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Old 05-28-2019, 11:54 AM   #81
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I think the best advice I could offer on this project would be to go take a class in mechanics. Not "mechanics" as in the guy who fixes your car, but "mechanics" as in physics and mechanical engineering 101. That will help you predict the outcome of various choices before you built something, rather that stumbling over it after you have built something.
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Old 05-29-2019, 07:57 AM   #82
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I think the best advice I could offer on this project would be to go take a class in mechanics. Not "mechanics" as in the guy who fixes your car, but "mechanics" as in physics and mechanical engineering 101. That will help you predict the outcome of various choices before you built something, rather that stumbling over it after you have built something.
If that is the best advice you got then I think your forum days are over. My physics background is not lacking. My boating and boat restoration experience may be. If you have something specific to add to the project it is appreciated.

BTW, I am an engineer with a proven track record of innovation and solving the hard problems.
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Old 05-29-2019, 08:58 AM   #83
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I hear you my lord,
Hmmm
It looks like mr. Tree is saying look at the big picture before getting immersed in details. Foresight. But I didn’t even take physics. I like pictures though.
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Old 05-29-2019, 09:14 AM   #84
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A couple of answers to questions about prop size.


In response to Gdavid - The issue with prop size is not the original engine type (gas or diesel). It is the design of the hull which limits prop size.



In response to Star-Lord - You currently have 23" diameter props with 5" tip clearance or about 16.5" from the shaft center line to the hull. The minimum prop tip clearance to the hull is about 15% of prop diameter or 30% of radius. So if 1.3 x radius = 16.5, you can fit up to about a 25.5" diameter prop. Since you will be running at slow speeds, you may be able to get away with a 26" prop. I haven't done the calculations, but I suspect you would have to up your shaft size to go up that much in prop size. Even if you maintain the prop diameter, but go to a higher blade count for more disc area, the additional torque at the prop may require a larger shaft. Changing shaft diameter will be expensive. You can also increase prop pitch, but the same considerations apply. Any prop shop can increase the pitch of your prop up to about 2". Note that the 15% number comes from Michigan Wheel. They also state that 20% is ideal. In that case your boat already has maximum diameter props.
I will stick with 23" but may consider changing pitch. I could not read the number markings on the prop. I don't want to change the shaft diameter.

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Old 05-29-2019, 10:20 AM   #85
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You need to figure out the output shaft rpm from the Prius motor/transaxle and base prop pitch on that number.
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Old 05-29-2019, 11:05 AM   #86
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You need to figure out the output shaft rpm from the Prius motor/transaxle and base prop pitch on that number.



And torque and/or hp. But I know you know that.
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Old 05-29-2019, 01:23 PM   #87
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And torque and/or hp. But I know you know that.
I really only have an idea of how must shaft torque and rpm I can produce with my electric drive. Shaft torque of 1200Nm up to 400rpm (50kW peak) then the torque will drop at higher shaft rpm. Can spin up to 1000rpm. I do not expect to have to produce this peak power for any length of time especially with limited battery.

The previous poster estimated 4.5kW@4kts and 9kW @5kts steady for my boat which is a helpful guideline for me. I am not sure how this was calculated.

simple math says 400rpm with 20" pitch is about 7.6mph (not including any slip)
I have no idea the pitch of the prop I currently have.

I don't really know how to get to thrust calculations for a given prop. Of course it will be a function of prop dimensions I do not have. I really haven't made much effort to make these predictions yet.

I have a very long list of to dos before selecting the prop which is why I appreciate the feedback I get from the forum. I think i am in the ball park with my setup.

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Old 05-29-2019, 01:35 PM   #88
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May be advantages to over prop w an electric motor.
Did I say that ???
I have no idea if applicable though.
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Old 05-29-2019, 01:52 PM   #89
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* I am not sure how this was calculated.
* I have no idea the pitch of the prop I currently have.
* I don't really know how to get to thrust calculations for a given prop.
* I really haven't made much effort to make these predictions yet.
I think i am in the ball park with my setup.
Oh Lord, not to be flippant here, but perhaps you'd be better off getting some solid answers before proceeding further on a trial and failure basis. So here's a starter - go visit www.boatdesign.net/forums as those guys really know their stuff.
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Old 05-29-2019, 02:55 PM   #90
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Is there any info and conversation on BoatDiesel?
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Old 05-29-2019, 03:04 PM   #91
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Is there any info and conversation on BoatDiesel?

I don't know about conversation, but there are prop calculators that can be used to explore different props, operating rpm, and required power/load. They will also calculate boat speed based on available propulsion power. That's where the projected speed came from that I posted, but i was based on a guess of 40,000 displacement. Someone later posted another projects which probably came from the same calculator, but they will have to confirm that. The later projected was based on a more accurate 22,000 lbs displacement and showed about .5 kt speed improvement.


That would be a good place to start to narrow down a drive train that utilizes as much electric power as the builder desires, and matches that to a prop that can deliver the power to the water. Also to be considered is whether additional gearing it required/desired, or if it can all be accomplished via prop pitch and diameter with a 1:1 drive.
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Old 05-30-2019, 06:19 AM   #92
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I will check out the boatdesign.net forum. Thank you

I am on multiple forums. I use other forums for details on motor and battery control for example. This seems to be a good forum for the boating experience in general.

My props may be 23x26, 1.5" shaft. I can barely make out the markings. They are in bad shape and will soon need to be replaced. However this size may be right in the sweet spot for my electric drive setup. Better lucky than smart.

26" pitch gives me about 40 rpm / mph neglecting slip. My motor speed is voltage limited to about 4000 rpm and produces max torque up to about 1600rpm. So below 1600 rpm is a safe place to operate without concerns of enough torque. I have a 4:1 gear reduction which gives me a 400 rpm shaft speed.

I am wondering what the disadvantages of not using counter-rotating props might be. There is a slight advantage in my motor mounting if I don't use counter rotating setup.

I am still grinding out blisters and more delamination on the hull below the water line. I am concerned that this hull may not be salvageable. I really hope it is. I love the boat.

Thanks
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Old 05-30-2019, 07:30 AM   #93
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Assuming that you keep the rudders, In my humble opinion, there is no need for counter rotating props in your application.
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Old 05-30-2019, 07:38 AM   #94
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Jeff,
Isn’t likely that prop will work. Too big for 40hp and way too much pitch.

Like Cliff says no need for CRP.

Hope the hull works out. It’s not ideal but very few easily driven hulls exist that are really easily driven.
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Old 05-30-2019, 08:56 AM   #95
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Calculating the propeller parameters (Torque, efficiency, etc.) is actually very simple for standard props like yours. I used Oosurveld and van Oossanen (1975) (link - https://pdfs.semanticscholar.org/33e...256f16a3fe.pdf ) to calculate the propeller thrust and torque coefficients, Kt and Kq, respectively for Wageningen B-Screw Series propellers. You will also need resistance calculations for the hull. I used the methods outlined in Larsson and Eliasson (1994) to calculate hull resistance.You will need hull parameters to calculate the hull resistance which will require having the hull lines, but I assume you can take the lines from the hull if you can't find the designer to get them from. All very easy to do.


Incidentally I considered going electric when I repowered my boat. My boat has a 32' waterline and the hull is a round chine full displacement hull which is very easy to drive. On flat water my boat requires about 5 kilowatts to maintain 6 knots. I have room for about a kilowatt of solar on my cabin top so it would take about two days to recover from 1 hour of cruising at 6 knots. At 4 knots my boat would take about 1.8 kilowatts so I could recover from an hour at four knots in a day most of the time. What decided me against going electric was the cost. I would need at least 20 kilowatts of batteries which was prohibitive cost wise back in 2010 when I was repowering. Even now usable 20 kilowatts of lithium iron phosphate batteries would cost me about $15,000, which is nearly twice what I paid for a new diesel. That cost doesn't include the electric motor, controller, battery charging capability, ancillary electrical components, mounting the motor and batteries or any of the costs for a solar array. My preliminary cost estimate back then was over $30K for a complete setup, which was cost prohibitive. Note that 20 kilowatts of battery power would give me a range of 44 nm at four knots and 24 nm at 6 knots. That would be adequate for a day cruiser that wasn't used every day, but would not be viable for multi day trips.


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Old 05-30-2019, 09:07 AM   #96
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Calculating the propeller parameters (Torque, efficiency, etc.) is actually very simple for standard props like yours. I used Oosurveld and van Oossanen (1975) (link - https://pdfs.semanticscholar.org/33e...256f16a3fe.pdf ) to calculate the propeller thrust and torque coefficients, Kt and Kq, respectively for Wageningen B-Screw Series propellers. You will also need resistance calculations for the hull. I used the methods outlined in Larsson and Eliasson (1994) to calculate hull resistance.You will need hull parameters to calculate the hull resistance which will require having the hull lines, but I assume you can take the lines from the hull if you can't find the designer to get them from. All very easy to do.
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Old 05-30-2019, 11:48 AM   #97
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Calculating the propeller parameters (Torque, efficiency, etc.) is actually very simple for standard props like yours. I used Oosurveld and van Oossanen (1975) (link - https://pdfs.semanticscholar.org/33e...256f16a3fe.pdf ) to calculate the propeller thrust and torque coefficients, Kt and Kq, respectively for Wageningen B-Screw Series propellers. You will also need resistance calculations for the hull. I used the methods outlined in Larsson and Eliasson (1994) to calculate hull resistance.You will need hull parameters to calculate the hull resistance which will require having the hull lines, but I assume you can take the lines from the hull if you can't find the designer to get them from. All very easy to do.


Incidentally I considered going electric when I repowered my boat. My boat has a 32' waterline and the hull is a round chine full displacement hull which is very easy to drive. On flat water my boat requires about 5 kilowatts to maintain 6 knots. I have room for about a kilowatt of solar on my cabin top so it would take about two days to recover from 1 hour of cruising at 6 knots. At 4 knots my boat would take about 1.8 kilowatts so I could recover from an hour at four knots in a day most of the time. What decided me against going electric was the cost. I would need at least 20 kilowatts of batteries which was prohibitive cost wise back in 2010 when I was repowering. Even now usable 20 kilowatts of lithium iron phosphate batteries would cost me about $15,000, which is nearly twice what I paid for a new diesel. That cost doesn't include the electric motor, controller, battery charging capability, ancillary electrical components, mounting the motor and batteries or any of the costs for a solar array. My preliminary cost estimate back then was over $30K for a complete setup, which was cost prohibitive. Note that 20 kilowatts of battery power would give me a range of 44 nm at four knots and 24 nm at 6 knots. That would be adequate for a day cruiser that wasn't used every day, but would not be viable for multi day trips.


Thank you for the detail in your analysis.
Even today off the shelf solutions are cost prohibitive for me.

I hope to be able to procure salvaged batteries around $200/kwh (ie 20kWh=$4000)
My motors+controllers, gear reduction,generator, solar charge controller, house inverter for less than $5k since it will be a hack of EV components and custom built interface circuits and software by myself.

My entire project is to try and reduce the cost of electric conversion and maybe someday demonstrate boating in a limited capacity.

Jeff
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Old 05-30-2019, 12:05 PM   #98
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Star-Lord,

Very interesting project. I've often said that if my single Lehman engine died, I would convert Sandpiper, a 40' - 40, 000 pound trawler to diesel electric.

Please continue posting the projects progress and don't let the negative comments deter you.

All you did was post your project and you started getting unsolicited advise

I'm on a lot of forums and criticism of unusual projects seems to be the norm. There are a lot of know it alls on the web that love to tell you how to do things, but have not done it themselves.
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Old 05-30-2019, 01:01 PM   #99
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Star-Lord,

Very interesting project. I've often said that if my single Lehman engine died, I would convert Sandpiper, a 40' - 40, 000 pound trawler to diesel electric.

Please continue posting the projects progress and don't let the negative comments deter you.

All you did was post your project and you started getting unsolicited advise

I'm on a lot of forums and criticism of unusual projects seems to be the norm. There are a lot of know it alls on the web that love to tell you how to do things, but have not done it themselves.
Thanks for the interest and encouragement.
Don't worry. I am pretty thick skinned.
I enjoy the negative feedback as much as the positive.
I am soliciting all feedback good and bad.
I can tell who backs it up and who doesn't.
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Old 05-30-2019, 01:34 PM   #100
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syjos,
Did you see/read the article on PMM about 8 years ago on a Mainship? I have no personal interest in all electric propulsion but I’d really like the diesel/electric option. I loved the high and instant torque in the harbors. Also single engine twin screws has some distinct advantages. And I think as a twin engine diesel/electric twin engines of different sizes would offer even more interesting advantages.
With DE (diesel electric) can one use the propulsion batteries for domestic power? I’m probably showing my grey hole in electric propulsion but ??
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