evinrudes & Johnsons have 2.47:1 gear sets and typically run 15 or in some cases 17P props. Put those engines on identical boats and they will run about the same speed. I know from experience. It's all in gearing and prop pitch.

 

[JB]

Re: Mercury vs evinrude

More hp has the potential for more speed if it is properly rigged and propped.

You need a tach, even if it is temporary, for setting up the rig and propping it correctly.

The Prop Forum is where to get advice on finding the best prop.

Good luck with the 'Rude.

 

[WillyBWright]

Re: Mercury vs evinrude

You're doubling the horsepower. I would expect more speed. Just make sure the boat is rated for a 35. I'm pretty sure the motors come with a stock prop which is close to what you'd need. Your boat is about what they would be targeting in determining what to put on.

 

[steelespike]

Re: Mercury vs evinrude

More pitch doesn't necessarily mean more speed it depends on the load and hull design.generally speaking more pitch = more speed and less power( ability to push a load).Less pitch= more power less speed.These generalizations depend on present speed/rpm load and pitch before making a change.