Trolling Prop Question

MAK_MR180

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Mar 8, 2010
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1
I would like to know if reducing the size and pitch of my kicker motor prop will help to keep my boat on a straighter course while trolling at low speeds (1.5 to 2.2 mph). I am often blown well off course while trolling and have to start my main motor up to get back on course, hold course, or turn around. Starting my main motor is aggravating, wastes time and fuel, and doesn?t allow me to maintain the slow speeds for trolling.

I have a 1988, 18-ft, center console Starcraft with an aluminum hull. The boat weighs approximately 850 lbs. My main motor is a 1989, 110 hp, 2-stroke, Evinrude with a stainless steel prop. My kicker motor is a 1990, 6 hp, 2-stroke, Evinrude, Model E6RESR, that is equipped with an 8.5" x 9" aluminum prop.

I really like my kicker motor, it was relatively inexpensive, it is quiet, fuel efficient, fits my boat very well, and allows me to easily troll at low speeds, until there?s a stiff wind that is. I often fish alone and stand/sit near the stern, so the bow rides a little higher out of the water than when I have company in the boat. I understand there are limitations for the size of my boat and that keeping the bow low will help with boat control, nonetheless, I am wondering if the smaller prop, like the available 8"x7" will help give me more control over the boat at slow trolling speeds when the wind kicks up and begins blowing me off course.

Help and/or comments would be appreciated.

Thank you
 

trendsetter240

Lieutenant
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Jun 22, 2009
Messages
1,458
Re: Trolling Prop Question

Hey Mak, welcome to iboats!


Well, going with the smaller pitch prop means that your motor will be turning at a higher RPM to achieve the same speed. The higher RPM will result in higher HP and therefore more thrust from the prop.

This will give you better control at trolling speeds, if it will be enough to fix your exact situation I don't know.

Cheers
 

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
16,623
Re: Trolling Prop Question

Well, going with the smaller pitch prop means that your motor will be turning at a higher RPM to achieve the same speed. The higher RPM will result in higher HP and therefore more thrust from the prop.
How does one increase thrust yet maintain the same speed?
 

trendsetter240

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Jun 22, 2009
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1,458
Re: Trolling Prop Question

How does one increase thrust yet maintain the same speed?

He is trying to maintain course and speed with the current prop and is not able to. Increasing HP available at the prop by increasing engine RPM and decreasing propellor pitch and consequently blade surface area, should improve the ability to maintain course.

If one propellor can't maintain a speed of 2mph under the conditions and the 2nd can.... the second is producing more thrust.
 

Silvertip

Supreme Mariner
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Sep 22, 2003
Messages
28,771
Re: Trolling Prop Question

It can maintain the same speed because engine rpm is higher with the lower pitch prop. You can run 30 MPH with your car in first gear, second gear, or third gear. The only difference is the engine rpm is higher. Same principle applies to boats since the prop is essentially the transmission -- but it has only one gear. You change the prop to change gears. Changing props will likely not make boat control any better, With the bow high it acts like a weather vane and will spin you around. As the sole occupant in a canoe for example you will immediately find that you cannot keep it pointed 90 degrees to the wind unless you sit paddle from the front of the canoe. Same principle again. This is exactly why bow mount trollers are so much more effective for boat control.
 

trendsetter240

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Jun 22, 2009
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Re: Trolling Prop Question

silvertip said:
Changing props will likely not make boat control any better, With the bow high it acts like a weather vane and will spin you around

mak_mr1980 said:
I am often blown well off course while trolling and have to start my main motor up to get back on course, hold course, or turn around.


well, we disagree. He can start up his larger motor to accomplish what he wants to. Why won't changing his prop setup to provide more thrust at lower speeds help him?

For that matter, why do prop manufactures make "high-thrust" props? Or sell "high-thrust" outboard models? The latter simply have lower gear ratios to provide the same effect as the lower pitched prop.

These type of setups are common when you have a small trolling or kicker motor on a large, heavy or non-aerodynamic boat.
 

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
16,623
Re: Trolling Prop Question

Why won't changing his prop setup to provide more thrust at lower speeds help him?

Becouse thrust isn't his issue. Thrust is not going to stop bow wonder. The only way to stop bow wonder is by increasing your speed or getting more hull in the water.

I can tell you from years of experience that at trolling speed (1.5 - 3 kts.), there is absolutely no difference in the way the boats handles if I have my 14 x 17? 3-blade aluminum prop on or my 14.5 x 17? 4-blade stainless prop.
 

trendsetter240

Lieutenant
Joined
Jun 22, 2009
Messages
1,458
Re: Trolling Prop Question

Becouse thrust isn't his issue. Thrust is not going to stop bow wonder. The only way to stop bow wonder is by increasing your speed or getting more hull in the water.

I can tell you from years of experience that at trolling speed (1.5 - 3 kts.), there is absolutely no difference in the way the boats handles if I have my 14 x 17? 3-blade aluminum prop on or my 14.5 x 17? 4-blade stainless prop.

ok, that is your experience so I will accept that. However in my experience the prop pitch makes a big difference in low speed handling. At least it did when I had a 20" sailboat that was powered by a 8hp kicker. Prop selection made all the difference in the world to docking and handling at or near trolling speeds. (though I had no idea why at the time). It also made a big difference when trying to keep the boat pointed into the wind during heavy chop while hoisting the sails.

I also believe my theoretical description of why it would work is correct. Please prove me wrong! That would only mean I learned something new today and that is good:)

cheers!
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,771
Re: Trolling Prop Question

Your sailboat did not have anywhere near the bow-high attitude that a small boat does. The vast majority of the weight is at the stern and therefore is the pivot point rather than the center on a sail boat. The sail boat also has a keel board that helps with directional control. The two boats simply cannot be compared in this example. What we don't know is how much throttle the big motor needs to get back on course. That may be more than six HP can provide with any prop.
 
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