Turbocharged IACC models & full size, CBTF,VPP's

Rcsailing.net General Discussion
101

Dick,

The angle of attack of the foils relative to the water does not change when you dial in the collective. If the foils were held straight relative to the boat, then the whole boat would have to sideslip at a 3 degree leeway angle in order for the foilf to have the 3 degree angle of attack needed to produce their lift.

Let me try to illustrate this with an aircraft mental picture: Imagine that symmetrical wings were mounted on the fusalage of the airplane at a zero angle. When flying, in order for those wings to produce lift, they have to go through the air at, say, a 3 degree angle of attack. Therefore, the whole aircraft would have to fly with a 3 degrees nose up attitude.

Now, suppose you took that plane back into the workshop and remounted the wings so that they were at a 3 degrees leading edge up angle to the fusalage. Then when you flew the plane, the wing would fly through the air at the exact same 3 degree angle of attack, but the fusalage would now be flying straight instead of nose up.

Back to our CBTF boat: when you dial in the collective by 3 degrees, the foils are still operating at a 3 degree angle of attack. No change there. The only difference is that the boat is not sideslipping to create that angle of attack. Instead the boat is going straight. So there will be no change in the amount of turbulency off the trailing edge of the foils, no change in the pressure distribution on the foils (and therefore no change in their tendancy toward flow seperation). There is however a change in the angle that the hull goes through the water. When the hull goes through the water at an angle, it is (as you say) dirty. When the hull goes through the water straight it is much cleaner. Therefore with the collective dialed in, the entire setup is cleaner, not dirtier…

As far as the looseness of the rudder shafts leading to vibration; Since the loading on the foils does not change when you dial in the collective, their tendancy to vibrate does not change either. If they are going to vibrate, they will do it with or without the collective. In fact, since the hull is sideslipping when the collective is not in use, the flow will be more turbulent without the collective than it would be with the collective. So I would guess that the tendancy to vibrate would be less when the hull was going straight than when it was sideslipping…

When I use the term planing, I am talking about any time the boat is sailing faster than the wave drag limited hull speed of the boat. For a one meter boat, this speed would be about 2.7 knots or 3.1 miles per hour. The US1Ms at the pond where I sail are able to sail faster than this in moderate to high wind conditions - especially on reaches or downwind. Given the low displacment of these boats, you do not see the bow up, spray flying, boat skidding down the wave type planing that is common in dinghies on windy days, but nevertheless the boats are technically planing. I have in fact seen some decent bow spray off of these US1Ms and close scrutiny of their wake tells you pretty quickly that they are planing.

  • Will

Will Gorgen

102

The Libera Class is a great thing - but how to use this technology in rc-sailing? - Any ideas?

Download Attachment: [ Libera A mit voller W?sche Auer56.jpg](http://www.rcsailing.net/forum1/data/idealist/200310981848_Libera A mit voller W?sche Auer56.jpg)
66.67KB

Professional shipwright - boatbuilder/-designer with 25 years of experience and a special interest in multhulls

103

Ernst(idealist) the Libera boats are exciting with multiple trapezes! On models an on-deck Trapeze Power Ballast System is the closest possible system to that. You can look on my site under "innovations"to see a Melges 24 model with the Trapeze system and under “monohulls” to see the microMOTH with such a system.
Those two boats illustrate two variations that I have sailed: the Melges version had a fin keel with a little ballast in it in case the boat took a knock down . The extra ballast helped to right it and reduced the “quickness” of movement characteristic of on-deck systems.
The microMOTH uses that same system with NO ballast underwater but uses "trainingfloats-sissy floats) to prevent the thing from immediately capsizing when first placed in the water.
Both these systems are MUCH harder to learn to sail with than is a canting keel but can potentially move weight further outboard and can therefore be lighter.

Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing

104

Dick C.,

I have been thinking a bit more about the term planing, and I think you are right - I have been mis-using that term. Planing specifically refers to dynamic lift caused by the hull skimming through the water. This is not what I was referring to. I was referring to a light displacement boats ability to break through her “wave resistance barrier”.

Unfortunately, I have scoured the relevant chapters in several of my yacht design texts and I have yet to find a term that describes whet I am referring to. The best I can come up with is the speed length ratio Vs/sqrt(L) - where Vs is the speed of the boat and L is the waterline length. Most displacement boats are limited to speed length ratio of around 1.5. A low displacement boat may be able to achieve a speed length ratio of 2 due to less wave making resulting in lower wave resistance. Dinghies, when planing, can achieve speed length ratios of 3.5 under ideal conditions.

If anyone has a better term that we can use to describe the effect of being able to sail faster than the wave resistance barrier speed, I am willing to change my terminology. I will keep looking as well.

Sorry for the confusion, it was not intentional…

  • Will

Will Gorgen

105

Planing or not - that’s the question! -
Maybe the following helps a bit.

The terms I’m used to, are:

1)Displacement conditions:
(Factor from O to 4.5)
the barrier is - square root of the waterline length of the boat in meters - devided by 2.43= kn, devided by 4.5=kmh. -
At this speed the given boat is ‘captured’ between it’s own bow and stern wavesystem. -

2)Supercritical displacement condition:
(Factor from 4.5 to approx. 6.0)
Beyond the speedbarrier - like during sailing down a big wave - you get the ‘supercritical displacement condition’, also known as SURFING. -

  1. Planing or Gliding:
    (Factor from 4.5 to approx. 14.2)
    Light and/or slim hulls with sharp bows and flat underwater stern sections (at or below 10? exit angle) can reach speeds of:
    square root of waterline length in meters devided by 7.7 = kn, devided by 14.2 = kmh

Does this help - or is it confusing for you?

Professional shipwright - boatbuilder/-designer with 25 years of experience and a special interest in multhulls

106

By “Factor” I presume you are referring to the Froude number?

MM

107

Dick L.,

Doug privatly suggested “catamaraning”. :slight_smile:

Skiffing? Maybe…

Ernst suggests “surfing”. As much as I enjoy surfing and would like to think of spend my time at the pond as surfing, I’m not sure this is 100% correct… I will do a little research and see if the strict definition of surfing encompasses what I am trying to get across…

Thanks for the suggestions, keep `em coming…

Will Gorgen

108

I’ve tried to stay out of this one so far but I gotta chime in now… [:D]

I guess this thread has nothing to do anymore with IACC boats…

I’ll buy into the claim that Doug’s new boat will be much faster than any IOM out there. Take a boat designed for a particular class rule and do away with displacement restrictions and sail area restrictions (and number of rigs you can choose from) and you’d have to go seriously, seriously wrong to fail in reaching that goal. I think we all agree that we don’t need Wolfson expertise for that one. [:D]

Now, whether or not the boat will be faster than any other F100 (non-CBTF) boat - you can debate that as much as you want but the answer can only be found on the race course. There aren’t that many F100s out there, so I’m not sure where the data for the VPP comparison could have come from… Not to mention that (F100 being an experimental class that it is) you can’t possibly predict what (non-CBTF) tricks your competition may have up their sleeve. So, rather than claiming 200-300 sec/mile in the cyber-pond - the only way to prove your claims is by showing 1 (or more) second at the FINISH LINE!

Finally, the one I find hardest to swallow, is this crabbing to windward business. C’mon. There is NO WAY that Wolfson or any other VPP can accurately measure drag vs gain-to-weather of something like that as it is simply outside of the envelope of it’s historical data. And if it isn’t - than it’s just you guessing that the effect would be beneficial. I for one would have to see that done to believe it. Intuitively (and I’m not going to claim that I’ve done the math or even capable of doing the math) - I’d say it’s way, way off. I’m not saying that it wouldn’t “work”, or even that it may not be “useful” tactically (for short periods of time) - but to claim that your boat will “eliminate leeway or even crab to weather” without doing the calculations or building the boat to demonstrate but simply on the basis of saying that “well, if both rudders are 3 degrees to leeward then they will generate sufficient lift to counter the side-force, and the overall drag will be reduced because now the hull points in the direction of the waterflow” is just plain ludicrous. It would be like me saying that on my IOM, I can eliminate leeway by dialing in a lot of weather helm which I will then counteract with the rudder and the net result will be that the boat will not side slip… Good theory, except that the boat will slow down to the point where the lift being generated is no longer sufficient to counteract the side-force and you will do nothing but side slip…

Now, twin foil arrangement is more efficient - so it MIGHT be possible to get some reduced leeway… Maybe even eliminate it completely for a short period of time. Who knows - maybe the VMG would improve even over a long haul using this approach. Personally, I’d be surprised but it’s not impossible. But you guys take it as a done deal… Build a boat - 2 in fact - and find out for yourself (and THEN tell us!!!) what is the fastest way to get to the weather mark.

I hope this post doesn’t seem too “negative” or “critical of new technology”. It’s only meant to be critical of unfounded claims. In fact, I am really curious to see this technology in action and hope that Doug will have a sailing prototype soon. In fact, there’s a Region 3 IOM Championship in Ft. Lauderdale in Florida - first weekend in February. They project 30-40 people there. Do you think you might be ready then to show? It’s not too far for you and you may even get a few orders…

Cheers,

Marko

109

Hey Marko,

The effects of Crabbing to windward (as you put it) were not included in the VPP predictions. Doug has stated that VPP could not handle that (nor could it handle the reduced wave making of the forward rudder position).

But I have experienced the effects of the collective for myself when I went for a sail on the Schock 40. The effects were subtle, but there was definitely an improvement of about 0.15 knots in our boatspeed which would translate into about .11 knots in VMG. We were able to sustain that speed improvement with no change in our true wind angle. Our course made good improved by around 2 degrees or so. We sailed for about 20 minutes on that tack with the collecive dialed in and the improved performance did not fade.

Before I go any further, I want to make one other clarification. The system is rarely if ever used to crab at a negative leeway angle. But it is used all the time to sail at a zero leeway angle (the hull going straight through the water rather than sideslipping). Tom schock did indicate that you could crab to windward if you wanted to, but seemed to feel that shooting up (turning head to wind) would be a more effective way to get around a mark that you weren’t quite laying…

Now it is still a matter of debate as to whether you will be able to fine tune the collective on a model boat where you don’t have the benefit of onboard instruments to tell you if you are performing up to your target boatspeed or not. given the subtleness of the effect, I would say that you would never be able to prove that the effect was there unless you could take accurate speed measurements with a very contoled set of conditions. There is a good chance that you could overdo the collective and shoot yourself in the foot. But that does not negate the areodynamic arguments I have been making in my previous posts.

My recommendation to Doug is that he design the boat with the ability to rig up a collective, but that he should get the rest of the systems on the boat working flawlessly before he starts experimenting with the collective. This was the same recommendation that Tom Schock goves to new Schock 40 owners - learn how to use the canting ballast system and get the boat speed tuned up first, then start playing with the collective to fine tune the performance.

  • Will

The principles I have discussed in my previous posts are fundamental aerodynamics.

Will Gorgen

110

Marko, apparently you didn’t read what I wrote about collective steering, and the wavemaking resistance being lowered due to proper placement of the foils: go to my October 7th post at 8:58AM(its the second one after Ryans last post). Grahams VPP predictions in the comparative data sheets DO NOT take into consideration collective steering or the wavemaking resistence reduction ; the figures quoted are comparisons made NOT using two of the most important aspects of CBTF yet they show the CBTF boat superior on every course in every condition. You’re right that the current VPP does not account for this and therefore the results are VERY CONSERVATIVE!!
Collective steering is one of the factors in CBTF design that scales directly with no scale effect whatsoever. And collective steering is used on Schock 40’s and on Wild Oats and has been shown to work over an 8 + year period on fullsize boats. Grahams assesment is that both collective steering and the wavemaking reduction due to the rudder placement will scale down exactly. What is somewhat different is the rudder AREA and ASPECT ratio: on the big boats the aspect ratio for CBTF rudders is around 7/1 ; on the F100 CBTF the aspect ratio is 3/1 since it was shown in testing that the lower aspect rudders worked better than the higher aspect foils…
Understanding the concept of collective steering seems very difficult for a number of people but the fact is that it will work on the model just as it has on the full size boats…
I don’t believe that collective steering will be very subtle when a cbtf boat is under and slightly in front of a fixed keel boat! In fact I have read several stories of the amazing upwind ability of Wild Oats when directly compared to fixed keel boats-the F100CBTF will show the same windward ability.
On the F100CBTF collective is extremely easy to set up since each rudder has its own servo and collective mixing is programmed into the radio and can be switched on or off or changed at will…
And Marko: the original point of this “IACC” topic was that if the IACC powers that be were serious about turbocharging the boats of all the things they could do CBTF would add the most. After all, most of the biggest and fastest new monohulls under 100’ are being built using the technology-its just a matter of time before CBTF reaches the America’s Cup–in my HUMBLE opinion…
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing

111

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Marko, apparently you didn’t read what I wrote about collective steering…<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>

Guilty… I don’t read EVERYTHING you post (not enough time). [:D] I just kind of figured one of two things is happening here - either the VPP program or yourself are throwing some unfounded, unsupported claims about collective steering and wavemaking resistance reduction benefits of TFs on this scale…

You state your case for VPP being CONSERVATIVE because it does not take these effects into account. In my HUMBLE [:D] opinion - the effect of twin rudders is anything BUT beneficial!!! Would you have the secondary (forward) rudder if you DIDN’T need lateral resistance? Looking at the experience with forward rudders and twin foils (non-CBTF - a-la NZ 92 IACC or the English boat in the last AC) all that hoolabaloo about beneficial side-effects are just that. Bottom line - twin foils are a NECESSARY EVIL required to overcome the defficiencies of canting ballast systems!!! In big boats the benefits of canting ballast like extra stability at lower displacement far outweigh (from what I can see so far) the drawbacks of extra drag. In our little ones - it remains to be seen!!!

But if your VPP program is NOT, in fact, taking into account the effect of the induced drag of twin foils - then it is not being CONSERVATIVE, it is being OPTIMISTIC. Which at the very best makes it UNCERTAIN!!!

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>Grahams assesment is that both collective steering and the wavemaking reduction due to the rudder placement will scale down exactly. What is somewhat different is the rudder AREA and ASPECT ratio: on the big boats the aspect ratio for CBTF rudders is around 7/1 ; on the F100 CBTF the aspect ratio is 3/1 since it was shown in testing that the lower aspect rudders worked better than the higher aspect foils..<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>

What gives? The effects of rudder placement on such elusive quantities as collective steering and dampening of the wavemaking resistance “scales down exactly”, despite the fact that the aspect ratios and overall (lateral) areas of the foils are vastly different (this latter part, by your own admission, having been determined and optimized EMPIRICALLY). Why? Because Doug Lord says so? Or wills it to be so? How can you even claim that something scales down exactly if the foil shapes are not the same?

Anyway, we are far, far into the realm of speculation here - and that is the ONLY thing I’m trying to point out to you. I’m not saying that the boat won’t go. In fact, I’m really curious about this technology and would LOVE to see it in action - so I’m going to repeat myself: I (along with 30+ other IOM skippers) will be in Florida in February. Do you think you might have a prototype finished by then? I know that (along with myself) there will be many other receptive and curious minds there - so it may well be worth your while… (and just so we’re clear here - I am NOT inviting you to a sail-off or some other sailing version of a steel cage grudge match or anything - I would just genuinly like to see a model CBTF boat sail).

Marko

P.S. My HUMBLE opinion: IACC would not benefit in the least from CBTF technology. For one - you’d have to can’t the balast using muscle power only and those 16 guys on board already have their hands full. Besides - true match racing demands ponderous, big boats with a lot of momentum and not so quick to accelerate requiring absolute skill from the helmsman (timing, precision steering, etc.). This, again, by no means implies that I am not FASCINATED by the modern CBTF boats…

112

…I’m just getting a kick out of the thought Doug devising a reason why he once again will not show up to Marko’s invitation to the region 3, … once again.
Come on Doug, surprise the hell out of all of us and show up to this thing, CBTF or not. Just bring something, …maybe the Melges? I know I would love to see that boat go!

113

Greg and Marko, I definitely will not be there in February! But thanks for the invitation.
A) the vpp takes into account twin foils but not collective steering or the attendent wavemaking drag reduction by the proper placement of BOTH foils.
B)-Graham Bantock in his report to me as well as the designer/inventor of the CBTF concept have both pointed out emphatically to me that the collective facility of CBTF will work as well on the model as it does on a full size boat. Both indicated to me that the wavemaking drag reduction associated with the proper placement of the twin foils will increase speed on the model in just the same way it does on the full size boat.
C)- You (Marko) seem to have trouble with the concept of a rudder turning and creating lift: while a rudder doesn’t scale down exactly in terms of area and aspect ratio the EFFECT of what the rudder does will scale down exactly if the design is done right. You see that every time you sail a model…
The facts are that the DESIGN of the F100CBTF was shown to be superior to an IOM or fixed keel F100 on every tested course(see previous post for exact description of courses angles and winds in which the models were tested comparatively) in every wind condition without using two of its most important advantages-collective and foil placement. Therefore the delta’s in the comparison data sheets underestimate what is possible with the real boat and are clearly conservative figures according to the designer.
This shows that the DESIGN of the boat and the CBTF concept are very fast-the final boat will do the real important talking…

Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing

114

<blockquote id=“quote”><font size=“1” face=“Verdana, Arial, Helvetica” id=“quote”>quote:<hr height=“1” noshade id=“quote”>the final boat will do the real important talking…<hr height=“1” noshade id=“quote”></blockquote id=“quote”></font id=“quote”>

Bingo!!! That’s all I was trying to say. It’s great that you have confidence/faith in your/GB’s design (and you would have to in order to embark on as much work as tooling and building a new production design will entail) - but we all know that this business of x seconds per mile is BS. It could be less, couldn’t it? It also could be more.

VPPs have been getting better and better (for big boat predictions) - but for our small boats (or should I say small boasts [:D]) even with Graham’s stuff (which apparently has been custom calibrated for smaller scale) it’s still far from accurate and we as model sailors, as Will pointed out, are far from being in a position to check against the predictions and thus work toward refining the collected empirical data - due to (among other things) lack of on-board instrumentation, difficulty to know whether you’re sailing in the optimum trim when the boat is 80 yards away, etc. Not to mention that your CBTF design is far outside of the envelope of GB’s VPP’s prior information.

Not to say that I would discount your VPP data - in relative terms it’s useful to provide confidence to go with (or pass on) a design. Looks like what you’ve got now is a resounding GO. Good for you!!! Good luck with building - and post pictures.

Re: Florida - I think you’re making a mistake for passing on that one (unless it’s too early and the boat won’t be ready yet). When trying to start a new class - there’s no better place to start than a large gathering of (racing) skippers like that (and there won’t be many next year larger than that). Wow them all (or some) and that’s how new classes are born (and orders are gotten).

Anyway, don’t bother responding to the last paragraph. You made your position clear and far be it for me to tell you how you should run your business (and I apologize if you took it that way). I guess it’s just my selfish indulgence (because I really WOULD like to see a CBTF model sail)…

Cheers,

Marko

115

[quote
This shows that the DESIGN of the boat and the CBTF concept are very fast-the final boat will do the real important talking…

Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing
[/quote]

Thank you for making the distinction between words and action!

Rob

116

Marko, why would the canting keel on an IACC boat have to be moved by hand? If they changed the rule enough to allow CBTF I imagine an electro- hydraulic or diesel hydraulic would be legalized(would souping up the diesel be legal?!).I guess we’ll get a taste of what it will be like when the new Reichel-Pugh maxZ86’s are launched and race each other–what a spectacle that will be!

Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing

117

No CBTF in the America’s Cup? Don’t think they are considering it? Think again!! This is SEGMENTS from an interview with Jim Pugh of Reichel-Pugh and there are other tidbits as well in the November issue of Seahorse. This interview is on page 24:
SH: In terms of monohull design is the Cup class in danger of being left behind?
JP: Yes, for sure. There’s been a lot of development in offshore boats and the America’s Cup -class boats are pretty much dinosaurs. The class dates back to the 1992 Cup-with technology moving so fast you can’t expect it to last as long as the 12-metres managed.
SH:The ACC has not been revamped significantly in 15 years?
JP: Correct.
SH: Do you favor a rule change or is stability the priority?
JP: I’d encourage change.A lot of money gets spent on the Cup but without it going very far. You are not really developing anything too useful.
SH: What’s achievable within the existing rule?
JP: Well, you could reduce displacement which would need the formulae to be reconfigured so that you’d have the same sail area.At the moment sail area is adequate. If you reduce displacement by cutting down on bulb sizes you’d have to come up with another way of achieving righting moment, such as canting ballast. (BINGO!–by dl)
SH: How much lighter displacement?
JP: It could be as much as 10 tons. All the bulbs weigh over 20 tons,which is why the current boats are upwind machines. They are good in the middle and upper range because they have enormous stability, but they suffer downwind because of that weight and because of wave drag. They are pretty hopeless downwind,frankly.

SH:Would a hull change under the existing deck and rig be feasible?
JP: By and large,yes.
SH: The history of rating rules has shown the timing of changes to be vital?
JP: It’s good to be fairly progressive. The America’s Cup is considered leading edge technology but you can’t get a lot of performance with 20 tons of lead hanging off the bottom of your boat.
SH: You and John Reichel have nailed your colors squarely to dynamic ballast. But are you convinced there is a wide benefit to the sport?
JP: I believe there is. Canting ballast technology improves performance all round.

So, I’d say that it’s only a matter of time…
Power to the Keel!

Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing

118

Since I also just got the November issue of “Seahorse” in the last few days, I was surprised no one pointed out the introductory article about VPP’s. The conclusion is particularly on point, I quote:

“VPPs are useful in well-budgeted racing teams and advanced amateur sailing. To be used as a real tool lots of testing time and correllation have to be done to make the figures accurate. VPPs are also useful as a design tool, but even with the latest tools outputs have to be tempered by sound judgment. You may end up chasing a theoretical possibility but it is in fact a practical impossibility.”

119

Just goes to show how good the design of the F100CBTF is: you can’t get better than Graham Bantock and the Wolfson Unit collaborating on a design for a model raceboat! Grahams extraordinary good judgement combined with his proprietary application of the science of yacht design to rc raceboat design coupled with his consultation with the guys from Southampton is good enough for me!
The F100CBTF design with such an outstanding team is sure to be a benchmark design in the history of model yachting…
And given my last post we’ve got to be thinking about an rc version of a CBTF powered IACC boat!

Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing

120

Gee, Doug, you made that quantum leap regarding CBTF in model yachts so easily. I could really use your input on the proofs of LeMarckian genetics and origin of DNA for tomorrow’s class in scientific methodology. You’ve already given me the proof for Cartesian logic that I needed: “I think, therefore it is.”