flex vibration

[Rumdog]

I have a 34" sprintcat. Running 5s2p, feigao 580L 1649 kv. Anyhow, the longest section of the stuffing tube extends from the hull towards the strut. It ends about3/16" before the strut. The strut is a bearing style strut. When bench testing, ( simply blipping the throttle), I notice quite a bit of vibration in this area of the tube. How can I get rid of this, being that there is so much unsupported tube? It is .187 flex, running linerless k@s brass.

[domwilson]

Got any pics?

[detox]

Here is a couple of things you can try:

Check your collet. It may be out of round or balance. To check...simply spin your motor in hand with collet attached. I have two of the Octura .187 collets and only one of them is in balance

OSE recommends using 7/32" brass tubing with .187 cable.

Try a slight S bend on your stuffing tube or crimp your stuffing tube slightly every 2 inches to reduce harmonics.

Use lots of grease.

Read here; http://forums.offshoreelectrics.com/showthread.php?t=11896


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[Rumdog]

here ya go...

[domwilson]

Is it the pic or is that tube not aligned with the strut? Maybe a small piece of teflon liner from the stuffing tube to the strut?

[Rumdog]

It's the pic. I'm running linerless. There is no room to go into the strut with teflon or the brass. I like the idea of the S bend but I may have to adjust my motor angle to raise the motor shaft a bit, or just put a much more aggresive type bend in it. My collet runs true and is balanced pretty well it seems.

[detox]

It's hard to see in picture, but you should have used the next size larger tubing epoxied to your hull. That way you can remove your stuffing tube from hull without having to cut it away from hull and cured epoxy. I would cut that out and re-do.


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[Rumdog]

how would you go about supporting the tube then?

[detox]

KS brass tubing is telescopic. Meaning the next larger size is a tight slip fit. If using a 1/4" or 7/32" stuffing tube use the next larger size epoxied to hull (short piece). That way your stuffing tube can be easily replaced. A slightly sharp bend or S bend will prevent tube from rotating while cable is spinning.

[m4a1usr]

Take your flex assy out and put it on a flat surface. Clean it well prior to. Roll it back and forth with your fingers where the rigid shaft is silver soldered to the flex, observe how well it was centered when soldered. You would be amazed at how many folks dont do the one simple check. It was probably misaligned when soldered, more common then you think from name brand sources. It will be appearent right away if its not properly centered. And its a huge source of power robbing friction.

A better method is to chuck up the rigid part in a drill press and spin it up. You can immediately see an out of tolerance solder/ misalignment job.

John

[Rumdog]

I'm likin' these ideas guys!

[domwilson]

Take your flex assy out and put it on a flat surface. Clean it well prior to. Roll it back and forth with your fingers where the rigid shaft is silver soldered to the flex, observe how well it was centered when soldered. You would be amazed at how many folks dont do the one simple check. It was probably misaligned when soldered, more common then you think from name brand sources. It will be appearent right away if its not properly centered. And its a huge source of power robbing friction.

A better method is to chuck up the rigid part in a drill press and spin it up. You can immediately see an out of tolerance solder/ misalignment job.

John

I agree. That would explain why the tube looks misaligned with the strut.

[Jeff Wohlt]

Sure looks like too small of a stuffing tube but hard to see in the pic.

Is the shaft soldered or loctited in the stub? I had a long flex on a hydro that slapped a bit but when under load in the water it was nothing.

[andym]

Most struts have a nose piece on them that your tube slides into, the fact that it is unsupported by the strut will cause many a problem. Any harmonic or balance related flexing will move the tube about instead of the tube limiting them. The tube is to small ID as Jeff stated as well. See if you can get a strut only { no mount=cheaper) with the nose and replace the stuffing tube. If you heat the epoxy with a hair dryer it will peal away easily.

[detox]

Most struts have a nose piece on them that your tube slides into, the fact that it is unsupported by the strut will cause many a problem. Any harmonic or balance related flexing will move the tube about instead of the tube limiting them. The tube is to small ID as Jeff stated as well. See if you can get a strut only { no mount=cheaper) with the nose and replace the stuffing tube. If you heat the epoxy with a hair dryer it will peal away easily.

Verygood observation. It does look like stuffing tube and cable is unsupported at strut. What happened to this strut? Was tapered section cut off?

[Fluid]

I run a similar setup and don't have an objectionable vibration - but my stuffing tube runs into the strut nose. Ditch the current funky strut and get a SpeedMaster strut with a sleeve bearing. Use 1/4" OD tubing for the stuffing tube. As suggested, use a short length (3") of the next size larger tubing epoxied through the hull and replace the current tube. Run the tube through the strut, and end it no more than 1/2" behind the coupler. When gluing the short tube into the hull, chuck up a 4"-6" length of 3/16" drill rod in the coupler to obtain perfect alignment between the motor and stuffing tube. This reduces drag and noise. Use plenty of a good lube on the cable. An "S" bend is not necessary at all, I stopped using "S" bends at least 15 years ago.

If all the pieces are true and not bent, perhaps the vibration is not excessive. Running the motor on the bench is so unlike what happens in the water that it is almost worthless in diagnosing driveline problems. Set the boat in the water, hold on tight and blip the throttle as before. Still have the vibration?



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[Rumdog]

Thanks so much guys. Yes, it is un-supported at the strut end. The strut is the original, it used to be a nitro hull and it used the brass cone behind the flex, in front of the strut. I'll go ahead and order up the speedmaster and bigger O.D. stuffing tube. The vibration right now is VERY excessive!

[Jeff Wohlt]

Yep...any vibe in that strut nose areas is only going to compound and shake the stuffing tube...eventually leading to possible stuffing tube issues at the hull.


Jay T has you on the right path. New stuffing tube and in to the strut.