Simpler stability underway ?low buck,

Discussion in 'Powerboats' started by FAST FRED, Jul 3, 2006.

  1. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    I look at the two main forms of power cruising stability and don't like what I see.

    Paravanes seem to work but require masts and gear that increase the vessels air draft ,,UGH Bridges are everywhere and low boats are easier to cruise.

    Fancy stabelizers require vast electronics and gyros and a power source to operate , not likely to be owner repairable.

    My concept is a centerboard trunk that has a shaped centerboard with an almost balanced tab at the rear. On running aground it would swing up as any board .

    For stability operation the tab would be able to give a good curve to the board and should be usefulkl to controll the roll.

    Power ?, the watch stander gets to be the gyro and power with a simple rudder bar as found on small aircraft.

    Light line and blocks could transmit the modest power , and IS repairable onboard.

    Hopefully the center board antiroll system would not cause a helm change , we dont need to keep the watchstander THAT busy.

    Will it work on a 39.5ft X 7.5 beam, container shipable boat?

    Hopefully,

    FAST FRED
     
  2. jehardiman
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    jehardiman Senior Member

    1) There is nothing wrong with a slack bilged power boat rolling at a modest period, indeed, most of the most stable do roll some. It is only where the periods are too long or too short that it becomes uncorfortable. Edit to add, that is as long as it doen't have a stability problem. And please do note that there is a difference betwen what is precieved as a "tippy" boat and what is true stability

    2) Bilge keels...it don't get no simplier

    3) Tuned anti-roll tanks, dirt simple but can get you into trouble if too small.
     
    1 person likes this.
  3. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    My current boat HAS bilge keels and they do reduce the roll a bit she still rolls merrily along.

    With the concept of a box boat , 39 long and fits in a std sea land shipping container 9ft 5 inches high , just under 8ft wide the space required for Framm or other internal slosh back & forth stabelization would be hard to find.

    So the question remains , could a simple "loose" centerboard with human trim controll, cancel as much roll as current electric Quantum or similar systems?

    On an aircraft the rudder induces some roll , can it be powered by foot power?

    FAST FRED
     
  4. Busman1965
    Joined: Jun 2007
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    Location: Florida/Bahamas

    Busman1965 Junior Member

    Centerboards are noisy, when they roll, as they have no side load from sail pressure, which is very annoying!!! Paravanes are no big deal to rig, and you can always make the mast in a tabernacle, to lower, easy. I have been using them for years on my troller, and they are the best cheap way to stop roll. I tried batwings....useless, tried bilge keels.....not much help, lots of drag, paravanes cost me $500 for the mast, wires and the vanes (Kolstrand's). After 15,000 miles of sea time with this system, I would not ever leave port without them!!!!!!
     
  5. Willallison
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    Location: Australia

    Willallison Senior Member

    I've seen a couple of commercial fishing boats what I'd describe as fold-up bilge keels. (Perhaps these are the same as Busman's batwings?). I'l try and find a pics and post one.
    Most have been fairly crude in nature - just a lrage, flat plate that is hinged just above the chine. When not in use it sits flush against the topsides. When lowered, it's held rigidly in place by the lowering mechanism.
    I can't attest as to their effectiveness, but they would seem to overcome one of the biggest potential dangers inherent in using paravanes - that being if one leaves the water and "enters" the cabin....
     
  6. Busman1965
    Joined: Jun 2007
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    Busman1965 Junior Member

    Paravanes

    I've worked on fishing boats my whole life, and have never seen a paravane do any damage to a boat, other than banging against the side when being deployed or retrieved. If they are allowed to go deep enough, they will not come out of the water. I have experimented with them on a short tether, just to see what happens, and if they do pull out of the water, they just sail right back in again. I could not imagine how you could get one to hit the boats hull if you try!
     
  7. tgwhite
    Joined: Oct 2006
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    Location: lima peru

    tgwhite tom white

    The difficulty with paravanes is largely esthetics. On newer waxed and polished boats they just don't sell. For coastal cruising they can become a nuisance, chasing crab pots and the like. So for newer coastal cruisers active stablizers are not necessarily a bad option. Within the active stabilizer arena they go from well designed and reliable to misdesigned and not workable. So FF's quest is not far fetched. I must say, my active stabilizers are a nice add on. Bluewater use though, why not both - like Dashew did on the Windhorse?
     
  8. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    "So FF's quest is not far fetched. I must say, my active stabilizers are a nice add on. Bluewater use though, why not both - like Dashew did on the Windhorse?"

    The problem with flopper stoppers is the need for a strong tall point to attach them , AND the drag under way , usually 1/2K to 1 K on displacement boats.

    The active stab is great , but very pri$y if it is to retract into the hull when not needed , or when aground , to keep from holing the boat or being damaged.

    The centerboard with control tab for stabilizing would suffer no problem in being retracted , or running aground.

    With a mechanical emergency setup , it could still operate , with no electric aboard.

    But what the proper location would be , will need a NA to work out to not also steer the boat.

    FF
     
  9. bananabender
    Joined: Apr 2006
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    Location: Australia

    bananabender Junior Member

    Stabiliser options

    Given this a lot of thought as I have a 40' Roberts steel displacement boat with a three second roll period - paravanes would make the boat look like a prawn (shrimp) trawler and pose structural challenges with ply topsides, active systems seem horribly complicated and expensive. Anyone considered hydraulically operated hyrdrofoil type with a manual joystick topsides... this would allow the anticipation advantages that a good helmsman gives in a following sea when the corrections are being made before the boat slews. With a deep keel the foils could be horizontal under the hull with the possibility of a support strut at the outer end. Bit more wetted area/drag but seems minor. Alternative auto control could be via a damped pendulum with appropriate sensing similar to power steering... any thoughts?
     
  10. jehardiman
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    jehardiman Senior Member

    3 seconds is pretty fast and may be the reason that it feels uncomfortable. What you might need is a longer roll period, not a shorter one.
     
  11. bananabender
    Joined: Apr 2006
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    bananabender Junior Member

    Stability

    Couldn't agree more... just a bit reluctant to start stacking mass topsides. I have considered even a single mexican hat roll stopper when anchored which would help somewhat without too much rigging junk and at least the Skipper could cook in comfort. The travelling options are still a challenge. Does anyone have any idea of the magnitude of the forces involved? It seems to me that to stop 15 tonnes of boat from going where nature intends needs a significant number of foot-pounds which has to wind up somewhere.
     
  12. Pierre R
    Joined: May 2007
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    Location: ohio, USA

    Pierre R Senior Member

    I thought that the paravanes would cause significant forces as well but I have been amazed at how little they actually pose.

    I have a 5 ton boat with a quick roll period. I have 105 square inch fish on 9' poles. I have a center mast mounted attop a white cedar pilot house. I have internal halyards that I can work from inside the pilot house.

    At a 6 knot cruise I can uncleat the halyards and actually haul up the fish by hand. I have only one mast top pully and no mechanical advantages. The halyards are 1/2" multi braid dacron. My total bridge clearance is 15'5"

    I have snagged the bottom in shallow water at full cruise speed. All it did was yank me about 10 degrees off course and yank the fish back off the bottom. Yup, I collected a crab pot and got yanked around and had to untangle it. I have had the booms under water, seems to cause no real problem. The fish have come out of the water without causing a problem. I have not broken anything yet.

    Yes you will look like a shrimper. I would like to have a dollar for every knucklhead who said "Hey, there ain't no shrimp in here" or everyone who tried to buy shrimp from me when I came back into port and that is in Lake Erie.
     

  13. FAST FRED
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

    "Couldn't agree more... just a bit reluctant to start stacking mass topsides. "

    If its an at anchor problem a simple system of hoisting a weight aloft shouldnt be that big a problem.

    Fish boats used to hoist the anchor in heavy weather.

    A few 50 lb (so you can stow them) , lead weights and a halyard might cure the harbor quickness.

    FF
     
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