Trolling with Auxiliary Engine

Optimizing the performance of Boston Whaler boats
Newportme
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Joined: Fri Oct 16, 2015 2:17 pm

Trolling with Auxiliary Engine

Postby Newportme » Mon May 09, 2016 8:33 am

I am trying to find an alternative to rigging drift socks to the front of my boat to reduce trolling speeds at idle to 0.7 to 0.8-MPH from around 1.1-MPH. The general consensus on fishing forums seems to be to rig a drift sock off the front of the boat. I am not sure that I want the sock, or the hardware chafing on the bottom and side of my boat for hours on end. I am using a Honda-8 HP engine for a auxiliary motor. I would like input from the knowledge base here.

I have been looking at other alternatives than the drift sock. The propeller I have on the kicker now is a 9.25 x 9 pitch. If I dropped to a 9.25 x 7 would drop my [boat] speed enough?

I know the drop in pitch should reduce boat speed but I have not tried this with the [engine speed] so low. There is also propeller slip to take into account. If the lower pitch propeller grips better at engine idle my boat speed may remain the same. I don't have enough experience messing with these slow speeds.

Bruce

jimh
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Re: Trolling with Auxiliary Engine

Postby jimh » Mon May 09, 2016 9:35 am

Reducing propeller pitch to 7-inch from 9-inch should reduce the boat speed proportionately. If the present boat speed at engine idle is 1.1-MPH with the 9-pitch, the anticipated boat speed with the 7-pitch would be 1.1 x 7/9 = 0.85-MPH.

I don't see any basis to avoid trying this. I don't see any basis to assume that the performance of two propellers from the same series that differ only in pitch would require that they have radically different characteristics in their calculated SLIP. It seems more logical to assume just the opposite, that is, that propellers from the same manufacturer and in the same series that differ only in pitch would tend to have very similar SLIP characteristics.

kwik_wurk
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Re: Trolling with Auxiliary Engine

Postby kwik_wurk » Mon May 09, 2016 5:35 pm

Have you tried putting your main engine in reverse, this locks the prop adds drag, and usually drops my Montauk a 0.1 kts.

Otherwise, yes if your kicker is their for trolling, get a different prop. That should do the trick.

(I would not set a drift sock, what a pain. It also affects steering/drift when windy out.)

Newportme
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Joined: Fri Oct 16, 2015 2:17 pm

Re: Trolling with Auxiliary Engine

Postby Newportme » Tue May 10, 2016 7:14 am

Thanks Jim and Kwik
I have never observed the prop on the main motor while trolling but I will try engaging reverse and see if that helps

Bruce

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Phil T
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Re: Trolling with Auxiliary Engine

Postby Phil T » Tue May 10, 2016 10:27 am

Bruce - I presume you are trolling on Sebago etc and not in Casco Bay? Most of the hardcore guys I know use a sock. A PITA but it works.
Member since 2003
1992 Outrage 17, 1992 Evinrude 115

Newportme
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Joined: Fri Oct 16, 2015 2:17 pm

Re: Trolling with Auxiliary Engine

Postby Newportme » Wed May 11, 2016 8:49 am

Phil--yes. Inland lakes for landlocked salmon, Rangeley, Sebago, Sebec, Richardson, I may have to resort to the drift sock but I'm exploring options. Good to hear from you again. Thanks again for the help with the trailer . The trailer is still running great. It was fun to meet another forum member. I hope all is well. --Bruce

Newportme
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Re: Trolling with Auxiliary Engine

Postby Newportme » Tue May 24, 2016 3:03 pm

Jim's math proved to be very accurate. Idle speed with 7-pitch propeller installed was 0.8-MPH on the GPS in calm conditions. This is the speed that I was looking for. Obviously in windy conditions I may still need to use something for drag to slow the boat. I am satisfied with this set up. Thanks for the comments, and I hope this will help someone in the future.--Bruce