Maldives has large number of 36 ft to 48 ft GRP speed boats catering for the fast ferry applications. Almost all of these boats are equipped with Petrol outboard motors ranging form 200hp to 350hp and beyond. However these Outboard motors or OBMs have a relatively short service life and are not designed to propel these typically 6 tons to 9 tons of displacement for prolonged periods.
The majority or over 75% of the worlds outboard engines are used in the US. Moreover 85% of these are used in leisure applications used for less than 50 to 100 hours a year. It therefore no surprise that manufacturer’s design these engines with this in mind and not the few hundred heavily abused OBMs in the Maldives.
OBMs are favoured because of their relatively low purchase cost and ease of maintenance and most importantly lower operational downtime as the motor can be replaced quickly. However the availability of high horsepower engines is now questionable because of the high global and more specifically the US demand. Many key brands are now restricted with quotas and hence the customer is left with little more than hollow promises. As most inboard engine packages are Diesel, professional or brand represented comprehensive service outlets are still limited in the Maldives. Having said that major companies such as Cummins, Caterpillar, John Deere, Nanni and Weichai have all initiated commitments towards changing this.
OBMs have a typical service life of 1000 to 1200 hours and a typical overhaul costs approximately MVR 100,000. It is also essential to keep in mind that typically OBMs need to be replaced after two overhauls and will most likely go through four major gearbox repairs or replacements within this period. Inboard diesels coupled to water-jets can easily increase this life by three to four times. The unique advantage of having water-jets is apart form from its high propulsion efficiency, the engine will no get overloaded under any circumstance. Increase in payload (passengers or cargo) or wave resistance form sea condition will have no effect on engine loading. This is the reason for the comfortable engine performance and prolonged service life.
A major obstacle faced by OBM propelled boats are that OBM has already reached its maximum threshold. That is the torque or thrust at transom has reached a point where increasing the number of engines is introducing only more drag and consequently burning exorbitant amounts of fuel to make no commercial sense. Additionally, these OBMs designed to push much lighter “center consoles” and “RIBS” cannot cope with these very heavy hulls and passenger payloads of up-to 50. As a result the weakest link in the installation, be it gearbox, valves or pistons, depending on model and manufacturer, has no option but to give way and lead to serious failures. It must also be noted that prolonged use at high speed which is the norm in the Maldives, is not suitable for the gearboxes as no OBM gearbox has oil coolers or filtration systems such as found in inboards. This means the lubricating oil begins to fail at operations in excess of three hours due to prolonged exposure to the high temperatures and shear stresses.