CP16 Electric Trolling Motor question

[MKBLK]

"Was a bit nervous about staying on the motor too long. I have no idea how long the battery will last and would rather not paddle back, although the jet-ski was an option. Having baked long enough on the Delaware, headed back in for a good landing at the dock. Wish I could determine how much juice is left in the battery. Wouldn't be as nervous about going out of sight of the dock... something of old like being afraid to leave sight of land. Anxious for some real air!"

I pilfered the above from my initial post (New CPYOA member and CP16 owner) because I thought it would be of general interest. Is there a chart or a formula that will let you calculate approximate running time? At present, I'm using a standard car battery (new) as opposed to a deep cycle marine battery. If I hook up a voltmeter in parallel, would that give a good indication of how much power is left? What I really am asking is: How long can I expect a fully charged battery to last before the paddles come out? I realize that there would be a huge difference between a lake and a river with current/tides.

Also, the Minn Kota trolling motor I'm using is 28 lbs. thrust. I can get a 45 lb. thrust motor, but how much run time will I sacrifice. And is there a serious penalty for ratcheting up the speed? Sorry for all the questions!

Marty K.

[Shawn]

Marty,

Get a deep cycle ASAP. A starting battery won't last long in that application both in run time and overall life.

There are many battery voltage charts available online. For example:

http://www.marxrv.com/12volt/voltchart1.gif

On a starting battery you should not drop down below about 90-95% of full charge or you are risking permanently damaging the battery. On a deep cycle you can safely go down to around 50%.

"And is there a serious penalty for ratcheting up the speed?"

Yes, huge difference in run time from full throttle down to a conservative speed.

"How long can I expect a fully charged battery to last before the paddles come out? "

You need the current draw of the trolling motor and you can calculate that.

Using totally made up draw numbers... if the trolling motor uses 20amps at full throttle that means each hour it needs 20 amp/hours of power.

If you have a deep cycle battery that is 100amp/hour capacity and you watch the 50% discharge limit that gives you 50amp/hours of real capacity. That means you could run for about 2.5 hours at full throttle. If instead you are using a 100amp/hour starting battery that should not go below 90% of fully charged you have 30 minutes of run time before you risk your batteries life.

If at 50% throttle the draw was 5 amps then your run time will be 10 hours on the deep cycle or 2 hours on the starting battery.

If you compare the current requirements of the 28 pound thrust vs the 45 pound thrust motor you can see how much of a difference it has on run time.

Shawn

[Shawn]

Was just reading on another site that for each pound of thrust a trolling motor will use roughly 1 amp. If that is accurate at full throttle you are pulling about 28 amp/hrs so you can adjust run times accordingly.

The 45 pounds of thrust model would have a little over an hour of full throttle run time on a 100amp/hr deep cycle and about 13 minutes on the starting battery.

If you are conservative with the throttle it will last much longer of course. If you want to be at hull speed all the time under power get an outboard.

Shawn

[MKBLK]

Shaun,

Wow! I knew I joined CPYOA for a reason! Thanks for the very helpful info. A deep cycle is definitely in the future. My aim is not to use the trolling motor at all. It is for emergencies and close quarters only. Not for cruising! That's why I opted for an electric over a far more powerful gas stinky motor. My only concern with an electric is having to fight the current in the river. The Delaware often flows at 7 knots... time to toss the anchor!

Marty K.

[Shawn]

Marty,

"My only concern with an electric is having to fight the current in the river. The Delaware often flows at 7 knots... time to toss the anchor!"

With that much current you would have no choice but to drop anchor and wait it out. Hull speed on a 16 is about 5 knots so if you were heading directly into the current your speed over ground would be -2knots.

BTW, saw your post on your battery charger. Just keep in mind its charge rate if/when you heavily use the Minn Kota. If you used 28 amp/hours from your battery it will take your charger about 19 hours to recover that.

Shawn

[MKBLK]

Shaun,

No problem with the charge rate... since I'm a true trailer sailor. The boat's at home after every cruise so the charger gets plugged in after each venture.
And I know I have to keep an eye on the tide tables, else my wife will be serving me cold porridge for dinner! Should I get caught by the tide, I have to make it over relatively close to shore in order to anchor... the channel is 55' deep! Besides it would be very embarrassing to be caught in the channel by an ocean going freighter! Another option, in a pinch, would be to tie up to a bouy and watch the river rush by. Just theorizing.

Marty K.

[Bob23]

Marty:
   Slight change of subject but where do you sail in the Delaware? I'm on the other side of the state near the mighty Atlantic.
Bob23

[skip1930]

I think I'd stick with gas or gas/oil engines. Never electric motors with no way to charge 'em up.
Lets see...180,000 btu's in one gallon of gasoline vs 3413 btu per kw. hummmmmm
Nothing wrong with electric motors, but for this application, getting home, takes a gaurantee.

skip.

[CaptRon28]

I'm using a 55 pound (of force) Minn Kota trolling motor on my 3500 pound Horizon. This wasn't voluntary, the reservoir near my house won't let me launch with the Yanmar working (I have to remove the prop). Saves me around 2 hours in drive time and additional setup, so a quick day sail is now a reality. Four hours of free time will get me over 3 on the water.

It's not a great multi-purpose solution, but the trolling motor works fairly well in this 1,000 acre lake (6 miles around). I don't think I would try it in a larger bay or river where current could be a major factor. Anything over 12 knots of wind could be a problem as well - if you have to motor in that direction. In the fairly still reservoir water I can get up to around 2 knots forward and maybe 1.5 in reverse. The boat already had 2 deep cycles batteries and a charging system, so that allows a much longer run time with the electric motor - not that I'd actually motor around the place. About a minute or two is normal. But I'm pretty sure that I can make it across the lake with either battery.

[Salty19]

That's too much current for a trolling motor.  You will be running backwards with 7 knots of current.
In fact, I doubt a real outboard could push you up river in those conditions.   Hmmm....better get a good anchor!

[MKBLK]

Marty:
   Slight change of subject but where do you sail in the Delaware? I'm on the other side of the state near the mighty Atlantic.
Bob23

I responded to this post earlier, but it seems to have dissappeared from the forum! Anyway, I launch from Fall Twp. Penn Quaker Park which is about 10 miles south of Trenton, NJ. I plan on cruising down to Bristol, PA and around Burlington Island initially. It's a real long way to the bay, so that may have to wait awhile. Probably an entire weekend with wind all the time (or just float with the current). I would love to be able to make it to Cape May someday! That would probably take an entire week for a round trip.

And, Skip - I agree that gas gives a lot more power, but that kind of negates one of the reasons I bought a sailboat. Admittedly, I have thought about investing in a little 1000 watt gas gen from Harbor Frt. Only $100.00. But, remember, the hull speed of a 16 is only 5 knots anyway!

Marty K.