David Morris wrote: > Seeing as there's already one rudder thread running, I've been meaning > to throw this one out for discussion at some point... > > A few weeks ago, a group of us had a bit of a boatman's holiday (we're > all crew on the Seth Ellis tripboat on the Chesterfield Canal at > Retford) and hired the two dayboats from Portland Basin for a trip to > Marple bottom and back. > > It was noticeable when we were reversing back into the moorings at > Dukinfield that both day boats handled much better going astern than > the Seth Ellis does and we commented as much to the marina chap (we're > only talking 35-40ft boats, so astern performance is probably not as > good as you'd expect with a longer boat - maybe). > > He reckoned it was (if I understood the diagrams and explanation > properly) that it was because of the 'wings' he's welded on to the > rudder which appear to stand out at 90degrees which it was reckoned > helped to "contain the water better", hence the better astern > performance. > > Is this fetid dingo's kidneys or is there any truth in it? If true, > what sort of parameters could be considered to enhance performance?
We so modified Beatty, as it was a suggested modification by Ray Denton (R&D). It made a lot of difference keeping the prop wash down going forward, but no difference going astern (Beatty was somewhat wayward in this respect, I put this down to its shortish 50ft length - generally the longer the narrowboat, the better they go astern.) Earnest had the rudder cavitation plates from new (infact it did had a pair at the bottom of the rudder blade, which did nothing apart from collect [EMAIL PROTECTED]). I have found that the cavitation plates make an incredible difference, especially when a lot of power is needed against tidal / river flows, but that may be due to Earnest's "slipper" stern taking water from under the boat. http://www.tuesdaynightclub.co.uk/T07_Imag/28_03_07/Pict7734.jpg I have heard that quite a few people have experimented with "keel" arrangements on shorter narrowboats to improve steering. The big thing that helped Earnest's rather good astern capabilities was the modified rudder blade, with 1" increased leading edge and 3" trailing edge. This also made a big difference, re the slight rudder shake Earnest had before. As others have said, it would seem from experience that the biggest things effecting rudder shake (assuming new, un damaged prop and rudder cup / bearing) is the style, size and pitch of the prop, amount of shaft exposed behind prop, distance from prop to leading edge of rudder blade. Size / proportion and amount of leading and trailing areas of the rudder, and angle of rudder stock. Most fabricators have fathomed out their ideal over the years, but some tweak the ideal to make the weight of the tiller a bit "girly" :-) Earnest now steers acceptably OUT of gear, as many times coming up too early on tidal rivers, I have steered out of gear (infact for half a hour on the tidal Nene, with the engine off). -- Neil Arlidge - NB Earnest
