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Thread: Re-powering my Palmer fantail launch

  1. #1
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    Default Re-powering my Palmer fantail launch

    This is a tale of partial success along with some disappointment.
    Two months ago, the 80 lb. thrust trolling motor that I installed during construction bit the dust. I debated back and forth with myself on the best way to replace it. The 80 lb. thrust motor worked OK, but wasn't powerful fighting into the wind. Of course, as a pure pleasure boat, I never would go out on really windy, wavy days anyway. An electric inboard would have been ideal, but it is simply not in my budget. The trolling motor truly fit my purposes. Silent, vibration free and good for a couple of hours of leisurely cruising.
    I had two choices. A traditional 112 lb. thrust motor or a 160lb. thrust engine mounted unit. These units mount on the cav plate of a large outboard engine. They are a fixed unit and you steer with the boat's steering wheel. I knew I could adapt that to the skeg of my launch. The price difference between the two was only a $100 or so. With that, I bought the 160 lb. unit. It consists of two 80 lb. pods mounted as one unit. Here it is sitting upside down on my workbench.
    IMG_4253.jpg

    I removed the bracket (just a handful of screws) as I wouldn't be needing it.

    Here's the boat as it was. 80lb. motor with fairing piece between the motor and skeg. Next shot is with those removed.

    IMG_4268.jpg

    IMG_4269.jpg
    I was born on a wooden boat that I built myself.

  2. #2
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    Default Re: Re-powering my Palmer fantail launch

    This new configuration would require a proper rudder. When I built the boat, I put a rudder tube in the spot for a rudder shown on the plans. I ran the leg of the trolling motor up this tube. With that motor now gone, I was able to but the new rudder in the exact place it's supposed to be. I had a local metal shop make up the stainless steel rudder/rudder post. I simply hooked it up to the same steering gear that attached to the old trolling motor.
    To attach the new motor, I had to add a 3" deep extension to the keel. This extension went about 6" past the end of the skeg. The new motor was bolted to this with a piece of rubber matting in between as a vibration dampener.
    IMG_4277.jpg

    The above picture was modified again after a test run, but you get the idea.

    Here's the final product.

    IMG_4306.jpg
    I was born on a wooden boat that I built myself.

  3. #3
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    Default Re: Re-powering my Palmer fantail launch

    Nice! That should move her quite well for sure.

    Steering may suffer a bit, esp. going from directed thrust to a rudder between the two props, but I don't imagine you are doing much tight maneuvering during your leisurely cruises anyway.

  4. #4
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    Default Re: Re-powering my Palmer fantail launch

    Nicely done, Rich. Has there been time for sea trials yet? How is speed, speed against head-winds, and steering (fwd & backing-down) as compared to the old setup?
    Hope for the best, but plan for the worst.

  5. #5
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    Default Re: Re-powering my Palmer fantail launch

    To run the wires up into the boat, I made another fiberglass tube just like the one I built for the rudder tube. The tube runs almost to deck level, so no fear of water entering the boat.
    Now for the results of this grand experiment.
    The old 80 lb. motor drove the boat at just over 5 mph. I was hoping with this new one to get another 1-2 mph. Turns out I get just the same speed as the old one. I was disappointed but then again, my wife and I find that cruising around the shoreline at 4 mph was our preferred speed, so really no big deal. I do feel, though, that I have that extra power to fight winds if needed.

    But now comes the bizarre part and if anyone can explain it: thank you in advance.
    When sitting on the trailer, the props go much faster in reverse then in forward. I didn't discover this until after the 30 day return policy was up. I thought something was wrong with it, so took it to a MinnKota certified repair place 1 1/2 hours away. It was a mystery to him also. He thought it might be the controller or throttle, so he replaced those but to no avail. He then contacted the factory and they told him it was designed like that. Some nonsense about the boat needing more power to stop then to go forward. I called MinnKota and got the same line of bs. What possible reason would there be to limit the forward speed of the motor? It makes absolutely no sense to me. Immensely frustrating because that's where my extra 1-2 mph would come from.
    I even tried fooling the controller by reversing the wiring so the motor would run in forward when put in reverse. The controller is a crafty little devil and still ran slower.
    Another reason for slower speed is the fact that these pods stick out and cause turbulence and drag. I had thought of this and experimented with dragging water filled milk jugs beyond the boat with the 80 lb. motor. (at this point, that motor ran only in forward, reverse was busted) There was a drop of 1 mph.
    Perhaps this winter I'll come up with some fairing fins so the water doesn't hit those pods head on.

    With the mixed results, I thought of keeping this somewhat-less-then-perfect project to myself. But, it's important that we share all our results with the Forum, whether good or bad so others can learn from them, again whether good or bad. But, I feel that my concept was sound, but that MinnKota's bizarre design screwed it up. 160 lb. thrust in reverse and hardly 80 lb. in forward???? Weird.
    I was born on a wooden boat that I built myself.

  6. #6
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    Default Re: Re-powering my Palmer fantail launch

    Quote Originally Posted by nedL View Post
    Nice! That should move her quite well for sure.

    Steering may suffer a bit, esp. going from directed thrust to a rudder between the two props, but I don't imagine you are doing much tight maneuvering during your leisurely cruises anyway.
    The steering is much improved with the rudder, especially when approaching shore. I can still steer while I'm drifting in after I shut the motor off.
    With that long straight keel, this boat has the turning radius of a freight train whether it's with motor steering or rudder!
    I was born on a wooden boat that I built myself.

  7. #7
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    Default Re: Re-powering my Palmer fantail launch

    Isn't 5 pushing your waterline hull speed?

  8. #8
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    Default Re: Re-powering my Palmer fantail launch

    Quote Originally Posted by Thad View Post
    Isn't 5 pushing your waterline hull speed?
    True. Hull speed is a bit over 6mph. Truth of the matter is that the old motor pushed the boat a little bit faster then the new one. Frustrating.
    I was born on a wooden boat that I built myself.

  9. #9
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    Default Re: Re-powering my Palmer fantail launch

    Hello again, Rich. Your issues with repowering and observations about steering are entirely predictable, and perfectly normal. MinnKota did not screw up. First, the steering:

    You can still steer even with the motors shut off because the rudder works due to the flow of water past it. It does not care whether that flow is from a propeller or merely the water flowing past it as the boat moves through the water. Steering is enhanced when the rudder is in the flow of water projected by the prop because that water is moving faster than the surrounding water, but as long as water is flowing by, the rudder will work. Under power, your boat would steer even better if you had a dual rudder system that put a rudder behind each prop, but that is way too complicated (but fun for us mechanical systems junkies).

    Now the 'faster in reverse than in forward' part. This is normal, and related to the propeller(s), not the motors or controllers. Propellers are more efficient going forward than in reverse, due to their shape. In most powertrains, the fact that the boat does not go as fast in reverse as forward is just an accepted fact, and operators learn to compensate for it. In an electric trolling motor it is desirable to have equal thrust in either direction so the operator/fisherman can have precise control over his fishing platform. The engineers at MinnKota knew the maximum output of the motor and selected a propeller that gave the best performance over a wide range of rpm in both forward and reverse. Given the characteristics of the propeller in both forward and reverse mode, they determined the maximum thrust of the prop in reverse at maximum motor rpms, then selected the motor rpm that would give the same amount of thrust when in forward mode, and locked that into the motor controller. If you could override the motor controller so that the motor ran at max rpm in both forward and reverse, you would see more boat speed going forward than in reverse. But (there is always a 'but'), doing so would most likely run the prop beyond its maximum rpm for its pitch/diameter ratio when in forward mode, and it would likely cavitate, yielding less-that-optimal performance and probably causing blade erosion due to cavitation. You could then go for a better prop, but I don't know of too many places that make custom props for MinnKota trolling motors. The bottom line is that, by using a trolling motor for main propulsion, you are boxed in to the parameters of performance needed for trolling, not for cruising.

    By the way, do not put anything in front of the pods to deflect the water flow from them. Doing so will starve the propellers of clean water, causing loss of performance and possibly increasing prop-induced vibration. You are seeing less or equal speed because the props are pitched for power, not speed. If the props are metal, you may be able to have them re-pitched to gain some speed, but if plastic you are SOL. If you do re-pitch for speed, you will lose power which will adversely affect your boat's speed into wind & waves.
    Last edited by mmd; 10-10-2018 at 12:05 PM.
    Hope for the best, but plan for the worst.

  10. #10
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    Default Re: Re-powering my Palmer fantail launch

    mmd,
    Thanks. What you say makes sense. I wonder why the folks at MinnKota couldn't explain it that way?
    Even at that, I've got two other smaller MinnKota's that run the same speed forward and reverse and I believe my old 80 lb motor did also.
    The only props I know that increase speed are RC airplane props. I've experimented with them, but they are too fragile. If one broke out in the middle of the lake, I'd have no way to get to it.
    As for fairings, they would be shaped to make the water flow smoother over the pods. Right now, the black plastic supports holding the pods are not very hydrodynamically friendly.
    I was born on a wooden boat that I built myself.

  11. #11
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    Default Re: Re-powering my Palmer fantail launch

    More on propellers.
    Last summer I experimented with a Torqueedo prop on my 80 lb. trolling motor. I had to re-bore the prop to fit my shaft plus you have to run in reverse to go forward since the prop turns the opposite of a MinnKota. Once I got up to 4 mph or so, the prop started to lurch badly, so I guess that's the cavitation that mmd was talking about. Anyway, a failed experiment.
    I had good luck with the three bladed replacement prop made by Kiwana so I put two of those on this motor.
    In post #2, I mentioned that I had to re-modify my skeg extension after a water test. The way I had it done, I believe the props were too close to the hull and not getting clean water. In any event, there was noise and vibration. After modifying it, the props are lower and further out away from the hull. There is a bit more vibration then with the single 80 lb motor, but that's understandable now that there are two. It could have something to do with the old motor hanging whereas the new one is bolted down.
    I was born on a wooden boat that I built myself.

  12. #12
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    Default Re: Re-powering my Palmer fantail launch

    "It could have something to do with the old motor hanging whereas the new one is bolted down."

    Almost certainly...
    Hope for the best, but plan for the worst.

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    Default Re: Re-powering my Palmer fantail launch

    Do you have an ammeter you could put around the motor feed? It would be interesting to see how much current the controller is feeding the motor forward vs reverse. That would tell you if the limitation/difference is coming from the controller or intrinsic to the motor.
    Is the controller a PWM?

    Travis.

  14. #14
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    Default Re: Re-powering my Palmer fantail launch

    Quote Originally Posted by Zuri View Post
    Do you have an ammeter you could put around the motor feed? It would be interesting to see how much current the controller is feeding the motor forward vs reverse. That would tell you if the limitation/difference is coming from the controller or intrinsic to the motor.
    Is the controller a PWM?

    Travis.
    Too late to tell now. I just pulled the batteries for the winter. It's going to get cold tomorrow and won't warm up again until spring.
    Forgive my ignorance ( I have an abundance of it!), but what is a PWM?
    The controller is that black box. About 7"x10"x2". Also shown is the battery switch and recommended 120 amp circuit breaker. The throttle is a wimpy little handheld thing with an 18' cord that can lead anywhere on a boat.
    IMG_4314.jpg

    IMG_4315.jpg
    I was born on a wooden boat that I built myself.

  15. #15
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    Default Re: Re-powering my Palmer fantail launch

    Hi Rich,

    PWM is Pulse Wave Modulation. It breaks up DC power into pulses like turning a switch on and off very quickly. It modulates the width of that pulse, meaning the longer the pulse the more power goes into the motor, the smaller the pulse, less power. It's an efficient way to use power vs resistance where you reduce power by bleeding off heat from a resistance circuit.

    If your motor is DC and the controller is a PWM you can just bypass the controller altogether to max out the power going into the motor. You would do this in the water under load so you don't over rev the motor. That will let you know what the motor can do as if the controller were at it's unregulated maximum.

    Travis.

  16. #16
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    Default Re: Re-powering my Palmer fantail launch

    Quote Originally Posted by Zuri View Post
    Hi Rich,

    PWM is Pulse Wave Modulation. It breaks up DC power into pulses like turning a switch on and off very quickly. It modulates the width of that pulse, meaning the longer the pulse the more power goes into the motor, the smaller the pulse, less power. It's an efficient way to use power vs resistance where you reduce power by bleeding off heat from a resistance circuit.

    If your motor is DC and the controller is a PWM you can just bypass the controller altogether to max out the power going into the motor. You would do this in the water under load so you don't over rev the motor. That will let you know what the motor can do as if the controller were at it's unregulated maximum.

    Travis.
    It would be an interesting experiment and I had thought of that, but I'm not about to risk blowing up my new $1,200 motor! Besides, as mmd says, the prop would probably cavitate at much faster speeds.
    I was born on a wooden boat that I built myself.

  17. #17
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    Default Re: Re-powering my Palmer fantail launch

    Shrouds around the props might increase their effectiveness a little. Search for info about "ducted fans/props".

  18. #18
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    Default Re: Re-powering my Palmer fantail launch

    I'm thinking the old "rudder " was actually fixed in a central position, and not a steering device at all, the rotating 80lb motor was the only steering device?

  19. #19
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    Default Re: Re-powering my Palmer fantail launch

    Quote Originally Posted by Phil Y View Post
    I'm thinking the old "rudder " was actually fixed in a central position, and not a steering device at all, the rotating 80lb motor was the only steering device?
    Yes, that was a fairing piece in the second picture in post #1 and not a rudder at all, although it certainly looked like one.
    I was born on a wooden boat that I built myself.

  20. #20
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    Default Re: Re-powering my Palmer fantail launch

    Quote Originally Posted by Rich Jones View Post
    It would be an interesting experiment and I had thought of that, but I'm not about to risk blowing up my new $1,200 motor! Besides, as mmd says, the prop would probably cavitate at much faster speeds.

    I don't blame you. That's a lot to risk.
    Thanks for sharing your experience. Good luck with your project.
    I'll keep an eye open for hopefully a successful update next season.

    Travis.

  21. #21
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    Default Re: Re-powering my Palmer fantail launch

    Any idea how much the launch weighs?
    There's the plan, then there's what actually happens.

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    Default Re: Re-powering my Palmer fantail launch

    [QUOTE=Rich Jones;5694738]More on propellers.

    I had good luck with the three bladed replacement prop made by Kiwana so I put two of those on this motor.

    Did you mean Kipawa?

    https://www.kipawapropellers.com/

    Did your range suffer with the new setup?

  23. #23
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    Default Re: Re-powering my Palmer fantail launch

    Regarding the propellers... since you've gone this far and designed your own propulsion system, why not take it a step further and experiment with making your own propellers using 3D printing? The print size limitations for a typical home or maker-lab sized printer would be a constraint against printing the props in one piece of course. But I think it wouldn't be too tough to design and print a hub that would be compatible with the power units and that would accept different blades, either using a fastener or glue (probably with some sort of positive location tab/notch). Given what you learned using RC plane props I suspect you could design a higher-aspect propeller that would give you more thrust and would be more robust than the lightweight airplane versions. You'd want to print using ABS for strength which would be a factor in choosing a printer. But if you don't want to spend to buy your own there are shops that will print to your design.

    (Maybe "not too tough" is understating the level of effort here. A propellor is a reasonably complex thing to model after all. But not out of the question I think?)
    Last edited by cstevens; 10-11-2018 at 05:07 PM.

  24. #24
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    Default Re: Re-powering my Palmer fantail launch

    Quote Originally Posted by BBSebens View Post
    Any idea how much the launch weighs?
    The boat is probably a few hundred pounds. Batteries and motors add another 200 plus assorted gear.
    I was born on a wooden boat that I built myself.

  25. #25
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    Default Re: Re-powering my Palmer fantail launch

    [QUOTE=Gib Etheridge;5695331]
    Quote Originally Posted by Rich Jones View Post
    More on propellers.

    I had good luck with the three bladed replacement prop made by Kiwana so I put two of those on this motor.

    Did you mean Kipawa?

    https://www.kipawapropellers.com/

    Did your range suffer with the new setup?
    True, it was Kipawa. Sorry for the typo. Further testing for range etc. will have to wait until spring. For my use, two hours at half throttle is all I'll ever use, so what I've got will be fine. I'm well aware of the high battery drain from trolling motors. For my boating needs and budget, however, it's still the best fit. Perhaps in 4-5 years I can justify spending the big $$ on a proper inboard system.
    I was born on a wooden boat that I built myself.

  26. #26
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    Default Re: Re-powering my Palmer fantail launch

    You know, if you are going to have 2 drive units mount them wide apart and with independent controls get all the advantages of twin screws. And while you are on it, mount them backwards and reverse the props. We can show those engineers a thing or two.

  27. #27
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    Default Re: Re-powering my Palmer fantail launch

    You mean like this, Phil?

    Hope for the best, but plan for the worst.

  28. #28
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    Default Re: Re-powering my Palmer fantail launch

    I can't help but wonder if the actual reason for restricting the wattage available in forward is that forward is most likely to be used continuously and they wanted to cut down on heat accumulation. Running in reverse all of the time might overheat the windings.

    Also, it can't hurt having the motor housing in the way to protect the props when underway.

  29. #29
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    Default Re: Re-powering my Palmer fantail launch

    The props will be more efficient when leading the pod.
    Hope for the best, but plan for the worst.

  30. #30
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    Default Re: Re-powering my Palmer fantail launch

    Quote Originally Posted by Phil Y View Post
    You know, if you are going to have 2 drive units mount them wide apart and with independent controls get all the advantages of twin screws. And while you are on it, mount them backwards and reverse the props. We can show those engineers a thing or two.
    The first thing I did was to mount the unit backwards and run it in reverse. Too much vibration or turbulence. Whatever the case, it did not work. That's why I didn't bother mentioning it earlier.
    I was born on a wooden boat that I built myself.

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