Twin keel research

[MikeJohns]

Anyone any idea what this has to do with keel science? I'm at the point of buying her to find out...
regards,

Sander

Sandar
The outer keels reduce roll damping significantly and give support when drying out albeit on an angle. The penalty is a significant increase in drag. Nothing whatsoever to do with enhancing sailing ability I'm afraid.

 

[MikeJohns]

I'm currently working on a 50-odd ft aluminum sloop with twin keels, but I can't find much in the way of hard data as far as CLR, lead, keel location etc goes. There's quite a bit that suggests a more aft location of the keels, but litle else.
I've attached an image of the preliminary model I'm working on. The boat isn't required to be a rocketship, simply provide comfortable handling.
Any suggestions, questions etc welcome......

Will
I really think that It is down to tank testing with models that you can easily shift the keels.

If you are really interested I still have the intention of building a test rig as a smooth water replacement for tank testing. Too busy to follow this up lately, perhaps later this year.

 

[Willallison]

Ok - thanks all...
Mike - for the purposes of this exercise, tank testing is beyond my needs - it's 'only' for a lesson submission...

 

[D'ARTOIS]

Some 20 odd years ago a few bilge-keel sailing yachts were build in Spaarndam, specifically as passagemakers.

Even a Dutch kitchenmanufacturer sponsored a twin-keel competition yacht, I forgot the name, so stupidly slow those boats aren't.

If speed is not your target, there won't be any other obstruction to do as you please. As Mike remarks, seagoing movement will be much easier and more pleasant than with a single keel yacht.

 

[Sander Rave]

Thanks Mike,
My girlfriend wil be pleased to hear that, as I have to make an offer in performance to keep her from turning pale ;-)

 

[Vega]

About twin keels and performance... how about that:

"With the assistance of Munich Technical University, the Seebruck Regatta Association and numerous sponsors, designer Helmuth Stöberl (Hall/Stand 17/ C 55) has developed the Quintas, a regatta yacht with adjustable twin bilge keels and a rotating wing mast. It is claimed that, with this new design, the 11.98-metre-long boat will be able to sail twice as close to the wind compared with similar-sized regatta yachts. "

http://www14.boot.de/cipp/md_boot/custom/pub/content,lang,2/oid,15298/ticket,g_u_e_s_t
http://www.yacht.de/yo/yo_news/pspic/bildgross//77/t_vision43a91fdfe2cae.jpg
http://www.stoeberl-sailing.de/mainsites/quintas_klein.htm
http://www.stoeberl.de/index.htm

Strange boat...what do you think of it?

 

[D'ARTOIS]

I have seen this type of keel before - it is a variant of a design developed by Van Oossaanen some ten years ago.

It would be interesting to see what the real advantages are, not so much is the paper-story.

For practical reasons - e.g. a reduction of draft - such a design is always welcome. Question is are the sailing capacities better that with a single deep keel? And did they try and make a comparison?

 

[mallo]

Bluebird of Thorne

Hi all
We have owned the original Lord Riverdale Bluebird of Thorne (1939) since 1970, she is a very sea kindly boat, added advantage of taking the ground (we have a tidal range of 40 ft on a spring tide, it turns a few heads when we go and dry out on a sand bank or a drying harbour amongst a load of small boats we are 48ft OA). We wouldn’t change the boat as she handles well (needed a bowthruster, it has been fitted about 10 years ago.) Please find a photo of her included, if anyone one wants to contact me try Michael@raffray.co.uk the twin keel design is definitely an interesting subject.
Best wishes to all
Michael Allo

 

[MikeJohns]

Mike Allo
Welcome and thanks for your post.

Tom Speer

FWIW, here are some model test results of a twin keel vs single keel yacht rolling at anchor: http://www.rina.org.uk/rfiles/IJSCT/Discuss/Klaka.pdf. I don't know how long the paper will be up, so download it if you want it for reference.

Bottom line is the twin keel rolled about 20% more than single keel of the same depth.

Tom I'm a bit tardy to visit this but I finally read it.

I would note that the experiment is largely to support a numerical model for rotational oscillation . Given a fairly poor error result the tests supported trend correlation but not magnitude they were also conducted on only one hullform/keel combination and that was a single keel .

All other conclusions are from running the numerical model only.

Also note that the twin keel numerical model is for twin keels equal in total area to a single fin. No variations in aspect ratio/area were run through the model for twin keels. No full size tests on a twin keel vessel to see whether the numerical model is valid for this combination.

I suppose to sum it up they prove a trend correlation (but not magnitude) for a single design of cruiser-racer between actual and theoretical, then they extrapolate for twin keels without any verification that the model is valid for such a change.

I wouldn't hinge any design or conclusion on that numerical model without considerably more correlation testing.

 

[jedclampit]

http://www.geocities.com/nelstomlinson/boats/Aleutka.html

Here is a link for a twin keel that I found. A good read only from a twin owner.

I too am interested in twins for all the reasons that are discussed about in the link, but I'm looking to design a 30-33 foot narrow beam (10') 12,000 lbs cruising sailboat that I can keep on a trailer... and I believe that the twin concept will sit on a float on trailer with the keels on the outside of the wheels of the trailer...

Still a work in progress...

 

[yipster]

retractable twin keels for a motorsailor?
anybody ever hear or seen anything that way?

 

[Vega]

retractable twin keels for a motorsailor?
anybody ever hear or seen anything that way?

Hello!
I even know one that have three keels, I bet you know that one too.

 

[globaldude]

Re; pale girl's performance offer !!

Thanks Mike,
My girlfriend wil be pleased to hear that, as I have to make an offer in performance to keep her from turning pale ;-)

Just remember Sander rave, it's not the size that counts, but positioning is crutial for best preformance. Good "sailing" and good luck .

 

[Vega]

retractable twin keels for a motorsailor?
anybody ever hear or seen anything that way?

Yipster, what are you talking about?

 

[yipster]

here the fastest 3 keels in the world but maybe i should have said foils

what i study is how to beach retractable twin keels, shapes, drag, too-in, hydrolics and stuff like that, i must be crazy