Interesting line comparison brought to my attention by Owen.

http://www.inorope.com/etheme_portfolio/comparatif-polyester-vs-dyneema-en-traction/

I got this note from someone reading a posting on Steamradio.

“Interestingly Shuttleworth recently posted on Steam radio re. Kevlar as follows:”
“We put Kevlar inside. It is partly because it is significantly better in tension than compression, but also when water penetrates the resin fibre matrix it acts like a wick and the water will migrate into the laminate – not something you want in a material that is very close to the water all the time. Small areas of damage that are not attended to can make this a problem. The third reason is that in an impact the outer skin will rupture – the foam will distort It is is either Airex R63.80 or Corecell A500 and the inside skin will stay intact even if the resin starts to fracture. The idea is that the foam and outer skin absorb a lot of the energy before it gets to the inner skin – which is ultra strong in tension. this combination has proved very successful in a number of cases of grounding or high impact on the hull.

Kevlar does need to be laid in a combination with glass, because the resin does not stick to the fibres very well. For the bigger boats we use a unidirectional fabric with alternate tows of kevlar and glass 50:50 by volume. This means that each layer is 660 gms/m2 Aramid/Glass – 237 gms/m2 Aramid, 422 Glass Unidirectional.”

Regards

John Shuttleworth
for Shuttleworth Design Ltd.

At first I thought, doesn’t he know?  So many things wrong as I see it. Those all seemed like reasons to never use Kevlar. A grounding or impact is usually bow or keel line. I cannot see tension strength helping against basically shear load.
The multihull will not sink so holing is not the worst of worlds. The disadvantage of tensile strength across in interior panel is that a small impact can make a huge delamination inside. Especially since the Kevlar is not bonding to anything else.
The Kevlar in combination with glass seemed to be a bad solution for a couple of reasons. Even if the glass is a good laminate, the poorly bonded Kevlar between glass lams means very poor shear transfer between layers. So why bother with the Kevlar at all?
Finally if the Kevlar is for impact, a woven fabric is much better than a uni or a knitted fabric.
Then I recalled my earlier comment that the only use for Kevlar is as a yuppie magnet, for boat sales.  I realized that the way he uses Kevlar is brilliant.  He puts it in the place on a hull where it can do the least harm.  Then the boat sellers can attract yuppies with it.  Like the carbon fiber cleat pads on Gunboats.  Utterly wrong material, but it confirms to yuppies that they are indeed high tech.  And that tiny bit of fabric visible is the evidence.  Brilliant.

Haiko and ocean racer Pamela are updating my beloved former F40 trimaran.  It will have more room inside and be much more usable for living in.

OK almost two weeks ago. Been busy. Everybody has a deadline.

The Fish Expo was mostly the usual stuff as before.  With the internet, it is not that important to get the literature now; just the links.

I did find some more composite bearings for both rudders and unstayed masts.  Should be much less cost than machining plastic.  And I’m game to try Rob Denny’s idea of using sloppy fit instead of spherical bearings.  Duramax.

This week will be tough on deadlines.
The dome acrylic project on the lunar lander dwelling came up two short. It seems the fabricators misunderstood the number 20.   The VHB tape is all ready in place on the dome.  The missing two panels must be installed as soon as possible.  I have a small weather window for tomorrow and wednesday there. Then Thursday is gone. I will be back in full next week.  This does keep me involved with all aspects of composite building, which benefits you the builders.

I just was given the digi pic of the launch of the first boat I built. Launched Oct. ’78. Hulls then were Piver AA31. The rest I adapted.  it got new CM amas in a couple of years, among many other things.

Not actual boat but boat construction.  On the lunar lander dwelling, my house built like a boat, I had planned to use the 3M VHB tape to stick the acrylic dome panels down.  I had understood that better results come from using an adhesive promoter in this cool time of year.  Uline, my tape supplier would only sell me large quanties of it.  I now now their minimum was enough to do about half a kilometer of tape.  Devon at 3M only had one idea of who in Seattle had some to sell, and they did not actually.  I had given up and went to Fish Expo.  At the Fisheries Supply booth there they had a 3M catalog.  Fisheries carries not the exact same AP111, but close enough, Tape Primer 94.  Fisheries comes through.  http://www.fisheriessupply.com/

This prime example of stuff done wrong was sitting right in front of me for a few days before I grasped the teachable moment in it.  And it is another example of what I have often seen where it is asserted “it must be right because they are famous.”  In today’s chapter, first the boat.  The bow broke off of this 50′ (I assume) trimaran in the Route de Rhum.  I have not seen the actual wreckage nor spoken to anyone who has.  But it seems like a lot can be understood by looking at these pictures.

Two things jump out immediately.  First, that sure looks like Kevlar, and second, the core looks thin.  It could be 19mm but it sure looks more like 12mm.  And the damage is quite clean, not ragged.

First, Kevlar?  Really?  In my opinion Kevlars’ only use is as a yuppie magnet.  Not only does it not actually stick to the resin matrix, but its compression strength is about 1/3 its tensile strength.  And it’s tensile strength is still 20% less than that of lowly E-glass. 

Now notice at the 3 corners of the hull section are tiny carbon fiber stacks.  That is bad practice on at least two counts.  First, the carbon has less than half the stretch to failure of Kevlar, so the carbon must fully fail before the Kevlar’s tepid strength is even at 50%.  Next, if it is a carbon stack as it looks, with the differing stretch, it could pop off the Kevlar with a shear failure. 

The clean break feels more like a tensile failure instead of buckling at first glance.  I see a scenario where there was a partial buckling failure which popped the resin matrix off of the Kevlar in a circumference line.  Later that weakened fabric is hit from the opposite direction and fails cleanly.

Why didn’t they know all this?  I can think of an elderly designer or two who would not know this kind of thing, but it has been out there for a long time.  Next, the Multi 50 rule is just as bad.

Spotted nice pic of Trilogy IV. It was built by Kevin Millet and began as Hula Girl. 48′. Foam/glass. 49 pasengers.  I think I designed it in mid 90s.  On Maui.

Once again it is time for Pacific Marine Expo, (formerly known as Fish Expo) in Seattle.  Again, this is the serious boat show.  Or you could go to METS in Amsterdam.