Classic runabout designs needed to electrify

1 KW is 1 KW whether electric, internal combustion engine, or a team of horses.

 

The proper calculation would be:

• 1 HP of rated power output = 1 HP for internal combustion engine
• electrical power is input η*Pe = Pm. The conversion is then kW*1.34 = HP

That means that the electrical power output will always be less than the input, not more.

Unless you also have the RPM, you can't compare power to torque directly. They are different dimensions.
Power (HP) = Torque (lb.in) x Speed (RPM) / 63,025 ... Power (kW) = Torque (N.m) x Speed (RPM) / 9.5488

 

@Algie Bennett , you need a boat that can carry a massive load, and still plane gracefully. You need a .... (wait for it) Sea Sled.

 

We should try to use SI units where possible as it is the international standard.

 

@Dolfiman , I'm skeptical about the claims of salesmen. Salesmen are almost by definition professional liars. Certainly the notion that a 750W electric motor has the magical ability to equal an ICE that is not also 750W is highly suspicious. Even more so coming from someone whose livelihood depends on convincing marks of that.

I agree that the electric motor's ability to develop torque under load, so that it can more reliably deliver the actual rated power makes it better than a poorly designed ICE installation. But not a well designed one.

 

Saying that an electrical kW is more powerful than an ICE kW is like saying that 1 meter of Dynema rope is longer than 1 meter of manila rope.

 

Well, I deleted my previous post of which wording seems confusing. Just put again this article here below which, better than me, detailed the issue of the comparison electric engine / internal combustion engine. And it’s practical conclusion for the average user, that you may share or not : 1kW of installed electric engine is roughly equivalent to 2 hp of installed internal combustion engine concerning the power.
https://www.e-navsystems.com/en/how-to-compare-thermal-and-electric-power/

 

That sales pitch is total nonsense. Repeating something time and time again does not change the laws of physics.

 

Sorry for radio silence I've been rather tied up.

I agree most claims on electric motors are ******** and tell our clients what they are exactly capable of based on our massive testing.

The weather here in the UK has finally turned a bit so I've managed to get out doing some testing which I thuhgt I would share.

So yesterday in Lymington River / The Solent, I took out the eGuardian 420 with the Mitek 15hp (10.5kW) tiller control unit as we are sold out of the remote steering motors and the 300Ah 48v batteries are in our console .

The motor was set up with the now standard Solas 3 blade 9.25" x 12" prop and it gives it some decent performance.

Here is a very short video as it takes quite a while to get a longer video edited up ready:


Acceleration good and straight up on the plane and hit 17mph one way with wind and tid eand 16mph the other way into the tide and wind which were both pretty strong - 2 hours before low tide and the wind was blowing 14-16 knots gusting up to 22 knots from the local weatherstation on the Lymington Starting Platform where I was between about 2pm and 3pm:


Here is the GPS track from my Garmin GPSMAP 86S that we always use:
Garmin Connect https://connect.garmin.com/modern/activity/15038692314

The motor was pulling up to around 300 amps so well over spec but handled it very well - if I can find a larger diamter and / or higher pitch prop it will be worth testing I think as it felt like it had some more to go.

I will be testing the 9.25" x 10" and 11" props as soon as I can as well.

Then got the 20hp / 13kW and 30hp / 22kW motors that are still 48v but will be pulling 400-500 amps I expect so should give us some decent extra kick for the eGuardian!

For our target sailing club safety boat market, the 15hp is ideal though as it clearly easily planes but can pootle about all day at 4 knots - quite literally all day and for most clubs probably 2 days before needing charging.

Yes it is not a panacea and yes the batteries weigh a lot, but it certainly works as required for this use case scenario.

If you want to plane at 25 knots all day then it won't do it - I'm not pretending or claiming that.

But what it will do is enable the removal of petrol motors from drinking water reservoirs and lakes which I think can only be a good thing.

Anyway, I'm off to a funeral now so no more time but we're testing with a 16ft catamran rowing chase boat hopefully tomorrow with the same motor and prop to see how that performs and will update you.

 

Well, we're testing a 16ft cat based on RS Cat sailing hulls - not a load carrier but will be interesting and we are working on a small cat for safety boat purposes.

 

Well done.

I have little experience with electric propulsion, and most of that was in a flume tank with industrial 415V 3 phase motors. It is a property of those that as load increases so does torque to the point the circuit cannot deliver the current required.

Is it similar with the modern breed of DC motors? If so you could possibly go one or more prop sizes above what a similarly rated engine would turn. Maybe even nudge 20Kn

 

The testing with the catamaran cancelled today unfortunately but rescheduled for next week so will report back then.

Will be doing some more testing with smaller non-planing capable motors today and tomorrow and will update once I have something useful.

FYI for the test with me the approximate details were as follows (rounded up to nearest 5 kg to make it worse):
Bare boat hull inc swim ladder: 190kg
Steering console / seat / battery storage: 50kg
300Ah of LiFePo4 batteries inc cabling etc: 140kg
Me: 85kg
RemigoOne motor and chargers etc: 20kg
Mitek 15hp motor: 50kg
Total: 535kg

Checking out prop options the 9.25" x 12" is the biggest I can get for the 8 spline motors but I am going to order a new 9.25" x 12" prop and have the pitch altered to 13" which is the maximum I can get as far as I can find and see if that has any material impact.

 

Thanks to report on your runs with data. Whit m 535 kg , P 15 hp and aft deadrise 14° to 21° (I don't know what can be relevant for the eGuardian 420), my Crouch-Savitsky tinkered formula gives (peak speed on calm water, no head wind) :
V = 502,56 (0,087-0,0015*Aft Deadrise)^0,5 (P/m)^0,5 (± 10% ) with Aft deadrise (°) , P (kW) , m (kg) , V (Knots)
Aft Deadrise P « petrol » « P petrol » m motor m total >> V V -10% V + 10%
(°) (hp) (kW) (kg) (kg) (Knots) (Knots) (Knots)
14 15 11,2 50,0 535 18,7 16,8 20,5
21 15 11,2 50,0 535 17,1 15,4 18,8
By hoping this can be relevant and helpful for your project.

 

Hi Dolfiman,

The deadrise is 17 degrees on the eGuardian 420.

I've now moved the console back a foot to change the weight distribution to see how that affects the performace with the current 12" pitch prop.

I did a quick scoot up to Hurst Castle on Saturday:




and here is the detailed GPS track:
2024-04-27 Lymington eGuardian 420 Mitek 15hp 300Ah Alg planing to Hurst https://connect.garmin.com/modern/activity/15105170389/share/1?lang=en

Conditions were varied with some reasonably strong wind from N/E and the tide going out.

At 26 minutes I stopped as I had only turned on one battery and as I accelerated slowly it tripped out. Turned them both and started again - what an imbecile.

This is actually a great security feature though as the BMS is password protected and I can block both charging and discharging via the app meaning it will be pretty painful to steal the boat.

I anchored up for a while outside Hurst then went briefly in and headed back - the trip home was quite bouncy and I had to stop at 1hr 8mins while I tried to sort out the camera....

We've got lots on today but will be going out tomorrow afternoon to do the same run to compare and can then get some video edited.

 

I noted 14,7 knots as peak speed within your third run . With aft deadrise 17°, m 535 kg and installed P 15 hp(11,2 kW), assuming that you were not in optimal sea state& wind conditions, I compared the resulting speed with V-10% and found a coefficient of 455,6 instead of 502,56 for the formula. Let’s continue this investigation with this new coefficient and possibly various hp and m. And thanks again for your experiences with data.