Aeolus
Well-Known Member
If I changed from a two blade 15 x 9 prop to a 3 blade prop, should the specification remain 15 x 9?
Jonathan
Jonathan
2 to 3 blade prop
- Thread starter Aeolus
- Start date
ex-Gladys
Well-Known Member
Nope... The third variable is blade area....
alanporter
Well-Known Member
I did just that, same dimensions from two blade to three blade. All I noticed was increased thrust under engine power, a blessing against heavy winds and seas, and when you need to "brake" hard. Only disadvantage was it cut a half knot under sail.
capt_courageous
Well-Known Member
Hi
A prop/boat fitting program says you should increase the diameter by 1 inch ( if there is the clearance ) and drop the pitch by about 2 ins. I changed from 2 to 3 blades using its advice. Only a small increase in top speed in calm conditions. But as Alan says there is more punch into wind and waves. Well worth doing if your engine power is a bit marginal.
A prop/boat fitting program says you should increase the diameter by 1 inch ( if there is the clearance ) and drop the pitch by about 2 ins. I changed from 2 to 3 blades using its advice. Only a small increase in top speed in calm conditions. But as Alan says there is more punch into wind and waves. Well worth doing if your engine power is a bit marginal.
LeonF
Well-Known Member
Good to hear....I changed from a 12" 2 blader, pitch 9, to a 13 " three blader,pitch 11, last year. I did it all ina hurry as I was going on holiday. The engine wouldn't get beyond 2800 when it should be around 3200. A year later with a heavily fouled bottom I could just get 2200. Have taken advice and had it repitched down to 9, and this should make a difference I have been told. The commercial guys who did it for me showed me a large tugs prop that they were repitching as the tug people were not happy that she was revving at 25 revs under!