controllable pitch propellers and regeneration

Discussion in 'Electric Propulsion' started by barrymac, Feb 19, 2021.

  1. philSweet
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    philSweet Senior Member

    Yeah, I'm still with you, but I almost quit at the 12-15 knot speed easy. I've manage 4.5 knots on a 50 foot Alia Aura on delivery under not very good conditions. I have yet to have my old 80s IOR leadmine be passed by any sailing cat that didn't have 10 feet more waterline than me, and I have sailed circles around several that did. Sailing a 50' cat at 6 knots is work. If you really want to go faster than that in terms of trip planning, you will want to hire a profession crew (or run a pair of 75hp diesels at decent load all week).

    To the best of my knowledge, no cruising cat has crossed the Atlantic at a 12 knot pace. Ever. And this includes some pretty hard core attempts from Gunboat 66s and the like.

    (Ignore the verbiage, they managed 10.7 knots point to point. I don't know if they were permitted to motor or not. I thought non-spinnaker classes could motor-sail the ARC. So the may have burned 400 gallons of diesel in the attempt as well.)
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    One wonders whether something streamed out of the back of the boat, when required, on a flexible cable, with an internal flexible drive, might be a better solution. In fact, I have the idea, have a drogue that doubles as a regenerative device, calm your nerves and charge the batteries at the same time, in heavy weather.
    Last edited: Mar 30, 2021
    kerosene likes this.
  3. Rumars
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    Rumars Senior Member

    Here you can here about how it works in real life. Straight from the horse's mouth, as they say.

    Will Gilmore likes this.
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    What gonzo said, about it best being used when the boat is largely already at the speed where there is a resistance "hump", made sense, how often that would apply, might be the problem.
  5. popobowa
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    popobowa Junior Member

    I was in the belief that a decent , not too heavy Cat would uphold 10 to 12 kt easily, in favourable winds and seastate...tradewind situation? with one at the helm watching vids on the laptop?!

    5kt avg speed is horrible, why have a cat. Alia Aura, thats a heavy charter model?
    Wouldnt a 8 to 10t Shionning or LeRouge Cat be able to reach 10kt to 12kt avg.? Or even one of the old Outremer 45ft to 50ft models . I spent a day on one , 50ft, and it kept 14 tp 15kt comfortably, sea was only .7m chop . ..
    But I am not an experienced sailor , just want a stable platform thats fun to sail and is efficient = autonomous not needing to refuel too often in spite of me using oven and stuff.

    May have to look for an efficient Powercat.....2l per nm @10kt... 60.000 l for a circumnav. @1.5$/l....but then you havent got much to do than look at horizons....
  6. Will Gilmore
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    Will Gilmore Senior Member

    What are the goals for this electric boat? Are you coastal cruising or crossing oceans, going around the World or island hoping in the Caribbean?

    I have an interest in this subject, but no exprience and even less learning on it. However, from reading this and other threads, it's beginning to look like a dedicated regen unit would serve you better than a convertible propeller on the main drive. Maybe a transmission that can switch shafts.

    @Mr Efficiency mentioned the drag behind hydro-generator. If such a device were set to run at a depth below surface wave turbulence, it might not experience the variations in speed of the boat laboring up a wave and surfing back down, since it would be dragged at an angle to its path through the water.

    Another thought is doing a comparison between regeneration from sail driven propulsion and wind turbine driven generation. Perhaps a wind turbine would be the more efficient way of generating electricity than from the water while under sail.

    I'm not into the word "efficiency" the way many others are. It's all relative to the actual goals and desires of the person. Speed and energy use are only two small considerations in the efficiency of a given system. I haven't a clue as to the answers to these questions; that's partly why I'm here, to learn. The convertible prop does seem like the least practical way to do it, though.

    Such an interesting discussion with all its side tracks and various thoughts on the subject.
  7. popobowa
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    popobowa Junior Member

    Dear Will Gilmore,
    my goal is to get a boat, catamaran, to generate its "houseloads" with the least poss diesel use...not that I am such a greeny..but if we can use diesel fuel more sensible, I am for it! Plus the gains in autonomy! me more time away from filling facilities. ports, marinas etc.

    A typical yacht running a genset of typically 5 to 10kW @1500 or 3000rpm to cook a meal ( 1.5 -2.0 kWh) and charge a Leadbattery bank of 4 to 5 kWh cap. with 50 to 100 Amps@ 12V or 24V is max 2.4 kW ovrr a period of the batteries can only take full Amps for a short while..lets the genset run too lightly loaded which will bring all kinds of problems with the set and have it running very inefficient...upto 370g/kWh I ve been told. Like that you manage to get thermal efficiencies of down to 2-3%!

    While if you only change your batteries to LiFePo in the same weight, you get 2x the rated Batt.capacity and 4 times the usable capacity as LiFePo can safely be 80% discharged and achieve min 1500 cycles while LeadAcid AGM deepcycle can be only 20% discharged to achieve 500cycles. You can get the kWh of Li batt in a metalbox with BMS for under 300$ from a good company choosing and matching each cell for assy. A good lead acid deepcycle batt costs 200$/kW.
    I wanted to say tht with LiPo and a good generator, maybe mounted together with your drive eng. you could achieve 30% thermal efficiency.
    I forget to include that LeadAcid had a charge/discharge efficiency of 75 to 80% while LiPo cycle is at 95%.......

    The other big advantage in this boat/genset case is, that Li batt. can be charged with 1C while a lead acid batt. only w max 0.25C. That lets me utilise thevgenset to its full capacity, but only for a short time, in case of a 50kWh bank discharged to 20% , runtime 4h in case of a 10kW genset, which if commonrail will burn 0.230 g/kWh = 2.7 l....which should keep me happy for at least 5 days if I am a powerhog, otherwise 8 to 9 (rainy) days.

    A good PV array of 1kW giving me 4 to 5kWh....a day will extend that.

    A hydro generation could keep me from using diesel until at anchor for longer period....

    that is my line of thought.

    I should sit down and create a spredsheet for all different setups...if I had more TIME
    kerosene and Will Gilmore like this.

  8. popobowa
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    popobowa Junior Member

    For thode seeking other hydro regen possibilities..
    Bruntons have recently advertised a CP prop with regen software in mind... with a wider cp range that gives settings from thrust to feather, to regen and reverse... software is still in the making. But i believe that most of the voltage control should be governed by the el. controler and Pitch only adjusted once a given prop rpm range is passed.?
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