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Thread: Redwing 18 electric repower

  1. #1
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    Default Redwing 18 electric repower

    After one season with my Redwing 18, I've decided to repower with electric. Out goes my Honda 20, in goes a Torqeedo Cruise 2rs.

    Why am I doing such a thing? Here's my list: the chance to tinker, the thrill of the chase (lots of incremental improvements open up), no gas, no gas tank or fuel gauge, no tach, no more shifter and throttle cable, less noise and vibration, no grease and oil, no more 140lb behemoth, aka the usual reasons one chooses for going electric.

    No turning back now, yesterday with the help of my homemade gantry (see below), chain hoist, and my father-in-law I yanked out the 20hp, holy moly is that thing a beast and I won't miss it!


    IMG_0479.jpg
    The Redwing is a displacement hull and pushing her past 6.5 mph took everything the Honda 20 could do. Admittedly, the Honda had completely the wrong prop, a 10 inch pitch which is designed to push a boat up to 20 mph or so. But the bottom line is that a 6hp equivalent is plenty for what I'm trying to accomplish on the water.

    I got a lot of help through posts here and on the electric boats group. I had originally planned on going with an 80lb trolling motor and I did purchase the critical pieces aka a shaft, motor and controller from Minnkota's parts window. But circumstances have directed me to the Torqeedo with the Minnkota as a redundant power source.

    I chose the Torqeedo 2 vs the 4 because of the smaller 24v source which I currently had 70ah of AGMs. Eventually I can increase battery capacity, install maybe 200w of solar, migrate to lithium, and perhaps get a generator.

    Assuming a top speed of 6.2, my estimated performance assuming Peukert effect and 80% DOD allows 2.5 hours of propulsion at 3.6 mph. My wife and typically motor around for 2.5 hours so right out of the box I'm assuming a 9 mile afternoon on the water, that's just fine for us.

    If I install 200w solar, I estimate motoring around at 2.9 mph all day on solar alone.

    Eventually, if I upgraded to 140ah of lithium batteries with 80% DOD, I estimate I can motor around for 5 mph for 2.5 hours, that's pretty much exactly right for us.

    I'm being pretty conservative on my numbers, based on evidence I've gathered. We'll see in 6-7 months, once the water is open again, if I'm anywhere in the ballpark. I'm also taking the winter to redo the cockpit for more floor space (less storage) and finish the cabin.
    Last edited by wdr99; 11-25-2020 at 10:12 AM.

  2. #2
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    Default

    So that’s what you are up to. Sounds good, a local TSCA member had a Redwing 18 with a 2 hp Honda if I recall. That was enough for the displacement hull. More photos of the install, please.

    -Rick

  3. #3
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    Default Re: Redwing 18 electric repower

    There's an awesome article in Professional Boatbuilder October/November 2020 No. 187 about electrical repowering equivalents. I highly recommend it.

  4. #4
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    Default Re: Redwing 18 electric repower

    'If I install 200w solar, I estimate motoring around at 2.9 mph all day on solar alone.'

    A 200W Solar Panel might produce a maximum of 140W in normal fixed conditions or so I have researched. However on a moving, rolling, pitching boat. Lets say maybe 100W. 100W is 0.134hp. Are you sure that's going to push you at 2.9mph? Doesn't sound right. How did you work it out?

  5. #5
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    Default Re: Redwing 18 electric repower

    Quote Originally Posted by Zakwaddell.ca View Post
    'If I install 200w solar, I estimate motoring around at 2.9 mph all day on solar alone.'

    A 200W Solar Panel might produce a maximum of 140W in normal fixed conditions or so I have researched. However on a moving, rolling, pitching boat. Lets say maybe 100W. 100W is 0.134hp. Are you sure that's going to push you at 2.9mph? Doesn't sound right. How did you work it out?
    Funnily enough, I had normally calced about 70% output and for whatever reason I had bumped into quotations of much higher output percents, but that might have been under much more optimal conditions than I could expect for flat panels on the water. So, on that I was unduly optimistic. But I'd say at 100w I'm more like 2.3 mph. I'm assuming a cube root relationship between power and speed. Most data I've seen is in that ballpark, sometimes less, sometimes more.

    I'll have to check out the Joe Grez article.

    Bill

  6. #6
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    Default Re: Redwing 18 electric repower

    Don't forget that the 100W you have is before losses from the charge controller, batteries, speed controller, electric motor and the big one the propeller. A propeller is only about 40% efficient. That means you only have about 50W pushing the boat.

    I am really interested because I want to build a very efficient monohull to cruise around the lakes and rivers here in North America. Electric is always on my radar but for the practicality and price. It would be real nice to cruise around all day only on electric power at any speed.

  7. #7
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    Default Re: Redwing 18 electric repower

    Quote Originally Posted by Zakwaddell.ca View Post
    Don't forget that the 100W you have is before losses from the charge controller, batteries, speed controller, electric motor and the big one the propeller. A propeller is only about 40% efficient. That means you only have about 50W pushing the boat.
    Does anyone measure power at the prop? I am measuring electrical power out of the battery on my solar skiff project. There will be losses in the battery, but the coulomb meters that measure charge in and out are used to monitor charge state so that must not be a lot of loss. For my 18' skiff, the battery has to supply 100 to 120 W to drive the boat at 3 kts. A 170 W rated solar panel is able to supply 100+ W for 6 to 8 summer hours.

  8. #8
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    Default Re: Redwing 18 electric repower

    Good choice to go with the Torqueedo instead of the trolling motor. I use an 80lb. thrust on my fantail launch and, while it worked, I'm glad I went to the 2k electric motor.
    My hull shape is very efficient and the 2k motor drives the 18' (16' waterline) displacement hull to it's hull speed of 6mph.
    If you haven't bought the motor yet, I'd go with the Torqueedo 4 as you have a heavier and less efficient hull.
    I was born on a wooden boat that I built myself.

  9. #9
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    Default Re: Redwing 18 electric repower

    I've already bought the T2. All things being equal I would have got the 4 but I would have had to start over with batteries and charger and that was a bridge just too far. 48v of AGM would be pretty doggone heavy, say 280 lbs for 100ah and 4.8kw of lithium would have been pretty expensive.

    Also, my performance math was predicated on a 2.5 hr trip at 80%DOD after Peukert in the case of AGMs. I estimate that a t4 would give me 4.6 mph (11 miles) and a t2 would be around 4.1 mph (10.3 miles). In this case I made the opportunity cost decision that the extra ~$1700 wasn't worth it to me. We'll see if I'm wrong in the end. I usually am! But the math alone has been very entertaining.

    And just by chance, after I placed my order for the Torqeedo I ran across a company called Symphony Boats from my hometown that puts T2s in a couple of their launches. It felt a bit like confirmation.

    Your launch and associated data has been very helpful to me. And it's an absolutely beautiful boat. Thanks for your efforts!

    Bill

    Quote Originally Posted by Rich Jones View Post
    Good choice to go with the Torqueedo instead of the trolling motor. I use an 80lb. thrust on my fantail launch and, while it worked, I'm glad I went to the 2k electric motor.
    My hull shape is very efficient and the 2k motor drives the 18' (16' waterline) displacement hull to it's hull speed of 6mph.
    If you haven't bought the motor yet, I'd go with the Torqueedo 4 as you have a heavier and less efficient hull.

  10. #10
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    Default Re: Redwing 18 electric repower

    I have one friend who built a Redwing 18, another who owns one, and an acquaintance that built the 23. I'll leave the details of the electrical conversion to the experts. My only experience with such an adventure is doing the woodworking bits required for fitting a Torqueedo 80 hp to replace a pair of smaller outboards. Watching the two factory reps (required) do the initial consultation and the final hookup a few weeks later left me ill-prepared to comment on the electonic bits/specs/requirements. But having spent some time aboard the R18... I would consider the design a good candidate for such a conversion. Good Luck!!
    David G
    Harbor Woodworks
    https://www.facebook.com/HarborWoodworks/

    "It was a Sunday morning and Goddard gave thanks that there were still places where one could worship in temples not made by human hands." -- L. F. Herreshoff (The Compleat Cruiser)

  11. #11
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    Default Re: Redwing 18 electric repower

    I agree that your runtime estimates on a full charge are conservative, but I think that your expectations for solar drive are very optimistic. The solar panels will reduce the rundown rate of the batteries, but I don't see being able to run all day on solar power with panel(s) rated at 200w. Even if you continually tilted them to face the sun directly, you'd be lucky to get that kind of power reliably. Clouds come and go, the sun gets low spring and fall, and so on and so forth. And that's before the losses in transmission to the motor.

    But as a point of comparison that I don't think is too far off. I put the MinKota 80 pound, 24V motor on Terrapin, my CLC Autumn Leaves yawl. This boat displaces about 2200 pounds ready to cruise, and has a waterline of about 18 feet. I power it with two 65 amp-hour lithium batteries (MillerTech LifePo4, 12V each in series) and the performance has surprised me. I have not tested the setup down to dead batteries to see what the ultimate range is. But after 2 hours runtime at a bit more than half throttle, doing about 3 knots, the digital charge meter showed 80 percent capacity remaining.

    It is said that lead-acid batteries of a given amp-hour rating will not go as far as the lithium batteries do because the voltage drops down at a quicker rate. On the other hand, Torqueedo claims their units are more efficient than the MinKota and other trolling motors. So as always, your mileage will vary. But I think you'll have decent range to start. I do highly recommend the lithium batteries - they weigh much less and take you farther than the lead acid AGMs, etc. Batteries and motor in my setup total about 70 pounds.
    -Dave

  12. #12
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    Default Re: Redwing 18 electric repower

    Quote Originally Posted by rgthom View Post
    So that’s what you are up to. Sounds good, a local TSCA member had a Redwing 18 with a 2 hp Honda if I recall. That was enough for the displacement hull. More photos of the install, please.

    -Rick
    Glad to hear of so many Redwings out there! I’m a bit jealous you folks with TSCA chapters in your backyards.

    An empty motorwell and a semi-demolished cockpit.

    ECB11316-45AC-4FCE-8CF0-1DE2B2215268.jpg
    00441E5F-08DB-40BB-BF4E-4BD5355871EC.jpg

  13. #13
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    Default Re: Redwing 18 electric repower

    Any of these electripickle conversions working out ?

  14. #14
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    Default Re: Redwing 18 electric repower

    Out with the old and in with the new.....

    1591F6EA-D6C0-4811-91BC-955828FE150C.jpg
    And cockpit reclamation work in progress....
    57682CF8-969E-4988-BC96-9F1B88424A5C.jpg

  15. #15
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    Default Re: Redwing 18 electric repower

    Gaw that looks like fun...and I'm not being sarcastic .
    where is the Torquedo going to go? The cutout a bit further aft?
    I'd love to customize a drag free arpeture/hole.

  16. #16
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    Default Re: Redwing 18 electric repower

    would be good if systems were measured in thrust.
    =~=~=~=~=~=~=~=~=~

    When we remember we are all mad, the mysteries disappear and life stands explained.

    Mark Twain

  17. #17
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    Default Re: Redwing 18 electric repower

    Quote Originally Posted by wizbang 13 View Post
    Gaw that looks like fun...and I'm not being sarcastic .
    where is the Torquedo going to go? The cutout a bit further aft?
    I'd love to customize a drag free arpeture/hole.
    The motorwell will be unchanged. I could shrink the well about six inches to donate to the cockpit. For now, though, I think it’s enough to leave it as is.

    3E7C3186-8E0C-4A50-B8CE-EE7500E1C277.jpg

  18. #18
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    Default Re: Redwing 18 electric repower

    Subscribing. I imagine the torqueedo will be just perfect for propelling your yacht up near displacement speed, and without the stink and noise of hanging a lawnmower off the back.

  19. #19
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    Default Re: Redwing 18 electric repower

    New roomier cockpit is coming together as is the patching of all the holes required for the antiquated gas power.

    9221956D-F1B0-447E-8DF5-E43E1F1D08B6.jpg

  20. #20
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    Default Re: Redwing 18 electric repower

    The cockpit is definitely coming together. The behind the scenes bits are painted mostly and the bench is now glued in. Plus the pedestal mounts are glued in.

    Next is glassing the bench and pedestal mounts plus blending it in with the existing cockpit bits. Then painting in earnest, cockpit soles, install Torqeedo throttle and battery box.

    When all that’s done, I can start making the cabin interior look good, with cedar paneling,vents, paint, and the rest.
    2795C6A5-BB83-4709-BA3C-D9AF875CBB12.jpeg

  21. #21
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    Default Re: Redwing 18 electric repower


  22. #22
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    Default Re: Redwing 18 electric repower

    Lots more is done with the Redwing. The cockpit is done. The Torqeedo and all the electric stuff is done. Now Iím wrapping up the cabin improvements. Hereís a few pictures of the improvements. The motor is so small, I feel like I really should refashion that whole aft end of the boat to make the motor more accesible and enlarge the cockpit as well. Maybe next winter, now itís time to get back on the water.

    9103C9A7-89D8-4F7D-860E-7B176FC83601.jpgBF54AF55-3823-4559-BF75-AE73BA1C694C.jpg5025F55F-CF0E-43CA-B276-671719C1EA8C.jpg6C188C33-E427-4AE2-B777-89B5F313AF33.jpgB7469196-0AC4-4C1E-AB4C-D9D3A6FFC136.jpg

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