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The time has come to retire the old steel beast, and I've found a fabricator who is happy to make a new one out of off cuts he has lying around.
He's quoted $275, using 6mm alloy, which seems a great price, but maybe a bit light on strength wise?
He also has 10mm off cuts too.
I believe there's a few other alloy mast bases in existence, wondering what thickness plate was used for those?
Michael.

Mike,
I think 6mm is a little light, but im only guessing. I have seen a few alloy girders & I know Phillip has one
cheers

Ask what grade aluminium it is as there's a marine grade.

Me too Mike!
I just wire brushed & angle grinded(ground) as much rust off mine as possible in situ. Hit it with an acid cleaner & RECOATED WITH FERROPRO but there's a few holes!
I'll be watching your reposts.
Larry

If you have a steel girder that needs a clean up and rust proofing, buy a tin of POR 15+. This is perhaps the best rust proofing product I've seen (no affiliation) there is a bit of prep involved and you will need to put a UV stable top coat on it, because it's black and the POR isn't UV stable, so it fades to a milky grey.

I've used it on my motorcycles, kombi and some posts I've had in the garden for 5 years and it's still going strong with no return of any rust yet.

As soon as I get aroundtuit I'll be doing my girder as well.

Seaka's girder is aluminium.

It measures at 7 mm. It appears to have been made then anodized.

Must be over 15 years old no with no signs of any deterioration.

There are photos in previous posts or the Gallery.

Sent from the Shaggers get-together at Cape Gloucester, Queensland with 120 plus other yachts.

I've decided to beef the sides up to 10mm. I'd guess 6mm would have done the job just fine, but for a non engineer like myself, peace of mind probably usually equates to overkill.

I'd intended to get it all in 8mm, but the fabricator doesn't usually work with it, so I'd lose my substantial 'off cuts' cost benefit.

I'm also getting the box made a bit larger to allow for plastic shims.

I'll check weather it's marine grade alloy next time I speak to the fabricator.

Michael.

Mike,
I wouldn't increase the size of the girder box as the mast shoe has to fit without movement.

One thing you have to remember is that the mast will and does move all the time and any plastic packing will soon wear away.

Stick to the present sizes to avoid having to redo it in the future.

From Cape Gloucester Queensland

I think what Phill is saying is that the internal dimensions are critical. You can and should increase the plate size if you are replacing steel with aluminium. Very important is that it it beds on the fibreglass deck with no gaps, so that the load is trasferred evenly.

Don't forget to allow for drain holes to let out water & SEDIMENT RUBBISH BUILDUP AT THE MAST BASE.