Quandary
Well-Known Member
Perhaps this info. may be useful to someone.
When we bought the Moody S31 (engine VP 2020 with saildrive) it had a two blade VP 15"x 9" folder, motoring seemed to be slower than expected, I did some tests in Loch Lochy and Loch Ness where there are no tides, using the speed from the gps
2250 revs= 5.2 knots, 2500= 5.5 kts. 2750= 5.9kts. 3000 = 6.3kts. (the Lochy figures were slightly better but there we had a light following wind on bare poles)
Against a stiff wind and a chop at sea it was sometimes a struggle to get 4.5kts.
The local engineering workshop quoted around £100+ for a rebuild with new pivot pins etc, but I could not see that making a big enough improvement.
So I decided to buy a new prop. After a lot of agonising over the crazy price I decided to go the whole hog and ordered a Flexofold 16"x 9" three blade folder from Darglow, I also got quotes from Denmark but Darglow's 10% winter discount and their more convincing conversations about size and pitch encouraged me to deal with them. Painful experience though, > £1900
Lovely looking bit of kit with a big aluminium anode over the hub and easy to fit, (the boat spends its resting time in 'fresh' water.)
The results so far
Flat water 2250 revs. gives us 6.25 kts (3000 gets her up to 7.3kts.) but the former is comfortable for cruising. Against a strongish blow, F5 and a breaking wave Sound of Mull chop, those speeds drop by nearly a knot but much better than last year.
The amazing thing is the fuel consumption, after launching, mast stepping and a half day transit of the canal plus eight hours motoring to Tobermory via Oban I tried to top her up, overflowed at 12 litres. Some of the improvement is down to the increased diameter but most to the third blade, I do have to be careful with the throttle because of the acceleration when leaving tight corners.
When we bought the Moody S31 (engine VP 2020 with saildrive) it had a two blade VP 15"x 9" folder, motoring seemed to be slower than expected, I did some tests in Loch Lochy and Loch Ness where there are no tides, using the speed from the gps
2250 revs= 5.2 knots, 2500= 5.5 kts. 2750= 5.9kts. 3000 = 6.3kts. (the Lochy figures were slightly better but there we had a light following wind on bare poles)
Against a stiff wind and a chop at sea it was sometimes a struggle to get 4.5kts.
The local engineering workshop quoted around £100+ for a rebuild with new pivot pins etc, but I could not see that making a big enough improvement.
So I decided to buy a new prop. After a lot of agonising over the crazy price I decided to go the whole hog and ordered a Flexofold 16"x 9" three blade folder from Darglow, I also got quotes from Denmark but Darglow's 10% winter discount and their more convincing conversations about size and pitch encouraged me to deal with them. Painful experience though, > £1900
Lovely looking bit of kit with a big aluminium anode over the hub and easy to fit, (the boat spends its resting time in 'fresh' water.)
The results so far
Flat water 2250 revs. gives us 6.25 kts (3000 gets her up to 7.3kts.) but the former is comfortable for cruising. Against a strongish blow, F5 and a breaking wave Sound of Mull chop, those speeds drop by nearly a knot but much better than last year.
The amazing thing is the fuel consumption, after launching, mast stepping and a half day transit of the canal plus eight hours motoring to Tobermory via Oban I tried to top her up, overflowed at 12 litres. Some of the improvement is down to the increased diameter but most to the third blade, I do have to be careful with the throttle because of the acceleration when leaving tight corners.