Alloy mast step (Sparlight): cracked

[Krusty]

Has anyone in the forum any expertise or experience relevant to the alloy mast steps used with Sparlight masts back in the 70's?. Mine is deck-stepped, with a thick foot casting engaging a female casting bolted through the deck to a beam over the main bulkhead. The two castings are locked together by a large bolt on the aft side. The female casting has a hairline crack round the forward arc where the upstand meets the flat deck-plate, and it is steadily extending.
I have to consider repair but I don't know the alloy, and whether it would be amenable to MIG or TIG welding.
The alternative seems to be to have a substitute fabricated in stainless steel, with an insulating separator capable of withstanding the crushing forces.
Any technical advice would be much appreciated.

 

[Signed Out]

I heard that Sparlight were taken over by someone, so I guess the "new" owners may be able to sort some troubles. I hope so, I want a mast step for mine also. I'll try and find out who took them over and get back in a dayor few.
Jem.

 

[bluedragon]

I have the same Sparlight step on mine, but thankfully it's OK! A thought...here in S.Wales there are still some small (often one-man and his dog) die-casters around who will do one-off replicas of boating bits, at least in bronze. You might find somebody similar in your area who could make a new one for you using a compatible alloy and the old one as a pattern?

 

[FullCircle]

First step is to prevent the crack propagating further. Drill a 3mm hole through the casting where the crack ends now. This should stop the crack where it is. You may fill this with epoxy if you wish afterwards.

If the casting is cracking, rather than a break, this may point to aweldable grade. The way to check this is a bit laborious, by matching the hardness value (done at a local machine shop) to the range of material specs. Usually, a local trade supplier like Alcoa will help you identify it. If not, the Aluminium Federation are helpful.

It is probably safe to weld, however, welding will decrease the UTS (Ultimate Tensile Strength) and the increase the ductility. Net result in average terms is if it starts out as a 20 tonne alloy, after welding it would be 6-8 tonne.

As a mast base, that may not be a bad thing, but it might increase the wear characteristics (i.e it is softer)

I dont know the shape here, or where the crack is, but you could drill and tap either side of the crack and bolt a plate over it?

 

[Krusty]

Re: Alloy mast step ; Full Circle

For info: the shape is like shoe, open at the heel and on top; the mast heel-casting stands in it and is through-bolted just forward of its 'achilles tendon'. The crack started at the toe, just above the sole, and has advanced slowly round the curve at the 'welt'. The sides are not yet affected. Stop-holes were drilled today; quite easily, so it is not one of the hard alloys, and I hope it will be weldable next winter. Thanks for your response.

 

[ShipsWoofy]

Re: Alloy mast step ; Full Circle

Like this?

 

[Krusty]

Re: Alloy mast step ; DogWatch

Exactly. I reason that the cause of cracking in mine may well be that most of the down-thrust of the mast has been on the through-bolt, and therefore the aft-end of the casting, tending to lever the forward end upwards and tearing it from the 'sole'. Perhaps the original installation had some kind if pressure-pad separating the castings, raising the load off the through-bolt, and distributing the load over the whole of the sole.
Has anyone any knowledge of this?

 

[ShipsWoofy]

Re: Alloy mast step ; DogWatch

I have no weight whatsoever on the through bolt. Prior to stepping I remove the bolt. It slips out without any trouble at all, in fact I wonder even under stress whether or not it is needed.

I always presumed it was there as, as we have used in the past, a hinge to drop the mast, not a funny experience!

I am not sure which part has broken on yours, the foot or shoe shall we say?

If you really struggle, I am sure a foundry should be able to backward cast from the piece you have. I watched a program recently where a van crashed into a house, right through the front window. The insurance came around and had to agree to put it back as it was. Around the bay window were originally cast iron decorated braces, a little like Victorian bandstand columns.

In the end they made a plug from the broken pieces and then cast new columns, I think, think they were in alloy. Not as expensive as first thought was the message conveyed by the narrator. I did some casting in college, it really isn't that difficult.

When you look at the mast bits they were never that clean, they may even have been done in sand type casts and cleaned off later. One thing though, from seeing countless aircraft alloy welds on cracked cases fail very quickly and knowing the material on these casts, I think, personally I would dismiss the welding option.

If you do actually find a supplier would you come back on here with the name for my own future reference (touching wood). Also...

When I was in Padstow a couple of years ago a boat came and rafted on me, a wooden motor-sailor, converted MFV I think. Had identical mast and fittings, the skipper was saying how inexpensive they were, as he had 'just' replaced the main mast. Nope, sorry can't remember the name, but I think he had sailed down from Cardiff or Swansea.

But it does mean, a supplier somewhere has these masts and fittings available.

 

[ShipsWoofy]

Also

In YM last year or so there was a letter from a skipper who was unhappy that his [possibly]McWester[/possibly] mast was not sitting properly in the foot and he was not getting any rake aft at all.

The answer came back that originally the foot had a piece of leather, maybe wood in a wedge shape under the mast to support the weight evenly. I wonder if you have something missing from your rig which has caused the damage you describe.

This is only thinking out loud.

On mine, at the apex of the curve there is a strengthening bar, like a horseshoe with a tail on the top, I wonder if it was added because some had been found to fail as yours has. I was planning a drill a hole in it to attach a block, but reading your post I think I will leave well alone!

 

[William_H]

Re: Also

Many boats around here Perth had castings made in a similar many style, the base had the up lugs and the mast part had the aft facing lugs. The lugs often fractured and are generally successfully weld repaired. The lugs tended to snap off when the mast was being lowered on the water and was allowed to swing sideways when partly down.

There should be no stress on the through bolt (axle) when the mast is vertical. In other words you shoulld be able to remove the bolt. If you can't then try releasing the forstays or backstay to allow the mast to tilt to relieve pressure. (probably forward)
(The bolt may be corroded in and actually splitting the Al with corrosion material.)
If the mast is not perpendicular to the base then the axle can be under load and this may be the cause of cracking. The base is often fitted on top of a wedge of plastic or material (ie btewen the cabin top and the Al base) to ensure that the two castings of the fitting sit with a mast down load near the centre line of the mast.
If the mast is sitting correctly then there should be no load on the lugs and bolt and so any cracking of the lug should be of no real concern the bolt and lug only being there to ensure the base does not slide forward aft or sideways under load. This is however highly unlikely due to the huge downward pressure holding the base in place. You could benefit (stop the cracking) by fitting a much smaller bolt through the lugs. This will ensure the 2 base parts take the compression not the bolt.

So if it is as I am imagining then your best approach is to hold off repairs until winter and if you do tilt the mast backwards for removal be very carefull of total failure of the lug and subsequent possible lift of the base and slide forward. (safest to get a crane)

You may be interested to know the base of my mast 27ft on 21ft boat has 2 lugs about 1cm apart of material about 1/8 inch thick welded to the aft part of the mast. (Softening of the mast with welding is not a great concern)
The mast bottom has a slot cut fore and aft about 1cm wide and 3cm deep. ie going vertical. The base attached to the cabin top has a SS flat plate with a web running for and aft with a single raised lug at the aft end.
The holes in the mast lug and base web are over sized so that it can move around to find it's own location with no load on the pin when sailing. The bolt is 1/4 inch diameter 6mm to indicate my point that the lugs don't take a load.
The advantage of this arrangement is that if the mast swings sideways when lowered the closeness of the lugs means a little bending will accomadate a large swing.

Finally yes you can build a new base out of SS (Stainless Steel) however it does not have to be so strong as it is only there to locate the base on the cabin top and must be able to accomadate various mast angles particularly fore and aft rake. good luck olewill (sorry am I harping on a themee here.)

 

[FullCircle]

If you do go to a foundry to have the part remade, remember that there will be shrinkage in the process of about 2%, so you will need to add tape to the important surface areas to get the wall thicknesses needed. Once taped, ensure you still have a casting drafting angle all over the part to make sure it will come out of the sand!, and give a light brushed coat of grp resin mix just to seal it. Should be easy enough to get off afterwards.
Prototype sand casting is very cheap, but be careful with the material, as there are many alloys out there, and for non structural casting of things like ornamental gate fittings, they use a special grade of aluminium - [--word removed--], or it's cousin CR4P. The material will have a high recycled content, and thus be prone to contamination. OK if your not looking for any structural qualities. Just ask, I am sure they will have virgin material in the LM series. Just dont have anything with a high magnesium content, as it will be eaten away with corrosion very quickly.

 

[Krusty]

Solutions to my problem are there for the taking: My thanks to all contributors. See your PM's. Good to have such a forum.