Amphibious Duck Boat

Overview

An amphibious duck boat is a passenger vehicle that drives on roads like a bus and then drives straight down a ramp into a lake or river and floats away under its own propeller. The name and the shape come from the DUKW, a wartime amphibious truck whose factory code gave it the nickname duck, and modern tour ducks keep the same idea: a watertight boat hull that also serves as the vehicle chassis, with road wheels and a marine propeller both driven by one engine. They run sightseeing tours in cities with both a downtown core and a waterfront, giving passengers a land tour that ends with a splash into the water.

The vehicle has to be two machines in one body. The Hull Body is a boat hull that doubles as the chassis. One Engine powers everything through a Transmission that splits drive between the Road Running Gear on land and the Marine Drive afloat. The Brake System stops it on the road, the Bilge System keeps it from sinking on the water, and the Passenger Fitout and Electrical System systems carry and serve the tour load.

Hull and body

The Hull Body is the heart of the dual nature. The Hull Shell is a welded watertight steel or aluminum boat hull, and built into it is a Chassis Frame that carries the axles, engine and running gear, so the same structure that floats also takes the road loads. The hull is divided by Bulkhead watertight bulkheads into separate compartments so that flooding in one section does not sink the whole vehicle, an important safety feature given the history of duck-boat accidents.

Keeping water out is constant work. A full Hull Seal Set set seals every hatch, shaft penetration and opening, the Deck Plate floor plating sits above the bilge to keep the cabin dry, and Fender rubber fenders protect the hull when coming alongside docks. The hull must be heavy and strong enough for road use yet still float with thirty passengers aboard, which makes these vehicles large and heavy for their length compared with an ordinary boat.

Engine and transmission

A single Engine does all the work. It is a marine-rated turbo-diesel: a cast Engine Block with Piston pistons on a Crankshaft, a Cylinder Head, a Turbocharger and Fuel Injection, cooled by a Radiator and breathing through a raised Air Filter intake placed high to keep water out. Marine rating matters because the engine must run hard at low road speed and then push a heavy hull through water, both of which load it more than ordinary truck duty.

The clever part is the Transmission. A road Gearbox drives the wheels on land, and a Transfer Case splits the engine's output between the axles and a Power Take-Off power take-off. When the driver enters the water, the transfer case sends drive through the PTO to the marine propeller instead of, or as well as, the wheels, while Driveshaft shafts and a Clutch manage the changeover. The transition from land to water is the most demanding moment in the whole machine, because drive has to move smoothly from wheels to propeller as the hull starts to float.

Marine drive and road running gear

Afloat, the Marine Drive takes over. The PTO turns a Propeller Shaft running through a sealed Stern Tube to a Propeller at the stern, supported on Ball Bearing bearings and kept watertight by an Oil Seal. Steering on the water is by a Water Rudder behind the propeller, worked through a Rudder Linkage from the same wheel that steers on the road. The boat is slow on the water, around five or six knots, because the blunt amphibious hull is a poor boat shape, but it is steady and easy to handle for a sightseeing run.

On land the Road Running Gear carries the load. Multiple driven Axle axles spread the heavy hull across six Wheel Assembly wheels on Leaf Spring springs, steered through a Steering Box and Tie Rod tie rods. A Central Tire Inflation central tire inflation system can drop tire pressure for grip on the soft, slippery launch ramp and raise it again for the road. Because the vehicle is heavy and tall, the Brake System uses Brake Drum drums on every wheel actuated by Brake Chamber air chambers fed by an Air Compressor, the same heavy-duty braking used on trucks and buses.

Safety, passengers and electrics

On the water the Bilge System is the last line of defence. Two Bilge Pump pumps clear any water that gets into the hull, discharging it overboard through Thru-Hull Fitting fittings, and a Bilge Alarm high-water alarm warns the driver of flooding before it becomes dangerous. After several fatal sinkings, regulators have pushed hard on bilge alarms, reserve buoyancy and crew procedures for these vehicles.

The Passenger Fitout carries up to thirty people on cross Bench Seat benches under a Canopy roof, with Grab Rail rails, Boarding Step steps for climbing into the high hull, and a Life Jacket for every passenger. A PA System carries the guide's commentary over the engine noise. The Electrical System system, run from twin Battery batteries charged by an Alternator, powers both road-legal Road Lights and marine Navigation Lights, read out on a combined Instrument Panel. Duck boats serve almost entirely as tourist attractions in waterfront cities, where the novelty of one vehicle that drives and then floats is the whole appeal.