Hi Cal,
"utterly silent"? I can hear my prop, the shaft in the cutlass bearing, the motor turn, but mine is a small boat and it is all under my feet. Here's a public demo but mostly it is just the sound of birds and water. https://www.facebook.com/ElektraYachts/videos/1010101222372956/ To get the kind of silence you refer to I'd have thought a bigger boat with sound deadening, one being a larger distance from the prop/cutlass would be the only way for utter silence. Much like running a 7kVA diesel genny on a big sailing yacht where you can barely hear it as one is so far removed from the source.
When I talk about cost and simplicity, I simply mean I don't need a gearbox (or for my application a separate thrust bearing, which would be nice but space without a redesign is an issue) and I only need 2 batteries - so logically this costs less than 4 batteries plus a gearing arrangement. I've done it this way for cost, because of a very small space (double ended boat) and wanting less weight than the old 10hp diesel.
I love my alcohol/bioethanol stove. Maybe you have never used a Dometic/Origo 3000, plus set top cooker for baking bread.
I have petrol onboard and a 900 Watt continuous Honda genny fixed outside on rails with 5l of petrol stored in the old (vented to sea) gas locker but having gas (propane or calor) for cooking would risk it going into the bilge, hence the Origo.
I'm not a professional electrical engineer either (steam to trade) so what I meant is over in the US you mostly seem to use the Motoenrgy motors which came out of the Lynch design. Over in UK it is mostly Saietta/AGNI/Lynch and the other 'copied' variants such as the Perm (you got the Etek). With direct drive I've gone for a no load Kt of 0.185 n-m/amp and the directly related 45 RPM/volt. I could choose a higher Kt/lower rpm/volt but under load I'd run out of volts (rpm) as the loaded rpm is 40 rpm/volt and Kt around 0.211, with efficiencies up to 93% subject to I squared R, losses, prop used. Regardless I reckon my motor efficiency on brushed direct drive at cruise is around 89% - so most of the brushless production motors 'over your side' that seemed to be used are no better than this and often less. Having said that the Zero IPM motor is ace. Also I think the frame of the types we generally use for boats is better naturally cooled due to it's design. Sure a British YASA or Slovenian Emrax or similar would be nice at some cost but I'm happy with the proven long standing Lynch type design and simplicity.
It took me some time to get 2 LiFePO4 batteries. Here again it is because of the voltage stability, lack of Peukert, weight and energy density by volume and weight plus the extra useable (200Ah in LFP is way more useable than 200Ah of dead lead) and the cycling ability of them that makes them ideal for my direct drive system. Indeed from my calculations I think there is a case for borrowing the money to invest in lithium as I think the costs compared to AGM work out better over time even with loan interest- but of course that has to be offset against capital risk. Again horses for courses...
John
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