Roger - I agree
I agree, the water dragged along by the hull will reduce the effects of prop drag as mentioned in my posting #29 last Thursday.
The YM "Ultimate Prop Test" did 15 props. I think the magazine specified 16 x 11 or thereabouts which was probably the size of the original prop supplied with the boat. This meant that all props were comparable even if they might not quite have suited the boat.
On test were 6 folders - Gori 3B, Flexofold 3B & 2B, Slipstream 3B & 2B and Varifold 2B. And 7 featherers - Autostream 3B, Autoprop 3B (Bruntons swinging blade), Featherstream 3B, Maxprop 3B & 2B, Kiwi 3B and Variprofile 3B. All were compared against a standard full turbine 3 blade with, what looks like, nearly 50% DAR. We do not see Campbell or Michigan wheel in the UK (and I have never believed the Campbell Sailer hype anyway - simply put narrow blades rather too thick) - don't want to start a war with Campbell devotees please.
Apart from exceptions, the folders gave the hull the most forward speed and had the highest forward bollard pull; but all markedly lacked the astern bollard pull and all had worse stopping distances. I had one of these. When put in reverse the hull carried on forwards and froth came out from under the stern!
I attribute the superior forward performance of the folders to their blades having 'washout' whilst the featherers have flat blades. I see no reason why the featherers could not have blades with washout as it is recommended to put the box into reverse whilst sailing and the drag penalty would not be too much.
By and large the featherers generated a higher percentage of their forward thrust as propwalk - up to 15.8% in the case of the Maxprop 2 blader. They had significantly wider blades.
Apologies to main for getting off his topic but this is such a terrific thread with knowledgable contributors.
I agree, the water dragged along by the hull will reduce the effects of prop drag as mentioned in my posting #29 last Thursday.
The YM "Ultimate Prop Test" did 15 props. I think the magazine specified 16 x 11 or thereabouts which was probably the size of the original prop supplied with the boat. This meant that all props were comparable even if they might not quite have suited the boat.
On test were 6 folders - Gori 3B, Flexofold 3B & 2B, Slipstream 3B & 2B and Varifold 2B. And 7 featherers - Autostream 3B, Autoprop 3B (Bruntons swinging blade), Featherstream 3B, Maxprop 3B & 2B, Kiwi 3B and Variprofile 3B. All were compared against a standard full turbine 3 blade with, what looks like, nearly 50% DAR. We do not see Campbell or Michigan wheel in the UK (and I have never believed the Campbell Sailer hype anyway - simply put narrow blades rather too thick) - don't want to start a war with Campbell devotees please.
Apart from exceptions, the folders gave the hull the most forward speed and had the highest forward bollard pull; but all markedly lacked the astern bollard pull and all had worse stopping distances. I had one of these. When put in reverse the hull carried on forwards and froth came out from under the stern!
I attribute the superior forward performance of the folders to their blades having 'washout' whilst the featherers have flat blades. I see no reason why the featherers could not have blades with washout as it is recommended to put the box into reverse whilst sailing and the drag penalty would not be too much.
By and large the featherers generated a higher percentage of their forward thrust as propwalk - up to 15.8% in the case of the Maxprop 2 blader. They had significantly wider blades.
Apologies to main for getting off his topic but this is such a terrific thread with knowledgable contributors.
