Prop Shaft Coupling Question

Ah sorry, yep, see what you mean! Good point!

If I got a Prop Protector, slide-on version, and a 10mm spacer, I'd have 6mm after the P-Bracket before the cutter, and 48mm of shaft left inside my coupler instead of the 56mm I have at the moment. Is 48mm enough?
 
You may have other options.
Shaver cutters require less space than scissor cutters, and in some cases dependant on the shape of the prop hub can require no additional space, 10.00mm could be OK.

They are also not subject to the shock loads of the two blades coming together with something like a fish hook between them which could be the reason for the fixed blade attachment failing at teh P bracket as mentioned above. From our experience of looking at worn blades on fishing boats it is often the fish hooks and steel traces that get picked up which can damage a cutter and not so often the rope. No shaver cutters have been damaged beyond use with a fish hook or steel trace (to date) as far as we are aware.

Drive shaft movement and clearance to allow water to exit from the cutless bearing is a seperate issue. We have seen up to 18.00mm total movement (9.00 fore and 9.00aft)
3.00mm is sufficient to allow water to exit bearing so a minimum of 12.00 is a good place to be.

If you look closely at shaft polishing you will see how much normal movement there is, and with such a small gap you may see evidence of the prop touching the bearing carrier, if not you can be farely happy that the engine mounts will allow less movement.
 
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A Cunning Plan?

What's to stop me simply using a 23mm thick bit of 100mm nylon 6 rod as a spacer?

I can buy a 23mm thick piece of 100mm diameter nylon rod for about £15 including P&P. That, and four new studs, gives me the correct extension for a clamp on Prop Protector.

Is there any problem with using a nylon 6 spacer?
 
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CaptainBob said:
What's to stop me simply using a 23mm thick bit of 100mm nylon 6 rod as a spacer?

Is there any problem with using a nylon 6 spacer?
Click to expand...

Yes, an easy job to make the spacer yourself, if you have the kit to drill it. You might find that the nylon is cut off the length using a donkey saw and not particularly square on the end, make sure that you tell them you need it to be accurate, they may be able to turn it for you. The other problem is the face of the clamp which, in all probability, has a lip machined on it's mating face. This will measure 21/2" * c 1/8", the easiest way around this would be to use fat spacing washers.
If you decide to look at SteveBirch's suggestion try C&O Engineering at Abbots Kerswell - 01626 367782. Last time I had one done it was less than £100 inc machined taper and new nut with nifty locking washer. That split clamp looks very much like the one they supply.
 
[QUOTE

I can buy a 23mm thick piece of 100mm diameter nylon rod for about £15 including P&P. That, and four new studs, gives me the correct extension for a clamp on Prop Protector.
Is there any problem with using a nylon 6 spacer?[/QUOTE]

The various parts of your coupling presumably have spigots and matching recesses to maintain radial alignment. Your piece of nylon bar will need to be machined to match, and also to ensure its 2 faces are accurately parallel.
This, and drilling 4 equally spaced bolt holes is a job that requires some care.
 
CaptainBob said:
What's to stop me simply using a 23mm thick bit of 100mm nylon 6 rod as a spacer?

I can buy a 23mm thick piece of 100mm diameter nylon rod for about £15 including P&P. That, and four new studs, gives me the correct extension for a clamp on Prop Protector.

Is there any problem with using a nylon 6 spacer?
Click to expand...

Nylon swells as it absorbs water. Whether this matters or not is gonna depend (like, on how much it will swell and how bad its strength decays as it does that). Delrin would be a better (and somewhat pricier) plastic to use, but I can't quantify how much better and again, I don't really know whether it matters or not.

SS 316L is the pukka stuff, but I guess you already knew that... If you can find people selling plastic versions then making one yourself would be less of a step in the dark, otherwise I personally would not want to experiment for the sake of £100 or so.

Boo2
 
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