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Author Topic:   Determing Horsepower for Auxiliary
picflight posted 07-08-2014 11:27 AM ET (US)   Profile for picflight  
How does one determine the appropriate size auxiliary or kicker or trolling motor?

The previous owner of my 1998 Outrage 17 (1,700-lbs) had a Remote-Troll bracket on the transom with a Mercury 8-HP long shaft. The motor was stolen before I got the boat, so now I am exploring the options of getting a new trolling motor.

In my area there are not that many Mercury 8-HP engines for sale, so I started looking at 6-HP as well. There is quite a bit of difference in weight between the 6-HP and 8-HP FOURSTROKE engines: 55-lbs compared to 84-lbs. Which one, 6-HP or 8-HP, would be suitable for trolling and as an auxiliary motor if needed? Thanks.

Alan Heckman posted 07-08-2014 01:41 PM ET (US)     Profile for Alan Heckman  Send Email to Alan Heckman     
I have a 1999 Alert 17 which weighs around 1000 lbs, and I just put a new kicker on this year. I put on a 6-HP Tohatsu Sail Pro. It replaced a Mercury 9.9-HP two-stroke outboard. The Tohatsu weighs 58-lbs, comes with an alternator, and a high thrust propeller. You must get the Sail Pro model to get the high thrust propeller. This motor will push my boat 6.1-MPH and will troll as slowly as you want. You will hear a lot about vibration in one-cylinder engines, but I don't think [the 6-HP Tohatsu Sail Pro] vibrates any more than my old kicker. The more hours it gets on it, the smoother it runs. The only vibration I really notice is at full throttle. Hull speed of 6,1-MPH is reached at half-throttle, and trolling is at less throttle. Vibration is not [a concern] at all for me. The high thrust propeller gets a good bite and it is nice to keep your battery charged when trolling. I can say I am very pleased. I re-powered with a new F70 Yamaha and was going to get a Yamaha 6-HP kicker until I researched the Tohatsu. I am glad I did--but you have to get the Sail Pro model. I have seen these motors used as kickers on boats of 20-feet or on Lake Erie where I fish. Hope this helps.
picflight posted 07-08-2014 02:09 PM ET (US)     Profile for picflight    
Alan, Thanks for the feedback and valuable real use experience.

My main motor is a Mercury 150, 500-lbs, if that makes a difference in the kicker motor selection criteria and weight calculations.

jimh posted 07-08-2014 03:32 PM ET (US)     Profile for jimh  Send Email to jimh     
In a REFERENCE section article at

there is a report of excellent performance with an 8-HP auxiliary on a 22-foot Boston Whaler. Interpolating that to a 17-foot hull suggests that 6-HP will probably be enough.

Check out the article (linked above) for some good ideas on installation and control of auxiliary outboard engines.

Jeff posted 07-08-2014 03:49 PM ET (US)     Profile for Jeff  Send Email to Jeff     
I use a 6.0hp 1992 Johnson Kicker on my 20 Grady White and it does great for Salmon trolling speeds and will push the hull to about 6-7mph in calm conditions.

I would say a 6hp would easily meet your needs.

mopee3 posted 07-08-2014 06:25 PM ET (US)     Profile for mopee3  Send Email to mopee3     
So Jeff you don't use the 23' Whaler WA for salmon fishing? My WA needs to be able to troll for Chinook. I don't want to add a bracket but not sure how to get around it. Nor how big an auxiliary to add.


mkelly posted 07-08-2014 06:49 PM ET (US)     Profile for mkelly  Send Email to mkelly     
I have a four stroke Mercury 4 HP for my 19' Outrage. It does just fine for salmon trolling--probably about 6 MPH if I need to run it out. Mine is 14 years old and hasn't missed a beat. If I recall, Mercury makes a one cylinder 4, 5, and 6 HP that weighs about 65-lbs. Go up to 8-HP and weight goes up significantly in the exact place you don't want it. I would take my trolling motor off during non-fishing seasons. Go for the smaller one, boat will perform better.

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