Boat hulls are layed up with alternating layers of roving and matt. The matt gives tensile strength resistance to shattering and puncture. The matt fills in the irregularities in the roving and stiffens the lay up.
Some manufacturers like Morgan
and Cheoy Lee
used Chopped matt mixed with resin dispensed from a gun to replace the matt sheets
. In theory it works just as well and takes less labor but requires a gun operator who knows what they are doing and cares. The operator has to spray on a thick enough layer that is relatively uniform. Most manufacturers stopped using chopper gun layup
in hulls because of applicator error. I had a Morgan hull
that had no chop on one side which resulted in every thing that was tabbed to that 1/2 of the hull on the inside 'printing' through to the outside and flexing. I came out whole after the law suit but it cost Morgan way more than if they'd just scrapped my boat and built me another one with a properly laid up hull. That boat may still be out there. I kept the boat as part of the settlement and sold it cheap
with everything disclosed. The new owner essentially used the hull as an armature and laid up a new hull on the outside of the defective side.
Without drilling holes in the hull, couldn't tell the difference in its thicknessl. Areas that didn't have an opaquing gel coat layer looked paper thin and almost transparent. When we attacked with the hole saw found they were actually the thickest areas of the hull. Other areas that looked fine were the thinnest. About the only thing that you can do is look at the hull and see that there is no print through of the bulkheads and other furniture tabbed to the hull. When you take it out sailing to weather
, go below and feel whether the hull flexes as it hits waves. Some flexing is inevitable but it should be virtually absent. Also check that the bulkheads, etc. are still tabbed to the hull. If they've broken loose the hull has either had some rough handling, is flexing too much or the tqbbing was badly done when the boat was built.
Chop, because it's made up of short strands, has lmited reistance to puncture so is structurally weak. All chop layups typically are used in things like FRP skirts and the like for cars, liners in hulls, and other things where strength is not an issue. They are almost always done with a chopper gun because matt sheets
are labor intensive and hard to work with.