Canting Keels In Production Yachts

People do use daggerboards with trimtabs in Australia and New Zealand. Skandia, Nicorette, and Maximus are the notable big boats. Maximus is supposedly currently involved in vaguely defined legal proceedings CBTFco over her daggerboard/trimtab arrangement, though Skandia and Nicorette have not been noticed(?) by CBTFco.
Doug is there any reason why CBTFco is ignoring them?

 

Rats! and there I thought I was on to something new! ... always a day late and a dollar short ...

 

Poppycock

Actually, it's not. By using the collective the (whole boat)induced drag is substantially less than it would be if collective was not used. Thats the point. The twin foils "relieve" the fin and the hull of any function in developing lateral resistance.
CBTF boats can be sailed with the twin foils at 0° angle of incidence; in that configuration the two foils , the hull and the keel strut+bulb together develop the same lateral resistance(lift) developed by the twin foils alone(at approx. +3° angle of incidence)albeit at a much higher cost in induced drag. So the lift required stays the same but the use of the twin high aspect foils to generate all the lift required w/o assistance from the hull and the fin+ bulb reduces (whole boat)induced drag.
Again, if the twin foils are set at 0° angle of incidence relative to the cl of the boat then the whole boat, foils ,fin and bulb will operate at an angle of attack(AOA) to the water flow thus generating lateral resistance-with high drag. With both foils turned to an approx. 3° angle of incidence relative to the hull cl the foils are operating at an approx. 3° angle of attack (AOA) while the hull ,fin and bulb are at 0° AOA. While lift is the same in both cases drag isn't since in the second case all the lift is being developed by twin ,high aspect foils which are much better suited to developing the lift required at lower drag(than the whole boat doing it).
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The Maximus system was one of the first prototype CBTF systems tried years ago-it is not as fast as the current version. CBTF does not ignore ANY infringers......

 

The conservative yacht clubs always had a number of arguements against multihulls. Some of the arguments were strong, some were weak. The two strongest ...

One was safety

Second was that it would split the fleet. The multis would always come in first, so the monos would be forgotton except in terms of handicap results and would become irrelevant to the watching public.

SAFETY
I won't argue strongly either way here - I think that over the last 45 years multis have developed sufficiently to be reasonably safe with families and others using them for sailing extended distance.

And this discussion is about the upper limits of performance where the occasional crash is newsworthy but not taken to be too serious - a bit like formula one car racing. Some risk but all participants know the risk of using a cutting edge bit of machinery at high speed.

SPLITTING THE FLEET
As canting keelers - the larger ones only possible through power assistance - become more popular they will completely outclass conventional keelers.

As we saw with the press for the Hobart Race - TV, newspapers, radio - EVERYTHING WAS ABOUT THE CANTING KEELERS - less than 10 percent mentioned the other boats.

By the time the conventional boats were starting to get to Hobart almost 24 hours later the press and presumably the public interest in the race had faded away.

Canting keelers have split the fleet the same way the monohull clubs have argued that allowing multihulls would

They make non-canting keelers obsolete in racing terms. If they become more popular the huge number of conventional boats will be ignored.

So if both of the traditional arguments of the conservative yacht clubs (who are the power behind the international bodies) have been voided - why not allow multihulls?

Multihulls are faster - the arguments for canting keel boats is made on the basis of performance - so more performance is better - Yes?

This indicates the irrationality of the excessive hyperbole about canting keel yachts.


("irrationality of the excessive hyperbole" is not a bad case of excessive hyperbole itself!)
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Canting keels (made possible in larger sizes by allowing engines to be run) don't improve monohulls in any way except performance.

1/ They don't make monohulls safer
2/ They don't make them more user friendly
3/ They don't integrate into the existing fleet
4/ They don't make them cheaper
5/ They don't improve the suitability of the boats for a variety of uses.

1/ Without getting too deeply into the safety aspect - my position is that multihulls have proven themselves to be pretty reliable for general use - even some quite quick ones.

2/ Anyone can sail most of the production multihulls that are around - including some quite quick ones

3/ Multihulls and canting keelers both fail to integrate with the current fleet

4/ Are multihulls cheaper in every way? I would argue here, since we are talking about performance - that they are cheaper because you can build a smaller, less complex boat for the same performance.

5/ Multis - are used for a huge range of activities by average people. Canting keelers (at least the ones with large canting angles) will always require crewing at the highest level of skill to deal with tacking and gybing, and may need MORE THAN A SKILLED CREW IF THE CANTING MECHANISM OR POWER ASSISTANCE, OR ELECTRICAL SYSTEM, OR THE ELECTRONICS FOR CO-ORDINATION OF RUDDER AND CANARD FAIL.
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So a disclaimer - Everyone can sail what they like. But there is a wider duty of care for all of us to discuss whether certain changes are good for the sport/recreation of sailing.

A second disclaimer - I am a dyed in the wool monohull sailor. However, there are two times in my experienc where multis are unexcelled.
1/ Ocean racing it makes sailing fun for even for those sitting on the rail. The speed makes ocean racing more tactical because of the speed available.
2/ Distance cruising it increases the distance that can be covered in a given time. These days most of us have restricted time available - so multis can give us an unprecedented variety in our cruising experience.

Michael Storer
my boat pages

 

canting keels

1)Canting keels can reduce the number of crew required on almost any monohull-big part of the attractiveness of the Schock 40.
2) Canting keels can improve the "rightability" of some big monohull designs like Open 60's.
3) I think you said that I was of the opinion that canting keel boats would beat normal multihulls. I do but only if the canting keel boats can be equiped with effective hydrofoils AND effective increased RM thru the keel strut. I do believe that SDB(sliding deck ballast) boats along somewhat similar lines of the Langman/ Bethwaite "Maxi Skifs" AND USING HYDROFOILS(bifoil "Moth" arrangement) can beat "normal" multihulls and even have a chance against three foil multifoilers.

 

For a given lift, the total area (of all elements) and the span of the longest element are used to determine the A:R of the system.

A single foil of area "s" and span "b" has an A:R of b^2/s. Splitting the area into two or more panels has no effect on total induced drag.

That's why we don't see canard or biplane gliders. You also don't see the area of wing-sail catamarans split into two foils of half span. The A:R of the entire lifting area governs the induced drag.

Two equal span and area foils is about the worst combination for the lowest total induce drag per unit lift you could possibly design.

No amount of trim change will reduce the induced drag of the two foils. Only changing the span will lower total induced drag.

The reduction in drag due to aligning non-lifting surfaces with the local streamline is real, but because the hull and bulb produce little or no lift, they have little or no induced drag. they have form drag and skin friction drag, but not induced drag.

So yes, reducing total induced drag by changing the trim of the foils is poppycock. It does not happen.

Do a Google on Munk and look at the math yourself. This has been proved fact for years.

 

Not if the reason that they are upside down is because the ballast strut sheared off (as it is designed to do on the Schock 40).

 

poppycock

No claim was made by me or CBTF for reducing the induced drag of the twin foils by changing their angle of incidence. Simply that the drag of the whole boat is reduced by the use of collective.
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There is no question that the total drag of a CBTF boat going upwind NOT using collective is higher that one using it-thats my point. And a proven fact.If a hull ,strut and bulb are moving at a leeway angle(angle of attack) they most certainly DO develop induced drag. On a CBTF boat when collective is used that induced drag is eliminated.

 

Oh really?

Just thought you should know that someone is using your log-in.

 

yes, really

One of us is missing something. Why don't you try to explain your point again in case it's me.
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Is this better?
If you (wrongly) assume that when the twin foils are at 0° angle of incidence the hull,strut,and bulb make no contribution to the production of leeway resistance then there would be no difference in the induced drag developed by the twin foils regardless of their angle of incidence.
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Don't confuse angle of incidence and angle of attack.
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But, IF the twin foils are set at 0° angle of incidence the hull, strut and bulb do,in fact, unload them to some extent since the whole boat is moving sideways(to some extent).
Now, when the angle of incidence of the foils is changed the angle of attack of the foils remains about what it was before or slightly increases and they are loaded more do to the contribuion to leeway resistance from the hull,strut and bulb being removed. So the induced drag of the twin foils would increase slightly from the 0° angle of incidence setting to the +3° setting. But the induced drag of the boat as a whole would drop.
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In one post you said that the induced drag was reduced, in the other post you said you didn't say that.

Either you made both posts and forgot that you said "the induced drag is substantially less" before you said "No claim was made by me or CBTF for reducing the induced drag of the twin foils by changing their angle of incidence. Simply that the drag of the whole boat is reduced by the use of collective."

So, do I conclude that CBTF reduces induced drag some other way? The span of the foils does not change, the area of the foils does not change, how then is induced drag reduced? As I understand the system the foils only have freedom of movement in one plane. Collective has been described as the ability to change the AOA of each foils in relation to both the other foil and to the hull. Thus, any reduction in induced drag must come from changing the angle of incidence.

One of the posts is in error, or was made by someone other than yourself.

Making claims that are not possible does nothing to promote the CBTF foil idea.

Given the task of reducing induced drag any first year aerodynamic student would come up with something better that two equal span foils.

My point is that for a given span and area the induced drag is independent of the number of foils. Thus the total area of the 2 CBTF system foils would generate exactly the same lift and drag as one foil of the same span and area.

 

collective

See #145. I think the whole thing comes down to the fact that when I've talked about induced drag(for the most part) I've used it in reference to the whole boat in the 0° angle of incidence(no collective) case and for just the twin foils in the +3° case.
My whole point is based on the hull, strut and bulb unloading the twin foils a bit(and producing induced drag) in the non-collective case and then loading up in the +3° case with the total induced drag(of the boat) dropping from the 0° case to the +3° case.
Switching from the one case to the other may be confusing you or you don't accept that the hull,strut and bulb create induced drag in the 0° case. The fact that the hull, strut an bulb DO create resistance to leeway(lift) and therefore do create induced drag is the central theme of what I'm saying. Because in the 0° case when they are doing that they do it much less efficiently that just the twin foils do when collective is used(+3° case). In other words, at the 0° case the hull,strut bulb and twin foils create more drag to develop the same amount of lift developed by JUST THE TWIN FOILS in the +3° case.

 

Wrong again.

If the hull lifts and produces induced drag, then the hull area below the waterline gets includes in the total. The total area and the maximum span are uses to calculate induced drag.

If the lift from the hull is reduced to 0, the lift from the foils must be higher. The total lift remains the same, as does the total induced drag.

You are confusing the added area of the bulb and hull due to the leeway angle with induced drag. The induced drag is a product of lift, if the lift is constant, the induced drag is constant unless the planform changes.

As I said before, I don't doubt that aligning the underwater bodies with the streamline reduces drag. It just does not reduce induced drag. Since induced drag is orders of magnitude higher than the form drag, the gain from aligning the bulb and hull with the streamline is small.

These are basic concepts, you cannot fool mother nature.

 

Dont two equal sized foils make more drag than 1 single foil that is twice the size of them? The wetted surface drag is the same, but thats not the only variable involved.

 

Planform

"....unless the planform changes." There you go- right almost. In essence, the planform DOES CHANGE between the lift being developed in the 0° case and the lift being developed in the +3° case.
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In the 0° case lift is developed by the hull, the strut, the twin foils and the bulb.The portion of the total lift developed by the hull,strut and bulb is done very inefficiently compared to that developed by the foils but in this case they all contribute to lift.So there are five contributions to induced drag in this case:1) the forward foil,2) the aft foil,3) the hull,4) the strut,5) the bulb.
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In the +3° case only the foils develop lift and very efficiently compared to the 0° case.Only the twin foils contribute to induced drag in this case.
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The total of induced drag in the second case is less than the total of the induced drag in the first case.
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The clearest possible explanation can be found by isolating the keel strut which on a CBTF boat is not designed to develop lift. But when the twin foils are aligned with the centerline of the boat thats EXACTLY what the strut is doing! It is being asked to operate at the leeway angle which gives the strut section an angle of attack which creates a large amount of drag! Same with the bulb ;same with the hull.In the 0° case,if you don't look at the hull ,bulb and strut as lift producing foils you're making mistake.