Cutting Fibreglass

[bluerm166]

I am considering cutting out a cockpit floor locker which prevents adequate access to everything to the rear of the gearbox ,so coupling ,stuffing box,greaser,muffler,sterntube,cockpit drain outlets,gudgeon bolts etc etc.

If I look at Bosch wired tools ( e.g. bare tool ) and buy separate blades specific to the task,what is best to buy for a horizontal cutting run of 2.4 metres of say 6mm fibreglass ? Rounded cutter or 'chisel' type.
Would have direct frontal access and work on top of a glued batten - edge would be concealed anyway.

 

[West Coast]

These are good - we use them in our fibreglass workshops on jigsaws and found them to have good cutting capability and longer life than most

EXPERT Fiber Plaster T341HM Jigsaw Blades Jigsaw Blades Saw Blades & Hole Saws | Bosch Professional

 

[SvenH]

Considering the length to be cut: Plunge saw with track?
Better get a blade with a negative tooth angle, that will cut aggressive yet more or less pleasant. Standard blade will probably not be very enjoyable on fiberglass.

 

[Geoff A]

Diamond edged 4inch cutting disc using a angle grinder mask and gloves. This is what was used in a GRP boat building factory i visited. The angle grinders were air powered. for small jobs I have used 240v grinder.

 

[PetiteFleur]

I went to our local builders merchant and bought a 'rough' blade specifically for grp, worked well. Not cheap but worked well.

 

[Refueler]

Job I hate doing !! GRP resin tends to harden when being cut by grinder or high speed tool ... can destroy most blades.

But my choice would be grinder disc ... two reasons - 1. it grinds the cut rather than tearing it - if resin is a bit sparse in any part - the laminated can become a torn hairy mess .. it also tends to seal the cut edges where resin heat welds ... 2. the way of holding the grinder in itself helps you cut straight instead of wandering as a jigsaw or similar tends to do.

 

[thinwater]

^^ As refueler said.

I've done many cuts like that. A grinder cuts it like butter. There will be a lot of dust, but the cuts will be clean and precise.

 

[Stemar]

I'd prefer a grinder for most GRP cutting, but for the OP's job, a jigsaw has the advantage of a finer cut, meaning the bit that's been cut out is a better fit in the hole when it becomes the lid.

 

[thinwater]

I'd prefer a grinder for most GRP cutting, but for the OP's job, a jigsaw has the advantage of a finer cut, meaning the bit that's been cut out is a better fit in the hole when it becomes the lid.

Maybe.

I have used a grinder for this, and you are going to have to grind a 12:1 bevel before reglassing anyway. It won't make a bit of practical difference IMO. The problem is matching non-skid, so I have ground away the old non-skid and made new.

 

[salar]

I have done a LOT of GRP cutting during boat rennovations and for long cuts a grinder with a thin cutting disc (NOT the normal grinding disk) is best, but makes a helluva dust. My go-to for smaller, finer work with very little mess is the multi tool with the semi circle blade. For rounded corners, and I'm sure you are not planning sharp corners (!!) I prefer a diamond hole cutter for neatness, as used on tiles. With the above you will have chip-free edges. All other types of saw have varying degrees of nastiness with the cut edge, particularly the gel coat which loves any excuse to chip.

 

[salar]

PS, are you mounting your floor locker actually on the floor or the vertical at floor level? If on the floor, I have had great difficulty sourcing hatches strong enough to bear the load of people tramping about, and of course it also needs to be waterproof. In the end I had a custom locker lid and drain system manufactured at great expense, but it was worth it.

 

[johnalison]

It is not clear from the OP's post, but I would be cautious if it appeared that the floor to be cut were part of the boat's structure.

 

[Stemar]

Maybe.

I have used a grinder for this, and you are going to have to grind a 12:1 bevel before reglassing anyway. It won't make a bit of practical difference IMO. The problem is matching non-skid, so I have ground away the old non-skid and made new.

From the OP's wording, I made the assumption that he was planning on making a hatch for regular access.

If that's the case, the hole would need to be reinforced with a lip to rest the lid on and to take care of johnalison's concern, as well as some means of holding the cover in place. I'd also put a bit of trim to cover the gap, but that would be purely decorative.

Also worth considering if the hatch needs to be properly waterproof, which would complicate matters significantly. Personally, unless going blue water, I'd be more inclined to get it as waterproof as I could conveniently and ensure there was an effective automatic bilge pump and a solar panel to keep the battery topped up.

 

[wingcommander]

Premium Marine Grade Deck Inspection Access Hatch, for Boat Yacht Caravan | eBay

Something like this i presume, i would think getting the hatch first ( if not done so already) will make the marking out and cutting easier. As mentioned grinding would be my first choice. PPE a must

 

[salar]

Premium Marine Grade Deck Inspection Access Hatch, for Boat Yacht Caravan | eBay

Something like this i presume, i would think getting the hatch first ( if not done so already) will make the marking out and cutting easier. As mentioned grinding would be my first choice. PPE a must

Those are the exact ones that I tried, and despite the label they aren't suitable for standing on. OK on a locker top for sitting on, and I have one on the foredeck covering the anchor locker which isn't easily stood on. Despite that, both catches have broken but they have been down 10 years.

 

[thinwater]

I have done a LOT of GRP cutting during boat rennovations and for long cuts a grinder with a thin cutting disc (NOT the normal grinding disk) is best, but makes a helluva dust. My go-to for smaller, finer work with very little mess is the multi tool with the semi circle blade. For rounded corners, and I'm sure you are not planning sharp corners (!!) I prefer a diamond hole cutter for neatness, as used on tiles. With the above you will have chip-free edges. All other types of saw have varying degrees of nastiness with the cut edge, particularly the gel coat which loves any excuse to chip.

Also second the multitool.

A mutitool can be walked around for curves in thin glass skins, but not so much for glass. A hole saw (if that is what salar meant) is also great, but not always if you are going to reuse the skins. But I have also done it that way. You do NOT want sharp corners.

Pictures always help. Then draw on them with Publisher or something similar.

 

[bluerm166]

Time to confirm that the cockpit floor locker already exists.Size nom. 800 x 400x 400 deep.Does not extend to the rising hull slope towards the transom.Original optional extra cost in 1987 on Parker Seal 27 was £180.Designed to accept a small rounded transom inflatable.Strongly built with drain channels etc. and seals.

BUT as original post - it is a pain to use,without kneeling clear of the lid ,keeping ropes clear and it doesn't take more than two fenders and a 3 person inflatable in no way fits.
Particular sin is to limit access via small side panels in the longitudinal bulkheads to single extended arm reach to all that needs two arms for maintenance both in front of,behind and under the locker,including for instance the rear engine feet.
Because the locker doesn't extend to the hull new side ports for access would not add much facility.A historical sketch attached to illustrate.

So would be cut off horizontally about 50/70mm down inside locker leaving the lid (14mm thick plus flanges )and deck perimeter intact . A perimeter ledge /batten added within that 50 /70 will support the present flat panel floor of the locker with semi permanent perimeter seal,which can be cut out at major interval and have negligible load to create flex.

My original thought was for a Bosch oscillating multi tool so all of your suggestions are of interest as I put project together.
Thank you so far.

 

[Daydream believer]

When I fitted a new engine in my boat last year I had to alter the panel that covered part of it. I took the panel home & cut out a section with my jig saw, That worked great. But when I got to the boat it was nowhere near enough. So I had a keyhole saw that I used for plaster board etc & just re cut the whole thing again. Not difficult & a cheap hole saw from a builder's merchant is nothing in the grand scheme of things. . No major dust etc gets in corners easly enough.
keyhole saw

 

[bluerm166]

Thanks to all for your helpful response and experience.
Looking through I favour the angle grinder with the Bosch blade suggested and the Multitool.Happily I can borrow both of these and couple with the optimum blades.
The specialist jigsaw blade looks absolutely the job but at rather a price and I don't already have a jigsaw.I do have a scorpion saw but that, although powerful ,has no specialist blades available.
Finally I do normally have the hand padsaw type used for plasterboard but had overlooked pucker keyhole saws suggested above,which might well come in for the internal corners or final cuts as the box drops under control.
It seems that two perimeter cuts will likely be necessary as the complete box could not be turned to pass through the hole and would be much too stiff to 'fold inwards'.
I will give all of these tools a try .Bearing in mind this awful changeable weather I am thinking of a tarp to allow some progress while we wait for continuity and I can't imagine much worse than a slurry of wet grp dust !

 

[bluerm166]

Feedback : There was no contest .The multitool using the semi circular blade generally and the chisel blade to complete at the internal corners was tried tentatively and did such a job of staying on line that I carried on and made the two perimeter cuts in about 3 hrs. of work.The tools had the particular benefit of limiting depth of cut so couldn't by mistake go too deep and hazard the few things in the immediate void behind the cut line ,such as the teleflex cables and the exhaust gooseneck .Also the action of the cutters produced limited dust and didn't project it .