Needs to maintain cat steering floating downriver

Discussion in 'Multihulls' started by Markusik, Dec 6, 2018 at 1:48 PM.

  1. Markusik
    Joined: Jun 2017
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    Location: Lake Michigan

    Markusik Junior Member

    We intend to do several trips downriver in a sail catamaran with masts lowered. Think Mississippi, Tombigbee, and Danube rivers.

    Without some speed difference between the flow of water and the boat, the rudders won’t produce much in the way of lift, just drag. I know the answer is “it depends” (on windage, conditions, rudder size and shape, etc.), but in general terms how much speed difference is required to maintain rudder steering when floating downriver?

    A potential cat currently for sale is 12m LOA 7m BOA 0.9m draft ~5000kg with mini keels and small skegged rudders. A hypothetical pre-design cat I’m contemplating is 14m LOA 7m BOA 0.45m draft ~6000kg with leeboards and midsize kick-up balanced elliptical spade rudders. Both use petrol outboards in bridgedeck wells for auxiliary propulsion. We won’t be in any mad rush, and would prefer not to use the petrol outboards more than necessary.

    I’m aware of issues with using pounds of thrust, but do you think a fore bridgedeck mounted electric trolling outboard (with remote control for deployment and +/- 180 degree rotation) producing 112 pounds of thrust would be any use to maintain steering when floating downriver, alone or together with rudders?

    Thanks,
     
  2. JamesG123
    Joined: Mar 2015
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    JamesG123 Senior Member

    A 112 lb. trolling motor should be more than enough for steering and for fine maneuvering in tight spaces. Hardest part will be deciding when you need to deploy it or keep it hauled up to minimize drag.

    Edit; cheapest, easiest solution of course is a skeg to lazily wag when you need to.
     
    Last edited: Dec 6, 2018 at 8:43 PM
  3. Richard Woods
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    Richard Woods Woods Designs

    The traditional way is to use quant poles to keep off the banks. But I doubt you'd want to do that for 1000miles. They used to do it on the Tamar but that's only navigable about 20 miles. I would think you sensibly want to maintain 4 knots through the water to be able to steer safely. And maybe faster if there is a crosswind (always worse than wind from dead ahead)

    RW
     
  4. JamesG123
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    JamesG123 Senior Member

    Or in any body of water that has fast mover or commercial barge traffic with serious people on board with their Coast Guard/River Police on speeddial, who would have zero patience with a private boat drifting back and forth thru the channel...
     
  5. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Not a fan of the 112# troller. Gotta admit it.

    Stick to a gas engine. Batteries won't support the adventure.
     
  6. JamesG123
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    JamesG123 Senior Member

    Boat in question has an gas outboard main engine. This is just for something to maintain positive control while drifting downriver without having to fire it up.
     
  7. fallguy
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    fallguy Senior Member

    Totally good then. Sorry friends. Carry on.
     
  8. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Controlling a drifting boat sounds like an oxymoron to me. And if the drift is slow, and with an adverse wind, you could be going upstream rather than down.
     
  9. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    I'd say 2 - 3 knots (speed through the water) while under sail to maintain reasonable control by rudder, depending on sea conditions.
    If it's an efficient cat, your river drift rate may give you enough apparent wind to sail on a calm day.
    Interesting question.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    He is going to have the sail rig lowered for the duration.
     
  11. BlueBell
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    BlueBell Ahhhhh...

    Right, my mistake.

    Then a drogue is really the only option, no?
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    The boat needs to be under power at all times, even if only idling, or there is no control.
     

  13. gonzo
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    gonzo Senior Member

    The barges have right of way and small recreational traffic must stay clear. A small trolling motor would not be adequate. The whirlpools from the tug propellers can make a smaller boat turn around at half a mile away. The rooster tail can be up to 18 feet tall. You need enough power to maintain control. I have done the Mississippi on a 25 foot monohull. When you go by Baton Rouge, the USCG will assign you a number for traffic control. You are required to maintain speed for maneuverability and to get out of the way.
     
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