Using too much throttle is actually pointless – and here’s why
I read Kevin Blick’s article ( CB, October) with great interest, and hope that I might be allowed to offer some thoughts of my own. My own perspective for this is a little unusual – my wife and I have been clocking up four weeks a year aboard hire boats for over 30 years now, and for most of that time I have deployed a GPS which accurately displays speeds accurate to 0.1 mph, so my views are based on sound facts rather than guesswork.
So let’s get down to the fundamentals. A boat’s prop works by drawing water through itself. This water usually has to come either from the sides or beneath, as the prop is generally too close to the hull for much water to be drawn from above. If the prop is unable to pull water through itself freely, as is the case, for instance, when the cut is either narrow or shallow, then no amount of extra throttle will change that fact.
Think, for instance, how all narrowboats labour when leaving locks, as well as when negotiating narrow bridge holes or aqueducts. Thus the maximum speed attainable by any boat is usually determined by the profile of the cut itself. Incidentally, everyone who has ever taken a boat onto a navigable river will know that, wind and current aside, any boat feels far more lively on a river than on a canal.
In a few places – Duke’s Cut springs to mind here – you can actually feel the change as the boat makes the transition from ‘wide and deep’ to ‘narrower and shallower’, or indeed vice versa. Conversely, I suspect that no one has ever achieved a true 4mph anywhere on the Macclesfield !
All this means that for the vast majority of the canals, the existing 4mph limit is in fact no more than an aspiration. Even attaining this speed is usually impossible, and any thoughts of maintaining an average of 4mph over an hour or more remain mere fantasy, especially as you will invariably be slowing down frequently for moored boats.
I use my own bespoke software for planning my trips, and I never plan for more than 3mph for UK canals, and for our forthcoming trip on the Southern Oxford, I have assumed an average of no more than 2.5mph.
Some stretches of, for instance, the Grand Union or the Trent & Mersey do permit slightly higher speeds, as would the Caledonian Canal, though sadly I have no personal experience of boating on the latter.
Now let us consider the matter of passing moored boats. There are actually two separate issues at play here, as both speed and throttle-setting are relevant. Happily, most narrowboats these days have efficient bows which produce relatively little wash and very few boats have the square sterns that produce noticeable stern wash – indeed the stern wash produced by most boats is pretty negligible these days.
My experience is that the thing that peeves most boaters, myself included, is that of having the boat pulled away from the bank by passing traffic.
The important thing to understand here is that the pull is not being produced by bow or stern wash, it’s that pesky prop trying to suck loads of water through, as the steerer is using too much throttle. It doesn’t matter how slowly that boat is moving, it’s the use of excessive throttle that will do the damage. In France we had the interesting experience of trying to moor a boat with a heavily loaded peniche passing us in the opposite direction.
This boat was only doing, maybe 1.5mph, but because the skipper hadn’t throttled back, the pull on the ropes was so severe that it was all that we could do to succeed in holding on to just one of the ropes, such was the pull on them as the peniche passed.
I would conclude by wholeheartedly agreeing with KB’s assertion that the blame for excessive speeding is equally shared by both owners and hirers. I believe it’s about 50/50, and has been for many years.
CHRIS DODGE, via email
It doesn’t take much to upset things