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Old 03-08-2015, 04:44   #31
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

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The strength is not equal in all areas. Metal boats have greater puncture resistance for example making them more likely to survive a grounding or collision with debris. This is why most yachts cruising ice prone areas are metal.
Puncture resistance is a non-technical term, so not sure what you mean there. It's true that metal handles abrasion better than FRP, which makes it more suitable for ice.

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In terms of displacement, aluminium is the same sort of weight as fibreglass. A little lighter than solid fibreglass and a little heavier than cored structures, but it depends on the details. It is only when you get to exotic lay ups that the weight of fibreglass becomes less.
Uncored FRP would be a terrible waste, and a very foolish design choice. It's not difficult to beat aluminium by a large weight margin with FRPs (cored, of course).

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There are some qualifications. The thinnest aluminium that can be welded without distortion is about 4mm. This means that aluminium construction will be heavier if you use it to build anthing smaller than medium/large cat or medium monohull. The minimum plate thickness means some parts will be overbuilt and hence heavier on a smaller vessel.
3mm aluminium is not a problem (I'm a naval architect who works on aluminium designs all day every day).

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In terms of cost aluminium is unfortunately the dearest material to build a boat from once again until you get to exotic hull lay ups.
I don't know what you consider "exotic", but my definition of it means I very strongly disagree. Aluminium boats would become a rarity if it were more expensive than FRPs, because FRPs can give a much lighter boat.
Aluminium remains a popular choice for its usual markets though (ferries, etc) because it's lighter than steel and cheaper than FRPs.
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Old 03-08-2015, 06:37   #32
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

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Puncture resistance is a non-technical term, so not sure what you mean there. It's true that metal handles abrasion better than FRP, which makes it more suitable for ice.
It may be non technical, but it is important property if you hit a container or get stranded on reef .

We could debate the issue technically discussing the plastic range etc of the materials, but I think looking at these photos of a metal boats illustrates the point better:










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Uncored FRP would be a terrible waste, and a very foolish design choice. It's not difficult to beat aluminium by a large weight margin with FRPs (cored, of course
Many cruising boats use uncored fibreglass for the the hull structure. There is much debate about the pros and cons between cored and uncored construction. The elimination of the risk of delamination and/or water penetration into the core still makes uncored fibreglass a preferred choice for many, especially below the waterline.

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3mm aluminium is not a problem (I'm a naval architect who works on aluminium designs all day every day).
It depends on definition of fair. 3mm is not generally considered acceptable by the standards expected when purchasing an expensive cruising yacht. It is very rare to see 3mm aluminium used in crusing yacht for this reason.


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I don't know what you consider "exotic", but my definition of it means I very strongly disagree. Aluminium boats would become a rarity if it were more expensive than FRPs, because FRPs can give a much lighter boat.
Aluminium remains a popular choice for its usual markets though (ferries, etc) because it's lighter than steel and cheaper than FRPs.
Fibreglass yacht hulls are typically produced in a mold in polyester resin. It is a very cost effective way of producing hulls that is not applicable to large commercial boats.
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Old 03-08-2015, 08:49   #33
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

Weren't the older Outremers solid (uncored) fg? They were and still are known as really good boats.
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Old 03-08-2015, 14:39   #34
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

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Many cruising boats use uncored fibreglass for the the hull structure. There is much debate about the pros and cons between cored and uncored construction. The elimination of the risk of delamination and/or water penetration into the core still makes uncored fibreglass a preferred choice for many, especially below the waterline.
No need for solid below the water line, cored structures are fine, and are, if properly constructed, just as resistant to delamination. As for water ingress, thats usually only an issue if you use polyester resins and or non foam cores. I know of one model of foam cored vinylester resined above and below the waterline that has not had a single case of delamination or osmosis in all its production.

However if you use polyester resins then solid below the waterline is marginally more preferable.


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Fibreglass yacht hulls are typically produced in a mold in polyester resin. It is a very cost effective way of producing hulls that is not applicable to large commercial boats.
Vinylester is a better choice, reduces the Lavezzi effect (Osmosis)
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Old 03-08-2015, 15:35   #35
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

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Vinylester is a better choice
I agree. While a token layer of vinylester resin is common, a complete vinylester layup or even better, epoxy, is rare.

The hull cost is only a fraction of the total build cost (most estimates seem to rate this as about 1/3) so the use of a much better quality of hull layup does not necessarily add a lot of cost to the finished boat. It is particularly disappointing that many premium yacht builders don't use better materials.

Part of the problem is that buyers do not place enough emphasis on the fundamental construction methods. Therefore yacht manufacturers are more inclined to spend money in areas that are more likely to attract customers.

Instances of delamination or core rot (with balsa cores) are not common with cored fibreglass structures, but when they occur they can be truly devastating. Very difficult to diagnose and repair completely, especially in out of the way places. The elimination of these potential problems on a cruising boat that will see hard use has appeal.
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Old 03-08-2015, 16:52   #36
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

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I know of one model of foam cored vinylester resined above and below the waterline that has not had a single case of delamination or osmosis in all its production.
Seawind or perhaps Manta?
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Old 03-08-2015, 16:53   #37
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

Vinyl ester has its difficulties in large-scale production because it is more sensitive to environmental conditions and wet out. Epoxy doesn't allow layups over multiple hours/days like air-inhibited ester resins, which is a difficulty in large-scale production.

It isn't a pure cost of materials thing.

If vacuum bagged or infused, where the entire layup is done at once, then these two make more sense for production scale.

Polyester is still a good choice for production boats. Choose a good resin, use good technique and procedures, maybe use vinyl ester for the first layer, and put on an epoxy barrier coat.

FP's problems were not due to using polyester resin itself - they were due to either poor resin, poor technique or poor process and environment.

If a one-off or low production scale boat, then vinyl ester or epoxy makes more sense.

Instances of delamination and core rot with balsa core is legendary throughout many decades and many boats. It is certainly not uncommon - and I would go as far to say that it IS common. However, it is rarely due to pure osmosis of water through polyester resin and into the core. It is almost always due to penetrations that were not handled properly - even straight from the manufacturer.

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Old 03-08-2015, 16:56   #38
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

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Seawind or perhaps Manta?
Manta only used an outer skin of vinyl ester - the rest of the layup is polyester resin. Also, nidacore was used as the core for about half of the boats before they moved to corecell foam. They are solid glass below the waterline, and all skin fittings and deck penetrations above the waterline had the core removed and made solid glass.

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Old 03-08-2015, 16:59   #39
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

Thanks for clearing that up. Doesn't Manta still have a near perfect track record on the osmosis issue?
Is Seawind all viny in the hulls?
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Old 03-08-2015, 17:12   #40
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

Garcia just released the SC48 wich is an awesome Alu Cat.
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Old 03-08-2015, 17:50   #41
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

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Manta only used an outer skin of vinyl ester - the rest of the layup is polyester resin. Also, nidacore was used as the core for about half of the boats before they moved to corecell foam. They are solid glass below the waterline, and all skin fittings and deck penetrations above the waterline had the core removed and made solid glass.

Mark
This is great information

The manufacturers brochures tend to gloss over the real construction methods, or even worse imply, on casual reading, that the layup is better than the reality.

The first, and most important requirement, is that the fundamental boat structure is constructed to highest possible standards consistent with price point.
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Old 03-08-2015, 18:22   #42
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

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This is great information

The manufacturers brochures tend to gloss over the real construction methods, or even worse imply, on casual reading, that the layup is better than the reality.

The first, and most important requirement, is that the fundamental boat structure is constructed to highest possible standards consistent with price point.
Manta is no longer in business, so no brochure.

However, when they were in business, they provided all of the information I gave in all of their marketing material (which is where I got it from - as well as personal experience that it is correct).

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Old 03-08-2015, 18:27   #43
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

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Doesn't Manta still have a near perfect track record on the osmosis issue?
AFAIK, there have been no Mantas with blisters or delamination issues. Mantas came standard from the factory with an interior outer layup layer of vinyl ester and an exterior epoxy barrier coat before the bottom paint.

Any possible water ingress would be into either polypropylene Nidacore or Corecell foam - no balsa was used, so rot would not be an issue.

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Old 03-08-2015, 20:49   #44
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

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T
Is Seawind all viny in the hulls?
Yes they are
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Old 04-08-2015, 02:17   #45
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Re: Would love to hear the cons and pros of ALUMINIUM vs FIBERGLASS catamaran Sailboa

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Is Seawind all viny in the hulls?
Seawind claim "Osmosis preventative vinyl ester resins being exclusively used throughout the hull construction"

However the details of the hull construction state only the outer layers between the gelcoat and the core are vinyl ester. The rest is polyester.
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