babylon

Aluminium Cats, any opinions?

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What are the pros and cons for Aluminium Cats?

I found this one that is currently build. They are usually cheaper but what are the downsides?

 

 

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32 minutes ago, Keith said:

weight

Pro or con?

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Weight is always never a good thing on a nice sailing multihull.

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Condensation, corrosion, electrolysis, distortion, Oh - and weight!

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Did anyone mention noise? Cats are loud enough slapping around in seas, I can't imagine he clamor that a metal hull would make! BTW, I have a cat being built in Titanium but as a daysailer that was not really a consideration.

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3 hours ago, Rasputin22 said:

Did anyone mention noise? Cats are loud enough slapping around in seas, I can't imagine he clamor that a metal hull would make! BTW, I have a cat being built in Titanium but as a daysailer that was not really a consideration.

Rasper, I have a few thousand blue water miles on a 43'  alloy cat, and never noticed noise apart from bridgedeck slamming in big waves - and then I think it's about the same as a glass cat, without the cracking sounds!  

One big advantage of an alloy (cruising) cat is the sheer strength - pushing a fully welded metal platform into big seas throws a lot of water around, but it is so strong!  Great for confidence.

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I became curious because I saw that Jimmy Cornell has choosen an Aluminium hull for his monohull.

https://cornellsailing.com/aventura/frequently-asked-questions-exploration-45/

 

Quote

Why aluminium?

Jimmy Cornell: The first Aventura was a strong and well-built GRP boat that survived in 1977 a three hour grounding on a reef on the Caicos Bank with only superficial scratches. She served me perfectly well during my first circumnavigation but for my next boat (launched in 1987) I decided to go for steel mainly because, once again, I was planning to explore some remote places and believed that a metal boat was better suited for such a purpose. Eventually I realized that while metal had indeed been the right choice, the proper maintenance of a steel hull could be a nightmare. Obviously I should have listened to my friend Erick Bouteleux and go for aluminium, as he had done himself.

In the following 13 years Aventura III, an aluminium OVNI 43 (launched in1998), took me all over the world, including Antarctica and Alaska, and I became totally converted to this wonderful material. One of the greatest advantages of aluminium over any other boat building material is that aluminium naturally forms a thin but durable oxide layer on the exposed surface that prevents further oxidation. Aluminium oxide is impermeable and, unlike the oxide layers on many other metals, it adheres strongly to the parent metal. If damaged, this oxide layer repairs itself immediately.

I must point out that Aventura’s hull, and any other “aluminium” hull, is not made of pure aluminium, but an alloy. Those used in boat construction contain magnesium, such alloys having excellent durability in seawater.

Why an unpainted hull?

Jimmy Cornell: As on my previous boat, my main priority was not only to have a strong boat but also a functional one, and, in my view, nothing can be more functional and maintenance free than an unpainted hull.

One of the great advantages of an unpainted aluminium hull, especially for those of us who do not buy a boat to sit in a marina but to be out sailing, is that you can forget worrying about your gleaming topsides. As most owners will surely agree, those beautiful topsides can be such a worry when confronted with rough docks, barnacle covered pilings, or being boarded by uncaring officials who often come alongside with their launch banging into your hull without any fenders.

While in Antarctica, colliding with bits of ice was practically unavoidable, and while we ended up without any scratches, friends of ours on two fibreglass boats fared much worse.

 

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11 hours ago, Rasputin22 said:

Did anyone mention noise? Cats are loud enough slapping around in seas, I can't imagine he clamor that a metal hull would make! BTW, I have a cat being built in Titanium but as a daysailer that was not really a consideration.

Details?  Sounds interesting.

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Nothing wrong in aluminum as the boat gets bigger (say 45' and above). It still will be heavier than most glass/foam core boats but in larger sizes, it starts getting more weight efficient IF you use lots of closely spaced, small T stringers to stiffen the plate. If you rely on heavy plate and fewer stiffeners, it will be very heavy.

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http://sailingmagazine.net/article-1794-explocat-52.html  Displ. 41,887 lbs

http://sailingmagazine.net/article-2093-leopard-50l.html  Displ. 41,888 lb.

http://sailingmagazine.net/article-1924-outremer-4x.html Displ. 16,400 lbs.

http://sailingmagazine.net/article-1842-hh55.html  Displ. 31,967 lbs. 

 

I don't think the weight is worth it unless you specifically want it for high latitude sailing.

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Good point here. I am trying to resolve the advantages to having been part and parcel to building a Titanium catamaran and will try and respond to the thinking behind that.

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13 hours ago, Rasputin22 said:

Good point here. I am trying to resolve the advantages to having been part and parcel to building a Titanium catamaran and will try and respond to the thinking behind that.

Can you give a few points about the pro/cons of titanium?
Pricepoint? Buildtime and difficulty to build?  Why is there no titanium catamaran in existence? 

 

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Quote

Can you give a few points about the pro/cons of titanium?
Pricepoint? Buildtime and difficulty to build?  Why is there no titanium catamaran in existence? 

Pros - light as aluminum, strong as steel. Excellent corrosion resistance

Cons - total bitch to weld well and safely, expensive

There is a reason it is widely used in aerospace but they tend to have bigger budgets for engineering and construction.

Why it is is not used in boat hulls - most people can't see the benefits outweighing the cons.

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The Mumby 48 supposedly weighs 8000-8500kg (17600-18700 lbs). Comes with daggerboards and fairly skinny hulls too!

Capture.thumb.JPG.b083541209422e7b702f86f43640efdf.JPG

Here's a short thread about 'em: 

 

There were two for sale, a 2011 and a 2018, not too long ago (when Soma was doing his catamaran shopping, I remember we discussed them in his "Over the Horizon" thread), but I think they've both been sold now.

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Ti has been a huge challenge. A lot of misconceptions out there about Ti. Boat is coming along with one hull done and the other half tackwelded with the inside skins still being fitted. Then a LOT of welding to make watertight. I hate to think of what just the argon welding gas cost has been.

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I have recently bought myself a Mumby 48. The original build is about 7.5t, so pretty light for a boat of its size and comparable to glass cats with a similar compromise between performance and space. She certainly gets up and goes quite a bit faster than expected! They are built a bit lighter than some other aluminium cats, but the design has been built since the early 2000s and of the 70+ boats built I haven't heard of any structural issues. Now that I think about it, the structure certainly seems to be very stiff no appreciable twisting or creaking.

Noise is a non-issue. No different to any glass boat. The mumbys are built with a foam layer between the outer aluminium skin and the inner glass skin.

The biggest concern for me is galvanic corrosion & the possibility of getting eaten by other boats in the marina. There are a few places on the boat where the previous owner has used SS fasteners into the aluminium with out tef gel or other methods of isolation that are showing corrosion. They are plenty with no corrosion at all. It's not a huge issue and it's a simple fix. One of these weekends I need to do some testing for stray currents in the marina.

When we hauled the boat for survey, I borrowed an ultrasonic thickness gauge to measure if there'd been any material loss from the hull, after having heard a few horror stories. It was bang of design thickness everywhere. The previous owner was quite fastidious about his maintenance fortunately.

 

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On 10/11/2019 at 4:31 PM, jmurph said:

The mumbys are built with a foam layer between the outer aluminium skin and the inner glass skin.

That is messed up! So not conventional stiffeners welded to the plate? 

How thick is the aluminum skin? 

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That's very conventional and typical alum construction. Shame about the graffiti on the bulkhead.

Maybe the foam/glass inner skin that jmurph described was foam insulation and a glass liner??

 

 

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2 hours ago, Zonker said:

That's very conventional and typical alum construction. Shame about the graffiti on the bulkhead.

Maybe the foam/glass inner skin that jmurph described was foam insulation and a glass liner??

Sorry! Yeah that's exactly what I meant! It's an expanding foam filler between the two layers.

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Build weight on mine is supposed to be 7.2t, but is no doubt a good chunk more than that now in full live aboard cruising trim. I haven't had much time with the boat yet to really push it, but on most sails so far we've bene up around 10 or more knots with a max of 15. The previous owner has seen 20.

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10 hours ago, Priscilla said:

The Garcia bridge deck is a wee bit industrial.
3C20EEE8-1775-4D4C-A967-B50C92191F63.thumb.jpeg.b996810d478a3d4ba8ae797b35a2d1be.jpeg

Thats the old design, the current new ones are more modern afaik.

I already read a few stories of Aluminium monohull and cat owners that switched to aluminium after wrecking their composite mono/multi.

Jimmy Cornell also went for Aluminium in his last two boats. 

I plan to buy a boat for 1-3 years liveaboard and a lot of miles and really distant places. (e.g. patagonia)

First I had the same criteria as soma in his thread. But now I started to wonder If I should maybe put more focus on reliability.

The Outremers are like a Porsche Panamera, Fast and comfortable. But would I really take it to a 10k miles roadtrip to explore the distant roads of mongolia?

Would like to hear some thoughts on the topic of hull reliability.

 

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Here is another interesting concept, they claim that the building cost for a custom Alu cat are not higher then for a production composite cat, as the sheets of aluminium can be lasercut much simpler.

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Choose whatever you prefer, every design has trade offs.

1 to 3 years will be a blink of the eye in cruising terms.

I'd recommend you go crew on some ocean passages with the designs you might like, you'll kill two birds with one stone.

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Where can I find such a crew? I have been searching on several crew finder sites but couldn't find anything.

I often read about this but it feels like some secret society to me I can't find a way in and don't know where to start.

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5 hours ago, babylon said:

Where can I find such a crew? I have been searching on several crew finder sites but couldn't find anything.

I often read about this but it feels like some secret society to me I can't find a way in and don't know where to start.

Best way is to be standing on the dock in a popular cruising port. Requires commitment, which is a trait the skippers want.

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On 10/15/2019 at 4:00 AM, babylon said:

Where can I find such a crew? I have been searching on several crew finder sites but couldn't find anything.

I often read about this but it feels like some secret society to me I can't find a way in and don't know where to start.

As Boracho said, maybe Aus is best as I think that is where a lot of Alu cats are built???  But if you are looking for alu cats that is a thin population. 

For just getting a ride on the ocean in a cat I've had luck with Cruisers Forum.  Also Latitude 38, mostly for California and Baja.   I've only used those two but there are others, google will find em I imagine.

There are Yahoo groups for Catana and Lagoon.  Hanging out there or others you find may yield an opportunity, especially if you can contribute to some of the conversations to get a good reputation.

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The garcia 52 on the road :

 

Hull built in Nantes, going up to Cherboug to get finished.

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That's awesome, I thought they lost it at the merge.... lol nice work!!!

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That's how they blow all the construction swarf out of the stringers

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4 hours ago, babylon said:

Here's another find.

From Allures, the top seems to be straight from the Outremer factory

https://www.allures.com/en/sailboats/catamaran/allures-c-47-9/

C47.9-integration-CAMERA-ANGLE-1-2018-10

 

Could very well be the case indeed, same architects( Barreau/Newman) and allures is part of grand large yachting, together with outremer, garcia, and gunboat. 

But except for really special purposes, I would clearly prefer an Outremer and avoid the additional 2 or 3 tons, if not more.. 

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And looking at the specs, this Allures is basically an Outremer 45/4X with Aluminium hulls, probably the whole deck is from the same molds.

(and the layout pics are also exactly the same as on the outremer site)

But no dagger boards ?

(most probably, the draft is listed as 1m5)

Perhaps some more volume in the hulls as well

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Is it intended to be an icebreaker? :D

That's crazy heavy and twice as thick as it needs to be.

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Crazy thick hull, even for a yachting icebreaker. You don't put the heavy plate on the bottom, you put it into the stem/bow plates and in an "ice belt" along the waterline

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That boat looks dope. I used to hate on aluminum after my experience growing up with Jon boats and their rivet problems. I went to grad school in New Zealand where we used welded  stabi-craft skiffs, which are far superior to anything Boston Whaler or Carolina Skiff has produced. I’m not experienced enough to evaluate sail area/displacement on multis but I’m watching this space with interest. If there are already kick ass 20’ skiffs Im not sure why we don’t have an aluminum Diam 24 like boat meant to last 50 years. 

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15 minutes ago, Geese said:

That boat looks dope. I used to hate on aluminum after my experience growing up with Jon boats and their rivet problems. I went to grad school in New Zealand where we used welded  stabi-craft skiffs, which are far superior to anything Boston Whaler or Carolina Skiff has produced. I’m not experienced enough to evaluate sail area/displacement on multis but I’m watching this space with interest. If there are already kick ass 20’ skiffs Im not sure why we don’t have an aluminum Diam 24 like boat meant to last 50 years. 

https://m.sailboatlistings.com/view/81515

Anyone have experience with one of these? It’s fine if you tell me it’s garbage, I’m here to learn.

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