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

Rcsailing.net General Discussion
81

Doug

Since you seem so adamant at stating that everyone who doesn’t believe VPP has no experience with it or computer aided design or just doesn’t understand it. I probably have more experience with CAE and log more Cray time daily then anyone else posting here which is exactly why I don’t take anything as fact just because a computer predicted it. Maybe a 50% chance at best of being correct without hardware testing to back it up and that is the best your going to do. Sorry, but there are always just to many assumptions and details that need to be neglected due to computer power and not understood phenomenon. Please. Don’t generalize and assume that just because we disagree with you and don’t blindly believe your post that we aren’t educated in the matter.

In a few years when the boat actually sails and can beat an IOM or US1m in an actual race then you will really have something to boast about. Until then it is still unproven.

82

Graham says;" Generally, the delta’s for all windspeeds, headings and courses are positive for the CBTF design compared with a fixed keel ( F100) indicating greatly superior performance. Typical margins are 200-to 500 seconds /mile> " " To put this in perspective the margin of superiority shown by the best fixed keel(F100) over the best IOM is typically 200 seconds/mile.
Margins between the best and average IOM’s are typically in the region of 20-50 seconds/mile."
Face it, from a design standpoint CBTF is unquestionably faster than a fixed keel F100 or IOM by large margins…
CBTF is a superior technology for use in both fullsize and rc sailboats and has been proving that time and again in full size boats for over 8 years; it’s turn is coming for rc raceboats where the DESIGN shows conclusively that it has the potential to be virtually unbeatable in rc racing…

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

83

Hey Doug,

I think we need to be clear that CBTF makes it possible to carry a very large sail area on the F100 (which the class rules allow). It is the combination of CBTF and the large sail area that results in those sorts of potential deltas.

Out of interest, I know you and Graham looked at fixed keel F100s as well. What sort of margin does the CBTF F100 have over the fixed keel F100 that you evaluated?

Also, I assume that the F100 is going to really shine in certain conditions and in other conditions it will have less of a performance advantage (thus the range of between 200 s/mile and 500 s/mile) can you give us some sense of what conditions the CBTF F100 has the 500 s/mile margin and what conditions it has the 200 s/mile margin?

This is of interest to me because I have some theories about what windspeeds my canting mast US1M will really shine in and what windspeeds it will not. And although the design philosophies for your F100 and my US1M are quite different, I have a feeling that they will both have advantages in similar conditions…

  • Will

Will Gorgen

84

Will, the answer to your question regarding the F100CBTF and a fixed keel F100 is in the first paragragh of my last post. The greatest margins for the CBTF boat are in moderate to heavy air.
The canting keel portion of the CBTF concept is what makes larger sail area(or lighter weight for the same sail area) possible and ,of course, that leads to the margins reported by Graham. Interestingly, because of limitations in the VPP’s ability to analyze CBTF two of the main speed producing factors inherent in the concept were NOT included or estimated for these results.
One, tests have shown that the proper placement of CBTF’s twin foils(rudders) leads to a reduction in wavemaking resistance. This fact will ADD to the predicted speed margins on the actual boat.
Two, CBTF includes a “collective” steering capability not found in any other canting keel
arrangement. Collective steering allows the CBTF boat to have both rudders turned slightly to weather upwind to “dial-out” leeway making the VMG of a properly sailed CBTF boat superior to any other boat.
The reduction in wavemaking resistance in One above as well as collective steering in Two above are unique to the CBTF concept and will add to the margins predicted by Graham since they weren’t included in his analysis.These two factors are why Graham recommends CBTF over, say, a canting keel and daggerboard combination…

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

85

double post removed…

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

86

The design facts(margin of superiority) in seconds per mile are derived from the same program used to produce the polars. The CBTF polars are not postable as presently supplied since they are way off the scale that Graham normally uses-in fact off the page on which the polar is printed. Graham will be supplying me with a readable polar soon I hope-but I probably won’t post it since his comparative data is supplied elsewhere.
Graham’s most important comparative data was supplied in a series of delta’s from from model tests on five different courses: windward,rcolympic,reaches,rc club and runs in wind ranges from 2 to 20 mph with a delta for the course every two mph of wind. This is how he compares the F100CBTF with a fixed keel F100 and a fixed keel F100 with an IOM.The design facts, previously mentioned, are derived from an analysis of this data -though it must be understood that the comparative data was produced from the same data used to produce a polar for each boat tested-just organized so that comparitive results can be veiwed at a glance.
In every test, on every course the F100CBTF proved superior to the fixed keel F100 which was already proven, from a design analysis point of view, way superior to an IOM.
When you add in the data that was NOT included in this study (see my previous post)you can see an even greater margin of superiority for the CBTF design over the F100 fixed keel design.

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

87

Thanks for the clarification Doug. In re-reading your post, you did in fact answer my question. I mis-read it the first time.

On the surface, it seems to support my gut instinct. I would love to see the polars though as they would really paint a more complete picture.

By way of a followup question, can you talk about the upwind deltas versus the downwind deltas? What kind of edge does the CBTF F100 have over the fixed keel F100 upwind (My experience says that this is where the CBTF really pays off)? Is there still an edge off the wind (I would think that depends on the displacement of the two boats)?

Also, does the F100 CBTF show a tendancy to need to sail hotter angles off the wind for max VMG (like the Schock 40 polar shows)? Without a spinnaker, I would tend to doubt it, but with all that sail area on the F100, maybe hotter angles do pay off…

Dick,

I’m not sure you can overlay an RC boat polar with a full sized boat polar. Hull speeds for model yachts are so much lower than full sized yachts that it is really not fair. Of course, the model yachts will tend to plane sooner, so you might win back some of that hull speed deficit. But given the assumptions of wind at the water level and the wave assumptions that are in the Schock 40 polar, I still don’t think it would be fair.

  • Will

Will Gorgen

88

Will,understanding that the design comparision shows that the F100 fixed keel is very much faster than an IOM in every condition and on every course here are the answers you
asked for.
Downwind delta’s of the CBTF version over the fixed keel version of the F100 are generally higher than upwind.
In 12 knots upwind the CBTF is 460 secs/mile faster.In the same wind downwind the CBTF boat is 626 seconds faster. And on a reach the CBTF version is 361 seconds faster.
Note that this data was not only supplied for varying courses and angles it was supplied for the CBTF version with different rudder aspect ratio,area , thickness as well as for different fin aspect ratios and thickness…
These design facts and the advantages mentioned in the previous post add up to an incredible potential for the new boat.
Its now up to me to build the actual boat to take maximum advantage of this design .

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

89

Dick: As an owner of the Wolfson VPP, I can say that you have pointed out some of its principal limitations. It is particularly good for comparing hull shape “A” to hull shape “B” especially when sailing in a straight line. Its ability to predict things like speed out of tacks or pointing ability of a design is limited. Further how a VPP can predict the effect of having a canting ballast package on the wrong side of a boat during a windshift or turning twin rudders too sharbly, I have no idea whatsoever.

90

You make a good point, Roy. VPP can only tell you the potential speed of a boat. It cannot tell you what the performance will be if you screw up. The same is true of any boat. So what you have to ask is “how likely is it that you won’t bee able to sail the boat up to its potential?”.

I race in several one design classes both full sized and RC. It is amazing to me that the lead boats can be 25% to 50% ahead of the rest of the fleet of boats that VPP would predict as being absolutely equal in speed. Could be that one guy has his outhaul too tight. Another guy might not be trimmed correctly. There are a myriad of things that might cause one boat to out perform another equal boat. That is what sailboat racing is all about…

So lets look at the F100 CBTF boat in particular.

You have the canting ballast system that must be moved from one side to the other during a tack. Certainly this will take some getting used to. but speaking as someone who just recently took up RC sailing, learning to steer with your thumbs takes some getting used to as well. If you get caught with your keel on the wrong side after a tack, you will be going every slow.

On the other hand, when I sailed on the Schock 40, we practiced a few Canting Ballast “roll tacks”. Oh my god! It was truely awesome to feel the boat heel up (as you eased the keel down before the tack), feel the windward helm build up guiding the boat into the tack, then have the boat come out of the tack with a decent heel and flatten as the ballast came up ointo the new tack. The boat just squirted out - just like the intercollegiate dinghies I used to race.

So if you practice and get the hang of it, I am pretty sure you will be able to do the same roll tacking with the F100. If you can get good at it, I think that the CBTF technology will be an advantage when tacking rather than a detriment.

If you turn the rudder too sharp on any boat, you can stop it dead in its tracks. There is nothing unique in the CBTF design that will prevent that. The dyna yacht guys did a lot of tuning of the ratio of how much the forward rudder turns relative to the aft rudder. Once this is tuned in on the F100, am am confident that this will not be any more of a concern on the F100 than it is on any other boat.

As far as getting auto tacked or caught head to wind by a massive shift. Shifts happen. The more boatspeed you have when you get hit by the shift, the more steerage you will have to get back on course and the sooner you will be back up to speed and sailing well. It is my experience that faster boats generally handle these adversities better.

I’m not sure any of these are good reasons to ignore VPP. And they are all reasons why we go out to the pond and race our boats instead of putting them head to head in some VPP simulation…

  • Will

Will Gorgen

91

Dick, I will try to explain CBTF it to you on the basis that you genuinely don’t understand…
The F100 CBTF boat has more sail area than a fixed keel boat the same size— as much as 30% more sail area than a IOM and or 30-40% less weight for the same sail area in the F100 class. The CBTF boat uses twin rudders to develop ALL the lateral resistance of the boat-NONE is developed by the keel fin. This is accomplished upwind by turning both rudders “collectively” the SAME direction which develops lift to windward eliminating leeway. This allows the CBTF boat to be superior to weather outpointing fixed keel boats.
The canting keel CBTF boat can cant it’s keel all the way to the max 55 degrees (+ 15 degrees for optimum upwind boat heel) without ANY loss of lateral resistance.
Downwind the superior sail area and/or lighter weight results in faster speed than the fixed keel boat. The CBTF boat is able to be between .55 and 1.6 lb.'s or more lighter .
Other speed producing factors ONLY available to the CBTF boat are the placement of the rudders which has been shown to reduce wavemaking resistance and much quicker manouvering speed in less space than a fixed keel due to the twin rudders turning opposite to each
other at the same time…

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

92

Doug: turning the rudders on a CBTF boat “collectively” to try to overcome leeway would seem to produce a lot of drag. The collective function might be something one could use occasionally, to try to put a little water between the CBTF boat and another boat immediately to leeward… like the IACC boats do now with the trim tab.
If you turn both rudders to windward, either you have the rudders going through the water slightly sideways and the hull tracking with no leeway, or the rudders are “biting” and the hull is crabbing to windward… or some combination of both.
Wouldn’t it be better to size your rudders such that they produce suficient lift to overcome leeway without using “collective”. This would probably result in larger rudders with more wetted surface area.
Also “quicker manouvering” would seem to be a way of killing speed rather than producing speed. I suppose if you need to manouver quickly, the twin rudders would probably give you very positive control. But from my experience, the people who win races seem to use less helm input, not more.
To paraphrase what Dick L. and Roy seem to be saying, the computer modeling of this boat says nothing about VMG? Is this the case?

Dick Carver

93

Dick C., In Grahams study the VMG upwind of the CBTF design is shown to be superior to the fixed keel F100 and IOM by large margins–see my earlier posts today.
The twin rudders are designed to develop all the lateral resitance required for the boat to sail upwind.THE KEEL FIN IS NOT USED FOR LATERAL RESISTANCE. If the two rudders were kept in line with the boats centerline and the boat sailed upwind it would develop leeway like every other boat: the hull, rudders, bulb and fin would all be moving two to three degrees sideways like any other boat.
But with collective steering when both rudders are turned, say three degrees to weather, then the only part of the boat moving sideways are the two rudders: the hull, fin ,and bulb are now moving straight thru the water creating far less total drag and allowing the boat to outpoint fixed keel boats.
So using collective steering REDUCES drag compared to a fixed keel configuration which increases speed in and of itself and because they also eliminate leeway the boat has a better VMG to windward(it points better). Combine that with the power of the canting keel and the reduced wavemaking resistance due to proper foil placement and you have a very fast upwind boat.
A tactic in close manuvering with other boats available ONLY to CBTF boats is the “weather sideslip” where the rudders are turned a few more degrees to weather allowing the boat to move sideways to windward for short periods…

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

94

Ok, now I really don’t understand. The current claim for why the CBTF boat is that it will be faster because it has “30% more sail area” than a fixed keel boat. But the proposed F100 class has no limitation on sail area and the ability to change ballast between every heat. I would think the design assumption for an f100 would be that all boats in this class would carry the maximum sail area at all times. Something doesn’t add up…

95

Yeah, thats my fault; I didn’t make it very clear regarding the F100CBTF and the F100 class.
In the F100 class since it is a variable displacement class in very lite air the F100CBTF would be 30 to 40% lighter than a fixed keel F100 assuming both had the same sail area. It would continue to have the advantages of collective steering ,manouvrability and lower wavemaking resistance as the wind picks up. Continuing to carry the number one rig will require both boats to add weight to the keel as the wind picks up(estimted max. weight range in keel bulb for F100CBTF 2lbs.;similar for the fixed keel version). The F100CBTF will be able to maintain an angle of heel of 15 degrees throughout the number one rig range carrying around 30% more sail area from the top of the number one (A )rig wind range thru to C rig conditons . The fixed keel F100 will have to shorten sail OR add more weight so that in whatever conditon the F100 CBTF will either be substantially lighter or carry substantially more sail area than the fixed keel version.
Again, while retaining the advantages of collective steering,higher manouverability,and lower wavemaking resistance.

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

96

Dick C.

I want to add some aerodynamic clarification to Doug’s explaination of the collective system.

First picture a normal sailboat (keelboat or dinghy, full sized or model, it doesn’t really matter). The keel or other symilar appendage is acting like a wing turned sidewise and is developing lift that is used as lateral resistance to keep the boat from going sideways. Because you need to sail on both tacks, that appendage is almost always symmetrical (it may even be a flat plate). Now, in order for a symmetric airfoil to generate lift, it must go through the fluid (in this case water) at an angle of attack. So in order for the keel to do its job on our “normal” boat, the boat sails at a leeway angle - usually only a few degrees - that is the result of the keel needing to go through the water at a certain angle of attack to generate the needed lift.

One point I need to make very clear is that the “needed lift” is dictated by the forces on the sails. As far as the keel is concerned it is a fixed quantity. Therefore, the leeway angle is the result of needing to produce a given amount of lateral resistance.

The drag produced by the keel is the result of producing that lift. Every wing-like planform produced a certain amount of drag for a given amount of lift. Some of that lift is induced drag and some is viscous drag. Ultimately for this discussion, it does not matter. All that matters is that you recognize that for a fixed set of conditions (boat speed, heel angle, etc) the drag of the keel is purely a function of lift.

It is important to note that there is also drag coming from other sources. In particular some of the overall drag is coming from the fact that the hull is not going through the water straight but is actually sailing with a small leeway angle.

Now let us consider our CBTF collective system. In a CBTF boat, the two rudders (one near the bow of the boat and the other near the stern) are our lift generating wings. They are symmetric and need to go through the water at an agle in order to produce their required lift. But instead of that angle coming from leeway, we can now adjust their angle relative to the boat so that the leeway of the hull is zero. The angle of attack of the foils themselves has not changed. Thier lift has not changed. Thier drag has not changed. the only thing that has changed is that the boat is sailing with zero leeway.

So the drag of the foils stays the same when we dial in our collective. However, the overall drag will be slightly less. This is because the hull drag is less when the hull is going straight through the water instead of sideways at a small leeway angle.

I hope this has helped to clarify this collective system.

Will Gorgen

97

Dick L.

If I read Doug’s posts about the VPP prediction correctly, he is talking about time around a given course. He specifically mentions a windward leeward corse so in that case, time to complete the course is a measure of the VMG of the boat, not its actual speed. The polar would tell us what heading is needed to achieve the max VMGW or VMGL. But it is the max VMG, not the max speed, that the VPP uses to calculate time deltas for a windward course or a leeward course.

As far as why the CBTF boat would be faster off the wind, that is simple - it is lighter or carries more sail area. The CBTF system is able to carry more sail area with less weight upwind because it can use that weight more effectively. So off the wind, you have a lighter boat with more sail area. So it is going to accelerate quicker and plane sooner than a heavier fixed keel boat.

Will Gorgen

98

I asked Doug in an earlier post if hotter angles gave a better VMG to leeward. I don’t think he answered.

In most planing boats with spinnakers, you get a lot better VMG at true wind angles of 140 to 160 degrees (as opposed to dead downwind). This is partially becasue the sails are acting as airfoils instead of barn doors. The sails will be trimmed in quite a bit due to the aparent wind angle which is usually in about the 90 to 110 degree range. Aparent wind strength also comes into the equation.

Imagine if you will that you are sailing dead downwind at 10 knots in 10 knots of breeze. your aparent wond strength would be zero and you would have no push to maintain your speed. So sailing DDW limits your boatspeed to something less than the true wind speed. But if you reach up a bit, you get an aparent wind that is the vecotr sum of your boatspeed and the true windspeed. Given the right conditions this can result in boatspeeds higher than the true wind speed. This is pretty aparent in the Schock 40 polar… An extreme example of this is iceboats that regularly sail downwind at 3 to 4 times the wind speed…

In fact, My father and I used to race iceboats a lot. He was a strong believer that anyone who could sail an iceboat downwind effectively would be able to sail a high performance “sport boat” downwind effectively. The same principles of reaching up to increase your boatspeed and then carrying your increased aparent wind strenght down. My experience growing up in Wisconsin and Minnesota was that the best iceboaters were also very fast downwind sailors.

I think a quick peek at the CBTF F100 polars woul;d shed some light on this question…

  • Will

Will Gorgen

99

Since, as I previously explained the polars are unreadable in their present form I’ll give you delta’s for reaches and runs.
On a reach as compared to the fixed keel boat at 2mph wind the CBTF boat was 533 seconds per mile ahead; in 8mph 581 seconds per mile ahead and in 12 mph 361 secs/mile ahead.
On runs the CBTF boat as compared to the fixed keel boat in 2mph wind the CBTF boat was 548 secs/mile ahead; in 8mph the CBTF was ahead by 907 sec/mile and in 12mph wind the CBTF boat was 628/secs/ mile according to the data supplied by Graham.
If this is accurate then it appears the boat would be better straight downwind as opposed to sailing up. My gut feeling is that I don’t believe it since the canting keel can generate power on reaches that it can’t on runs. The polar will show the boat faster dead downwind as per the above since the comparison data(delta’s) come from the same source.
In this case I’m not comfortable with the results but the real thing will answer all.

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

100

Will, some of what you wrote I aggree with. But when you state:
“So the drag of the foils stays the same when we dial in our collective. However, the overall drag will be slightly less. This is because the hull drag is less when the hull is going straight through the water instead of sideways at a small leeway angle.”
You are assuming a lot here, that can only be “proven” by putting a boat on the water.
I disagree that drag on the rudders will stay the same as you dial in incidence. Doug mentioned 3 degrees as being a potential amount of “collective incidence”. My opinion, that’s a lot!
Fron my experience with aircraft and boats, 3 deg. of deflection will cause a pretty fair amount of turbulent flow off the trailing edge, and very possibly some flow detachment on the windward surface.
Also, given the rather sloppy fit of most R/C boat rudders, dragging a rudder through the water with 3 deg. of deflection could very possibly give you an induced vibration. All of this will cause significant drag. In other words, enough to slow the boat down quite a bit. When I flew airplanes, we would call this a very “dirty” set up… dirty = dragy.
One other thing. You seem to use the term “plane” a lot when referring to R/C boats with displacement hulls. Perhaps you and I have a different definition of the term. I have yet to see an R/C sailboat with a displacement hull “plane”. I’ve heard people say the Wheeler can plane when the wind is up. I would like to see that. However, I don’t believe any of the boats in the 1 meter monohull classes is capable of planeing.

Dick Carver