Bigger boat outboard

joshw5144 · #1 05-21-2010

Hi All,
I was wondering if anyone would know how to calculate the amount of horsepower I would need to move my boat. I have a 34' Hunter, with an inboard diesel, but I am looking to add an outboard for trolling (kicker?). I would only need to move at 3-4 kts max. But more often around 2 kts.. Right now I use my diesel, but I hat leaving it at 1500 rpm for any amount of time. Also could it be offset on the transom or would that cause steering issues? Any input is appreciated. Thanks.

FSMike · #2 05-21-2010

I would imagine that 10hp would be adequate for pushing your boat at 3-4 knots in calm conditions. Offset installation shouldn't make any appreciable difference for trolling. Why don't you want to use the diesel?
Better yet, why not sail whenever possible?

joshw5144 · #3 05-21-2010

Quote:

Originally Posted by FSMike

I would imagine that 10hp would be adequate for pushing your boat at 3-4 knots in calm conditions. Offset installation shouldn't make any appreciable difference for trolling. Why don't you want to use the diesel?
Better yet, why not sail whenever possible?

I do sail when appropriate, but sometimes due to lack of/direction of wind or confinded spaces I need to use the engine. I don't really like to use the main engine because it goes to fast most times, which means in and out of gear every minute or so. And when its not to fast it's just at an idle which I don't like to leave it at for hours.

dabnis · #4 05-21-2010

Josh,

I had a commercial salmon troller with a Detroit Diesel, aka "Jimmie", used to troll for hours on end with no problems. Lots of theories on this issue but I think as long as the engine is run hard after trolling it should be OK. lots of commercial boats with 2 and 4 stroke diesels out there doing the same thing for many years. Perhaps your idle speed is set too high if you are going too fast?

Dabnis

blt2ski · #5 05-21-2010

I was going to say idle speed is set too high, OR, the prop is pitched incorrectly. Not that I know props and how they work, but too much pitch? I believe would potentially be the issue.

For trolling, 3-5 hp motor would work. You will not need 10HP to go 2-4 knots in reasonably smooth water. Throw some seas into the mess, along with some current, not we need more like 5-10 minimum, and you might as well use the diesel for these conditions.

marty

joshw5144 · #6 05-25-2010

Thanks for the input guys. I guess I'll stick to my dielsel.