Prop clearance

Jjammer

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Circling back on prop venting.

Have others done it and liked it? Any change in performance?

Was visiting with the boys at Soundown and we discussed this as another technique to really quiet down a prop.
 

Downrigga

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Circling back on prop venting.

Have others done it and liked it? Any change in performance?

Was visiting with the boys at Soundown and we discussed this as another technique to really quiet down a prop.
Lots of guys have prop vents
 
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I've heard 15% suggested as a general rule of thumb, but I've never had that much clearance on my boats. I try to stay in the 11%-13% range from the bottom of the hull, and it has worked great for the boats I've built. So currently the 22" prop has 12.5% tip clearance. I guess you could jump up to a 23" prop and have 9.8% tip clearance, but I would probably stay with the 22" diameter and go with a skewed 4 blade like the DQX. What kind of hp are you thinking of upgrading to and what does the boat weigh?
I think Powderpro is right. Going over 10% seems to work fine. I did have trouble with the DQX though. It's Michigan's version of the old HyTorq. It came apart on me from blade over loading. Since 5 blades aren't available in under 20"s I moved to the DQ486. Brought blade area from .72 to .86. Solved the problems I was having and is a lot heavier than the HyTorq. Somewhere way back is the thread I had on it.
 

Full Circle

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Full Circle

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c1steve

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I had a similar "singing" problem after replacing the engine in a sailboat. We thought the transmission had a bad bearing. The engine mfg. rep came by and replaced the transmission, no change. Ended up being that the shorter shaft we installed was the cause of the noise. Fixed with by installing a quality vibration isolator at the coupling. Shaft was perfectly machined, but something about it being short was the problem.
 

Downrigga

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The sound was like a bearing going out. Unbelievable. I was teady to pull the boat and change the cutlass bearings, etc. I tried everything, shaft seal, engine mounts, stern tune, zincs and line cutter. A guy came up while I was docking the boat and asked if I’ve been fishing. I told him the story and he said “I had that”. It turned out to be prop sing. I’ve been boating for over fifty years and never heard of it. Good luck!
Common, i had it. Just redid the pitch slightly and it went away.
 

Full Circle

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ArchHibb

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I’m all but convinced I developed prop sing this season after redoing the engine isolators. Just as Full Circle said, the noise sounds like a bearing going out, right at the prop. and occurs only 1,000-1,200 rpms. Shaft is aligned to .002 and spins freely, no play in the cutlass. Guess I’ll pull the prop and take it to H&H for the 45-treatment. Thanks for sharing gang.
 

Downrigga

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Good for you. How did you determine it was prop sing? Mine was so loud no one that heard it thought about prop sing. Perhaps you had known about it before we didn’t. The prop guy determined the fix by putting an angle on the trailing edge which did fix it. My aim with the post was to hopefully prevent others who had never heard about it some aggravation and time.
Mine was loud too and right at trolling speed. I had sent it out to get tuned up and when i got it back it was singing. I called him and he said prop sing, bring it back. Had it back on the boat same day no singing. He did something to the edge like you said.
 

Full Circle

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