Project: Canting keel for cruising yachts

[SubForce Keel]

Hi everyone. Our long-term keel-design project is nearing completion in 2018-2019. The project consists of installing a canting keel to a 35-40 ft cruising yacht. We are searching for a yacht builder to build a yacht like this.

Our goal is not extreme sailing, but rather, the idea is to sail faster and further in comfort with a family crew and create an exhilarating sailing experience for everyone.

Please give us feedback on this project. I am happy to discuss it further in this forum. I am very interested to read your comments and tips.

 

[gonzo]

Are you having a new yacht built or modifying an existing one?

 

[Bruce Woods]

Are you having a new yacht built or modifying an existing one?

Have you considered a catamaran?

 

[luff tension]

What Bruce said.
Why have the complications of canting keel and the draft limitations that imposes when you can have the same or better speed, more space and a better choice of anchorages with shallow draft.

 

[SubForce Keel]

Are you having a new yacht built or modifying an existing one?

Hi Gonzo,

Thanks for your reply. Here are my answers.

It would, of course, be a lot more economical to modify an existing boat design rather than to design and build a whole new one. But that would present many challenges of its own.

Starting with the hull, the original intended speed range may be different and the weight of the boat may be a lot more than originally intended.

But, for example, the Melges 40 hull might work well. However, as we are not building an extreme racer, it would be ideal to not build the boat out of carbon composites. In addition, as the boat is intended for cruising, it would be heavier than the Melges 40, which is of course a full-bloodied racer. It also has a crew ready to balance the boat, whereas the cruising version will not. So, if we were to use the Melges 40 hull, our boat would likely be heavier and the speed range would be different than what it was originally designed for. Consequently, the end result might not be optimum.

At this point we envision the ideal boat to have a deck saloon. The deck structure could be similar to a Moody 45. In addition to having a comfortable and spacious main cabin, it has other advantages that could be used in a canting-keel boat.

There does not seem to be a sailboat on the market with a deck saloon and that is optimized for semi-planing speed ranges. I doubt that we would be able to utilize an existing boat or hull design for our keel project.

Our goal is that more than one of these boats will be built, in which case the design and building costs will go down significantly. We hope and believe that our project will be sufficiently interesting and desirable so that a boat can be designed and built specifically for this purpose.

 

[SubForce Keel]

Hello Bruce and luff tension,

Thank you for your feedback. I will reply to you in a couple of days with better time.

 

[SubForce Keel]

What Bruce said.
Why have the complications of canting keel and the draft limitations that imposes when you can have the same or better speed, more space and a better choice of anchorages with shallow draft.

Hello Bruce and luff tension,


Thank you for your feedback. Here is my reply:


The question as to why we would not just build a catamaran is excellent! Catamarans have many desirable qualities and it is not a wonder why they have become so popular. Our goal is actually to bring some of those good qualities to mono-hull sailboats, as not everyone wants a cat. Some of those qualities are possible with a canting keel.


Heeling is a common problem with mono-hull boats, while many consider it to be the whole point sailing. Living, however, on board a boat that heels 20 degrees or more and bounces around in rough seas can be difficult. Just getting dressed can be a challenge, not to mention cooking dinner for the whole family or crew. But with a canting keel the heeling is usually less when compared to sailboats with a traditional keel. When required, canting-keel sailboats can be sailed with minimal heeling or no heeling at all.


The new Baltic 142 is equipped with a foil, with the intention of increasing speed but after reading about it I concluded that one of the main goals has also been to decrease heeling and increase comfort. Foils work well when the speed is more than 20 knots, which a 142-foot carbon-composite boat should handle with ease. But a for 35-40 ft sailboat built with less expensive materials and not intended for extreme sailing, 10 knots can be considered an achievement. In such a case a canting keel is a better alternative.


The main saloon on a catamaran is typically very large and comfortable. On a wide-hull canting-keel boat something similar can be achieved. Canting-keel boats sail at semi-planing speed ranges and it is advantageous for such boats to have a wide hull, particularly in the stern. In addition, it is fashionable for modern boats to have angled, vertical sides. When a boat is equipped with a canting keel that produces 1000 kg/m of torque, equal to 10 men sitting on the side, a cruising yacht does not need to have wide side decks.


As I mentioned earlier, our ideal cruising yacht with a canting keel would have a deck saloon/pilot house. A wide-hull boat with narrow side decks and a deck saloon/pilot house can have an exceptionally large main cabin. Maybe not as nice as on a cat, but much more spacious than most conventional yachts on the market today.



Luff tension posed an excellent point on the catamaran alternative because of its speed. On the racing side, catamarans tend be to faster than mono-hull boats. But when comparing cruising yachts, it appears to be the other way around: mono-hull boats might be faster after all. For example, Lucia 40 catamaran vs. Elan 400 mono-hull. According to their polar diagrams, the Elan 400 achieves a speed of 8 knots in a 9-knot wind and the Lucia 40 achieves, at the most, less than 7 knots in a 9-knot wind. In tacking, the speed differential is even greater.


Were it possible to build the Elan 400 sailboat 1000-2000 kg lighter, with a semi-planing hull and equip it with a 1000 kg/m-torque canting keel, it would be 1-2 knots faster under most circumstances and many knots faster in tailwind.


As to the comparability of these two boats: is the Lucia 40 exceptionally slow and the Elan 400 exceptionally fast? I do not know. I picked these two boats in a random fashion, as they seemed to be good representatives of their own kind and their polar diagrams were available.


I will comment on the draft and canting-keel intricacies and complications in another post.


Thank you for interest and comments!


Happy sailing,


SubForce keel crew

 

[Doug Lord]

This info is around 6 years old but there may be some tidbits that would be beneficial. Note that Steve Clark is a member here and might be willing to help in some way: List of Canting Keel Racing, Racer/Cruiser or Cruising Sailboats https://www.boatdesign.net/threads/list-of-canting-keel-racing-racer-cruiser-or-cruising-sailboats.39460/

 

[SubForce Keel]

This info is around 6 years old but there may be some tidbits that would be beneficial. Note that Steve Clark is a member here and might be willing to help in some way: List of Canting Keel Racing, Racer/Cruiser or Cruising Sailboats https://www.boatdesign.net/threads/list-of-canting-keel-racing-racer-cruiser-or-cruising-sailboats.39460/

Thank you for your list of existing canting-keel boats, Doug.


I agree, Steve Clark could possibly help us. He might also know people that could be interested in helping us develop our project further. In my observation, and what Steve’s list confirmed, there aren’t and never have been any canting-keel cruising yachts in the 30-45 ft range. They are almost exclusively large or very large boats.


In other words, we are alone with our intention to build comfortable, canting-keel cruising yachts. Undoubtedly, there are several important factors that have contributed to an almost total lack of interest among boat builders to build these kinds of boats. A few come to mind:


· Numerous safety concerns

· Deep draft

· Limited cabin space

· High expense

· Considerable electric power consumption under sail


We also would have buried our project a long time ago, if we did not have good, practical solutions to the many challenges that canting keels present.


Baltic Yachts has built a 56 ft canting-keel boat but it does not seem to be included in Steve’s list. But, the Dibley 40 was news to me! Did they actually end up installing any canting keels? Online, the boats seemed to be in early building stages without canting keels. The boats seem to have a centerboard-type keel instead.


The Schock 40 is a familiar case. The steering mechanism combined with a canting keel was an ingenious idea. But the canting keel was quite ineffective. To my recall, the Schock 40 draft was 2.2 meters, which made the keel depth only 1.9 meters. The canting angle was still 40 degrees, which was reasonable. In contrast, the keel ballast (weight) was only 600 kg, which can be considered extremely light for a 40 ft sailboat.


The hull of the Schock 40 was also quite narrow, 3.2-3.4 meters as I recall, and the hull main frame is quite round, at least by today’s design standards. These two factors make the hull less stable. In addition, the cabin and deck configuration does not make for very comfortable accommodation arrangements, although it is possible to sleep onboard one.


The performance-defining specs of our keel design are:


· Keel + keel fin weight 950 kg

· Keel fin + bulb depth 2.6 meters (measured from the shaft center line to the bottom surface of the bulb)

· Canting angle 50 degrees

· Upright, the boat produces 1000 kgm of torque


The torque is in the same class as in the best racing boats and equals 10 men sitting on the side. Without the weight of the men and their gear onboard the boat, of course.


Thanks again.


SubForce keel crew

 

[SubForce Keel]

Hello again. Here are some pros and cons of a canting-keel sailboat with a deck saloon.

In our opinion, a deck saloon would be an ideal layout for a canting-keel cruising yacht. It might well be the solution for many comfort-and-safety related issues. The challenge, however, could be the potential weight of additional deck structures.

The lighter the boat, the greater the benefit is from a canting keel. For that reason, the deck saloon should also be as light as possible. For example, large glass surfaces are heavy, therefore the deck saloon might end up not being quite as luxurious as in the Moody 45 or other similar boats, but it would still be plenty spacious and well-lit. It would make sense to avoid expensive and special building materials for most parts of the structure, but it might make sense to build the deck saloon partially out of carbon-fiber composites.

Canting-keel boats have one particular safety issue with normal sailing situations: the stability curve is flatter. The stability curve of a traditional fixed-keel sailboat resembles a sine curve. The righting moment of the boat is zero while the boat is upright. When the boat heels, the righting moment increases and arrives at the maximum value when the heeling is about 60 degrees. When the boat heels past this point, the righting moment decreases.

Whereas, canting-keel boats have a significant righting moment with the boat upright, with the keel canted. The keel is also always lighter, which makes the center of gravity higher and as a result, the maximum righting moment is less. For these reasons, the stability curve of canting-keel boats is lower and flatter under normal sailing conditions. The flatter curve is manifested in wind gusts, with the boat heeling faster and further than on fixed-keel boats. It might occasionally lead into further-than-anticipated heeling situations, particularly with an inexperienced crew.

The deck saloon would increase safety in extreme situations. With really large angles of heel the deck saloon would be partially submersed and would increase the righting moment significantly. According to my calculations, at 90 degrees of heel, the deck saloon could potentially completely compensate the missing righting moment of a traditional fixed keel and a flat and low deck structure.

Canting-keels boats are faster and lighter, with the result of faster and more aggressive boat behavior and a wetter ride. The deck saloon would provide cover from spray and large water masses. It goes without saying that the deck structure would have to be such as to make it unnecessary to have to perform sailing duties on the foredeck while sailing.

Traditionally, the space underneath the aft deck and the cockpit floor has been utilized for living quarters. This is problematic, as the space tends to be quite low. On a deck-saloon-type boat with a canting keel, the cockpit/aft cabin configuration could be arranged in a much more comfortable way.

Typically, it is beneficial for a canting-keel boat to have a wide stern. This makes it possible for a deck saloon to reach further back without the cockpit becoming small and tight. And, much more of the hull could be utilized for standing-height living quarters. With the cockpit further back, the cockpit floor could also be a bit lower without it encroaching significantly the usable living space (as the tightest and the most uncomfortable living space tends to be near the stern on traditional boats and with the deck saloon, there would be plenty of standing-height cabin space).

A cockpit situated deeper in the deck would offer more protection and be safer and more secure even in surprising sailing situations. The space behind the deck saloon would make for a very safe and well-protected cockpit, suitable for even the smallest and youngest members of the crew.

In summary, the benefits of a wide-stern, canting-keel sailboat with a deck saloon near the stern would consist of:

· The deck saloon increases the righting moment in extreme situations and prevents capsizing

· Near catamaran-like, spacious and comfortable cabin space

· Opportunities for completely new cabin and cockpit designs

· A bigger portion of the hull can be utilized for standing-height cabin space

· A protected, comfortable and safe cockpit


A challenge could be a heavier than normal total weight.


Comments?


Happy sailing to all!

SubForce Keel crew

 

[SubForce Keel]

Canting-keel failures and accidents

When talking about canting keels, one topic tops all others: keel breakage and the accidents caused by such. Hydraulic cylinders have failed, keel fins have broken, and boats have capsized and sunk with serious consequences.

The core concept of our project is a canting keel which is not completely traditional. In cruising, a canting keel must not be an obstacle to a comfortable and safe sailing experience. Our main goal is to specifically increase the sailing comfort, safety and enjoyment of sailing with our keel alone.

One practical feature of our keel design is that the keel can be raised before docking or dry-docking the boat, so that the boat draft becomes approximately 2 meters, although the keel fin alone has a draft of 2.6 meters.

A 2-meter draft is nice and practical for a 45-40 ft sailboat, or at the very least it is common, and our keel does not limit comfortable cruising-type sailing. Dry-docking and maintaining the boat at the dry-docking facility is easier and safer, with the deck height less than 4 meters off the ground.

With the new and uncommon features and advantages of our keel, it is perfectly appropriate to ask whether the keel breaks easily. Is the keel more complicated and fragile and is it safe?

At this point I am unable to elaborate on the details of our keel design. As far as the keel strength is concerned, I can say that the keel has three components under heavy load with the boat under sail. If one of these three components fail a serious accident may follow. However, the keel design can accommodate these three components with any dimensions or strength rating. In other words, the keel can be built to survive the most extreme sailing conditions. The final strength ratings and dimensions are up to the boat builder.

As there are only 3 components under heavy load and the keel design does not limit the dimensions of the components, our canting keel can be built with today’s technology without any risk of keel failure at all, while using common building materials only. Of course, it is always possible to build an even better performing keel with more expensive materials, but that is up to the boat builder and what the likely owners of the boat would desire from such a cruising yacht.

Happy sailing,

The SubForce Keel crew

 

[Doug Lord]

You might find this interesting: a cruising boat designed with a canting keel that also lifts: MARTEN 65: Canting-Keel Cruiser by Owen Clarke http://wavetrain.net/boats-a-gear/287-marten-65-canting-keel-cruiser-by-owen-clarke
Excerpt:
But certainly the most amazing feature is the deep-draft keel, which, as mentioned, not only cants horizontally to increase righting moment, but also can be lifted vertically so the boat can access shoal-water harbors and anchorages. The operation of this versatile appendage depends on a very large hydraulic system. There is one set of hydraulic rams to shift the keel up and down inside its casing, plus another set to cant both the casing and keel together from side to side. The 24-volt hydraulic power pack that does this heavy lifting also runs a retractable bow thruster, a windlass integrated with a retractable bow-roller system, the main halyard winch, and an in-boom mainsail furling system.

 

[SubForce Keel]

You might find this interesting: a cruising boat designed with a canting keel that also lifts: MARTEN 65: Canting-Keel Cruiser by Owen Clarke http://wavetrain.net/boats-a-gear/287-marten-65-canting-keel-cruiser-by-owen-clarke
Excerpt:
But certainly the most amazing feature is the deep-draft keel, which, as mentioned, not only cants horizontally to increase righting moment, but also can be lifted vertically so the boat can access shoal-water harbors and anchorages. The operation of this versatile appendage depends on a very large hydraulic system. There is one set of hydraulic rams to shift the keel up and down inside its casing, plus another set to cant both the casing and keel together from side to side. The 24-volt hydraulic power pack that does this heavy lifting also runs a retractable bow thruster, a windlass integrated with a retractable bow-roller system, the main halyard winch, and an in-boom mainsail furling system.

Daggerboard keels and canting keels

Thank you for the information, Doug. I checked out the Marten 65 and here are my thoughts.

Italian boat builder Cariboni has built daggerboard keels and canting keels. The mechanics are similar to the keel in the Marten 65. Did Cariboni build that one too? The mechanics on our canting keel is simpler and lighter. The draft of it is only 1 meter less when compared to a daggerboard keel or typical a fixed keel, but I would still consider it significant advantage.

Due to the increased stability and the more upright position of the sailboat, our canting keel can increase the forward thrust provided by the sails as much as 60-70 %. However, because of hydrodynamic drag, the increase in speed may be only 10-25 % (when compared to a fixed-keel boat). In downwind, the speed increase may be greater, particularly if the boat can achieve a planing speed. In our opinion, the canting keel must be high performing before it can help achieve a whole new speed range and provide real benefit. Installing an underperforming canting keel is not worth it, not to a racing boat and for sure not to a cruising yacht.

The keel fin on the Marten 65 has a depth of approximately 3.6 meters and the length of the boat 21.5 meters, which makes the boat length/keel depth ratio about 6. According to our plans, the keel fin depth should be about 2.6 meters on a 12.5-meter boat, which would make the boat length/keel depth ratio about 3.3. With this ratio, our keel would be about 85 % effective than the keel on the Marten 65. In addition, the canting angle on our keel is about 50 degrees, whereas on the Marten 65 it is about 32 degrees.

A Baltic Yachts designer once told me that stability calculations are different on bigger boats, so perhaps the Marten 65 keel is effective enough after all. But in my humble opinion, an increase of 1 meter in depth and 8 degrees more canting angle would not hurt!

The Marten 65 has many of the same elements that we too are trying to achieve. In a previous post, we discussed the benefits of a deck house/saloon on a sailboat. The Marten 65 has a deck house, but according to our calculations, it would have provided many advantages had it been significantly longer, wider and higher. It would have provided an unbelievably spacious main cabin and a much more protected cockpit.

In his article, Mr. Charles Doane was quite critical of the Marten 65 stability in extreme situations: “Her capsize screening value is also quite high for a blue water cruising boat.” Indeed, a big deck house can compensate entirely the lesser stability due to lighter keel weight in extreme heeling situations.

Perhaps a big deck house was not in fashion at the time the Marten 65 was designed (2004), but it is becoming more and more popular today.

Mr. Doane also doubts whether the rough-water behavior of the Marten is appropriate for cruising yacht: "Though the canting keel obviously reduces heeling (and, of course, increases stability when correctly deployed), the boat's motion is still apt to be very lively when sailing at speed, particularly while going to windward in a steep chop. Take a look at that super-low comfort ratio".

In my opinion, the criticism is not called for. In an analogy, nobody says, “You should not buy a BMW with a top speed of 220 km/h, as sometimes the roads can be slick, and you can only drive it at 70 km/h.”

My point is, is it always necessary to take the sailing to the limit? Or drive the BMW at 220 km/h? If the chop is steep, can you not reduce your speed? Or sail at a shallower angle? And still arrive at your destination at the same time with the fixed-keel boats.

In addition to us wanting to bring a canting keel as a high-performance option to cruising, above all we want to create opportunities for yachtsmen to experience sailing at a whole new level. The goal is not extreme sailing, but rather, when the sun is shining, and the winds are perfect, you can sail much faster and much further and in more comfort with “a tuned-up sailboat”. Preferably in downwind. In bad weather, you can slow down or drop the sails and start the engine.

Sound like fun?

 

[SubForce Keel]

To sail or to sail fast? That is the question…


The biggest European sailboat builders build performance sailboats, according to the information published on their websites. Based on what they say, one can conclude that speed is an important quality to a sailboat and desirable one at that.


A jet airliner has a cruising speed of 400-500 knots (740-926 km/h). A normal cruising speed for most cars is at least 70 km/h (38 knots), when taking road and traffic conditions into account. If a medium-size sailboat has a calculated speed of 6 knots (11 km/h) it is good, taking weather and wind conditions into account. That said, if one is trying to get anywhere, 6 knots is really, really, really slow. Enter the saying, “When you step aboard a sailboat, you have arrived”. But, not everyone who owns a sailboat thinks like that. Some actually want to go places! I am one of those people.


The easiest way to make a faster sailboat is to make it bigger and longer. But that is not always possible. What if you just wanted to make a faster boat, not a bigger one? Start modifying! If two sailboats are the same size, a speed increase of just a few tenths of a knot requires vast modifications. A carbon-fiber-mast adds only a few tenths of a knot over an aluminum-mast on a sailboat. The list of potential modifications is long, and it gets very expensive, very quickly.


But if you want to sail 10-35 % faster, depending on wind conditions and direction, and cannot afford to buy a much bigger boat, a canting keel can be the solution. Perhaps the only solution at this point in time.


A speed increase of just 2-4 knots, does it really make difference? It does, if you are trying to get someplace. It doesn’t, if you are happy just sailing and not in a hurry to get anywhere. But I tend to think that it does make a big difference to cruising, and to sailing as a mode of transportation.


What do you think?


Happy sailing,


SubForce Keel

 

[CT249]

Due to the increased stability and the more upright position of the sailboat, our canting keel can increase the forward thrust provided by the sails as much as 60-70 %. However, because of hydrodynamic drag, the increase in speed may be only 10-25 % (when compared to a fixed-keel boat). In downwind, the speed increase may be greater, particularly if the boat can achieve a planing speed.

What canter has such an enormous speed increase? The Cookson 50 canter, for example, is only something like 3% faster than the fixed keel version if I recall correctly.

Your numbers don't seem to have any relationship on the speed that real canters provide.