Planing Trimarans

From Tom Speer on another thread-for the record:

"A Farrier tri does plane, but it's the main hull that is planing. They have flat sections with rounded chines. At speed, the main hull is being unloaded and the difference in speed is significant when it starts planing.

The drag of a narrow displacement hull like an ama is pretty low, even at speeds normally associated with planing. A stepped ama would have much more wetted area, not to mention the drag from separation at the step, at lower speeds. When going fast, the ama is getting loaded up, which makes it harder to plane.

Also, the drag due to dynamic lift when planing is inversely proportional to the square of the width of the planing surface, so if you try to plane on a narrow hull form, the drag from the lift is greater than the reduction in drag from reduced wetted area, and the performance can actually be worse."
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Tom Speer

 

And Tom Speer has re-opened a full-blown can of worms... much to his own detriment, I'm afraid.

Tom's a great guy and uniquely knowledgeable about sailing craft. He has made this claim before and failed to back-up said claim with either unaltered video, or sequential imagery demonstrating said condition. Same with Mr. Farrier.

When they produce said data in support of the claims, we can talk about the functional correctness of the potential.

My position is now and has always been... sailing trimarans do not plane when they have one of their amas supporting a significant portion of the boat's weight. Simply heeling the boat over on the leeward hull while the main hull is being levered out of the water is not planing. If it were, every single beach cat ever made is now to be considered a planing cat. Now, that's a very curious claim that I've never heard a single cat sailor ever make, yet some among the tri community want to completely break with logic and get their boats into the planing pantheon.

Now, if a sailing f-boat could be shown planing without the amas in contact with the water... we might have something to talk about. That condition, too, has never been shown on video, or photos.

The AC tri, USA17, makes no claim at all about planing, yet it flies its main hull with far greater ease than any F-boat ever will. These boats are already fast, so really guys.... what's the point of the unnecessary noise on this topic?

Below you can find a small collection of photos showing various cats, from small to large, on plane... as described by others on this forum. Just get that windward hull skimming, er... planing and you're in there. ;-)

 

A "planing" hull is much more sensitive to overloading than a "displacement " one. So if we increase the loading of the hull by, say, 10 %, and then measure the speed decrease, we should be able to tell if we can still call this hull, at that speed range, a displacement hull or a planing hull,I guess.

 

This post seems a bit like splitting hairs, where would you like the part? A hull that generates dynamic lift will move to the surface reducing wetted area faster than a non lift inducing hull. If this involves an angle of attack there will be an element of drag. The fastest combination will be the the one that has the least resistance over the widest range of parameters generated by the wind strength and resulting waves. The faster way of sharing knowledge might be to illustrate/document measurable events/parameters instead of attempting to support positions by attacking the opposition. My vintage tri does go faster when it rides over its bow wave leaving the transverse wave systems behind. And it does this sooner on a reach when the ama is carriing part of the load. And it was documented back in the 1960's and is still true now....Obviously with enough power and good enough foils hulls can be flown clear of the water for higher speeds yet but everyone knew this in the 1950's but were ahead of the technology. Technology now , like then, costs money so maybe everybody should exchange friendly evaluations in terms of bang for the buck. Or perhaps pony up for the real world.....

 

Sorry Tom and Doug, I'm with Chris. If you check out the wake of a Farrier's main hull at speed, sure, it looks flat and the wake looks almost as if planing BUT that is only because the leeward float, which is buried plenty and sending up a rooster tail, is doing all the work, taking near all the boat's weight and sail loads. Now if that leeward float had a flat wake and the float was skimming the surface, yes, that would be planing ... but just checking, ah, no, no, it's not doing that at all.
I remember years ago an Australian cat named Big Bandicoot, had very wide, planing shaped after end hulls; it is by the by that the rig failed during a record attempt dash but a boat like that maybe, maybe able to plane .... but you're paying heaps for wetted surface area and drag in light winds. If a Farrier had floats with a large posterior like the main hull, okay, it might too ... but what a dog that boat would be.

 

Have you experienced planing in a dinghy? It is evident when the boat transitions from purely displacement sailing to planing.

The same thing happens with a Farrier trimaran. There is a hump speed, and the boat will be trapped at the hump speed in marginal conditions. But when there's enough wind, the boat takes off, and the behavior is like that of a planing dinghy. The ama is not planing, but the main hull is.

I don't know why it's so hard for people to accept that this happens. Perhaps because they haven't observed it first hand. All I can say is, go out in a Farrier design, pop the chute in 20 kt of wind, and see whether you still say the boat doesn't plane.

 

Jeez Tom, this could go on forever, but you said it yourself, the ama is not planing - and the main hull has been levered out ... so it is skimming the surface, (and looks like it is planing, and I guess it is) - but the main hull is not being lifted by dynamic lift from planing (like a planing monohull), it's lifted because the platform is being levered up from leaning on the ama. Anyway, all light multihulls feel like they jumping off a hump when they accelerate viciously - and that can feel very much like a dinghy planing.

 

I agree with Tom that the main hull can plane regardless of the ama type. A non planing hull will ride deeper for the same load on the sails. Obviously both hulls can be flown clear of the water if there is enough buoyancy in the ama but a planing hull will be skimming the surface sooner. The object of combining planing with non planing hulls is to widen a boats high performance envelope over a larger range of conditions. The Catri tri has tail fins on its amas for lift, maybe horizontal retracting ama planing surfaces would give you an ama that would suit your requirements for planing definitions. In the meantime I'll have fun watching the mainhull on my Nicol plane like a dinghy when the wind picks up.

 

It CAN plane or you'd like to BELIEVE that it CAN plane?

Ask Tom for some photographic evidence upon which you can base your empirical evaluation. For that matter, ask Ian for the same stuff. I asked Ian for the substantive visual material and he sent me a picture of two F-31's both flying their main hull while side by side... neither of which were even close to a state of planing, even if it were possible for the hull design.

I would suggest that this planing F-boat thing is something akin to claiming that a piano can fly if you wheel out a piano connected to a tricked-out structure, attach a bitchin' engine and Voila!, the musical beast gets off the ground... while fully supported.

Yes, it is off the ground and yes, I suppose that you could say it was flying, but look closer... do you see that amalgam of aluminum tubing that holds the thing up from the runway? In my book, this is not flying. If you were riding on the piano, it would feel just like flying and the faster it sped around the airport, you'd become more and more convinced of the effect.

In the theater, when stage scenery is brought down from the overhead volume above the stage via a system of cables, it is called, “flying it in”. Very clearly, the massive collection of thin plywood and two by fours is not really flying, but the expression would suggest that it is. So, is it really flying because stage craft refers to it as such, or is it simply a figure of speech with no connection at all, to the business of actually flying? By the way, that big volume above the stage is called, The Flyspace.

This is an obvious comedic retort to the condition that is being expressed, but you get the point.

Now, if any of the folks with a stake in this discussion can produce the unaltered, right from the camera, video that a sailing F-boat can plane its main hull while totally unsupported by either ama, I'll be glad to issue a sincere apology.

In fact, since it would look like an F-boat doesn't need to have amas for static floating stability from the main hull, why not simply remove said amas, tie that bad dude into a ripping 18 knot breeze going downwind and put it up on plane with the cameras rolling? If the boat in question actually does get up on plane and is controllable, I'll shrink into the background and not bring it up again as an antagonist in the argument.

I get marketing hyperbole, I wrote and directed hundreds of promotional videos over the years in which someone was looking to get their piece of the pie through iffy, non-supportable claims. I balked then and I balk at the smoke and mirrors thing now. Isn't our world filled with too much hyperbole as it is? Why do we need to add more, just so that we can feel good about one disconnected moment in a sailing experience?

 

My last:
F22

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Factors indicating that the boat will plane:
1)D/L ratio around 50(at 1lb. sq.ft. pressure with ama supporting some of the weight.
2) SA/D ratio 42(27 required to plane according to Pierre Gutelle in "Design of Saling Yachts"). This is with UPWIND sail area only. Downwind SA increaes this number and reduces the wind pressure required to plane.
3) Has over 500sq.ft.SA per metric ton just in upwind SA. 400 requred according to Douglas Phillips-Birt(Sailing Yacht Design)
4) Should easily exceed speed length ratio of 2-the threshold of planing according to Skenes and others..
Pierre Gutelle in "Design of Sailing Yachts" second edition says a sailboat will begin to plane at a speed length ratio of 1.5
5) Ian Farrier says the boat will plane.
6) Tom Speer who has spent many hours ACTUALLY SAILING on a Farrier designed tri(if I remember correctly) says it is a planing(main hull) design.

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Polars , People & On the Water Experience

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Sure, and there are polars available for at least the F27 .
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But one damn good indication is F-boat owners talking about planing which is an important aspect of F-boat sailing/racing:
"F27 planing speed from F- boat forum: "8.2 knot minimum....At 7.5 knots the boat is lifting."
Martyn Adams,owner
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" An F32 can do 12-14 knots planing to windward when the wind is between 15-20kts. under full main and jib"
Glen Howell F32 #221
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" Just look at Bob Harkrider. It's all in the name(Bad Boyz). He is a rebel. He is always the first one to get on a plane. The entire herd will be sailing the same angle,fairly slow, then you see Bob out of the corner of your eye. He is the one sailing 15 degrees higher and 10 knots faster." Todd Hutchins, owner
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" Visualize a curve expressing power required(y axis) vs. boatspeed(x axis). This curve has a very gentle slope at first. As it approaches the displacement hull speed(maybe a knot below) this curve starts to steepen. There is a step (much steeper slope) from say 7 kts to 9 kts for an F27. Then the slope decreases at higher speeds because you're on a plane,and finally steepens up again in the teens,say above 15kts, because the hull-water interface has changed geometry(Think of the leeward beam plowing into the water).
Many races seem to be won or lost based on who gets on a plane and stays there."
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So we have the Science, the Designer, and the Sailors all saying that F boats plane. There is NO DOUBT WHATSOEVER !

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I really think the most important comment yet made was Tom Speers several posts back. I don't think that some people can ever understand without sailing a tri with a planing hull and actually feel it begin to plane. I have ,with my 20 footer and 14 footer both of which planed with the ama loaded.
Planing is planing-just because the ama is carrying some of the weight of the boat doesn't mean that the main hull can't dynamicaly lift(plane) with the balance of the weight.
It is an observable, but most importantly "feelable" fact if you sail a tri that does this. No ifs ands or buts.......

My 20' planing tri(30+ years ago)-slow in light air-fast as hell in 10k up:

 

All with their leeward amas fully planted in the sea, accepting massive portions of the boat's overall weight and wind load.

That's not planing. Not now, not last year, not next year, not even if Hayzeus, Budda, or Ganesh came around and got out on an F22. Stick that ama in the sea, transfer the load that should be lifted dynamically by the main hull alone and you lose the claim of being able to plane. Performance monohull sailors are laughing about this posturing regarding the state of plane. Just what the multihull community needs... another point to dis the genre because its reach exceeded its grasp.

Like I said, there's no traction here, Doug, you've once again wasted your time.

Can anyone hear that tinny sound of a lame planing tune being played on a can of worms?

End of discussion... once again.

 

Re: Planing Trimarans
Doug, this topic on planing multis is exceptional, I mean how many words have been, and how much hot air has been expended on the subject? I don't know of any other which has triggered so much interest .... and repetition. Maybe Moth foilers.
Can a main hull plane if the ama is loaded? ... yes, it is sort of planing, but more like skittering ... so it's cheating planing, not true blue planing like say, my Cox's Bay Skimmer - which is a real planing fool. The point about F-boat leeward amas not planing; everyone agrees they don't ... but if they should .... then everyone would agree that F-boats plane. But they don't.
cheers Gary
ps: if you're in touch with Tom, send this to him too

 

If the ama doesn't plane, but the main hull suddenly starts planing, wouldn't the thing start spinning in a circle?

Take the amas off, add racks with beefy crew hiking, and go for a sail. Take a video. That will answer the question with no more discussion.

 

Given enough wind (easy to find lots of hot air!) Nicols can actually take off and fly (after planing) with no hulls touching the water. Hedley barrel rolled one after exceeding 27 knots with full sail in gale force winds in flat water. A steady altitude of 3 feet was reached before it was discovered that flying boats need aircraft control surfaces and aerobatics commenced. The lift on all hulls at speeds over 20 knots was a measured 8 inches . These boats retain near midsection width to the stern for more lift at speed. It might be easiest to take people sailing on a F boat so they can observe for themselves, along the lines of seeing is believing

 

Hey Cavalier mk2, I did a number of seasons on a stretched Nicol to 38 feet, called Drumbeat. The tri has been altered since then into much more a cruising boat but in those days, Drumbeat was a competitive boat, owned by Keith McClane, a good driver, led by example (once climbed damned near to the masthead in plastic jandals, no bosuns chair, to retrieve a lost halyard -and put all us young crew to shame) and the boat won a number of series, mostly on handicap, but took line honours a few times when the faster boats screwed up, like turning over or impossible spinnaker wraps... so I know about how fast these Nicols can go - but just over 21 knots was our limit. And doing that Drumbeast definitely felt like a big planing dinghy ... however I checked the leeward ama and guess what? - that ama was down deep and geyser-ing a good rooster tail ..... and it definitely wasn't planing. Endastory.