Suggestions for detachable trolling motor wiring?

[JeffM]

I've got me a big ol deep cycle battery I'm planning on setting up under the seat in the bow, and figure I'll run 6 guage wire through pvc against the seat edges the 15' to the aft end of the cockpit. Then I have to figure out how to attach the wires from a (so far hypothetical) trolling motor to the ends of the 6 guage wire. The connection needs to be one that will carry the amperage, easily detach so I can put the motor into the lazarette, and not cause me too many salt water headaches. Nothing at the local box store or auto parts store gives me any ideas. What do you all use?

[Barry Pyeatt]

Jeff,

Try your local RV dealer with a good service shop. You'll find that most of them will have a broad assortment of panel mount recepticals and plugs that will work for you.

You may find the enclosed link some food for thought regarding appropriate wire size vs. run length.

http://www.e-marine-inc.com/products/alternators/cables.html

Hope this helps some.

[JeffM]

Thanks for the tip! Barry, I'm going to assume a 50lb thrust motor will draw about 50 amps. True? Also, please don't tell me that the "AWG" on that link is the same as guage--I'd need a solid copper boat to carry the current!

[Barry Pyeatt]

Most builders are astounded by the demands of Marine wiring. One real consideration is to stick to marine rated wire when you do this. Corrosion on the terminals and junctions is a real issue. A bit more of an outlay initially but it will be there for as long as you have the boat. You really don't want to have to replace it. Go up one size over the recommended size and you will never have a problem. Just think about it. 15' away is really a 30' run on battery power.

Most new builders are used to house wiring with 120 V and 240V AC. The loss in a long run is still substantial but we're dealing with only 12 V DC and it takes a lot more surface area to keep the loss at a managable stage. Remember, most of the loss is in the form of heat. Even short runs with 12 V generate a substantial amount. Be sure that the PVC pipe is oversized for the run and rated for electrical use. Also you might consider how you run it to eliminate any possiblity of water staying inside the conduit. From condensation primarily. So have weep holes in the low spots.

[umop_apisdn]

A 50lb motor will draw about 40 amps at full throttle. With 30 plus feet of cable, you are looking at probably 2 gauge wire.

http://www.skingco.com/portable_power/wiring_size_chart.htm

You might get by with 4 gauge, but the wire will get warm under full load. Water + heat = corrosion in your wire.

For connectors, these look heavy duty and pretty reasonable:

http://www.grizzly.com/products/G9124

It sounds like you haven't bought the motor yet? if that is the case, you should seriously consider a 24 volt motor. Or move the battery to the transom.

Finally, I second Barry's suggestion of using marine rated wire. Once corrosion gets up inside the wire, you can't get it out and you have to re-wire. Marine wire is fully tinned from one end to the other.

Solder connections when at all possible, use a dielectric grease on all non-soldered connections. Oh, and of course put a fuse or breaker very close to the battery.

Noel.

[JeffM]

Thanks, all! This is beginning to look really expensive.

Ray, I've got a borrowed 27lb thrust that could barely give me steerageway going into a 5-10kt wind with furled sails. I was definitely doing less than a kt. It was only me and middle son aboard, and seas were under 1'. Is something wrong with the motor? I had the battery at my feet and the motor's aligator clips right on the terminals. It was the (lack of) performance that led me to think I needed a much bigger motor.

[Barry Pyeatt]

No, there probably isn't anything wrong with the motor. That is a fine motor for a small inflateable or dingy or calm water areas. The alligator clips don't make for the best connection though. You probably loose some of the current flow using them.

We have a wide variety of issues with currents here in the Pacific Northwest. Tidal, river and of course AC and DC.

On the Sound, there are tidal flows of over 8 knots in some areas. Obviously you can't expect any electric trolling motor or even gas outboard engine on any of these hull designs to work against it. Hull speed is lower than the current flow.

Against gentle to moderate river flows a 27# thrust will allow you to eventually get upstream or across stream. But don't be in any hurry and have a backup battery. Same with moderate to moderately heavy winds.

A 40#-50# thrust trolling motor with an after market "performance" prop will work just fine in most instances against moderate flows and most moderately heavy wind conditions. Without going to full speed on the controller. Again, if you have far to go, a second battery is a good hedge against using the paddle.

Here is a link for a prop that seems to do the job for most of the smaller sailing boats around here, both glass and wood. These props give you greater thrust and better overall performance but at a slight increase in battery drain.

http://www.kipawapropellers.com/331655.html

Plan on spending about $45 plus shipping on one to fit almost any electric trolling motor. They are easy to change out and they do make a noticeable difference in performance.

As Ray stated, a 35# thrust will certainly move your boat under most normal conditions. The extra thrust and performance prop with a larger trolling motor will give you some peace of mind and work in wind and currents better.

[JeffM]

Barry, the first time out with this motor and its dinky wires and alligator clips I got smoke and melted some of the insulation where the clips attach to their wires. The entire length of wire got noticeably warm. Afterwards I chopped out most of the original wires and replace them with 8 guage I had lying around. (I did still have my doubts about the concept of clips, though.) By the way, earlier discussions of electric motors, to which you were a prominent contributor, are part of the motor "primer" I keep handy for consultation.

[Barry Pyeatt]

Here is a Minn Kota plug and receptical on e-bay.

http://cgi.ebay.com/ebaymotors/Minn-Kota-Trolling-Motor-Plug-and-Receptacle-New-In-Box_W0QQitemZ110036595670QQihZ001QQcategoryZ26451QQrdZ1QQcmdZViewItem

[Dave R1]

Jeff, for what it is worth, I ran marine grade 6 ga wire from the battery in the forepeak on my Weekender to the lazarette where it terminates in a waterproof twist lock connector that I mounted on the lazarette bulkhead. I have a 47lb thrust motor which is certainly beefy enough for my boat.

[JeffM]

Thanks for all the advice and hardware ideas! I'm beginning to wonder whether I should test This Old Motor before I run out and get a big new one. I wonder if I could get an idea of the real thrust by running the thing full throttle in a trash can full of water? For that matter, how can something as simple as an electric motor seem to work okay, but put out significantly less than its rated thrust?

[Barry Pyeatt]

Number of factors to take into consideration. How much use has the motor had. Electric motors get tired as they get used a lot. None of them work forever at rated output. Primary consideration is how much actual current is getting to the motor. Line loss, poor connections account for major differences in potential output. Props on trolling motors are not designed to give peak output thrust measurements. They are designed to get through weeds without fouling up. Thrust is sacrificed for consistent trolling speed and the ability to move about without getting fouled up. An after market "performance" prop will bring you closer to using rated output.

Running it in a barrel will only make a lot of thrashing about. Won't tell you anything about how much thrust is actually there. Putting a pull scale on the upshaft will only give you how much pull there is against the scale, not a close to accurate thrust measurement.

Best thing is to have a fully charged marine battery, direct connection to the battery terminals with one size large wire than it needs for that distance. So you don't loose more thru heat than necessary. Then with as little windage as possible to restrict movement. No currents to deal with, etc. Then you can see if it will actually move the boat reasonably in "ideal" circumstances. Then try it in a current or into the wind. See if it still moves better than the first outing with just clips to conduct the current from the battery.

There are people up here that use 35# thrust motors in the Sound on a lot heavier boats than we are talking about. But they are only getting away from the docks or launch and back to it from relatively close in. And they are not in a hurry to get there.

[JeffM]

Thanks, Barry. Ray, I don't have GPS and there were no aids to navigation conveniently placed (timing passage between which is my preferred way to get speed made good). [Tide was also against me--again confounding that method.] So I used sea foam on the surface as markers: it took 15-20 seconds for my whole 20ft length to pass them. I make that out as well under one kt. In addition, it was so difficult to keep the boat pointed into the wind (with the windage of two furled sails up forward in main and reefing steps), that I eventually gave up steering with the tiller and just used the motor. The rudder wouldn't have become so ineffective at any useful speed.