Quote:
Originally Posted by Dockhead
Well, the last quote confirms what I just said -- that balsa is preferable where strength is needed. And if you Google "Open 60 balsa" you will see that Open 60's are built the same way -- Nomex honeycomb and foam of various types in big panels -- this is lighter -- and balsa -- heavier but far stronger -- in high stress areas. I have seen them built. Honeycomb is not practical on cruising boats because of the voids, which would instantly fill up with water in case of any hull breach. And even Nomex honeycomb doesn't quite match balsa for strength. |
I believe that was long ago. Now IMOCA boats and other carbon racers use a honeycomb, called nomex and sometimes the same thing made of kevlar. As you said I
Google "Open60 core" and what I found was
references to really old boats, 15 year old ones. If you look at new boats you will not find any reference to the use of balsa. Maybe you can post a
single one referring a
new boat, meaning 2007 and over using a balsa
core?
"In the spring of 2005 construction started in Canada on the fourth Owen Clarke Open 60, the first pre-preg carbon Nomex yacht of its type to be built in North America."
IMOCA Open 60 : Owen Clarke Design - Yacht Design and Naval Architects
Launched 1997, at CNB France for Giovanni Soldini she went on to produce some fine results for this veteran Italian sailor and in so doing helping to establish his name amongst the heroes of the IMOCA 60 Class. Constructed of Nomex cored T700 Pre-preg carbon fibre for hull and deck
IMOCA Open 60 Eco Class - Ex 'Fila','Saga' : Owen Clarke Design - Yacht Design and Naval Architects
Like all the racing prototypes built by Multiplast, Brit Air will be made of a carbon sandwich using a honeycomb (Nomex ) core, and oven cured. The build process will imply female carbon moulds, in order to ensure perfect dilatation homogeneity during the curing phase.
Multiplast to build the new Brit Air Imoca Open 60’
As you know multiplast build most of the French big
racing boats, have a look:
MULTIPLAST Boat Yard – Building of racing multihulls, conception, composite material fitting
MULTIPLAST boat yard – building of racing monohull
They all are built this way:Like all the racing prototypes built by Multiplast, ... made of a carbon sandwich using a honeycomb (Nomex ) core,[/COLOR][/B] and
oven cured. The build process will imply female carbon moulds, in order to ensure perfect dilatation homogeneity during the curing phase.
As you know there are
safety rules regarding the way a Imoca (Open60) can be built and there are authorized materials that are considered to be the ones that would give them the strength to survive the conditions they encounter.
Balsa for core is not authorized. This are the 2014 rules and these are the authorized materials for the hull building:
B.10.1: Boats having a first measurement certificate issued after 1, May 2013:
The hull of the boat less associated deck hardware and all the corrector weights shall be built with respect for the following specifications:
- HR fibers are allowed and limited to the following fibers :
o Toray T800H
o Toray M30S
o Toray T700S
o Mitsubishi Rayon MR40
o Hexcel IM 7 (6k)
o Tornel T650/42
o And any fiber having been a prior acceptance of the Chief Measurer
- Nomex core maerial or foam
- Film adhesive 300g/m² minimum
- Non-adjuvanted resin (no nano-techs)
- Weight of the tissues150g/m² minimum
Quote:
Originally Posted by Dockhead
Most high-end boats still use balsa, at least in high stress areas of the hull, and certainly in decks, where the strength and stiffness are especially important.
It is not true to say that balsa is "old school"; foam is "modern". An engineer would laugh at such an idea. They are different materials with different properties; not football teams. Balsa is supreme for compressive strength, but may be too heavy for very large panels which have been engineered to have enough strength without it. Balsa is also less elastic and absorbs less energy -- so where a design needs energy absorption, then foam is better for that. Balsa is more tedious to work with -- another reason to use foam if the strength of balsa is not needed. Engineers decide what tradeoffs to make in any given design. |
Yes, balsa core can be used on small
parts of the hull to make it more rigid but
when we say that a hull is balsa core that means that all the hull is balsa cored and not some small portions.
When we say that a hull is foam cored that means that almost all the hull is foam cored even if it has aluminium or balsa small inserts on areas subject to more stress.
I am curious about those "most high end yachts that use balsa core" can you name a few? I mean not ones that use only top sides (out of the water) cored like
Oyster but ones that use a full cored hull?
Halberg Rassy use foam core, Swan use foam core, Solaris use Airex for core, Aeroyacht (wally) use foam core, wally monohulls that are carbon yachts use
"The hull core is mainly of Nomex aramid honeycomb, though CoreCell styrene acrylonitrile (SAN) has been used for the high-stress slamming areas.", Brenta use foam core, Arcona use Divinycell, Xyachts use foam core, Advanced yachts use PVC core, Discovery yachts use Corecell M-Foam core, Waukiez use foam (used balsa years ago), Faurby use divinycel core, Grand soleil use PVC foam, Comar use Airex,
Najad use Dyvinicell, Luffe use foam and so on
You can still find some builders that use balsa cored hulls, most for topsides where the risk of water abortion is smaller but they are invariably very conservative brands, the ones that took more time to pass from a modified fin
keel to a fin
keel and from a skeg
rudder to a spade
rudder. But with time they will change from Balsa to one of the polyesters. The risk of water intrusion is just too big, balsa absorbs water and as all
wood it swells and that provokes
delamination.
There would have no reason for all of those top boat builders not to be using top end balsa instead of foams since
balsa is cheaper.
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