which core material ?

which core material is good as core sandwich:
nomex, end grain balsa, divinycell, pvc foam, etc ?
what do the materials feature ?
thanks in advance

 

Balsa: Good stiffness and strenght, and local impact resistance. Heavy and low cost
PVC foams: thermoplastic material, conform to the hull's curves.
Nomex: low weight high tech material, phenolic resin, difficult to bond to complex geometry. expensive

 

Corecell: SAN foam specifically engineered to be a marine core material. Better impact resistance than urethane foam, better stiffness than polyvinyl foam.

I have a friend building a 40-something catamaran. He's used western red cedar for the hulls, balsa for the deck, and Corecell for the cabin. He says if he did it all over again, he'd go all Corecell.

 

The answer about core materials depends on more variables than simple tech specs. I've used almost all of them as naval engineer and builder, so I have some experience.
The best core is the core you can afford and get good result with it...

What dou you plan to build and what are your technical and financial means?

I assume you're an amateur builder making one boat. In this case it's better to forget high tech products like Nomex which requires female molds, vacuum and an oven to cook the epox resin.

I assume you take the simplest way for an one off boat: the male mold (female molds are very expensive...). Finishing is the hardest and most exhausting part of the construction.

1/ Core wood like Western Red Cedar in strip plank with glass (triaxial, biaxial et satin and some carb) and epoxy resin. The easiest and the most forgiving for a "low tech" construction, delamination problems are unknown, so engineering calculations (which may be problematic with sandwiches) are kept to a minimum The mold is strong and vacuum is easy to use if needed. The cheaper also. I use it for the custom boats. Easy finishing.

2/ An almost forgotten material: marine plywood (the true one like meranti norm 1088) or skin door 3 mm triplay. It's not a true sandwich as the plywood is a very strong material by itself but coated with glass and epox resin is a very good material for small and not so small boats. Make a search in Google with the words "cylinder mold" and Kurt Hughes.

3/ Nida (a thermoplastic honeycomb) is very efficient and easy to use for the "flat" surfaces as decks.

4/ We arrive to the foams. For an amateur builder that becomes more complicated. The molds become far more expensive as it wil require a lot of stringers and finishing
is more difficult. You'll use tons of putties and you'll sand a lot... Foams permit to make very good boats but with the following requirements:
- very good engineering specially in the high stress points.
- great care during the construction for ensuring a perfect bond between the skins and the core.
The Airex has very good reports. All the french race trimarans of the 80's and 90's have been made with airex and they last... Some have more than 15 years of hard racing and are structurally sound.
Each foam has its pros and cons, their fabricants making high claims and despising the other brands...

Other advantage of foams (and Nida) is you can use polyester. On small boats (until 25-30 feet) foam is not specially light because the ratio putty/foam is very high...a 1/4" open cell foam pull of putty is heavier than wood...

Good foams are very expensive and require a lot of labor unless you have the means of a female mold.

If your boat will be named "Regardless of Cost" it's sure that carbon fiber/Nomex/epox vacumm molded and cured in oven is the best for racing...

 

You might want to visit this forum as well <http://www.steamradio.com/mailman/listinfo/multihulls> . Currently there is a discussion of cores applicable for resin infusion.

You've ask a really broad question about cores. You might also try a 'search' in this forum for past postings.

 

aldo
balteck end grain balsa has a new copper impreg version. not an excuse for poor bonding but should help in the long run

 

Ilan, very good reply and very well presented! I am completely with you.....

 

If your doing a one off with compound curves think about sheathed strip construction using a low density wood. Very strong, and resistant to abuse.

Down side is it takes a while to strip plank the forms. You can also use corecell in strips to plank with.

 

Nida sheeting, Where is that most available? Thanks,
Lane THomas
Teacher/Sailor