Project: Canting keel for cruising yachts

Discussion in 'Boat Design' started by SubForce Keel, Apr 4, 2018.

  1. Doug Lord
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    Doug Lord Flight Ready

    Comparing a canting keel with only 35 degrees of travel to a high tech fin keel with trim tab is probably not a good comparison. Try comparing a Schock 40 with 55 degree canting keel(or Melges 40 with 45 degree canting keel) to a heavy displacement 40 footer with long fixed keel!
    Last edited: May 10, 2018
  2. CT249
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    CT249 Senior Member

    Well if the point under discussion is how much speed a canting keel would add, of course no one's going to be stupid enough to compare a Melges 40 to a heavy long keeler. One may as well compare a Folkboat to a garbage scow to "prove" that a clinker hull is fast. One has to compare like for like.

    Comparing Cookson 50s seems to be a reasonable way of assessing the speed of the canter. While the canting arrangement is unusual, the point is that we have can compare boats from the same mould with different keel arrangements.

    Looking at ORC certificates shows that when I said I thought the canters were 3% quicker, I was over-estimating it. I was comparing light canting C50s with big rigs to heavier fixed-keel versions of the same boat with smaller rigs.

    In fact it seems that when the other dimensions are roughly equal, the canting keel version is only about 1% quicker. This estimate comes from looking at the ORC certificates of Triple Lindy (canter) and About Time (fixed keel) which seem to be the closest pair in all other respects. TL is 147kg lighter, her spinnaker is 2m bigger, her headsail .3m bigger, and her mainsail 5m smaller. The ORC ratings indicate that the canter is 5 seconds per mile or 1% quicker.

    There's an interesting comparison between About Time in her current configuration and when she carried smaller sails under her old owner, under the name Terra Firma. The displacement and righting moment have remained unchanged, but the boat now carries a mainsail that is 5m bigger, a jib that is 3.5m bigger, and a spinnaker that is 14m2 bigger. The increase in sail area appears to have increased her speed by 5 second per mile, which is of course the same speed increase as the canting keel appears to give.

    An old article about the Cookson 50s indicates that a standard canting keel and daggerboard arrangement (which is more expensive but probably faster than the system that was actually used) would have increased the cost of the boat by $150,000, or 15%.

    So all up, it appears that the Cookson 50 style canting keel increases speed by only 1% or so, which can lead us to gravely doubt any claims of a speed increase of 25% or more from a different canting system. Secondly, adding a C50 type canting keel may only increase speed as much as adding 6% in sail area, which would probably be much cheaper than going for a canting keel. Thirdly, at least one major builder estimated that a normal canting system added a whopping 15% to the price of a boat, which seems to indicate that canting keels increase cost much more than they increase performance. No wonder there seems to be no canting keel offshore boats in full production these days.
    Last edited: May 10, 2018
  3. Doug Lord
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    Doug Lord Flight Ready

    It is truly absurd to think that all Open 60's/IMOCA boats and many top raceboats would use canting keels for a 1% gain!!! Probably the best combination would be with a canting keel and DSS together- like the Infinity 53 and the IMOCA boats(using "DSS like" foils!).
    The combination offers tremendous advantages. The gains would be much, much greater than 1% as shown by Hugo Boss and others.
    This video illustrates the speed possible with a canting keel AND a lifting foil working together:
    Last edited: May 10, 2018
  4. CT249
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    CT249 Senior Member

    The fact that Doug tries to prove many of his other claims with very basic ratios but then dismisses the incomparably more sophisticated ORC VPP when it suits his case is.....very odd. It's unreasonable to dismiss the years of tank testing and on-the-water checks that have gone into the ORC VPP in such a cavalier fashion.

    To the OP and anyone else who is interested in a reasoned discussion - obviously, if the ORC VPP significantly under-rated the speed of the C50 style canters then the canting C50s would always beat the fixed keelers on corrected time, and many keen racers would build canters for ORC racing. Neither of these occur. Therefore it is apparent that the true increase with a canting keel is closer to 1%, as the ORC VPP indicates, and that claims that a canting keel can increase speed by over 25% are obviously way over the top.

    I did actually make an error - I didn't realise that Triple Lindy had been fitted with the canard daggerboard upgrade. That means she's an even better yardstick to show that even a standard canting keel + canard arrangement is only about 1% faster than a fixed keel sister, according to the evidence available. It would be interesting to know of any other examples where we could compare a fixed keel to a canting keel sistership.

    As another way of looking at it - we know the Cookson 50 fixed keeler takes about 470 seconds to sail a mile, on average. If a canting version was 25% faster, they would be almost as fast as the canting-keel 66 footers like Wild Oats X and Alive, and they would beat every TP52 in the world by miles. We know that doesn't happen, therefore we know that canting keels cannot make a boat go faster by anything like that amount.

    Anyone who has actually had significant offshore racing experience (say doing major races and winning championships) knows that a 1% speed gain is actually a huge advantage. Of course, to simply look at Vendee, Open 60 or Mini experience is to ignore the fact that such boats are very different from C50s or cruiser/racers and that they normally do long courses where reaching speed in strong winds is vital.

    Designers like Farr, Reichel Pugh, Mills etc are not stupid. If canters were actually significantly faster than the 1-3% or so that the rating rules state, then the designers would create more canters for ORC and IRC racing.
    Last edited: May 11, 2018
  5. SubForce Keel
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    SubForce Keel Junior Member


    Thank you all for your keen interest and the spirited conversation!

    Measuring the speed and performance of the same boat that has either a canting keel or a fixed keel is not a comprehensive and completely accurate measurement of a canting keel performance. Pen name CT249 is comparing a Cookson 50 with a fixed keel against the same boat with a canting keel, with the result that a canting keel has a speed increase of only 1 %.
    For his arguments, Doug Lord provided an exciting video clip with the Hugo Boss boat. Consider this: Were Alex Thomson to modify his boat with a big, heavy keel with a 3.5-meter draft, the video clip in question would look quite different and Alex might not be too happy!

    Sailboat designers normally design boats around the speed range limited by the boat’s hull speed. The most important contributing factors to the hydrodynamic drag are the wetted surface area and the longitudinal center of gravity (LCG), which is near the longitudinal center of the boat. A non-planing boat, i.e. one whose maximum speed is the hull speed, must also move easily at very low speeds (1-3 knots). A hull like this does not perform well at speeds exceeding its hull speed.

    Whereas, a canting -keel boat is intended to sail at semi-planing or even at full-planing speeds and that being the case, entirely different hydrodynamic laws are in operation affecting the hydrodynamic drag. To achieve the lowest possible hydrodynamic drag, the most important factors to consider are:

    1. The weight of the boat;

    2. The shape of the bottom;

    3. The width of the stern;

    4. A submerged transom;

    5. The wetted surface area and

    6. The LCG.

    The optimal LCG location for a full-planing boat is near the stern (in the speed range of Fn = 0.475 - 0.750, where the drag caused by the LCG is determined by the term c3 X LCB, and where c3 remains a positive standard figure and LCB = in % of length at the waterline (LWL) forward of midship). In summary, the mathematical truth is, that the further back the LCG, the lower the drag.

    Mick Cookson stated at one time that they designed Cookson 50 hull to accommodate a fixed keel and a crew hanging on the side: Cookson 50

    If one can conclude anything from the Cookson 50 hull shape, it seems to have a typical, light-displacement, fixed-keel sailboat hull: cookson 50 design - Google Search

    A low wetted surface area and the LCG near the longitudinal center point have both been important factors influencing this boat design, making the boat somewhat round-bottomed. Compare that to the flat hull shape of the Hugo Boss boat as shown in the video clip provided by Doug Lord and it is easy to see that the hull designs are completely different.

    If the design goal were to create a boat with speeds into the semi-planing range, weight is everything. If one was to reduce the total weight of the Cookson by 20 %, which would be helpful to achieve a semi-planing speed range, the boat would no longer perform optimally even in the speed range the designers had intended, not to even mention faster speeds.

    On the other hand, were one to move the LCG significantly further back, the end result would again be non-optimum.

    In addition to the weight, the shape of the bottom and the LCG, there are other factors that one must consider when starting to design a boat in a high-speed range. The beam of the boat and a submerged transom are couple worth mentioning.

    Longer boats are usually narrower in comparison to their length than their shorter counterparts. Nevertheless, the Hugo Boss is clearly wider (5,8m) in comparison to its length than the Cookson 50 with a 4.3-meter beam. A 5-meter beam would be more comparable to the Hugo Boss beam.

    I own a sailboat that was originally designed for the ILC 30 class. It has a carbon-fiber mast, epoxy/glass-laminated hull and deck and a keel fin cast from steel. The sailing weight of the boat is about 3000 kg and the designer has intended a 500-kg (6-8 people) crew to sail the boat. The keel alone weighs 1200 kg.

    We were planning to install a canting keel of our own design to the boat. The weight of the keel with the hydraulic cylinders, machinery and support structures were to be approximately 1050 kg. Considering that the new keel would not need the existing keel support structures, the overall weight reduction would be about 200 kg. I had also planned that a 250-kg (3-4 people) crew could easily sail the boat. Adding it all up, the boat and the crew would be about 450 kg or 15 % lighter than the original. Sounded promising!

    Then, I had an ORC VPP (Velocity Prediction Program) done on my designs. The result was very much like what pen name CT249 had concluded: the potential speed increase was so insignificant that installing a canting keel would not have made any sense. That said, the speed increase would have been 3-5 %, not 1 %. Relatively speaking, the keel would still have been much more efficient than the keel on the Cookson 50. Regardless, the result was surprising to say the least, considering that the righting torque would have increased by 70 % and the weight would have decreased by 15 %. That begs the question, is the science-to-art turned boat weight reduction and the crew hanging off the side of the boat for their dear lives really worth it? I mean really, does the boat actually go faster? Been there, done that and got the t-shirt…

    After learning all these disappointing news, I decided to not ruin my boat with a new keel. Instead, we sketched out a new boat that was identical to my existing boat except the hull lines were different. The crew weight remained at 250 kg and the boat weight was 200 kg less. Except to the hull lines, we changed nothing else. Even the beam stayed the same.

    In the diagram below I have displayed the canting-keel influence on the sketched-out boat speed.

    (Exhibit 1)

    On the next table, I have marked out the original fixed-keel and the sketched-out canting-keel boat speeds in a 16-knot wind. The result? The canting-keel boat is 10-25 % faster under most circumstances.

    (Exhibit 2)

    The result is still not optimal, not even close. The sketched-out boat does not have optimized hull lines analyzed with VPP or CFD programs. We have not moved the LCG, have not optimized the beam nor have we optimized any other factors. In the VPP, we equipped our sketched-out canting-keel boat with a fixed daggerboard.

    I base my claim on the results of this VPP analysis that a canting-keel boat is 10-25 % faster under most circumstances.

    Pen name CT249 uses the boat median speeds on the ORC certificates to base his arguments, which is reasonable. We have in fact not compared any ORC median speeds to our VPP analysis results because our goals are different, and it did not seem relevant to us. Our goal is to integrate the canting-keel to cruising.

    When I say that a canting-keel boat is 10-25 % faster, I mean that under some circumstances the boat is 10 % faster and under some other circumstances it is 25 % faster, as per the ORC VPP results. I do not intend to claim that our sketched-out boat design has a median speed that is 25 % higher under all circumstances. It does not.

    Because of a high wetted surface and a submerged transom, a full-bloodied canting-keel boat is likely to be slower than their fixed-keel counterparts under weak wind conditions if the sail area remains the same. Is it significant to the cruising sailor, if the boat goes 2 knots instead of 1.5 knots, even if the speed increase is a whopping 33.33 %? Probably not. If one is trying to get someplace, one must start the engine in either case.

    I know a few cruising sailors who will always go sailing, even in headwind. But I have never met a sailor who would always choose a headwind as their chosen heading. Instead, quite a few sailors choose their compass course and the time and date of their sailing excursion so that they get to sail in downwind; and that is where the canting-keel boat is most at home. The speed differential can become extreme, when compared to fixed-keel boats.

    I consider it very likely that the canting-keel boat ORC median speed will not be 25 % higher, when compared to a fixed-keel boat with comparable dimensions and budget without the cost of a canting keel.

    But, when one considers the cruising sailor who wants to traverse from point A to point B, sail in downwind and who starts the engine when the winds calm down, a 10-25 % speed advantage over a fixed-keel boat is likely under most sailing circumstances.

    Wisihing everyone robust winds and lots of sunshine,

    SubForce Keel

    Attached Files:

  6. JosephT
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    JosephT Senior Member

    Good info Subforce Keel. We are seeing more chatter with companies and teams like yourself who are considering the canting keels for cruising yachts. As a yacht cruiser myself I'll offer some of my own pros & cons below:

    • Slight performance increase.
    • Beneficial to cruiser + racer type sailor.
    • Can walk the mast like Alex Thompson (ha!)
    • Canting keel = very deep draft, which means reduced access to many harbors and vacation islands.
    • Increase in parts (mechanical, electrical) means potential for failure.
    • Fatigue life of long, thin canting keel is less than ordinary keel.
    Above all else I would factor safety and accessibility to harbors as my main hesitations in choosing a canting keel. If I were a frequent racer I might opt for one. Presently there aren't too many racing divisions for a monohull with canting keels. Fixed keels are still the main choice.

    Anxious to read your next post that describes this concept further!

    Fast & furious winds! __/)__/)__/)
  7. Doug Lord
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    Doug Lord Flight Ready

    Joseph, don't forget the Volvo 70's -100% canting, IMOCA 60's -100% canting, Mini proto's mostly canting...... Winners of the Sydney-Hobart on elapsed time --mostly canting. Canting keels are the choice of most of the fastest monohulls.
    Performance increase in many cases is substantially more than "slight"!
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  8. JosephT
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    JosephT Senior Member

    Hi Doug, agree on the faster racing boats. I was under the impression his inquiry was targeting cruising boats only. Aside from the cons above, the cruising boats are typically heavier due to the extra interior furnishings (and bottles of rum :D).

    If a canting keel can be retracted to clear 5 or 6ft that would allow it to enter most harbors. It would need to be a reliable, stable design too with few parts to ensure it doesn't morph into a safety issue for cruising skippers.

    The AC36 monohull twin retractable foils, which also double as a shallow water keel are promising. I can see a spin-off of that concept gathering traction for cruisers so long as the hardware is robust and doesn't require flying lessons! :eek:
  9. Doug Lord
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    Doug Lord Flight Ready

    Joseph, there's a boat on page one of this thread with a retractable canting keel. That seems like the near ultimate in canting keel difficulty but a great idea if it will work reliably. The new AC boats don't do much for me-they could have used a much simpler foil system that would be nearly as fast. But, oh man!-they will be exciting to watch.... I can't see any cruising people (that haven't hit the rum yet) being very interested in the system -particularly the submerged pivot axis on both sides-sort of like having two canting keels! I'd hate to see two owners with this system get mad at each other.

  10. JosephT
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    JosephT Senior Member

    Hi Doug, I checked out the Marten 65. A valiant attempt it was, but no cigar. Too many manual tasks & questionable specs for a good cruising boat. Subforce and that article do a good job scrutinizing it’s shortcomings. No question that’s part of the reason it was for sale.

    Also, it’s too big & much too expensive. The market would appreciate a 40-45ft vessel at $350k US or less in my opinion. Forget the overpriced materials & hardware used by race boats. It is possible to build a great boat out of fiberglass with reasonably priced cruising hardware. No more, no less.

    Anything beyond this will limit it’s viability & acceptance. We have seen quite a few yacht builders throw a lot of money around only to end up shuttering their doors.
    Doug Lord likes this.

  11. rwatson
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    rwatson Senior Member


    The terms "Cruiser" and "Canting Keel" is like saying "Lamborghini" and "Range Rover"

    Some people try to shoehorn every little "advanced feature" into what is ostensibly a utilitarian vessel. The Tardis is fiction, remember ?

    For goodness sake, if you need some speed, just up your motors size. That won't increase heel. And don't whine about sail being cheaper. Sail was never cheaper than diesel, by the time you factor in costs of rig, sails, hull configuration and equipment. Especially when you enigneer in canting mechanisms.
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