Radically Different Yacht Keel - "Loop Keel"

Very, very interesting documentation of process, Jon. Thanks for taking the time to share your journey to this point. I truly hope that the long hours and shop time will return huge rewards for the efforts of both you and James.

I really appreciate the time you have taken to provide the process description.

Chris

 

I'll be very interested in looking at your data in more details.

This is not very precise, what area? wetted? planform?.

Affecting the results and therefore the conclusion drawn for them?


From a performance point of view, this is a compromise between

'+'
*increase in righting moment

'-'
*higher viscous drag
*higher induced drag
*higher structural weight
*downward appendages force (=increase in displacement = higher drag)

which can only be studied using a good VPP.

 

Nico,

We are producing a designers pack that should give you everything you need

I think that you have misunderstood earlier posts: Your list of + and - is not reflecting what we have actually achieved on our final version:

You said:

"'+'
*increase in righting moment

'-'
*higher viscous drag
*higher induced drag
*higher structural weight
*downward appendages force (=increase in displacement = higher drag)"

Actually it is:

+

Increase in righting moment
Lower induced drag (read the other posts, you are confusing development with the end result)
Lower structural weight (this is key, we are MUCH stronger than a fin for the same weight)

Downward force is only present when heeled, the induced forces on the hull when upright offset any downwards force and the nett force is zero

Viscous drag is the same as we match the wetted areas of the equivalent fin keel.

-

Slightly increased wave drag

VPPs are a problem as we have not found one that can accomodate dynamic righting. (Including the Wolfson Unit VPP). The reference to effective area was not referring to skin drag area. This came from lift-curve considerations and refers soley to effective lift producing area, ie, not skin ie VERY IMPORTANT!!!!!!!!

Jon.

 

Loop Keel

Jon, I like the way you think; thanks for sharing this and for the detail-I've got some studying to do. Best of luck-any clients lined up to give this a shot on the race course? Any rules problems that you forsee? Brilliant work!

 

very nice ,,I am not a fan of the extended bulb keel,, or kanting keels ,but with the support of heavy chine ,,this looks real good, perhaps in the future ,this can be made mobile ,,or swing keel,by shifting ,,,good work ,,longliner

 

Doug, Longliner,

Take a look at post #9 in this thread. We are considering a particularly (we think) appealing possibility for canting the loop keel.

We did not want to make too much of it until we had developed the concept and so we have only just publicly launched. We are looking for candidate projects to apply it to and, due to the possiblity for getting it wrong if badly applied, expect to be deeply involved in at least the first few design matching excercises.

Thanks for your encouraging comments.

Jon.

 

loop canting keel

Jon, I'm not sure I fully understand the balance of your loop keel theory but the circular arc/loop canting keel I do and think it has huge potential. It seems ,though, that a canting fin keel would still be able to get the weight out further but not with the safety advantages of the loop version. Sealing the two entry/exit points requires a lot of thought but I imagine you've got that solved. Very interesting stuff here, Jon!

 

Hi Doug,

I am not sure what the maximum angles they now achieve on a canting fin, but the canting loop could easily go over 90 degrees from vertical either side.

From a rating rule this looks interesting as most open 60's are only allowed to heel 20 degrees with their canting ballast out. In this situation we would be measured solely on the benefit of the canting ballast on the loop, but with the additional advantage of extra dynamic righting and no daggerboard/fin.

In terms of sealing the entry/exit points - it is not an issue, although you would have some form of gland to stop water passing too freely. If you look at the drawing on post 5 and imagine the loop is circular and joined up in the centre of the yacht, then you will realise that it is well above the waterline. You therefore only need a sealed housing for the keel to run in, with the controls entering at the highest point. This means that if you suffer keel or some form of control failure then there should still be no path for water into the vessel. Obviously a keel failure that did major structural damage/holed the vessel could still sink the craft.

James

 

Doug,

After we applied for our patent we found that others (unsurprisingly) had explored joined tip twin keel configs. What no one had done before was to impose a deliberate, sideslip independent, continuous circulation around the path of keel limbs and interconnecting hull to generate added mass. Sweep back in conjunction with a loop form keel had also not been used to reduce or eliminate broaching before and these two aspects form the primary inventive steps that we have made in this concept.

The rolling loop keel for canting is a secondary patent claim but a rather appealing one we think as this couples shifting ballast with dynamic righting, probably a rather powerful combination! For a class like the Open 60 there is no reason why the loop should not extend to the lateral limits normally found in a canting keel, awkward in harbour but then Open 60s are not supposed to be quayside queens. A loop like this could obviously move the ballast to the same extent as a conventional canting keel. As a loop this size would generate a ferocious dynamic righting moment and have canting ballast it would make for a rather powerful vessel. Note also that CBTF boats need the twin foils to resist leeway when the ballast strut is fully deflected. The canting loop keel does not as it is a perfectly adequate keel in its own right and so the overall viscous appendage drag is likley to be lower than that of a CBTF boat.

Sealing it is actually really easy.... Don't! Just make the through hull trunking continuous and drive the keel with a toothed rack on the keel inside the hull and a handle which turns a pinion inside the trunking. Then the only sealing needed is for the bearing of the crank handle (or hydraulic motor if you like spending money).

A pity it is not America's cup legal (from the America's cup design rules): (f) appendages which contain ballast shall not rotate.

There is one more rather interesting characteristic in this device that we want to explore but have not managed to test in a controlled fashion yet... This one can really make your head start to throb.... A version with flaps is needed for this. The circulation system from the keel stores an amouint of energy in the water surrounding the boat. This energy can be added to by deflecting the flaps to increase the circulation, this will obviously increase drag temporarily as the increased circulation takes energy from the boat until the point at which flap angle and circulation are matched (about 5 chord lengths of travel typically for a step input to the flaps). By the same rationale, reducing flap will take energy back from the water and should give a temporary thrust to the boat. This could be very interesting when approaching a racing mark: Approach the mark behind a boat that you wish to overtake, slowly add flap to store energy in the water and hold the boat back as you do it, get right on the tail of your opponent and reduce flap.... Instant overlap and round the mark on the inside! To be further explored but very appealing to me.

Jon.

 

Here's a link to more on this....

http://www.ybw.com/yw/podcast/ywapr_07_leadedge.pdf

Thanks Crag!

 

the ballast could be on a trac or guide,,and 2 hydrolic hand pumps ( one on each sideof topside ,would work, thus beating the engine assist argument of sailboat racing ,,,,,,,,,,,,good luck,longliner

 

"We obtained acouple of old Laser hulls and fitted one with a very crude loop keel with a ballast bulb (Clark Y section... more on this very shortly!) and a fin and bulb on the other with similar area. When we sailed them two things were apparent, the loop keel boat was incredibly stiff and so the dynamic righting moment was very evident also, the fin keel boat whistled straight past the loop keeled boat so this was only a partial success! A secondary observation was that inspite of the poor speed of the loop keel boat it did point higher and was able to keep sailing when pressed hard whereas the fin keel boat rapidly descended into a broaching display. Downwind things were even more dramatic with the loop keel being remarkably easy to sail even in a force 7 while the fin keel by then spent most of its time only marginally under control."

Is it fair to judge the loop keel against a boat fitted with a keel that is, by your own admission, very crude?

It must have been a very crude keel indeed to make a Laser into a "broaching display"!!

 

CT249
You have slightly mis-read my post, what I actually said was "We obtained acouple of old Laser hulls and fitted one with a very crude loop keel with a ballast bulb (Clark Y section... more on this very shortly!) and a fin and bulb on the other with similar area."

The fin keel was only crude in the way it was made (mdf fairing over a steel spar with welded steel ballast inside the bulb, then skinned with glass/epoxy). It was quite stiff enough and had a perfectly adequate and accurately cut section and the bulb was the same size and shape as that used on the loop keel variant. The hydrodynamic centre was in exactly the same location as the normal Laser daggerboard. The loop keel was crude, constant chord, constant section but was entirely appropriate for the purposes of a first experiment. What we actually had was a fairly competent fin keel vs a very rough and ready loop keel, the results were still interesting enough to go further.

Lasers are normally sailed flat when used as dinghies. If you ballast them like a yacht and let them heel like a yacht and then take them out in beaufort force seven and upwards, unsurprisingly, they can show some tendency towards broaching. Heeling like a yacht was the entire point of the excercise so I am of the view that it was a fair demonstration of the difference between a loop keel and a fin keel.

We not only tested Lasers of course. One series of tank tests at the Southapton Wolfson Unit used a superyacht hull model loaned for the purpose. We were particularly pleased to gain the use of this hull as full data was available for it with its original fin keel. This keel was the one originally designed for the boat so the comparison with the same hull with a loop keel was highly relevant. More details/pictures on our website.

You have also highlighted the reason that I am not particularly keen on posting accounts of idea development on forums... Bits of them always get taken out of context and there is a tendency for early work to become confused with later developments the more this happens, perhaps it may be best to remove my earlier account?


Jon.

 

Jon-don't get discouraged about posting here. Some people will always be hypercritical or criticize w/o knowing (or understanding )the facts. Forget it.
Many of us very much appreciate the effort you guys have put in as well as the effort to tell us about it!

 

Jon, this looks very interesting. About the Laser test sail, do you have repeated it with the improved loop keel? It seems to me that if you have an increased rightening moment you can carry more sail in the laser with the loop keel that in the one with the fin keel. Is that so? Was this taken in consideration? If I understand correctly the rightening moment will increase with speed. Is that so?
You talk about an apparent mass increase of about 1/6. This happens at what speed?

It seems clear to me that this concept, can be very interesting even if does not provide a superior speed. If there is not a significant loss in speed, and this keel provide a superior handling and superior safety of the boat (by increasing apparent mass and rightening moment), it would be very interesting for the Cruising boat market. It would provide more seaworthy light fast cruising boats.