Nootka Dancer

...few more photos

 

This boat just broke in half off of Jacksonville Fl.

http://coastguardnews.com/4-mariners-dog-rescued-after-boat-breaks-in-half/2014/12/30/

 

Just heard about it, didn't notice before they cantilevered the rig which is a pretty scary thing with the low bury available on a cat deck.....Somebody got the engineering (if they had any) wrong.

 

Do you think it really sank?

 

If it did there was even more wrong......what was the load, engines etc....what about build material? They changed a lot, maybe it wasn't made of ply or foam but sheet glass, were there steel beams? It would be interesting to get more details on this one.

 

Looking at the old pictures it does appear to have the lashings, the ropes might have been old/wrong material, or perhaps the attach points let go. There would be much higher load on the lashings with the cantilevered rig than the Pahi rig stayed out to the hull sides...

 

It was grossly overweight on launch, and needed layers of foam and maybe the waterline extensions aft to have a chance. It didn't have the house or aero rig when I saw it

The rig could have been buried enough, certainly they didn't hold back much from extreme modifications. It takes something like a 10% bury to get it enough support, and they might have run it through the house, and down to a pod. If it hadn't been deep enough, it should have been dismasted, not sunk.

 

Nootka Dancer Sinks

Nootka Dancer Sinks

This was reported on Cruiser's Network Online, a Yahoo Group. Reports are the multihull broke in half.

Pat Ross

 

Here is the question I had (and was the reason I finally registered instead of just lurking)

Most Cats you see the cabin top is wider than the bridge deck, this one doesn't seem to be. I am no engineer but the cabin top being wider makes sense to me as it would spread out the load, making it four points as opposed to only 2 if the bridgedeck and cabintop were the same width.

I am not sure that even makes sense. But I did a quick drawing to illustrate.
https://www.facebook.com/photo.php?fbid=10152747612603173&set=p.10152747612603173&type=1&theater

And Yes, I am told it did have steel beams. But even steel can't resist the stress of pounding, pumping and a bad design forever. Can it?

 

Steel beams would be fine for strength and fatigue if they were the right section, witness the durability of the steel frame bicycle.

Spreading the load is the problem, in this case not enough lashings would be my guess until we know more.

Thom, when the mast is stayed to the hull the rigging loads pull the hull into the beam which takes the primary loads.

A cantilevered mast on a central beam/pod structure is going to put all the loads on the beam to hull attachment, in this case the lashings. The lashings were not designed for that regardless of the amount of bury. The rigid structure would always be trying to pull up off the beam. Once separated the steel beams would sink the boat if there was no flotation, if the windward hull was left clear it might not have been puled under.

Fishengirl, a wide cabin to hull area can spread loads but properly designed and built boats can be strong enough without a cabin at all.

 

Well clearly the boat was a complete abortion and yes, obviously based on a Pahi 42. Shows the dangers of meddling with a design without the original designers input. I assume it was not insured as no responsible/sensible insurer would have touched it.

The boat was at least 15 years old, and I don't think there was a Pahi between the 42 and 63 at that time. The 42 was a narrow boat with 4 main crossbeams (I worked on the original design). The photos show only three, and yes, maybe the overall beam is proportionately wider

To me the beams look like wood, certainly if built in steel someone did some fancy welding in the beam lashing area. So I suspect that the beams had rotted, check the Wharram blog for the work Hanneke has been doing on their own Pahi beams/mast steps, and she could see the beams, unlike the hidden ones on this boat

Fitting a cuddy cabin like that on a flexibly mounted boat is asking for trouble. Remember Team Phillips?

In principle there is nothing structurally wrong with the Aerorig on a cuddy cat, I've done it quite successfully on a 26ft boat. And of course many catamarans with a conventional rig and a central cuddy

I doubt if we will ever know the truth as to why it broke

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Fishengirl, where did you hear Nooka had steel beams? A source would be good on that one. Someone out there must know the boat.

There is a youtube video out there of a Wharram off England that "broke in 2" because of rotten beams, hulls didn't sink though.....If they had insurance I imagine the insurer will be looking for answers.

 

Nootka Dancer was the first Catamaran I ever saw,since I live inland on L.Ontario and was just getting into multihulls.
There she sat at a marina in Hamilton On.,beautiful ,bright with a huge carving from a totem pole on the bow ,impressive!
Right off I could see a water line from the muddy bay water way above the painted water line .
Watched as the owner builder added a lot of foam ( corecell) & then glassed.
Talked to owner/ builder ,he mentioned they started with the Pahi 42 plans and streeeetched them etc.He mentioned he had studied a course in nautical engineering or some such and calculated etc etc.
He declined further to be " interviewed" saying he would write the whole story himself one day.....
Nootka Dancer was featured on Scott Browns multihull forum a decade or more ago..
John had a large diesel engine between the hulls and aft of Bridgedeck ,hooked up to twin props which raised and lowered by hydraulics ( heavy).
We got to walk around on the teak decks for a short tour,a boat of beauty for sure!
Sad story ,but,Crew rescued and safe.
Saw Nootka Dancer for sale on a site,beam listed as 28'.......original Pahi 42 beam is 22'.

 

If rotten beams broke on the lee side the Wharrams could advertise the unexpected strength of lashings...thanks JimMath your post adds to the picture.

 

I couldn't get to your picture. Basically any design is possible, if it is designed properly. Wharrams have for years said there was some overall benefit to their/traditional beam method, other than moving to site. The flexi propositions. But the reality is that the rest of the best have used a different method. Wharram engineering is considerably compartmentalized in a way were each element has to stand on it's own, rather than being used to support every other element, to some extent. I am not sure who engineers their designs, the approach has always looked more like management where you make educated guesses and the haircut comes off other stuff like volume, speed, etc... These shortcomings are then called advantages. This is in some ways the traditional method of design, and the success of the Wharram range is for all to see in their prevalence and safety record.

It is a heck of a lot easier to build in massive strength by spanning the whole boat with cabins and cockpits that amount to trusses with orders of magnitude increases in strength and stiffness. Pal just finished his 46, the beams are like 12 inches deep, if I recall. Standing headroom of 6' would allow trusses of that magnitude to be built, and they do not need to be anything like the weight of the Wharram beams, which are built nearly as inefficiently as possible in the larger designs. They are also nearly impossible to effectively protect from rot, as designed. The standing head room trusses would have a strength increase of 36 times for the extra height, and stiffness increase of over 200 times. Inch for inch of width. You can see how important that would be where one later ads an aero rig, and in the process eliminates the support to the beam network of the shrouds.

The problem with these larger Wharrams is that you have certain problems whether you stick with the plans, or you don't.

Of course, without knowing how the boat failed, I have no idea how it failed, but just to the question of whether the most efficient way to build beams would be to employ a pod only partially over vastly reduced height beams, no that is not the best way. Wharram has had reservations about pods and deck accommodations from the outset. Eventually he called them good, but only as shacks built on deck, between the hulls without integration into the overall load bearing structure. This was a huge missed opportunity, and while it might even be pretty cool on his 63 foot behemoth, it gets to be less and less sensible on the mid size designs where a pod's relative size is perfect for strengthening the structure while even potentially improving aero, and reducing weight.

As much as the sailors may appreciate a properly sized accommodation on deck, so do the structural components that are also protected from the weather. Even today, wood is a good choice for such components, but the issue of protecting wood from rot is non-trivial particularly as the sections needed to deal with the loads get larger. And may require the use of timber spars that are more difficult to sheath. Hardware attachments also run a huge risk of compromising either the beams or the hulls in larger sections, or more complex forms. Nothing succeeds like hiding all this stuff in massive parts of the house or cockpit, and thereby using smaller, more easily inspected, and protected sections, at greatly reduced cost of construction, and all glued together in a one time only assembly. On most of these larger boats, the only time the demount options is beneficial, is for the original launch, or the subsequent repairs these poorly designed components may require.