With their truck engines mounted on the transom, the propeller shaft directly connected to the crankshaft, they look a bit crude in design. But don't get fooled, they are much smarter than they may look...
The typical longtail boat is around 9 metre long by 2 metre wide, with a draft less than half-metre.
Historically, they appear in the late 60s' when the British motor vehicle Construction and Use Regulations changed the minimum power-to-weight ratio allowed for trucks in the UK, resulting in lots of trucks equipped with Perkins P4 and Gardner LX motors becoming obsolete. These trucks were either scrapped or retrofitted, making available a lot of reliable and serviceable diesel truck engines. A smart company bought all these old engines and sold them to chandlers in Singapore and Hong-kong where they were fitted by local boat building companies on boats, giving birth the the longtail boats (source).
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The longtail boats are still constructed in plain teak wood and their prices have rocketed-up following the rise in the price of wood. At the stern of the boat is a plaque under water functioning as a trim to prevent the back of the boat to sinking under water while operated by engine. You can see it on the pictures above (left) and below, just under the water line, and attached to the stern by two arms. Two hose pipes are connected to the plaque. These hose pipes are connected to a basic heat exchanger consisting of a few metres of plumbing pipes set along the hull and connected to the white hose pipes. In addition, looking carefully on the top right picture, you can see the diesel hose pipe going through the filter, to the engine (small hose pipe on the bottom left) as well as the black battery connectors on the right.
With the propeller directly connected to the crankshaft, such boats have neither neutral nor reverse for manoeuvring. Neutral is achieved by pulling the engine down in order to get the propeller out of water (picture below). Besides, it requires an engine running on a maximum of 3,500 rotation per minute in order to get the propeller acting effectively.
With such a long tail, sharp-turning can be a bit acrobatic. It requires that the engine weight is well balanced on the mount, with a six kilo excess towards the propeller shaft (source).
The accelerator consists of a rope attached along the handle.
While in operation, our pilot used a rope to adjust the height of the propeller, allowing the propeller to just "touch" the water.
The propeller only "touching" the water creates a typical spray of water at the end of the tail. While this would tend to appear as a waste of power, it is in fact at the top of the current technology for boat engines. Latest high-speed motor boats are using "surface drive" technology, meaning that the propellers are only touching water in their lower part, with the propeller shaft aligned with the water level (source: boatingmag.com and Arneson surface drive). In short, having only the lower part of the propeller in the water reduces considerably the water drag and result in a more effective use of the engine power.
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Note on the above right picture how the anchor is set, with the line pulling the anchor crown first by being attached to one of the arms. This is to avoid that the anchor is getting hooked under rocks while being used close to the coral reef, in quiet waters.
Sun set at the entrance in the small lagoon through the coral reef.
So, in conclusion, longtail boats are smarter than they look, and well adapted to the environment in which these boats are operating. If you are not convinced yet, see the latest technology on longtail boats used in the US here...
And a short video of our experience with longtail boats...
Not to forget the cult longtail boat pursuit in the James Bond movie the "The Man with the Golden Gun" in the longs of Bangkok.
Wow! very interesting and curious! thanks
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