Difference between Tohatsu 6hp Sail Pro vs Non-Sail Pro

Mar 31, 2019
59
Catalina 22 12640 Rose City Yacht Club
Hey all,

I purchased a new Tohatsu 6hp long-shaft outboard a year ago (Model MFS6CL, 20" shaft). I only just now realized that Tohatsu sells a sail specific version of this outboard, aka the Sail Pro model.

Whoops.

Besides the alternator, which I don't think I need, is the propellor the only other difference between the sail and non-sail models? Does the high-thrust propellor make a big difference? Even with a clean bottom and as little weight onboard as possible, I find that my boat struggles to get upriver against a 2-3 knot current, and I'm wondering if swapping out the propellor will make a difference. I also see that the Sail Pro model has a 25" shaft option, too.
 
Nov 26, 2012
1,536
Hunter 34 Berkeley
Why wouldn't ALL of the engines have a prop that gives max thrust? What is the point of having a prop that doesn't?
 
Mar 31, 2019
59
Catalina 22 12640 Rose City Yacht Club
Why wouldn't ALL of the engines have a prop that gives max thrust? What is the point of having a prop that doesn't?
It's a fair question. I'm guessing there's some tradeoff in another dimension. For instance, maybe the high-thrust prop uses more gas, or maybe it doesn't provide as much top-end speed as it does low end torque. Just guesses, I'm sure someone with more propellor knowledge than me can chime in.

Cheers,
Andre
 
Sep 15, 2016
617
Catalina 22 Minnesota
"the high-thrust prop uses more gas, or maybe it doesn't provide as much top-end speed as it does low end torque."

Bingo!

The pitch of a prop determines its thrust or torque in reference to the water. While a high thrust is great to get the boat moving too steep a pitch will limit your top end speed as the motor RPM will not be high enough. Eventually you reach a speed where the pitch of the prop and the motor RPM fight one another in drag. This is why most modern ships use variable pitch props. They need high torque to get moving and higher RPM to keep moving at speed and save on fuel.

On a sailboat we don't worry about top speed as we will never exceed hull speed anyway. Also our boats are typically heavier in the water (displacement vs planning hull) and so torque is preferred over top end speed. Outboard manufactures tend to choose a prop that is somewhere in the middle as they have no idea what type of boat its going on when they make the motor. The Sailpro version is specifically designed for displacement hulled vessels and thus the steeper pitched prop for more torque is preferred.

Back to your original question though has anyone ever run both props to compare? Or has anyone actually motored beside someone who has the high thrust prop while you have the standard one? I too would be curious on the benefit in speed against current, swells, and wind. I have the standard prop and have wondered if it was worth the upgrade as well.
 

Ward H

.
Nov 7, 2011
3,129
Catalina 30 Mk II Barnegat, NJ
Why wouldn't ALL of the engines have a prop that gives max thrust? What is the point of having a prop that doesn't?
Probably because most outboards are purchased for fishing boats with planning hulls and the displacement hulls of sailboats benefit from different prop designs and pitch.

@LakeShark posted while I was typing and explains it much better.
 
Sep 30, 2013
3,293
1988 Catalina 22 central Florida
Why wouldn't ALL of the engines have a prop that gives max thrust? What is the point of having a prop that doesn't?
There's a lot more to propellers than meets the eye. There's diameter of course, number of blades, pitch, and cup. All this has to come together with hull type, size and weight of the vessel, horsepower, gear ratio, torque, max RPM, etc, etc.

Thus, the ideal prop for a 6hp Tohatsu on a 300lb aluminum Jon boat (just for instance) is nothing at ALL like the ideal prop for the same motor on a 3,000lb sailboat.

Fiddlesticks. I just realized I'm more or less repeating what LakeShark said. :biggrin:
 
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