Drijfsijs is a dutch slang word for birds that sit on the water, but this Drijfsijs is a Bombard Aerotec 380 inflatable boat.
When deflated the boat fits into the back of a car so it is easy to take it to lots of different places. It generally takes about 45 minutes to pump the boat up, attach the motor and launch it. A pair of launching wheels that bolt onto the transom allow the boat and the motor to be moved around easily by one person. The boat is usually assembled right next to the car so there is no need to carry the heavy motor.
The motor is a Suzuki DF15, 15 hp, 4-stroke, short-shaft outboard. It is the lightest 15 hp 4-stroke outboard motor that was available in 2010 and weighs 44kg. I considered buying a 20 hp Yamaha 4-stroke that weighed 51 kg, but I decided that the extra 7 kg would make that motor too heavy to lift in and out of the car without help. Overall I'm very satisfied with the motor. The boat jumps on to the plane almost instantly with 2 adults on board even with a lot of gear. It's fine with four people as well. In calm water the top speed is about 35 km/h with just me, 32 km/h with two people and about 25 km/h with 4 people.
The graph below shows the theoretical top speed of an Aerotec 380 for various engine and cargo weight combinations estimated using Crouch's formula. The boat, engine, fuel tank, fuel and driver are not considered cargo but everything else is. Note that Crouch's formula is only valid for a planing boat. The results are invalid where the engine is too small to plane the boat.
Kts = C / (LB/SHP)^0.5
Where: Kts = planing speed in knots, C = boat specific constant, LB = displacement in pounds and SHP = shaft horse power at the propeller. I used a value of 150 for C. Crouch estimated C empirically as: 150 for average runabouts; 190 for high-speed runabouts and 210 for race-type boats.
The figure shows that Crouch's formula overestimates the speed of Drijfsijs. The boat is level on the plane so I think the engine trim is set about right. The motor is a short-shaft model, but the propeller is probably still a few centimeters deeper in the water than ideal. Some Bombard Aerotech 380 owners have added strips of wood to the top of their transoms to raise the propeller, they claim that this increases the top speed a bit.
Although the boat has a nice v-shaped hull, it tends to ride over waves rather than cut through them the way a deeper rigid v-hull would. It's not really much fun to travel through waves larger than a meter at full speed. The transom of the Aerotec 380 is quite low which leaves the top of the outboard rather close to the water. I sometimes slow down to reduce the amount of water splashing over the engine. I have noticed that inflatables designed for professional rather than leisure use tend to have a higher transom and use long-shaft outboards.
At full throttle the motor is supposed to use about 5 litres per hour so it should run for about 3 hours on a 14 litre tank. I would say that is about right. I have made several trips of about 40 km and every time I used about half a tank
I mostly use the boat to go on short trips around Tromsų in Northern Norway. Before moving to Tromsų I used to sail an Enterprise dingy at Rollesby Broad Sailing Club in Norfolk and before that at Chipstead Sailing Club in Kent (both in England). But the weather in Tromsų is a bit cold for dingy sailing.