I'm advised to change Tohatsu MFS9.9El's prop...

[hapibeli]

I am installing a 2021 Tohatsu MFS9.9El on a 16.6 Double Eagle that has a 2008 Mercury 60Hp 4-stroke as the main engine. The Tohatsu will be the kicker.

I was advised as follows, but it is Greek to me????
"Was the current motor factory delivered with an installed prop ? if so should be a 10 pitch prop which it's a medium pitched prop not suited for all applications specially large and heavy ones. With new installed motors and after the ten hour break in period ends must install a less pitch prop for motor to rev towards max wot rpm range to get the max out of that motor if plan using it as a kicker or aux to the main motor. Check the Owner's Manual under Propeller Table

With an installed tach will know what's the current wot rpm the motor is revving at and if revving towards the min lugging side which is bad for the motor if revving full throttle say at an emergency cruising against hard winds, tides , strong currents, etc."

 

[racerone]

Correct.----On a large boat you need less pitch on the prop ( say 8 " ) for FULL THROTTLE operation.-----You truck has a transmission to select proper gear for the load.-----The little outboard does not have a transmission.----There for you change the prop.-----But if you are not planning to run the kicker at full throttle you are good as is.

 

[Sea Rider]

The main use of a kicker motor is to return you, your family to terra firme in case the main motor failed. At an emergency it's much better to run a under powered motor at full throttle. If propped right to run towards max wot rpm range the better, will push the combo on its way back more efficiently, safer and in less time compared to run say a 10 pitch factory delivered prop which its ideal to power light applications.

Sort of : It's better and safer being top propped than not. Less pitch alum props are cheap and a vise investment, but before going that route Read the Owner's Manual Prop Chart. Been there twice that's why the Recommendation

Happy Boating​

 

[Sea Rider]

Same as the 4 stokes version the 2 stroke 9.8 HP which is the lightest motor in the 170 CC group although being top notch in their respective groups, both needs a correct prop maximization especially if powering large applications as main or aux. In reality any motor factory delivered with a prop should be tached at wot as loaded to get the max HP out of them...

Happy Boating​

 

[Texasmark]

The main use of a kicker motor is to return you, your family to terra firme in case the main motor failed. At an emergency it's much better to run a under powered motor at full throttle. If propped right to run towards max wot rpm range the better, will push the combo on its way back more efficiently, safer and in less time compared to run say a 10 pitch factory delivered prop which its ideal to power light applications.

Sort of : It's better and safer being top propped than not. Less pitch alum props are cheap and a vise investment, but before going that route Read the Owner's Manual Prop Chart. Been there twice that's why the Recommendation

Happy Boating​

The main use for trollers in the Great Lakes and such is for trolling and slow speed is a must.

 

[Sea Rider]

The main use for trollers in the Great Lakes and such is for trolling and slow speed is a must.

The use of a troller will depend entirely on the boater's location and his intended needs, down here we don't have lakes just plain open Pacific Ocean, portable range motors are used only by a few boaters as aux ones and none are propped right...

Happy Boating​

 

[JimS123]

Trolling at low speed and running full throttle to get you home in an emergency are the same requirement. The engine needs to run WOT at the engine's spec rpm range.

In "most" cases, the lowest pitch prop available for that motor will be the one required for your application.

Buy that prop and be happy. If you want to be sure, tach it out.

I have run kickers for 45 years. In some cases, the ONLY props available would still not enable full rpm. No choice except to have a prop shop repitch. Nevertheless, if its a 2-stroke, you might see some plug fouling. If a 4-stroke, just live with it.

 

[Sea Rider]

The OP will use that motor as a kicker powering a large hull, in that particular case prop it right to run towards max 6 K wot range as usually loaded. Once there min throttle if plan trolling.

Tohatsu Tech Data : It is highly recommended that the outboard be checked with a tachometer to ensure that the engine is operating within the correct MAXIMUM RPM RANGE. The selection of the correct propeller will allow the engine to obtain it's full RPM as well as the designated horsepower. Engine horsepower is very closely related to the max RPM the outboard can obtain. In other words, if the outboard can not reach its specified max RPM it cannot reach its specified rated horsepower... You Decide!!

Happy Boating
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