Rudder positioning powered catamaran

Discussion in 'Multihulls' started by SolGato, May 13, 2019.

  1. SolGato
    Joined: May 2019
    Posts: 32
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    Location: Kauai

    SolGato Junior Member

    Aloha!

    I have a Hobie Getaway that I have converted into a solar electric sailing hybrid. I run dual independent controlled brushless motors mounted at the aft end of each hull and I use the forward and reverse independent thrust to propel and steer the boat.

    As a safety precaution and a necessary feature for sailing, I have fabricated a mount for a removable single Hobie rudder positioned in the middle of the aft aka or rear beam. I had hoped that in the event of a motor malfunction, I could pin the rudder in place and still be able to steer the boat using one motor and the single rudder.

    Unfortunately when tested, the rudder was ineffective.

    I’m thinking the main reason is because it is forward of the motor and the Hobie with its built in keel fin really likes to stay on tack. I haven’t yet tested the rudder under sail, but don’t foresee any issues since the motors will be out of the water and I’m sailing a Crab Claw lateen type sail and not pushing the boat hard or flying a hull, just cruising to conserve battery capacity when conditions are ideal.

    What do you all think I need to do to try to make a single rudder work in this scenario with my particular configuration?

    Should I move it closer to the centerline of the hull that has the working motor? Or maybe outboard of that hull?

    This is all an experiment and I have left plenty of adjustment in the design. Just thought I would get your input to see what position to try next.

    Thanks!
     
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  2. baeckmo
    Joined: Jun 2009
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    Location: Sweden

    baeckmo Hydrodynamics

    Hi and welcome! Generally speaking you get better propulsion efficiency (=longer operational radius) when both propellers are similarly loaded, ie sharing the total thrust equally. This means that the use of differential power for steering will use up more of your battery capacity, than running both props and using well designed rudders for steering.

    Now, rudders aft of the props may recover part of the swirl energy in the flow downstream of the props, meaning that this arrangement is a better solution than the one you selected. With the rudder side forces applied as far aft as possible, smaller wetted surfaces can be used for the same course-keeping effort, resulting in smaller losses.
     
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  3. Blueknarr
    Joined: Aug 2017
    Posts: 526
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    Location: Colorado

    Blueknarr Senior Member

    Welcome to the forum.

    What are the underwater dimensions of the rudder.

    Being on the cross beam, it may not be projecting far enough into the water.
    I second Beakmo's comments.
     
  4. Dejay
    Joined: Mar 2018
    Posts: 289
    Likes: 33, Points: 28
    Location: Europe

    Dejay Senior Newbie

    I can't help you with the rudder, but I'd love to see some pictures! And also curious about what motors and how much solar power and batteries. And how well it performs. And welcome to the forum :)
     
  5. SolGato
    Joined: May 2019
    Posts: 32
    Likes: 12, Points: 8
    Location: Kauai

    SolGato Junior Member

    Thanks for your input.

    Agreed that a traditional motor with with rudder setup is more efficient as @baeckmo stated, but the benefits of not having to be at a helm along with the spacecraft-like maneuverability of a dual independent thrust system definitely outweigh the loss in efficiently. With the dual independent setup, I can operate and steer the boat from any location with wired remote, and maneuver the boat like a tank by increasing thrust or decreasing thrust of one motor to make course corrections while underway. I am also able to do 360 degree turns without losing ground and use reverse thrust like brakes.

    Unfortunately in order to make the motors perform well while not adding any holes to a plastic boat, I designed my motor mounts to use the existing factory rudder mount holes. This allows the boat to be extremely responsive to throttle input since the motors are basically hanging off the back of each hull, but does not allow for the ability to hang a rudder behind them. For this reason I chose the center of the aft beam since it can handle the load and allows for good tiller positioning.

    I also agree as @Blueknarr suggested that I may not have enough rudder below the water surface, although I figured I would at least get some kind of steer-ability.

    I fabricated my rudder mount knowing that there might be some performance issues, so it was designed to be able to be positioned anywhere along the aft beam. I think next time out I will experiment moving it toward the hull with the working motor to see if I can gain some steering ability. I’ll take a flat blade paddle along as well and see what affect steering from the front beam opposite of the working motor hull might have.

    Here you go @Dejay. I built the boat some years ago using a pair of Minn Kota EM55lbs for proof of concept but just recently upgraded to a pair of Caroute 120lbs brushless motors. The guys at Caroute are great and the motors are smartly designed and far more efficient than my old brushed MK’s. My battery bank is 24V with two group 27 deep cycle batteries in series. They are mounted low inside each hull. The solar system is comprised of two grids -fore and aft with each having 3x100W Sunpower flexible panels in series feeding a Victron Bluetooth 75/15 MPPT solar charge controller. So system total is 600W at 120V. From the data Caroute was able to provide, I determined my motors to be most efficient when drawing 15A each, so I designed my solar system to be able to supply 15A to offset that load while maintaining my bank float point thus allowing me to cruise at a nice pace purely on sun power. It’s easy to find this zero point using the Victron battery monitor which predicts state of charge like a gas gauge just by throttling back until the value for estimated runtime reads “Infinity”. Anyway, the boat performs great. It worked great before with the old motors, and now even better. Still have some experimenting with 3D printing of props with hopes to gain a little more top end speed since the motors don’t have to work too hard to push the Hobie Cat hulls through the water. They are rated at 60A max draw each and from a dead stop to full throttle the max they are pulling is about 25A each so there is room for improvement with a more aggressively pitched pair of props.

    I have lots of photos and videos of SolGato’s build on my Instagram page: willdesignsandbuilds 7712F6BF-836B-45D5-A071-8C6F706E5FAC.jpeg C13B84B2-0903-4558-B13F-15BA31A8438D.jpeg 7FFA06D5-07DA-4B2B-BBEE-3F570C5CABF3.jpeg 50C7FCF9-65A9-4838-AD64-BA12739C9622.jpeg A146BF0F-8016-4C42-9FE7-1557527ADBF6.jpeg 43721FF6-C15A-4905-9532-CCD3D1DCBF96.jpeg 29C3CD06-2886-4959-8C38-AC17CDA48E6E.jpeg
     
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  6. SolGato
    Joined: May 2019
    Posts: 32
    Likes: 12, Points: 8
    Location: Kauai

    SolGato Junior Member

    I would upload some video so you can see SolGato in action, but it seems I am unable.
     
  7. Dejay
    Joined: Mar 2018
    Posts: 289
    Likes: 33, Points: 28
    Location: Europe

    Dejay Senior Newbie

    Youtube or vimeo? :) Thanks for the pictures, looks like a really cool experimental platform!
     
  8. SolGato
    Joined: May 2019
    Posts: 32
    Likes: 12, Points: 8
    Location: Kauai

    SolGato Junior Member

  9. Dejay
    Joined: Mar 2018
    Posts: 289
    Likes: 33, Points: 28
    Location: Europe

    Dejay Senior Newbie

    Haha wow that looks so awesome! Thanks for sharing.
    Really nice way to get around!
     
  10. Blueknarr
    Joined: Aug 2017
    Posts: 526
    Likes: 78, Points: 28
    Location: Colorado

    Blueknarr Senior Member

    Fun little toy.
    I suggest reinstalling original twin rudders and hanging the thrusters from the aft aka as far outboard as they can and still maintain prop clearance with the amas. Thrust differential steering will still be available at low speed with rudder steering at higher speeds. The vessel would have originally been equipped with a rudder connecting bar and hiking stick which allows rudder control from anywhere on the trampoline.

    Keep the grove on
     
  11. SolGato
    Joined: May 2019
    Posts: 32
    Likes: 12, Points: 8
    Location: Kauai

    SolGato Junior Member

    I’ve used this boat and a Hobie 14 previously as a platform to try a lot of ideas before spending big money on components like brushless motors and solar panels. Every system and design choice I have made is based on seasons of testing in the bodies of waters I frequent and based on the patterns of how I use the boat. In the Summer I use it as a dinghy to get to my Trimaran on mooring and winter to explore our rivers. The differential motors are key to being able to maneuver quickly and accurately when docking with a boat swinging on mooring or when navigating our narrow rivers with strong currents. It would be hard for me to ever go back to a traditional single tiller motor setup, as hard as it would be for me to go back to a Mono which is good because differential steering doesn't work as well on a Mono.

    The fitting of the removable rudder came about (ha ha) because a few seasons ago I was making some full speed (6.5MPH woohoo!) passes under full moon light late at night in the mooring area in Hanalei Bay when one motor lost propulsion. Of course all the boat would do is donuts and then suddenly the wind picked up and I started drifting further out. I used the one motor and the wind and beam windage to align a drift up against my buddy’s big boat where I held onto it with one arm while rewiring the controller with the other. Turns out a crimp connector had failed. Anyway, after that I decided I would fabricate a removable rudder for emergency and for sailing as eventually I planned to design a rig for the boat.

    The rudder as an emergency backup is not a deal breaker for me and certainly not something that warrants a redesign or giving up the greatest qualities of the boat. The motors work amazingly mounted where they are. I have tested single and dual motors in various positions. Hanging a motor off a beam without it being behind a transom can really affect performance, shifting loads on a small boat can cause problems if the motor motor is mounted further forward, not having a cavitation plate to provide bite for the prop can cause the prop to cavitation with loss of speed and increased operating noise, etc.. I’ve learned a lot from testing over the years which I started why I settled on mounting my motors in place of the rudders with mounts that are simply designed with two boards of Ipe hinged at the bottom with a slot cut in the board that is mounted to the transom of each hull, and the bottom board doubling as a cavitation plate. The tubular arms allow you to deploy and trim the motors easily and have collars that can be slid and locked in place for various preset trim depths catching against the board slot. At the same time this design also allows for the motor to kick up if it runs aground or strikes an object. I use 3 collar positions at the moment, one for trailering, launching, and sailing (all the way up), one for shallow water, and one for full deployment. The system allows for easy adjustment to compensate for loads or in the latest case, more powerful motors that weigh more causing the boat to drag *** a bit. By adjusting my fully deployed collar further up the tube I can get the thrust of the motors to stick the bow a bit more when at speed.

    Now I had always wanted to fit a camper shell to a small catamaran just for shits and giggles, that and because they can be had cheap and hold up well in the marine environment, so last season I ran the boat with the most deluxe high top multi window model I could find for free. Camped up river a few times which was awesome. Even had a few people think someone got drunk and drove their truck into the river! In the end, I ditched the high top shell for a hard tonneau bimini because you want to be outside but protected from the sun as much as possible, and I found my self out on the forward tramp most of the time and only under the shell during a downpour .org when’s camping. So eventually I will make a 4 panel drop down safari enclosure for the hard bimini so that I can still stay dry in the rain and also be able to camp with some privacy without squitos.

    So if you’ve ever wondered what a camper shell would look like on a Hobiecat, check this out. The boat looks like a storm trooper reconnoissance craft patrolling the the river. People would freak out a bit when I cruised by a local restaurant along the river with me inside and not seen through the tinted windows:

    WillDesignsandBuilds on Instagram: “Video footage of SolGato in action. I designed this electric boat to be highly maneuverable so I could dock with moored boats and navigate…” https://www.instagram.com/p/Bc1bk1rhxH1/?utm_source=ig_share_sheet&igshid=eyf0qu9rfhg7
    C323DB83-B8F0-45AB-836B-C7823E5E04FD.jpeg
     
    Last edited: May 14, 2019
    Doug Lord and Dejay like this.
  12. Dejay
    Joined: Mar 2018
    Posts: 289
    Likes: 33, Points: 28
    Location: Europe

    Dejay Senior Newbie

    Haha so awesome!

    I think the closer to the axis of rotation your rudder is, the less effect it will have. So moving it as far back as possible should help. And increasing length / aspect ratio might help.

    Why not tent cloth hanging from the bimini? Should shield from moskitos and rain.
     
  13. SolGato
    Joined: May 2019
    Posts: 32
    Likes: 12, Points: 8
    Location: Kauai

    SolGato Junior Member

    Thanks! Yes, tent cloth is exactly what I will probably use unless I decide to build one big shower curtain with a seam at the front. I have some sections of aluminum T-slot and a bunch of sail slides so this may be the way to go. Simple and effective, and easy to install and remove.
     
  14. SolGato
    Joined: May 2019
    Posts: 32
    Likes: 12, Points: 8
    Location: Kauai

    SolGato Junior Member

    6FD15C8E-EAAC-442D-BA48-74F173AF3086.jpeg I got the boat back out for another test. Didn’t experiment with the rudder this time out. More focused on accessing changes I made to motors and performance of solar system in less than ideal conditions.

    I made two changes to the motors -increased toe and alignment. My mounts are slotted with large backing plates, so I can adjust toe and play with alignment to offset weight. The other change was to move one of my trim collars (full depth) up the motor arms to add trim to see if I could get the bow to plane a little better when under way. The alignment and toe adjustment worked well, but the trim adjustment didn’t. Adding more trim depth caused the motors to cavitate more which created more water noise and also caused a vibration/pulsing at low speed as the props bit, so I’ll be moving them back to my original position.

    Next time out I’ll take the mast rig and an extra person and see what the attitude of the boat will be with two people at the rear and the rig up front.

    Since I use this boat in so many different ways with different accessories and various amount of people and gear on boat at different times, I’m thinking I might add a ballast bladder bag like a wakeboard boat fat sac with a high volume pump mounted in front of the main fore beam to allow me to adjust the boat in all conditions.
     

  15. Dejay
    Joined: Mar 2018
    Posts: 289
    Likes: 33, Points: 28
    Location: Europe

    Dejay Senior Newbie

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