Stuffing Tube Curvature and Resonant Vibration

[Mike W]

I know for many experts on here this may be as old of an argument as the teflon-or-not debate and either may work, but I still question what is best.

For the sake of debate lets consider the longer sport hydro type tubes. I see the smooth gradual curve along almost the entire length of the tube with fairly short straight sections at either end, and the type with longer straight sections at either end with a more abrupt curve just after the hull exit.

Can anyone make an argument for which is definitively better? I tend to rate my installations by the amount of resonant vibration I can detect bench-testing and there doesn't seem to be any definitive explanation why some run smooth on the bench and some do not. I've been told not to worry about it, and that once under load in the water all is well regardless...

Any thoughts to share from the experts?

[properchopper]

Mike - I'll chime in knowing that there are other ways of looking at this also. To begin with when I first started building FE30's for Insane customers I had longer straight sections at either end with just one bend in the middle. Jeff M. (owner of Insane at the time and a VERY SMART designer) told me to go to the longer gradual curve (and I did from then on). What I know is that noisier, vibrating drivetrains will convert some of the power energy to noise rather than to rotational energy. Seems logical. FWIW my SAW record experience lead me to determine that a wire drive AND a ball bearing strut give the least parasitic drag and will end up as a faster, quieter setup. Never could keep those ball strut bearings from early demise 'tho

[Mike W]

Yes replacing needle bearings in Octura struts was a common job back in the 90s when I raced nitro. And you couldn't hear any drivetrain resonance with nitro either.

Thanks for the info I am in agreement with you but I know many prefer the other stuffing tube bend design. I would say its close to 50-50 on boats I have seen. Surprised there is so little interest in this topic. It is bench racing season in most of the country.

[RaceMechaniX]

A single gentle bend is the lowest drag installation.

[Mike W]

Yes that is what I have always done and believed to be true. You can feel it just spinning the shaft by hand. But, my Q hydro had a horrible resonant vibration I had to be rid of, and wondered if maybe the sharper bend corrected this problem in some way with longer driveshafts as on sport hydros. On most of my twin cats and monos it is a non-issue because I run very short driveshafts.