Round the back of Portsea Island

A couple of years back I navigated the Hilsea Channel that connects Portsmouth and Langstone harbours, in company with Conrad Natzio, designer of my Sandpiper spritsail boat. He sailed his own Oystercatcher.
Everyone has to do Hilsea Channel eventually because it looks so tempting on the map and forms a 'voyage' (we sailed from Bosham to Fareham) but it is a bit dismal to be honest. The channel is completely canalised and although one side is formed by the grassy ramparts of the Hilsea Lines, built in Victorian times to defend Portsmouth from the French, the other side is the M27 motorway.
The best plan is to start on a rising tide about two hours before HT to allow a decent air space under the bridges. There is no alternative to rowing (sorry sailing types!).
We went east to west, starting from the hospitable Tudor Sailing Club. The first bridge is the Eastern Road, which is not a problem.
We anchored and had lunch, being entertained by a broken-down van being towed off the bridge.
A member of the Langstone Cutters who had done the trip told me that the railway bridge was so low they had to lie down in their seats and hand themselves under it, avoiding threatening-looking ducting with 'High Voltage - Danger of Death' on which must have been alarming but we had plenty of room at this state of the tide.
This is a footbridge with a great big water pipe (at least, I assume it was water...) slung under it. This is looking back towards the railway bridge (rower's viewpoint).

This flying footbridge is not a problem for sailors but we might as well be complete.

Next challenge is the bridge under the Cosham Roundabout, which is actually a pair of bridges separated by a short culvert. Dark and uninviting but not a problem. It is entertaining to note that the older bridge (1920s?) has fancy stone balustrades but the later one, built when the roundabout was constructed in the 1970s, is brutally functional. I don't know which is worse - the half-hearted ornament or the don't-care functionalism.
That is the last of the low bridges. The next problem was that the new lagoon formed by the loop of the M275 didn't have enough water in it. Here is Cap'n Conrad scouring the horizon for a channel.
An inexplicable thing floats in the middle of the lagoon. Is it art, or some sort of beacon, possibly to attract alien spacecraft to Pompey?
The end is in sight when you reach the motorway bridge. It looks as though the traffic engineers have been generous to sailors this time, but the height is really there to provide headroom for the interchanges further down the road. Beyond the bridge on the north is a handy inlet for setting sail before entering Portsmouth Harbour.