Subject: [harryproa] Re: Attention australian builders
From: "brag_rotor" <>
Date: 4/19/2007, 6:34 PM

Very interesting development, Rob.

Derek's technique is similar to the approach used at Nicklow
Engineering to build light hovercraft in the early 1970s & on - this
was a mould table method with a -

(polyester resin/glass)(airex PVC foam)(polyester resin/glass)

laminate that was tailored to make the entire hull.
16 feet long, ~7 feet wide, ~3 feet deep with Porsche power and a big
JLO single for lift.

The Airex PVC foam was excellent, although there was difficulty in
getting 100% adhesion when laying foam onto GRP skin to follow the
first glass layup on the mould table. Bagging was in its infancy at
that time, and it was found that it paid to warm the foam before use
and to work at higher temperatures so that it was more malleable - it
was reluctant to lay dead flat in the draughty shed during an English
winter. Can't see that problem in Urunga!

The structure met all its performance goals on first assembly, the
prototype 'Mistrale' machine setting a new water speed record on its
first run, exhibiting great toughness in the face of the continual
impacts an amphibious racing machine experiences, particularly in the
water-land transitions.

That PVC foam is tough as old boots, and lasts forever, I can vouch
for it. But there were some problems.

The secondary bonds between cut laminates proved unreliable, and
delamination started after a couple of years.
The edges were also a problem - inset timber strips that were glassed
into the laminate edges tended to work free where the secondary glass
bonds lifted. Polyester resin/timber bonds could be iffy in that era,
but these were treated with accelerator in the (then) approved manner
to prevent styrene migration

This was well over 30 years ago, and that first hull was still in one
piece after 25 years, so the problem was not that serious, but much
structural maintenance was needed. Resins have changed dramatically
in intervening years, too.

Later hulls seem to have survived much better, so it may have been
down to technique - but these later hulls did omit the 'tailoring'
approach (dedicated moulds were made) and the foam edges were closed
down from GRP/foam/GRP to a heavy GRP edge. No timber in the edge -
this was heavier but tougher. The hulls were mostly smaller, too.

The later craft were most successful, one was still racing and winning
in European F1 competition nearly ten years after it was first built.
Think "amphibious moto-cross racing"....

Derek is of course an icon in multihull design and construction, his
pioneering use of foam, and his wonderful 'Toria' - a design that set
the standard for tris so many years ago (so sadly lost at sea by
fire), just two of his contributions to the field.

I will be most interested to hear the opinions of the attendees on the
latest implementation of KSS - it looks to me (on his website) that
the method has evolved a long way, and should be particularly suited
to high-prismatic hulls like the HarryProa.

Can't wait to hear about it!

All the best, Ben

PS Been to SW Rocks to see Rare Bird - will post pix and impressions
when we can find the camera cable. But what a boat! Oh yes!

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