Electric outboard

[Searush]

How long would a charge last?

Yeah, I know, that's a "how long is a piece of string" sort of question, but lets assume;

rubber duck or other small tender,
one occupant
calm water, light beam breeze
fully charged typical 50Ah car battery

Would that get me 100 mtrs, 10 miles, an hour, or half a day at a steady reasonable pace - say 3-4kts?

Or is 3-4kts out of the question?

 

[pvb]

You need to say which electric outboard you have in mind.

 

[FWB]

Most people will not use their outboard motor continuously, but in many short trips.
The Torqeedo 1003 which I have will run continuously at 2kts for about 10 hrs, at 3kts for 3h30 and at full throttle say 5kts for about half an hour.
In real use it will last for several days of going to and fro before needing a recharge. However that recharge can be done when back on board by trickle charging directly from the ship's batteries. There is a lot of "range anxiety" about electric outboards, I bought a second battery but I've never needed to use it.

 

[pvb]

Most people will not use their outboard motor continuously, but in many short trips.
The Torqeedo 1003 which I have will run continuously at 2kts for about 10 hrs, at 3kts for 3h30 and at full throttle say 5kts for about half an hour.
In real use it will last for several days of going to and fro before needing a recharge. However that recharge can be done when back on board by trickle charging directly from the ship's batteries. There is a lot of "range anxiety" about electric outboards, I bought a second battery but I've never needed to use it.

As Searush mentioned a 50Ah car battery, we can assume he's not looking at a Torqeedo! Having said that, the Torqeedo is by far the best electric outboard on the market, and is stunningly well engineered. I've been very impressed by mine. Ordinary electric outboards are very variable in efficiency, which is why it would help to know which one he's looking at.

 

[Searush]

I've seen the Rhino VX-44 recommended, not sure if an electric will suit my needs anyway, hence the question. Why do you say a Torqueedo would not use a car battery?

A range of 2-3 miles makes them crap for cruising, doesn't it?


Edit: a 50AH car battery is cheap to buy & not too heavy to lug around a boat, what do people use then? 150AH traction batteries weigh a ton & cost the earth.

 

[FWB]

Why do you say a Torqeedo would not use a car battery?

 

[Searush]

Jeez, that's as awkward as a petrol o/b. I can't watch vids on my "narrowband" so does it have an internal battery? What capacity is it?

One of the benefits of an electric OB for me is the lightness of the power unit & the separate power source.

 

[FWB]

Pity, the video explains it all. Yes built in battery. The unit is light and splits into three parts.
See here http://www.torqeedo.com/images/kataloge/TQ_Katalog_EN.pdf
The manual is here http://www.torqeedo.com/images/gaw/GAW_Travel503_1003_deutsch_english.pdf

 

[pvb]

Jeez, that's as awkward as a petrol o/b. I can't watch vids on my "narrowband" so does it have an internal battery? What capacity is it?

One of the benefits of an electric OB for me is the lightness of the power unit & the separate power source.

The Torqeedo has its own integral battery, which can be recharged from the boat's 12v supply. It splits into several pieces, each light enough to carry easily, so is easy to stow and easy to mount on a dinghy.

The Rhino you mentioned is basically a trolling motor, so would be better on non-tidal waters. I can't find any current draw figures for it, but would imagine it wouldn't last very long on a 50Ah battery; probably a 100Ah would be about the minimum for sensible use. The Rhino also needs flushing in fresh water after use (like most electric outboards).

Edit: The Rhino apparently draws 52A max, so running it flat out would drain a battery in just a few minutes. At lower speeds, the battery would last longer.

 

[Searush]

Oh beggar that then, not that I would want it flat out & I was not thinking of use on tidal waters, just possibly on a Canadian canoe or the GP14 on a lake. I had a suspicion they were a bit "chocolate teapot"-ish but there were a couple offered on a site I frequent & it tickled my fancy as something that could be bunged in the MH relatively easily.

 

[pvb]

Oh beggar that then, not that I would want it flat out & I was not thinking of use on tidal waters, just possibly on a Canadian canoe or the GP14 on a lake. I had a suspicion they were a bit "chocolate teapot"-ish but there were a couple offered on a site I frequent & it tickled my fancy as something that could be bunged in the MH relatively easily.

The Rhino would be OK on a lake, at trolling speeds. But you'd still need something like a 100Ah battery.

 

[Tranona]

Oh beggar that then, not that I would want it flat out & I was not thinking of use on tidal waters, just possibly on a Canadian canoe or the GP14 on a lake. I had a suspicion they were a bit "chocolate teapot"-ish but there were a couple offered on a site I frequent & it tickled my fancy as something that could be bunged in the MH relatively easily.

Those things were designed as trolling motors for lake fishing in the US where you blast to your fishing spot in you 20' dory using your 200hp outboard. Then turn it off, open a cold beer, and use your trolling motor to move slowly or hold in position while fishing. Normally would use the main boat battery bank which is recharged on the journeys out and back by the main motor. Completely different usage pattern. Explains why you see so few here in the UK despite the low price. PBO did a review of them a couple of months ago with predictable conclusions.

 

[Pete54]

I've got a Shakespear 50lb electric outboard. We use it on a canoe in inland waters. At 50% odd power it moves the canoe at a decent walking pace 2 kts-ish. Using a 75A/hr leisure battery it runs for over 3 hrs continuously without any noticeable loss of power. It then takes about 6 to 8 hours to re-charge so I would guess it is using a fair amount of the battery's available capacity. Generally it is a good option, although the 75 a/hr battery is not light (come to thinking out it the outboard is not much lighter than my old Seabee outboard!).

 

[ianfr]

I just bought a Bison 40ft/lb model from Amazon at £99.
We tested it with our inflatable Seago 2.9 airdeck with 2 adults and a fairly big dog, and managed about 50 minutes on a 17.5Ah emergency start kit battery.
This was at varying speeds, on what was a fairly quiet day, but it managed a good walking pace or better at all times.
At one point we put our Suzuki 2.5hp engine in the boat to take it back to the car. So 2 adults, 1 dog and an fairly heavy engine no problems, against a 1 - 1.5 knot tide.
The manufacturers recommend a 90Ah battery which I would guess would give you a good couple of hours with amps in the tank.

Ian

 

[FishyInverness]

Edit: The Rhino apparently draws 52A max, so running it flat out would drain a battery in just a few minutes. At lower speeds, the battery would last longer.

Surely it would last about 57minutes?

50ah Battery
52 amp draw
50/52 = 0.96
0.96 of an hour - 57 minutes....

Or have I failed to grasp something electric-y?

 

[Pete54]

I've copied the following which has a basic explanation of the A/h rating;

"

An amp hour (AH) is a rating usually found on deep cycle batteries. The standard rating is an Amp rating taken for 20 Hours. What this means, say for a 100 AH rated battery is this: Draw from the battery for 20 hours and it will provide a total of 100 amp-hours. That translates to about 5 amps an hour. 5 x 20 = 100. However, it's very important to know that the total time of discharge and load applied is not a linear relationship. As your load increases, your realized capacity decreases. This means if you discharged that same 100 AH battery by a 100 amp load, it will not give you one hour of runtime. On the contrary, the perceived capacity of the battery will be that of 64 Amp Hours.

Hence my comment above, of the duration of the electrical supply without any obvious voltage drop-off. However the time the battery required to recharge would suggest there was not a lot of usable capacity left. But as with most things battery your mileage may differ.....

 

[Pete54]

I've copied the following which has a basic explanation of the A/h rating;

"

An amp hour (AH) is a rating usually found on deep cycle batteries. The standard rating is an Amp rating taken for 20 Hours. What this means, say for a 100 AH rated battery is this: Draw from the battery for 20 hours and it will provide a total of 100 amp-hours. That translates to about 5 amps an hour. 5 x 20 = 100. However, it's very important to know that the total time of discharge and load applied is not a linear relationship. As your load increases, your realized capacity decreases. This means if you discharged that same 100 AH battery by a 100 amp load, it will not give you one hour of runtime. On the contrary, the perceived capacity of the battery will be that of 64 Amp Hours.

Hence my comment above, of the duration of the electrical supply without any obvious voltage drop-off. However the time the battery required to recharge would suggest there was not a lot of usable capacity left. But as with most things battery your mileage may differ.....

 

[pvb]

Surely it would last about 57minutes?

50ah Battery
52 amp draw
50/52 = 0.96
0.96 of an hour - 57 minutes....

Or have I failed to grasp something electric-y?

You've forgotten about the effect of Peukert's law, which quantifies the way in which the battery's effective capacity is reduced as the discharge current rises. The battery would in fact be 50% discharged in about 9 minutes, and it isn't good to go below 50% discharge if you want the battery to have a reasonable life.

 

[FishyInverness]

Thanks, I figured I might be under a misapprehension, but didn't know where it was!

 

[Searush]

Cheers guys you've save me 60 squid plus postage & the cost of a gash battery from the scrap yard.