Trolling motors

[ralay]

We're considering getting a trolling motor for our dinghy (Portland Pudgy).  We don't have room to store a outboard on deck and don't want to bring a gasoline-powered outboard down below or have gasoline aboard at all.

We've gotten by rowing for many of these years, but we've been spending a lot of time on this trip confined to the boat by winds we can't row into.  It's been blowing 35kts here in Narragansett Bay for two days and is forecast to blow 25kts for 2-3 days more.  We're right near Newport, but we can't visit because we're not sure we could row back to the boat.

Who has experience using electric outboards on dinghies?  How much thrust is required to push two folks in an 8ft dinghy when it's gusting over 20kts?  How many amps are we talking?

Also, what's the best way to charge the battery?  We are free range folks.  Our boat isn't wired for 110V and we don't have an inverter.  All our power comes from solar or the alternator.  Supposedly it's not great to charge batteries of different capacities/ages/types in parallel, so I don't just want to hook it in with our other 3 batteries (105Ah AGM, all purchased last year).  I could put switches in after our solar regulator to switch between the trolling battery and the other batteries, but they would be really hard to access unless I made all the switches remote via relays.  Or I could get a panel and regulator just for the trolling battery.  Do they make 12VDC- 12VDC chargers (obviously this would only work when the house bank was at 14+V)?  Other ideas? 

I like the simplicity of just rowing, but it's enraging to be confined to the boat for 3-5 days. 

[Norman]

I believe that connecting a second charge controller to the solar cells to charge the trolling battery would be far better than any of the other possibilities you mentioned.  The new connection could be either at the cells, or at the input to the existing controller.  The controller would then be a match for the exact battery you use.

Any series additions to the house bank charging circuit increases the risk of failure to charge in your most important battery bank.

The easy removal of the trolling motor to store below in a clean environment is an obvious advantage, but adds risk at the dinghy dock.  When practical, store in a secure place when ashore.

My sympathy for both of you, marooned on a weather trapped boat, might as well be in the middle of the ocean!  I am on land waiting for the weather and other issues to line up in order to sail too.

[ralay]

What's the danger at the dinghy dock?  Theft? 

[CharlieJ]

exactly. When I was using the inflatable, with outboard, I stripped the core from some double braid, replaced it with 7x19,made a nicropress loop in each end and secured boat and motor to dock with a padlock. At least one person got a real surprise when they tried to cut the line :)

[ralay]

The PP has holes so you can run a chain right through the side/a motor/the dock.

[lance on cloud nine]

keeping with the theme of simplicity, I wonder if you could use one on your existing batteries for the motor? And if at anchor for a long while, just rotate them in and out...so that they are always on charge with your current setup? Do you think your system would keep up?

[ralay]

Our batteries are 105Ah each and way too heavy to be shuffling daily.  The house batteries live way back in the engine room.  I think Norm's idea is probably the best.  But, honestly, neither of us is eager to drop the money and time to set it all up.  Unless our cruising/living situation changes, I think we'll just suffer occasional periods of confinement.