Bigger Hole needed

[BlueSkyNick]

Having returned from the Boat Show with stacks of glossy brochures for replacement instruments, etc, I am contemplating the work required, in readiness for the boat coming out of the water during the winter.

I want to replace the original (14yr old) Stowe speed log (as well as depth sounder). I am assuming that the transducer will be a different diameter, and will require the hole in the hull to be enlarged. Unless I choose one with a smaller transducer of course, in which case I have a different problem.

I think the GRP is approx 1cm thick and the new hole needs to be perfectly circular to prevent ingress of water.

What is the recommended tools and method for doing this?

I am no DIY expert and rather fancy that the best answer is to get somebody else to do it for me!

<hr width=100% size=1>Have a holiday on The Broads? Norfolk Enchants !!

 

[Mirelle]

Bigger Hole = easy. Smaller hole = trouble!

It's worth keeping in mind that the new hole does not need to share the same centre as the old one, so a slight error in centring does not matter.

To make the new hole bigger than the old, bung up the old hole with something that wil stay put - ideally, glue a wooden blank in, and ensure it is a tight fit.

Then, using your weapon of choice, normally electric drill and hole cutter, have at it! It is certainly best to take many small cuts and allow the area to cool, but eventually you will get half way, at which point you go to the other side and bore in towards the middle again.

Making a hole smaller is much trickier and I chickened out of this when replacing the ball valves on my cockpit drains with Blakes. To judge by the boatyard bill, they did not find it too easy, either!

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[Avocet]

Re: Bigger Hole = easy. Smaller hole = trouble!

How much bigger would you like it? If you're only after an increase in diameter of (say) 5mm, it wouldn't take long with an abrasive flap-wheel in an electric drill. As it's a gradual process, you can stop periodically to see how close you are. You can get flap wheels from DIY shops - get a coarse one - 40 or 60 grit.

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[tcm]

Re: Hole cutting

Agere with Mirelle BUT

I would accentuate the potential problems of enlarging (never mind reducing = even worse)

In virgin materail, a hole cutter invariably uses a central pilot drill for locatiing the external hole cuter itself , for which you sould prepare by making a pilot hole.

If, however, you start of with a larger hole, then there's no easy locator for the hole cutter and the thing can fly about.

So, even if you plan to install the larger item over the small hole ...

1) start the process by bunging the old hole with a wooden plug, fairing off the plug (probably on the exterior) and then drilling a pil;ot hole into that plug.

2) Protect the extrnal surface, outside where the hole should be with a generous layer of gaffer tape strips. This guards against damage caused by any "dancing" or breakage of the tool.

3) Lubricate with dipping the drill piece (especially the big external cutter which run s at high speed) in a bowl of light oil occassionally

4) You need a decent drill with good speed controls, to allow the cutter to rotate at sensibly (low) speed, perhaps rent a 110volt unit. A £20 Black and decker screamer wil not do.

5) As the hole progresses, the risk of the cutter jamming increases. Keep thumb out of the dril (so don't "pistol grip" ), keep everthing lubricated wear goggles.

6) If you have a drilling jig, this will ensure that the drill stays on line, not weavering about making the hole larger or perhaps jamming the cutter. Setupa sight (pieceof carboard atthe side and beyond the drill, so you have something to keep the thing on line.

7) In a thick or very expensive hull, or with larger diameters, or if you really don't fancy it consider hiring a specialist drilling company, who drilll large diameter holes all the time. You will find them under "diamond drilling". You specifically want them to set up a jig to ensure a tight fit. Itneedn't be super-expensivbe as they are generally aimed at the building trade, not the marine retail market.



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[Avocet]

Re: Hole cutting

Do you really need that accurate a fit on diameter? Most skin fittings I've seen come with a generous flange on the outside and a nut with an equally generous flange on the inside! I think it would be better to have the hole a bit too big and make sure that the exposed laminate edges were well sealed with gelcoat or epoxy than to have a tight fit. You can always bed it into the hull with a sealant.

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[burgundyben]

Even Better...

...I had to enlarge some holes on the Fablon Express, here's what I did.

I selected a hole saw that was the size used to cut the hole that was already in the hull, found a scrap peice of plywood, 1/2 inch thick. I used the selected hole saw to cut a hole in the scrap ply, took the round bit from the middle of the hole saw and glued it onto another section of the scrap ply.

This gave me a piece of ply about 6 inches square with a round bit stuck on that had a pilot hole in the middle.

A mate went under the boat and placed the round stuck on bit into the existing hole thus filling the existing hole, I went inside the boat with the drill and hole saw of the size I required, used the pilot hole in the middle of the plywood to centralise the drill whilst cutting the new hole, mate under boat held the plywood up in place.

Bish bash bosh.

<hr width=100% size=1>Sod the Healey - I think I'll buy an E-Type.

 

[tcm]

Re: Fablon Express

sounds very good.

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[AndrewJ]

I did something a bit different in putting in my new depth sounder. I filled in the existing hole and used a depth sounder that
worked thru the hull. Of course the hull is FRP, not metal. and it seems to work well, even thru the bottom paint.

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[richardandtracy]

Much, much better idea.

No holes = no possibility of leaks.

Regards

Richard.


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[MrFish]

I replaced a Standard Horizon depth sounder with a Navman, and found the units to be the same diameter. There seems to be an industry standard, as the speed log unit was the same diameter as well. You may well find transducer instalation instructions on the company web site, which may let you decide on one brand over another based on ease of instalation!
All the best

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