Propeller sizing issues
I have an old 31' Columbia with an atomic4 . It has an 11" dia. 2 blade prop the pitich I haven't quite figured out (but I'm working on). The boat idles at ~800-1000 rpm. I have been told that the transmission is 1:1 so I'm guessing the prop at idle speed is turning 800-1000 times/minute. The problem with this is that at idle speed the boat travels at ~5 knots and let me tell you how much fun that is pulling into my slip!! What I do is sort of ride the clutch so to speak moving from forward to reverse. I didn't put the boat in last year and this year when I put it in, it was stuck in forward gear.....Pulling the transmission cover and spraying wd40(sidebar: I want to meet the engineer who put this engine in this boat as I had to put a towel over the engine and climb over it) Working the lever back and forth freed the gear. I don't think my strategy of forward and reverse is the best solution to happy sailing. Anyway any ideas on sizing a proper propeller so that I actually have an idle speed.
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I too pull into my slip precisely as Neil describes.
(It'll save you "entertaining" your dock mates) Attached is the procedure for adjusting the Reverse Gear (Tranny) Also, HERE is a good video about it. |
Your current prop must have a pitch on the order of 10-12 inches based on your reported boat speed of 5 kts at 1000 RPM. Most likely your WOT RPM is only 1200-1300 RPM. That is way too much pitch all the way around!
Neil is correct in stating that a larger diameter prop will most likely function better in a "broad deadwood" application such as yours. Having said that, we have props on probably 50 Alberg 30s and Pearson Tritons with the same deadwood condition and I have had no reports of any issues. I have always been a bit concerned that reverse performance would be compromised by the deadwood issue but experience has not shown that to be the case. A small 3 blade prop will improve the prop walk in the astern direction due to the smaller diameter and also reduce vibration in the ahead direction as only one blade at a time will be in the disturbed water flow associated with the deadwood. BTW, the Indigo prop is 10 X 7.4 pitch and they are in stock for immediate shipment. Tom Stevens Indigo |
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