Bi-rig

[BigCat]

Originally Posted by freetime

Sounds good.

It must be easy to single handle a bi-rig?

Well, in the usual format, you have the equivalent to two mainsails-so it all depends on how you feel about mainsails.

In my rig, you have two sails that are modifications of the easiest rig in the world to handle, junk sails. I sailed a mono across the Pacific that was junk rigged, and it was immensely easier to handle than a marconi sloop-I have a lot of experience with both rigs, as I sailed a sloop from Los Angeles to Hawaii to Seattle to Los Angeles My modifications just make the rig more weatherly and give a better lift to drag ratio than a traditional junk rig.

IMHO, free standing masts are much more reliable, cheaper, and maintenance free compared to stayed rigs.

[freetime]

Originally Posted by BigCat

IMHO, free standing masts are much more reliable, cheaper, and maintenance free compared to stayed rigs.

It´s just the feeling to have a mast without any stay at all...

[BigCat]

Originally Posted by freetime

It´s just the feeling to have a mast without any stay at all...

Airplanes gave them up long ago-The boat I sailed across the Pacific, from Seattle to Hong Kong, has unstayed masts. The next owner sailed it around the world, and the current owners are on a voyage that has taken them from the Seattle area to Venezuela. The boat is named Batwing, and it just keeps on going with the original masts, about 35 years and 50,000 miles so far- The engineering principle is known as the cantilever, and the math isn't complicated. You don't want unstayed aluminum masts IMHO, because aluminum is prone to fatigue. Now let us consider the issue of crevice corrosion on small, highly loaded stainless steel parts-which is what brings down most masts that fail.

See: Originally Batwing was built by a boatbuilder named Skookum

[freetime]

Originally Posted by BigCat

Airplanes gave them up long ago-

A good point.

I like the boat in your link. Would be fun to se a map where she have been in her life..

Do you have simular sailarea in a Nordic Cat style catamaran as you have with traditional sailrig?

[BigCat]

Originally Posted by freetime

A good point.

I like the boat in your link. Would be fun to se a map where she have been in her life..

Do you have simular sailarea in a Nordic Cat style catamaran as you have with traditional sailrig?

Yes, the sail area is about the same, counting the wing foil as sail area. It is a low aspect ratio rig, in my design, because I don't see any point in going fast if you are going to spend the whole time you are doing so worrying about turning turtle.

Under my ownership, Batwing visited western Canada, coastal harbors on the US west coast, the Marquesas Islands, all major Society Islands, both Samoas, northern Tonga, North Island in New Zealand, Fiji, Tuvalu, Kiribati, Guam, the Caroline Islands, New Guinea, Palau, the Philippines, and Hong Kong. All I know about Loyd's voyage is that he changed to a larger motor some where in Skandanavia. (I almost always sailed, even into and out of strange harbors and docks, and had only a 20 hp motor for a 9 ton boat,) and you can read about the current owner's voyage on their blogs. (They keep changing hosts. Here's one: http://www.sailblogs.com/member/batwingchronicles/ )

The boat's rig had my philosophy, which I still adhere to, of having a huge, easily reefed working rig and no light air sails. I am a very lazy sailor, and too cheap to have a big sail inventory, but I love to sail fast.

[freetime]

Thanks, and the windsurfer bom vs standard bom on a bi-rig. On pics it looks like the model with windsurfing sail are placed more forward on the boats and have bigger sails.

[BigCat]

Originally Posted by freetime

Thanks, and the windsurfer bom vs standard bom on a bi-rig. On pics it looks like the model with windsurfing sail are placed more forward on the boats and have bigger sails.

My concern about windsurfer type booms is that it isn't so convenient for reefing. Eric Sponberg has had structural problems with them, as well.

Rig placement fore and aft is related to the profile under water of the boat. For more about this, read:
Good Old Boat: The Rest of the Ratios - On Helm Balance by Ted Brewer . I prefer to keep the sails as far aft as is reasonable, so as to lead to less force depressing the bows-and on catamarans, the lee bows especially.

[freetime]

Originally Posted by BigCat

I prefer to keep the sails as far aft as is reasonable, so as to lead to less force depressing the bows-and on catamarans, the lee bows especially.

Sounds logical. There is a big difference in the planning of a mono vs a multihull.

You don´t want a boat that will go up against the wind or the opposite. In different winds. A friend of me have a BR 65 (the one on the pic)
And he feel very big difference if he sail with the aft sail or not.

[freetime]

From Nordic cat.
I have chosen to use 2 unstayed masts that can rotate 360 degrees. Masts are 19 meters (62 ft) off the waterline and will be teardrop shaped profiles with a chord of 10% of the mast/sail length. Sail area on each mast around 62 m2 and each mast around 5 m2. Gennaker on the lee side for light winds. No forward beam. Mainsail sheets can be released/adjusted from either cockpit.

This sounds very good. It´s very simular to a aero rig.

[BigCat]

Originally Posted by freetime

Sounds logical. There is a big difference in the planning of a mono vs a multihull.

You don´t want a boat that will go up against the wind or the opposite. In different winds. A friend of me have a BR 65 (the one on the pic)
And he feel very big difference if he sail with the aft sail or not.

Actually, on Batwing, we would run in strong winds under just the foresail sometimes, but we had a very flaring (flam, to be technical,) bow. That is to say, the deck was much wider than the waterline, especially at the bow, and each waterline was quite a bit wider than the one below it. We didn't notice any depression of the bow, even though the mast raked forward and the bottom of it was somewhere near the start of the designed waterline. (See: flare: Definition, Synonyms from Answers.com )


However, multihulls typically don't have much flare or flam forward, though my designs do. The big fear, of course, is burying the lee bow while running hard, and pitchpoling.

[BigCat]

Originally Posted by freetime

From Nordic cat.
I have chosen to use 2 unstayed masts that can rotate 360 degrees. Masts are 19 meters (62 ft) off the waterline and will be teardrop shaped profiles with a chord of 10% of the mast/sail length. Sail area on each mast around 62 m2 and each mast around 5 m2. Gennaker on the lee side for light winds. No forward beam. Mainsail sheets can be released/adjusted from either cockpit.

This sounds very good. It´s very simular to a aero rig.

No, it's more like Cool Change. The aero rig was a brand of balestron rig, with a jib on a boom fixed to the front of the mast, as well as a mainsail aft of the mast, but they did a poor job of quality control and went bankrupt.

[freetime]

And it looks very heavy.

What material is best for the bi-rig catamaran? Not aluminium as i understand.
http://cruisingresources.com/Junk_Rig Junk Rig

http://cruisingresources.com/Unstayed_Rig Unstayed Rig

[BigCat]

Originally Posted by freetime

And it looks very heavy.

What material is best for the bi-rig catamaran? Not aluminium as i understand.
Junk Rig - resources for cruising sailors Junk Rig

Unstayed Rig - resources for cruising sailors Unstayed Rig

Either wood or carbon fiber / vinylester, or carbon fiber / epoxy. Glass can be used for the +45 -45 laminate that is placed in between uni carbon layers, to resist torque (wringing) strains. I am using carbon fiber / glass / vinylester. Vinylester and epoxys used in boat building have similar properties, though epoxy is a better glue if you are laminating over, for example, red cedar.

[freetime]

Carbon sounds very nice for me.

The pressure on a rig must be more on a multi than a monohull. Or?

[BigCat]

Originally Posted by freetime

Carbon sounds very nice for me.

The pressure on a rig must be more on a multi than a monohull. Or?

Yes, of course, since it doesn't heel much. My BigCat 65 has a righting moment of 630,000 foot pounds (854,280 Newton Meters.)

My masts are 63 feet (a bit less than 20 meters) above deck, and the carbon fiber is about .55 (14mm) inches on average. The masts are 17" in diameter at the deck (425mm) tapering to 8" (200mm.) The US Coast Guard checked our calculations and approved them.