Choice of electric motors as inboards for a catamaran

Good luck putting too many passengers on a commercial vessel.

Jazz 30 is a much better way to go by the sounds of it. I moved toward it and ultimately am building a demountable Skoota 32. But if you build in plywood, even making a good decision in plywood might reduce the vessel weight by 400 pounds; okume v meranti, for example. At any rate, you need to determine the loads you plan to get and especially if you want a charter vessel. The Skoota 28 is just very short on available displacement and I wanted to point that out to you. One thing that might help you with the government is redundancy. If you have independent systems; you'd be a much safer vessel, so independent steering and independent motors, for example, create a safer boat. Boats for hire have a whole different set of rules, though; I'd be making sure I understood all that well before I built. They might even have boarding gate requirements, etc.

 

I definitely won't try to push above limits, especially since i am aiming at charter fishing. I'm still going through requirements for different boat applications. Difficult to get used, at times Japanese check-ups or rules touch only surface and sometimes really strict and detailed with no logic behind on why. I bought plans since now i'm more or less sure that i can get good quality okoume marine ply. Another reason why i want electric propulsion, it has almost no vibration.

 

I'd plan the boat build for electric. Too hard to remodel later.

Consider
Motor location could be above WL.
Bulkhead locations could be wrong for motor/shaft locations.
Battery compartment must be sized correctly.
Access to motor must be planned.
Cabling conduits planned.
Rudders?
Shaft log.

None of this matters much for outboard. The transom can be ob; the fuel could fit in the battery compartment.

The rebuild to electric would be potentially very expensive and time consuming v done upfront at nearly no xtra cost. When you switch; you open a hatch or cut a hatch in; the structure is ready.

There is probably a way to even prep the shaft log so it is available.

Anyhow, converting the boat after would cost a lot; nearly zero now vs regular build.

 

That's actually what i was thinking too, but a nice check list. Makes perfect sense to get ready during building. Currently i'm stuck on battery pack, price/energy density/safety and where to buy. There are many sources of lifepo4 battery packs, but they are on the heavy side, i see that NMC type cells are made, but can't find a source of complete battery packs yet. This might be one of reasons why i'll have to use outboards for a while.

 

NMC is good for increased power. However, you need to find batteries with increased capacity. High power cells are indicated for starting power, which is not your application. Also, it is very important to make sure the operating temperature is correct. Batteries made for cars are optimized at the median temperature, which is really low compared to a boat's engineroom. You will find better results with cells designed for higher temperatures.

 

NMC has various designs as i'm aware, although any of those designs still have higher energy density than lifepo4 and safety is on about same level. Cycle life is comparable too. But energy density can be above 200wh/kg. What i can buy right now from source in Japan is lifepo4 with less than 100wh/kg. So even if go with modest 150-170wh/kg, still a major weight saving.

 

Xellz, you could try black (if he still works for them)
Hi Bert
Our factory / office will be closed on 1st – 7th October 2015 due to China National holiday, will resume to work on 8th- October 2015
If you have battery business talk with me,we can talk once i come back.
ih you have a good time.
Best regards
Black

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I bought 7 years ago my lifepo4 batteries from them and they should have improved and more energy dens. However you may have to built your own battery pack. I have them 10 parallel and 4 in serial. If their prices are attractive, you must insist on soldering tags. You are worried about balancing? You must be yoking that is good for the hobby single cell packs. Not if you place them yourself parallel and groups in serial. You may have to monitor groups. i.e. if you have 20 batteries parallel and 12 groups in serial. ( 40 Volt) You have to monitor occasionally the 12 groups. If they are out too much, you have to charge them until its reaches the same voltage as the other groups. It has not happen to me with the 4 groups I have. Why do you want to buy battery packs? Are you not able to make your own battery pack. There is no real reason why you could not do it if the price is very attractive. Bert

 

Biggest reason is safety, since i want 50-60kW and if weight allows increase more as the time passes. I'm not confident that i can keep this amount in good condition or safe without decent BMS. Another point is, i'm planning to use this boat commercially, at least sometimes. To do so, i need to follow quite many and rather strict rules. But i will research a bit more. Especially since my friend here got kind of infected with electric boats, but hes certainly not a DIY type, so maybe for practice purposes i can make sit on top canoe type boat with electric motor for him. Materials, motor, etc he'll buy and i'll just assemble. Why sit on top, to use shaft and seal motor/batteries from waves and to be able to return in case boat flips over. Single person, 4-4.5m long about 80cm wide, might be good idea to learn and practice on small scale first.

 

The paper, Bert cited above, says at page 408 (PDF Document): "Unless otherwise noted, this article is referring to currents and voltages of 60 (or 50) Hz AC rms."
That means, the sentences cited above are referring to AC voltages and currents.
It says at page 416 (PDF):
"Nearly all cases of inability to let go involve alternating current. Alternating current repetitively stimulates nerves and muscles, resulting in a tetanic (sustained) contraction that lasts as long as the contact is continued. If this leads to the subject tightening his or her grip on a conductor, the result is continued electric current flow through the person and lowered contact resistance. With alternating current, there is a feeling of electric shock as long as contact is made. In contrast, with direct current, there is only a feeling of shock when the circuit is made or broken. While the contact is maintained, there is no sensation of shock. Below 300 mA DC rms, there is no let-go phenomenon because the hand is not involuntarily clamped. There is a feeling of warmth while the current travels through the arm. Making or breaking the circuit leads to painful unpleasant shocks. Above 300 mA, letting go may be impossible." (Emphasized by me).
Conduction of Electrical Current to and Through the Human Body: A Review https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763825/

So the AC Voltage is not less harmfull than DC. The opposit is the case.

Anyway, thank you for the (implicit) link, Bert.

 

Heimfried what are trying to prove. We talk about DC and now suddenly you bring 50 Hz DC rms in the picture.
I capitulate, you have won. I am not going to fight about it. But for your info, I rather touch 300 Volt AC or 300 Volt RMS DC then 300 VOLT DC. Try it.
Bert

 

I have touched 7000+ volt DC several times. Probably the worst was only 3000+ volts when my hand touched electric fence while chest was against well grounded steel gate. That hurt even hours afterwards. I know well that electric fence shocks are quick and limited energy - still they hurt a lot if well grounded.

 

Hi Kerosene, that is not DC , it is pulsed every 1 second. One charges a electrolytic capacitor to 300 Volt DC and discharge this 300 Volt DC over a coil with secondary high numbered winding's. That is not DC. That is pulsed DC with a recovery period of normally 1 second.
I promise you, 10 batteries of 12 Volt in serial and you are on a boat with bare feet, wet salty hands and you touch the DC plus 120 Volt connection and your feet, or other parts of your body to minus, you will die. Your muscles will contract and not let go until death takes place.
You are very welcome to try it, but I recommend if you like life, don't try it. Bert

 

Don’t you think its kind of relevant that the source material (you provided) contradicted your claim?

(And yes my electric fence example was just for entertainment, I get that it is just a single pulse at a time)

 

In the days when we have youth taking .45 calibers to the chest via phone book dares; a little decorum is necessary.

Sarcasm when it comes to electricity is irresponsible on a public forum. Suggesting try it to the uninformed or drive by reader might be harmful.

Suggesting, well I have touched high voltage and getting into a conversation about the types, etc. is not only irresponsible, but not to the point.

Both of you fellows are off base.

My only problem is I am bold enough to tell you fellows that you are carrying on in poor fashion.

Many, many people have died through stupidity, error, malfeasance, and a host of other reasons around electricity.

Please make the posts professional and not sarcastic, and avoid anecdotal experiences that are or might be irrelevant to electric boat motors.

The OP left the building on this long ago when he understood cost.

I actually might need help from you fellows someday, so try to not take it personal and instead of talking to each other when you post; consider some 18 year old might read this for advice; misread and think it is okay to touch high voltage DC.

 

If it was unclear to anyone my example of cattle fencing was not sarcastic. They do run in the thousands of volts. Often near 10,000. I clearly stated that they carry low energy and not as such comparable. If every post requires a disclaimer that one should not do play with electricity beyond one’s knowledge then it is going to be utterly difficult to discuss _anything_.

I really don’t see how my post could come off as encouraging irresponsible behaviour.

This or that I have no desire to grab 300V DC or AC leads. Nor do I think anyone should. Still if we are discussing risks it is important that we can do so in realistic manner.