Outboard Motor

Evinrude claims a unit whose propeller can be set at various angles and various depths relative to the stern. Angle gives steering; depth gives shallow-water clearance.

Cut a flat-bottomed hull 400 mm long with a 120 mm square transom from 6 mm plywood. A simple punt shape is enough — the hull is a test bed, not the subject.

Seal the seams and float it. Trim with ballast until it sits level — an out-of-trim hull will fake a steering result later.

Make a vertical leg from a 250 mm hardwood strip with a dowel shaft running down its length to the propeller. This is the spine of the unit.

Carve a 60 mm propeller from balsa with both blades twisted to the same pitch. Unequal blades vibrate and give a false thrust reading.

Run a twisted rubber band from the top of the leg to the propeller shaft. It stores a repeatable amount of energy, which matters for comparing runs.

Make a wooden clamp with a screw that grips the transom. Nothing may pass through the hull — that restriction is the whole design.

Pin the leg to the clamp so the whole unit rotates about a vertical axis. Fit a tiller arm at the top so you can hold an angle.

Add a second pin allowing the leg to tilt back out of the water. Both freedoms are named in the patent and both must work.

Wind 40 turns, set the leg dead ahead, release. Time the run over 3 m. Repeat three times and average.

Same 40 turns, leg swivelled 20°. Measure the sideways displacement at 3 m. The boat turns with no rudder at all.

Repeat at 10°, 20°, 30° and 40°. Note that turning force keeps rising while forward speed falls — thrust is being traded, not added.

Lay a board in the water 30 mm below the surface. Run over it with the leg down, then tilted. Down, it strikes; tilted, it clears.

Take the whole assembly off. The hull is unmodified and undamaged — no shaft hole, no bed, no rudder. That reversibility is what sold the invention.

The patent. US 1,001,260, "Marine propulsion mechanism", filed 16 September 1910 and granted 22 August 1911 to Ole Evinrude (born in Vossestrand, Norway, emigrated as a child to Wisconsin), assigned to the Evinrude Motor Company he had founded with his wife Bess.

Evinrude did not build the first outboard motor, and the priority is not close. Cameron B. Waterman's US 851,389, "Boat-propelling device", was filed 6 December 1905 and granted 23 April 1907 — roughly five years ahead of Evinrude's filing. Waterman tested his engine in 1905 and sold detachable outboards commercially before Evinrude built his first. There were earlier attempts still, going back to electric-powered detachable units in the 1890s. What Evinrude has an unambiguous claim to is the market: launched in 1910, his company sold over a thousand units in its first year and turned the outboard from a curiosity into an ordinary object. Being second to the patent and first to the market is a common shape in this programme, and it is worth stating plainly rather than resolving in the inventor's favour.

The ice-cream story. The popular origin tale is that Evinrude rowed across a lake to fetch ice cream for Bess, that it melted on the way back, and that he resolved to motorise the boat. It is repeated everywhere, it may well have a kernel of truth, and it is not documentation. It is included here as folklore, labelled as folklore. The patent record says nothing about ice cream.

Why swivelling the whole unit is the real idea. An inboard installation separates the two jobs: the propeller makes thrust in a fixed direction and a rudder deflects the water leaving it. That works, but it needs a hole through the hull, a watertight gland around the turning shaft, a fixed shaft angle, and a second control surface. Swivelling the entire drive collapses all of that into one moving part — steering becomes thrust vectoring. It also means steering authority disappears the moment the engine stops, which is the outboard's genuine weakness and is why a drifting boat with a dead outboard cannot be steered at all. Step 12 shows the trade honestly: past about 30° you are turning hard and going nowhere.

The tilt is not a convenience feature. Small boats work in shallow water, over sandbars, and get dragged up beaches. A fixed propeller below the hull is destroyed by all three. Tilting the leg is what makes a motorised small boat survivable in the places small boats actually go, and it is why the two adjustments in step 1 belong in the same patent — an outboard that could steer but not tilt would have been an interesting failure.