stiffening a grp deck

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ripvan1

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any suggestions welcomed foredeck on prospective restoration is a bit soft. i have several ideas, from past ply, wood and steel projects but not grp
 
Hi John, the hulls and deck are double skinned GRP with foam infill. No signs of water ingress just a general sag when I get on and off (I'm about 15 stone so not surprising on small boat (22ft). I know about drilling and filling core filled decks drying and filling but was thinking more about strenghtening it's load bearing properties, maybe adding more glass, putting beams across below and even laminating some thin guage ply to existing deck.

Just ideas at present but all suggestions gratefully received.

Think I may ask YBW if they would start a Project section, there's a wealth of info out there :)
 
ripvan1 said:
Hi John, the hulls and deck are double skinned GRP with foam infill. No signs of water ingress just a general sag when I get on and off (I'm about 15 stone so not surprising on small boat (22ft). I know about drilling and filling core filled decks drying and filling but was thinking more about strenghtening it's load bearing properties, maybe adding more glass, putting beams across below and even laminating some thin guage ply to existing deck.

Just ideas at present but all suggestions gratefully received.

Think I may ask YBW if they would start a Project section, there's a wealth of info out there :)
Click to expand...
I am not convinced about adding layers of ply.

Tubular stiffening stringers epoxied onto the underside might do it, but be careful about adding 'hard spots' where the stringers begin and end. If the boat was designed with any thought at all, then the whole structure might have been thought through and adding stiffening might also add unforeseen consequences. We had some star crazing in the gel coat on the topsides where some internal ply dividers hade been added without thought for the consequences.

PS its very unusual for the hull to be double skinned below the waterline. A few boats were made that way, but it brings a myriad of potential problems with it and manufacturers stopped doing it a while ago.

Alternatively extra beams laminated to fit the curve exactly and epoxied to the underside would be another possibility? Depends on the underneath and the headlining and access etc etc.
 
An underdeck storage locker can be an option. On a smaller boat you have to be careful as it can get in the way and be a real pain. On the other hand it need only be 6in or so deep and still offer useful storage and leave room for drop down door at the front.
It is the locker front that offers the rigidity to the deck so has to be tied in pretty well. This option has the advantage of hiding its secondary purpose in supporting the structure and can look very neat.
 
Thanks, not sure I understand the locker suggestion :confused:

Also 2 suggestions for tubular strengthening, why tubular and not flat ? Am I missing something here?
 
Aha, see what you mean, but don't think this would cure the "springiness across the centre of foredeck but would definitely add support the sides.
 
OP

This may or may not be of interest to you but, I am restoring an old 17ft single skin cruiser. I replaced all the stringers, re-glassed them in and then added a layer of heavy woven roving to the deck floor. The floor is now very solid and feels firm and robust underfoot. It had a major test recently too as it fell of the chocs (while I was sitting in it).

The work I refer to starts around page 16 of my restoration thread here - http://www.boards.ie/vbulletin/showthread.php?t=2056217528&page=16

I'd really recommend a coat of heavy woven roving, then when almost cured, mix up a batch of resin and thincken it with colloidal sillica, then paint this into and onto the roving. It fills it and stiffens it even more.
 
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Stiffening

Assuming you want to put ribs under the deck rather than the stronger solution of a bulkhead....
To get a stiffening rib under the deck to be stiff it must have depth. This to give triangulation strength. The depth gives more stiffness (as a beam) than any other dimension increase. However the depth may encroach into your usable area underneath so you keep it reasonable.
A square cross section piece of wood is suitable for stiffening but again the depth is the working dimension.
However if you want to lay fibreglass over the wood you need to have large radius curves for the glass to follow. Hence half round or semicircular cross section is best. However you still have the problem of getting the glass to follow the inside rightangle from deck to side wall of the wood. So either carve the wood to have a gentle hill shape in cross section or put a fillet of filler into the corner to make it a smooth transition without air bubbles.
You can use fibreglass cut diagonally so that it will bend more easily or buy a twill weave cloth also made to bend more easily.
good luck olewill
 
that makes sense olewill, thanks. from an aesthetic point oe view would laminating strips of wood, attaching to under the foredeck (glue and staples or bolts) then glassing inbetween the beams be an option?
 
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ripvan1 said:
that makes sense olewill, thanks. from an aesthetic point oe view would laminating strips of wood, attaching to under the foredeck (glue and staples or bolts) then glassing inbetween the beams be an option?
Click to expand...

No the glassing in between the beams would do nothing or at least very little. Glass around the beams will do a lot more. olewill
 
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