Modified Paddle boat. Need more power!

Discussion in 'Jet Drives' started by Chris A Farwell, Nov 22, 2019.

  1. upchurchmr
    Joined: Feb 2011
    Posts: 2,869
    Likes: 89, Points: 48, Legacy Rep: 579
    Location: Ft. Worth, Tx, USA

    upchurchmr Senior Member

    From your previous discussion, that's what I thought you'd want.
     
  2. Chris A Farwell
    Joined: Nov 2019
    Posts: 12
    Likes: 1, Points: 3
    Location: Spring Hill Fl

    Chris A Farwell Junior Member

    I thought I did too. I have to pick my battles with the missus. It's technically her boat
     
  3. Chris A Farwell
    Joined: Nov 2019
    Posts: 12
    Likes: 1, Points: 3
    Location: Spring Hill Fl

    Chris A Farwell Junior Member

    I've been reading about "surface drives". With my setup, that would be really simple to do. All I would have to do is raise the motor in the pipe that is supporting it and drill a new hole for the PTO clip to go through. Will this help with fighting the current on the rivers we like to cruise on? I'm kinda grabbing at straws now....

    I'm VERY limited as to what I can do with this boat. I can not change the hull in anyway (my wife and I had a "discussion" about it the other day). I have decided to go with 4 - 60 AH LiFePo battery packs. 2 sets of 2 in series with a switch to go from "main" to "reserve" and the new fuse/ relay block is on it's way. I figure this way I can pretty much forget about batteries for the next 10-15 years. "We" agreed that I can do anything I want under the boat but the top needs to stay as it is/ was. "We" want to keep it looking stock and I want to keep people guessing as to how we are moving w/o a paddle or pedals. It starts many a discussion at the boat ramp and we are "people" people.

    I have found that if one or both of us lean forward on the boat while in "high" the prop cavitates although we don't "feel" any difference in forward thrust when it does this. Simple physics tells me that when cavitating, we are losing thrust due to pushing air and not water but, neither one of us can "feel" it. Should I drop the prop down lower to avoid this (also easy to do)?

    I've tried to watch and see where my wake is going but we are never really going fast enough to make one. When going against the current there is a slight one that breaks about 1/3 of the way back (if that means anything to anyone) and I notice a lot of turbulence behind us. When going down river we are basically moving with the current so no wake to speak of and are on medium so very little behind us.

    The motor I'm using is a 12 Volt 30 Lb Motorguide that used to be controlled by a foot pedal. I just cut the top off the shaft and stuck it in a 1 inch galv. pipe and secured with a PTO clip. There are 4 wires. I figured out (by the size of the wire and testing) that there is 1 ground (black 10 Gauge) and 3 positive leads. Low (blue 18 Gauge) is basically useless and does not move the boat at all, Medium (Red 14 Gauge) works well for no current or with current, and high (Yellow 10 Gauge) is what is needed (and still lacking) for the fight up river. I'm using 40 amp automotive relays and a 4 position rotary switch to change between then (see pic in previous post). I reverse the motor by changing the polarity. If anyone has experience with these and sees something I've done wrong, please let me know. It's supposed to have 5 speeds but, I can't figure out how to get the other 2. Maybe there is something higher than what I think "high" is. That, by itself, would help my situation!

    I also have a 3 blade prop (from the same manufacturer) that I can replace the 2 blade prop that is currently on it. Will this change the amount of thrust I get if all other things are equal? I don't want much more thrust. Just enough so that when the current is really strong we still have noticeable forward momentum. I'm determined to make it to the river head (about 4-5 miles) and have only made it about 1/3 of the way so far before my 2 60AH lead acids and 35 AH AGM batteries are just too drained for my taste (about 50-60%). Still trying to figure out the tides so I can meet with the least resistance going up-river and I'm getting close but not quite there yet. Judging by the speed in which we go back down river compared to the speed we go against the current, it flows at about 4-5 MPH. Coming down river we exceed the 5 MPH (by 1 MPH) speed limit on medium and on high we are doing about 7-8 (all according to a GPS speedo on my phone). Average I've gotten going up-stream is 1-2 MPH. In some of the turns we drop to almost 0. Is there something I can put on the front, below the water line, that will help make this mini-barge cut through the water faster or am I just stuck with what I've got and need either a bigger motor and/or more/bigger batteries?
     
  4. BlueBell
    Joined: May 2017
    Posts: 852
    Likes: 93, Points: 28
    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    Try moving you and the misus forward, and back.
    Or move the batteries forward, or back and see
    if you go faster or slower... or no difference.

    What do the two of you weigh together, if I may ask?

    Have you Googled for a wiring diagram to figure out engine speeds?

    And you're prop wasn't cavitating, it was ventilating.
    Big difference.

    Two bladed model R/C airplane props are more efficient,
    but they are fragile and weed-up easily.

    I don't believe adding anything below the waterline forward would make any difference in top speed.
    It may make a difference on the stern, but negligible.

    Sorting out top speed in the wiring my be the ticket!
     
  5. Yellowjacket
    Joined: May 2009
    Posts: 619
    Likes: 91, Points: 28, Legacy Rep: 447
    Location: Landlocked...

    Yellowjacket Senior Member

    Sorry, but you're not hearing what a couple of us have explained to you that adding more power isn't going to make this hull go any faster unless you add enough power to plane it off, and that isn't going to happen with batteries. You could double the power and the battery weight and you might only go a few tenths of a knot faster. If you look at the drag curve for a hull like this it's a parabola. As speed goes up a few tenths of a knot, the drag more than doubles. Pushing a hull at low speeds is very efficient, it doesn't take much power. But as the speed increases the power required to push that hull without planning goes through the roof. You can add all the batteries you want and it isn't going to make much difference. You'll get some more range, but your pinch point is trying to go upstream, and you've got to go faster to make any headway. That is, if you've got a 3 knot current, and you've got a 4 knot capability, you're only going one knot upstream. Adding a knot of speed doubles your true speed and that makes a huge difference. This is why you need to look at a long hull. Adding length and keeping the hulls thin will improve the fineness and will also increase the hull speed. The bottom line is you can fool around with batteries and motors all you want, but you aren't going to get much if any more speed unless you do something with your hulls. You can load it up with batteries and get some more range at low speed, but you aren't going to address the real problem without addressing the fundamental problem.
     
  6. Chris A Farwell
    Joined: Nov 2019
    Posts: 12
    Likes: 1, Points: 3
    Location: Spring Hill Fl

    Chris A Farwell Junior Member

    We have tried moving our location on the boat and also moving batteries around to try to find the "sweet spot". Getting the motor deeper in the water seems to help, will lower the whole unit next time I work on her. Crew, batteries, and stowage for this boat is usually around 400 Lbs. I have LiFePo4 batteries on the radar but need to get through Christmas first. Need a longer run-time. I calculated that at the current max speed, I can make it to the river head in 5-7 hours so I need a litte over 210 AH to achieve this. I have googled the wiring for the motor but can't seem to find anything of use. I'll probably see if I can find the switch that came off of it and see what contacts close in each position (should have thought of this sooner). What is the difference between cavitating and ventilating? is one bad and the other not bad?
     
  7. Chris A Farwell
    Joined: Nov 2019
    Posts: 12
    Likes: 1, Points: 3
    Location: Spring Hill Fl

    Chris A Farwell Junior Member

    I think I have finally understood that no matter what I do, it just won't go any faster and I'm OK with it. The entire river is a no wake zone so getting it up on plane just isn't an option no matter what. At the end of the day I just want to make it to the rivers head. As it sits we were able to make it about 2 miles up the 4.5 mile river before draining the batteries below the 60% mark and had to turn around. The current was fight us the whole way. Planning on dropping the motor a little deeper so that all of the power it's using is going to move the boat forward (correct me if my logic is wrong here) and get lots of LiFePo batteries. Will probably just make an array so I can get the shape and capacity I need to keep the stealth thing going. I figure I can just slowly fight my way against the current and also need to make sure the tide is coming in while I'm headed up river for minimal resistance.

    We took her out on the Homosassa river which went great due to very little current. This is when the whole "fighting the current" thing started to make sense. In calm water she will do about 5 MPH on high and about 3.5 on medium. The Weeki Wachi has a current of about 4 MPH so we will only do 1 MPH while fighting. On the flip side once we make it to the top (or have to turn around) we can turn the motor off and still move along at a pretty good clip, only having to apply power to get around some sharp turns. Was out there for better than 6 hours and was able to putter around on medium which draws much less power.

    I almost have the wife talked into making something out of a pair of kayaks and 2-30 Lb trolling motors we have. I'm thinking a form of catamaran with steering via PWM motor control. But, that is a possible project for another day because I now have to replace the prop on the vintage '66 Searay 17 footer which I nailed yesterday in water that I had no business being in (too shallow-rookie mistake). On the plus side of that, I have proven to myself that I can still rebuild a carb (or 3).

    I want to thank everyone for their insight and patience while I tried to get my (stubborn) head around all of this.
     
  8. Yellowjacket
    Joined: May 2009
    Posts: 619
    Likes: 91, Points: 28, Legacy Rep: 447
    Location: Landlocked...

    Yellowjacket Senior Member

    Bolting a couple of kayaks under a platform isn't going to be a very good catamaran. Kayaks are wider to provide some roll stability, you really don't want a hull that wide for a catamaran because you have two hulls to provide the roll stiffness and the wider hulls have more interference. A narrower hull would be lighter and have lower drag. They also have rocker in the bottom to allow them to be pivoted easily when they are being paddled. A narrow hull with no rocker would be more like what you're looking for here. A couple of kayaks will work but aren't optimum. Think more like two narrow rowing sculls and that's more like what is called for here.
     

  9. KeithO
    Joined: Jul 2019
    Posts: 118
    Likes: 13, Points: 18
    Location: Michigan

    KeithO Senior Member

    What you are saying is correct, however, it is easy for the OP to go out and buy a pair of standard kayaks. If the connecting lattice is built right, the kayaks could still be used for their original purpose and even rowed through narrow streams to a point that would allow them to be joined together. And they could be driven way more efficiently....

     
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.