Using Interceptors for Steering

Discussion in 'Hydrodynamics and Aerodynamics' started by fpjeepy05, Feb 6, 2013.

  1. fpjeepy05
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    fpjeepy05 Senior Member

    Can anyone provide any references in this area. The ideal of not carrying around the extra drag of a rudder when not turning sounds rather appealing. This would also allow the shifting back of the power train, moving back the CG. Some useful design tools.
     
  2. keysdisease
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    keysdisease Senior Member

    Have done it on small (21ft) o/b boat with trim tabs and steering failure. It can be done at planing speeds in open water with some sea room because there is nothing precise about it, but is way way too slow at slower speeds.

    Interceptors work better at higher speeds so I think the slow speed performance would be even worse with them over trim tabs.

    I also believe the hull form might play a part, a deep V might be more difficult to steer than other hulls for instance.

    $0.02 Steve
     
  3. fpjeepy05
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    fpjeepy05 Senior Member

    But what about interceptors for high speed steering and twin engines for low speed steering?
     
  4. tunnels

    tunnels Previous Member

    On what the big cats do up in the barrier reef ! the trim tabs have a curved rubber blade on there trim tabs ,straight ahead running the trim tabs are up way out of the water ,as you want to turn they lower the tab !the further down the more blade is in the water the harder the turn !!!! then lift it up and straight ahead again the trim tab on the other side had the blade curved the opposite way naturally ! so straight ahead for minor changes use the engine speed to go one way or the other . its really simple and effective and was 1985 i saw this . so nothing is new !!!! :D.;):p:p
     
  5. tunnels

    tunnels Previous Member

    AM I MISSING SOMETHING ?? THIS REALLY DOSENT MAKE MUCH SENSE AT ALL ????:eek:INTERCEPTORS ?? WHAT THE HELL ARE INTERCEPTORS ?? i invissage a slot in the hull and pushing a garden spade down the slot !!

    A good well designed foiled shaped rudder blade is very efficent and very effective and affords very little drag in the water but adds a hell of a lot of directional control and stabillity !! if there a better way the speed freaks would have found it by now !!!
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    This is nothing new, been around for ages. But it does depend upon the speed of your boat and of course how larger and far apart the interceptor is place from each other. Typical commercially available products such as this:
    http://www.humphree.com/learn-more/interceptor-guide/

    may yield quick solutions for you.
     
  7. BMcF
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    BMcF Senior Member

    Adding lateral intereceptors for high-speed steering has a lot of benefits for fast waterjet-propelled catamarans. Faster responding, than the jet nozzles, interceptors can provide tighter course keeping when under control of suitable autopilot that includes yaw damping.

    In the more advanced implementations, the steering is automated so that when the autopilot is engaged, the interceptors (or small flapped skegs too) take care of all steering and the jet nozzles remain unmoved straight ahead..until a predefined headring error threshold is exceeded, with the jet nozzles then being brough in to play.
     
  8. tunnels

    tunnels Previous Member

    Sorry not going there . :):D:p:p;)
     
  9. BMcF
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    BMcF Senior Member

    Was that response supposed to make any sense relative to the current discussion?

    If so..it eluded me.

    My experience is somewhat limited to the application of dynamic steering control so that very high-speed (40-55 knots) catamarans and slender monohulls in the 75-120m length range could maintain a course within 2 or 3 degrees of desired value, something they could/can never do with slew-rate-limited jet nozzle steering. Not to mention the rather significant savings in hydraulic power and jet steering system wear and tear that comes with keeping course with, instead, small highly responsive interceptors and/or flapped skegs.

    But I would assume that limited experience is not of much use to other possible applications. Call it a "data point".
     
  10. DCockey
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    DCockey Senior Member

    Does roll due to differential interceptor deployment for steering become a factor which needs to be considered?
     
  11. Ad Hoc
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    Ad Hoc Naval Architect

    Bill

    It's pointless background chatter...as always :eek:

    We designed a small high speed rudder..very small, to do that too...about 10years ago..fitted in on several of our high speed cat's. Works well.
     
  12. tom kane
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    tom kane Senior Member

    Dipping rudders work well, that is two curved rudders that dip in water as needed. The left rudder turns you right and the right rudder turns you left. no drag when not in use. they are a bit tricky to tune and need fast or high geared hydraulics and go well with surface drive.
    Both rudders down give high speed stops and can be cambered to give reverse thrust. Lots of fun to maneuver with in confined space.Better if they are on a trim-able shaft drive.
    A quick sketch.
     

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    Last edited: Feb 26, 2013
  13. BMcF
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    BMcF Senior Member

    The coupling that can occurr between roll (and roll control effectors) and yaw (and directional control effectors) must (*should*) always be taken in to account. Nearly all of our stabilization systems have included the necessary terms and connects to prevent adverse yaw-roll coupling.

    That said...when we employ interceptors for high-speed course keeping, they deploy in the lateral direction; sticking past the side of the transom. We've never employed vertical interceptors for anything but pitch and roll control and do not plan to...though I understand using them to augment steering has at least been tried before.

    Our "favorite" auxilliary high-speed steering effector is the flapped skeg. They are very efficient and can be relatively quite small. The two on the USN x-craft catamaran, for example, are approximately a total of 2 quare meters area each and the trailing edge flap requires less than 7 kw to operate at high rates and duty cycles. (Compare that to the power required to throw a set of the jet nozzles around..;)) Interceptors are similarly low-power-demand devices; one of the reasons they are as popular as they are.
     
  14. DCockey
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    DCockey Senior Member

    Thanks for the explaination.
     

  15. fpjeepy05
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    fpjeepy05 Senior Member

    Thanks BMcF. The reason I had asked was because I was reading about the Harley 40x10. Its my understanding that that howard himself might be a little strange. I've only ever talked to him on the phone, so I can't say for myself. He has made some very unique boats over the years. In the quest for ultimate efficiency for a high speed planning hull, I think he has a good idea. Lightweight, long, narrow, diesel to surface drive. I guess if there is less drag with interceptors than rudders, it might add that extra little bit to the fuel efficiency.

    I wouldn't buy the first one, but I have a lot of respect for what he is trying to accomplish. I think once fuel hits $10/gal he'll be one step ahead of the game.
     
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