Planing Trimarans

Discussion in 'Multihulls' started by Doug Lord, Sep 30, 2006.

  1. Doug Lord

    Doug Lord Guest

    planing tri

    This thread is about all F boats as well as about the F22-just review the posts as well as
    the definitions in post #1. And it is not limited to just F boats either-see the discussion about Jim Antrims 30 footer with outside hulls he describes as "planing ama's".
    When the F boat heels the ama absorbs some of the weight of the boat unloading the main hull allowing it to plane-as designed by Ian Farrier, proved by the science, and confirmed by the owners. And, like it or not, no debate will alter the science, the design or the opinions of those experienced with the boat(s)/technology.
    Case closed(for all practical ,non-linguistic, non- semantic purposes).
  2. Dan S
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    Dan S Junior Member


    Thanks Doug, I really needed a good laugh; I almost spewed coffee all over my keyboard.
  3. BWD
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    BWD Senior Member

    From the Farrier videos it is very clear. Look up the displacement of the amas. Look at the waterline on the amas. Look at the wake of the ama and the vaka.

    The alternative hypothesis is the main hull is not planing. Yet it leaves a flat wake and is sailing above its lines. Yet the ama is not depressed. Therefore it must be being held up by a Sikorskiy or something. That could also explain the speed.... but honestly, I don't see any skyhooks there folks....

    Reductio ad nauticam.
    Planing is as planing does!
  4. CT 249
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    CT 249 Senior Member

    How is it clear?

    You refer to the displacement of the amas; unless we have some way of measuring the volume of the amas and an accurate estimate of how deeply they are immersed at the time the vids were taken, we don't have any way of knowing how much of the displacement is being taken by the ama. In my recollection of sailing Farriers (some time ago) the ama was clearly depressed at speed. Therefore it could be the case that the displacement was simply being transferred. Of course, maybe the depression of the ama wasn't enough, and the main hull WAS planing - but until we have more evidence surely we have the right to remain undecided.

    Look at

    The amas in the boats that are powered up and moving fast are clearly depressed significantly more than the amas of the boats that are moving slowly or stopped. So it seems clear to me that there is a significant shift of weight into the ama at "planing speed". We simply haven't been given enough detail to prove wWhether all of the lift of the main hull is due to that or to planing. It can't be as simple as saying that if the ama doesn't look depressed and the main hull is sailing above its lines then the main hull must be planing. Look at the pic enclosed here; the knuckle of the ama is out of the water so it doesn't look too depressed. The main hull is clearly sailing above its lines - so is the main hull planing? On what - air?

    One thing I found interesting was that I thought I could clearly remember racing against Trailertri 680s and 720s and seeing them semi-planing. However, look at the hull sections of the TT680 and TT720 from the Farrier site, and compare them to the hull sections of the F22. The later boat is clearly much, much flatter and capable of developing much more dynamic lift (especially since it would be inherently quicker anyway). So does the TT720, with its much more Vee shaped hull, really plane as well - or did the 720 just look as if it was planing because the load was being taken by the ama? Or is the 720 hull fat enough to generate planing lift?

    We already know that what even the best sailors and designers think is not conclusive evidence about whether a slim hull planes, because even the best Moth sailors and designers are divided on the issue. If it was as simple as looking at a boat, then we wouldn't have the case where the guy who invented the narrow Moth thinks they don't plane, and the guy who creates the latest ones thinks they do. We wouldn't have a case where one multi world champ thinks they don't plane, and another thinks they do.

    I still think the case hasn't been 100% proven by science here; you could argue that it's little use to use ratios derived from monohulls which are fatter, since greater beam is efficient in planing hulls. To quote one excellent source, confirmed by another excellent source; drag from planing is "inversely proportional to the square of the width of the planing surface and inversely proportional to the square of the speed. So a wide hull producing the same amount of dynamic lift will have less drag from that source than will a slender hull carrying the same amount of lift."

    The Moth designers illustrated this; Doug C and Alan Smith referred to the fact that narrow hulls plane later than beamy hulls. Since this factor has not been allowed for in the "science", surely the case remains unproven. This doesn't mean the F Boats DON'T plane. One of the sources I quoted above says they do, and he's in an excellent position to know. All I'm saying is that the "science" AS PRESENTED HERE IN THIS THREAD seems to have some holes that means it can't necessarily be taken as proof.

    The problems of theoretical calculations are underlined by the fact that another recent study showed a 27% shortfall in "real life" performance compared to the calcs. The problems of discussing planing are underlined by the fact that there are many quite different definitions (as Savitsky points out). Since even the gurus have different definitions of what "planing" is, how can we laymen be so adamant that our own definitions of planing are right?

    This is NOT saying that Farriers don't plane. They may well do so. On balance, I'd vote that they do. We know that even slim hulls can plane surprisingly well. I'm just saying that it seems reasonable to find the case not 100% proven ON THE EVIDENCE PRESENTED HERE.

  5. BWD
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    BWD Senior Member

    Well, you're right CT. Maybe not so clear. Looking at the vids again, the amas do look dug in more than I thought.
    And certainly there are lots of tricky situations. I still think it's likely the F tris plane pretty often though... Sorry if I polluted the thread a bit -it's a good one!
  6. fhrussell
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    fhrussell Boatbuilder

    Out of curiosity, what is this study you mention? Is it a study only regarding F-boats or is it more general?
    Thank you!
  7. Doug Lord

    Doug Lord Guest

    planing tri

    This is a summary of the science that has been used to prove that the F22 will plane. However,I've added information relating to the F24 to show that the ratios and formula agree with a boat that is already sailing and are not just theoretical as on the F22. Further, I have added a formula from Sailing Yacht Design that takes into account the planing area of the hulls.
    A) F24 2010 sailing weight 364 sq.ft. upwind SA
    17' cl-cl beam (NOTE_ the F24 requires about 1.75 knots more wind to plane than does the F22. That translates to 1.25lb. per sq.ft. pressure.)
    1) Sq. Ft. per ton: 364 sq.ft. upwind SA ; main hull load 1222 lb. in 1.25 lb. sq.ft. pressure;2200 divided by 1222= 1.8 ; 1.8 X 364 = 655. This equals 655 sq. ft. per ton/ 500 required to plane.
    2) The F24 center of buoyancy moves 3.332' to leeward in 1.25lb pressure with the ama absorbing 788 pounds of the displacement leaving a load on the main hull of 1222 lb.. The all up weight is 2010 and the righting moment is 3.332 X 2010=
    3) To apply Bethwaites "SCP divided by total weight" formula to the F24 the load absorbed by the ama (788lb.) is subtracted from the total weight: 2010-788= 1222lb =main hull load.
    SCP(sail carrypower) = RM divided by CE-CLR distance=6697 divided by 14.72= 455 .
    SCP divided by main hull load=455 divided by 1222lb.=37% According to Bethwaite 30% and above allows upwind planing.
    4) planing formula from Philips-Birt= Displ.(main hull load) divided by [ area of LWL plane in sq.ft. X LWL in ft.} = 1222lb. divided by [ 48 X 22.67]= 1.12 International 14=1.22 ; International Canoe .82 According to Birt some degree of planing can be expected up to 1.5 .

    B) F22 1800lb sailing weight 294 sq.ft.upwind SA
    17' cl-cl beam
    1) Sq.ft. per ton: 294sq.ft.upwind SA ; main hull load 1200lb in 1lb.sq.ft. pressure.2200 divided by 1200=1.83 ; 1.83 X 294=539 . This equals 539 sq.ft. per ton when 500 sq.ft. per on is necessary to plane.
    2) In the original example given in post #1 the F22 ama is displacing 600 pounds
    and the main hull is supporting 1200 pounds so the CB of the boat has moved one third of the distance between the main hull CB/CG and ama CB to leeward or .33 X 8.5 = 2.8' . So the righting arm (2.8)times the total boat weight(1800)
    3) Bethwaites ratio "SCP divided by boat weight" applied to the F22 means that you subtract the displacement of the ama(at 1lb. per sq.ft. pressure) from total boat weight(1800-600 =1200) to arrive at the actual loading of the main hull:
    SCP=5049 (RM) divided by 12.75(CE-CLR distance)=
    396. The ratio "SCP(396) divided by total weight( load on the planing hull=1200)" = 396/1200= 33%.
    According to Bethwaite anything 30% and above is capable of upwind planing.
    4) planing hull formula from Philips Birt;
    Displ. in lb. divided by [LWL plane in sq.ft. X LWL in ft.]= 1200 divided by[ 46.1 X 21.74]= 1.19
    International 14=1.22; International Canoe .82
    According to Philips- Birt some planing can be expected up to 1.5 .

    From before:
    "It is simply absurd to use any other figure for the load on the planing main hull than the actual load; if the total weight of the boat was used it would not plane(in addition to being completely inaccurate). You must deduct the displacement of the partially immersed ama to arrive at the actual load on the planing hull....
    Once you understand that the numbers all fit from the old axiom "500 sq.ft. per ton" to the
    Bethwaite formula ,to the SA/D."
    Add to this information the planing formula in the book Sailing Yacht Design by Douglas Phillps-Birt that takes into account the planing area of the hull and is shown above for both boats and you have irrefutable evidence of the fact that both the F22 and F24 plane. The F24 info was added above to show that the ratios and formula work and agree with the ACTUAL OBSERVED PERFORMANCE of an existing boat as opposed to being "theoretical" on the F22. The Philips-Birt formula places the "planability" of the F22 and F24 very close to(slightly better) that of an
    International 14( 1.22) ! Ian Farrier said to me that the F22 will plane earlier than any other design he has done and the facts above back that up showing the F24 needs about 1.75 knots more wind to plane. I would not have been able to apply the Philips-Birt formula without the information kindly supplied by Ian Farrier and I thank him for that and for his participation in this thread.
    It is completely absurd to use a study about a hydrofoil PROTOTYPE( as CT249 did) to cast doubt on PROVEN ratio's and formula's used for decades to evaluate performance and that are shown to match exactly ACTUAL OBSERVED PERFORMANCE in the case of the F24.

    One thing I want to say is that Ian Farrier has produced 2000 boats over something like 30 years
    and his description of how his boats perform is backed up by the owners of the boats.(see the f-boat forum)
    You don't really need a damn formula: if Ian Farrier says the boat planes, it planes......
    Last edited by a moderator: Oct 24, 2006
  8. CT 249
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    CT 249 Senior Member

    FH, it's not an F-Boat study but one about a foiling cat, brought up on this forum by the thread originator. I used it because it was fresh in my mind.

    The foiling cat is the subject of a master's thesis and the product of a bunch of uni guys. They're obviously cluey guys but the real-world speed is about 30% less than the calculated speed. So even when (as in the foiler's case) the calcs and testing are undeniably vastly more sophisticated than some of the rules of thumb cited here for planing, the result is still out of whack. Add in the fact that many of the rules of thumb for planing in this thread are related to monos and not to more slender tris and there still seems to be room to say that the proof as presented here allows for reasonable doubt.

    This isn't doubting that F boats plane, or doubting Ian Farrier's word. After all, we're not doubting the word of Nigel Irens when he says things work differently to the way Laurent Proviot (sp?) says; we're not doubting the word of one Moth designer when he says they don't plane or they plane at a different speed to what another designer says. We're not doubting the word of Phil Morrison when he says his 14 shape is better than Paul Bieker's, when Bieker says his shape is better than Phil's. It's just differing opinions on a subject that has few hard and fast rules.

    Hi BWD, you're not polluting the thread as far as I can see! :)

    PS - Doug, it's not absurd to use foiling calcs to show the general problems involved in using rules of thumb and theory to predict actual performance. Those involved in the foiling cat seem very smart. They used "mathematical model used for design and the one fifth and one third model test results". YET THEY GOT IT WRONG. That is a clear example of the fact that numbers do not equal proof of real world performance.

    Secondly, if it is absurd to use a foiler in a multi thread as a very general philosophical example of the problems of performance prediction, then it's at least as absurd to use monohull ratios as a specific prediction of a multi's performance. Your ratios using planing area don't address planing beam. Planing beam and planing area are not the same thing. The calcs you present are from mono designers about planing monos.

    Thirdly, many of the ratios you present as "proof" that F boats plane also apply to boats that certainly do NOT plane. As far as I can see, the Taipan 4.9 fits into the planing regime according to the Phillips-Birt rule of thumb- yet the very experienced designers and all or most of the top sailors say it doesn't plane.

    Something like a Crowther Twiggy would also fit into the "planing regime" according to your rules of thumb.

    3200 lb / (say 80ft2 x 28 lwl = 2240) = 1.4.

    But the Twiggy wasn't designed to plane and it doesn't plane.

    The Marstrom M20 cat is 20 feet long, just 115kg sailing and has 10.5sq m of sail. It is very definitely a "planing boat" according to your rules of thumb. Yet the Swedish Speed Sailing Challenge team refers to as a "non-planing" boat. That's a team with two fluid dynamacists (one with a PhD) in it. Marstrom themselves refer to the M20 as a "semi planing" boat and then apparently only downwind.

    Here we have a boat with awesome specs that definitely class it as a planing hull according to your tests - yet it's not a true planing hull according to fluid dynamacists or its designer. Once again, your rules of thumb have identified a boat as being a planing hull, when in fact it clearly isn't.

    Malcolm Tennant, vastly experienced multi designer, writes about a comparison of resistance curves "for a displacement catamaran and a planing catamaran of the same displacement..... (and) very similar dimensions, including length and horsepower."

    So according to Tennant, we can have two multis that have the same displacement, length and horsepower - yet one can be a planing hull and one a displacement hull. Therefore once again, we see that the planing/displacement question involves more factors than you have mentioned in your rules of thumb. Tennant says that a displacement hull has a different sectional shape to a planing hull - yet this is a factor your rules of thumb ignore. It's also interesting that Tennant also says "it is not possible to separate the planing and displacement catamarans on a straight performance basis in the same way as is possible with monohulls." While this is is a reference to power cats, it may also be seen as an indication that monohull planing concepts may not be applicable to multis very easily.

    Clearly not all boats that fit into the planing regime according to the rules of thumb actually plane. Therefore, the fact that a boat fits into the planing regime according to your rules of thumb is not proof that it actually planes.

    That's not saying that the F boats don't plane. I think they probably do. It's merely showing that the case has not been proven by the rules of thumb presented here.
  9. fhrussell
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    fhrussell Boatbuilder

    Thank you, sir, for the clarification!

    In design and calculations, it is always interesting to discover the calculated performance vs. the real world performance. I have done some calculations on some designs 'post build' and some where I 'back-tracked' on a design (not mine) to see if the calculations were 'real world'. I find that there are usually dicrepancies..... Maybe I have funny math.......:)
  10. Dan S
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    Dan S Junior Member

    Your math’s not funny; it’s the math some people use to support claims that’s funny. Some people get all puffed up and bent out of shape, when the grade school formulas they live by don’t bare fruit.:rolleyes:

    I come from a science background, and a professor of mine once told me “anything simple isn’t worth studying.”
  11. RHough
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    RHough Retro Dude

    What do the "proven" ratios say about this:

    LOA: 16 feet (4.87 meters)
    Beam: Overall: 8 feet (2.44 meters); Hull: 3 feet (.91 meter)
    Displacement: Hull weight: 150 lb (68 kg); ready to sail:190 lb (86 kg) ;crew:2 -320 lb (145 kg.); minimum crew: 250 lb (113.6 kg). all up sailing weight: 510 lb (231.8 kg.) with minimum crew:440 lb. (200 kg.)
    Sail Area: upwind:182 sq. ft. (16.9sq. meters); downwind: 332 sq. ft. (30.8sq.meters) including 150 sq. ft. (13.9 sq. meter) spinnaker.
    Foils: two: one on daggerboard; one on rudder
    Draft: foils down: position one: 2 feet (.6 meter); position two: 3 feet (.91 meter)

    I'll bet the "proven" ratios say that this boat will foil successfully ...

    In the the time I've spent on this forum, I have yet to see Mr. Lord be able to "prove" anything. It seems to me that when confronted with questions that require more than plugging number's into a cook book, he struggles, and starts calling contrary positions "absurd" ...

    The very fact that Mr. Lord says Farrier Tri's plane makes the statement doubtful.

    Cookbook design?:

  12. Chris Ostlind

    Chris Ostlind Previous Member

    Quick... Somebody call the guys in Iraq

    You will have to forgive me for not being more timely with my response on this, but... I had left the building late last week to go watch my daughter play college soccer in SoCal and to go surfing with some very old friends in 6' waves at Trestles.

    Hey, Ian said I needed to get outdoors. Trouble is for Ian, I had the departure scheduled long before he had a chance to drop his epithet. The guy who he should be sending that message to is none other than our resident Hypenstein.

    Couple of things in response to Ian's last letter:

    1. When will you quit making the claims for planing when you unweight your vaka hulls through the amas?

    2. Your videos have been watched... repeatedly, and I still don't see any significant indication through the imagery, that there is any planing capacity being demonstrated. I see maybe, sorta, kinda,... ahh, it's really surfing going on there. This is especially true when one considers the submerged ama argument against the entire planing claim.

    I wonder, have you ever taken the time to hire a professional cameraman with specific instructions as to what to look for and what angles on the boat (or chase boat) may actually create the desired, end result? If you want it to be really well done, then hire a multi-camera crew, have them roll tape on all scenarios in unison with matched time codes so the tapes can be referenced correctly and provide a factual, non-intoned narrative to support the prepared documentation… if you can.

    I wouldn't expect the videos to show anything even close to the claims (or the inability to meet the claims) without a person who was trained and experientially qualified to render the proper imagery. The simple process of getting an engineer out on the tramp (or wherever) to shoot a cheesy, amateur camera in the general direction of the vaka hull is not the answer.

    Instead, what we see is non-attributed video with absolutely no reference to the statistical evidence of the particular shooting session for reference.

    If this aspect of your design work is so important that you repeatedly make the claims, why then do you not spend the money to properly document the phenomenon so that interested and educated persons may analyze it for content? Without this proper, scientific documentation, you are simply claiming that which is not in existence. It then reverts to what is known as marketing hype.

    Now, marketing stuff for marketing sake is really OK as far as I'm concerned, as boat stuff needs to have some marketing representation in order to fluff things up a bit for curb appeal, as it were. But fluff is not science, it doesn't purport to be scientific in nature and it doesn't have to follow the regimen that technical claims must adhere to in order to have legitimacy. We can take a shot or two at your marketing hype position for that purpose, but it doesn’t really go anywhere because nobody really expects marketing hype to be factual anymore. So, which shall it be? Of the real side and properly presented... or of the marketing side and filled with that snazzy, Devil May Care, sort of attitude?

    Others on this forum have already listed numerous references for you that show that simple, "paper proofs" are not appropriate in light of this particular area of nautical design work. Perhaps the work of the Marstrom guys is not professionally definitive enough for you as an indicator. Yet, Marstrom has chosen the less fluffy side of the claim scenario in order to keep it under control and not have to answer to the “Hey, Wait a minute” folks, who are now everywhere on this planet with very specifc knowledge in their hands.

    You can't get dinged for outrageous claims which you did not make.

    Take a look at Post #158 on page 11 of this discussion and contemplate what the paper ideology looks like when compared to the reality of other, top-flight designers. Stunning ain't it?

    You say,
    and yet, BWD of the forum says,
    I'm now more than curious... just which wake style is truly indicative of an efficient, sailboat planing hull in all its glory... if either are? Is it a crappy rudder system? Is it planing? Is it going too slowly?... or is it all just more hype? Is it because the rooster tail that you mention in your quote is a distinctly specific indicator for a prop driven craft? Who knows, really, since the whole thing is systematically obscured for clarity.

    You might want to clear all that up because it doesn't look to be very consistent to me as well as a lot of other people

    It comes down to this, Ian... Just how do you depress an ama as a means of weight unloading support for the vaka hull and still call the situation "planing"? I would request that you not haul-out the previously tried argument;
    That argument would be more than dandy if the sailboat in question were a monohull and not dependent upon an auxiliary flotation form in order to get the main hull to the suggested planing state. And that is where this argument hits a really big snag.

    To coin a familiar phrase from a previous post on this thread... "I guess the old saying that there is none so blind as those who continue to make false claims, is actually true."

    Now, to you Doug...

    You don't have to answer the question I put to you in my last post regarding your reverence for Ian Farrier as God. (as if you ever would actually acknowledge the obvious)

    This last bit from you pretty much proves the whole issue to anyone who would read between the lines. My only question would be.... Would that be in the Eric Clapton style of God worship or would it be in the whole enchilada, Jesus style of things, Doug?

    There is a difference and you should know what it is.
  13. Willallison
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    Willallison Senior Member

    Chris, I can see that this is some kind of personal crusade on your part. And (as from the beginning) I want to have no part in arguing for or against that.
    But can you answer the proposition that I put fwd before.
    Is a rigid hull inflatable powerboat, that is partially supported by its inflatable tubes, considered to be planing in your opinion?
  14. Paul B

    Paul B Previous Member

    Hope you had a good time at Trestles. Our friends in local gov't are doing their best to close it off for good with a toll road going through there.

    I want to make clear now, before saying anything, that I AM NOT AGREEING WITH LORD ON THIS TOPIC. I have not seen any "proof" of planing.

    However, there is an F24 sitting on her trailer two spaces down from my boat in the yard. There are a couple of Melges 24s a couple of rows over.

    My monohull keelboat is a bit longer and heavier than the F24, at 8.5 m and 850 kg. My boat planes. Recently we sailed for more than a half hour at 15 to 20 knots in dead flat water in a river. Pure planing, very little heeling moment with the wind aft of 150 degrees true.

    Melges 24s plane, no doubt about that. They have a bit more sail and are a bit lighter than my boat. They are about 50 kg lighter than an F24.

    Looking at the F24 hull shape it is definitely not as much a planing surface as the Melges or my boat, but it is fairly flat buttocked and has a good bit of area to build hydrodynamic pressure up under the mast.

    If you sailed the F24 at about 160-170 degrees true in 25 knots of wind with a nice ASO kite up, sailing fairly flat (little to no heel, amas not taking much load at all) I suppose the boat should pop up on a plane. I haven't seen it, but I can't imagine why it wouldn't.

    I suppose most multi guys would not sail this deep, they would be reaching more. With the ama depressed and taking load I'm not sure I would say the boat is planing. What sort of sectional shape is presented when the boat is pressing the ama? Is there a good planing area for building pressure?

    Attached Files:

  15. Chris Ostlind

    Chris Ostlind Previous Member

    Hi Will,

    The beef is entirely that the component elements of a given, complete structure need to be operating in the same mode for the claim to be made. All this has been said, ad nauseum, at this point.

    The "other guys" feel it's OK to give an overall craft assessment to a supposed condition to a partial component of the complete craft. It is my opinion (as well as others) that the boat must be supporting its own weight on the planing surface and not just a convenient segment of that weight while the rest is somewhere in displacement mode, being looked at with less than a significant value.

    So, here's the answer to your question, Will:

    Is the affixed, inflatable component of the RIB also planing when the hardshell hull is doing so? If it is, then the boat is planing.

    If it is not, the boat is not planing. Lift the inflatable component from the water on plane, so that it does not carry the weight of the hull and I don't care if it's papier mache or chicken wire, the boat would still be planing.

    Get that collar back down in the water in displacement mode and you have lost the claim.

    No specific beef with Ian at all, other than he insists that the whole boat can be treated as separate components for the purposes of what amounts to a marketing claim. Yet, as an engineer, he has to make decisions on a global structural basis for design solutions and in that mode, it suits him to think of the boat as a complete structure. Those two approaches are distinctly different and as far as I'm concerned, they are wrong.

    I was at the beach the other day and a Coast Guard helicopter flew by just off the water. It flashed through my noggin that the tip speed of the rotors was infinitely faster than the airspeed of the helicopter itself.

    Wouldn't it be marvelous if the manufacturers of the helicopter claimed the top speed of their aircraft to be the tip speed of the rotors so that they could boost their claims when marketing the craft to foreign nations for purchase? With typical rotor tip speeds about three times that of the air speed of the helicopter, that would make the CG ship I saw at the beach have a potential claim of about 500-600 knots. Pretty damn fast for a helicopter, wouldn't you say?

    Hey, why not? It's all a part of the same aircraft moving through the air. All I have done is separate out the individual component elements and applied the most beneficial data to boost the performance claims for the entire craft; Much like that which is used to describe a planing F-Boat.

    Ya think, for just a few moments in time, that other aeronautical engineers and designers of helicopters wouldn't just rock back in their chairs and let out a big laugh at that one?

    Here's the solution... Drop the marketing hype, define the condition in other terms that more appropriately describe the behavior and we can all move along.
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