Cracked mast step - replace cast aluminium with plate?

Hi all,

Mast step crack of unknown age (to the point of having old looking metal putty in the gap) .

Is there any reason not to have a replacement made from plate aluminium with a welded cuff and loops for anchor points?

Any insight how the the #$%@ this happened...? 3 cracks can be seen: aft, port aft and stb aft. From vague history, I suspect a dismasting. I also had 2 cracks on the mast (fwd centre, aft port quarter) fixed with welded plate before I noticed the one INSIDE the mast track... great

1980 Beneteau First 35
Thanks

 

My first thought is metal fatigue. A welded part would be fine if done properly.

 

It looks like the bedding under the step has broken down and the mast's down pressure on the plate has pushed the centre down, flexing and cracking it. A dis-masting could have strained it to breaking point too, if that happened. Getting that intricate shape fabricated will cost a small fortune. I'd remove it, get a professional welder to repair it, and grind the underside flat again. Maybe get a machine shop to mill the mast base footing groove back to shape after the welding so the mast sits flat, not up on lumpy welds, unless you are a good fettler with a die grinder and burr bit. Then clean off all the old bedding compound from the glass surface, and re-bed it with something recommended by an expert, with new bolts / screws. It should last another 20 years, unless it is a poor casting to begin with. If it is riddled with deep corrosion and porosity out of site underneath, then think about replacing it.

 

If in a region where freezing could happen, I'd say frost split. The crack seems to continue along the SB (?) side of the step as well. The shackle pockets have drain holes that must be kept open. Difficult/impossible to clean the horizontal parts of the crack for welding. It might be possible to mill away the underside until you reach "fresh" material, then add a welded plate to restore thickness.

 

Well the crack goes all the way through the aft anchor points on both sides too, so the plate is likely in 3 separate pieces. Possibly easier to clean up. What luck. Very happy to hear welding it back together may be an option. Worst case, I imagine an aluminium plate base with a simple enough sleeve piece welded there could work.

Thanks for you input

 

The part looks like a casting.
If you can live with it turning out about 2-3% smaller than the original, the original could be used as the casting pattern with some follow-on machining to the part to fit the mast and mounting holes and shackles. Beyond that, an enlarged pattern for casting or a fabricated or machined replacement makes sense too.

 

Fabricated or milled from extrusions. Should have been done way from the factory. Die cast aluminium is not that great, any of it. Probably force from the mast caused the failure. Unlikely to be fatigue as that stuff has near zero flex.

 

Those cracks could well have been there in much smaller form from the time it was cast.Was that recess used for vang attachment?I wouldn't set too much store on the welding route as the crack is very likely full of oxidation and algae,which isn't to say that it couldn't be done,but it would need thorough preparation first as well as pre-heating and careful cooling.Then you would face the issue of coating as it looks to my untrained eye like either anodising or chromating has been applied.Which is the same challenge that a replacement would face.

I certainly wouldn't rule out the idea of frost damage if the boat lives in an area prone to freezing and that drain channel would very likely be clogged with detritus that trickled down the mast.The easiest solution would be to either seek out a new part or to look for a sister ship that has suffered major damage and is only useful as a parts donor,but there may not be too many of those.To re-manufacture an identical part might be costly as it isn't the simplest of pieces and coring for those recesses would be time consuming as well as perpetuating the problems that the design has.A simpler casting to contain the mast foot and a fabricated base plate with lugs for shackles might be a viable alternative approach.