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Thanks Coots, getting started on "stuff"


Electri-Cal
 

I see Jove got me to relook at the gauge, I installed it yesterday.  I used a bridge that was there all ready, so just double the voltage figures, easy to do.  Same for the larger amp draw gauge, ordered a convenient rated unit, so both can be looked at and read as a 12 volt setup,  As i mentioned, when under clear water easy cruise. solo minimum weight to push it also works, I think.  Plan is to periodically change from one 80 lb. thrust single to the other to minimize wear factors, cruise then should be pretty good with all 4 batts,. on one motor at a time.

When Myles Swift and I at the very first trial used my 40 lb clamp on Minn Kota at Dexter, we had a great time.  Same at first Fern Ridge trip, clamp on 40 lb. --  big ol' stick handle up in the air, no other power needed. So, back to the beginning, using one 80 lb., like the one on John Kohnens sail boat, coupled to 4 series 27's and the "close "enough for now" gauges ought to run for quite a while.  I might even try the original 2 blade props, since one 3 blade prop shut down, has more drag.  For testing, I plan on the same 2 - 24 volt packs and see if the in water range gets extended by much, using each alone -- so the reserve power is still there, for now.

Still planning on that genset, or back up pack, since I own two extra batts. for later options.   That should give me (estimate here)  from notes in summary -- 15 amp. is 2.8 mph --  then jumps to 20 amps at  3.1 mph.  -- 30 amps at 3.6 so that is not so hot.  That's with both motors, cut that close to half draw, don't add more speed to compensate over 3 mph.   Does 10/12 amps at about 3.0 mph one motor running make sense, in the right weather and load??   I'm an optimist of course, so a repeated testing at Dexter looks to be a good step, soon as the easier reading wider scale amp meter comes in next week. 

PS, older Honda (small) 400 gensets do NOT use standard fuses, odd special sizes from 1978 types.  I ordered mini blade type fuse holders to take modern fuses, some stuff can not be predicted !!

Later, Coots time for home chores, lunch with John K. here, yay !! ---  Cal



Anyhoo!!  That is the plan, as always observations are welcome 




 

I visited Cal today. His ammeter was hooked up somehow so it measured the current going to the motors, at least, but he was using a 200 amp shunt for a 100 amp gauge. which I now know isn't kosher. We moved the shunt to the common ground and replaced the shunt with a 100 amp one Cal had lying around. Maybe even the one that originally came with the gauge. <g> He should be getting more accurate and complete current readings now -- if the shunt's mV rating matches the gauge -- but we can't tell until we get the boat in the water, and Cal bunged up his knee so that'll be later, after he gets it rested up.

The dial ammeter Cal's been using isn't very precise. It has a range up to 100 amps, and the swing of the needle is only about 90 degrees. We really should keep trying to talk him into getting a digital gauge so he can keep better track of the current draw under different conditions. Like trying different propellers.

Cal's idea about switching off one motor to save juice is an interesting one to ponder while sitting in our armchairs. Since he started dreaming up Surprise I thought Cal only needed one of the 80 lb. motors for her. But now he's got two bolted to her bottom. Let's say he's cruising along with both motors at 3 mph. the switches one off and "throttles" up the other until he's going 3 mph again. Will he use less juice? The motors have a fairly efficient pulse width modulated speed control, so not much juice is wasted when running both motors at a reduced speed. If he switches off one motor it's still there under the boat with its propeller free wheeling causing drag. Two motors running slow, or one motor running harder and dragging a dead motor. Which will give longer range? If we can rig up a more precise ammeter in Surprise we can have fun doing some experimenting. :o)

I looked at the documentation that came with Cal's motors. Their instructions for installing them are probably OK, but I was looking for specifications. In vain. <sigh> But I did find something interesting. They said that the rule of thumb for current draw for their 12 volt motors is 1 amp per pound of thrust, but the rule of thumb for 24 volt motors is 3/4 amp per pound of thrust! I wonder whty it isn't just half the draw of the 12 volt jobs, as you'd expect... So Tuffy;s 50ish amp draw at full chat isn't above her rating. Cal's motors could draw 120 amps at full power,

On 9/2/2020 7:56 AM, Electri-Cal wrote:
...
When Myles Swift and I at the very first trial used my 40 lb clamp on Minn Kota at Dexter, we had a great time.  Same at first Fern Ridge trip, clamp on 40 lb. --  big ol' stick handle up in the air, no other power needed. So, back to the beginning, using one 80 lb., like the one on John Kohnens sail boat, coupled to 4 series 27's and the "close "enough for now" gauges ought to run for quite a while. ...
--
John <@Jkohnen>
A strong nation, like a strong person, can afford to be gentle, firm, thoughtful, and restrained. It can afford to extend a helping hand to others. It is a weak nation, like a weak person, that must behave with bluster and boasting and rashness and other signs of insecurity. (Jimmy Carter)
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Myles Twete
 

It would be an interesting experiment to compare running one vs two motors driving the boat at a given speed. It's likely a wash in terms of loss in the controller and given near identical prop characteristics between the two, you're talking about doubling the prop loading in the 1-motor scenario compared to 2. At low loads (and speeds), that might not amount to much of an efficiency reduction to drive with just 1 prop, and might even result in the prop operating closer to its higher efficiency zone (Gerr's prop manual might inform here). But as the boat drag goes up with the square of the speed, at the higher speeds, having the dual props and dual motors sharing the load likely wins out big time assuming we're talking about speeds where the loading nears the high end of the motor's rating. And motor torque via motor current delivers that force.

Motor heat loss (2mtrs) ~ 2 * k2 * Rmtr * (Fdrag/2)^2
= k2 * (Rmtr * Fdrag ^ 2) / 2

Motor heat loss (1mtr) ~ k1* Rmtr * Fdrag ^ 2

Assuming k1 ~ k2 (conversion losses in controller, prop loading, etc. are near same), we should expect the single-motor configuration to have about 2-times the heat loss as for the 2-motor case.

So even if prop efficiency for the 1- or 2-motor scenario were identical (unlikely) at the high speeds, we should expect twice the heat loss.

Now, how much of the total power to the controller(s) is lost to motor heat due to motor current? It's a lot, but the efficiency of the propeller, combined with the drivetrain is the shortest stick---this could be as high as 70% at speed or as low as 50-55%. This, compared to a difference between 90% vs 80% efficiency for a lightly, vs highly loaded motor. Controller efficiency is likely in the 95% zone. Cable and battery losses also factor in.

Add to this, dragging an undriven prop thru the water---best to drive that prop with just the right amount of power that its current draw just starts to increase. At that point, it is presenting minimal drag.

Bottom line: Prop efficiency is paramount. Loading the prop to the point that its operating point moves out of the higher efficiency zones quickly defeats other gains you might attain elsewhere (e.g. by driving with just 1 motor). Add to this, I^2R losses in the motor and battery/cabling quickly conspire against you. But it all depends on the loading. At low speeds and loads, the single prop drive likely wins out. As speed and load increases, single prop loses.

Still, let the data speak :-) .

-MylesT

-----Original Message-----
From: oregoncoots@groups.io [mailto:oregoncoots@groups.io] On Behalf Of John Kohnen
Sent: Wednesday, September 2, 2020 10:55 PM
To: oregoncoots@groups.io
Subject: Re: [oregoncoots] Thanks Coots, getting started on "stuff"

I visited Cal today. His ammeter was hooked up somehow so it measured the current going to the motors, at least, but he was using a 200 amp shunt for a 100 amp gauge. which I now know isn't kosher. We moved the shunt to the common ground and replaced the shunt with a 100 amp one Cal had lying around. Maybe even the one that originally came with the gauge. <g> He should be getting more accurate and complete current readings now -- if the shunt's mV rating matches the gauge -- but we can't tell until we get the boat in the water, and Cal bunged up his knee so that'll be later, after he gets it rested up.

The dial ammeter Cal's been using isn't very precise. It has a range up to 100 amps, and the swing of the needle is only about 90 degrees. We really should keep trying to talk him into getting a digital gauge so he can keep better track of the current draw under different conditions.
Like trying different propellers.

Cal's idea about switching off one motor to save juice is an interesting one to ponder while sitting in our armchairs. Since he started dreaming up Surprise I thought Cal only needed one of the 80 lb. motors for her.
But now he's got two bolted to her bottom. Let's say he's cruising along with both motors at 3 mph. the switches one off and "throttles" up the other until he's going 3 mph again. Will he use less juice? The motors have a fairly efficient pulse width modulated speed control, so not much juice is wasted when running both motors at a reduced speed. If he switches off one motor it's still there under the boat with its propeller free wheeling causing drag. Two motors running slow, or one motor running harder and dragging a dead motor. Which will give longer range? If we can rig up a more precise ammeter in Surprise we can have fun doing some experimenting. :o)

I looked at the documentation that came with Cal's motors. Their instructions for installing them are probably OK, but I was looking for specifications. In vain. <sigh> But I did find something interesting.
They said that the rule of thumb for current draw for their 12 volt motors is 1 amp per pound of thrust, but the rule of thumb for 24 volt motors is 3/4 amp per pound of thrust! I wonder whty it isn't just half the draw of the 12 volt jobs, as you'd expect... So Tuffy;s 50ish amp draw at full chat isn't above her rating. Cal's motors could draw 120 amps at full power,


On 9/2/2020 7:56 AM, Electri-Cal wrote:
...
When Myles Swift and I at the very first trial used my 40 lb clamp on
Minn Kota at Dexter, we had a great time. Same at first Fern Ridge
trip, clamp on 40 lb. -- big ol' stick handle up in the air, no other
power needed. So, back to the beginning, using one 80 lb., like the
one on John Kohnens sail boat, coupled to 4 series 27's and the "close
"enough for now" gauges ought to run for quite a while.
...
--
John <@Jkohnen>
A strong nation, like a strong person, can afford to be gentle, firm, thoughtful, and restrained. It can afford to extend a helping hand to others. It is a weak nation, like a weak person, that must behave with bluster and boasting and rashness and other signs of insecurity. (Jimmy
Carter)


--
This email has been checked for viruses by AVG.
https://www.avg.com


 

Tuffy ghosts along pretty good in almost imperceptible breezes, despite having a dead motor like one of Cal's bolted to the side of her keel. At such low speed surface friction is just about all of the drag, there's no turbulence from the motor, propeller and struts. That's probably the case up to maybe about 2 mph (I could check, but I'm lazy), so running Cal's boat on only one of its motors should win out at slow speeds. Things get more interesting when we go a little faster... <g>

Cal can turn off one of the motors, but there's no way to control their speeds separately. It's well known that running an electric motor very slowly when a boat is sailing reduces drag significantly.

It'll be fun to do some experimenting with Surprise. :o)

On 9/3/2020 10:33 AM, Myles T wrote:
It would be an interesting experiment to compare running one vs two motors driving the boat at a given speed. It's likely a wash in terms of loss in the controller and given near identical prop characteristics between the two, you're talking about doubling the prop loading in the 1-motor scenario compared to 2. At low loads (and speeds), that might not amount to much of an efficiency reduction to drive with just 1 prop, and might even result in the prop operating closer to its higher efficiency zone (Gerr's prop manual might inform here). But as the boat drag goes up with the square of the speed, at the higher speeds, having the dual props and dual motors sharing the load likely wins out big time assuming we're talking about speeds where the loading nears the high end of the motor's rating. And motor torque via motor current delivers that force.
Motor heat loss (2mtrs) ~ 2 * k2 * Rmtr * (Fdrag/2)^2
= k2 * (Rmtr * Fdrag ^ 2) / 2
Motor heat loss (1mtr) ~ k1* Rmtr * Fdrag ^ 2
Assuming k1 ~ k2 (conversion losses in controller, prop loading, etc. are near same), we should expect the single-motor configuration to have about 2-times the heat loss as for the 2-motor case.
So even if prop efficiency for the 1- or 2-motor scenario were identical (unlikely) at the high speeds, we should expect twice the heat loss.
Now, how much of the total power to the controller(s) is lost to motor heat due to motor current? It's a lot, but the efficiency of the propeller, combined with the drivetrain is the shortest stick---this could be as high as 70% at speed or as low as 50-55%. This, compared to a difference between 90% vs 80% efficiency for a lightly, vs highly loaded motor. Controller efficiency is likely in the 95% zone. Cable and battery losses also factor in.
Add to this, dragging an undriven prop thru the water---best to drive that prop with just the right amount of power that its current draw just starts to increase. At that point, it is presenting minimal drag.
Bottom line: Prop efficiency is paramount. Loading the prop to the point that its operating point moves out of the higher efficiency zones quickly defeats other gains you might attain elsewhere (e.g. by driving with just 1 motor). Add to this, I^2R losses in the motor and battery/cabling quickly conspire against you. But it all depends on the loading. At low speeds and loads, the single prop drive likely wins out. As speed and load increases, single prop loses.
Still, let the data speak :-) .

--
John <@Jkohnen>
Assistance given to the weak makes the one who gives it strong. (Booker T. Washington)
--
This email has been checked for viruses by AVG.
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Electri-Cal
 

What I always liked doing, in lighter morning or evening airs was simple and effective. With Windsong, my Atomic 4 at 25 hp., ticking at around 600 to 900 rpm helped take water resistance away, plus prop drag and made ghosting along in the am run to Catalina isl. a lot more fun.  Same with my lapstrake sailer, the MinnK barely churning in the morning helped get offshore and get back as the wind moderated --  without noise and fuss with sail gear. 

Just as info. -- I still have a couple Lido 14 size sails in the bag.  I could easy set up a "mini mast" and do some sailing too.  The rudder is deep and larger for the twin motors, kicks up also.  The addition would be a side mounted leaboard  with weights and a reinforced pivot block, again not a big deal.  I would bet that my Chesapeake flat bottom  hull shape would do well, better without  part of the battery lead !!  I keep thinking about a wishbbone rig.  Anchoring to the gunnels at 4 ft. wide, and tall as the sail allows that to lie aft, sail comes down in the cockpit if dropped by releasing the fore stay rope, loose footed, (furling??) wire luff, sounds like I need to reread a few books.  Another way to possibly not dismiss wind or ev  power, but that doesn't require rowing the last mile.  Power at 3 mph -- sail at 3 mph, -- row at 3 mph  was the way my lighter lapstrake handled everything, from one seat.  Couldn't take 2 people in good seats though, like Surprise does.

Heading out,   Cal