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! :-)
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! :-)
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.
will a 740mm long by 385mm wide panel be strong enough
Chris Green <cl@isbd.net> wrote:
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.
Chris Green wrote:
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 <cl@isbd.net> wrote:
Ok, it's the engine hatch covers again. :-)
More expensive but for that job I would use phenolic ply sometimes known as buffalo board.
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.
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.
On 16/02/2025 10:11, Marland wrote:
Chris Green <cl@isbd.net> wrote:
Ok, it's the engine hatch covers again. :-)
More expensive but for that job I would use phenolic ply sometimes known as buffalo board.
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.
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.
Andy Burns <usenet@andyburns.uk> wrote:
Chris Green wrote:
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.
Chris Green <cl@isbd.net> wrote:
Ok, it's the engine hatch covers again. :-)
More expensive but for that job I would use phenolic ply sometimes known as buffalo board.
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.
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
On 16/02/2025 10:19, Chris Green wrote:Nobody has yet mentioned Marine ply which I believe is made without
Andy Burns <usenet@andyburns.uk> wrote:Beware, there is 'external' ply which won't last long and good
Chris Green wrote:
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.
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.
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.
On 16/02/2025 18:26, Andrew wrote:
On 16/02/2025 10:19, Chris Green wrote:Nobody has yet mentioned Marine ply which I believe is made without
Andy Burns <usenet@andyburns.uk> wrote:Beware, there is 'external' ply which won't last long and good
Chris Green wrote:
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.
quality stuff.
voids and uses waterproof resin. Cost will escalate!
Fredxx <fredxx@spam.invalid> wrote:
On 16/02/2025 10:11, Marland wrote:
Chris Green <cl@isbd.net> wrote:
Ok, it's the engine hatch covers again. :-)More expensive but for that job I would use phenolic ply sometimes known as >>> buffalo board.
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.
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.
On 16/02/2025 18:26, Andrew wrote:
On 16/02/2025 10:19, Chris Green wrote:Nobody has yet mentioned Marine ply which I believe is made without
Andy Burns <usenet@andyburns.uk> wrote:Beware, there is 'external' ply which won't last long and good
Chris Green wrote:
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.
quality stuff.
voids and uses waterproof resin. Cost will escalate!
On 16/02/2025 15:34, Chris Green wrote:
Fredxx <fredxx@spam.invalid> wrote:
On 16/02/2025 10:11, Marland wrote:
Chris Green <cl@isbd.net> wrote:
Ok, it's the engine hatch covers again. :-)More expensive but for that job I would use phenolic ply sometimes known as
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.
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!
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.
Fredxx <fredxx@spam.invalid> wrote:
On 16/02/2025 15:34, Chris Green wrote:OK, thanks, it sounds as if I should be OK then. I think I have some
Fredxx <fredxx@spam.invalid> wrote:
On 16/02/2025 10:11, Marland wrote:
Chris Green <cl@isbd.net> wrote:
Ok, it's the engine hatch covers again. :-)More expensive but for that job I would use phenolic ply sometimes known as
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.
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!
scrap pieces of 18mm ply around, I will try out with one of them if I
can find one big enough.
This is why the existing engine covers are so unmanageable, they areHowever, 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.
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 <fredxx@spam.invalid> wrote:
On 16/02/2025 15:34, Chris Green wrote:OK, thanks, it sounds as if I should be OK then. I think I have some
Fredxx <fredxx@spam.invalid> wrote:
On 16/02/2025 10:11, Marland wrote:
Chris Green <cl@isbd.net> wrote:
Ok, it's the engine hatch covers again. :-)More expensive but for that job I would use phenolic ply sometimes known as
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.
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!
scrap pieces of 18mm ply around, I will try out with one of them if I
can find one big enough.
This is why the existing engine covers are so unmanageable, they areHowever, 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.
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.
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