Anonymous wrote:I wonder how this will all play out in terms of service life. There was a time when we all said salt water and electrics don’t mix.

While this is true, try putting a gas or diesel motor under water, salt or otherwise, and see how well it works. Most inboard IC (internal combustion) motors use a heat exchanger to keep salt water as far away from working components as possible and that salt water loop probably causes more trouble than any other part. Outboards, while using salt water directly for cooling, still use a cowling and baffle the intake air to keep salt water out. Outboards are also made with different metals throughout. Car manufactures found out long ago how to deal with salted roads and electronics which can outlast the engine in most cases.

So the use in salt water is not really an argument for or against electric vs. IC propulsion. Both require dealing with salt and it's effects. Electric does have the advantage of being sealable and run under water. Even a 2 stroke outboard has many many moving parts to wear out.... an electric motor setup may have as few as one shaft with two bearings and a seal. Using an electrical control for speed and directional control is effectively a non-issue simply because the actual mechanism is electronic anyway and so there is no control for a cable to hook up to. A gear box would only add complexity and inefficiency to the system. The other advantage is that switching from forward to reverse does not take a huge throw but rather dead slow in which ever direction happens with the first part of the control's movement. A lack of cable drag and mechanical linkage drag are other bonuses. Cables do not like salt water any more than a control pot, both being encapsulated against water ingress.

Thanks for the link, David Ty; I will re-read that thread.
I can see the point with doing away with smell and noise, and have the engine power available more readably.

I too have done a bit to improve that while still using my 6hp Tohatsu:
The main thing has been to switch to burning Alkylate petrol. This keeps the sparkplug perfectly clean even if just about all my use of the motor is when it is half-cold and at low power-setting. This means that the engine always starts at first or second pull. The main obstacle before starting my engine is that I have to move aft and swing it down first. As for noise, the benefit of the engine back there is reduced noise level. At moderate cruising speed we can chat easily in the cockpit.

That Alkylate petrol is over twice as expensive as standard petrol, but with the little use my engine sees, that is no issue. The sparkplug from 2018 still looks like new. If I were to do more serious cruising, I would have two tanks and burn ordinary petrol most of the time, when the engine will be warm and keep the plug clean anyway.

Arne

Arne wrote:

An easily handled and well-sailing boat is the greenest boat.

I cant’ help being a little sceptical to this strong focus on fitting our sailboats with electric propulsion systems. What do we gain in the big picture?
By all means, I too want to reduce my CO2 footprints, but then I think we must count with all big CO2 sources, like travelling by plane, by car, as well as by boat.

aland?

I certainly agree with your thoughts Arne. It is good that people are exploring electric propulsion options and trying out different systems, and as with many innovations, David Tyler has given his system a good tryout and seemed very happy with it. I looked at an electric outboard for my new 6 meter catamaran, but when looking at the costs involved, and the added weight on a small boat, and the savings in terms of fuel costs, and environmental benefit it just did not stack up for me. I certainly agree that we need to do everything we can to save the environment and reducing emissions from internal combustion engines is a very helpful way to do this. But as Arne has found, with a very low per annum fuel burn the buyback period in terms of saving would be many years, and even though my motor burns petrol it is an ultra low emission motor.

This also applies to electric vehicles. Here in New Zealand there is now a big push to get us into electric vehicles and I certainly would like one as I do drive about 20,000km each year. But for the same money I would spend on a good low mileage petrol vehicle I can only buy an older reduced range electric car and one which is not at all suited to the rural environment in which I live. So once again although I would like to save all that fuel money, and do my bit to help the environment, it just does not stack up. Better to have a car such as Arne's little Suzuki Ignis which slowly sips it's way through not much petrol at all.

As Arne has pointed out, at least with a yacht the more we actually sail the better and save the motor for those time when there is not enough wind to sail, or for inner harbour maneuvering.

Thanks Arne for correcting the parameters for the Yamaha HT propeller. I don't recall now where I got my figures from.

Edit: Most sources googgled quote 9.25" as the diameter for a Hi Thrust motor, but that can't be right. I did find one source in another forum which verifies Arne's figures.

"engine: T9.9 high thrust 4-stroke
gear: 2.92
prop: 11-3/4" x 9-1/4P"

I'm a bit confused now, because a four stroke should be F9.9 not T9.9 as quoted above, but anyway, if those figures are correct then at 5 knots and 3,500 rpm (say) the propeller slip would be 45%

Quoting Johanna at "full speed" (5,000 rpm?) 6.4 knots, the propeller slip works out at 51%.  If the revs drop back to 4,000 rpm then at 6.4 knots the slip becomes 39%.

I don't think a small outboard motor can ever be very efficient pushing a displacement hull - but it certainly can be effective, at least in moderate conditions.

Electricity in New Zealand? 

30 years ago it was 90% from renewable resources, but we've gone backwards a bit, and I believe it is now about 81% from renewables, mainly from hydrogeneration.

The figures below are from the Ministry of Business, Innovation and Employment. Retrieved 16 July 2021.  [I don't quite understand how the renewables add up to 81% here, but anyway, hydro, geothermal and wind make up about 74%]

Yes David, Kurt specifically mentioned the motor you had, but I couldn’t remember the make and am not sure that we have them here. Kurt though there might also have been a 36V version of your motor.

Anyway, according to Aussi prices (just for comparison) two of the model you had would about equal in price the approximately 5kw model as depicted in your recent post. It’s an interesting idea, and I like the fact that with trolling motors you can adjust them up and down the shaft to vary the immersion.  I wonder how two trolling motors would compare with that single 5kw outboard, in terms of thrust? Anyway, I think in my situation a single motor would probably be more convenient. 

I reckon that Amarda T8.0/10.0 would do just fine, probably about the equivalent of the Evo “Navy” 9.9 which is supposed to be 6kw and which I rather fancy. Cheaper in price too it seems (again, looking at Australian prices for comparison), but I don’t think anyone is importing them in New Zealand. One thing surprised me: the blurb says they are rated at 65 decibels. That seems a bit noisy. The Evo doesn’t give a noise rating in their literature.

It is interesting to see how now, quite suddenly, we are beginning to get lots to choose from: inboard motor installations, pod motors, trolling motors, outboards, sail drives all now offering electric power options. There’s more than just electric technology here – they are becoming increasingly dependent on electronics (even replacing the old control cables) and watertight seals (allowing for totally immersed engines in some cases) – I wonder how this will all play out in terms of service life. There was a time when we all said salt water and electrics don’t mix.