Bi-rig performance cruiser

[Nordic Cat]

Hi Stefano,

We have been working on a bunch of other things, and have pretty much finalised the internals, enginerooms etc. Presently working on the rigs. Have also been busy with a new rig for my Tobago, its 1.5 meters taller , a 330 mm rotating aluminium section, with a lovely flat-top main adding nearly 15 m2 on the main.I'm waiting for my new self tacking jib that will be about 9m2 bigger, but up to now the improvement in light winds has been awesome!

On the underwater hull shapes, I am leaning towards a little known Norwegian designer. His designs are extremely fast, and the Dragonflys have a tough time keeping up with his cats.

He has his maximum hull width further back than most.

See here:

http://home.online.no/~uthaug/about/about.htm

Check out the gallery.


Regards

Alan

[Spiv]

Originally Posted by Nordic Cat

On the underwater hull shapes, I am leaning towards a little known Norwegian designer. His designs are extremely fast, and the Dragonflys have a tough time keeping up with his cats.

He has his maximum hull width further back than most.

Alan, The light bulb shape and longer forward hulls are my favourite shape too.
The more I look at your boat, the more I like it. It looks like you have captured the good points of all the best design and put them gracefully together.
If I was to make any change, I'd add a metre or so at the transoms... but on the other hand I have not seen your complete drawings and am only judging from the plan view. As I said, I have had my cockpit swamped by big, fast following waves a few times...

Have you thought of being able to turn the forward cockpit into a jacuzzi when at anchor? All you need is a (removable) watertight board blocking the passageway just forward of the windows. It only has to be 600mm high, so one can climb over it and be in the passage where he can dry his feet before entering the saloon.
That is one of the little luxuries I want.

[brian eiland]

Some problems with tacking the bi-rig have come to light in this subject thread HERE

...and on this subject thread there have been a few voices of concern

Originally Posted by Alan

...The Radical Bay has an inefficent rig in my opinion. They are chanaging the rudder design due to issues with tacking in strong winds and waves.

Originally Posted by Nordic Cat

Derek Kelsall, a designer I respect alot, was kind enough to comment on the bi-rig concept on another thread. He has sailed on both the larger bi-rig cats I have been able to find.

Derek commented, but he never addressed the tacking problem that might occur

I posted this message at the other forum in hopes of soliciting replies by those few folks out there sailing these rigs, and to suggest a possible solution to the tacking problem of a vessel design you have put a lot of excellent work into.

Asymmetrical CB's, nacelle mounted on centerline
http://www.cruisersforum.com/forums/...1&postcount=93

[yipster]

installing new pc and thinking of a fast one meter wide hd media monitor tv but cleaning new virusses

Originally Posted by brian eiland

Asymmetrical CB's, nacelle mounted on centerline
http://www.cruisersforum.com/forums/...1&postcount=93

most interesting and got to keep up much harder i see, from dual lateral rigs francescofabbrovich on steering a biplane rig

[Nordic Cat]

Thanks for the comments and links guys. Francescos site has been around for a long time, and he does an excellent job of explaining how he tacks his boats.

I'm not too worried anymore that my boat won't tack, but "the proof of the pudding will be in the eating". I hope to be able to start building by september this year if all goes as planned.

We are presently working on the design of the rig, which is a bit of a challenge, not so much the structural stuff, but more the lines, where to run them etc.

I want to be able to let the booms/masts rotate through 360 degrees, to enable reefing at any wind angle. So the mast rotator controls will be linked to the boom/vang. I have come up with an idea of adding an horisontal "plate" on each side of the mast the extends far enough out to give a decent purchase for the rotator controls. The secondary function will be to use this as a step to stand on when flaking the main. Does this make sense?

As the booms are relatively short, the main sheet will have to be a 2 piece job,or else there will be chafing issues on the coachroof. So we are looking at having 2 sheets for the booms, one on the coachroof and one at the outside edge of the deck. A bit like some of the Catanas had, where the 2 sheets could be moved around the boat for optimum leech control.


Any ideas/suggestions are welcome..

We have found an experienced engineer to do the FEA for us, so that is now covered.

The jury is still out on underwater lines in the aft sections, but I'm tending to go towards slightly submerged transoms, to avoid wave slap at rest, but also for the hydrodynamics. Did any of you read the article I posted by the french guy on the "submerged transoms thread"??


Regards

Alan

[yipster]

Originally Posted by Nordic Cat

We are presently working on the design of the rig, which is a bit of a challenge, not so much the structural stuff, but more the lines, where to run them etc.

I want to be able to let the booms/masts rotate through 360 degrees, to enable reefing at any wind angle. So the mast rotator controls will be linked to the boom/vang. I have come up with an idea of adding an horisontal "plate" on each side of the mast the extends far enough out to give a decent purchase for the rotator controls. The secondary function will be to use this as a step to stand on when flaking the main. Does this make sense?

As the booms are relatively short, the main sheet will have to be a 2 piece job,or else there will be chafing issues on the coachroof. So we are looking at having 2 sheets for the booms, one on the coachroof and one at the outside edge of the deck. A bit like some of the Catanas had, where the 2 sheets could be moved around the boat for optimum leech control.

doing other things text above keeps crossing my mind while a rough sketch might help visualise your idea.. ok i re-read and think again

[rayaldridge]

I don't think tacking problems are intrinsic to biplane rigs. Thomas Firth Jones tried such a rig on his last boat, Dandy, and gave it up after a couple of years, because it was inefficient, slow, and presented handling problems. However, he said that Dandy tacked like a monohull with the biplane rig.

Ray

[Nordic Cat]

Ray, do you have any references/articles tthat you can point me to for this boat? I have heard it mentioned several times, but have no definite information. I would like to try an avoid any mistakes he thought he made.

I wonder why he thought it was inefficent?

Regards

Alan

[cats4me]

Hi Alan,

Thx for email and link to this thread. Your design looks awesome and all the best with it. Hopefully we can use SL to give you a virtual better "feel" for it

BTW: Your "tulip/bulb" sections look extremely close to some sketches I did for a similar concept. Except where you have the forward cockpit with saloon entrance, I was experimenting with twin 'side-cockpits' also each with saloon entrances - each cockpit having pilot stations and all-round seating (thus I needed the said "tulip" flare for upper hull volume) ... and also the flared hull would be a pre-requisite to reduce spray on a side-cockpit design.

We are presently working on the design of the rig, which is a bit of a challenge, ....

I want to be able to let the booms/masts rotate through 360 degrees, to enable reefing at any wind angle. .....

Any ideas/suggestions are welcome..

(having the rotating mast I also believe is a great for emergency depowering)

Ok, you asked for it ... here's some radical ones ...

As you may have seen I have this setup on my 'virtual' bi-rig cats in SL (which supposedly have fully rotating wing-masts)

First off : As with my 'virtual' cats, these thoughts on bi-rigs are 'virtual' - no RL experience. Also I cannot take credit : I read about something like this somewhere but unfortunately the reference I think is back in SA (I'm in UK atm)- I do remember it was by a fellow South African but clueless on name. However its stuck with me as the logical solution for cats - thus my virtual designs. I will try find the reference on it if its of interest to you.

The general idea is having twin rotating sheeted wing masts, but with some form of stay, which would distribute stresses better vs unstayed, and gives a possibility to trim the CE.

Basically, you'd have a spreader beam across the mast tips (possibly even 'H' shaped for better sheet clearance), and you'd secure that to the corners of the yacht with adjustable 'stays' / rigging. By cross rigging each mast to opposite corners there is more clearance for the rotating sheets, and better staying of the rigs (as the speader keeps them apart).

Keeping the stays adjustable has several advantages - for one you can do some fore and aft trimming to move the CE, plus its an easy way to raise and lower the entire setup.

Because of the 'stay' system, the mast design can be a lot more efficient and cost-effective, and the foot would be a ball-and-socket or similar design as opposed to bearing - which should make for a simpler mast base setup and less operational torque stresses.

Having dual rigs also gives you the option of setting the masts at a camber - angled in towards each other at the tips, even with your unstayed masts. A camber setup like that would add a safety feature and try to negate heeling force when reaching etc, specially in strong winds were reefing the windward sheet, the forces on the leeside would still have a small vertical downward component - working against the overall heeling force.

Enjoy

Something like this ... (although the camber is not obvious in this pic due to the perspective)...

[Nordic Cat]

The guy who inspired you is probably Richard Glanville who came up with his Freewing bi-rig setup that is exactly as you described it. He has been SA based for many years but also works out of Scotland apparently.

Google him,otherwise there is an article here: http://www.hie.co.uk/Default.aspx.Lo...0d.Lang-EN.htm

Unstayed masts are alot simpler than what you describe, why have the hassle of all those attachments? If one key fixture fails you lose a mast.

A key feature of the unstayed rig is the ability to let the booms and masts feather for reefing regardless of wind direction. In big seas, and the main pressed up against the shrouds, you have to come in to the wind to get the main down, that can be quite hairy, I have done it.

Camber is not necessary as the unstayed mast has automatic depowering in gusts, it can easily flex more than a meter, this can be a slight disadvantage when hard on the wind, but if there is alot of wind, a reef will be in, so flexing won't be such an issue.

There are a couple of boats in NZ that have unstayed bi-rigs that seem to perform well compared to their traditional counterparts.

I will get back to you on the rendering a bit later.

Thanks

Alan

[yipster]

Nordic Cat, well.. here is some merrit in cats4me idea i think. back on installing windows media centre (all in one and nice for onboard)

and installing the softwares after building a desk and bed i now see bed could have been a inch deeper in the box and other small flaws, ok its better than ikea builds
but... having an adjustable mastfoot stays etc may have big advantages when its trimming time

me i'm after a motorsailor and dreaming up the rig and more plus dozens of handling systems, only half get your idea tho

your going for sleefed surfsails like cris white and shioning right? did you consider a bi aerorig maybe with a lateral swivelling jib line?

than there is spiv: "my young brother just bought himself a 2004 40' Lavezzi for 170,000 euros!" have you seen them? awesome and like some others they allready build a few

[Nordic Cat]

Hi Yipster,

No I'm not going for sleeved sails, the sails will be flat-topped fully battened sails on sliders.

I agree that a stayed rig is easier to trim for balance, I was considering having the daggerboards in a "casette" that can be moved fore/aft before final glassing, but I've been convinced that it isn't necessary on a cat.

There will be provisions for a forward halyard for either mounting a jib or a gennaker if this proves necessary.

The boat will have 2 small fixed LAR keels for beaching and a symmetrical daggerboard each side, so we should be able to balance her under all conditions. Rudders will also be slightly larger than required.

Hope this clarifies my thoughts at present...

regards

Alan

[cats4me]

The guy who inspired you is probably Richard Glanville

Yes, that seems to be him thanks - I just googled him and although I didn't find the original article I remember, I did find a patent of his on the design I referred to at : http://www.freepatentsonline.com/WO2003101822.html ... so I guess it must be him.

Unstayed masts are a lot simpler than what you describe, why have the hassle of all those attachments? If one key fixture fails you lose a mast.

Simpler agreed, but they also transmit a lot more torque stresses, although stresses on a dual rig are a lot less, also their location over the hulls helps so it should be fine. In Richards design I don't think there is all that many attachments, but yes good design is necessary throughout all systems.

On the other hand, his design wins hands down when it comes to trimming.

Some other thoughts on unstayed masts : I'm not sure what you're planning to put up there, but unstayed masts may restrict the equipment that you can get up there - having a 'spreader' up there is handy from that aspect, not that its a reason to change your design! Also, I once read unstayed masts are also very tough on battens, although I'm sure the designers will be aware of that if it is an issue.

A key feature of the unstayed rig is the ability to let the booms and masts feather for reefing regardless of wind direction.

Yes, but its the same feature his design has, its not limited to unstayed masts only.

In big seas, and the main pressed up against the shrouds, you have to come in to the wind to get the main down, that can be quite hairy, I have done it.

Why? As I mentioned, Richards design has fully rotating wing masts ... the same as yours - they can also be depowered / feathered in an instant.

Camber is not necessary as the unstayed mast has automatic depowering in gusts

Yes you have a good point - for unstayed masts the flex may be of additional assistance in gusts, whether or not the effect offers as much assistance as the camber idea I'm not sure - I'd think not as the anti-heeling force created by the camber is always there - just more-so in gusts. On his design it still makes sense though ... you did ask for ideas.

There are a couple of boats in NZ that have unstayed bi-rigs that seem to perform well compared to their traditional counterparts.

I don't see many reasons why they shouldn't.

I will get back to you on the rendering a bit later.

np

[rayaldridge]

Originally Posted by Nordic Cat

Ray, do you have any references/articles tthat you can point me to for this boat? I have heard it mentioned several times, but have no definite information. I would like to try an avoid any mistakes he thought he made.

I wonder why he thought it was inefficent?

Alan, Jones describes his troubles with Dandy in his excellent book, Multihull Voyaging.

Jones sailed the boat with biplane rig for 2 years and 2000 miles before converting to a conventional fractional rig. He describes the advantages of Dandy's biplane rig as quick tacking and high-pointing-- he could make some progress tacking in 60 degrees, but the boat was not fast even when tacking in 90 degrees. He suffered from the lee sail being blanketed when reaching, and no amount of variable sheeting seemed able to cure the problem. The boat was disappointingly slow, except downwind-- at one point he hoisted a square sail between the masts.

Jones doesn't attempt to generalize from his experience to all biplane rigs, so apart from the lee sail problem there isn't any information about why he thought the rig was inefficient, just that it was. I know that many folks believe this lee-blanketing is not a problem, but I've been unable to discover any plausible theoretical reason why some biplane cats seem to do well and others poorly. Even some cruising boats that have generally been well-received, like the Radical Bay, have not been fast compared to similar boats with conventional rigs. A little research also turned up the fact that the RB has some problems with lee-blanketing.

Dandy's masts were stayed, but there have been some problems with fast multis using unstayed masts. See Chris White's description of Juniper (his big tri) and the unstayed masts she was originally fitted with. He eventually refitted Juniper with stayed masts.

Ray

[yipster]

Originally Posted by rayaldridge

I've been unable to discover any plausible theoretical reason why some biplane cats seem to do well and others poorly

asked for that book before and called the library again to work on it