electric boats

[CWSmith]

At the risk of plugging another magazine, the June 2010 issue of "Water Craft" has a very interesting article on electric boats including a speed boat modeled after the customary mahogany runabout and another made narrower to assist the electric motor. Wooden Boat has run some similar articles, although I think using other boat styles.

I've also seen small electric motors used to push small sailboats when needed.

My question is what risk does that bank of batteries present to (1) water in the bilge and (2) swamping. Is it a risk to life if the boat capsizes?

I love the idea of speeding quietly across the harbor without the intrusion of a combustion engine so I can hear the waves lap under the hull!

[wizbang 13]

Recently,I rescued a chap who had an electric motor mounted on the rudder of his Gig Harbor Boatworks boat. I don't know the exact model, about 17'. he took a "swampdown" under sail,and went for a swim in the cold Gig Harbor water. I was nearby and came to pull him out and so on. There were 2 good size 12v batteries next to the cb trunk, and we both got shocked to s**t and were frightened of the batt acid spilling around. So,yea, it's something to think about!

[CWSmith]

Wow! Thanks. I didn't even think of the battery acid. Can you imagine what would happen if you had enough juice to drive a mahogany runabout and then got swamped? Maybe rowing's not so bad. Thanks for the lesson

[paladin]

You only have leaking battery acid with wet cell lead acid batteries. the shock hazard is caused by your skin getting wet, and more so in salt water. Normally 12 volts is not enough to really hurt, but some systems use 24/36/48 volts for propulsion or higher. I just finished calculating all the parameters for a 107 hp electric vehicle with 3 hours running time, and 1000 hp (twin 500's for a few days at a time. Although I am not doing the actual programming, I have to create the working outline and parameters for an automatic battery equalizer/charger/test system.

[v10builder1]

The dream we all have for electric propulsion systems for boats, quiet, clean, just plug it in to refuel - or even let the sun refuel for us.

Negative reality #1 - limitations to current battery technology.

Negative reality #2 - required dimensions (area) of photovoltaic (PV) array needed to capture enough power to support propulsion.

Negative reality #3 - electric motors of sufficient efficiency and control systems of sufficient sophistication (I just said that?) are available (as noted by other posters - electric vehicle (EV)applications) are robust, reliable, and insanely expensive right now.

Design notes:
1. The hull must be easily driven, the hull must be easily driven.
2. Shaft and wheel must be free of gears and such to avoid wasting energy.
3. If you are looking for a battery technology, in my view, you just can't beat (lead/acid) golf cart batteries from a cost benefit ratio right now. Many posts to the trawler forums I subscribe to agree, and not a few of these posters are of the opinion that the AGM battery technology has a way to go too - most frequent gripe is damaging/shortening AGM life by improper/inadvertent charging.

Golf carts are heavy, 65 pounds or more each, and if you discharge to more that 50%, the # of recharges (lifetime) goes down. My references cite thousands of discharge cycles to 50% discharge, way fewer if more.

So you have to take a bunch of these along. Because our PV array isn't helping much while we are underway. The weight is good ballast, and low in the hull tends to keep battery temperature down, which will help to maximize battery life.

Battery acid:
Battery acid won't eat cured epoxy - just glass in a "tub" around the bottom of the battery boxes. If the batteries are well secured, (the US Battery product has securing fixtures cast in to the tops) and not overfilled, there won't be much spillage out of the cell caps. If the batteries are drowned, it is not likely acid of sufficient concentration to cause harm will be in the swamping water. Hell, the weight will probably sink the boat anyway.

If you leave the heavy old thing in the water all the time and plug in a good sized charger when you are not using her, might work out OK. There is a 2000 watt Honda gas generator (there is also a nice blue inverter type 1000 watt Yamaha expensive one) you could carry to recharge on the hook - would take a while.

What the world needs is a fantastically powerful, light, cheap battery.

I dream on and move with a Cummins 6-BT 5.9 diesel for now.

Regards.

Joe Wharton

[CWSmith]

None of you are wrong, but my question was less practical and more survival. I imagined the boat going over, two battery poles fairly close together, and me in the water 5 or 10 feet away. Was the potential across my body sufficient to cause me harm or death? More and more I'm thinking that if there's enough voltage to make the boat lively there's enough to make me deathly (poor pun). People are building these things, and we worry about whether a boat will sink if swamped, but how about floating and killing the occupants with stray current? It sounds too much like taking a bath with a toaster. Am I missing something?

[Todd D]

12 V batteries won't kill you. Battery acid isn't a problem if you use sealed batteries (gel cel or AGM). However, as was stated above, if you have a bunch of batteries wired in series to generate high voltage, there will be some risk. That said, the batteries will tend to discharge along the shortest path between the poles. If you stay a bit away from the batteries you should be fine although a bunch of batteries in series will cause some chlorine gas liberation in salt water. Shorting in fresh water isn't as much of a problem.

[wizbang 13]

Slightly off topic, a buddy of mine is a fireman.He has spoken of special training /danger of electric car fires/accidents.

[electric joe]

We have about the same conductivity as salt water so we just become part of the normal field pattern of two poles in a conductive medium. It's not exactly like touching two poles while in air where our body is the preferred path and your heart can fall within a more directed field but its still capable of providing a sensible shock in itself. A good battery case nearly shields battery poles because it partially isolates the field resistively; if a battery case is used, theres a much better electrical path within the box than outside it meaning that if dunked, one would be safer from a conductive medium field shock from the battery terminals directly. But in a swamping, the bigger danger is the field path between the battery case and the motor or other large "hot" components. I think this might be what you felt in the trolling motor case ad those field points can be far apart enough to fit a man's chest. To combat this issue, as a minimum. a shielded contactor should be used to disconnect any components if the boat is swamped. In my conversion there is an easily accessible contactor and the battery is shielded using dielectric materials so that the field outside the box, if swamped, is minimal.

But the more I think about this, we might start to think of electronics aboard converted E-boats as industrial "wet location" electrics with no conductive exposures, totally waterproofed interconnections and no loose acid especially in small open boats prone to swamping. This is easy to do for consumer products because you do the engineering and parts sourcing once and make a bunch of the all the same. But not so easy for home conversions. Perhaps there's an electrician in the group that can help us identify parts that help to create isolated conversion systems. Joe

[Richard Jones]

I spent twenty minutes today trying to get my damned 15hp 4-stroke Merc to start up. First time for the season and it would start but immediately stall. Never did get it going. Not being mechancially inclined, I've just about had it with marine gas engines. One of those new electric outboards is becoming more and more a reality for me. So what if I go slow? The tiny lakes I navigate in don't require speed. Plus, if I hook it up to a solar cell to re-charge, I won't be sending money to crazy people.

[Soundman67]

I got rid of the little 3 horse 2 stroke that was on my 9 foot dinghy. I bought a 32lb thrust 12 volt trolling motor. So fat I love it. Maybe its not as powerful as a real outboard but for my purpose it pushes the boat around just fine. I am using 12 volt AGM batteries that are surplus from communications sites. Each one is 85lbs and is 100 amp hour. With 2 batteries on board I am never concerned about having getting home again.