Planing Trimarans

planing tri

AP, hydrofoils work on the same princible as a wing and require both sides to function properly.
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Can you put into your own words why you don't think that the mainhull of the F boat will plane with the ama partialy loaded? You've accepted that the main hull will plane and we know that since the ama is a high beam to length hull that it will be capable of matching planing mainhull speeds(up to a point) w/o undue drag. We know that the boat has the power under just upwind SA to plane and would plane even earlier under downwind SA.
So please give it a shot-I'd like to hear your reasoning.
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PS- I agree 100% that the fastest tri will fly the main hull...

 

Comedy Central

Quote from Doug Lord:

So, let me get this right...

Foilborne boats are not planing when their hulls are just skimming the surface, but trimarans with their amas immersed and their main hulls skimming... are...?

Boy, oh boy, it's nice when you can fiddle with the definitions so frivolously to justify the argument.

When will it ever cease; this endless search for all things claimed in the upper end of boat speed?

Go take a long look at hulls that really do plane. Look at them at rest in the water and on the trailer, look at them at speed when they are doing their task. The hull is not supported by any external flotation device whatsoever.. no amas, no foils, no training wheels, as I've heard reference to amas in the past... no nothing! They just go about their delivered task and get it on. The proof is out there for all to see and it happens at the flick of a wrist. No special conditions or wind angles to sea states; you just fire it up and planing you are.

Now, Mr. Lord admits to the fact that foilborne boats should not be considered on plane. One can only hope that the next revelation will actually be that an ama-supported hull is not, in fact, planing. We wait with baited breath for the exclamation from on high.

 

voodoo

Mr. Ostlind: how could a "foilborne"(foilborne =100% supported by hydrofoils) boats' hull be skimming the surface? In that case it wouldn't be "foilborne", would it? Now, in the TRANSITION from not moving to being foilborne it's quite likely to plane.

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"ama supported main hull" When the science is discarded, when the designer is discarded ,when the owner/sailors are discarded-- only then do you arrive at a description of an F boat NOT planing on the main hull with the ama partially loaded.
Only then do you arrive at the heigth of convoluted thinking that says that Jim Antrims self described "planing ama's" don't plane even though the lift they generate is a central theme of his design of the Antrim 30.
Antrim 30+
Address:http://www.antrimdesign.com/trimarans/erin/ Changed:1:17 PM on Friday, September 30, 2005


---What we have here is a failure to communicate(sorry about that) coupled with throwing out the science, the designers and the owner/sailors in a dogmatic, emotional application of the old saying:" Don't confuse my mind with facts-it's already made up!"

 

Doug

These concepts are so trivial, is boggles my mind that you can’t grasp them.

• Having a planning hull shape doesn’t mean a boat will plane.
• Just because a boat is designed to plane doesn’t mean it will actually do it.
• Most companies have a thing called a “sales department” that devotes a great deal of time to come up with phrases to sell things. I.E. "planning ama's", “planning shape”, “designed to plane”.

Please provide a reference where Farrier definitively states that the F22 will plane; you won’t find one, because they aren’t that stupid.


Before I forget, are you dressing up as scarecrow from the wizard of oz for Halloween?

 

Doug; without going into the debate per se about planing Farriers, what about the fact that a narrow hull is not very good at developing planing lift? Basic planing physics a la Savitsky teach us this; the interesting answers from Doug C and Alan Smith which you gave earlier also bring up this point. Modern "widestyle" windsurfers as developed by real-life rocket scientist Jim Drake are designed around the relationship with efficient planing and wide beam.

Hydrocomp suggest the following factors in a formula to calculate planing efficiency;

k = 4.0 for feet and 7.2 for meters,
LCG = longitudinal center of gravity from the transom, and
B = the planing beam.

That formula doesn't mention displacement, or surface, or anything apart from three factors - because (as I understand it) everyone knows that the basic physics of the planing effect indicate that greater beam makes for better planing performance and narrow beam (a la tri) for inferior planing performance. Didn't you point out in an earlier thread about Parlier's planing cat that the step actually creates a short and fat (ie efficient) planing surface? So why ignore the important factor of aspect ratio now?

Remember, the two people you brought into this interesting thread who produced calcs, specifically mention that a narrow planing hull planes later than a "normal" hull. In view of the fact that the experts you introduced bring in factors that your formulas don't cover, is it reasonable to be so insistent that you have proved the case for the planing tri?

Don't misunderstand me, I'm not saying the Farriers don't produce a considerable degree of dynamic lift. I am merely suggesting that when the formulas Doug C and Alan brought in prove that your earlier formulas are incomplete, you maybe don't have such a watertight case.

 

planing tri

Ct 249, I'm at a bit of a disadvantage in PROVING that the F boats plane since I don't have access to some of the data I'd need. That being said there is enough evidence to prove that the F22 has enough power to plane upwind with the ama partially loaded. I don't know the actual or heeled beam to length ratio of the F22 main hull but in looking at an F24 I'd say it was around 8/1 static and maybe 6/1 with the ama absorbing some of the load. The guys I quoted all back up my description of beam to length being a major factor along with weight,geometry, speed and power.And they back up the fact that a slender hull can have some characteristics of both displacement and planing hulls. By extension,they back up the analysis that a high beam to length ratio hull like the ama can perform right alongside a lower beam to length main hull that is planing. A tri can be designed with any combination of planing or displacement hulls
depending on what the designer is trying to achieve. It seems obvious to me that what Farrier was after was more interior room in the main hull-room he couldn't have with a very narrow high beam to length ratio main hull. Instead, he chose a lower beam to length ratio planing hull.
And you can't ignore the designer and F boat owners. The F22 designer says it will plane; it has the power to plane; F boat owners on the F boat forum talk at length about those boats planing on the main hull.
Jim Antrim talks about his "planing ama's" and the lift they generate being central to the pitch stability of his design.That is not "hype"; it is fact on a proven race winning boat.
The key to understanding, I think, is in trying to see what the designer tried to achieve and then comparing that with other options. It is clear that Farrier's designs opt for a lower beam to length ratio main hull and a high beam to length ratio ama. Why? Probably because the planing shape offers more interior room while allowing the boat to perform as well as if it had a high beam to length ratio main hull especially in any wind.The disadvantage is more wetted surface in light air.
But the biggest problem I've seen here is the inability of some to conceive of two different types of hull doing different things at the same speed. It seems hard to grasp the fact that one hull could be acting as a displacement hull while at the same speed the other hull could be planing.
It seems to me to fit perfectly with Farriers intention to maximize interior room in the main hull and is a brilliant design compromise. It also fits perfectly with the science and observable characteristics of similar boats on the water.

 

1.So maybe the Sydney Harbour Hydrofoil ferries used the foils as foils as they rose, then used them as planing surfaces once up. It sure looked like they had no water flow over the top when in full flight.
2. I guess it comes back to your definition of planing.
I reject "it feels like planing" and "the designer says it should be planing" and "it is exceeding 'hull speed' so it must be planing".
My definition is something like: "it has risen up and is supported by hydrodynamic forces only". So if it has risen up by any other force it is not planing. So a planing centre hull on a trimaran will be planing when it has risen up with amas taking no part in the rise. Originally I said both amas out but on further thought I concede that the windward ama could be in the water and not contributing to rise. I don't see how the leeward ama could be in the water and not contributing to rise except when sailing DDW.
Regarding the narrow hulled moths, seems to me that if they rise they are planing and if they don't they are just cheating 'hull speed' by being so narrow.

 

"The guys I quoted all back up my description of beam to length being a major factor along with weight,geometry, speed and power."

But it's well known (and contained in some of the Moths posts) that being narrow REDUCES planing lift, and the figures you gave earlier don't allow for that.


"It seems obvious to me that what Farrier was after was more interior room in the main hull-room he couldn't have with a very narrow high beam to length ratio main hull. Instead, he chose a lower beam to length ratio planing hull."

As I said earlier, my information is that you are correct.


"And you can't ignore the designer and F boat owners. The F22 designer says it will plane; it has the power to plane; F boat owners on the F boat forum talk at length about those boats planing on the main hull."

Maybe you can not so much ignore the designers and owners, as look at their information in light of the fact that planing is a very murky area (as Julian Bethwaite etc agree). That's why I brought up the Moth example; there is a wide variety of opinions from designers and owners in that class as to whether they plane. Even among those who you quoted, who all believe that they do plane, have a wide variety of estimates of the minimum planing speed. That surely just underlines that the opinions of designers and sailors are subject to great variation and therefore they underline that there's a great deal of difference of opinion; ergo the opinion of some people doesn't have to be taken as gospel.

Having said that, I have something vaguely along the dimensions and shape (albiet much smaller and very different in other ways) to the F boat main hull and it certainly planes, and quickly. The F boat seems to look and feel "planey". It just seems like one of those areas that's so murky that neither side can get all uptight about whether or not it planes, without much better evidence than any of us possess!

 

planing tri's

I think you may have misread or misunderstood: I pointed out that the beam to length on the main hull of the F boat is rather low and gets lower as the boat heels improving it's planing potential.

It's not a question of geting uptight about whether it planes or not so much but about the lack of evidence cited for the supposed inability of the F boat mainhull to plane while the ama is partially loaded or for Antrims boat to plane on it's ama's. The rationale seems to be limited to accusing each designer of hype and the F boat owners of concocting tall tales in the bar after sailing. That kind of rationalization is totally worthless and insulting excess directed at two very competent and well respected designers. Just read there various websites and you'll find no hype-just matter of fact discussion.I think there is plenty of evidence to support each designers contention and none at all that supports the aforementioned rationalizations.
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AP, I'm not familiar with the ferry you mention but it is possible it has surface piercing foils that enter the water at a 40-45° angle which could give you the impression of planing, I guess. But, any hydrofoil fully supported by foils requires that both sides of the foil contribute to lift-foils are wings- whereas planing surfaces have only one side used for lift.

 

Yes, but the boat is still very skinny compared to a mono; therefore it has less planing potential than would be achieved if it was a beamy mono. The formulas you presented earlier ignored the fact that narrow boats plane (comparatively) poorly. Therefore perhaps the formulas presented as proof aren't in fact very good proof.

While I'm firmly sitting on the fence about whether or not Farriers plane, I can see the point of view of those who demand more evidence. There are plenty of well-respected designers who can be found on either side of many questions. There are plenty of owners of all types of boats who DO present tall tales.

As they say, extraordinary claims require extraordinary evidence.

 

Please correct me if I stray ...

One of the characteristics of a planing hull are flat runs to the transom. Rocker in the hull aft is to be avoided if you wish the hull to behave well when on a plane. Another characteristic of planing hulls is that the planing surface has a positive angle of attack.

Now look at the main hull of the F-22. What attitude would the main hull have to be in to plane? What forces from the sails would put it into that attitude?



What am I missing?

 

planing tri's

CT249: What "formula's presented as proof"? Where? Do you mean ratio's?
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RHOUGH- according to the designer there is less
rocker in the 22 than some other boats he designed. Looks about the same to me as the 24
which we "know" planes.
the current page
Address:http://www.corsairmarine.com/1Corsair24.htm Changed:3:40 PM on Wednesday, February 23, 2005
By the way the back end of the boat does NOT have to be at a positive angle of incidence in order to plane. I designed an 18' swing keel boat years ago-the TS 18(80 built)- that had a similar knuckle and it planed well.(at about a 3° pitch up)
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Farrier says this on the F22 site:
"The production F27 then followed, this being the first 'second generation' design and represented a major leap forward in hull shapes with it's low rocker, and planing center hull..." "The F22....will retain the current well proven hull lines..." "Main hull lines have been optimized further with a higher displacement being achieved, but with lower wetted surface area while it has a slightly flatter bottom with less rocker so it will plane earlier."

Farrier F-22 Trailerable Trimaran
Address:http://www.f-boat.com/pages/trimarans/F-22.html Changed:2:31 AM on Sunday, August 13, 2006

 

"WE" "know" nothing of the sort. Quoting the words of the designer (that we have all read on his web site) proves nothing.

Ask a designer of planing hulls what rocker at the transom does for planing performance. I never said that the hull at the transom had to have a positive angle, only that the planing surface has to have a positive angle. What force from the sails is acting to pitch the boat up to give the planing surface a positive angle?

What other effects does a planing vaka have? If the main hull planes (uses dynamic lift to offset weight) doesn't that reduce the RM? Wouldn't it be like wearing a helium filled Michelin Man costume on a trapeze? In what case would reducing RM at higher speeds be a benefit?

 

planing tri

Insignificant change in HM-less than 2% resulting in insignificant change in angle of heel.
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My 20 footer would plane in 10kts and in moderately strong winds(18) with approx 5' of the front of the main hull out of the water with the ama supporting about 25% of total displacement.
Angle of heel upwind in 18 was about 12°-13°; mainhull beam to length with ama supporting part of the load was less than 5/1 while ama beam to length was 14/1.
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Showing that the boat has the power to plane, that the owners of similar boats talk about planing as an important race winning strategy,and yes, that a respected designer says that it will plane are important pieces of circumstantial evidence that indeed the F22 will plane as does the larger F 24. Discounting a respected designer is absurd because all he has going for him is his professional opinion and his proven track record and to accuse Farrier or Antrim of deliberately falsifying performance characteristics or deliberately misleading potential customers is the height of folly.

 

Our good friend, Doug Lord, wrote:

And this pretty much says it all about the claim. The boat has to be on its ama in order to get to this, rather circumspect, position. This is reduced wetted surface area through transfer of displacement and nothing more. It also illuminates the previous post in this thread that pointed out that a heeled trimaran presents a rather vee shaped hull to the water if it originally had such a great planing surface at rest. The motorboat crowd will tell you, at length, just how much more power one needs in order to plane a vee hulled craft over a flat bottomed example. Yet, there's been no set of calcs provided to that reality. One wonders what all the numerical gyrations have been about when that simple aspect has been overlooked?

The secret lies in the immersed ama and the transfer of weight. Something like a magician's misdirection technique so he can slip his hand in his pants undetected.

Again, from Mr. Lord:

Is that it... really? All he has going for him are these two items? How about the individual’s inherent intellect, his sense of honesty, the ability to work well under pressure, etc, etc.? It's a rare experience when a person is reduced to two simple tag lines. Mr. Lord can only hope that he is regarded in a more full expression of the human condition than two notations on his obituary such as these.

Once again from the previous source:

I haven't accused anyone of anything, if you care to examine the comments. I did call the claims of Farrier into question and asked for proof that has not been supplied to this point. I never questioned any of the written statements of Antrim. It is my opinion that Mr. Lord has chosen to interpret Antrim’s written copy on his website in a fashion that is at once, incorrect, as well as desperate. To hit the point again: Antrim does not say the amas plane. He says they have planing shapes.

The proper interpretation of the website comment by Antrim is that his amas could provide additional dynamic lift from their form, but he stops short of stating that they plane. If a guy with as much cred as Jim, can show that his amas plane with the full weight of the boat placed upon them, you won't have to wonder if there is any question in his mind about the fact. He’ll tell you so directly.

Take a good look at the photo below, showing Antrim's, 31' "Erin" design, absolutely cooking across San Francisco Bay on a reach. By Mr. Lord's standards, the main hull would be planing. Yet, the leeward ama, still an integral element of the complete boat structure, is clearly immersed to the decks. I'm sure that this is the view that more than one, planing F-31 has had of Erin.

This makes Erin a very fast boat, to be sure, but since the leeward hull component of the overall, three-hulled, vessel is clearly supporting virtually all of the full weight of the boat,(and it is not planing, because it's almost totally underwater) it is impossible to claim the complete vessel is planing.

Since a trimaran is not a "loosely affiliated group of hulls" type of vessel that just happens to be moving along at speed in the same general direction through serendipity, one can only surmise that all the elements are cohesively designed to work together as one unit. And that is something that we do know about trimarans. In order for this one unit to plane, it must be completely supported on that plane by one or more of the hulls at the same time, all of the hulls in question planing in concert.


Without this interesting bit of necessity, the boat is merely doing a nice design dance in which the wetted surface is being reduced through ama immersion. It's terrifically advantageous to do, this lifting of the main hull routine, but it doesn't qualify as planing.

If Lord's claim is how it is to be viewed, then every beach cat can also plane, at will in most cases, and I still don't see anyone stepping forward in sincerity to claim that beach cats do that.

There's a certain interesting quality to the position of the claims for planing tris in the limited view as presented by Mr. Lord (and others). I don't pretend to know what makes the need for these types of performance claims so important. It is relatively amusing to watch the argument get tweaked in some very peculiar ways in order to make the claims seem more valid. Certainly marketing position is being staked-out, but since Mr.Lord has no viable multihull product in the marketplace, it begins to appear as if another dynamic is at work in his effort to make the claim out of thin air.

Still, this discussion has gone on for some time now and there has not been one single stab at producing a clear, clean, video clip that can demonstrate anything even close to a planing trimaran. And that, all by itself, is reason to believe it is more of the smoke and less of the substance.

Please produce a proper set of video proofs so that the discussion can move beyond the, "well, it's supposed to work" level that it currently holds with Mr. Lord's claims.

For the record, I feel that a planing main hull tri is "possible", but it would have to meet many, very stringent criteria, such as: the amas out of the water, or planing unto themselves with the main hull, not being the least of them. I'm of the opinion that for a trimaran to do that, it would, out of necessity, be an absolute pig in light air scenarios. So, what exactly, was bought for all the effort? Additional interior volume is evident and for a cruising design, that is a critical enhancement.

Please, get the video collection and let's move on to better discussions.

Chris