The Colac, Gembrook and Walhalla railways were built with a gauge of 2 foot 6 inches.
Was there be a reason why this line decided to be different and use 3ft?
Why didn't Colac / Gembrook / Walhalla use 3ft? I am no engineer, but it seems 2ft 6 is very very narrow and would severely limit the maximum weight or size of carriages.
Very interesting questions.
The Whitfield, Colac-Crowes, Gembrook, and Walhalla railways were all built by the Victorian Government. As an economy measure it was their intention to use 2ft gauge. Based on overseas experience, and considering the amount of likely traffic, 2ft gauge would have been capable of handling the traffic.
The management of the Victorian Railways tried to convince the government that this was false economy, and strongly recommended 5ft 3in. They could not convince the government of this, but they did manage to convince them that 2ft 6in would be better than 2ft. This change was made so late in the design process that the rolling stock (but not the locomotives) was built much narrower than 2 ft 6 in would have allowed. The decision to use this gauge was made in 1898.
The Powelltown tramway was built by the Victorian Powell Wood Process Ltd (VPWP) in 1912-13. They had no reason to follow Victorian Railway practice, so they chose what they considered to be the best gauge for their particular purpose. As there were many existing horse-drawn timber tramways in the area, all of 3ft gauge, they chose 3ft gauge in the hope of drawing a lot of this traffic to their line.
In fact, if it was not for these existing 3ft gauge tramways, I feel confident it would have been built to 3 ft 6 in gauge. The VPWP Co. was mainly financed and managed from Western Australia, and everything associated with the tramway and the sawmill followed Western Australian practice. The gauge there was 3ft 6in. The 3 ton and 5 ton wagons used on the Powelltown tramway seem to be identical to WA 3 ft 6 in gauge designs, the curves on the tramway were suitable for 3 ft 6 in gauge, and the design of the bridges and culverts seem to be copies of WA designs.
2ft 6 in was considered too narrow for timber tramways. This was because of the instability of large logs carried on such a narrow gauge, especially when the track was rough, which was often the case with timber tramways. There were some 2 ft 6 in gauge timber tramways in the Tyers Valley area of Victoria, near Erica. They seem to have adopted this gauge because 2ft 6in gauge wheel sets were available from the firewood tramways of Walhalla, but the gauge was by no means ideal for timber tramways - but fine for firewood!