Matthew's blog

Where's the good wood?

When I built my little runabout fifteen (!) years ago, it was pretty easy to find suitable plywood. The boat was a Phil Bolger / Harold Payson design, and neither man was big on spending money where it wasn't required. Payson's advice was something along the lines of "well, she's glass-sheathed, so you don't need the fancy exotic plywood – just use local AC exterior ply with the boil-tested glue." He was right; after fifteen years there's no evidence at all of any kind of rot, deterioration, delamination or other trouble with Sunset Chaser's fir plywood hull.

Criticality One

Anything that people make is going to break. This is inevitable. It's a direct consequence of unavoidable, fundamental laws of the universe.

Part of the art of engineering is to control where, and after how long, things will break. We can't prevent failure entirely, but we can focus our efforts on the most critical items and we can ensure that the complete system – an engine, boat, spacecraft, whatever – is unlikely to fail at all within a certain service life.

Crossbeam bits & pieces

Progress on the Starwind 860 prototype continues. It does seem, however, that I've fallen behind in posting updates about the boat.

The aft crossbeams are nearly done; they still need the fibreglass tape on their outer edges and a final fairing coat before painting.

The front crossbeams now have their upper mid-beam structure installed and are ready to be closed in. That task will probably take place tomorrow.

The Factor Of Ignorance

"Safety factor." It's probably one of the most common, and most misused, terms in engineering.

The "factor of safety" might be better described as a "factor of ignorance". It's a multiplier, applied to loads and/or structural components in a design, to account for things that weren't explicitly taken into account in the design calculations. Those things could include variations in material quality or workmanship, uncertain overload conditions, accidents, and other hard-to-predict conditions that could cause a failure.

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