Filling "spare" holes in deck ?

[Boo2]

Hi,

Sunrunner (34' gf sloop) has a number of "spare" holes in her decks. These are from eg a diesel heater chimney which had been removed long before I bought her, as well as things that I don't need which I want to remove to make room for things I do need. Holes vary from 6mm (screw holes) to around 100mm (vents and redundant heater chimney).

The 6mm holes I am just going to fill with marine padding epoxy filler, but what do I do about 100mm sized holes ? Below the waterline I understand you need to cone out the hole edges to something like 6 times the laminate thickness then layer in increasing widths of cloth from both sides so as to form a mechanically bonded plug which can't come out.

But surely I don't need to go to all that trouble on the decks ? Can anyone tell me what the best way of plugging holes of this size in a deck is ? (Deck is 1" thick with a balsa (I think) core).

Thanks,

Boo2

 

[Deleted member 36384]

The quick answer is yes you do need to taper. Reinstating the balsa core and especially tapering establishes a strength in the repair that is equal to or better than the original. A simple butt joint with say a circular GRP panel will not be of the same strength as the surrounding GRP. The taper distributes any stresses over a greater surface area and compensates for the fact that bonding to cured resin produces a weaker joint than bonding to uncured resin. Its still a strong joint; bonding to fully cured resin.

A simple butt type joint will concentrate the stress at the joint. This may not be an issue until the boat is hard on the wind and flexing, then over time the weakness may be exposed as a failed joint.

I am sure you have these from another post: http://www.westsystem.com/ss/use-guides/

 

[VicS]

Screw holes something along the lines you suggest.

I've not had to fill any in balsa cored decks but in just plain GRP I cover the inside with a layer of resin and glass mat, fill the hole with a hard type of body filler, when set drill out the outer most layer and fill with gelcoat filler.

I think I'd consider dealing with the 100mm hole by installing a vent of some description.

With holes in the hull chamfer the edges as you say ( I have seen a figure of 12 times the thickness but you end up with an enormous repair) but I think you will find that when laying in the cloth you start with the max diameter (Outside diameter of the chamfered area) then progressively smaller ones.
( I have a redundant hole below the water line to deal with and will be using biaxial cloth and epoxy resin)

 

[Deleted member 36384]

.... but I think you will find that when laying in the cloth you start with the max diameter (Outside diameter of the chamfered area) then progressively smaller ones ....

Yep that's correct, largest first and then smallest last. It confused me when I first started planning a hole filling job but it works very well and makes for easy fairing later.

 

[Scotty_Tradewind]

I think I'd consider dealing with the 100mm hole by installing a vent of some description.

+1
not only fairly easy to do and to make waterproof, but useful.
How about a Vetus mushroom type vent?
http://www.google.co.uk/products?q=vetus+mushroom+ventilator&hl=en

I'm fitting a couple to replace old dorade ventilators on my foredeck. I've bought the dorade type fitting as well to go on top with old style scoops, but not sure I'll fit those unless I go to warmer climes to help scoop in some air.

 

[Boo2]

@various : I can't use a mushroom vent in the case of one hole because that's what I'm taking out so I can run the anchor chain over where the existing vent is.

@BlowingOldBoots : I'm not sure what the reply about the balsa core meant ? Did you mean to replace where the core had been with more balsa then re-laminate just the iner and outer skins, feathering off just 6/12 times the skin thickness not 6/12 times the total deck thickness? But doesn't doing it this way mean the laminate "plug" could fall out because it's not bonded to the new inside skin ?

@VicS/BlowingOldBoots : I suppose the largest goes in first to stop everything falling through the hole ? Is it advisable to temporarily put eg fablon inside to laminate onto from one side ?


Thanks to all for the replies,

Boo2

 

[VicS]

@VicS/BlowingOldBoots : I suppose the largest goes in first to stop everything falling through the hole ? Is it advisable to temporarily put eg fablon inside to laminate onto from one side ?

Something I am still looking into but I think the correct procedure ( i've seen it i think on one of the glass fibre or resin suppliers sites) is to chamfer the outside only. Put something tight up against the inside to laminate against.

If you chamfer 12 times the thickness you end up with a huge area to finish off on the outside though. OK for the professionals but a bit daunting for the amateur.

Maybe possible to work from both sides ?

 

[Deleted member 36384]

Did you mean to replace where the core had been with more balsa then re-laminate just the iner and outer skins, feathering off just 6/12 times the skin thickness not 6/12 times the total deck thickness

Yes and only 6/12 skin thickness (or whatever West recommends). If the hole in the deck is through a balsa core, then you should replace the balsa core by gluing in a section to fit the gap. You may find that any existing balsa core that surrounds the hole has deteriorated. The opportunity should be used to scoop any soft balsa core back to sound balsa.

The new balsa core can be added in sections to fit the space and glued together with epoxy as required i.e. you dont need to fit a single section. Personnaly if the core is balsa I would replace the missing piece with balsa but there is no reason why another material could not be used as it only serves to give shape.

But doesn't doing it this way mean the laminate "plug" could fall out because it's not bonded to the new inside skin ?

The new core is glued in place first and if required faired to the same thickness as the existing core. The tapered sections are stuck to the core replicating the original lay up.

So the sequence is: -

1. Cut out any rotten core.
2. Taper inside and outside GRP "skin".
3. Glue in a new core section and allow to set.
4. Do inside GRP tapered patch.
5. Do outside GRP tapered patch. Or outside first, inside last, it doesn't matter.

I suppose the largest goes in first to stop everything falling through the hole ? Is it advisable to temporarily put eg fablon inside to laminate onto from one side

To be honest I am not sure why its largest first. If there is no core, then a backing material can be used and just taper from outside only i.e. a single skin structure.

Pragmatism Point
The fact that there is a hole there already and assuming the boat has been sailed hard, then if there is no issue with stress or cracking around the hole, then just blanking the outside GRP skin would be OK, assuming the hole is through a cored deck. This just leaves the internal side of old deck hole to be hidden some how.

 

[Boo2]

To be honest I am not sure why its largest first. If there is no core, then a backing material can be used and just taper from outside only i.e. a single skin structure.

I've just looked it up in the Fiberglass Boat Repair and Maintenance guide you linked to above and it says it is to ensure that the cloth is not sanded through when fairing after the patch is made.

Thanks to all for the advice, in the case of the forward vent I probably have no choice but to fill it but the blanked off heater chimney hole I may try to fill with a dorade style vent as I would like to add a couple of these anyway.

Boo2

 

[ms.lau]

boo2

if you want to sell me the spare hole in your deck i need one for the wood burner i'm putting in my boat.

oh, wait, it's only 100mm and i need 125mm for the twinwall stovepipe.

damn!

laura