A family Sunday, then on to Boston

21st & 22nd June

One other bit of wild life news I missed out from last time: on our approach to Burton Waters, we saw a black swan. Now we've seen these before, particularly on the Great Ouse, but this one was hanging around with a full family of mute swans. Normally the mute cob would drive off any other adult swan which started lurking about the family like that, but in this case there was no hassle at all.

Back to yesterday: after a quick paper and milk shopping trip, we ran back down river to Kirkstead Bridge, having agreed to meet Cathy, Graeme and the grandkids there in the afternoon. On some stretches the water was totally calm without any sign of other boats, fishermen or any other description of river user, and this on a fine Sunday in June.

I took the opportunity to do some speed trials, winding the engine up by 100 rpm at a time and observing the effect on our speed. Normally you can't do this because the comparatively narrow and shallow channel of a canal imposes restrictions long before you've reached the boat's design maxima.

Sanity is, if anything, a touch overpropped, with a 19" x 11" Crowther. It means that the engine doesn't work very hard at any time, and on this occasion, 1500 rpm was the effective top speed. We were doing 6 mph over the ground, with very little flow on the river to help, and the prop was just starting to cavitate.

Discussions about prop performance on canal boats often confuse cavitation with ventilation of the prop. The latter is far commoner, usually because the stern isn't ballasted deeply enough, so that air gets drawn down into the flow into the prop, reducing its efficiency.

That certainly wasn't happening here; the stern was digging down far enough that the fenders were starting to drag in the water.

Cavitation is when the water can't get past the swim fast enough to feed the prop. The pressure in front of the prop falls so low that first air starts forming bubbles of gas, then the water itself starts vapourising. There's a distinctive noise and shuddering, and of course the boat doesn't go any faster for faster prop revs. Having demonstrated these facts to my satisfaction I throttled back to around 1300, at which we were making 5 mph and everything felt comfortable.

There was plenty of room at Kirkstead when we got there, and various other boats came and went during the day. We had an interesting chat with a guy involved in the Sleaford Navigation Trust; he advised us not to attempt the Kyme Eau at this time of year, as it has completely weeded over. Apparently the Trust is thinking of buying a weed cutter boat, so that folk can explore the four miles that's currently open in the summer rather than in the window in April and May between the water levels being reasonable and the weed filling the channel.

The kids duly rolled up just after lunch, and we had an excellent family afternoon in the hot weather. The moorings have a shelf of grass about half way up the flood bank that's been mown, and makes a great place for a picnic.

It was a quiet night last night, and this morning we decided to do the whole run down to Boston. We got away early and Sheila mainly steered. This is a really quiet bit of river. Not possibly to everyone's taste, I admit, being pretty straight with high flood banks on each side, but there's a lot of bird life to observe, and as I said last time, it's just very relaxing to chug steadily along.

The mooring in Boston hasn't improved in four years, with very short and high finger moorings, but there's plenty of room, and you just have to tie using the bowline and centreline reversed in spring fashion, so that the bowline stops the bow from riding up onto the grass bank.

The other thing to mention is that, despite what the signs say, the first night is free. After that it's £6.45 per night, so no big encouragement to hang about. There's an Asda within easy reach, just on the other side of the river from the moorings, and the rest of the town isn't far away either.

We've spent the afternoon wandering round, viewing the Maud Foster Windmill and the like. Tomorrow we'll head back to Kirkstead, for a planned boat trip for the family on Wednesday.