29th June 2022 – To body go where no 73 has gone before!

As you may have read in my previous diary entry, I have this week been working 4Y19 Tonbridge to Southampton Western Docks returning back to Tonbridge West Yard as 6Y83.

For context the train starts its day at Tonbridge West Yard, running loaded to Mountfield sidings then empty to Southampton. My duty requires me to relieve the train at Tonbridge and work it to Southampton and back.

Due to a windscreen wiper fault and routine exam 69001 was unavailable to work the train. A class 66 was sourced to work the first part of the journey to Mountfield and back to Tonbridge. The plan being that on arrival at Tonbridge the 66 would be taken of and 69001 put back on the train having been released to traffic following its exam.

Things rarely go to plan though and 69001 was not released into traffic in time. The train run into Tonbridge Yard and the 66 was detached. The 66 was needed for other workings so couldn’t carry on to Southampton. It may seem sometimes that we have an abundance of locomotives sitting in yards, but this is far from true. A spare locomotive is not a profitable locomotive. Most locomotives you see in yards are simply waiting for their next booked turn.

With no Locomotive to work the train forward a cancellation seemed unavoidable. Now those of you who know Tonbridge will know in complete contradiction to my previous point that we have a fleet of class 73 locomotives that are used primarily for seasonal work.

The Class 73s were built in the late 60s early 70s and can certainly be called heritage traction. They are reasonably reliable locomotives and are capable of 1600hp on DC 3rd rail and 650HP on diesel power. To put that in context a 66 will generate around 3000hp.

The gypsum working is what I would call a medium heavy train at around 1700 tons. The difficulty is that the route to Southampton features some challenging gradients, especially in the London area where the line speed is low.

For this and other reasons using the class 73s on heavy trains is not something that happens very often. A class 66 or 69 being the preferred traction, so much so that 73s have not been used on the gypsum before so there is no president as to whether it can be done or not. This makes using them in uncharted territory risky. The cost of a failed train, especially in the busy London area can run into many thousands of pounds a risk that nobody wants to take. You could of course run the train with less wagons thus reducing the weight, but you then loose revenue. The margins on freight trains are already pretty tight often being 3 figures only, an amount that can easily disappear in delay payments!

Today though was different. Myself and other driver have often speculated that 2xclass 73s could easily pull the 1700 ton gypsum train. After all 2 locomotives give you 3200hp on electric compared with the 3000hp of a class 66.

After much conversation and debate my manager who is a bit of a rail enthusiast put his reputation on the line and convinced the powers that be to allow the train to run with 2 x 73s working in multiple.

After some manic shunting around in Tonbridge Yard, the locos were shunted onto the train, brake tested and ready to go.

Being a bit of an enthusiast and the fact that he had put his reputation on the line my manager decided he was going to drive the train, with me as route conductor as he does not sign the route Southampton. I know I know. Managers picking and choosing what trains they want to drive, only the rare interesting moves and never the routine stuff. To be fair the 73s do require a bit of special touch on the handles, and I’m not experienced driving heavy trains with these locomotives. I’m pleased he was driving in the end.

The journey to Southampton was mostly uneventful. We were empty and only 500tons so no issues. The train flew along even making up a little time on the route. The locos easily pulled the class 4 train at 75mph. The ride was smooth and quite compared with the constant ying ying ying of a diesel.

We got to Southampton over an hour late so to save some time my manager took care of the loading whilst I went out and got us both a bite to eat. The loaders at Southampton are very efficient and we were on our way back now only 40 late. On leaving Southampton the line climbs for around 20 miles to Litchfield Tunnel. The train now weighing in at 1700tons performed admirably. Coming through the fast lines at Eastleigh we had reached our maximum speed of 60mph, something that you could only dream of on a 66 or 69. We continued happily for miles on end making up time as we went. On arrival at Clapham Junction we were back on time and the locos were showing that despite their age they could keep up with the best of them. 

As is always the way though challenges lay ahead. One of the biggest problems with 3rail locomotives, especially old ones like the 73s are conductor rail gaps. These are areas such as at level crossings or points and junctions where the conductor rail is missing. this isn’t normally a problem as the train can simply coast through them. Most EMU stock have collector shoes at either end of the unit so part of the train is always in contact with the 3rd rail. Class 73s on the other hand are short so they can easily become gapped. That is where no part of the train is in contact with the conductor rail.

The 73s are fitted with all the mod cons of a 1960s locomotive and gaps pose a problem. Imagine drawing 1500 amps of power at 750-1000v and then the loco drops into a gap. That sudden loss of power causes a massive arc, not to mention when the loco picks up the conductor rail again. The amount of power that the loco draws through gaps is huge and can make the electrical substations go pop as well as the resistors and relays on the locomotive. To prevent this we always run down the amps approaching gaps. Basically you lower the power notch so when you pass through the gap the locomotive is drawing no more than 500 amps. Running down the amps is not instant though it takes a few seconds for the amps to run down and then time to build them back up again once the locomotive is back on the 3rd rail.

Due to the severe gradients at Nunhead, we had arranged for the train to take a slightly different route via Herne Hill. Unfortunately for us things didn’t go to plan.

In order to access the mainline via Herne Hill we needed to cross from the down Atlantic line to the Down Chatham line. This shouldn’t have been to much drama but unfortunately for us the signaller decided to cross us over at Wandsworth Road, a station with a nice little up hill gradient. What’s more we had to stop at a red light before being crossed over. This meant we were now stopped on a steep uphill gradient, about to be crossed through points that have gaps. Eventually the signal came of and we started to move forwards. Although slow the 73s managed to ease the train forward. We entered the fist set of points and conductor rail gap but managed to just about coast through it The second gap however was a different story. We were going too slow and the train didn’t have enough momentum to clear the gap, we unfortunately came to a stand blocking all lines at Wandsworth Road.

Trusty old class 73s however are fitted with a small 650hp Diesel engine. But even with 2 locos it’s a big ask for 1300hp to pull a 1700ton train up a gradient. With fingers and toes crossed we started the Diesel engines and prayed. Fortunately for us we managed to move the train at a whopping 3mph engines screaming at us, but eventually we cleared the points and got the train back on the conductor rail, loosing 15 minutes and delaying a Dartford service in the process.

After all that excitement the remainder of the journey was uneventful and we even made time back arriving in Tonbridge West Yard 10 minutes early, proving to all the sceptics that it can be done, sort of.



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