Help me troubleshoot docking my catamaran

Discussion in 'Boat Design' started by patrickza, Nov 13, 2023.

  1. patrickza
    Joined: Mar 2023
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    Location: Adriatic

    patrickza New Member

    I bought an 1976 Catalac Catamaran with dead diesels and converted it to electric drive with two ePropulsion 6kW outboards. I also added 3200W of solar , and for the most part the boat is running absolutely brilliantly, even though I didn't have time to get the sails functioning. The efficiency of these motors combined with the large solar array means I have pretty much an unlimited motoring range dependent on speed, as long as the sun is shining:

    We also have enough power to make water, heat water, cook electrically, run the Starlink 24/7 and pretty much live like we're in a house electricity wise.

    Where the problem comes in is related to the maneuverability at low speed. The prop center lines are only 1 meter apart, and that means I don't have the leverage to use differential thrust, something I've previously relied on when docking catamarans, using "tank steer".

    The way I see it, I have a few options:

    1) Cut my losses, sell these motors and fit pods. That should solve both issues, with the downside being the inability to lift the motors out of the water in case I need to clear seagrass or fishing line. I probably lose some efficiency with the props pushing onto the rudders, and I also lost the ability to lift the motors for sailing or checking on them.
    2) Make the motors steerable. The steering bar is around 30 cm in front of the motors, but I'm not sure how to attach them, as the bar can likely move far more than the motors. Any thoughts, or is there a better way?
    3) Fit the anti-cavitation plates to the motors and hope that the extra thrust before cavitation would be enough to "tank steer" the boat.
    4) Try and find a new location for the outboards. I could move them around 30cm further apart, but I'm not sure that'll be enough. Any thoughts or any other locations you can think of?
    5) Set the motors to "toe in". Someone mentioned that if I could set the motors toe in while docking it would allow me to use the thrust for steering. The question is how much would this help, and how much toe in is the right amount? And of course how could I do this reasonably easily for docking.

    Below is a picture from before I launched to give you an idea of how the motors are placed:

    And here's one showing the steering bar before I fitted the walkway over it: SteeringBar.jpeg

    Any ideas?
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  2. alan craig
    Joined: Jul 2012
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    alan craig Senior Member

    Make the motors steerable - but you may have to introduce a lever linkage to match the steering bar range to the arc of the motors.
  3. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    What about installing a bow thruster?
  4. kapnD
    Joined: Jan 2003
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    kapnD Senior Member

    Fix them in straight ahead position for cruising, but lock one motor sideways for docking.
    Fore and aft movement by the straight ahead motor, side to side movement by operating the 90* motor forward/reverse.
    Go slow!
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  5. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    I like KapnD's suggestion above!

    Alternatively, would it not be possible to mount the motors on the transoms, rather than on the bracket between the hulls?
    They would then be fairly far apart, and would give you much better manoeuvreability.

    I like your transom extensions / swim platforms as well - did you build them, or did you buy the boat with them?
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  6. SolGato
    Joined: May 2019
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    Location: Kauai

    SolGato Senior Member

    Regarding your proposed options:

    1. I would not go to the trouble and expense of permanently modifying your hulls to install Pod versions of the same motor for X2 main reasons -the finish on most electric propulsion products is unlikely to hold up well if left in the water, and most are prone to housing seal failure due to corrosion of the sealing surfaces.

    2. A steering bar would help, but I don’t think you would benefit from independent thrust of each motor nearly as much as if you used them up as KapnD proposed. Also if a steering bar was installed, would you be able to fully tilt the motors out of the water?

    3. Anti cavitation plates will help across the board based on other large displacement applications I’ve seen with small electric outboards positioned between the hulls.

    4. This would be the most ideal way to take full advantage of independent thrust for maneuvering. I imagine your reluctance to go this route has to do with keeping your transom scoops clutter free. Maybe you could modify the motor well area to into a grand “staircase” instead and mount the motors behind each hull.

    5. I don’t think this would do much for you. Again, I would go with KapnD’s idea and fabricate a quick lock system for each motor.

    Another idea along the same lines as above is to install linear actuators instead of the steering system with an independent actuator attached to each motor that can be remotely controlled to lock each motor independently so that one could be used as a side thruster and one for forward/reverse thrust.
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  7. tlouth7
    Joined: Jun 2013
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    Location: Cambridge, UK

    tlouth7 Senior Member

    I think you actually want toe out to improve differential thrust - this would move the thrust line from each motor further from the rotation axis of the boat.

    You could just practice manoeuvring without recourse to differential thrust...
  8. patrickza
    Joined: Mar 2023
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    Location: Adriatic

    patrickza New Member

    Very interesting suggestion. I think I'll add it to my testing for next season!

    Definitely possible, and would likely solve the issues, but something I'd rather avoid if possible as it would make getting on and off more difficult, and potentially be a problem when moored stern to in strong conditions. Also if it's lumpy out they might be even more prone to cavitating. The scoops were on the boat when I bought it, and I love them!

    Very good points all around. I think I'll give the anti-cavitation plates along with KapnD's suggestion a try next season. I'll also try with both motors toe-in to see if that helps. If any of that is enough then I don't need to spend more money on steering, and I don't need to modify the hull in any way.
  9. BlueBell
    Joined: May 2017
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    BlueBell . . . _ _ _ . . . _ _ _

    Really good suggestions.

    Practice can take you a long way too.
    There is still differential thrust there, the couple is just smaller.
    Use it to exaggerate/prolong any induced yaw to your advantage.
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  10. Will Gilmore
    Joined: Aug 2017
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    Will Gilmore Senior Member

    My suggestion is to add a small bow thruster. Perhaps, with such deep rocker, you might only need a remote controlled trolling motor. You did say for very slow maneuvering speeds. A Minn Kota may do the trick for under $2000.
    Minn Kota trolling motor on Amazon
    Last edited: Nov 16, 2023
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  11. mitchgrunes
    Joined: Jul 2020
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    Location: Maryland

    mitchgrunes Senior Member

    Kind of a pretty looking boat, even prettier if you can stow your possessions out of site. :)

    You use the rudders too, to steer, right? After all, once you rig it to sail, the rudders should ideally work well enough to steer and tack, without using motors.

    Is that too heavy a boat to use boat hook(s) to pull you into the peer, or push yourself away?
  12. patrickza
    Joined: Mar 2023
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    Location: Adriatic

    patrickza New Member

    I'm going to work on this solution in the spring:
    Aside from a number of other good ideas, such as a lot of practice, and the one which said to mount one motor sideways (can't with their current positions) this to me looks like it will give me some of the benefits of both a steerable outboard, as well as being able to use differential thrust more effectively.

    In the docking setup I can use this like a standard steerable outboard and pull the rear of the boat at an angle using one motor, or I'm hoping that for example when I want to rotate left the left hand motor will pull the left rear corner of the boat towards the right, while the right hand motor will push the right rear corner in the same direction and let me turn on the spot.

    Happy to hear any feedback on the plan
  13. SolGato
    Joined: May 2019
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    SolGato Senior Member

    Not trying to be pessimistic, but I don’t think your plan will work very well given the boat length and displacement and the close proximity of the X2 motors and their props.

    Using one as a side thruster and the other as a forward/reverse thruster as suggested before is the next best thing to full independent differential thrust, but it seems what you are saying is that there is not adequate clearance for the motor heads to be able to spin 90 degrees without hitting the inside wall of the hulls?

    I still think using the motors this way will be the best option if you can’t mount them further apart behind each hull which is the only way you’ll get optimum independent thrust steering.

    I would suggest temporarily moving the motors closer together using a spacer plate to double up the transom and provide a good clamping surface and testing the idea first, then if it works satisfactorily you can permanently modify the transom mounting area for closer mounting.

    What is the max angle you can turn a motor to in the current configuration?
  14. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    personally, I'd hate to switch the motors to a different angle

    for about a grand; you can get a trolling motor that can even drop remotely

    so, you motor in and drop the trolling motor; bow preferred and push it to port
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  15. SolGato
    Joined: May 2019
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    SolGato Senior Member

    I agree, however finding a “trolling motor” that has a shaft long/strong enough to reach the water depth needed to be effective might pose a challenge given they are typically designed for low profile low freeboard fishing boats and not high sailboat bows.

    Would be easy enough to to modify a standard motor with a longer shaft, but the self deploying/remote steerable versions are a bit more complicated from what I’ve seen.

    Caroute will make motors with custom length stainless shafts.

    If the poster hasn’t converted his tender to EP, perhaps he can kill two birds with one stone and one motor can share both duties.
    bajansailor likes this.
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