Archive for August, 2014

Miss America X

I am fascinated by the early generation of high-speed powerboats from the early part of the 20th century. These vessels had some interesting features such as bow rudders, low deadrise stepped hydroplane hulls, wood construction. The most outrageous example was Miss America X with four 1800 hp Packard V12 engines which were later used in PT boats. Fitted with a 300% step up gearbox driving 16 inch propellers, I sometimes use this boat as an example for clients as one end of the spectrum on how speed effects optimum propellers diameter (the other end is a tug boat)

This collection of you tube videos is a fascinating collection of primary source material which has a little bit of something for everybody. My petrol head friends should listen to the first video as the noise of a boat powered by 4 V12 engines is excellent. My wooden boat friends will appreciate the construction but went into one of these monsters.





First aircraft carrier fitted with surface piecing propellers

seasled1The surface piercing propeller was invented prior to World War I by the Canadian Albert Hickman. His logic being that at high speed water has the consistency of hard cheese and the propeller should cut the water like a cheese knife. His propellers were large diameter, a good match for the slow revving early Aero engines used to power his boats. With engines like the Liberty V12 having a better power to weight ratio than a modern outboard motor many of these vessels were extremely fast.

The technical highlight of Hickman’s career was his high-speed planning boats, the Seasled a kind of tunnel hull catamaran. Was used as an aircraft carrier. A 55-foot sea sled. The sea sled carried a 5 tonne Carponi bomber at 47 knots. To launch the bomber, the pilot and the sea sled captain both ran their engines to full throttle. The sea sled would reach 53 knots and the bomber would take off.

Engine Liberty L12 SUZUKI DF 300AP
Year 1917 2010
Weight 383 kg 279 kg
Power 449hp 300 hp
Capacity 27.03 L 4.02 L
RPM 2000 6300
hp/kg 1.172 1.075

MANIAC – Linux cluster for OpenFOAM

maniac-02

This is my new computer, named after the 50s era Princeton valve computer the mathematical analyser, numerical integrator, and computer, which is how I chose to spend my money on some computer power to solve openFOAM problems. I benchmarked a number of computers with a typical problem and came to the conclusion that my work would be memory bound. In simple terms going up to a quad core chip without also having four memory channels would not produce any increase in performance. At best this would double the performance, but more than double the price. At the other end of the commodity price curve a Pentium Haswell chip still has the same memory bandwidth as its more expensive cousins. The set up benchmarked within a few percent of my i7 desk top computer.

My final node specification used very cheap motherboards with H81 chipsets and built-in gigabit ethernet ports, Pentium CPU, and 2 x 2 GB of RAM. The nodes are set up as diskless booting off a common NFS image, with one node having additional RAM for meshing and decomposition. My head node is an old machine with a core Duo CPU which I upgraded with an SSD hard drive and converted to linux. The interconnect is just gigabit ethernet. The nodes are powered by a single main PSU and Pico PSU boards running off the main PSU 12 V power supply. To finish everything off I built a case.

The final design, has five dual core nodes which, using the same benchmark, has a speed up of 9.1 over the single CPU. One thing I have learnt from this project, apart from the new systems admin skills, is the importance of benchmarking your hardware with your software and problem. It would be possible spend a lot more money and achieve a lot less. In a measure of how far we have come,If NASA were trying to reproduce the power of this computer in 1984, they would have had to spend 8.14 billion dollars in today’s money on Cray 2 supercomputers.

Avoid a Grade T time bomb

Alloy chain, normally sold as grade T or grade 800 is typically 2 to 3 times stronger than the chain normally used in moorings. Occasionally, you see this chain and more often the associated fittings making its way onto moorings when parts get substituted as mooring components wear. Unfortunately this high-strength chain undergoes chemical changes when immersed in “aqueous chloride solutions” aka seawater. The process is known as hydrogen embrittlement makes the chain susceptible to failure under shock loadings which is generally considered to be a bad thing for moorings. Suspiciously small shackles, hammer locks and oblong lifting links are all usually grade T and should be avoided in moorings.