Sealing the stuffing tube with o-ring from the outside for wire drive sistems

I've been running Speedmaster Stinger with 3/16 propeller shaft and .078 wire drive.
In the last months I've tried to seal the stuffing tube from the inside with a piece of silicone tubing with medium result. The silicone tube seals very good for the first couple of discharges and then begin to leak again due to the wear.
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I read here on this forum on one thread to use a grommet or cut a piece of silicon line and put it between the drive dog and the strut/stinger.
So instead of a grommet I took an o-ring made of viton with dimensions internal diameter 4,6mm and cord diameter 2mm (I have it at works).
For the first 3 discharges and for a time of about 25 minutes I had a perfect dry boat inside.
Now I have both seals inside and outside.
I'll keep on testing this solution and will report here the results.
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Seven discharges and not a drop of water from the stuffing tube so far.

I did the same thing but on the outside only. I used a 1/8" I.D. O-ring on a 3/16 shaft. Worked great. No water inside. Bench tested with RC Wattmeter and there was no difference in current drawn.

how do you set the drive dog gap? does the drive dog press the o-ring against the strut?

When I install the wire drive there is no gap between the drive dog, o-r and stinger. I simply slide the wire drive inside the stuffing tube until the o-r touches the stinger and then tighten the coupler set screws. While the boat is running I guess there is a little pressure from the prop that seals the water out

sounds like a very good solution . if you push the prop hard against the front of the boat (with the coupler tightened ) can you feel drag against strut?

I use rubber o-ring between the strut and the drive dog. The sequence is strut-oring-teflon washer-drive dog. When I use this sequence, the o-ring sheared/melt after a few run (500m total distance).

The destruction of the o- ring demonstrates you are getting a lot of drag, robbing power to the prop. The best location to stop water intrusion into the hull is on the inside. Using a short length of silicone tubing on the inside of the stuffing tube to seal the flex shaft works very well in my boats, only a few drops get into my boats during a race heat. The is no good reason to get more into any FE boat. Water and electronics do not mix and reliability is poor with a wet boat. Keeping your boat dry is the best way to insure reliability. Most of my club members have learned this and their dry boats are more reliable than most. Do not accept a wet boat!


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Thanks Fluid for your explanation and comments. By the way, can I use teflon tube with ID 5mm? Currently, I use 3/16" (4.76mm) flex shaft. Worried if use 4mm ID teflon tube, it will chuck the flex shaft and cause more friction.

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Originally Posted by Fluid

The destruction of the o- ring demonstrates you are getting a lot of drag, robbing power to the prop. The best location to stop water intrusion into the hull is on the inside. Using a short length of silicone tubing on the inside of the stuffing tube to seal the flex shaft works very well in my boats, only a few drops get into my boats during a race heat. The is no good reason to get more into any FE boat. Water and electronics do not mix and reliability is poor with a wet boat. Keeping your boat dry is the best way to insure reliability. Most of my club members have learned this and their dry boats are more reliable than most. Do not accept a wet boat!


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Would mind sharing a picture?

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Originally Posted by danzigneg

Currently, I use 3/16" (4.76mm) flex shaft.

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This o-ring system works for me with wire drive and I don't know if it could be used with flex shaft. From what I read flex shaft shrinks under load so you need to let some gap between drive dog and strut.

Unless the "o-ring" is teflon it will cause a lot of friction, adding heat and reducing speed. A teflon washer is best for a wire drive, I used one for years when I ran that type of system. Sealing the wire drive is easy with the right size of silicon tubing inside the hull - see photo below. Same idea works for flex cable, just different tubing sizes. I haven't used teflon liners for years with flex cable or wire, for 3/16" cable I use 1/4" brass tubing and automotive gear oil with an EP additive. I have never replaced a brass stuffing tube due to wear using this system; that includes boats which have been raced for over four years. Friction is less without the teflon as long as a quality lube is used, and reliability is improved too.


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