Trolling motors for dinghies

ssobol · Posted: Sat Jun 28, 2014 10:33 am Post subject: Trolling motors for dinghies

For those of you who use electric trolling motors on your dinghies (if any) I would like to know what you think of using a trolling motor vs. a gas outboard. What do you use (if anything other than a pair of wires) to recharge the trolling motor while on board?

I know there is the Torqueedo motor. It looks very nice, but I can't justify $2K on something that I am not likely to use all that much. I can get a trolling motor and a battery for 1/10th cost of the Torqueedo.

Thanks.

potter water · Posted: Sat Jun 28, 2014 12:14 pm Post subject:

we've been using a standard small trolling motor with an AGM battery for several years. It works great. However in a strong wind, it is hopeless. But then, we are seldom out in the dinghy in strong winds. We get a couple knots. I have a 2.5 hp Suzuki 4 stroke that is better in the winds.

Love the electric though. Works fine for short trips if you are not in a hurry. My 900 dollar Suzy opposite the 2000 dollar torquedo? I can buy a couple lifetimes of fuel for the Suzi for the 1100 dollar difference. Or a lifetime of running the generator to charge the AGM for the troller.

T.R. Bauer · Posted: Sat Jun 28, 2014 12:38 pm Post subject:

Even my 3.5 hp Tohatsu struggles with 2 in the dingy, a load, and wind. Empty, it is great entertainment for a 11 year old kid.....LOL....

However, I have had electric trolling motors before on small boats and I think they would be fine. They are surprisingly powerful. For that matter, oars are just fine most of the time. If you already have a trolling motor and a battery, you should give it a try.

If not and you are spending money, I suggest to take a close look at the gas powered ones as in just a few seasons you will probably have a good chunk of money invested into battery replacements.

Aurelia · Posted: Sat Jun 28, 2014 1:02 pm Post subject:

We have used a 55lb minnkota and a 30lb motorguide model on a couple of dinghys and they worked well for protected putting around. The prop seemed to be important enough that the three bladed unit on the smaller motor powered as well as the 2 bladed prop on the larger motor. It wasn't the blade count but other specifics of the props that made the difference.

If I were to do it again I would try to live with just a U1 sized standard or AGM battery that is easily carried in a box with a small built in charger.

Like this one I use for RC truck mobile charging and air compressor use.

I would start with a cheap freshwater unit (even used) to test the concept yourself and go from there.

Greg

ssobol · Posted: Sat Jun 28, 2014 1:18 pm Post subject:

I have an inflatable dinghy. Other than to try it out when I got it, it hasn't been inflated for a year. Since the C-Dory can go pretty much anywhere, in my use there really isn't that much call for using a dinghy. I can row it, but it might be nice to have a small motor for it.

About the only time I can see using it would be when anchored out and needing to get to shore without getting too wet. In those cases running a line to shore with a spare anchor (or a convenient tree) and then just pulling the dinghy by hand might work as well as rowing.

Having a gas engine for this type of infrequent use might be more trouble than an electric motor.

thataway · Posted: Sat Jun 28, 2014 1:20 pm Post subject:

I have used trolling motors in many applications--including on inflatable dinghies, a 12 foot Duraboat (with two golf cart 220 amp hour batteries), and then the Torqueedo.

The small trolling motor just does not have enough power in an inflatable against the wind. I had an experience many years ago when a 2 hp gas was not enough power against the wind. So be very cautious.

Rating electric motors in thrust vs HP in gas motors: This is difficult to do, but generally 80 lbs thrust is thought to be equivalent to 1 hp gas engine--so you have to go way up in thrust to equal a 2 hp wide open.

In calm water the small (40 or so lbs thrust) motors work fine. They are light weight. Some are made for salt water, The quality motors are more expensive. For example I have a 83 lb thrust trolling motor, which uses 2 group 27 batteries. (24volts), and has considerable power, but this has a complex mount for a fishing boat, and weight about 60 lbs--so not the lightweight of the smaller motors which are 40 or so lbs thrust.

The salt water rated motors even in the small size start at over $400. How well will the fresh water motors hold up in salt water? I have used one for several years, and washed it with fresh water after each use--but they do start to rust.

The next issue is the size and weight of battery. To be safe you should have the battery in a semi sealed, or at latched box. You do have to use an AGM battery--a flooded lead acid could be catastrophic, with an acid spill.
The weight of a battery more than makes up for the lightness of the trolling motor--and you will have total weight more than the 30 lb small gas outboard. I have used a U1 (garden tractor battery weight in the low 20# range) in several inflatables for the lights and depth sounder/chart plotter. This size is OK even for starting up to 25 hp outboards. But it does not have a lot of time to run a trolling motor because of the low amp hours (32 amp hours).

The advantages or the Torqueedo--It can be put on the dinghy in 3 pieces As I recollect the heaviest is about 14 lbs. Thus it can be more easily handled--and that is one of the major reasons I have one for the dinghy. It also has an integral battery which is far more powerful than the much heavier AGM. It has more thrust than most trolling motors. The down size is two fold--one is cost, another is the shaft length--it is a long shaft--so it has to be carefully managed in shallow water.

If you only have short distances to go, in calm water--the trolling motor will work fine. There is no weight advantage, and there is an issue of charging the battery.

I have a neighbor who has been experimenting with two 40 lbs thrust trolling motors, with kortz nozzles he has made, and using outboard props. He has li ion batteries, and solar panels. He can do a sustained speed of 4 knots all day long (if enough sun) and has a range of about 10 miles to get home, latter in the day. The "boat" is an old Prindle 16 cat, and is very light. He finds for each knot increase in speed he uses twice the power. This will probably hold true for any trolling motor.

Aurelia · Posted: Sat Jun 28, 2014 3:09 pm Post subject:

There is another electric option that might be worth considering as well.

http://www.electricpaddle.com/index.html

I have only run one in a tank but at about half the price of a torqeedo, it at least has the price advantage. Very light weight as well.

Greg

Stan Major · Posted: Sun Jun 29, 2014 7:24 am Post subject:

I fished out of a 9 foot inflatable using the Minnkota 55 lb thrust saltwater trolling motor and an Optima 12 volt battery. Most days that was fine for where I wanted to go though it was slow. One day the wind picks up and the tide is strong coming right at me. I am about a mile from where the trailer is parked and turning the handle on the motor the little inflatable is going no where due to the wind and incoming tide. Fortunately I managed to have enough power to get across the channel to where the water was shallow and the mangroves gave some protection from the wind.

Sea Wolf · Posted: Sun Jun 29, 2014 7:28 am Post subject:

OK, I know you Tech Gear Heads will have to find out what a Kort Nozzle (discussed in Bob's post above) is all about!

Do not design a tug, submarine, or electric C-Dory without this feature:

Kort Nozzle

Joe.

thataway · Posted: Sun Jun 29, 2014 3:32 pm Post subject:

Or you can go on a smaller scale for the Kort Nozzel:
This is not my neighbor's, but one I found on the internet where a person has put a Scott 24v 1 hp electric motor on a 2 1/2 hp Nissan with the power head removed. In this case, the motor pushed a 12 foot fishing boat at 6 mph, and the Kort nozzle added 1/2 mph and decreased the current draw by 5 amps. Not practical for our uses.