Sizing an electric trolling motor

[bloggs68]

Hi all,

read the threads on trolling motors but still looking for some more info.

I am looking to power a 15' double ended daysailer, of around 4-450pound displacement. Main use of the motor is for getting to/from launching ramp and when the wind dies. I was looking at the minn kota range and motors are all described in pounds of thrust which doesn't really enlighten me as to correct sizing for this boat. Equivalent outboard motor that would easily do the job would be a 2hp Honda 4 stroke.

Any of you guys out there have experience in sizing up one of these?

tia

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[paladin]

You will find the electric need be a lot smaller than the gas job.....from experience I would say something in the 25 pound thrust range...

[Thorne]

For that size boat I'd go for something in the 45# range, but a lot depends on actual use. If you'd ever be using it in high winds or swell, you'll need the extra power to deal with the windage of the boat, mast, etc.

You don't mention the distance or waters, which is critical info. If it is offshore or off a rocky lee shore, you'll want either a larger electric setup or a small outboard. Even fans of electric propulsion will admit that pound-for-pound a small outboard is more effective by a large factor.

See if you can borrow a trolling motor of any size for testing, or find a used one. No matter what the size of the motor, you'll need enough battery storage to push the boat the required distance.

[bloggs68]

Motor will only being used in sheltered waters. Local supplier here today advised they have been using a 40lb thrust minn kota on up to 16' fishing boats with nearly double the displacement so a 40lb motor sounds like it would do the trick. Motor is sucking 10amps flat out so a couple of small AGMs should give plenty of reserve for what's required.

Not having used electric before it must be rather weird - no noise or smell.

regards,

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[Rational Root]

let us know how this works out. I'll be in the same boat (when the same boat is built :D )

[ssor]

Consider how fast you can pull the boat with a rope and the force you apply to that rope. 40 pounds of pull/push moves my 9500 pound 30 foot boat around the docks very nicely.

[tonydezoc]

I have used a large Minn kota 55lb as an additional motor on a heavy 18' clinker boat mainly for manoevreing silently upwind of feeding trout on lakes, on that boat I wouldn't want to be relying on that motor for any long distance it wasn't particularly fast either. I'm probably going to put a torqeedo 801 on the caledonia yawl when I manage to finish it , the 801 is supposed to be the equivalent to a 2hp, there is a smaller model a 402 equivalent to 1hp which is cheaper, both have integral batteries and fold up but they are quite expensive . heres a link to the Aussie supplier www.torqeedoaustralia.com (http://www.torqeedoaustralia.com/)
Tony

[Thorne]

Try a search of this Forum as we've had some very detailed and informative discussions on this topic.

We still don't have distance information, which can be critical to determining how many batteries you have to carry.

A lot comes down to your tolerance for loading/unloading heavy batteries out of the boat, as they are too heavy for most lighter designs to be trailered with them in place. You'll also need a smart charger, and possibly a small solar trickle charger to keep them maintained. Factor in the cost of heavy copper cables running from the batteries back to the motor, and how you'll lay them into the boat's interior. You'll either need a remote control or be sitting within range of the motor's controls.

I'm a fan of electric power, but as many people find out, oars are more efficient for shorter distances in calm water, and a small outboard more efficient for longer distances in rough water. By more efficient I mean by weight, cost, and hassle.

Electric seems to work best for larger launches -- boats that stay in the water and where the weight of batteries provides beneficial ballast. For smaller boats the issues with long cables to allow the batteries to be placed forward, loading/unloading batteries, stowage of the trolling motor itself, and battery maintenance seem to limit electric motor use.

I've also seen it used as how you envision it, but with the trolling motor head built into the rudder blade. Works well and the problem of where to store and how to deploy the motor are eliminated.

http://www.luckhardt.com/electric_rudder1.jpg

[marshcat]

I have a 15ft catboat, much beamier than your double ender I assume. I use a Minn Kota 55 lb Riptide motor, which is their saltwater version. It pushes me around fine, on semi protected waters (Chesapeake Bay and tributaries). If you get the version with the "Digital Maximizer" that uses pulse width modulation, you get a lot more distance out of the battery. I would think 40-50# would do fine for you. I run mine around 50-75% of full power most of the time (getting up a narrow channel against wind and tide, leaving/returning to dock), which also helps conserve. I have never run it down completely, and the longest I have run it is probably around 70 minutes. I have one Group 24 (or 27 - can't remember) battery, which I recharge during the week with a solar panel. I agree that this setup may not work for everyone, but it meets my needs for weekend cruising.

[JimD]

I use a 24 volt 65# minnkota for our Glen-L 15. That's far more than is required to get in and out of a dock but add a little wind and wave and the the extra power can be handy.

[Rational Root]

Good to know, since I'm working on a Glen-L 14 at the moment.
Thanks

Dave


I use a 24 volt 65# minnkota for our Glen-L 15. That's far more than is required to get in and out of a dock but add a little wind and wave and the the extra power can be handy.

[Tom Robb]

I don't suppose you gave any thought to ordinary oars or a sculling oar?
Quiet, cheap, shippy, no batteries to run down at the worst possible moment, etc.

[bloggs68]

I don't suppose you gave any thought to ordinary oars or a sculling oar?
Quiet, cheap, shippy, no batteries to run down at the worst possible moment, etc.

Tom,

If it was my boat I wouldn't bother about a motor but it is for a client. I like this sculling helper http://www.duckworksbbs.com/gear/scullmatix/index.htm which may persuade a few owners to forgo the motor.

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[Thorne]

For a client I'd go for a 65# trolling motor of the new pulse modification design, and consider one of the wireless remotes -- that way they don't have to sit in the very stern to control the motor.

http://www.cabelas.com/cabelas/en/content/Pod/01/77/95/p017795hz05.jpg

[bloggs68]

For a client I'd go for a 65# trolling motor of the new pulse modification design, and consider one of the wireless remotes -- that way they don't have to sit in the very stern to control the motor.

http://www.cabelas.com/cabelas/en/content/Pod/01/77/95/p017795hz05.jpg

Nice looking idea Thorne but the unit costs out here are too high in proportion to the rest of the build - makes an outboard look attractive.

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[Thorne]

Even fans of electric propulsion will admit that pound-for-pound a small outboard is more effective by a large factor.

That's what I said in my first post. But you didn't ask what to use, just asked what size electric for the boat...

;0 )

[py]

I bought a 2nd hand one on fleabay a while back. 24v 80lb jarvis watersnake. Finally tried it a couple of weekends ago on my oughtred acron skiff. I wasn't exactly blown away by the power, or speed. I wonder if its a bit like a diesel-would push a much larger boat at about the same speed without much extra effort? Maybe its a gearing/prop pitch thing, just won't go any faster. i didn't take the gps with me, but my sense was that we were only going 2 1/2 knots or so. Ran for about an hour, pretty much continuously on 2 75ah 12 v batteries wired in series. overall I 'd have to say I was somewhat dissapointed ini the performance. Slipping along with just a quiet hum was pretty cool though.

[ssor]

I bought a 2nd hand one on fleabay a while back. 24v 80lb jarvis watersnake. Finally tried it a couple of weekends ago on my oughtred acron skiff. I wasn't exactly blown away by the power, or speed. I wonder if its a bit like a diesel-would push a much larger boat at about the same speed without much extra effort? Maybe its a gearing/prop pitch thing, just won't go any faster. i didn't take the gps with me, but my sense was that we were only going 2 1/2 knots or so. Ran for about an hour, pretty much continuously on 2 75ah 12 v batteries wired in series. overall I 'd have to say I was somewhat dissapointed ini the performance. Slipping along with just a quiet hum was pretty cool though.
You would be pleasantly surprized at how fast you could row that little boat with that electric assist.