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[DJW]

Hi All

An update as it's been a while...

Not had the 1/10 out as much as I'd liked this year, and missed a few Open Days for various reasons.

She's had some outing's to Bushy Park:



And did make it up to the excellent Wicksteed MBM event back in May:



Have had a bit of a problem with the port prop shaft, a nasty vibration at anything over half power.  Investigating it, I can see the prop blades are now marking the hull paint...  Not good.  I can see the Teflon washer between the prop and the P bracket has worn and thinned, but I thought the thrust was being transferred to the motor mount by a fixed collar on the shaft, well I've obviously screwed up it seems.  This has brought the blades closer to the hull.  Still find it odd that its after half power that the blades strike the hull...  Can the bronze blades really be flexing...  Or maybe the Teflon washer just compresses more under load, I think that's more likely.



It's one thing diagnosing the problem, another matter fixing it...

I made a few mistakes putting the drive lines together, (hindsight is a wonderful thing...) I used red threadlock on the various 3mm grub screws that hold props and collars onto the prop shafts.  Big mistake, that's the permanent one, should have used blue.  Had a lot of trouble getting the shafts out as some of the collars were very tricky to reach, and very tricky to get the grub screws out...  If you google how to remove red threadlock, best suggestion is heat to 350 degrees, not ideal.

But I've now got the boat on the bench, shafts out, had to drill out the grub screw on one of the props.



Plan is to rebuild with slightly smaller props, and use blue threadlock...

Very best regards to all.
David.

[Capt Podge]

Hi there David, I've been 'off-air' for a number of months as well, slowly getting caught up with things.
That's some serious problem you've had, but at least you have a plan of action to rectify / repair it.


Aye,
Ray.

[derekwarner]

Yes David........obviously the Teflon has extruded/or and thinned under rotational load......running the motors out of the water could also created a heat greater than the teflon is suitable  for?


The solution will be a stainless washer running against the bronze/brass...and water will be the lubricant......the bronze blades will not have been flexing


Again, in hindsight, any running out of the water,     would be advisable for a few drops of oil at the washer/bronze interface

----------------------

A well-known Asian manufacturer of steam products was using Teflon flat-faced washers in the banjo fittings of his piston water pumps


The Teflon extruded and wept and I could not attain @ 3 Bar when pumping up a cold boiler .......just a continual bubbles or drops of water from under the pressure side of the Teflon washers, I changed out the Teflon washers for Red fiber washers......problem solved

The revised design by the Manufacturer is now captive o-ring seals........
I have two of these pumps, however my discussions ended abruptly when I requested some sort of retro-fit, as I suggested the original design was defective
 
---------------------


So obviously Teflon has it's place, but not in your application....nor sealing in water pumps


Derek

[Circlip]

Any chance the hull is flexing around the prop struts allowing 'whip' when increasing revs due to prop pitch?


 Regards Ian.

[DJW]

Hi All


Thanks for the comments.


@Ian. I don't think the P brackets or their mounts are flexing, I think if they were it would have been a problem from day one.  And looking at the surrounding areas there's no paint crazing or stress marks that I can see.  I've checked the shafts and they seem to be running true, your thought did make me wonder if I'd bent a shaft.


@Derek. I'll be using stainless washers for sure going forward.  I think I was surprised about the Teflon for two reasons.  1. It shouldn't have been taking any force from the prop...  2. I don't remember them wearing quite so badly so quickly...


@Ray.  Good to hear from you, I think everyone's build take a slow down over the summer...  Never mind, a nice dark winter to look forward to now..!!


I'll report back once the fixes are in place and tested...
Very best regards to all.
David.

[ChrisF]

Hi David

That's a shame about the paintwork, hope you can patch it up Ok. Your props must be running very close to the hull for that very small amount of movement to cause contact? I note you're going to use smaller props now.

Chris

[DJW]

Hi Chris


Yes...  With hindsight the prop blades were too close to the hull. When I built the boat I wanted a nice shallow angle for the shafts, but maybe went a bit too far, compounded by initially underestimating the prop size that the motors could spin. So when I put the slightly larger props on, the performance went up, but the blade clearance went down. But to be honest the smaller props will be fine, better clearance and still a scale speed. Putting the boat back together now and looking forward to getting her back on the water..!
Very best regards
David.