Efficient electric boat

Part of the problem then (and maybe even today) was the inherent conservatism of the Royal Navy, and government in general. Just prior to the Triton project, we'd had an interesting debate over the FSC design, when a group put forward the view that a "short, fat" frigate might be far better for the role, as it was largely about having enough room to fit and carry stuff (the research going on in the research establishment I ran at that time was trying to find innovative ways to fit all the myriad of sensors and weapons systems on to a relatively small deck area).

I believe that the Triton RV project only got as far as it did for two reasons. The first was that it was marginally more acceptable in appearance than the "short, fat" designs, so was seen as the lesser of two evils, the second was the single-minded determination of my boss, who just pushed and pushed until the idea was accepted.

To the best of my knowledge there aren't any significant problems with the concept that couldn't be resolved fairly readily. The biggest challenge remains getting such a radical idea accepted by an inherently conservative body - it would be viewed as a colossal risk even today. We struggled to get the slightly faceted topsides concept (for reduced RCS) agreed back when the Type 23 was being designed and the concept for the new Type 45 was more radical than the ship has turned out to be.

Overall, I think the long, narrow trimaran concept seems sound for any vessel where low propulsion power, good roll stability and a large deck area is desired. I suppose the challenge is getting usable accommodation space down below in the narrow hull, although this can perhaps be eased to some extent by putting fixed systems out in the outriggers (perhaps with the risk of increasing the roll polar moment, not sure whether that's good or bad in a boat - it's generally bad in an aeroplane).

Jeremy

 

Jeremy the ideal faux-tri for live-aboard cruising would be about 12m with 3m beam but it is then not trailerable and that is one of my requirements.

Mine will have usable accommodation. The centre hull becomes the passage way to give headroom. I am still playing around with the interior. It may be something I do after the thing is trialled.

My first yacht was purchased as sailaway. Meaning it had bare interior. Over the first year or so I fitted it out on the water. I worked on it on Saturday and raced with it on Sunday. I spent quite a few Saturday nights on it in harbour and that was a good time. I am impatient. I like to try things as they develop rather than get it all done before it is tested.

Rick W

 

Hi Jeremy,

Did you see my previous post (#82).

I have since learned the batteries I have may just not stand up to 8kw loading even if intermittent (that from "dragonfire").

Would you agree?

Thanks, Tom

 

Rick,

Thanks again for the Freeship and Javaprop work. I ran a bunch of trials this afternoon and can now quantify the trade offs between smaller less efficient prop that are easier to house and can spin faster reducing the gearbox problems vs larger props . I also finally see the merit of a "square" prop where dia = pitch.

I was just looking at your lines plan for the faux-tri. Great concept for minimising drag and maximixing accomodations. The plan doesn't look like it has enough displacement at the design lwl to support the weight of the structure, crew and supplies. You have probably made sure it does, though. I supose I am like the Jeremy's Navy officers saying they wouldn't build it because it didnt look right.

 

JavaProp is not perfect. It provides a design option that is reasonably good. There is some interesting work done on optimum blade shapes and different pitch to diameter ratios. My pedal boat props have a ratio of about 2 for P/D. If you look back at the photo of the milled one you will see it is very aggressive.

The faux-tri is just going through initial design development. The aim is to make it quite spartan and very light. It will primarily be for my own use. My wife prefers to fly these days. I am not sure of what can be achieved as I have not gone into that detail. The weight target is extremely ambitious though. Similar to what is achieved with the high performance cats and tris.

In a way the boat needs to be thought of as high performance because solar energy is not really intense and I do not want to have a huge turbine.

Rick W

 

I have some data from testing today. It was not overly exciting. I ended up breaking the small drive belt at just over 11kph. But I did get some video and photos. I use the photos to record data.

You will see I have a GPS for speed and a there is a little wattmeter for power. The Power reading is in the lower right of the display.

The video is at various speeds. I wanted to give an idea of how the noise changes as the motor picks up speed.

Even with the new little final drive belt the no load losses are quite high. At full motor rpm I was using 130W just to turnover the belts. Admittedly this was at 1200rpm output speed with a 9:1 reduction. In the testing the prop would have got to a maximum of 550rpm for the 11kph. No load losses at 550rpm is around 45W.

The one reading I managed to get at 11+kph was 444W. This is higher than I expected but the belt may have already been skipping or I may have been still building speed. At the end of the video you can hear the belt failing.

I used 1870mAh for about 2km during the test. Rough average is 7kph.

Jeremy - This boat would have similar drag to an optimum boat for your 4kts if it was designed to be optimum there. You can see this motor does 100 to 200W very easily. This is the motor details:
http://www.hobbycity.com/hobbycity/...TGY_AerodriveXp_SK_Series_50-55_580Kv_/_1580w
6.5kts is not too bad for a 329g motor. It was not particularly pressed at 11kph. It could do better but I am not sure if I want to be bothered with another belt. I think the best option is a slightly bigger motor and a single reduction. I have learnt what I wanted to know so I doubt that I will do any more with these little motors until I build my model.

Rick W

 

Hi Tom,

I'm afraid that your working outside my range of experience with these systems, so there's not much help I can give. I've been experimenting with lower power systems, using brushless RC model motors in the main, so don't have much knowledge of systems up at the power levels that your hoping to work at.

What I do know is that reasonably good AGM lead acid batteries are capable of delivering very high power levels, but I've no direct experience of using them. I did try some smaller, surplus (i.e. free.....) sealed lead acid batteries on my electric bike, but found that they wouldn't deliver anything over a few amps without the voltage dropping a lot. I later found that these were used as standby packs in alarms, so were optimised for long life, low current operation.

Jeremy

 

Rick,

Your experience with the losses in the belt drive mirrors my first experiment with these. I used a single stage reduction, using a 16mm wide, 5mm pitch HTD belt, a 60 tooth driven pulley and an 18 tooth drive pulley. This was really a bit of an overkill for this sort of low power level and incurred a high loss from the belt, even with no load.

I think you’re right about getting away with a single reduction, that would cut the losses a fair bit. I’ve run my motor with no load and plotted the motor-only losses, in a nutshell, the motor and controller together draw 0.85 amps at full speed on 26 volts (~22 watts), and about 0.25 amps (~6.5 watts) at the speed I want to operate at. The controller on it’s own draws 0.065 amps, less than the cheap RC one I have (that draws nearly 0.2 amps when idle).

I note that the motor you’ve chosen has a pretty high value of Kv, 580. I’ve opted to go for as low a value of Kv as possible, using a motor that is just a bit bigger in diameter than yours and reconfigured to get the Kv even lower. This significantly reduces the reduction drive ratio required, so reducing the losses.

These motors can easily be modified to reduce the Kv by a factor of 1.73, as they come as standard wired as delta. Reconfiguring the internal windings to star on your motor would reduce the value of Kv to about 335, which would be a worthwhile contribution to reducing power losses. It only takes about half an hour or so.

My motor started out with a Kv of 215, it was about the lowest I could find at the time (there is now a 170Kv Turnigy available, this one: http://www.hobbycity.com/hobbycity...TGY_AerodriveXp_SK_Series_63-74_170Kv_/_3250W). This 170Kv motor could be easily reconfigured to give a Kv of about 98, which would reduce the demands on the reduction drive still further. My motor is running at a Kv of about 124 now that it’s reconfigured as star, giving me a maximum motor rpm on 24 volts of about 3000.

I’ve changed the reduction drive to use a 15mm wide, 3mm pitch, HTD belt, with a ratio of 4:1. On 24V this gives a full throttle RPM at the prop of about 750, with cruise being much slower, perhaps half this RPM. Coupled with a bigger diameter prop I’m hopeful that I can get the efficiency up a bit. I’m just finishing off putting it in a watertight enclosure, ready for some more tests. Hopefully I should be able to post some photos later today (perhaps later tonight for you!).

Jeremy

 

Rick,

On noise: The video sounds like there is a resonance in the system at maybe 3/4 of the way from slow to fast. I've been reading up on BLDC motor noise and find many mentions of it but no info about what to do about it. My own experience with three different MARS bldc motors (two 20 turn, and one 28 turn) is that they all make exactly the same resonant whine at about 50% power. The noise is clearly independent of rpm.

BTW, what controller are you using?

On belt drives: www.gates.com has an excellent drive system calculator called "design flex" on their website. You have to register to use it but it is free. You put in hp, shaft sizes, center distances, desired reduction. It gives a list of part combinations that fit your criteria and even ranks them by cost.

Another possible motor/gearbox combo from the RC world potentially useful to us: Neu Motors 1912-270 with P32 6.7:1 planetary gearbox. 50mm motor dia x 50mm length. It comes wye wound with Kv = 270. 1500w max continuous. Estimated speed under load at 24v ~ 800 rpm. Cost ~ US$ 200. I've emailed them asking about the suitability for the large torque and axial thrust loads marine use would create. Also asked about the noise of the gear box. I'll post their reply when (if!) I get it.

 

I've had the same thing with that resonance, but only with some combinations of motor and controller. The cheap RC model controllers seem worse, particularly those that don't have programmable timing. I switched from a cheap (around $40) 120 amp RC controller to a slightly more expensive one, set the timing to "high" and the resonance problem went away. It doesn't seem to be there using the ebike controller I'm using now, but that maybe just the dynamics of the test set up.

Here are a couple of pictures of the new, inboard, RC motor drive system prototype. I've fitted the motor and 4:1 reduction drive into a watertight diecast alloy box. The turned flange at the bottom is where the prop shaft tube is going to fit. The prop shaft itself will couple directly to the 10mm shaft coming from the bearing support. Thrust loads will be taken by the pulley support bearings; the coupler will have a sleeve that bears against the aft bearing inner race. The loads should be low for the size boat this is going in, so well within the axial load that a deep groove bearing will take.

I just need to sort out the motor wiring and I'll be be ready to test it.

Jeremy

 

Jeremy, Nice job. Is that a water pump bearing spindle?

 

Battery Caps

I have some information on a product called a Hydrocap Catalyst Battery Cap. I would appreciate any information or testimonials on the product. It is supposed to replace the cell caps on deep cycle batteries and retain the hydrogen and oxygen gases that would be emitted...eliminating the mess of acid fumes and vapors and returning electrolytes to the cell, etc.

At about $12. each, a bank of 6-6 volt batteries would require 36 of these caps, making my inexpensive deep cell batteries not so cheap any more. I would appreciate any unbiased opinions about these and how would they compare with the "water miser battery cap" that retains the water only and costs about a third as much. Thanks

slonez (but frugal)

 

Thanks for the kind words, Denny.

That bearing mount was just turned from a piece of 1 1/2" 6082-T6 aluminium alloy. I invested in a cheap Chinese lathe a few years ago, the best tool I have ever purchased. Without it, I'd have not been able to make many of the parts for recent projects.

I'm almost done with the rewiring, so should be ready to do some off-load testing later this evening (or whatever time it is in your part of the World).

Jeremy

 

Nice Job

Nice job Jeremy!

Don't forget your desiccant pack(s) when you seal it up.

Tom

P.S. Thanks for your previous response re: battery loading.

 

Jeremy
I looked at the Neumotors gearbox before and the efficiency quoted was quite poor. However after playing with the belts it might not be so bad.

I need to do some accurate calculation on the belt losses. They seem worse than chains.

Your set up with the wide small belt looks good. Overall your selection of components should work out close to the best you can get for the power level you will need for 4kts.

I thought an overall efficiency from battery to moving the hull could be as high as 60% but my little motor and belt combinations did not achieve this. My assumptions about the toothed belt were poor. It is something I will have to allow for and design well as I plan on using a toothed belt with my Mars motor at full scale.

I also have a toothed belt for my pedal boat. I really need to see what losses I can expect from this as it might be worse than a chain.

I have a nice little Chinese built bench lathe. I also have a bench mounted mill drill. They are wonderful tools for working with aluminium.

Rick W