Thickness of plywood for flooring

[Chris Green]

Ok, it's the engine hatch covers again. :-)

How can I decide how thick they need to be? They need to be strong
enough to walk on but, in addition (and this will probably be the
important thing) they need to be stiff enough so they don't deform too
much when you walk on them.

The 'hole' to cover is 1540mm long by 1335mm wide. There's a
lengthwise support 595mm from one side and 740mm from the other side.

The 'design' at the moment consists of four separate plywood panels
across the 1335mm width. The support is not quite in the middle, so
each panel will make two spans of 595mm and 740mm. Since the panels
have to be lifted independently there will be no 'mutual support' as
there would be if they were T&G panels. Each panel will be 385mm
wide. The total size of the hole is 1335mm x 1540mm so there will be
four panels.

So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.

I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.

Thanks everyone for the thoughts so far, I think I am getting there
slowly! :-)

[No mail]

Post by Chris Green
Ok, it's the engine hatch covers again. :-)
How can I decide how thick they need to be? They need to be strong
enough to walk on but, in addition (and this will probably be the
important thing) they need to be stiff enough so they don't deform too
much when you walk on them.
The 'hole' to cover is 1540mm long by 1335mm wide. There's a
lengthwise support 595mm from one side and 740mm from the other side.
The 'design' at the moment consists of four separate plywood panels
across the 1335mm width. The support is not quite in the middle, so
each panel will make two spans of 595mm and 740mm. Since the panels
have to be lifted independently there will be no 'mutual support' as
there would be if they were T&G panels. Each panel will be 385mm
wide. The total size of the hole is 1335mm x 1540mm so there will be
four panels.
So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.
I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.
Thanks everyone for the thoughts so far, I think I am getting there
slowly! :-)

Try searching: calculate plywood deflection
Also, might be worth contacting these people:
https://www.panelsystems.co.uk/product/lightweight-sandwich-panels
https://www.coretexgroup.co.uk/6.html

[Tricky Dicky]

Post by Chris Green
Ok, it's the engine hatch covers again. :-)
How can I decide how thick they need to be? They need to be strong
enough to walk on but, in addition (and this will probably be the
important thing) they need to be stiff enough so they don't deform too
much when you walk on them.
The 'hole' to cover is 1540mm long by 1335mm wide. There's a
lengthwise support 595mm from one side and 740mm from the other side.
The 'design' at the moment consists of four separate plywood panels
across the 1335mm width. The support is not quite in the middle, so
each panel will make two spans of 595mm and 740mm. Since the panels
have to be lifted independently there will be no 'mutual support' as
there would be if they were T&G panels. Each panel will be 385mm
wide. The total size of the hole is 1335mm x 1540mm so there will be
four panels.
So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.
I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.
Thanks everyone for the thoughts so far, I think I am getting there
slowly! :-)

The thicker you go with the plywood the heavier it becomes and start to get
awkward to manipulate within the confines of a boat. Have you considered
removable supports that span either the width or length of the hatchway?
This would enable you to use thinner ply yet removing the supporting spars
would give you unrestricted access to the engine compartment.

Richard

[Chris Green]

Post by Tricky Dicky

Post by Chris Green
Ok, it's the engine hatch covers again. :-)
How can I decide how thick they need to be? They need to be strong
enough to walk on but, in addition (and this will probably be the
important thing) they need to be stiff enough so they don't deform too
much when you walk on them.
The 'hole' to cover is 1540mm long by 1335mm wide. There's a
lengthwise support 595mm from one side and 740mm from the other side.
The 'design' at the moment consists of four separate plywood panels
across the 1335mm width. The support is not quite in the middle, so
each panel will make two spans of 595mm and 740mm. Since the panels
have to be lifted independently there will be no 'mutual support' as
there would be if they were T&G panels. Each panel will be 385mm
wide. The total size of the hole is 1335mm x 1540mm so there will be
four panels.
So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.
I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.
Thanks everyone for the thoughts so far, I think I am getting there
slowly! :-)

The thicker you go with the plywood the heavier it becomes and start to get
awkward to manipulate within the confines of a boat. Have you considered
removable supports that span either the width or length of the hatchway?
This would enable you to use thinner ply yet removing the supporting spars
would give you unrestricted access to the engine compartment.

As noted above there is already one support lengthwise. I guess it
would be fairly easy to add some more, some tabs fixed to the existing
surround and put some lengths of U angle on them so easy to lift out.

In fact a total redesign removing the existing (fixed) lengthwise
piece of angle and replacing it with two or three removable ones might
well be the way to go.

However the weight of the hatch panels does make it more soundproof so
I don't want to make them too thin.

[Andy Burns]

Post by Chris Green
will a 740mm long by 385mm wide panel be strong enough

Assuming you mean 3/4" ply, then I'd would say so, it's slightly better
than 400mm centres, I'm quite a fat bastard and I *just* *about* sense
some deflection on my garage roof, so if you want to feel no deflection
at all maybe 1" ply?

But I'd struggle to justify these prices

<https://www.diy.com/timber-joinery/sheet-wood/plywood.cat?Thickness+%28mm%29=25>

[Chris Green]

Post by Andy Burns

Post by Chris Green
will a 740mm long by 385mm wide panel be strong enough

Assuming you mean 3/4" ply, then I'd would say so, it's slightly better
than 400mm centres, I'm quite a fat bastard and I *just* *about* sense
some deflection on my garage roof, so if you want to feel no deflection
at all maybe 1" ply?
But I'd struggle to justify these prices
<https://www.diy.com/timber-joinery/sheet-wood/plywood.cat?Thickness+%28mm%29=25>

Quite! Plywood prices do seem to be all over the place with some
sellers charging ridiculous amounts. Fortunately we have a local
sawmill who sell ply at sensible prices. An 8' x 4' 18mm exterior
hardwood ply sheet from them is £30.72 including VAT.

It turns out that the existing panels are thicker than I thought, I've
found a measurement I made a while ago that says that they are 29mm or
so thick. Thus I can make the panels of 18mm + 9mm and simply cut
holes in the 9mm to provide the recesses for handles.

[Andrew]

Post by Chris Green

Post by Andy Burns

Post by Chris Green
will a 740mm long by 385mm wide panel be strong enough

Assuming you mean 3/4" ply, then I'd would say so, it's slightly better
than 400mm centres, I'm quite a fat bastard and I *just* *about* sense
some deflection on my garage roof, so if you want to feel no deflection
at all maybe 1" ply?
But I'd struggle to justify these prices
<https://www.diy.com/timber-joinery/sheet-wood/plywood.cat?Thickness+%28mm%29=25>

Quite! Plywood prices do seem to be all over the place with some
sellers charging ridiculous amounts. Fortunately we have a local
sawmill who sell ply at sensible prices. An 8' x 4' 18mm exterior
hardwood ply sheet from them is £30.72 including VAT.

Beware, there is 'external' ply which won't last long and good
quality stuff.

Normal house flooring is (or was) 18mm chipboard on joists at 450mm
centres, or 22mm on joists at 600mm centres, so your dimensions
should allow 18mm, but a better way might be to just get a sheet of
12mm external ply and plenty of 'blue' glue and make your own 24mm
thick panels.

Post by Chris Green
It turns out that the existing panels are thicker than I thought, I've
found a measurement I made a while ago that says that they are 29mm or
so thick. Thus I can make the panels of 18mm + 9mm and simply cut
holes in the 9mm to provide the recesses for handles.

[Timatmarford]

Post by Andrew

Post by Andy Burns

Post by Chris Green
will a 740mm long by 385mm wide panel be strong enough

Assuming you mean 3/4" ply, then I'd would say so, it's slightly better
than 400mm centres, I'm quite a fat bastard and I *just* *about* sense
some deflection on my garage roof, so if you want to feel no deflection
at all maybe 1" ply?
But I'd struggle to justify these prices
<https://www.diy.com/timber-joinery/sheet-wood/plywood.cat?Thickness+
%28mm%29=25>

Quite!  Plywood prices do seem to be all over the place with some
sellers charging ridiculous amounts.  Fortunately we have a local
sawmill who sell ply at sensible prices.  An 8' x 4' 18mm exterior
hardwood ply sheet from them is £30.72 including VAT.

Beware, there is 'external' ply which won't last long and good
quality stuff.

Nobody has yet mentioned Marine ply which I believe is made without
voids and uses waterproof resin. Cost will escalate!

Post by Andrew
Normal house flooring is (or was) 18mm chipboard on joists at 450mm
centres, or 22mm on joists at 600mm centres, so your dimensions
should allow 18mm, but a better way might be to just get a sheet of
12mm external ply and plenty of 'blue' glue and make your own 24mm
thick panels.

It turns out that the existing panels are thicker than I thought, I've
found a measurement I made a while ago that says that they are 29mm or
so thick.  Thus I can make the panels of 18mm + 9mm and simply cut
holes in the 9mm to provide the recesses for handles.

[Chris Green]

Post by Timatmarford

Post by Andrew

Post by Andy Burns

Post by Chris Green
will a 740mm long by 385mm wide panel be strong enough

Assuming you mean 3/4" ply, then I'd would say so, it's slightly better
than 400mm centres, I'm quite a fat bastard and I *just* *about* sense
some deflection on my garage roof, so if you want to feel no deflection
at all maybe 1" ply?
But I'd struggle to justify these prices
<https://www.diy.com/timber-joinery/sheet-wood/plywood.cat?Thickness+
%28mm%29=25>

Quite!  Plywood prices do seem to be all over the place with some
sellers charging ridiculous amounts.  Fortunately we have a local
sawmill who sell ply at sensible prices.  An 8' x 4' 18mm exterior
hardwood ply sheet from them is £30.72 including VAT.

Beware, there is 'external' ply which won't last long and good
quality stuff.

Nobody has yet mentioned Marine ply which I believe is made without
voids and uses waterproof resin. Cost will escalate!

But Marine Ply isn't necessarily **stronger**, it's just guaranteed
not to have voids and to have waterproof glue, etc.

If I wanted guaranteed strength I'd surely need to go for Structural
Ply.

I have used the 'external hardwood ply' from my inexpensive supplier
and it seems fine so far. None of what I'm making is going to be
outdoors, nor would failure be catastrophic in any major way.

[Fredxx]

Post by Timatmarford

Post by Andrew

Post by Andy Burns

Post by Chris Green
will a 740mm long by 385mm wide panel be strong enough

Assuming you mean 3/4" ply, then I'd would say so, it's slightly better
than 400mm centres, I'm quite a fat bastard and I *just* *about* sense
some deflection on my garage roof, so if you want to feel no deflection
at all maybe 1" ply?
But I'd struggle to justify these prices
<https://www.diy.com/timber-joinery/sheet-wood/plywood.cat?
Thickness+ %28mm%29=25>

Quite!  Plywood prices do seem to be all over the place with some
sellers charging ridiculous amounts.  Fortunately we have a local
sawmill who sell ply at sensible prices.  An 8' x 4' 18mm exterior
hardwood ply sheet from them is £30.72 including VAT.

Beware, there is 'external' ply which won't last long and good
quality stuff.

Nobody has yet mentioned Marine ply which I believe is made without
voids and uses waterproof resin. Cost will escalate!

You have to be careful. Some marine ply can deal with moisture but not
necessarily waterproof. You really need ply that is quoted as WBP, some
marine ply is.

Marine ply is void free whereas normal WBP can have inner layers that
are not void free.

Personally I would use Buffalo board. Marine ply looks filthy after a
short with any foot traffic unless painted. Even then the paint would
likely lift or get worn in short time.

[Marland]

Post by Chris Green
Ok, it's the engine hatch covers again. :-)
So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.
I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.

More expensive but for that job I would use phenolic ply sometimes known as
buffalo board.
Often used as flooring in trailers and horse boxes. Has high resistance to
moisture brought in on footwear , and many varieties have a non slip
pattern already formed on the surface.

GH

[Fredxx]

Post by Marland

Post by Chris Green
Ok, it's the engine hatch covers again. :-)
So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.
I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.

More expensive but for that job I would use phenolic ply sometimes known as
buffalo board.
Often used as flooring in trailers and horse boxes. Has high resistance to
moisture brought in on footwear , and many varieties have a non slip
pattern already formed on the surface.

I have used this in an outside situation and I recommend it's use. It
also provides a convenient anti-slip surface and is of course
waterproof. It's not cheap though/

I also feel the spans the OP requires can be accomplished with 19mm /
3/4" board without too much deflection. I'm sure my spans are the best
part of 700mm and their narrowest point and happy with the result.

[Chris Green]

Post by Fredxx

Post by Marland

Post by Chris Green
Ok, it's the engine hatch covers again. :-)
So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.
I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.

More expensive but for that job I would use phenolic ply sometimes known as
buffalo board.
Often used as flooring in trailers and horse boxes. Has high resistance to
moisture brought in on footwear , and many varieties have a non slip
pattern already formed on the surface.

I have used this in an outside situation and I recommend it's use. It
also provides a convenient anti-slip surface and is of course
waterproof. It's not cheap though/
I also feel the spans the OP requires can be accomplished with 19mm /
3/4" board without too much deflection. I'm sure my spans are the best
part of 700mm and their narrowest point and happy with the result.

OP here. How wide are your pieces of ply running across a 700mm span?
Remember that I'm aiming for strips that will only be 385mm wide, not
whole 8' x 4' chunks.

However, as noted earlier, I've discovered that the thickness can be
up to almost 30mm so that should help.

[Fredxx]

Post by Chris Green

Post by Fredxx

Post by Marland

Post by Chris Green
Ok, it's the engine hatch covers again. :-)
So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.
I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.

More expensive but for that job I would use phenolic ply sometimes known as
buffalo board.
Often used as flooring in trailers and horse boxes. Has high resistance to
moisture brought in on footwear , and many varieties have a non slip
pattern already formed on the surface.

I have used this in an outside situation and I recommend it's use. It
also provides a convenient anti-slip surface and is of course
waterproof. It's not cheap though/
I also feel the spans the OP requires can be accomplished with 19mm /
3/4" board without too much deflection. I'm sure my spans are the best
part of 700mm and their narrowest point and happy with the result.

OP here. How wide are your pieces of ply running across a 700mm span?
Remember that I'm aiming for strips that will only be 385mm wide, not
whole 8' x 4' chunks.

This is a narrowboat application where I would say the width of the
hatch is >600mm. I haven't measured it.

One hatch is possibly 1m long, the other 2 probably 500mm each. I found
it to be substantive, doesn't (perceptively) bow and replaced the
existing buffalo of the same thickness that was in a poor state.

Some heavyweights have walked on it without drama!

Post by Chris Green
However, as noted earlier, I've discovered that the thickness can be
up to almost 30mm so that should help.

A 30mm sheet sounds pretty unmanageable as well as expensive. If you are
concerned then ribs can be added after.

[Chris Green]

Post by Fredxx

Post by Chris Green

Post by Fredxx

Post by Marland

Post by Chris Green
Ok, it's the engine hatch covers again. :-)
So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.
I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.

More expensive but for that job I would use phenolic ply sometimes known as
buffalo board.
Often used as flooring in trailers and horse boxes. Has high resistance to
moisture brought in on footwear , and many varieties have a non slip
pattern already formed on the surface.

I have used this in an outside situation and I recommend it's use. It
also provides a convenient anti-slip surface and is of course
waterproof. It's not cheap though/
I also feel the spans the OP requires can be accomplished with 19mm /
3/4" board without too much deflection. I'm sure my spans are the best
part of 700mm and their narrowest point and happy with the result.

OP here. How wide are your pieces of ply running across a 700mm span?
Remember that I'm aiming for strips that will only be 385mm wide, not
whole 8' x 4' chunks.

This is a narrowboat application where I would say the width of the
hatch is >600mm. I haven't measured it.
One hatch is possibly 1m long, the other 2 probably 500mm each. I found
it to be substantive, doesn't (perceptively) bow and replaced the
existing buffalo of the same thickness that was in a poor state.
Some heavyweights have walked on it without drama!

OK, thanks, it sounds as if I should be OK then. I think I have some
scrap pieces of 18mm ply around, I will try out with one of them if I
can find one big enough.

Post by Fredxx

Post by Chris Green
However, as noted earlier, I've discovered that the thickness can be
up to almost 30mm so that should help.

A 30mm sheet sounds pretty unmanageable as well as expensive. If you are
concerned then ribs can be added after.

This is why the existing engine covers are so unmanageable, they are
made of 30mm material of some sort, probably ply or similar. Lifting
the larger one (1540mm x 740mm) with its single finger pull is, shall
we say, difficult.

I reckon my proposed single pieces of ply 1335mm x 385mm should be
manageable, even if 28 to 30mm thick. I'm putting proper hand width
lifting handles in, not just a finger pull. Making it the same
thickness as the old covers means it can sit on the same supports.

[Fredxx]

Post by Chris Green

Post by Fredxx

Post by Chris Green

Post by Fredxx

Post by Marland

Post by Chris Green
Ok, it's the engine hatch covers again. :-)
So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.
I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.

More expensive but for that job I would use phenolic ply sometimes known as
buffalo board.
Often used as flooring in trailers and horse boxes. Has high resistance to
moisture brought in on footwear , and many varieties have a non slip
pattern already formed on the surface.

I have used this in an outside situation and I recommend it's use. It
also provides a convenient anti-slip surface and is of course
waterproof. It's not cheap though/
I also feel the spans the OP requires can be accomplished with 19mm /
3/4" board without too much deflection. I'm sure my spans are the best
part of 700mm and their narrowest point and happy with the result.

OP here. How wide are your pieces of ply running across a 700mm span?
Remember that I'm aiming for strips that will only be 385mm wide, not
whole 8' x 4' chunks.

This is a narrowboat application where I would say the width of the
hatch is >600mm. I haven't measured it.
One hatch is possibly 1m long, the other 2 probably 500mm each. I found
it to be substantive, doesn't (perceptively) bow and replaced the
existing buffalo of the same thickness that was in a poor state.
Some heavyweights have walked on it without drama!

OK, thanks, it sounds as if I should be OK then. I think I have some
scrap pieces of 18mm ply around, I will try out with one of them if I
can find one big enough.

That's a good plan, it will give you confidence. Mine are support on
each of the 4 edges.

Post by Chris Green

Post by Fredxx

Post by Chris Green
However, as noted earlier, I've discovered that the thickness can be
up to almost 30mm so that should help.

A 30mm sheet sounds pretty unmanageable as well as expensive. If you are
concerned then ribs can be added after.

This is why the existing engine covers are so unmanageable, they are
made of 30mm material of some sort, probably ply or similar. Lifting
the larger one (1540mm x 740mm) with its single finger pull is, shall
we say, difficult.
I reckon my proposed single pieces of ply 1335mm x 385mm should be
manageable, even if 28 to 30mm thick. I'm putting proper hand width
lifting handles in, not just a finger pull. Making it the same
thickness as the old covers means it can sit on the same supports.

My first section is 500 x 600mm x 19mm and has a single finger pull.
Apart from the pull being stiff, it does come up quite easily and easy
to put to one side for access. The larger one ~900 x ~600mm is more
cumbersome and I wouldn't want it to be twice the weight whilst perched
on thin supports and performing a near tightrope balance!

Once the first one is up the others can be slid and removed equally as easy.

[Andrew]

Post by Chris Green

Post by Fredxx

Post by Chris Green

Post by Fredxx

Post by Marland

Post by Chris Green
Ok, it's the engine hatch covers again. :-)
So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.
I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.

More expensive but for that job I would use phenolic ply sometimes known as
buffalo board.
Often used as flooring in trailers and horse boxes. Has high resistance to
moisture brought in on footwear , and many varieties have a non slip
pattern already formed on the surface.

I have used this in an outside situation and I recommend it's use. It
also provides a convenient anti-slip surface and is of course
waterproof. It's not cheap though/
I also feel the spans the OP requires can be accomplished with 19mm /
3/4" board without too much deflection. I'm sure my spans are the best
part of 700mm and their narrowest point and happy with the result.

OP here. How wide are your pieces of ply running across a 700mm span?
Remember that I'm aiming for strips that will only be 385mm wide, not
whole 8' x 4' chunks.

This is a narrowboat application where I would say the width of the
hatch is >600mm. I haven't measured it.
One hatch is possibly 1m long, the other 2 probably 500mm each. I found
it to be substantive, doesn't (perceptively) bow and replaced the
existing buffalo of the same thickness that was in a poor state.
Some heavyweights have walked on it without drama!

OK, thanks, it sounds as if I should be OK then. I think I have some
scrap pieces of 18mm ply around, I will try out with one of them if I
can find one big enough.

Post by Fredxx

Post by Chris Green
However, as noted earlier, I've discovered that the thickness can be
up to almost 30mm so that should help.

A 30mm sheet sounds pretty unmanageable as well as expensive. If you are
concerned then ribs can be added after.

This is why the existing engine covers are so unmanageable, they are
made of 30mm material of some sort, probably ply or similar. Lifting
the larger one (1540mm x 740mm) with its single finger pull is, shall
we say, difficult.

You could dispense with the single finger pull and have two
10mm holes with Tee nuts hammered into the underside of the cover and
then have a couple of 10mm bolts with suitably sized metal rings
welded to the head. Then you just screw these two bolts into the
Tee nuts when ever you need to access the engine cover, which hopefully
is only rarely.

Post by Chris Green
I reckon my proposed single pieces of ply 1335mm x 385mm should be
manageable, even if 28 to 30mm thick. I'm putting proper hand width
lifting handles in, not just a finger pull. Making it the same
thickness as the old covers means it can sit on the same supports.

[Andrew]

Post by Marland

Post by Chris Green
Ok, it's the engine hatch covers again. :-)
So, will a 740mm long by 385mm wide panel be strong enough and stiff
enough if made of, say 25mm thick plywood? If it's not going to be
stiff enough than I can add something like aluminium angle to stiffen
it. However I'd like some sort of idea of whether this is 'obviously'
going to be necessary or not.
I think plywood plus (if necessary) aluminium stiffening is probably
the lightest practical (and affordable) material to use but if there's
anything else then I'd be interested to hear.

More expensive but for that job I would use phenolic ply sometimes known as
buffalo board.
Often used as flooring in trailers and horse boxes. Has high resistance to
moisture brought in on footwear , and many varieties have a non slip
pattern already formed on the surface.
GH

Two different suppliers quote £160 and just over £60 for the same
2.4x1.2x18mm sheet !

https://www.clevelandtimber.co.uk/products/buffalo-board-8x4-18mm

[Andy Burns]

Post by Andrew
Two different suppliers quote £160 and just over £60 for the same
2.4x1.2x18mm sheet !
https://www.clevelandtimber.co.uk/products/buffalo-board-8x4-18mm

Unless you lie on Teesside, not very flexible for delivery, eBay sellers
seem to be better for that and not horribly expensive, I've got a
trailer that could do with a new bed ...