Electric Outboard Speed

I have a 3hp electric ePropulsion Spirit Plus outboard which runs at 1200 rpm max with a fibre(plastic?) 11 X 5.8p propeller.
I use it in a 10' Portabote which weighs 75 lbs and the engine + battery weigh 40 lbs.
I would like to increase the speed?
I've been thinking about a higher pitch prop and maybe reducing the diameter since the boat is so small and light but thought it best to check with experts.
Any and all thoughts?
Thanks
Ron West

 

Your thought to switch to a higher pitch prop is logical and would provide better top speed, but unfortunately companies like EPropulsion design and market their motors to be able to work on a variety of applications, and so they tend to play it safe in order to protect the electronic components and provide a reliable long lasting product.

Unlike a ICE motor which would just bog down and not reach max RPM, when you put too aggressive of a prop on an electric motor like yours, you risk the possibility of the motor trying to pull too much current which may overheat and shorten the life of the ESC.

So experimenting with props is risky with electric motors like yours.

You are right that with your application you might be able to safely swing a more aggressive prop, but without proper testing equipment you could easily damage your motor, although some have quite a bit of built in protection which may result in throwing a code or trigger a limp mode.

Torqeedo after some time introduced a few higher pitch prop options for their customers specifically for light displacement applications like yours in an effort to increase speed and even make planing achievable on some hulls, but they were designed for their motors which use a gear reduction.

Your motor is a direct brushless design and limited in max RPM, so other than switching to a 2-blade (if you now have a 3), you really don’t have any easy options because EP doesn’t offer optional props like Torqeedo. You’re only option would be modifying something to fit.

Maybe EP will offer more prop options in the future, but I think it’s unlikely simce efficiency and battery range is the more important design factor for most electric outboard manufacturers.

 

Agree that Modifying a propeller to fit is probably your only option. This link will give you an idea of what might be involved, should you have the interest to try it. You probably will need the EP external battery cable kit to monitor amperage as you try out different options.

Upgrading trolling motor prop https://www.boatdesign.net/threads/upgrading-trolling-motor-prop.68235/

Hope this helps.

 

It's not 3hp, that's just marketing. It's 1kW which is about 1.3hp. The pitch speed is just over 6mph which might get you 5mph with a suitably slim boat. Your boat is quite short and wide which will limit its' speed; also you may be dragging the transom if you are sitting right at the stern to steer so you could try moving forward to get the transom out of the water if this is happening. I've seen this on an electric powered folder in the UK and it was making more turbulence than go.

 

No, the motor is 500W if you want to compare it to an ICE.

Again, ICE outboards are rated in HP at the prop.

The EP Spirit is 1kW input power with an output power of about half that at the prop.

So horsepower wise, it’s actually more like 2/3 a horsepower.

When you take that into account, you can really appreciate the performance because I would bet it easily outperforms a 2/3 ICE in its ability to push and maneuver a vessel.

Given that with the exception of top speed it should perform the task of pushing and maneuvering a vessel just as well as an ICE motor of 6X the power, one can now begin to understand why “propulsive thrust equivalent” ratings are used in marketing.

Why limited in speed? Again, because the industry is more focused on efficiency and range with 1hr of runtime at about 5/6 MPH being the benchmark for integrated battery systems.

 

I have a older polypropylene version of the double point 12' porta boat in storage which I no longer use much. It is definitely energy gobbler, because of the lack of a rigid frame, it's like trying to power a jellyfish boat. Maybe it's better once you get it up on plane, but I was never able to do that even with a 5hp IC. The polypropylene panels that contact water Flex in and out in response to various water pressures as you use more power, and it is my guess that flexing In-N-Out dissipates a lot of the energy applied. The flexible frame with slick outside top layer did come in handy when used in shallow River current water and around rocks because any collisions with hard objects at medium speed temporarily distorted the shape allowing shock absorption, protecting the passengers from being pitched out. The Slick coating provided lubrication to the surface, so the hull remained unmarked and undented even with the sharpest objects.

I think it's difficult to define the equivalent power of IC versus Electric as there are a considerable number of variables, with the torque curve being especially significant. I think that electric motor is near full torque at near zero RPM and full torque continuing to near Max RPM, versus near zero torque at near zero RPM and peaking at a particular RPM for IC?

 

I think it's difficult to compare the equivalency of electric versus IC power, because there are a number of variables which might defy compatibility. The torque curve is one of these, because it is vastly different for the two types. For electric motors, the torque can be near maximum at near 0 rpm with torque continuing at near Max to maximum rpm, versus IC which has near zero torque at near 0 RPM and the torque Peaks at a particular rpm below the maximum rpm?

 

The comparison is simple and direct for top speed, which is what the OP is asking. 1 HP is 1 HP regardless of how the power is generated.

 

Why Diesel Locomotive uses Electric Motor to Drive Wheels? - Electrical Concepts https://electricalbaba.com/why-diesel-locomotive-uses-electric-motor-to-drive-wheels/

Sometimes 4,500 HP IC is not enough to get up to top speed, even with a gearbox?

 

Interesting diacussion, this comparison of IC engine and electric motor, sorry for a degression from the OPs topic.

There are few more reasons for use of electric motors powered by diesel engine turning the generator in locomotives or even in those big dumper trucks used in mining fields. Even though in mining dumper trucks is probably used diesel engine of around 2000 HP. Those heavy weight vehicles, especially under heavy load, when driven down the slope can lead to the IC engine overrevving leading to premature failures and for such kind of applications that is very costly thing. On the other side, generator is almost perfect load for IC engine to last long (relatively narrow RPM range required and matched with optimum IC engine load/torque/etc. curves). The other reason is that mechanical breaks must be used in case of IC engine. At such loads their design must be very robust/expensive and in case of "extreme driver" they can also prematurely fail, again expensive beside also being dangerous. In case of electric motors, the motors themselves can be used as breaks (they work as generators, no mechanical friction involved) and this is especially easy to do in case of train where the breaking energy translated to electric energy can be returned to the electric power line.

Regarding comparison of torque characteristics between IC engine and electric motor, it is always mentioned that electric motor have almost flat/constant torque characteristic from 0 RPM to max RPM. This is not fully truth or not stated correct (DC motor is exception which really has maximum torque at 0 RPM). Each AC motor, depending on type has different looking characteristic depending on the type of motor, not every type is good for max torque at 0 RPM, or at some different application requirement. Beside that, especially AC motors have so called "natural torque" characteristic which is given at single power source frequency and you could be very supprised how that looks like depending on the type of motor (this comes from history reasons because most AC electric motors were used in industry and mostly not vehicles and were attached directly to 50/60Hz power network without electronic motor controllers which are used today). Due to development of high speed microcontrollers and also power transistors capable of delivering high electric currents at high frequencies (mind this came in ~1990s, even though electric motors in principle are still very similar to those in 1900s), today it is possible to generate/imitate power source at demanded/wished/required frequency and voltage/current by the means of electronic motor controller/driver. What this means is that by the means of electric motor controller/driver we can shift the "natural" torque characteristic of electric motor where we wish it to be, so as a result we achieve constant torque at the whole range of RPMs. Still if you know the limitations of motor type and natural characteristic, only then you know the limitations of that setup and if it is good for specific application. That is the reason why now more types of motors are developed in recent times (e.g. to try to unify different requirements as much as possible) and why e.g. some electric cars have two different electric motors in one vehicle, to achieve different goals. Therefore, it would be correct to say that electric motor with integrated electric controller has almost flat torque characteristic, but not just electric motor. Some motor types by itself have torque ripples due to their design, but can be cheap and use cheap and simple controllers and they are ok in e.g. cloths washing machines or such applications, some types are great at zero torque, some types are great at higher RPMs, but not so good at low RPMs, some characteristics are diminishing with the RPM increasing above some specific value and have to be compensated in electronic controller at the expense of e.g. torque which becomes not constant above that RPM, so you still need good engineers to match the electric motor/controller/application similar to what you had with ICE/gearbox/application, it is just now even broader multi disciplinary topic. From my point of view, electric motor/electronic driver combination excells the IC engine/gearbox in terms of capability/simplicity/efficiency/maintenance, but I am still not delighted with current batery solutions or let's say power source solutions, whataver that will be in future. We still need to work on that. Motor/driver combination already achieves between 90% and 100% efficency, in industry, you can see even ~99% efficency machines.

I would skip ecology and comparison with fuels since it is different topic. I was sticking to what can be compared from purely electro/mechanical point of view. You can consider me as agnostic in case of fuel/battery topic - I would still not give up IC engine and fuel compared to current battery due to simple convenience of usage, but once we have proper solution in place of battery leading to same convenience, I would not think twice of switching to it. Will that be better for ecology, we shall see. Whatever we humans did to make something "better", it costed us later down the road. I mean, I recently saw on this forum so called reaction ferry used to cross the river, no motor/engine required, I really like it, but now instead of walking up/down the river after crossing it, we want to sail, well it seems we as humans are hard to satisfy living beans and that is the key issue . Therefore, we now suffer to achieve 99% of whatever, even though we could just be raction ferring or walking . Brain is a strange hungry animal and I think most of people on this forum will agree to this , no matter if you are fuel or battery lovers

 

Does anyone know what happens to the electric system overall efficiency, if / when- high, above room temperature superconductivity is achieved? If efficiency is already at 99% for some motors, it doesn't seem like it could get much better for Motors using superconducting wire? Or does it help with the battery end of the system somehow?

An electric fuel cell, plus other options for Electric Power storage or real time electric Railway type or track induction systems can also be used for those that don't like batteries...

 

You could in this case think in absolute values about your application, e.g. is 1% (let's assume dissipation only for the purpose of simplicity), equal to 100W or 1MW and how much energy you need to add to achieve superconductivity. (99% is extreme case, e.g. constant speed motor running 24/7 in some process in factory, vehicle is more complex application). And it could affect your application diiferently if you must provide this additional energy from power network or from storage (e.g. battery).

Wire connection to power network works reliably for at least half a century (railway, tram, troley bus, etc.), no doubt in that direction. Wireless challenge is in trend. Fuel cells are still exotic compared to batteries, but rising fast. Personally, I will wait for more infrastructure to consider it convenient (no matter which type), but of course, this is also not developing at the same paste depending on the region you live in. Of course, if not pursuaded by convenience, I will be by law/economy at some point in time in future.

 

It appears that the power to weight ratio of superconducting Motors using tiny wiring for coils would be extremely high, perhaps exceeding that ratio of jet fuel turbines?

https://www.engineering.com/story/fully-superconducting-motor-prepares-for-testing

 

Hey Portacruise, thank you for revealing this very interesting project to me, a lot of interesting stuff to read. Food for the brain.
As stated before, does it "payoff" depends on what you get and what you lose, here is an extract from the research papers: "the input power of the cryocooler is smaller than 50 kW (less than 5 % of motor power)." And from your link 20kW/kg (impresive), but not clear to me if this value is with or without cryogenic cooling system. On the photo in research paper there is the box below motor, which I assume is mostly the cryogenic cooling system and maybe also electronic driver and the box is bigger than the motor (it was just prototype though, of course). Cryogenic cooler with Helium or Nitrogen or at best Hydrogen...interesting topic, but I bet all this is nightmare for aircraft safety engineers.
Do you kow if this is still cooking, since the latest papers are from 2020? I would be interested. Also, one of the key companies involved could be stuck due to the current situation.
Also nice that permanent magnets are avoided.

 

I haven't been able to find anything else about the project referenced to in the article.

One of the most interesting comments in the article,

"a loop of superconductor can store a charge by allowing the current to flow around it indefinitely".

Curious to know how a loop of superconductor would compare in storage, versus lithium batteries?

If above room temperature superconductivity can be achieved, it would avoid all of the hazards, and some of the weight and drawbacks of using cryogenic liquids?