To enlarge a hole

PabloPicasso

PabloPicasso

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I am replacing a log paddle wheel through hull. The old system is past it's best. The new through hull fitting is a few mm bigger in diameter. I haven't removed the old fitting yet but it seems likely the new one is just too big to fit in the old hole.

So what wound be the easiest way to enlarge the hole in the GRP hull? File it? Router? Hole saw? Jig saw? Any other methods to consider?

Any advice on the best method to remove the old through hull, it seems to be made of black plastic.

I was thinking of using trek 7 as a sealant between fitting and hull outside and in, then class over the backing nut with epoxy and fibre mat. Does this seem like a good plan?

So 3 questions in one thread.
 
I did the exact same task 2 seasons ago.... removing the old fitting ended up being a destruction job.... I used a hacksaw blade to cut it in half and pried both bits out.

I enlarged the hole using a flap sander... a sort of drill attachment with flaps of sandpaper on it... worked well through 2" of hull material, but took a while. It came from a local DIY superstore. I'd imagine that any other method would prove very difficult to keep the hole round, and ensure a tight fit for the new fitting, and a something like a hole saw would be very difficult to control with no central hole to locate the arbor and drill bit into, and fibreglass kills hole saws in no time at all.

I fixed mine in with Sikaflex 291, which is recommended for underwater use.
 
Ah yes. A great idea. I have a flap wheel attachment somewhere.

Great advice.

Did you epoxy and mat over the interior nut?
 
Phoenix of Hamble said:
something like a hole saw would be very difficult to control with no central hole to locate the arbor and drill bit into,
Click to expand...

Do you not think that the wood glued to the exterior of the hole would not be enough to keep the drill bit centered until the hole saw (or hole cutter) bit into the grp?

EDIT: Sorry, did not read OP properly. Missed bit about only needing a few mm. Frapper seems ideal.

Haven't done this job before but may need to one day.

Did you wet the area as you worked with the frapper to avoid dust? Or just use a mask and vacuum / extractor?

I installed an inspection hatch for a mate and the jigsaw created so much dust I resorted to a dust mask (plus some wetting down). The angle grinder with cutting disc was even worse for dust creation.
 
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Working with GRP is dusty. Using a hole saw with pilot bit would be the least dusty & most accurate,though the hole does not need to be a jam fit,so either way will work.
Chamfer/bevel the hole on the outside a bit & sealant will make an o-ring in this chamfer. Putting a bit of sealer on threads up to just above the nut will lock the nut in place.
No need to glass over it-you might have to remove it someday.
Have done hundreds of thru hulls-none leaked,that were done this way. Cheers/ Len
 
Did this just last weekend.
Followed past advice on here and put a wooden plug/bung tight in the in the hole from the inside and made sure it was flush. Then used a hole saw with the pilot drill centered on the plug.
The old fitting came out easily enough by tapping round the lock ring with a chisel.
I've bedded the new one with lots of sikaflex as it has worked well previously for me.

All the best
 
PabloPicasso said:
I am replacing a log paddle wheel through hull. The old system is past it's best. The new through hull fitting is a few mm bigger in diameter. I haven't removed the old fitting yet but it seems likely the new one is just too big to fit in the old hole.

So what wound be the easiest way to enlarge the hole in the GRP hull? File it? Router? Hole saw? Jig saw? Any other methods to consider?

Any advice on the best method to remove the old through hull, it seems to be made of black plastic.

I was thinking of using trek 7 as a sealant between fitting and hull outside and in, then class over the backing nut with epoxy and fibre mat. Does this seem like a good plan?

So 3 questions in one thread.
Click to expand...
a coarse 1/2 round file would be easiest with no possibility of added damage via a skidding hole saw. i have both so its easy for me to say ;)
 
A wooden plug tapped into the hole to provide a guide to the pilot drill of a hole saw is the simplest way. You only need ti keep the tool centred until the outer ring has got a good bite into the hull. After that the centre is almost superfluous. If your hull is more than about 20mm or 25mm thick the hole saw may bottom out requiring either working from both sides using the one pilot hole or other more inventive methods.

Those flap wheels are rarely waterproof so adding water to keep the dust down just destroys the flapper.

Working with glassfibre a facemask is essential. A vacuum is a good idea too.

A very coarse rasp may delaminate hull material on the 'outward' stroke and glassfibre will quickly destroy the sharp edges required for your rasp to ever work decently on timber ever again. A Barstard metal working file is a better bet imho.
 
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For an increase of just a few millimetres, which is what the OP wants, I would most definitely use a flap sander. Working from inside the boat the majority of the dust will fall out and if you were really concerned you could use a vacuum cleaner on 'blow' to ensure that it did. Using a hole saw seems like overkill for such a small increase.
 
If there's more than 1 or 2 mm to shift, drilling a lot of small holes, or removing what you can with a jigsaw or pad saw helps.
Even just making small radial cuts shifts material and helps check progress.
Wear a mask with the flap wheel.
Something round eg plastic pipe, a few mm smaller than the old hole, wrapped with coarse sand paper is effective too.
Cheaper than a flap wheel, which will be ready for the bin at the end of the day.
Last time I did this, I wanted to move the hole centre a bit to move the fitting away from a bulkhead.
 
vyv_cox said:
For an increase of just a few millimetres, which is what the OP wants, I would most definitely use a flap sander. Working from inside the boat the majority of the dust will fall out and if you were really concerned you could use a vacuum cleaner on 'blow' to ensure that it did. Using a hole saw seems like overkill for such a small increase.
Click to expand...

My thoughts exactly. Nor would fancy using a router for this job on a boat, things can go wrong very quicky
Pete
 
Temporary wood and holesaw for larger increases, but I agree with the coarse flap wheel for just a few millimetres. Half-round rasp would work too, but likely to end up with a slightly wobbly-shaped hole.

Pete
 
Ok I'll try a flap wheel first. But I like the idea of course sand paper wrapped around a pipe or fat piece of wooden dowel. For a few mm a hole saw seems to much hassle, and I'm not sure I have one the right size.
 
Hi I did this last winter assuming grp take 40 grit sandpaper wrap round a bit of plastic pipe that is marginally smaller than current hole - just seems to eat through & leaves a surprisingly regular circular hole - pipe diameter didnt even seem that crucial very simple cheap & worked a treat
 
I did this by jamming a boatyard prop flush against the original hole, then opening the hole out using a hole saw. But my boat is bilge keel so not to far off ground. Sealed with Sikaflex.
 
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