Electricity, water, what can go wrong?
November 4, 2024 1:32 PM Subscribe
We have a small(ish) sailboat. Our outboard motor has been giving us a lot of grief this year and we are thinking of replacing it with an electric motor. Yea, nay?
Our current motor is a Yamaha F5A, which we use as little as possible to get in and out of the harbour so that we can get to sailing as quickly as possible. However, for the past year it has been giving us a lot of grief: it has died several times while returning into the harbour (see previous question), and on one trip it just... wouldn't start. We took it into a shop, and they could find nothing actually wrong with it.
In short, we are not happy with the motor and now that the boat is away for the winter, have decided that this motor will not go back on the boat in the spring. We are thinking of replacing it with an electric motor, but it seems hard to get good information on them online. In particular, a lot of what we can find seems to be from smaller, newer companies, and half of the articles feel as much like SEO-optimised ad-copy as anything, making it hard to gauge if such a motor is right for us.
Several questions:
* Many of the specs describe their power output as being around 1kW (3hp) which is... not right. Admittedly an electric motor is not the same as a petrol motor, so it is possible that they are more efficient (sort of like LED light bulbs vs incandescent ones). Is there some logic to this, or is it just marketing buzz?
* Is this actually reasonable for our boat (Maxi 77; 25ft long, 2000kg)? Or would we find ourselves with an extremely underpowered motor?
* Does anyone have any experience with these motors or good review sites that they trust?
Our current motor is a Yamaha F5A, which we use as little as possible to get in and out of the harbour so that we can get to sailing as quickly as possible. However, for the past year it has been giving us a lot of grief: it has died several times while returning into the harbour (see previous question), and on one trip it just... wouldn't start. We took it into a shop, and they could find nothing actually wrong with it.
In short, we are not happy with the motor and now that the boat is away for the winter, have decided that this motor will not go back on the boat in the spring. We are thinking of replacing it with an electric motor, but it seems hard to get good information on them online. In particular, a lot of what we can find seems to be from smaller, newer companies, and half of the articles feel as much like SEO-optimised ad-copy as anything, making it hard to gauge if such a motor is right for us.
Several questions:
* Many of the specs describe their power output as being around 1kW (3hp) which is... not right. Admittedly an electric motor is not the same as a petrol motor, so it is possible that they are more efficient (sort of like LED light bulbs vs incandescent ones). Is there some logic to this, or is it just marketing buzz?
* Is this actually reasonable for our boat (Maxi 77; 25ft long, 2000kg)? Or would we find ourselves with an extremely underpowered motor?
* Does anyone have any experience with these motors or good review sites that they trust?
These charts from Minn Kota might help:
https://minnkota.johnsonoutdoors.com/us/support/trolling-motor-installation-guides/motor-selection-boat-size-guide
posted by at at 8:57 PM on November 4
https://minnkota.johnsonoutdoors.com/us/support/trolling-motor-installation-guides/motor-selection-boat-size-guide
posted by at at 8:57 PM on November 4
A friend of ours has a sailboat about the size of yours, and has an electric outboard to get it out of the marina and back in of course. Quite small, IIRC 2hp, and it does the job. We've sailed with them once, two years back, and it had sufficient power to make headway into a force 3..4 wind, and according to the owner it could do so for at least half an hour in addition to the manoeuvring in and out of the harbour.
Unfortunately I don't have any details on the engine and battery, and they're often not that quick to react if I were to ask them. One thing I found a bit odd was that the battery pack was sitting on the top of the 'shaft' (which it doesn't have, the motor being down under water directly driving the propeller). The pack is not that heavy, but it still looked a bit awkward handling it to attach it to the shaft when that's already on the engine mount. Control was like a conventional outboard, throttle on the helm, though you could hook up a wired remote.
posted by Stoneshop at 1:57 AM on November 5
Unfortunately I don't have any details on the engine and battery, and they're often not that quick to react if I were to ask them. One thing I found a bit odd was that the battery pack was sitting on the top of the 'shaft' (which it doesn't have, the motor being down under water directly driving the propeller). The pack is not that heavy, but it still looked a bit awkward handling it to attach it to the shaft when that's already on the engine mount. Control was like a conventional outboard, throttle on the helm, though you could hook up a wired remote.
posted by Stoneshop at 1:57 AM on November 5
About 15 years ago, I knew a guy who had a Torqeedo on a 19 footer. As far as I know, it was satifactory but expensive. IIRC, he got 5 miles out of a charge. There more entries in the better-than-trolling motor market now than then. Going electric is fine. The question is to much to spend.
In your place, I'd think about the worst, or at least, bad case scenarios. What are your options if the motor fails, or the headwind is too strong, or whatever? Can you tie up somewhere you can sail to for long enough get a tow, or charge s battery, or otherwise cope? If not, maybe don't cheap out.
posted by SemiSalt at 5:16 AM on November 5
In your place, I'd think about the worst, or at least, bad case scenarios. What are your options if the motor fails, or the headwind is too strong, or whatever? Can you tie up somewhere you can sail to for long enough get a tow, or charge s battery, or otherwise cope? If not, maybe don't cheap out.
posted by SemiSalt at 5:16 AM on November 5
You are not logged in, either login or create an account to post comments
"1HP is 750W.
A 12V 100Ah battery is 1200Wh if you drain it completely.
If you are going to be gentle on your batteries then you might say that a 100Ah battery is good for 1HP for 1 hour.
If you need 10HP to move your boat and want to motor for 10 hours, then you need 10 * 10 * 100Ah -> 10,000Ah. That is, of course, a lot of batteries.
On the other hand, if the motor is just to get in and out of the marina, then you don't need to hit hull speed or go very far. So 2kW electric motor and small battery bank could be plenty to slowly motor out of the marina and then put up your sails."
I like Dakota lithium batteries for my outboard. They last about 3x as long as comparable lead acid batteries before they need to be replaced. But you do need to be aware that lithium batteries have their own pros and cons. If you overcharge them you can create a runaway process of overheating that won't stop even if you disconnect the battery from the charger. And with a boat like yours, you'll probably be using a much different system than the one I have on my little guy.
Here's some more info about lithium boat batteries.
So the short answer is yes, this is possible, with some safety precautions.
posted by ananci at 2:56 PM on November 4