15-footer: Electric Trolling Motor Thrust

Optimizing the performance of Boston Whaler boats
Oldslowandugly
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Location: Queens NY

15-footer: Electric Trolling Motor Thrust

Postby Oldslowandugly » Sat Feb 17, 2018 9:41 pm

How much thrust is recommended for a bow mounted electric trolling motor on a 15-footer?

[The 15-footer] would be used inshore on Long Island back bays and channels. Tide and wind are major concerns. I would prefer to stay with a 12-Volt motor if at all possible.

rtk
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Re: Electric trolling motor

Postby rtk » Sun Feb 18, 2018 10:05 am

I have used electric trolling motors with 80-lbs and 45-lbs thrust on my 1966 16-foot Boston Whaler. Both moved the boat very well. The main difference is top speed. I prefer the 24-Volt 80-lbs-thrust motor because I want to be able to move the boat at a constant 1.5 to 2-MPH speed for salmon trolling with an electric motor instead of the main engine.

The 12-volt 45-lbs thrust motor would push the boat 2-MPH at full throttle setting, but for a very short duration due to the single Group-24 battery's capacity. The 24-Volt 80-lbs thrust motor will push the boat around 3-MPH at full-throttle setting and 2-MPH at much lower full throttle setting.

My available trolling time at a constant 1.5 to 2-MPH with the 80-lbs thrust motor and standard two-battery 24-Volt system set-up greatly exceeded the available trolling time at a constant 1.5 to 2-MPH with the 45-lbs thrust motor and standard one-battery 12-Volt system set-up. Yes, I could have increased battery capacity for the 12-Volt 45-lbs thrust motor to extend running time, but to make a meaningful change in 12-Volt energy available two batteries in parallel or a massive single 12-Volt battery would be necessary.

I also use this trolling motor for slow trolling for fluke when there is no wind available to drift. If your boating area is anything like Barnegat Bay, New Jersey, there may be chop but no wind. In choppy conditions the shaft length of the electric bow mount motor will need to be long enough to keep the lower unit of the electric motor submerged while the bow is moving up and down. You may have no choice but to go with a 24-Volt model if a 12-Volt model does not offer a shaft length that is adequate for your needs; check the available shaft length of any trolling motor before purchasing.

Rich

Oldslowandugly
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Re: 15-footer: Electric Trolling Motor Thrust

Postby Oldslowandugly » Sun Feb 18, 2018 12:37 pm

Rich--excellent info. My most likely use would be to stem the tide so I could cast to weedy shore lines without having to anchor. I also haunt secluded back bay coves and channels casting for Bass and Blues. Dropping a noisy anchor is always a problem. But I'm rarely out doing that more than an hour at a time so maybe a single battery would work for me. Thanks.

rtk
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Re: 15-footer: Electric Trolling Motor Thrust

Postby rtk » Mon Feb 19, 2018 11:28 am

No problem happy to share my experiences with this hope it helps with your decision.

The 45 pound thrust electric trolling motor with the one group 24 standard marine dual purpose wet cell battery I used resulted in adequate amperage and thrust available to make minor adjustments in the boats position while fishing (not trolling) pretty much all day. I have used this set up this way while casting for small mouth / large mouth bass along a shore line. If I was heavy on the throttle though (move boat short distance at high speed- throttle "burst") the battery was depleted much quicker then when I only used moderate application of throttle.

Moral of the story is it is just like a car: some people jam the accelerator pedal to the floor when leaving a stop sign when traveling to the next traffic light then stop abruptly. Some simply depress the accelerator pedal enough to bring the vehicle to cruising speed because the vehicle will need to stop in a half a minute for another stop sign. If you are constantly stomping on a gas pedal fuel efficiency over a short distance will be a lot less than if you simply operate the throttle to produce necessary speed to get from stop sign to stop sign.

I found the same thing to be true with an electric motor. Constant full throttle bursts does impact the amperage draw from the battery. So I try to use only enough throttle to move the boat so I have adequate amperage available the whole day to power the engine.

Save a ton of money and start with a 12 volt basic trolling motor setup. See how it works. If you need to go to a 24 volt higher thrust system you can likely utilize the same mounting bracket system and main engine wiring. So the fixed cost of the basic install is the same for each system. Just leave adequate room to install a second battery so you can wire two batteries in series to create the 24 volt system if needed. A minor modification and a couple bucks and you have a 24 volt trolling motor mount and electrical system. Just make sure the breakers and power plug-in receptacles, etc are rated for both 12 and 24 volt use and meet the amperage specification for both engines.

Rich

Oldslowandugly
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Re: 15-footer: Electric Trolling Motor Thrust

Postby Oldslowandugly » Mon Feb 19, 2018 2:58 pm

That [advice] makes a lot of sense. Top speed is not a concern. I shoot around using the 48-HP main engine. When I see a likely spot or breaking fish, I would want to sneak up quietly.

Locating a second battery, if needed, is a concern. My center console is located forward and I uses the space between the bow hatch bulkhead and console to mount my single battery box. That location should result in little if no voltage drop between the electric motor and battery. But there is no room for another battery. I agree with your advice to start with 12-Volts and see how it performs. Thanks.

jimh
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Re: 15-footer: Electric Trolling Motor Thrust

Postby jimh » Tue Feb 20, 2018 9:28 am

Regarding voltage drop with 12-Volt and 24-Volt systems: the current in a 24-Volt system will likely be lower than in a 12-Volt system, so there will be less voltage drop due to resistance in the wires distributing the power. Also, with a 24-Volt system, you can have twice as much voltage drop compared to a 12-Volt system for the same percentage of voltage lost. Even if you have to increase the length of the wiring for a 24-Volt system, the power distribution should tend to be more efficient than the 12-Volt system.

Oldslowandugly
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Re: 15-footer: Electric Trolling Motor Thrust

Postby Oldslowandugly » Tue Feb 20, 2018 5:08 pm

Hmmmm. So if I go to 24 volts the trolling motor will not only run longer but the system would be more efficient? I would love to add two dedicated deep cycle batteries just for the trolling motor and keep my starting battery separate. But if I add any another battery the only place it could go is at the stern. That would require a long battery cable run up to the bow for the trolling motor. Unless I placed the trolling motor at the stern. I already have two six gallon gas tanks back there under the heavy Mahogany bench. That's a lot of weight. The main reason I put my starting battery up front was to get some weight off the stern. Once I'm in the water I guess I could test the weight out by placing cement blocks in the stern to simulate batteries. IIRC they are around 30 pounds each. Looking at the pic, my battery box is under the front swivel seat. The bench at the stern hides two gas tanks, two waterproof tool/first aid boxes, and a wiring confluence as well as sundry cleaning items. Space is tight. Image

El Rollo
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Re: 15-footer: Electric Trolling Motor Thrust

Postby El Rollo » Wed Feb 21, 2018 5:43 am

I have a motorguide 24 volt 80 lb thrust trolling motor mounted on the bow of my 1988 15 Whaler.
I use 2 Lifeline GPL-U1T AGM Batteries and am very pleased with their performance.
They are pretty compact at 7.71 inches in length 5.18 Wide and 6.89 inches tall, weighing 24 lbs.
The lifespan on mine have been incredible . . . i am on my 4th year of use and have noticed zero loss in run time.

OldKenT
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Re: 15-footer: Electric Trolling Motor Thrust

Postby OldKenT » Wed Feb 21, 2018 7:22 am

Since two of your concerns are tide and wind, the 24-volt motor is going to give you much better performance and safety than a 12-volt system. After a few hours of working against tide and wind, an 80-pound thrust 24-volt system will still have reserves where the 12-volt system might not, and if your outboard should fail to start, can move you more quickly and for a greater distance. I have used mine on both my 17 foot and 13 foot Whalers and a previous 18 foot 2300 pound V-hull. Although space for batteries is certainly a consideration, if you can fit them in, go with the larger system.

Simon
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Re: 15-footer: Electric Trolling Motor Thrust

Postby Simon » Thu Feb 22, 2018 12:50 am

El Rollo wrote:I have a motorguide 24 volt 80 lb thrust trolling motor mounted on the bow of my 1988 15 Whaler.
I use 2 Lifeline GPL-U1T AGM Batteries and am very pleased with their performance.
They are pretty compact at 7.71 inches in length 5.18 Wide and 6.89 inches tall, weighing 24 lbs.
The lifespan on mine have been incredible . I am on the fourh year of use and have noticed zero loss in run time.


I have a motorguide 24-Volt 80-lbs-thrust trolling motor as well. How long do your batteries last if you were to run it at quarter-power throughout the day? I'm trying to shave off some weight due to the heavy batteries currently running the trolling motor. I also have a 15 classic whaler.

Simon
1987 15' Sport CC

Oldslowandugly
Posts: 472
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Location: Queens NY

Re: 15-footer: Electric Trolling Motor Thrust

Postby Oldslowandugly » Thu Feb 22, 2018 11:35 am

El Rollo- I went to the Lifeline site and looked up [the Lifeline GPL-U1T AGM Batteries]. I like the size and weight. They seem to sell for around $150 which is in line with most AGM batteries like Odyssey. It looks like two [the Lifeline GPL-U1T AGM Batteries] wired for 24-Volts are the same weight as one big 12-Volt battery. That could work for me.

I will need to measure and plan this out. Thanks for that info! http://lifelinebatteries.com/products/marine-batteries/gpl-u1t/

El Rollo
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Re: 15-footer: Electric Trolling Motor Thrust

Postby El Rollo » Thu Feb 22, 2018 2:05 pm

Oldslowandungly--I think you will be happy if you decide to go that route. I have mine mounted on their side for clearance under my seat. (one of the nice features of agm). I have them secured with a bracket/ holder I built to eliminate any movement etc.
They seem to charge rather quickly, and hold onto a charge extremely well during periods of non-use. Sorry that I don't have more 'technical' information to share.

One thing--I went to my local welding supply shop and purchased (what I believe was) 6-AWG welding cable to run power from the batteries to the trolling motor. The reason I used this as opposed to tinned marine wire was for the flexibility. That tinned marine wire is not very flexible compared to welding cable. I placed two heavy duty-plugs on the cable end and the trolling motor end. When not in use, I simply dicsonnect the plug, coil up [the cable], and it fits nice and neatly under my console.

I understand that tinned wire is much preferred in marine applications. I took as many precautions as possible with my connections to make them as weather sealed as possible. Occasionally I will remove any of the 'green' color on the connections with fine wet-dry sandpaper, then coat them all with dielectric grease. I have noticed zero voltage drop in the four years I've had this set-up. If you plan on making a more permanent set up, then tinned wire would obviously be preferred.

Just offering some options, even though I realize it has its short coming.

Also, I use that same Lifeline battery as my main house battery for my Yamaha F70. It too has worked flawlessly. I don't run any lights, pumps, or electronics for any length of time, so I can't vouch for the reserve capacity. But it has always cranked my outboard with no problem.

Good Luck in your project !

Oldslowandugly
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Location: Queens NY

Re: 15-footer: Electric Trolling Motor Thrust

Postby Oldslowandugly » Thu Feb 22, 2018 10:51 pm

El Rollo- I forgot about being able to lay AGM batteries on their side. And no gassing. I should have known that because I used one in the Wife's trunk-mounted Chevy Cobalt. One bad feature of them is that they are prone to sudden failure with no warning. I got 8 years of use before that happened. But that makes for a whole new arrangement factor. I could even stack them together on their sides with proper mounting. Again- you have been invaluable to me! Thanks!

FISHNFF
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Re: 15-footer: Electric Trolling Motor Thrust

Postby FISHNFF » Sun Feb 25, 2018 1:53 am

On my 1989 15-footer with a 2016 Mercury 60 FOURSTROKE I have a foot-controlled 24-Volt 70-lbs-thrust Minn Kota electric motor mounted on the port bow step and two AC Delco deep-cycle Group 24 [12-Volt batteries] mounted inside a Rubbermaid ActionPack held against the bow locker by the thwart seat--plenty of power for days.--FISHFF