Why was the Explorer powered by a triple expansion steam engine when contemporary trawlers were being powered by diesel engines? This is a question which has vexed us here at the SSEPS for years. A couple of bits of information have revealed themselves over the past few days which give rise to a theory.
First of all, in John Dunn’s “Herring Larval Blog” below, it is clear that it was necessary for Explorer to steam at slow speeds of considerably less than 5kts for some tasks.
Second, her slipway companion Sir William Hardy (Subsequently Rainbow Warrior), a research ship being built for the Ministry of Agriculture and Food for the same purpose as Explorer was fitted with diesel electric propulsion.
Contemporary trawlers were fitted with medium speed geared diesels. A Diesel engine of course has a minimum tick over speed which means that the ship it is propelling has a minimum cruising speed. This will vary a bit, but I would estimate it to be four to five knots. This would make low speed tasks difficult to impossible.
So I am theorising that Explorer and the Sir William Hardy were built with machinery which would comfortably cruise at speeds of one or two knots. The Scottish Office conservatively opting for a traditional steam plant. The MAFF being more adventurous and fitting the first diesel electric plant in a trawler. This adventurous decision would bite them on the bum for a while as inevitably with new technology, there were teething problems.
“During the trials it was found that insufficient air was entering the engine-room when the propulsive machinery was operating at normal power. There has been a six months’ delay due to this. The cost of the additions to the ventilation will be about £3,000. I am afraid it is impossible to assess the cost of the delay in the use of the vessel.”
Sir William Hardy