Can I put a Tohatsu 8-3/8dx6p prop on my 2006 Mercury 4 HP 4-stroke?

[gloposailor]

Hello, and thank you in advance for your help.

I have a 2006 Mercury 4 HP 4-stroke long shaft outboard. I use it to power my 1974 Seafarer 22 sailboat. The sailboat has a displacement of 2400 lbs. I do not have a tachometer for the motor, so I cannot offer the actual RPM's that the engine generates at full throttle. I find that the sound of the motor will steadily change as I increase throttle from idle to half-throttle, but there is no noticeable change in sound from half-throttle all the way up to full throttle. I think that the motor is not reaching its maximum RPM range, and is therefore not making full power at WOT.

The motor has the original propeller. I imagine that it is a 7.5 or 8 pitch prop. I have read about the "elephant ear" prop offered by Mercury and Tohatsu. Assuming that no one has any reasonable objection to me putting the "elephant ear" prop on my motor, I have two questions regarding changing the prop.

Question 1: Is the Tohatsu prop interchangeable with the Mercury prop? Tohatsu part # is 399B645121. The Mercury part # is 812951A 1.


Question 2: What other parts/tools will I need to have on hand to exchange the propellers? Nuts, washers, grease, puller, etc. Please let me know since I've never changed a prop before.

Thanks all,

Chase

 

[Sea Rider]

Does both props have same number of splines ? The Tohatsu prop is already available or plan buying one ? You need an induction tach to play with props or could damage the engine if doesn't work inside safe 4500-5500 rpm wot range. 4HP is a very basic engine for sailboat use, too much hull drag and weight to overcome fast. You can bump that 4 into a 6 HP as both are same 123 CC and if maximizing prop will push much better.

To change prop, remove split pin from shaft, remove nut and pull prop out. Grease prop shaft when installing new prop.

Happy Boating

 

[gloposailor]

Sea Rider Thank you for your advice! I haven't been able to confirm that both props have the same number of splines, but I will make sure before I purchase one. I will also be sure to have an induction tach on hand in order to verify the effect of changing the prop. I have read about the 6HP upgrade for my motor, and I'm keeping that in mind as a potential upgrade for the future. Thanks again!