Next question - Alu Treadplate

[Razorbill RIBs]

On the back of the success of my Perspex revival thread, want to ask another question of the RIBnet massive.....

Bilges painted out and engine having had a fresh klick of paint, the new deck (was talked into it by carpenter friend) is going down ready for glass (ala Matts Martini II build)......

However, we will be making two large removeable sections atop the propshaft and Jet unit and over the fuel tanks forward.....

These will be bolted down using some 3m tape (waterproof in compression as used by Halmatic when they built it) into Bighead fixings in the ply (have shelled out for some top notch ply too).....

Had considered SS treadplate, but having seen some in a friends metalwork shop, weight is an issue.....so am leaning towards Aluminium.

Question is.....the widest span (centre) is around 500mm. What thickness of alu treadplate shoudl I go for to avoid bending under load? 3mm def too thin (had an offcut we played with)......anyone know what thickness the decks of say an OceanDynamics RIB are made up of?

Oh, and does anyone know if S/S Big heads /Big strip fixings can be bonded to Alu or will it fail?

Thanks in anticipation....

[captnjack]

Almost any thickness I imagine is going to flex if you stand on it. The flat surface is not going to like a load. I would go with 5mm or so but put backing bars on it, in a square pattern to minimize the flex.

[Pikey Dave]

I can't quite picture the layup, but you don't want your stainless bigheads in contact with ally treadplate, or any ally for that matter, in a saltwater environment. I'd go 3mm stainless treadplate & weld ribs on the back as already mentioned & then have the plates bead blasted & electropolished.

[Razorbill RIBs]

Originally Posted by captnjack

Almost any thickness I imagine is going to flex if you stand on it. The flat surface is not going to like a load. I would go with 5mm or so but put backing bars on it, in a square pattern to minimize the flex.

Thanks captnjack, had thought we might need to put backing bars on.....top of my head had been to use thin ss bar, square pattern makes better sense

Originally Posted by Pikey Dave

I can't quite picture the layup, but you don't want your stainless bigheads in contact with ally treadplate, or any ally for that matter, in a saltwater environment. I'd go 3mm stainless treadplate & weld ribs on the back as already mentioned & then have the plates bead blasted & electropolished.

Dave, thanks.....3mm SS had been first choice, but it was the weight which was causing me concern, but in the grand scheme of things I guess..... Also easier to weld SS studs directly rather than bonding on bigheads (Having looked through the Bighead echspec they have an adhesive which works with alu and my thought had been that the adhesive would provide the 'barrier' between the SS and Alu).

In my ignorance, what is the benefit to electropolishing (just aesthetic?)

Will let you know how we get on......

[Pikey Dave]

Originally Posted by Razorbill RIBs

In my ignorance, what is the benefit to electropolishing (just aesthetic?)

Will let you know how we get on......

Electropolishing is the reverse of electroplating, when applied to stainless, it removes the top layer of iron & leaves behind the chrome & nickel. This is very hard & extremely durable. We use it a lot on sewage handling kit. It's not as expensive as you might think & leaves a really nice finish. I use these

[jyasaki]

Polaris Inflatables in Canada uses 3/16" (4.8mm) 5200 series aluminum for hulls and deck. It is braced up pretty well, I think though.

With a 20" span you could probably get by with just one or two ribs of the same material, along the lines of 1/4" high. Maybe 2 each direction?

If you go with Aluminum, consider using a cold anodizing finish (Alodine or similar) to minimize corrosion problems.

jky

[Leapy]

Originally Posted by Pikey Dave

Electropolishing is the reverse of electroplating, when applied to stainless, it removes the top layer of iron & leaves behind the chrome & nickel...We use it a lot on sewage handling kit...& leaves a really nice finish

Refreshing approach...to be honest, you just can't beat a really nice finish on your sewage handling kit

[Pikey Dave]

Originally Posted by Leapy

Refreshing approach...to be honest, you just can't beat a really nice finish on your sewage handling kit

Exactly 1up 1down & 1 to polish

[captnjack]

Originally Posted by jyasaki

Polaris Inflatables in Canada uses 3/16" (4.8mm) 5200 series aluminum for hulls and deck. It is braced up pretty well, I think though.

My hull is made of this and there's very minimal flex, but its also in a "cup" shape (they bend it to form the keel) which is naturally flex resistant. Its 5000 series ali.

Not sure if I would bother with fancy anodizing or worrying about galvanic corrosion either. I have some SS fitting into various places in my deck and yes the ali corrodes a bit. But not to the point of needing to do much about it. Just greasing your fitting will be adequate in my opinion.

[jyasaki]

I actually should have said Polaris uses 3/16" for *some* hulls. 1/4" for others.

I recommended Alodine as it's relatively cheap to do, and will give the treadplate (likely not 5000 series, or any particularly corrosion resistant aluminum) some surface protection.

jky

[b-pacific]

I have two deck hatches on the PAC- one 500x300 and one 600x500 both made in 5 mm alloy chequer plate. Neither is strengthened underneath and I stand on the larger at the back as a steering position. With my 13.5 stones bouncing on it I can't recall any flexing.
It is heavy stuff!!!