I get your point Steyne. But the big ferry needed 3250 ihp to reach 17 knots, The dieselised Bs could do 16 knots on 2000 bhp and as steamers, 15 knots on 1400 ihp. My point is South Steyne had no running mate and her additional capacity was wasted at peak hour as there was no equalivant running in the opposite direction. Its a lot of horsepower and fuel for 270 additional passengers. The Curl Curl and Dee Why had the same engine power as the Steyne for no gain in passengers over the "B"s. They must have been expensive to run compared to the diesel boats in the late 50s.
The twins were expensive to run but in the beginning cost wasn't relevant. The manly co. used the simple method of increasing power rather than demanding engineering gains to increase the speed of their boats. The twins in particular came at a time when talk of the northern beaches railway again reared it's head - the co. needed very fast boats in case that competition arrived.
For most of their lives these two boats were the workhorses of the fleet, South Steyne not so much so - there's a published timetable (http://www.ferriesofsydney.com/index.php?topic=1491.msg6855#msg6855
) from 1952 that shows how the boats were utilised:
Bellubera - 14
Curl Curl - 16
Dee Why - 22
North Head - 20
South Steyne - 12
South Steyne was the least used. Balgowlah was out of service by then and it looks like Baragoola was probably a spare boat (at that time she would have been the slowest of the remaining steamers). North Head was relatively new to the service and the bulk of the work was done by her and Dee Why.
This was a time when costs began to tell against the company and passenger numbers had started declining, so I would assume the expensive-to-run high capacity South Steyne was already being looked at as a bit of a burden. I suspect what saved that boat was the opportunity taken a year or two later to utilise her for something other than passenger services and recoup some of her operating costs.
The remaining boats all carried roughly the same (lesser) number of passengers and operated at roughly the same speed.
Certainly the return of Baragoola in '61 as cheaper to operate MV would have placed the three remaining steamers operating costs under the spotlight. I suspect the imminent return of Baragoola was the "kiss of death" for Curl Curl.
Dee Why followed no long thereafter and in her last few years was the spare boat of the fleet. They were never considered for conversion as their steel had apparently not aged well.
This left the three diesel boats carrying the majority of the service. I would conjecture that had another one (possibly two) diesel boats been available then South Steyne would also have exited stage left at this time and certainly the company records indicate that South Steyne was considered for replacement in the late 60's with the remaining three boats to be retired a few years afterwards. History shows otherwise and the worn out Bellubera was lost first (a crying shame that, she should still be with us today) and North Head and Goola became the backbone of the fleet until the arrival of the Freshwater class.
North Head of course (despite Tom Mead's appellation of "the greatest of them all" to the South Steyne) proved to be the truly greatest and longest lived Manly ferry - I doubt we'll ever see anything match her 74 years in the saddle. Though I do wonder why Goola became such a favourite and received such a send off and North Head just went quietly into retirement.