p bracket sheared

[boo1966]

Just found out my p bracket has sheared off flush to the hull any ideas what could have caused this . I am pretty certain i havn't picked up a rope or hit anything. Engine setup is a 1 gm yanmar connected directly to the shaft(no space for flexi coupler) through stern gland with a cutless bearing in the stern tube and another bearing in the p bracket checked alignment and shaft for bend (3 thou out over 4ft)last year both ok . The engine does jump about a bit when motoring the mountings are not great and the folding prop opens with a bang but there is no vibration when motoring. The engine is only used to get out of the marina to the start line for racing and has done very few hours this season. Getting it fixed at present (new prop and p bracket) so any ideas what caused it and to stop it happening again would be very helpful.Thanks

 

[Anthony]

Not my expert area, but just as a thought, has it suffered corrosion that has weakend its structurte thru insuffient anodic protection?

Anthony

 

[boo1966]

Thanks Anthony new anode fitted to shaft last year but not electicly bonded to p bracket so possible

 

[bendyone]

The problem with yanmar mounts is that you cannot easily see if they have failed and the bonding between the metal and rubber has parted. If your engine "jumps" around a bit check the mounts.

 

[mikejames]

I have had a similar issue. P bracket not electrically bonded. When I hit it with a hammer while fitting a new cutless bearing , it crumbled. No Zinc in the surface area.

P bracket from Lancing Marine for about £210 inc postage with a cutless bearing already fitted. Not quite the same as the old one and I needed to cut it down because it was about 8 inches too long for my GK24. The job took about 3 days, one day removing the old bracket, hacking away with a Tescos £1.00 chisel and a wooden mallet, filing a point back onto the chisel when needed and hammering it flat when needed.

Then two days of filling, glassing and more glassing inside the hull. I couldnt see clearly all round the bracket so the fibreglassing is a bit messy in places but I put in about 6 layers of tape .... I may well write up the experience.

I have added a bonding wire to the bracket this time , and I now hang a large zinc lump over the side to act as an anode - I can see when it has gone and its bigger and the same price as the shaft anode I used before which didnt protect the P bracket. Of course I also had to bond the shaft across the semi-rigid coupler which has plastic in it. I ended up using Monel mousing wire, because all attempts to do it properly with crimp terminals and wire just vanish at 1500 rpm... .

Also when I hacked the old P bracket out, I found it wasnt really bonded to the hull and water was seeping all around it.

My Yanmar 1GM was OK but I had severe vibration problems caused by the semi-rigid coupler where one of the metal straps had been worn through and broken by the end of the prop shaft. Every time I tried to line up the engine it would vibrate again.
One day I was pulling the engine forward to get at the oil pipes and a bit fell out of the coupler that shouldnt have .. .
£10 at a local steel fabricators for a new strap and some bolts with threads.

P bracket lasted 1983-2007 before bad corrosion set in.
Semirigid coupler lasted 1983-2005 as far as I can tell.

 

[vyv_cox]

A photograph would be helpful.
Two possibilities are dezincification and fatigue, the former probably the more likely. Does the fractured face have a pink appearance? Even if it has suffered since fracture it would still have a pink appearance if the surface was dressed up with a file.
A fatigued face would normally have a two-zone appearance, one part smoother than the other. Probably the fracture face would look brighter than the DZ one. This is not obvious to the untrained eye, hence the request for a photo.

 

[Spyro]

As you say there is a bearing in the stern tube I would think the movement of the engine has caused the shaft to pivot at this point and snap off the p bracket I think it must have been weak or corroded though to snap it off.