FeatherStream A-Hub 3B
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Practical Boat Owner – September 2015
As the engine turned the opposite way and the gearbox was a slightly different ratio (2.14 ahead and 1.96 astern), a different propeller was going to be required.
I spent ages deciding which type to buy but I really wanted something that didn’t try to spin when sailing, and that was also adjustable in pitch for forwards and astern.
Therefore, I ordered a three-bladed, 16in x 101/2in Darglow Featherstream propeller: it wasn’t exactly cheap, but the staff there were very helpful and patient with my questions, and they’re rated highly by marine engineers which was comforting.
It was now time to get the ‘engine finished and running in the boatyard. The French Marine engineer re-checked the shaft alignment: he couldn’t get it consistent until he discovered a small area of paint on the mating flange.
Once this was cleaned off the shaft was quickly realigned, so the fuel, oil and electrics were checked one last time, and a temporary water-cooling rig was set up. The button was pushed and the engine fired, but it was very lumpy.
Air in the fuel was immediately diagnosed and a connection that wasn’t tight discovered: minutes later, the engine was running sweetly.
Launch day finally arrived, and I was eager to check it all out in the water. Engineer Jason arrived again as it is a precondition for warranty that the drive is checked along with the engine’s ability to (briefly) reach full power to check the propeller match. On a perfect day the mooring was slipped and power gradually increased to 3,200rpm.
All was fine: the boat briefly reached over 7 knots, and it felt like we could tow a couple of water-skiers) I was pleased to note that there were no vibration bands throughout the rpm range, except perhaps at the slow tickover speed.
Back on the mooring, Jason increased the tickover slightly to smooth the engine vibration and signed it off. Since then I have been testing it at every opportunity, and to date it has has more than 40 trouble-free hours on the clock.
I am delighted to report that so far there have been no problems at all: the Darglow Featherstream prop is very smooth and seems to give a greater top speed by almost one knot than the old two-bladed prop. The three-bladed prop should also give more punch in a short sea. It handles well in astern, and once feathered the prop stops turning while in neutral (that’s a first for me) and everything goes quiet. The yacht slips along very sweetly in this mode, and I hope the reduced drag will enable me to creep up on my cruising friends.
On top of this the calculated (but adjustable) pitch ahead and astern seems perfect. I did email the performance figures of speed versus rpm to Darglow, and they reported that they are spot-on. I had factored in a lift-out for a possible pitch adjustment, but this hasn’t proved necessary. To adjust the pitch, a simple free-issue cassette is changed over on the front of the prop.
I am really pleased that I had a go at this task. Being retired, I had the time to spend on it, and I took much longer over the job than professional engineers would have done, but I now know so much more about how everything goes together – in an emergency that might prove very helpful. All at French Marine were really supportive in giving an amateur like myself the advice necessary to carry out the work correctly and avoid some common pitfalls that others have encountered. And did I enjoy it? Yes indeed.