5-Meter Power Cat with 6kW Outboard

Thirty-foot hulls! Any pictures? Are they displacement or semi-displacement?

I get the idea of starting with smaller motors, so when you upgrade, you aren't out as much. The other side of the argument is that the 3's aren't that much lighter or cheaper than the 6s, certainly more than half the weight and cost. And you can always run the 6s at half power, but you can't run the 3s at 'twice power'.

I think you want to get some idea of what power levels it will take to achieve various speeds. Depending on where that lands, the 6s could be overkill. But I don't know what a good way to determine that is without experimentation. At least with my hull I had power-to-speed data points from the manufacturer.

If you do upgrade to some other brand of motor after the ePropulsions, I don't know how compatible their batteries will be with the new motors, especially if they use a different voltage. Four 'generic' 12v x 200Ah LFP batteries per motor (for example) will give you more total capacity for less cost, and leave you more adaptable to different voltage requirements in the future. You just have to charge a little differently (in 12V segments instead of as one big 48V battery).

These days I'm looking closely at the Propel S1. They're claiming 73.5% "overall efficiency", so for the 10kW of input power, you get 7.35kW of propulsive power. Note that this takes into account the propeller efficiency. That's head-and-shoulders above the best I've seen elsewhere, including the Navy 6.0 Evo I have. That has 57% overall efficiency, yielding 3.42kW of propulsive power. So for just 40% more power consumption I could have over double the propulsive power, which would yield about 50% more speed (~19mph). Very attractive, but they have no immediate plans to sell in the USA. I have a question in to them about how they address different speed requirements with what seems like just one propeller. No answer yet, but it's only been one day.

EDIT: Got my math wrong: it's 67% more power consumption (not 40%). For 114% more propulsive thrust.

 

I hear ya on the difference in price/value of going with the 6’s, but unfortunately I’d have to commit to dual battery systems, whereas I could power X2 of the 3’s with a single big battery.

I don’t trust most of these “generic” LifePo4 batteries hitting the market. I’m in the electronics biz, so I know what that means as far as the quality of the internal components go, and I’m going to be operating this vessel in the Pacific off a small island, so the need for reliability is on a whole different level.

That said, when you crunch the numbers EPropulsions battery system are actually pretty competitively priced considering how compact and feature laden they are, and I like that they are easy to daisy chain incase I find I need more range. Also, I feel the system would have better resale value down the line if it was a complete plug and play setup, and that it would have broader appeal.

Anyway I’ll have to check out Propel system you mentioned, I’m not familiar with it.

I’m primarily interested in a Pod Drive type system that I can adapt my own trim setup to so I can leave my transom scoops open and usable for boarding from the water when the motors are deployed, yet still allowing for full trim in shallow launching and navigation conditions.

Here’s a photo of the hulls. I’ve been pursuing their purchase for almost a year now. As soon as I saw them I knew they were exactly what I wanted as they have all the characteristics for being well suited for electric propulsion in our Hawaiian waters, and they are the largest and lightest hulls I can manage to trailer and assemble at launch.

The builder who originally converted these hulls from performance sailboat to power catamaran said he was achieving unheard of fuel economy running twin Tohatsu 20HP outboards at an overall beam of 10’ with a cabin on top. He increased the waterline length of the hulls from 27’ to 30’ adding transom scoops and reverse bow extensions. The hulls are knife edged and have a lot of freeboard not unlike some of the more modern electric cruising boats you see being designed and manufactured today.

 

I just checked out the Propel motor and the way I read it, the motor puts out 10kW and then due to propellor slip (with their in house developed propellor as they state almost like a disclaimer), and the loss in the bevel gearing, that 10kW then gets reduced to 7.35kw of actual propulsive power.

So the slippage and gearing is good for a 26.5% loss.

What they don’t state is how much power the motor draws to provide the initial 10kW output before driveline losses.

In a product release statement, they claim their motor has an overall efficiency upwards of 62%, presumably that includes the controller and driveline losses, so that means watts in would be about 16kW for 10kW output and 7.35kW in propulsive power.

That kind of efficiency is what I would expect from a motor that size at 48V with a gear reduction.

So my guess is that it is likely not much more efficient overall than your Navy motor, being that it is a smaller direct drive design.

The prop design does however look interesting, and with that much power has probably been optimized to be a good all around performer. With the gear reduction and high RPM pancake motor, they are able to swing an aggressive 4 blade and still reach high enough RPM for better top speeds.

 

Nice looking hulls . . . they should work very well. Another consideration on the 6.0-versus-3.0 question is that the 6.0 comes with two propellers, but just one with the 3.0. Prop pitches for the 6.0 are good for (at most) either 11mph or 14mph, whereas the 3.0 prop pitch looks to be good for at most 12.5mph. Also, from page 9 of the Owners Manual, the 3.0 efficiency is 51%, not as good as the 57% the 6.0 has, most likely due to the 50%-higher propeller RPM.

Your take on the Propel S1 makes me reconsider their value. 62% overall efficiency is better than the 57% of the 6.0, but not as good as the 73.5% I initially thought. Another source of drivetrain loss is in pumping the coolant. That's a nice thing with the Navy Evo line, there's none of that extra complexity. I guess if they ever get back to me, I'll be sure to ask about input power consumption. It's not like I can buy one now anyway.

I see your 'broader appeal' point with resale including OEM batteries. While not suggesting one approach over the other, needing to sell the batteries with the motor could actually rule out someone like me who builds their own. I guess in that case, hanging on to them might be an option, assuming the motors you upgrade to are compatible.

On battery prices, I see ePropulsion right at $500/kWh for the largest model. I understand avoiding no-name brands, especially with reliability being critical. One decent brand is Battle Born, but I see their best battery at $625/kWh. Another brand I have experience with (and can recommend) is Ohmmu. Their G31 battery holds right at 2kWh (12.8V x 156Ah) and sells for $1,000 (so $500/kWh). Four of those would come to 124 pounds, versus 192 pounds for the E175, so considerably more watt-hours per pound with Ohmmu (64 versus 47). Paralleling is easy enough as long as the packs involved are close on SOC.

As always, not trying to suggest what's best for you, only get some options out there for you to consider.

 

Being in the electronics biz, I always try to find out who makes the products for the brand names being sold and just buy direct from the factory, especially since there will be no support from a mainland retailer here in the islands and the majority refuse to ship here, although they are often happy to ship themselves over for a vacation

So I have no problem buying direct due to those issues.

Battery wise, I purchase batteries direct from EWT who makes them for a lot of the popular brands. Factories like EWT have the shipping logistics in place to ship Lithium direct, and many accept PayPal and other popular payments with protection from Alibaba and the likes.

The last few EWT 100ah 12v batteries I bought were less than $500 each shipped FedEx Air direct from China, and I was able to custom order them to be wired and programmed for a higher max continuous discharge. I have seen their construction inside, the cells are well connected, and I know that they use a quality BMS and battery case.

Battleborne has built their reputation on product support, and for anyone not knowledgeable, that is the product I typically recommend. They have someone they can call to ask questions, and if there’s a problem BB stands behind their product. That kind of support is worth the retail price of admission for a novice or someone who just wants peace of mind.

With my brushless motors I did the same thing, I went direct to the factory and had them built to my specifications.

With flexible solar, I ended up becoming a SunPower dealer and purchased a crate of them at wholesale cost which was less than half what retailers were charging. I planned to sell off the remaining to cover the cost of the number I needed, but now that I’m building this bigger Cat, I’m going to just keep them.

The other factor that I have to always keep in mind when designing, building and specking out complements and materials, is our tropical environment.

The lesser the number of wiring connections, switches, dissimilar metals, etc.. the better. DC current in a tropical salt water environment creates a lot of corrosion issues. So products that minimize potential failure points using water proof connections are advantageous.

Wiring up a bunch of batteries in parallel or series with bus bars, balancers, shunts, master disconnect switches, etc.. is asking for trouble and requires constant maintenance in our environment.

Anyway, I appreciate the suggestions as they sometimes lead to products/options I was not aware of like the Propel product, which BTW is really not much different in design from the old Briggs and Stratton electric, Elco outboards, and a number of home builders who have adapted the pancake motors to the leg of a lightweight outboard in place of the ICE motor.

I think if I were open to a traditional outboard unit (not Pod), I would probably just modify and build my own considering the cost of buying new. The key is having a good controller and proper cooling for the electronics.

On that note, if you take a closer look at your Navy manual you’ll see their motors do have built in cooling in addition to the oil in the lower unit. I assume it either uses a mechanical or electric pump for flow, so either way some efficiently is lost in the process as well.

The big advantage the Propel motor has (aside from it being more powerful) is that it uses a gear reduction to be able to take advantage of a more aggressive prop.

This is why you can use a planing prop with the bigger Torqeedo motors on smaller boats and get them on step.

The downside with the gear reduction is typically an annoying whine and more often than not, a little less efficiency.

I feel unless you are pushing a planing hull, the gear reduction isn’t necessary as you will exceed the limits of the hull and likely waste a lot of power to only gain a slight increase in speed.

So quiet brushless direct motors are what I prefer for cruising for now, that is until someone develops a gear reduced brushless motor that is as quiet as a direct drive.

I’m very curious about Yamaha’s rim drive HARMO unit and whether or not it is noisy.

 

Candela is claiming 'most efficient outboard' with their C-POD:

Introducing the Candela C-POD https://candela.com/introducing-the-candela-c-pod/

80% efficiency on the propeller means that you just need 94% efficiency on the motor to achieve 75% overall efficiency.

Not suitable for my application until they make a much smaller version (at least 2x less power).

 

Unfortunately as more and more of these electric propulsion options come to market, the vocabulary and terminology gets skewed and you really have to read between the lines to know what the true specifications are.

Trolling motors and early electric outboards fell into this same trap when they started rating motors based on Thrust and comparing them to ICE’s of equivalent size and HP. This lead the consumer to believe an electric motor that is stated to be equivalent to its equal ICE in HP would offer the same performance, but what they are really saying is that it has the same propulsive power. Many then are frustrated and annoyed when they find out that the electric “equivalent” will not allow their boats to reach the same speeds as the ICE.

My point is when reading all the marketing hype, certain companies choose to focus on certain things they they feel they have improved over others.

In the case of Propel, it is their Prop, and here we see with Candela that it’s their prop and slim case.

However paying close attention to the numbers and verbiage, it seems they are claiming 80% efficiency with their prop design and then go on to say their motor is 23% more efficient in drag over others due to its slim case design.

Also you have to keep in mind the data they are using has likely been collected based on an application that uses foils, which is also why they have designed a slim long motor case.

Anyway, my point is the best way to judge the true performance and efficiency of these motors across the board regardless of application, is to know what the Watts consumed is versus Watts out in propulsive thrust tested in a tank, then if they have tested the prop to determine it’s efficiency, you can add that in, and all that should be a good basis for comparison.

In the case of my Caroute motors, the manufacturer was able to provide actual load data not from a tank, but by pushing a small inflatable dinghy with a single operator with a shunt attached measuring voltage and current.

I have posted this data on other threads, but I will post it here for you.

What’s interesting is to see the relationship between efficiency, the motor controller, and the prop RPM.

You’ll note there is a sweet spot where the controller is still Pulse Width Modulating, a peak efficiency if you will, and that should be the target RPM one should ideally to shoot for when designing an efficient cruiser. This data then becomes extremely helpful to determine battery and solar sizing based on range goals.

Unfortunately not all manufactures collect this kind of real world data, and on top of that every boat is different and used in various conditions, so data like this is just a helpful but important reference point to build off of.

On your setup, the question as to whether there is any more top speed to be gained can be answered by monitoring the Amp draw of the motors.

If you are not loading the motor to its peak Max draw, you could probably get away with a more aggressive prop.

But you have to check the amperage loaded, under full acceleration, etc.. when testing a new prop to make sure it isn’t exceeded trying to get the boat up to speed.

As was discussed before, its probable you may be reaching the speed limitation of your hulls based on their length, shape and displacement and the limitations of a direct drive electric motor.

Just like racing, you reach a point where that last bit of speed is exponentially harder to achieve. And since we are so mindful of efficiency being electric, it’s often not worth it.

Just look at some of these crazy electric “motor” boats being announced with huge motors, giant battery banks, and thrilling top speeds that they can only sustain for an hour.

Foiling combined with electric propulsion is definitely the future, especially as the batteries get lighter and lighter. If you can remove all that wetted surface from the equation, develop a low drag motor like Candela, and use foils to sustain lift, suddenly speed and range start to become more real world like with the way people are used to using their boats.

Anyway, fun stuff. Have a great weekend!

 

Longest run yet on this motor:

 

Next outing, see what kind of power the motor is drawing at about 70% throttle and what speed you are reaching.

This should be the point at which the motor is running as efficiently as possible without hitting the limitations of the hulls.

Typically most PWM motor controllers are still pulsing up to about 3/4 throttle.

In the case of my motors, you can see that they hit a peak efficiency at 520W of propulsive power turning the props at 1700rpm while pulling about 30A consuming about 700W.

This test was done in an inflatable dinghy so peak efficiency was achieved closer to half throttle as the hull shape was poor.

With hulls like ours, the peak efficiency moves further up the throttle range up to the point where the controller stops pulsing power.

This is one of the reasons to go one size bigger so to speak with electric motors, the idea being that your max cruising speed should be targeted around 70% throttle efficient hull shape, and then above that is reserve power for getting through rough weather, current, back to the docks and to the bathroom more quickly, etc..

 

Thing is, the only way I know I'm at a certain throttle level (say 75%) is because I see the power readout at 75% of maximum (4,500 watts in this case).

I've chosen a cruising power level of 50%, which gets me ~9mph (for three hours). Of course I could increase that if I don't might the decrease in total range that would result in. 75% power should get me 11.25mph, but then only for two hours.

More cells are on the way, but they take months to get here. Should arrive in June.

 

Sorry, to clarify I mean 75% physical throttle position.

The throttle uses a potentiometer and typically the value of that corresponds to the value range the motor controller wants to see for forward and reverse thrust.

For example, a 10Kohm potentiometer might be set so that a value of 0-4999 is your reverse range, and then 5K is your “neutral” and 5001-10,000k is your forward speed range.

If I’m not mistaken, one neat feature of the EPropulsion line is the ability to set safety measures for max throttle, at least in reverse but perhaps even in forward.

They likely do this by running a different programmed set of values to limit the range.

Anyway, most of the PWM motors I have tested go to a full power mode above 70-75% of the physical throttle position.

Below this, the motor controller is pulsing power to conserve energy which greatly increases range and efficiency.

I don’t know how accurate EPropulsions estimations are on their display.

Since they don’t use a shunt and you are using your own battery, I suspect they must use a Hall sensor of some kind to monitor power draw.

Anyway, the reason for asking is because you may find with a different prop that you could tune for better cruising speed versus top speed.

When I went to bigger props on my boat, I found my cruising speed not only increased a bit, but more importantly the props were pulling less power at the same throttle position.

At full speed, they of course pull more power than the old props, from a dead stop as well.

One other thing, if you get a chance could you tell me what diameter the prop shaft is on your motor as well as the diameter of the shear pin?

Strangely, a Tech at EPropulsion refused to provide this info to me which is pretty ridiculous since I could just measure it myself if I had access to one. Every other spec is shown in there design diagram.

Asking because I have a list of various props with their properties and some of EPropulsions props fall somewhere between Torqeedo and others.

I have reamed Torqeedo props to fit my motor and am curious if I will have to do the same with EP’s.

The one thing I like about the Torqeedo props is they are a much more dense and ridged FRP material versus some of the softer props I have run, and the softer ones tend to get really chewed up by waterlogged coconuts! I assume being a direct competitor that EP’s props are similarly constructed. I do however note that replacements are much more reasonably priced.

And lastly, in your tuning quest for your boat I should also point out the importance of the trim and tilt of the motor when under power.

I spent a lot of time on this and made my motor mounting system easily adjustable and had the advantage of a wired remote with my display mounted which allowed me to go to the front of the boat at a certain speed settings and determine if the boat picked up speed with the bow down, or if it slowed.

In the end, I found that the boat performed better with the bow planted so I reset my trim points to keep the leading edge of my bows slicing through the water, whereas before the front few inches were out under power and the water was pushing against the bottom mid section of the hulls where they are fattest, slowing me by about 1/2 MPH (what may be happening on your boat based on hull shape).

The same thing happens when I’m hit with a gust of wind and it gets under my hard Bimini lifting the bows. Once the front of the top is lowered, the boat trims out and picks up speed.

Anyway, it’s fun to experiment and dial things in.

 

I think any attempt I might make to put the throttle at 75% position will just be an approximation. I also don't think there's any 'flat zone' at the end of the throttle position range, where full power is delivered over the zone. My recollection is that any backing off of the throttle position from full results in reduced power being read out. And that readout seems to be computed as opposed to 'predicted': at full power, the numbers will fluctuate slightly above/below 6,000. I.e. the controller is asking for 6,000 watts but slight variations in load result in the actual power delivered to dance around that slightly. I suspect there is a feedback loop taking the computed power value and comparing it against what's being asked for, and modulating accordingly.

There could be a shunt inside the motor casing. Output from that would be an input to the actual-power-delivered computation (along with voltage).

I'm all for trying different prop pitch/diameter/rake/blades/cup/etc., but don't have many options and I'm not at the point of reaming out other brands to fit. Plus I feel like I'm pretty close to predicted performance with my power level, which was around 14mph.

And yes, motor trim angle is something I'm tweaking, along with fore/aft loading, transom height and possibly moving the anti-ventilation plate up closer to the waterline (it's currently about one inch below). I do feel like I'm at the limit of how much transom height I can use: I'm back to the original height there and on the most recent outing I was getting ventilation until I trimmed the motor out five degrees from 'square'. If anything I might need to come down maybe 1/4", then slide the plate up to get it out of the water as much as possible without losing its effectiveness.

On prop shaft dimensions, I have a shear pin here for the second prop and it comes to 4.95mm diameter by 40mm length. The forward face of the prop has a step in the hole for the prop shaft. Outer hole dimension is 16mm, but the inner hole is harder to measure (calipers won't fit in the outer hole). Best I can determine by lining the calipers up is 12.5mm for the main part of the prop shaft. The depth of the outer hole looks to be 12mm. IOW, there's a step on the prop shaft with 16mm diameter on the forward portion, then 12mm of that penetrates the prop, and the rest of the prop shaft is 12.5mm diameter. Then there's another diameter decrease for the threaded portion where the washer/nut goes (the nut is M10, 1.5mm pitch I think).

 

Longest run yet up the Sammamish River:

 

Thanks for the prop measurements. I will post a list here at some point of various manufactures prop shaft and prop specs for those that want to experiment.

The main thing to remember when it comes to these motors is that they have been tuned to provide reliable performance up to a certain size vessel.

In some cases, electric outboards and trolling motors are rated to be able to push a multi ton displacement vessel, and that means the motor controller has been designed to be able to handle the load associated with that task.

Now if you are using that same motor to push a light displacement efficient hull, the motor will draw full power and reach its max RPM, but it’s not being asked to work that hard.

This is where monitoring amperage draw comes into play. If one finds they are not reaching the max Amp draw of their motor, this is a good indication they could experiment with a more aggressive prop. This will in turn increase the “load” on the motor and motor controller, so it’s important to make sure you don’t overload the motor and exceed it’s rated max Amp draw by monitoring it closely during testing.

In my case, my motors are rated to be able to push 2 tons each, and as I have mentioned in previous posts, when I first built my Cat, I saw that my motors were barely pulling 100A under load up river against current and wind. So I started experimenting with props and in the end was able to increase my top speed by 2mph and my cruising speed with more aggressive larger diameter 2-blade props, and the motors now pull their rated 120A under load.

BTW, as a follow up to our discussion about cheap LifePo4, my friend just bought a pair of Power Queen 300ah 12V LifePo4 batteries off Amazon for about $1k each. He has a Cat made from two canoes that he will be pushing with a single Haswig 24V motor and 600W of solar. He takes his kids and their friends out all day and pulls them behind in the water so he wanted max capacity. Will be interesting to see how the batteries perform and hold up. We figure even if they only last 5 years he’ll still be money ahead over more expensive well established brands.

 

As mentioned, my motor controller readout shows almost exactly 6,000 watts at full throttle. That's no doubt regulated by the motor to not be exceeded, even under varying load and voltage. So it's not so much maintaining 125 amps as it is keeping input power steady.

I agree that buying off-brand LFPs is a gamble, but can be worth it depending on the application. Redundancy helps with reliability issues. If I were that guy with the two 12V LFPs and a 24V motor, I'd consider bringing along a 12V-to-24V step-up converter, in case one of the LFPs were to fail. The converter wouldn't need to be that high-powered as you just need enough to limp home.

Regarding propeller selection, I see these motors:

E-TECH OUTBOARD POD ENGINES – StarBoats – Electric drives, custom boats, yacht insurance https://starboats.eu/electric-drives/e-tech-outboard-pod-engines/

They come in inboard, outboard, and pod variants, so could fit both of our applications. On the expensive side though, and not made here, so availability could be an issue.

The big upside is they take standard inboard propellers. If I were to move in this direction, I'd wonder if they could be easily made to rotate in the opposite direction, then I'd consider a two-motor approach with 10kW per motor. After trying just one of course. It remains to be seen what the power-in-to-prop-shaft efficiency is, but if that's at all decent (90% plus), a good prop could complete a very efficient propulsion package. Prop speeds are relatively low (1300 rpm).