Enlarging hole for through-hull

[Babylon]

Replacing 1/2" cooling water through-hull with a 3/4" version, question is how to enlarge hole?

And once I've cut the hole, is there anything I should do to the cut fibreglass before inserting the fitting and sealing it with sikaflex?

TIA

 

[ghostlymoron]

Fit a 1/2" wooden plug in the existing hole then use a hole cutter with the pilot centred in the plug. Treat cut edges with resin.

 

[prv]

Instead of the plug, you can just fix a batten across the inside of the hole. All you're doing is providing something for the pilot drill to locate into. Once it's started cutting the main hole you don't even need that.

I've successfully cut a few holes in fibreglass "freehand", holding the drill very firmly and slowly introducing more and more of the holesaw to the material, but I wouldn't recommend this unless you're confident and have no easy alternative.

On the holes in the hull, I whacked some epoxy on the cut edges because I had it handy. Polyester would be fine too. I don't know if either is considered mandatory - after all, there shouldn't be water inside the hole.

Pete

 

[ghostlymoron]

Can't see that it would be easier to fit a batten a roughly cut 1/2" plug would jam in the existing hole with no further fixing.

 

[Martin_J]

Plugging then drilling sounds the easiest... although sbdy on one side holding a piece of wood over the hole would work...

I've not seem them here but there is such a thing as an 'oops arbor'.. it takes both hole cutters at once.. the small original size and the new large size...

http://www.mcfeelys.com/product/HS-0019/Starrett-quotOOPSquot-Arbor

 

[vyv_cox]

Replacing 1/2" cooling water through-hull with a 3/4" version, question is how to enlarge hole?

And once I've cut the hole, is there anything I should do to the cut fibreglass before inserting the fitting and sealing it with sikaflex?

TIA

For such a small increase I use a set of burrs just like these. Well worth buying a set as they come in handy on many occasions. Very little risk of making the hole too big as they don't cut fast enough.

 

[Sire]

Maybe you could use a step cutter, if the thickness isn't too great?

http://www.thesitebox.com/Category/4163/step-cutter.aspx

 

[fireball]

I would go for the batten of wood method - if you've got the space to work.
I have hand held a holecutter for this before - but you've got to be very careful - and mine wasn't a throughhull ...

 

[earlybird]

You're enlarging the diameter by little more than 0.2". A hole-saw won't really be cutting properly.
I'd say that the safest, surest, and probably the quickest approach is a large, coarse cut, round file.
( 14", Bas*ard cut, rat-tail in the vernacular!). Or Bar steward on this forum!

 

[Poignard]

Been there - done that.

I replaced a 1/2" Stuart seacock/strainer with a Blake's 3/4" seacock.

I used a cone cutter. Something like these but a different make:

http://www.lawson-his.co.uk/scripts/products.php?cat=Cone Cutter Drill Bits

I sealed the edges of the enlarged hole with epoxy.

The boat hasn't sunk yet so it must be an ok method.