Hull material in Catamarans

[cat man do]

I reckon a core is better under the waterline as I have had a few hits over the years (shallow draft reefie areas)

Cored hull had a localised puncture but not through the inner skin where I would suspect the solid hull would have had fractures over a larger area which may not have been as obvious.

Dave

[BigCat]

Originally Posted by Robertcateran

Hi Big Cat,
Have you looked at the impact tests done on polycore polypropylene honeycomb against that of balsa core. Balsa core is stiffer but does not resist impact as well. I agree with you about fire retardant resin, especially on the inside. I have also been looking at bamboo fibre as it is stiffer and lighter than glass but am having trouble sourcing it in smaller quantities than a container load. I will probably use fire retardent vinylester on the inside and epoxy below the waterline outside. The strenght of the laminate seems pretty close with either but there is a very slight water penetration difference- probably not enough to worry about.
don't know why you want to go to solid below the waterline. A fair bit of extra weight and not necessarily any better for puncture proofing. Polycore polyprop seems to be up to it.

Hi, Robertcateran - Several experienced boat builders have expressed concern about the ability of polypropylene honeycomb to resist sheer stresses, stating that if you take a piece and push the skins in opposite directions with your hands it is easy to collapse. Balsa and foam are, of course, also much easier to infuse than honeycomb.

I am infusing my laminates, so having different types of resins is not an option in a given panel, as both sides are infused at once. The Jamestown boatyard reckons that vinylester is actually better than epoxy at resisting water penetration of laminate: See http://www.jby.com/OSMO_web.pdf In any case, it certainly is blister-proof. See: www.zahnisers.com/repair/blister/blister1.htm

With a solid bottom, hull penetrations caused by impact can't lead to core problems, and you have better penetration resistance to highly concentrated loads. A solid bottom is best if you hit something like coral or rocks, where you can get highly concentrated loads that would pierce the thin skin of a cored laminate. When solid laminate has been damaged, it is easy to identify the extent of the damage, and that is not always the case with core.

I can afford the weight of solid bottoms because with the 'little big boat' philosophy, I already have a very, light boat, with a D/L ratio of 61 lightship and 78.5 in cruising trim with 1000 gallons of liquids aboard. Amusingly, that is about half the D/L ratio of a (so called) Fastcat 435, and that is possible because the boat is so large. (64.5' x 35.5') Everything Gideon says about the relative weight and strength of materials is completely wrong, as my much lighter D/L ratio so clearly demonstrates.

I am building to the ABS Rules for Offshore Yachts, and the high strength of balsa lets me satisfy that rule and still build a very light boat. By the way, the claim that balsa is lighter than foam is outdated, as light density balsa (6 pounds per cubic foot) is the same weight as light foam (80 kilos per cubic meter.) Balsa comes in three densities, light, medium, and heavy. I am using medium density (10 pounds per cubic foot) in my topsides, and light balsa elsewhere. For that matter, claims that balsa soaks up a lot of resin are also outdated, as it is normally used precoated now.

[Bob August]

The old argument of sheer being a problem with Polypropylene honeycomb is a misnomer, current product Polycore has a sheer of .8 equal to most high quality foams, another plus for PP is elastic resilience it will give a long way before it sheers, I have heard some interesting things about PP of late all of which are totally misleading and flawed! one of which I have answered to a great many people building boats from PP, the first and foremost is the ingress of water and the movement between cells. first of all try a simple test for yourself purchase a polypropylene container and fill it with water, leave it out in the sun or put it anywhere you wish with a suitable container underneath watch it on a daily basis and check the tray underneath for any seepage from the container this will tell you a lot. I have a great respect and admiration for our great pioneers in the design and manufacture of boats.
But if tests on products are to be carried out in a fit and proper manner they should should be conducted within the realms of possibility not with a test that the material will never face in reality, and the material being subjected to the test should be confirmed that it was designed for the application that the material is being tested for!
It is a terrible shame when those pioneer people who defied the experts of their time and in so doing brought about a whole new era of boat construction! decry a product and do exactly as the people who they defied and proved wrong in the past, before passing the death nell on a product, shouldn't they gain a full knowledge of the product they are testing and passing judgement upon, after all didn,t they face the same problem those many years ago!
Condemning a product without full knowledge of the product that you are testing and putting that product to a test that it will never face in reality is tantamount to stupidity! None the less I remain in awe of those pioneers that paved the way into the modern era of boat construction all though they are now doing the same as those that put them down in the past!

[Robertcateran]

Polypropylene is used quite successfully in hot water pipes so I am not worried about water moving through polypropylene providing the skins are well bonded to the core. Sheer stiffness is very different from sheer strength at failure. Polyprop stretches considerably before breakage and thus can absorb significant quantities of energy before failure. much greater than with stiffer cores or with solid glass. My own suspicions is that punctures will do less broad damage to a polyprop cored hull than a solid one

[cat man do]

Originally Posted by BigCat

Hi, Robertcateran - Several experienced boat builders have expressed concern about the ability of polypropylene honeycomb to resist sheer stresses, stating that if you take a piece and push the skins in opposite directions with your hands it is easy to collapse. Balsa and foam are, of course, also much easier to infuse than honeycomb.

.

I call ********

Dave

[C--man]

What do you guys think of this boat Windspeed 40?

I went sailing on it and it sailed really well I thought (my first Cat sail)

9 knots to weather in 12-15kn breeze and 7.5kn downwind in only 5kn wind. it seem to slide through the water effortlessly.

There is a story on the website somewhere where they dragged it through 1500m the paddack behind a buldoser without any damage to launch it.

http://www.windspeedyachts.com.au/sa...multihulls.htm

www.windspeed.com.au

[fastcat435]

Hallo all the next boat to be laid up, will be build in carbon Fiber, the price of carbon has almost halved since one year so this financial crisis is good for somethings and the weight savings are worth while.
I expect the weight of a carbon fiber Fastcat to come in around the 6000 kilo instead of 6500 now

Greetings

Gideon

[mikereed100]

Originally Posted by BigCat

Hi, Robertcateran - Several experienced boat builders have expressed concern about the ability of polypropylene honeycomb to resist sheer stresses, stating that if you take a piece and push the skins in opposite directions with your hands it is easy to collapse.
.

I have heard reservations concerning the shear strength of PP honeycomb before, but I have never seen any data relating to exactly how much shear strength is necesary in a composite boat hull. Is it possible that while the shear strength is less than that of other materials of the same density, it is plenty for the job at hand? (Just for fun I tried to collapse some honeycomb of different thicknesses with my hands and failed miserably.)

While the shear strength of PP honeycomb is less than that of equivalent density PVC or SAN foams, it's compression strength is superior to either. It is also substantially cheaper than other core materials, including plywood.

On the downside, treating the edges of panels requires more labor and it is more difficult to form rebates for windows and such.

As with all materials it has it's plusses and minusses. Sailors and boatbuilders are a conservative lot and rightly so. But, while there is a lot of resistance to it's use currently, I would not be surprised to see it appear in more builds as time goes by.

Full disclosure: My Hulls, deck and cabin are made of the stuff so i have a completely irrational, emotional stake in this debate.

Mike

[Robertcateran]

The way I look at it,
much of the so called sheer strength is more about sheer stiffness. Polypropylene can stretch a long way before it breaks and absorbs a fair amount of energy in the process. If it is stiff enough to do the job, and is less likely to have catastrophic failure from impact or flexing, then what is the problem. fibreglass skins can do a lot of bending before they have problems or there would never have been fibreglass fishing rods. Provided the scrim is well welded, they should be waterproof if any holes do occur. Edging and rebates seems to be the worst of the problems and possibly more chances of creasing if bending.

[S.R.Hathaway]

Originally Posted by fastcat435

Freydis = Polyester hand laminated
Outremer = Polyester hand laminated
FastCat = Epoxy infusion
Leopard = Polyester hand laminated
F-P = polyester
Lagoon = polyester
Antares ???
St Francis = Polyester
Fusion = Vinylester
Gunboat = Epoxy prepreg

Polyester is cured with styrene so it has a styrene smell for a couple of years the main advantage it is cheap.
Vinylester is a bit better and definitely stronger since it is a modified polyester .
Epoxy is the ( in my book ) best resin but also the most expensive stronger and a bit more elesaticity.

Greetings

Just to fill in the blank - I pulled the following information from the Antares website:

Antares= vinylester/polyester laminate/epoxy barrier coat