CNC Plans not Included

Its not... and doesnt have to be, why so surprised?

 

first one I've seen.

 

Playstation, orange 2, hydroptere to name but a few...

 

That explains it, not my thing.

 

Only way to have a roof at this height with a low wind break is to keep it simple and flat, looks stupid otherwise. I reframed the area so the mast fits into a socket, will show detail on that later but it looks good to me. Ok, next up weight spread sheet!!!!!!

 

I got the specs of the powerwall II, even that is probably not the right battery for me, and looked for places to put them.

In the end I settled for 4 on the BD shelf because it offers easy access. It would also be possible to put them under the floor with some creative framing but that becomes a pain in the butt for maintenance. I can put 8 batteries (120KW) at a bit over a ton. I have room for more in the space chosen, including room for ac units or ... and the drives are about 6 feet away plus I have easy access for the wiring to solar roof, galley and everywhere else for that matter.

Even better, check out how much space is left over in front of the access panel... About 26" to edge of passageway door which means I can put a full pantry or washer or extra freezer .... or even a sofa

Also check out the galley after the hulls have been narrowed and the beam reduced. I have a ton of floor space because I also reduced that windbreak. The mast socket fits well too. Pic one show's almost the entire fitout for the hulls, as you can see not much fiddling with little parts. I want to add ac's ducting and plumbing before I start on weight to make sure that it all fits right.

 

The powerwall 2 is a great product and very competitively priced - im excited about what comes next. However theres one thing youll need to consider if you use them. They are integrated package unit. Unless you break them open, void your warranty etc you cant take DC power from them- they only output AC voltage. So you cant use them for any DC house loads or a DC electric drive unless you run the AC through another inverter to get your DC voltage you need. No big deal for most of the house loads, a small 12v inverter is cheap. Its the main drives which are the main issue- the cheapest way out is to use commercial variable speed drive to a large induction motor for propulsion. Downside is theyre heavier than a DC traction motor and controller...

 

Yeah I remember you mentioning that. I probably won't end up with that product but it gives me proof of concept as far as KW and space and weight. Now look at these pics, I have room for a 6 foot long freezer and pantry above. The freezer will be structural, the pantry removable so I can get in to that space if I ever need to. The quick access panels will allow battery change or access to other things as well.

What I won't have is hanging closets for clothes. All clothes and shoes has to fit in the bed dressers. The linen closets will be huge and in the baths. Got to think on what I should put on the other side?!!

 

Electric vehicle battery cost dropped 80% in 6 years down to $227/kWh – Tesla claims to be below $190/kWh https://electrek.co/2017/01/30/electric-vehicle-battery-cost-dropped-80-6-years-227kwh-tesla-190kwh/

Why not just buy the Tesla car battery, it's much cheaper than the Wall. Prices have dropped to below $227 per KW. 8 Wall batteries would cost me about $48K for 120KW or 100KW of car battery for only $23K. I would still need the controlers etc... but not to the tune of another $20K !!!

Also check this - The 85 kWh battery pack weighs 1,200 lb (540 kg) and contains 7,104 lithium-ion battery cells in 16 modules wired in series (14 in the flat section and two stacked on the front) I'd be happy with 85KW )))

 

I think theyre wholesale prices or what tesla pays - theyre not retail prices... tesla sells a commercial battery pack called the powerpack- 100kwh for $40k @ todays prices.

You also get the inverter, charge controller, cell balance and management system, and protective devices built into the powerwall- so all these secondary systems have to be added to a battery bank you build from scratch. The tesla powerwall is a very good value product- if you can get them. Try buying them- its not so easy as they cant meet the demand...i think theres like a 12 month wait or more after you place your order with 10% down payment.

 

I found the pics of the offgrid power system i installed a year ago to a home in the bush. 5kw solar on roof, 2 strings at 340VDC, AC coupled (white inverter) to a 7.5kw continuous output/input rated invterter (black inverter), 15kwh lithium iron phosphate battery with separate BMS.



To run a propulsion system from this- i would add a 7.5kw variable frequency drive fed from the switch board which is supplied by the black inverter. The VFD controls a 7.5kw 8 pole induction motor which turns your prop. I would duplicate the system in the other hull. If you need more than 7.5kw per hull, you would have to goto a larger inverter. I think 7.5kw would be ok for starters provided it was coupled to a large diameter, fine pitch propeller for max thrust and efficiency. The 8 pole motor will have good torque as they spin at 730rpm @ 50hz and is the slowest motor commonly found in that size/type. You might get a 10 pole via custom source etc... these big induction motors are very heavy however.

The other way to drive it is via a dc motor and drive from the battery. Then you can use a smaller supply inverter for your general usage as its not feeding the propulsion system. However this may not be ideal if your looking at heavy AC loads such as air conditioning and electric cooking as youll need significant power for those anyway... some food for thought for you

 

That pic intimidates the heck out of me lol. I won't be doing that part of the job.

What do you think of this - AC Electric Boat Motors vs. DC Electric Boat Motors https://www.elcomotoryachts.com/ac-vs-dc-motors.shtml

 

I think what he says is only half the story. These days when we say DC motors, what we really mean is BLDC motors for 99% of the time. Brushless dc motors dont have any of the shortcomings he refers to, infact they are very similar to an induction motor. If you swap out the squirrel cage loops where the EMF is induced and replace it with a permanent magnet rotor, thats essentially the difference. They both only have 1 moving part and 1 set of bearings that can wear. Maintenance is the same for either. The BLDC motor controller or variable speed drive is very similar for both motors also, only subtle differences.

I had a look at some torque and prop numbers and theres no need for an 8 pole motor. A 6 pole or 1000rpm motor can easily turn an 18in prop directly without a gearbox reduction which means you would end up with more than 60% more thrust than a 9.9hp high trust outboard motor which only turns a 9.25in prop for the same horsepower. This is not an electric hp is more than diesel hp argument - but rather due to efficiency gains of larger slower turning propellers vs smaller faster ones. If you implement drives like you showed earlier, you dont really have a diameter restriction on the size of prop you can swing... this is not the case for saildrive legs and outboard motors etc where there is a very limited size of prop you can swing. We simply need to pick a motor with appropriate torque for maximum practical size you choose.

 

Thanks Groper, good details on basics
what would be rough weight and size of the 6-pole motor?

 

7.5kw 6 pole 70kg or so aluminium frame motor, 100+kg steel frame... should provide about 340lb bollard pull each so 680lbs pull for 2 motors. We can do resistance calcs on 3kN and see what speeds that ends up- probably 7 kts or so depending on the final displacment as a rough guess...

The challenge will be figuring out how to keep the water out if the motor is inside a pod which submerges.... hopefully some really good seals are available, then you have perhaps some custom work fitting it into the pod and changing the fan cooling to simply conducting the heat away from the motor frame to the alum pod- which is probably fairly easy. And then lastly a custom prop hub with a dome shaped spinner to fair it into the pod cylinder.