What is the oyster marine of the catamarans? It's personal

[Francois1er]

Actually, I find the Privilège very much in the direction of what I want, in terms of wood, of usage of the front roof to put beds.


The one thing that makes me nervous are the windows, which are not vertical. It must be extremely hot in Summer or under the tropics

[frederic_b]

I d go for Privilege or Garcia’s explocat.
The later was our pick after a long searching process.
For seaworthiness, cats need to run light. So it’s unlikely to find one with the same look and feel an Oyster will provide.
There are other benefits thought.
Garcia can be pretty well personalized to your taste, including changing layout, colors, etc (we re in this process right now). Aluminium provided a stiffness which is unlikely to ne matched by non-carbon cat.

[redneckrob]

Originally Posted by frederic_b

I d go for Privilege or Garcia’s explocat.
The later was our pick after a long searching process.
For seaworthiness, cats need to run light. So it’s unlikely to find one with the same look and feel an Oyster will provide.
There are other benefits thought.
Garcia can be pretty well personalized to your taste, including changing layout, colors, etc (we re in this process right now). Aluminium provided a stiffness which is unlikely to ne matched by non-carbon cat.

Curious what practical benefits you see in increased stiffness? I've never been sailing and thought, "I really wish my cat was stiffer!"

[frederic_b]

Originally Posted by redneckrob

Curious what practical benefits you see in increased stiffness? I've never been sailing and thought, "I really wish my cat was stiffer!"

Well … it s a where-to-start kind of question.
As for me, there hasn’t t been many days when I wouldn’t think “oh god, please make this thing stiffer” :-) so much about perceptions.

In rough seas, windy conditions, my current cat would make lots of twist-and-shout noises. The stress induced on the large forward windows seems such that I had to change twice the sealant fixing them (an ugly work) over the last 8 years.
Generally speaking, torsion noises and stress are exceeding comfortable level.

Inside, reaching over F5, it feels like everything is going to dislocate.
Outside, I suspect some gel oat cracks at high stress points would result from These torsions.

And then there is the Lagoon-450-gate, according to which a significant unit number have crashed forward bulkhead because of torsion stress exceeding build standards (these being the issue of course). With no official position from the yard, hard to know the extend of this, appart that torsion is high on a cat. And I haven’t yet examined mine.

I d say that it probably does impact sailing performance (and sail durability), but that’s not limited to cats, and as well related to mast stiffness. The theory is that the less parasite movement, the more forward moving energy is transmitted to the boat. The Explocat #1 unit I tried was equipped with a carbon mast, adding to the sail perf the stiffness of its aluminium construction.

The level of noise inside was nothing compared to GRP cats I tried (very much an Oyster experience, to come back to the post’s topic), including our current one, and the response to the moderate wind condition was quite surprising for a 52 footer.

[Tupaia]

Originally Posted by frederic_b

Well … it s a where-to-start kind of question.
As for me, there hasn’t t been many days when I wouldn’t think “oh god, please make this thing stiffer” :-) so much about perceptions.

In rough seas, windy conditions, my current cat would make lots of twist-and-shout noises. The stress induced on the large forward windows seems such that I had to change twice the sealant fixing them (an ugly work) over the last 8 years.
Generally speaking, torsion noises and stress are exceeding comfortable level.

Inside, reaching over F5, it feels like everything is going to dislocate.
Outside, I suspect some gel oat cracks at high stress points would result from These torsions.

And then there is the Lagoon-450-gate, according to which a significant unit number have crashed forward bulkhead because of torsion stress exceeding build standards (these being the issue of course). With no official position from the yard, hard to know the extend of this, appart that torsion is high on a cat. And I haven’t yet examined mine.

I d say that it probably does impact sailing performance (and sail durability), but that’s not limited to cats, and as well related to mast stiffness. The theory is that the less parasite movement, the more forward moving energy is transmitted to the boat. The Explocat #1 unit I tried was equipped with a carbon mast, adding to the sail perf the stiffness of its aluminium construction.

The level of noise inside was nothing compared to GRP cats I tried (very much an Oyster experience, to come back to the post’s topic), including our current one, and the response to the moderate wind condition was quite surprising for a 52 footer.

What you are really describing here is the difference between a performance catamaran and a "charter" cat.

Lagoons are designed and built for "CHARTER" rather than performance, absolutely nothing wrong with this as shown by their dominance of that market place and has proved to be an excellent business model (not withstanding broken bulkheads).

But, when you compare beam and light displacement figures; Lagoon 560 56ft, beam 31ft is 28 tonnes; Garcia cat 56ft, beam 27ft is 18 tonnes; Dazcat 1895 62ft beam 28ft is 14 tonnes; Shuttleworth 63, beam 35ft is 14 tonnes. Neither of the latter, very wide cats make twist and shout noises. None of these are full carbon. Putting a carbon mast on a relatively heavy boat is more marketing than engineering.

Stiffness is down to good engineering design. Garcia is very limited by the choice of material, by opting for a moderate beam and mediocre displacement in order to provide a robust structure and at the same time deal with the linear stress and fatigue limitations of aluminium. Whereas composite structures are infinitely variable to cope with non uniform stresses and long term cyclic fatigue.

The OP makes reference to turn of the century "wood" a la Oyster, so by default must accept the weight and performance penalties this will bring to a catamaran. Neither should anyone be surprised when a charter cat makes twist and shout noises when subjected to conditions it was not normally expected to experience.

There is no wood on space craft or jet aeroplanes, technology has moved on.

[redneckrob]

Originally Posted by frederic_b

Well … it s a where-to-start kind of question.
As for me, there hasn’t t been many days when I wouldn’t think “oh god, please make this thing stiffer” :-) so much about perceptions.

In rough seas, windy conditions, my current cat would make lots of twist-and-shout noises. The stress induced on the large forward windows seems such that I had to change twice the sealant fixing them (an ugly work) over the last 8 years.
Generally speaking, torsion noises and stress are exceeding comfortable level.

Inside, reaching over F5, it feels like everything is going to dislocate.
Outside, I suspect some gel oat cracks at high stress points would result from These torsions.

And then there is the Lagoon-450-gate, according to which a significant unit number have crashed forward bulkhead because of torsion stress exceeding build standards (these being the issue of course). With no official position from the yard, hard to know the extend of this, appart that torsion is high on a cat. And I haven’t yet examined mine.

I d say that it probably does impact sailing performance (and sail durability), but that’s not limited to cats, and as well related to mast stiffness. The theory is that the less parasite movement, the more forward moving energy is transmitted to the boat. The Explocat #1 unit I tried was equipped with a carbon mast, adding to the sail perf the stiffness of its aluminium construction.

The level of noise inside was nothing compared to GRP cats I tried (very much an Oyster experience, to come back to the post’s topic), including our current one, and the response to the moderate wind condition was quite surprising for a 52 footer.

That all sounds like poor engineering, not an inherent issue of stiffness (except maybe the parasite movement thing which has got to be so small that only the most hardcore racers would care about it). I'm a former professional pilot, aircraft flex and twist way more than you're describing with none of the ill effects you describe. Take a look at the wing on your commercial aircraft next time you fly through some light chop.

Building a boat out of aluminum to fix what you describe is not only massive overkill but poorly engineered excessive stiffness can cause just as many and potential even more dangerous issues. Wait until you deal with cracking, metal fatigue, and corrosion!

Stiffness or lack thereof isn't inherently good or bad, it's all about properly engineering for the material you're using.

[fillintheblank]

I have heard privilege's labeled as the rolls royce of cats, and from what I have seen on sailing zatara it seems to be accurate. They are not speed boats, but just very pretty and solid comfortable boats.

[JustMurph]

Tupaia & redneck, have either of you any real world experience on aluminium cats, or large aluminium boats for that matter?

[Tupaia]

Originally Posted by JustMurph

Tupaia & redneck, have either of you any real world experience on aluminium cats, or large aluminium boats for that matter?

Yes.


Don't get me wrong I think aluminium boats are excellent as long as you understand the material limitations and build accordingly a la Tim Mumby.



Aluminium is a linear material limited by sheet thickness. Primary reason why there are few if any aluminium sailing "cats" under 45ft as limiting the weight the necessarily thin sheet would suffer flexing, cracking and fatigue. Aluminium is able to sustain flexing without failure but fatigue is an issue.



Composite if properly engineered is not linear so can be used in a wider range of sizes without compromising the weight. Designed in this way composite is able to sustain cyclic fatigue but unlike aluminium if it is not done properly the failure mode is catastrophic.


With reference to Oyster they originated from wooden boat builders and that is essentially their skill set and what is in their toolbox and Oyster build very beautiful monohulls but the methodology is not appropriate to catamarans.

[JustMurph]

So what about plethora of other boats built out of aluminium in smaller sizes? Why do they work? Also worth mentioning, the sheeting on the Mumby's is pretty thin. 4mm hulls and 3mm topsides and deck. Most other aluminium cats are a fair bit thicker. I haven't heard of a single Mumby with fatigue issues.

[Tupaia]

Originally Posted by JustMurph

So what about plethora of other boats built out of aluminium in smaller sizes? Why do they work? Also worth mentioning, the sheeting on the Mumby's is pretty thin. 4mm hulls and 3mm topsides and deck. Most other aluminium cats are a fair bit thicker. I haven't heard of a single Mumby with fatigue issues.

Smaller boats are not catamarans and therefore do not experience wracking loads to the same extent. The exception are power cat, work boats where weight is not a critical design consideration so can use thicker plate but are still lighter and stronger than steel.



4mm/3mm is about as thin as you can reasonable build with so a sailing cat smaller than 45ft would be disproportionately heavy. I didn't say that Mumby's had fatigue issues I said that the failure mode of aluminium is usually the result of fatigue whereas the failure mode for composite is catastrophic, get it wrong and it snaps.

[JustMurph]

Given that these boats are only 6.5t light ship, you’d still be able to build a sub 6t 40 footer using the same plate thickness. Which would be well lighter than most fibreglass cats of the size.

I see what you mean re the failure modes, it just didn’t read that way. From what I’ve seen first hand with aluminium cats, the material works very well and makes for light, stiff and strong boats. One bonus of the relatively thin playing is that when you do screw up and bump something, it pops right on back.

[Tupaia]

Originally Posted by JustMurph

Given that these boats are only 6.5t light ship, you’d still be able to build a sub 6t 40 footer using the same plate thickness. Which would be well lighter than most fibreglass cats of the size.

I see what you mean re the failure modes, it just didn’t read that way. From what I’ve seen first hand with aluminium cats, the material works very well and makes for light, stiff and strong boats. One bonus of the relatively thin playing is that when you do screw up and bump something, it pops right on back.

It is certainly possible to scale down to 40ft, Owen Easton had a 12m and a 42ft design in the mid 1990's but the fact nobody is currently doing it would suggest 45ft an above make the most sense either from a structural/weight viewpoint or for commercial reasons.

It would seem that market pressure is forcing a lot of the traditional aluminium monohull builders to offer catamarans, Garcia and Onvi with their Ovnicat 48 being obvious examples of the trend.