I need a guesstimate

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Aznative

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I thinking about putting an auxiliary engine on my 21 ft bayliner. It weighs about 4,000 lbs loaded. The auxiliary engine is a 9.8 HP four stroke that weights 100 lbs. I would appreciate any and all top speed estimates. I would like to use it for trolling and as a backup to limp in with. '
Thank you all in advance for the help
 
The engine has the stock prop. I'm sure I would have to get a slower speed prop to make it push such a heavy boat at an optimal torque rpm. I would be happy to have 6 mph.
 
How true Sealegs. And a small gas engine with plenty of gas is better than an electric trolling motor especially when you are fishing the Great Bend on the San Juan.
 
I think you will be lucky to get 5 MPH.

I had a 8 HP Honda on my 16’ Lund - that boat weighed less than 2000 pounds and wouldn’t push it more than 6 MPH.
 
I have a 21 Lund that weighs about 4000 pounds as well. It came with a 15 HP 4 stroke mercury kicker. It goes about 5.5 MPH wide open. Will go as slow as .5 MPH at an idle. Sure is nice to troll with. Difficult to turn to the right especially against a wind because it sits on the right side of the boat.
 
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I run 9.8 on my 26 foot sailboat probably 7000 pounds loaded I get 6.5 at Powell and 7 at Havasu I’m bet 7 would be your max half throttle is about 5
 
Thanks to everyone for the input. It gives me the encouragement to go thru with this project. It would be great for trolling and a possible lifesaver if my main engine went down on this huge lake.
 
Less than 5MPH. I have a six horse four stroke kicker on my 24' bay boat that's about 2,500 lbs total and get about 5mph.
 
Any one use a high thrust prop if not unless you can plane with that motor you are just getting a lot of prop slip and wasting fuel and running inefficient
 
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