Cheap electric outboard - make and thrust

[FL390]

I know the topic has been covered extensively. Has anyone tried a 55lbs thrust trolling motor on a small yacht?

I have a 21’ 1500kg sail boat. Prior to lockdown my 5hp outboard failed with a blocked carb jet. I was able to get a tow from the marina staff from the entrance of the marina. It made me realise I was quiet dependent on my outboard. I don’t really fancy my skills of sailing onto the marina pontoon. (Always singlehanded, no furling head sail, not particularly skilled at sailing close to other people’s pride and joy!).

So am looking at a back up to ensure I’m a little more self sufficient. Not in a heavy sea, but a nil wind situation of at least being able to keep the boat under control and to the pontoon in safety, even if that is at 1kt!

Options are a Bison 55 or a cheap ebay 2hp 2 stroke I know the petrol outboard would drive the boat, but it will be awkward and smelly to store. Any thoughts?

 

[Jim@sea]

Believe me C that nothing yet beats a Torqeedo. I know the OP doesn't want one but once you've got over the initial cost you've got an easy to use powerful outboard needing no separate battery.
Regards, S.

And as a brand leader if you wanted to sell it more people would bid on it if it was on eBay.

 

[Stemar]

The Torqeedo also includes the battery, which is significant in terms of price, but more importantly weight.

But it is a lot of money...

 

[JumbleDuck]

I know the topic has been covered extensively. Has anyone tried a 55lbs thrust trolling motor on a small yacht?

My crew has had quite satisfactory results from experiments with a Bison 55lb on our Drascombe Longboat. Didn't half munch its way through a 36Ah battery, though.

 

[Alan S]

FL390, I had a Bison 55lb on my Corribee, same loa as you although lighter. Worked a treat for manoeuvring and getting in and out of harbour. Useless against a headwind over about f2 but that's what sails are for. I would reccomend it especially if you already have 12v ship's battery and solar power. Lowest cost and greenest option.
Cheers.

 

[pvb]

My crew has had quite satisfactory results from experiments with a Bison 55lb on our Drascombe Longboat. Didn't half munch its way through a 36Ah battery, though.

Out of interest, how long would it last?

 

[Poignard]

Seen at Beale Park boatshow in 2011

 

[Stemar]

Those two give a whole new meaning to the expression trolling motors!

 

[Poignard]

Of course if you want an outboard with a bit more oomph:

 

[Poignard]

Those two give a whole new meaning to the expression trolling motors!

Interesting to see one motor going full ahead and the other full astern!

 

[lw395]

I know the topic has been covered extensively. Has anyone tried a 55lbs thrust trolling motor on a small yacht?

I have a 21’ 1500kg sail boat. Prior to lockdown my 5hp outboard failed with a blocked carb jet. I was able to get a tow from the marina staff from the entrance of the marina. It made me realise I was quiet dependent on my outboard. I don’t really fancy my skills of sailing onto the marina pontoon. (Always singlehanded, no furling head sail, not particularly skilled at sailing close to other people’s pride and joy!).

So am looking at a back up to ensure I’m a little more self sufficient. Not in a heavy sea, but a nil wind situation of at least being able to keep the boat under control and to the pontoon in safety, even if that is at 1kt!

Options are a Bison 55 or a cheap ebay 2hp 2 stroke I know the petrol outboard would drive the boat, but it will be awkward and smelly to store. Any thoughts?

The problem won't be propelling the boat, it will be keeping it going in the right direction.
Zero wind you can take your time.
The difficulty is that the wind rattles around the marina and blows the bow this way and that.

One thing we find very effective is a big canadian-canoe style paddle.
But single handed is asking a lot. You can only operate from the cockpit, so you need more power.
Think of it as needing quite a lot of action from a 3HP engine to do what's easy with a few squirts from a 1kW bow thruster.
A couple of strokes to get the bow around is easy paddling from the foredeck.

Could you fit a jib furler? Maybe even the dinghy type furler rather than a reefing system?

 

[artistnomad]

Ok, So in 2021, are we closer to having a 400-500 euros awesome electric outboard engine? I notice the more expensive ones are just getting more expensive.

 

[fredrussell]

Ok, So in 2021, are we closer to having a 400-500 euros awesome electric outboard engine? I notice the more expensive ones are just getting more expensive.

Well, sort of... Electric trolling motors as discussed in this thread are much the same, but Lithium batteries are getting cheaper, which means extra range costs less, and weighs less (than same a/h lead acid batteries). My mate bought a 100 a/h lithium battery for £300. Uses it with a 70 lb thrust trolling motor on his dinghy and it romps along. If memory serves, he said it would do three knots for at least as hour.

 

[artistnomad]

Well, sort of... Electric trolling motors as discussed in this thread are much the same, but Lithium batteries are getting cheaper, which means extra range costs less, and weighs less (than same a/h lead acid batteries). My mate bought a 100 a/h lithium battery for £300. Uses it with a 70 lb thrust trolling motor on his dinghy and it romps along. If memory serves, he said it would do three knots for at least as hour.

From what I see the 70 lb thrust trolling motor need 24v and when you add them together you get close to 1000 euros and a battery bouncing around your feet ... sounds shocking.

 

[Kelpie]

Lithium for a trolling motor sounds great. I've spent a wee bit of time looking into it.
For my use I only wanted something like half an hour of range, which in theory means about a 25Ah battery. With lithium cells currently available at around £1.50/Ah/12v it sounds like there must be a cheap and cheerful solution to be had. £35 for half an hour range? Sounds great!

Problem 1: unless you look for high-output cells, you can't go that small because the cells won't handle the discharge rate. So straight away you've got to double the size of the cells. That's OK though, it's all more range, and it's still small and light compared to lead-acid. And still only £70. In theory.
Problem 2: cells at that size are not at the 'sweet spot' of pricing, at least just now. The best prices currently are on 280Ah cells, which should cost around £400. I've been unable to find smaller cells at anything like that price. In fact the cheapest you can get any set of four cells is going to be about £200. This is starting to get pricey.
Problem 3: you can't just hook up the cells and go. You need to do it through a Battery Management System. And not just any BMS, one rated for a high continuous current. Not a deal-breaker but it's easily another £50+ even at wholesale prices.

So that's how a £35 battery project becomes a £250 one. And you still have to put it in a case with suitable connectors, and buy a charger.
I've not given up on the idea just yet, but the old car battery I'm currently using has had a stay of execution whilst I decide whether I can be bothered with the project.

I'm absolutely certain that if a Chinese company thought the market for a Torqeedo clone was big enough, they could be producing them for less than £500. Just look at what they've done to the Eberspacher marker. Maybe I should wait until that happens?

 

[William_H]

I know the topic has been covered extensively. Has anyone tried a 55lbs thrust trolling motor on a small yacht?

I have a 21’ 1500kg sail boat. Prior to lockdown my 5hp outboard failed with a blocked carb jet. I was able to get a tow from the marina staff from the entrance of the marina. It made me realise I was quiet dependent on my outboard. I don’t really fancy my skills of sailing onto the marina pontoon. (Always singlehanded, no furling head sail, not particularly skilled at sailing close to other people’s pride and joy!).

So am looking at a back up to ensure I’m a little more self sufficient. Not in a heavy sea, but a nil wind situation of at least being able to keep the boat under control and to the pontoon in safety, even if that is at 1kt!

Options are a Bison 55 or a cheap ebay 2hp 2 stroke I know the petrol outboard would drive the boat, but it will be awkward and smelly to store. Any thoughts?

Far better and more reliable would be a decent rowing arrangement. On my 21fter I can use the base(s) of the stern rail as a rowlock and face backwards to pull on 2 paddle/oars that are quite long. Will move the boat quite nicely in calm conditions. Probably better than an electric o/b. ol'will

 

[William_H]

The OP question is a very valid one. No amount of advertising and performance claims can avert the simple facts of physics. 650 watts equals one horsepower. Electric motors are generally close to 100% efficient. Obviously less than 100% but no place for improvement in motor design. So assuming reasonable efficiency in gearbox which again we could expect to be good with no place for improvement. Then it is the propeller size and pitch which we know much about which must match the hull and speed desired. Lastly we come down to battery weight and performance. Lithium or lead acid? Lithium probably better but more expensive. If you have a separate battery then you have the choice.
So my point is that there is no reason to believe an expensive electric outboard can ever be any much better than a cheap one. Certainly not to justify the double or more cost. Provided you factor in the value of batteries if they are built in the Torquedo. ol'will

 

[Moodysailor]

This helps to explain why outboards are so much more thirsty than inboards, although I"d expect sail drives to be "equally" inefficient.

Saildrives exist to make sailing more efficient (less drag in underwater appendages), and to give more interior space. however, they are probably extremely close in terms of mechanical drag as a conventional transmission, stuffing box & p-bracket arrangement as these aren't exactly low-friction, and the SD wins back as the thrust is directly inline with the direction of travel.
The real inefficiency with petrol outboards is that fact that the simple carbureted petrol 2-stroke engines as found on small tender engines are only about 15-20% mechanically efficient, the diesel inboard is closer to (or exceeding depending on age) 40%. Even the very best IC engines only approach 55-ish%....

 

[rogerthebodger]

What you need is to add a solar panel to you electric outboard battery combination. This will not only increase the range but more importantly continue to charge the battery from the sun when the electric outboard is not being used.

 

[Moodysailor]

The OP question is a very valid one. No amount of advertising and performance claims can avert the simple facts of physics. 650 watts equals one horsepower. Electric motors are generally close to 100% efficient. Obviously less than 100% but no place for improvement in motor design. So assuming reasonable efficiency in gearbox which again we could expect to be good with no place for improvement. Then it is the propeller size and pitch which we know much about which must match the hull and speed desired. Lastly we come down to battery weight and performance. Lithium or lead acid? Lithium probably better but more expensive. If you have a separate battery then you have the choice.
So my point is that there is no reason to believe an expensive electric outboard can ever be any much better than a cheap one. Certainly not to justify the double or more cost. Provided you factor in the value of batteries if they are built in the Torquedo. ol'will

This is a valid point, and gets to the crux of the issue - which is how the power is delivered to the water.

Range etc, etc is all about power density and storage. Like it or not, petrol has the highest power density - i.e the amount of energy it can deliver for the volume space it takes up.. We just don't have the technology yet to store as much electrical energy in the same space. So to match the range it comes down to sizing the batteries appropriately for the journey/use.

kW are kW, and hp is hp as mentioned. How it's delivered to the water is the important aspect, and this is where (from my limited knowledge of the products on the market) there are divisions. One one side is the trolling motor camp - high torque, low speed designed for maximum efficiency at low speed, seperate batteries to allow use of existing power or to size banks as needed. On the other side are the Torqueedo et. al designs which are clearly targeting the leisure use market as conventional outboard replacements (it's no coincidence that the basic design is even similar) - lower torque (though still very high compared to an IC outboard), higher speed, inbuilt battery for convenience and compactness.

So, once the OP picks their use requirement, the choice is much easier. As long as you don't expect one design to do the things it is not designed to do (i.e high speed out a trolling motor, or all-day range from the leisure type) then you shouldn't be disappointed.

Apologies, but I can't advise anything on thrust or sizing as I have little experience with this.