which cat for me?

Griz!
I sense your preference for aluminum over fiberglass is more visceral than objective. Let me relate a few of my experiences.
A certain naval vessel carrying a Captain's Gig was sprayed by gunfire. Small calibre rounds penetrated the aluminum superstructure injuring two sailors. Identical rounds hit but did not penetrate the old Gig, built twenty years before out of fiberglass. One sailor repaired the Gig in one afternoon. The holes in the superstructure were covered with patches and were not repaired until the next yard period.
In a recent Huricane, a sturdy fiberglass cruiser was blown over a concrete seawall, breaking the capstones and scratching the hull. A well respected aluminum power cruiser close by was torn open at the wagterline on the same wall. The fiberglass boat is still sailing. The aluminum boat is now beer cans.

 

Hi Sandy, thanks for the thought.

Yup, I prefer aluminum for personal reasons, that's just how it is.

My experience is from half a life time in various boats in Alaska. I've seen lots of different variations on that theme. And I still believe that I can build a very good one for my needs from aluminum.

I like the illustration of the BoxCat I posted above. That looks like it's made for metal doesn't it?

 

I might have an opinion if I could see it, but it's so dark I cannot distinguish the shape. Can you re-post it using colors that are clearer and easier to see?

 

http://www.planet.fi/~kcad/boxcat26.htm

Here's the designer's website. I should have posted the link earlier. I like the looks of the boat because it's got perfect shapes for metal.

but there aren't any experts who like aluminum in this size range.

very interesting

 

kenneth and grizz, loot at here:

http://picasaweb.google.fi/terhohalme/Catharsis27#

The old Boxcat 26 never built and I have no access into that site anymore. Now there are two Catharsis 27 under construction. This one is also "a plate" construction. Plywood, sandwich or aluminium (just can't see why), what ever. And much better from hydrodynamic point of view.

Terho Halme

 

Catharsis is a good looking boat. Are you the designer? Or the builder? Are there pictures of finished boats?

What is the displacement?

The rudders appear vulnerable. Can they damage the hulls if they hit something, say a submerged container or rock?

Thanks

Grizz

 

Yes, I am the designer of Catharsis catamarans. The two first Catharsis 27 are under constuction in Omnia vocational college in Finland, Kirkkonummi. I'll send more pictures to web when there is some progress.

Estimated displacement of the empty boat is about 1500 kg (nidacore sandwich) and about 1800 kg (plywood). Full loaded mass is 2600 kg.

In every catamaran rudders can be damaged if they are hitting something hard and heavy. The skeg doesn't help much.

The rudders for the mini keel version are normal spade rudders with a shaft. They have some shelter from mini keels as they are on the same draft.
In the centerboard version, the rudders are pivoting up like in dighnies.

 

Thanks for the reply.

I am interested in the swing up rudders for several reasons. I want a boat I can feel free to beach. And I want a rudder that I can make at-sea repairs to if necessary. And I want a rudder shaft that is not in the water-tight area so it can not sink the boat if damaged.

I am interested in aluminum because I want to be able to travel in high latitudes with less worry. I spent half my life fishing commercially in Alaska. Most new boats built for that area are either steel or aluminum.

Did you design BoxCat? I like the shapes for building. Easy to plate and weld, or easy plywood shapes. I like the additional displacement down low compared to the Vee shape of the Wharrams.

Regards,

Grizz

 

Yes, I designed BoxCat, she was just a proposal. Catharsis 27 is as easy to build as BoxCat. Can't see why she couldn't be beached. The mini keels are strong enough.

 

Nice boat with very nice lines !

Interesting weight estimates . Seems the plywood is still quite light in comparison to the Nidacore.Are the weight estimates for 9 mm Ply ?

Do you need to add stringers or additional ring frames if you build in plywood , or is the build the same as Nidacore ?

I assume the Nidacore hull is taped then glassed over inside and out ?

 

Yes, 9 mm plywood. The stucture is very similar for both material.
Nidacore is fist infused with glass, then nc-machined and then taped together. Nidaplast as is was too flexible into jig frames.

 

Thank you terhohalme.

Your boat will have a lovely clean interior .Those lines are really nice .
You have a good eye.

 

terhohalme, my best compliments, it's a very neat design. You have worked hard the design for a simple construction. I'm impatient to see the pics when finished and to read the memo of the sea trials.

The panels glass-nidacore are beautiful. Where have you bought the Nidacore? It's produced in France by Nidaplast, and sold in the States by Baltek, I believe, under the name Nidacore. The interior is very clean without stringers and this composite has plenty of insulation by itself.


In Canada aluminium is used because it's "dirt" cheap as the Canadian are one of the major producers of this metal. In Mexico marine aluminium is close to 7 dollars a kilo, more expensive than polyester and glass...

Fishing boats have no great concerns about weight savings as a heavy displacement boat has softer reactions to sea (greater inertia) so making the work of the fishermen more confortable. But in multihulls YES weight is a concern, because of the great surfaces involved. And 1/8 inch aluminium (the minimum for welding) is simply too heavy, not enough rigid, and will need miles of stringers and weldings, plus a complete insulation...very expensive.

It's seems after the bad experiences of multihulls made in aluminium in the years 1978-1982 in France, that this metal have acute problems of fatigue and corrosion for this use.

All these multihulls had big structural problems: Elf Aquitaine almost broke in two, Roger et Gallet became a piece of junk, Paul Ricard same thing, PenDuick IV (Manureva) sank probably of a structural problem. And all were too heavy, truly very heavy. None has been a good boat.

Even for cruising sailing multihulls of less than 20 meters, metal is disregarded for the reasons exposed supra.

 

warram cats

for what its worth I had a 42 Warrem cat for about a month before i lost it in a massive storm.
She was absolutely brilliant. The guy I bought her from built her in airex foam. An inch think core that was sheathed in glass. He also built a bridge deck that straddled the hulls.

Though we lost her in this massive storm she stood up to it brilliantly- it was only when we got rammed by one of the rescue boats9 a large container ship) that she broke up- well the first 6 feet of the bow. The amazing thing is even after that she didn’t completely sink- which gave us a huge platform to hang onto while the rescuers sorted themselves out.

Warram cats are great – airex foam is also an amazing product to build one out of. I would hate to think what would have happened to us if she was made of anything else.

 

Thanks guys for you nice words...

Would be fun to build a Wharram from Nidaplast and glass... Need some calculations though...

Nidaplast has a Finnish distributor, Muovikemia Oy. Can't tell a Mexican one.

Try: http://nida-core.com/

Terho