Tricky deck reinforcement

[seaangler23]

It does seem strange to me that on such a large area with no other support they might have used the opportunity to install something that would aid to the strength but I guess when new and dry it would have worked but then they drill straight into it and add all the fittings with little thought to sealing it

 

[30boat]

Yeah my plan is to make the roof in sections that will fit through the door, make them with stepped so one if the pieces of ply will overlay the next section so I can epoxy them in place. When they are made il lay up the laminate on some peel ply on top of them or a template, just gives me a good idea of the size.
Then in goes the ply and epoxy in place with plenty of supports and the laminate can be held in place with screws and battons until it dries, then all the deck fittings drilled out and epoxy filled. It's a crap job but as it's a keeper it's getting done as well as possible, I'm not doing it again in 30 years

One word of warning.You'll find that if you drive a screw through wet laminate it'll catch on the fibers and spin them around making a huge mess!
If I got you explanation right,you're going to lay some laminate on the flat and them stick it on the underside of the deck,right?

 

[seaangler23]

Il make up the laminate outside the boat let it set, rough up the back of it with course sandpaper and epoxy it to the ply from below so will be more like a fiberglass panel going on. The plan is the only glassing il be doing overhead is glassing in around the edges

 

[30boat]

Il make up the laminate outside the boat let it set, rough up the back of it with course sandpaper and epoxy it to the ply from below so will be more like a fiberglass panel going on. The plan is the only glassing il be doing overhead is glassing in around the edges

That's what I thought.It'll be easy that way.If you use epoxy putty you'll get a very strong bond.I would mix epoxy resin with talc to a peanut butter consistency.It makes a very easy to use putty.When glassing around the edges use fiberglass tape in short lengths.This way it'll have much less of a tendency to peel off while still uncured.

 

[seaangler23]

Cheers I was going to order some colodial silica for some other jobs and use that it am I going ott for laminating?

 

[lw395]

A mate of mine has done this although on a smaller scale.
He did it in sections, vacuum bagging glass/resin, closed cell foam and resin/glass bubble paste, to form a proper foam sandwich.

Maybe working with planks of foam 6 to 12 inches wide would be a sensible way to go?

I think there were a few sweary moments getting the vacuum bag to seal, but it did the job.

 

[30boat]

A mate of mine has done this although on a smaller scale.
He did it in sections, vacuum bagging glass/resin, closed cell foam and resin/glass bubble paste, to form a proper foam sandwich.

Maybe working with planks of foam 6 to 12 inches wide would be a sensible way to go?

I think there were a few sweary moments getting the vacuum bag to seal, but it did the job.

Vacuum bagging is a bit ott for this job.Props will do just fine as long as the pressure points are evenly spaced.I'd put some wide plywood pads between the prop and the laminate obviously. The talc epoxy mix will spread under the pressure and fill all the voids.

 

[30boat]

You should not exceed a certain amout of silica to resin ratio.Talc is much cheaper and probaby more effective. There's no point in using coloidal silica for laminating unless you're working overhead when the extra viscosity helps to keep things in place.

 

[lw395]

Vacuum bagging is a bit ott for this job.Props will do just fine as long as the pressure points are evenly spaced.I'd put some wide plywood pads between the prop and the laminate obviously. The talc epoxy mix will spread under the pressure and fill all the voids.

Vacuum is the best way to get an even pressure over the whole bond.
You can get a much better bond using lot less gloop.
Like lots of techniques, it's not that hard if you've done it before.
A big advantage is that it avoids having a load of props pushing the deck up. Of course you may need that if the deck is floppy and sagging.

 

[30boat]

Vacuum is the best way to get an even pressure over the whole bond.
You can get a much better bond using lot less gloop.
Like lots of techniques, it's not that hard if you've done it before.
A big advantage is that it avoids having a load of props pushing the deck up. Of course you may need that if the deck is floppy and sagging.

Vacuum bagging is a great system that is difficult to execute unless you're working in ideal conditions which is hardly the case here.You'll need a vacuum pump to begin with.A vacuum cleaner won't do.Then you need a layer of felt or at a pinch bubble wrap between the work and the bag.You will have to keep the laminate covered in wet rovings or thickened epoxy in place over head while you apply the felt or bubble wrap which will have to be held in place somehow ,tricky because it will try and fall off like everything else.After that you'll need to put the bag in place and seal it around which implies an area that's smooth and clean enough for the tape to take a hold and also seal.
Several pairs of hands will be needed and even then there are no garanties that the whole thing won't turn into a huge sticky mess.
Props and panels on the other hand will achieve basically the same result with almost no effort.The fiberglass panels can be cut into small sections that are easy to handle and to wedge into place with precut props.They don't even need to be glued in all at the same time.There's plenty of time to clean any runs and to apply as many props as deemed necessary to achieve the correct pressure and shape.Once al the panels have been done it's just a simple matter of joining them with some fiberglass tape .The end result will be just as strong as with vacuum bagging but it won't have been a stressful job.
I've done a lot of vacuum bagging and own a pump but would never use it for this sort of job.

 

[lw395]

I 'm only saying what I've seen done successfully.
The result is rock solid and very professional looking.

There are many ways to do the job, but the key thing with any sandwich contruction is that the two skins and the core must be properly stuck together, any significant voids make the whole thing very weak.
The OP's boat probably relied on the wood as structure if it's not balsa?
So the top skin might be too thin if used with a softer core?
Decks tend to get point loaded more than hull skins.

 

[30boat]

I 'm only saying what I've seen done successfully.
The result is rock solid and very professional looking.

There are many ways to do the job, but the key thing with any sandwich contruction is that the two skins and the core must be properly stuck together, any significant voids make the whole thing very weak.
The OP's boat probably relied on the wood as structure if it's not balsa?
So the top skin might be too thin if used with a softer core?
Decks tend to get point loaded more than hull skins.

I'm not disagreeing with you.Ideally,like working on the flat,it would be a good way to do it with guaranteed results.In practice however there are more ways to skin a cat .I rebuilt the whole decks on my previous boat,a Peterson 30 and used nothing but polyester putty,countless plywood squares and polyester resin and mat.That was in 1992.The boat is still around with perfect decks.The PO should stick the plywood core (heavy but very strong in compression) in place and after the epoxy has kicked ,fill all the woids with more putty,fair the surface with a knife (spatula) and then apply the lower skin liberally coated in epoxy putty. The pressure from the props will squeeze the excess stuff out and there will be no voids to speak of.
When I did my boat I started from below at the bow,like the OP, and working with polyester, stuck the lower (reused) skin with loads of fluffed up resin soaked mat.It was a nightmare with resin dripping all over us but in the end it worked perfectly.

 

[seaangler23]

Finally started on this, been picking at it for months getting the old core out but I have taken a week off to get it done. So far all the core is out just to clean up around the edges and can get on with rebuilding.
About half of the core had delaminated and most of the remainder has signs of water ingress, very little was still good.
I have everything to rebuild and I'm going with balsa core again after having a boat builder look at it and point me in the right direction.'
My plan was to cut a 2 piece template out of 12mm ply to hold the core in place from bellow and do it in one go so I could apply pressure to the balsa with supports and get the deck shape right,but I braced the deck today with a single beam running up the middle and a couple of uprights tapped in and the deck shape is really good, better than it has ever been and doesn't need much fettling.
Would there be any harm in replacing the core in 2 parts ( outer edges up to the central brace let it set then remove the brace and fill in the middle)of course with proper bracing then when it's all in il make a laminate up on the floor using my template and tape/ glass it in again with braces.
Probably sounds more complicated than it is.


An old bathroom extractor fan really helps