Stabilizers, Ride Control and other wiggly bits

Discussion in 'OnBoard Electronics & Controls' started by BMcF, Mar 16, 2007.

  1. BMcF
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    BMcF Senior Member

    Any interest in the topic of 'stuff that makes boats move less'? This is a subject near and dear that can cause me to write long posts..;)
     
  2. TerryKing
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    TerryKing On The Water SOON

    "Ride Control" etc....

    BMcF, one of the great things about boatdesign.net is that we can know a lot about one thing, but admit that we know little about another.

    I know next-to-nothing about the various active and passive (is that even right?) Ride Control approaches. I'd really appreciate an overview of this whole area, assuming the reader knows simpler boats and basic boat designs, but nothing else...
     
  3. BMcF
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    BMcF Senior Member

    I asked the question, in part, because I found very little on the subject after numerous forum searches. But I wasn't sure if the lack of threads on the topic was due to a general lack of interest as well. Obviously, active stabilization is not going to be a 'hot topic' for sailboat folks (which I am also one of those too, btw;) ) or quite a few other vessel categories too for that matter.


    Then you stirred the pot about expanding the categories where such might fit in ..Jeff graciously made the change..and here we are.:D
     
  4. Tad
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    Tad Boat Designer

    BMcf,

    There are a number of articles on the Hydrospeed site, here http://www.hydrospeed.co.za

    Note the site does not work for me in Firefox.

    The Hysucat (for which Hydrospeed is a dealer?) site does not have much info at all.

    As for active stabilization of sailing vessels....I would include canting keels in this discussion.

    All the best, Tad
     
  5. Portager
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    Portager Senior Member

    Active Roll Stabilizers

    I am interested in active and passive roll stabilization techniques for my boat "Portager".

    The "Admirable" has had back surgery and she finds roll motion undesirable (she asks me to slow down for tight turns on the freeway :)) so the better the stabilization the more areas and conditions that she will tolerate.

    I plan to have active roll stabilizers for use underway and passive stabilizers (flopper stoppers) for use at anchor and if the active roll stabilizers malfunction. I believe most if not all active roll stabilizers require hydraulic power, so I plan to have hydraulic pumps of the main and auxiliary engines.

    I would appreciate a discussion of roll stabilizer options and their pros and cons.
     
  6. BMcF
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    BMcF Senior Member

    Tad;

    Quite familiar with Dr. Hoppe's foil systems..in fact a colleague and business former partner is involved with Hoppe now on some size cat project or other. That is a 'lifting' solution that increases L/D for certain (not all) cat hull types and does add some passive damping as a consequence of it's being there in the first place..but it's not an active motion control system and producing lift is the system's primary function. I've done two 'cross-foil' systems on multihulls that were actively controlled for pitch and roll damping..but one was on a big yacht..'Moecca' and the other on a trimaran demonstration testcraft.

    The canting keel thing is not one I'm familiar with..so I'll be the one needing the education on what is involved there. Could you so enlighten me?

    -Bill
     
  7. BMcF
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    BMcF Senior Member

    round-bilge hullform? (sorry..too lazy to got look up info on your boat..:p )

    Several outfits make conventional roll stabilizer fin packages for your vessel size range (Wesmar, ABT, Vetus and Naiaad to name a few). These systems all comand fin angles in response to primarily roll angular rate, though some advertise that they have three-term (even four-term) controllers (responding to angular acceleration, rate and actual roll angle..and integrated roll angle in the case of the 4-term units). Here is what that stuff means:

    A 'perfect' roll damping system (perfect in the sense that there are no lags or delays betwen measured roll rate and resulting fin position) requires only angular rate to produce the roll damping force (force of fins that opposes roll rate).

    Boats with long roll periods(tender round bilge forms for example) have low roll rates but often large roll amplitudes and tend to 'hang' longer at each end of their roll cycle. Having the roll angle term also commanding fin position, in addition to roll rate, can benefit these vessels compared to having roll rate input alone. Imagine your vessel is heeled but not rolling..if you have only the roll rate term in you stabilizer system, the fins will be centered (zero angle of attack..no lift) at that point. With the roll angle term, they will still be producing a restoring roll moment proportional to the actual heeled roll angle.

    Roll acceleration in a roll stabilizer is a means of compensating for sluggish fin hydraulics and slow control computers..though there is not necessarily anything horribly wrong with that because sluggish fin servos and related actuation hardware often last longer between overhauls than 'snappy acting' ones. But beware of the fancy claims about systems that include roll acceleration..because it is only in there really to compenste for 'low performance' hardware in many cases..thus it might be making that particular sytsem work better than it otherwise would..but does not mean that it's making that system work better than one from another mfr that has faster servos and controller unit.

    Integrated roll angle, or long-term list correction, adds more 'muscle' in terms of righting moments from the fins when a persistent heel is present..from windage, for example.

    Pros and cons? Most of both relate to whose system you buy. All are hydraulically operated, as you correctly assumed. Today's servo valves are much more reliable and far less finicky than those of 10-15 years ago and can tolerate a lot more 'bad stuff' in the oil - the number one cause of stabilizer malfunctions historically. The motion sensors are all solid-state MEMS devices now..no more expensive gyros with moving parts. A good stabilizer system design will last many years with minimal maintenance and without requiring any kind of repair or overhaul. Note the word 'good'...I'd rather not discuss specific vendor systems in here but please don't hesitate to PM me with any questions about specific packages you decide to look at and I'll give you my honest opinion. I could even help you 'pick and choose' to get the best of each..;)

    Zero-speed roll damping is now an established technology with over 100 such systems installed and working quite to their owner's delight. The fins are different in shape and balance to traditional roll fins and the top plates and actuation must be more robust. However, to my knowledge, none have been built or installed on a vessel under 100' yet...and of course there must be a source of hydraulic power available while moored. The larger yachts typically have big gensets and electric hydraulic power units..while on smaller vessels, it is usually easier to get the stabilizer power from a PTO-pump on main engine or gearbox.

    Something else to consider that is gaining acceptance - active trim tabs for roll damping/control (and in most cases pitch control too). Though usually reserved for hard-chine hulls that are operating at higher speeds (say 10 knots and above), the trim tab roll damping systems are often (usually, in fact) more effective than the fin stabilizers that would be recommended for the same hull and have the added benefits of not adding as much drag, being mechanically simpler (hence more reliable) and easier to install and not vulnerable to strike damage. For vessels with speeds above 25 knots or so, which is the typical limit for fins, the active trim tab solution is the only option for motion damping. Another 'cool' thing about active trim tabs is that the zero-speed control algorithms work quite nicely..but again there is the power required at anchor thing to deal with.

    Active trim tabs take a bit more power to operate than fins do though. They are also considerably larger than their 'Bennet' bretheren and should be 'hidden' under protective cover of a swim platform to avoid striking them against quay walls and such. Tab on a 57' pilot cruiser hull shown in pic so you get what I mean. The swim platform was not installed yet.

    [​IMG]
     
  8. Tad
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    Tad Boat Designer

    Bill,

    Apparently I'm just another guy talking before thinking.....:D

    Agree that the Hysucat foil system is passive and thus outside this discussion. Flume tanks and dagger boards interest me, but I'm not sure where they fall in the active/passive strata? Gyro's and moving weights used to interest me, but the added weight and power requirements are negative factors. Currently much more interested in what can be done with fixed or retractable bilge fins (non-powered).

    The tabs in your picture are interesting; width is about 1/4 beam? Length about 2/3's width? You mention they are more effective than fins? Is this due to added area or lever arm? How about burying them under the boat, flush with the bottom, as is done with trim tabs? Or do they rotate up a lot?

    Thanks for the clear discussion of the fins above.

    All the best, Tad
     

  9. Portager
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    Portager Senior Member

    Thanks for the overview BMcF, it was very helpful.

    Portager will be an aluminum hull, so she will have a hard chine. She will be ~58' long and have a 12' beam. Empty weight will be ~32,000 lbs and fully loaded she will be ~44,000 lbs. She will have a semi-displacement hull with a maximum speed of 11 knots full-load and 12 knots empty, but cruising speed is 8 to 9 knots, so tabs probably wouldn't work very well.

    Power is the main problem with zero speed active stabilization. I do not plan to have an AC generator and an electric hydraulic power supply would probably drain the battery bank pretty fast. I'd probably need to run the auxiliary, which would mean noise. Not to mention the noise of the actuators.

    I like the idea of using passive roll stabilization on the hook. I can deploy the flopper stoppers and have minimal roll and peace and quite. The passive roll stabilization also provides a back-up for the active system.
     
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