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Old 08-06-2012, 14:15   #31
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Re: can you make a steel or aluminum cat? or tri?

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Originally Posted by psneeld View Post
Well...like a lot of Tom, Dick and Harry's of the world who self proclaim to be an expert and write a few books (to make money).....he's flat out wrong.

There are numerous boats out there of both metals well under 50 feet that are cruisin' just fine. Want to see oil canning? Look at a lot of coastal patrol boats of different governments.

Some are almost new and being scrapped...others are 40+ years old and going strong. Depends...as I and others have said....do it right and it's fine...do it wrong and pay the piper.

Maybe he's one of those engineers without the skills to design a metal boat under 50 feet or just feels that' it's better to do it in FRP...and that's OK...but doesn't mean it's not possible bcause there are plenty of boats out there proving him wrong.
Gregor Tarjan's comments were specific to catamarans (not monohulls) and from memory he was saying generally need greater than 50ft to make Al work.

There are however a couple of Australian designers/builders mentioned previously who have successfully built Al cats less than 50ft. it can be done.
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Old 08-06-2012, 14:29   #32
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Re: can you make a steel or aluminum cat? or tri?

here is another <50ft aluminum cat;
NG YACHT DESIGN | NICOLAS GRUET | TAHITI

@Sandcrab;I believe the Yapluka's are born again through Havana ;
Welcome on the Havana sailing catamarans

well they look suspiciously like Yapluka's

Once again they will be built by Alu Marine.

Cheers,

JJ
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Old 08-06-2012, 15:36   #33
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Re: can you make a steel or aluminum cat? or tri?

I had a Marine Architect do consulting on a job once. He commented that our small powerboats (23-30 ft) were way too heavily built with 1/4 thick bottom hulls. His comment was "I designed a 100 passenger ferry with 1/4 plate once" A typical 40 foot cruising boat is likely 1" to 1.12" glass on the bottom near the keel. I suspect 1/4 alum is lighter than the glass. I'm not sure on cats though.... many are cored hulls... how thick is the outer layer? or those with solid bottoms, how thick are they?
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Old 08-06-2012, 16:41   #34
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Re: can you make a steel or aluminum cat? or tri?

For those interested in ALumarine : www.alumarine.fr

Unfortunately in France / Europe for those that are in America...they have done (and still doing...) some of the largest aluminium catamarans (sail) in the world as "douce france".
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Old 08-06-2012, 19:47   #35
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Re: can you make a steel or aluminum cat? or tri?

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Originally Posted by JJ77 View Post
here is another <50ft aluminum cat;
NG YACHT DESIGN | NICOLAS GRUET | TAHITI

@Sandcrab;I believe the Yapluka's are born again through Havana ;
Welcome on the Havana sailing catamarans

well they look suspiciously like Yapluka's

Once again they will be built by Alu Marine.

Cheers,

JJ
The NGs 41' is about 18,000 lbs lightship and the 53 Havana is about 41,000 lbs lightship. These are heavy boats. I'm just sayin.....................
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Old 08-06-2012, 19:47   #36
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Re: can you make a steel or aluminum cat? or tri?

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I'm just quoting Tarjan.
Here's his bio and his site. Sailing Catamarans | Fountaine Pajot Catamarans | Power Catamarans | Multihull Dealer Brokerage
This is a multihull thread so if the other metal you are referring to is steel it doesn't apply here.

Gregor Tarjans 25 year professional background include his active involvement in the 1986 “Stars and Stripes” America’s Cup campaign, a USCG-100 Ton Masters License, a degree in Yacht Design and Art History, which all contribute in providing exceptional service to clients. He is a US Merchant Marine officer, has owned numerous large catamarans and trimarans and has participated in the Olympic Star Class, North American Championships. Gregor is fluent in German and French and his passion and theoretical knowledge of cruising multihulls can only be matched by his 30 years of practical experience sailing them across the oceans. He has performed multiple transatlantic crossings and has sailed all types of catamarans from 20-120′ in the most diverse waters from the North Sea, South Atlantic to the alpine lakes of Nepal. He is co-author of the SAILORS MULTIHULL GUIDE, writer of numerous articles for MULTIHULL, SAIL and CRUISING magazines.
Gregor Tarjan’s is considered a leading multihull expert and has published 3 important reference books:
Catamarans, Every Sailors Guide” (photos by Gilles Martin Raget) was first published in July 2006. Because of its success Mc Graw Hill Publishers, New York purchased the rights to the book and have reprinted it several times under the title
Catamarans, the Complete Guide for Cruising Sailors
In 2009 Gregor Tarjan self-published his 3rd reference book on multihulls:
Catamarans, Tomorrow’s Superyachts“. (photos by Billy Black) It is the first publication of its type and deals with the subject of large catamarans.
Gregor Tarjan is a certified, New York State licensed Yacht Broker a member of SNAME (Society of Naval Architects and Marine Engineers) and YBAA (Yacht Brokers Association of America).
Well I guess all the smaller steel and aluminum cats/tris out there are destined for failure....

I'm not arguing hypothetical here like you or this "engineer"...there are hundreds of successful examples out there as we speak..

Maybe he should be arguing that old "the world is flat" or the "men can't fly" concepts since the metal cat/tri theory is already in operation and working just fine...
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Old 08-06-2012, 20:52   #37
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Re: can you make a steel or aluminum cat? or tri?

Geesh, Tarjan is not arguing whether they are bad boats and doomed to failure just that heavier boats no matter what they are made of. There are so few lighter boats that it gets very difficult naming more than a handful of that specialize in light boats. The one offs and customs are where the affordable light boats are. And as I said before nobody builds a sailing multi out of steel.
BTW Tarjan owns a smaller Outremer and is a dealer for them as well and used to be a dealer for Yapluka so he goes both ways.
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Old 08-06-2012, 22:47   #38
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Re: can you make a steel or aluminum cat? or tri?

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Originally Posted by psneeld View Post
Well I guess all the smaller steel and aluminum cats/tris out there are destined for failure....

I'm not arguing hypothetical here like you or this "engineer"...there are hundreds of successful examples out there as we speak..

Maybe he should be arguing that old "the world is flat" or the "men can't fly" concepts since the metal cat/tri theory is already in operation and working just fine...
No Not at all.

Reality is that none of the larger manufacturers of catamarans have chosen to go this way althougth it is not uncommon above 50ft. Effectively what Tarjan said if you read his whole book, not that it is impossible. I am sure he could advise you if you wanted an aluminium cat, his view is that composite such as it the outremers makes for a lighter an thus faster vessel.

There are a number of smaller manufacturers/builders of Al cats under 50ft but they are mostly built to order (custom) rather than production runs. There is also some european builders of smaller cats (would have to look up).

Cheers
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Old 09-06-2012, 00:29   #39
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Re: can you make a steel or aluminum cat? or tri?

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For those interested in ALumarine : www.alumarine.fr

Unfortunately in France / Europe for those that are in America...they have done (and still doing...) some of the largest aluminium catamarans (sail) in the world as "douce france".
They also build some very nice custom aluminium monohull boats.

The quality of the welding is first rate. In any aluminim hull this together with using the right grade of aluminim is the first and perhaps the most important requirement.
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Old 30-07-2012, 03:25   #40
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Re: can you make a steel or aluminum cat? or tri?

Here is a new trimaran in aluminium,and it folds too;

http://advancecruising.com/

Cheers,
JJ
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Old 30-07-2012, 05:14   #41
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I owned an aluminum Mumby Cat great cat. Google Mumby catamaran or cyber yachts.
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Old 30-07-2012, 11:11   #42
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Re: can you make a steel or aluminum cat? or tri?

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I agree, there are 2 boats on yacht world right now, aluminium (uh-loo-mi-num) and under 50 feet, an one is over ten yrs old.
I know this thread is dated a little, but I can't help ask "why"?

I can only imagine disadvantages to a metal hulled boat. Noise, weld cracks, weight, corrosion. How would you field-patch a boat like that? With fiberglass, most likely, and not very well.

What advantages are you anticipating from a metal boat? I can see the possibilty of better strength in an impact, but then the repair will be so much more complicated if/when you ever do tear a hole. I would think the aluminum would be so that thin (to keep the weight down) that it would likely tear very easily.

Because most cruising cats have a high saloon, they typically have smallish sailplans. This works with the composite boats because of their extremely low weight. I would think that the weight of an all-metal boat would impact your design choices in undesirable ways.
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Old 30-07-2012, 14:22   #43
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Re: can you make a steel or aluminum cat? or tri?

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I know this thread is dated a little, but I can't help ask "why"?

I can only imagine disadvantages to a metal hulled boat. Noise, weld cracks, weight, corrosion. How would you field-patch a boat like that? With fiberglass, most likely, and not very well.

What advantages are you anticipating from a metal boat? I can see the possibilty of better strength in an impact, but then the repair will be so much more complicated if/when you ever do tear a hole. I would think the aluminum would be so that thin (to keep the weight down) that it would likely tear very easily.

Because most cruising cats have a high saloon, they typically have smallish sailplans. This works with the composite boats because of their extremely low weight. I would think that the weight of an all-metal boat would impact your design choices in undesirable ways.
There is no perfect boat building material. One of the big advantages of aluminium over fiberglass is that in a collision or grounding it is much better at retaining its watertight integrity.
In your recent grounding it's likely an aluminium cat would have remained watertight, which not only vastly improves saftey it makes repair much easier.

In an aluminium boat new sections can be welded in place to replace damaged panels retaining 100% of the the original strength, with no adittional weight. There is no need to scarf joints, no need to use dissimilar materials. The repaired boat will be exactly like the original design.

Aluminium is lighter than solid fiberglass construction for the same strength. About the same as cored fiberglass without the delamination / rot problems. For racing boats a composite expoxy carbon fiber layup is by far the lightest.

Crusing aluminium boats are quieter and better insulated than the equivelent fiberglass boat. Metal fatigue is never seen, the structure does not flex enough ( unlike a 747 wing, or even an aluminium yacht mast)
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Old 30-07-2012, 16:31   #44
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Re: can you make a steel or aluminum cat? or tri?

There was a Wharram catamaran under fifty feet built from light gauge aluminium I think 3mm for hull and stringers and heavier frames. Apparently it spends most of its time at anchor but has been cruised extensively--i\was built in the seventies and apparently is in good condition--which is more than can be said for many Wharrams built at the time out of plywood.

Aluminium is good stuff but everything electrical needs to be insulated from the hull except for the zinc anodes--and copper earth plates are asking for trouble. It can not be successfully welded by the average bloke capable of using a stick welder. Alloy is a better conductor of heat--so it does need pre-heating and scrupulous cleanliness. I will have a go at most things but I would leave aluminium welding to those properly equipped for it, because it needs to be done to the highest industry standards.

Cats can be made from steel--but three millimetres is getting a bit heavy for small cats.
I have seen a ferro-cement trimaran with fibreglass amas--and I am sure a steel trimaran would be just fine if the metal fatigue problems could be overcome. Only the centre hull would be steel, the amas could be glass.

One can make some sort of tiny-tots assessment of the suitability of any material for a specific purpose by drawing graphs of its advantages versus costs--or weight--and by using similar scales can see at which point one material becomes feasible or impractical.

Strength to weight is one good graph--worry about size versus costs later--
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