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 The Engine.

 

I think one of the nicest engines on the market that will suit my needs is the Smart CDI-Motor OM 660, fabricated by DaimlerChrysler (Mercedes) and better known from the Smart-Car. Main reason for this preference is the low weight but high performance. Decide yourself.

Due to the high-tech involved this is a typical example of a 21th century engine and at the same time this is also the main disadvantage. It's not K.I.S.S.* but neither is the F-39, being a 21th century sailing vessel also.

Tinker by yourself isn't possible anymore (at least for me), but on the other hand the OM 660 is a widely used engine in the automotive industry and thus accompanied by worldwide service opportunities.

Surprise yourself with these incredible characteristics:

Weight = engine + gearbox + marine gear = 65 + 14 + 22 = 101 kg. (223 lb)

Power = 30 kW (41 Hp), a little overdone for the F-39, but look at the weight!

Max torque 100 Nm at 1700 rpm., ideal for a boat.

3 cylinder 800 cm3, turbocharged

In the Smart-Car this engine is known for the modest fuel consumption of 3 ltr. diesel every 100 km.

 

Feathering propeller

When thinking about a low drag propeller, my first thoughts were about an automatic feathering propeller, like the MaxProp.
MaxProp automatic feathering propeller This type of prop feathers to a low drag shape and is very efficient under power in both forward and reverse. 

The torque of the prop shaft acting on a "differential" type design will open the blades in unison to the pre-set pitch at any throttle setting.

However, from different sources I am informed about the possibility of unbalance at high sailing speeds. Around 20 knots of boatspeed the water flow can start the prop spinning, even with enough force to turn the engine if left in reverse. Of course this is very unwanted and can ruin the engine. 

With this in mind I concluded that a feathering prop is not suitable for my fast trimaran.

 

Folding propeller

The other type of low drag propeller is the folding prop, like the one's from Gori. The propeller opens under engine power due to centrifugal forces.

At the right a nice example of the three bladed Gori propeller, with an extra overdrive function incorporated.

Gori three bladed folding propeller
 

Voidth-Schneider propeller
A complete different design, but extensively used in tugboats, is the Voidth-Schneider propeller, not seen in yachts yet! (except in experimental stage, see picture at right).

However, a promising principle with maneuvering capabilities one can only dream from. The German company SPW GmbH is developing this promising system.

Voidth-Schneider propeller
 

Another retractable propulsion system
 
 

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