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prop venting
So sometimes when I get upset I sit down on the dock and discuss life's problems with my prop and feel a heck of a lot better. But then when I take her out and when I cut sharp turns, she starts venting. It typically only rises about 100 or 200rpms at most but yesterday she kicked in the turn(similar to slipping) and you could feel the prop re-bite. I told the installer and I brought the boat back and we measured everything in the back and determined that the placement on the bracket was correct (even had a second party confirm placement). I don't mind the the subtle rise in RPM's but she can't be kickin like that.
Anyone have any ideas or similar situations????? Its a Yammy F150 with a 14 1/2 x 17SS.
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- The charm of fishing is that it is the pursuit of what is elusive but obtainable, a perpetual series of occasions for hope. Lucky Jack - .......The Surprise is not old; no one would call her old. She has a bluff bow, lovely lines. She's a fine seaboat: weatherly, stiff and fast, very fast, if she's well handled. No, she's not old; she's in her prime. 85' Wellcraft 20 Fisherman "Guale Girl" 1979 Alumnacraft 14 - STILL got holes in it 2006 WS Tarpon160f - "Mudd Butt" 
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#3
07-31-2011, 10:44 PM
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Can we assume the sharp turns are with the motor trimmed all the way down?...
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'74 V-20/ BF 150 '95 V-21/ BF 150 '84 V-20/ 200 2.4 Merc '87 V-20/'18 F150 Yamaha 
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#4
08-01-2011, 07:07 AM
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Ive tried the turns both with the engine level and trimmed all the way down. Its not as bad with the engine trimmed all the way down but it still does it. I meant to correct my post the other day but the comp. was slow. The sublte rise in rpm's will come on regular turns(turning 90deg over 100/150yrds) not necessarily tight turns. But the kicking came in on tight turns.
What is the ideology behind a 4-blade keeping this from happening? I've never had one.........
__________________
- The charm of fishing is that it is the pursuit of what is elusive but obtainable, a perpetual series of occasions for hope. Lucky Jack - .......The Surprise is not old; no one would call her old. She has a bluff bow, lovely lines. She's a fine seaboat: weatherly, stiff and fast, very fast, if she's well handled. No, she's not old; she's in her prime. 85' Wellcraft 20 Fisherman "Guale Girl" 1979 Alumnacraft 14 - STILL got holes in it 2006 WS Tarpon160f - "Mudd Butt"
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#5
08-01-2011, 10:34 AM
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Think of a prop as you would a machine screw. Course thread holds well, but fine thread holds better, more surface area to grab onto. More surface area = better bite. The harder you turn, the more slip angle increases. This can be mitigated by trimming the motor down or getting the prop as deep as you can with a jack plate (i.e getting the prop into clean water). However, the nature of prop bite is linear, and as soon as you begin asking it to side load (i.e. turn), slip angle increases and the prop becomes less efficient. Adding another blade gives the prop 20% more surface area to "grab onto" and thus masks some of the inherent inefficiency of the turn.
The upshot is better hole shot and quicker onto plane along with more stern lift and likely the ability to stay on plane at lower RPMs and speeds (read greater midrange performance and economy). The theoretical trade-off is less top end due to drag, however, prop design has come a long way in the last 20 or 30 years and the actual compromise will likely be undetectable for you considering hull shape and power available and speeds likely to be achieved.
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#6
08-01-2011, 12:22 PM
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Thanks Shrek.......
You know it really wouldn't even be a trade-off. I can count on one hand how many times I can run WOT, and still don't even when conditions allow. This was probably the result of the F150 adding weight because she didn't do it when I had the 2-stroke on there. She is Heiney-heavy and switching would probably be the best bet since we ruled height out. Now, what to do with that shiny prop I have now.........
__________________
- The charm of fishing is that it is the pursuit of what is elusive but obtainable, a perpetual series of occasions for hope. Lucky Jack - .......The Surprise is not old; no one would call her old. She has a bluff bow, lovely lines. She's a fine seaboat: weatherly, stiff and fast, very fast, if she's well handled. No, she's not old; she's in her prime. 85' Wellcraft 20 Fisherman "Guale Girl" 1979 Alumnacraft 14 - STILL got holes in it 2006 WS Tarpon160f - "Mudd Butt"
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