Cutting a bigger hole for a Log.

[dolabriform]

Hi all

I'm going to replace my Nasa Log with something better for a number of reasons, but the current hole is not big enough to take an Airmar DST800 which is my preferred option.

The yard have suggested that I file out the hole ( currently 41mm but needs to be 51mm), as a hole saw won't have anything to guide the central drill bit and will skip all over the place.

This is obviously going to be hard work, and so I thought about screwing a piece of half inch ply to the inside of the hull, to give something for the drill bit in the centre of the hole saw to work with. The boat is a Leisure 23 SL so the hull is quite ( very ) thick.

Any thoughts folks?

Thanks

David

 

[Motor_Sailor]

That could well work, but I use one of the soft wood plugs; bang it into the hole, trim it off if necessary, mark the centre and drill away with the 51mm hole saw.

If you don't want to use one of your 'best' bungs, then get a piece of 2x2 and whittle one with a knife. It only has to be good enough to jamb securely in place - it doesn't have to be waterproof.

 

[knuterikt]

I used a smaller diameter hole saw to cut a plug with center hole fitting inside the existing tube. Adjusting outer diameter with gaffer tape to get a snug fit. Inserted this plug into the old tube and used it to cut the flange of the old pipe and the hull. Replaced it in less than 30 minutes.
Plug was prepared inn advance.

 

[Lodesman77]

Just file it

 

[noelex]

Some holesaw spindles will allow you to mount two holesaw blades.

The inside one needs to match the existing hole size and will keep everything centred. The larger, outside, holesaw will cut a new hole.

 

[ithet]

I did this. Jammed a prop so its top was flush under the existing existing hole, which gave me something to centre the hole saw onto.

Drilled the hole from the inside.

 

[lpdsn]

That could well work, but I use one of the soft wood plugs; bang it into the hole, trim it off if necessary, mark the centre and drill away with the 51mm hole saw.

I have to do this sometime in the next year or so and that was my plan.

 

[yoda]

Some holesaw spindles will allow you to mount two holesaw blades.

The inside one needs to match the existing hole size and will keep everything centred. The larger, outside, holesaw will cut a new hole.

Alternatively use a bolt to hold the 2 together and use it just enough to score the new hole such that a single hole saw will run in the grove without the need for a centre.

 

[Teko]

Only one solution really. Place the larger please on the the pilot bit followed by the smaller one. The smaller one will fit in the existing hole and allow the larger one to cut a new hole the correct size. Done it many times kitchen fitting

 

[fisherman]

Only one solution really. Place the larger please on the the pilot bit followed by the smaller one. The smaller one will fit in the existing hole and allow the larger one to cut a new hole the correct size. Done it many times kitchen fitting

That's a neat answer, I always bang in any old bit of wood in GRP, not much good for a kitchen.

 

[earlybird]

I'd file it but a decent sized file is quite expensive if you haven't already got one. I once enlarged a hole in my deck with an abrasive flap wheel. That worked quite well.

 

[fisherman]

I did a hole in wood with a thole pin wrapped in wet and dry.

 

[dolabriform]

I'd file it but a decent sized file is quite expensive if you haven't already got one. I once enlarged a hole in my deck with an abrasive flap wheel. That worked quite well.

I don't have a file and the grp is well over an inch thick, so if I can avoid 3 to 4 hours on my back under the boat I would prefer it.

I thought of using a Dremmel, but I think that would be really slow going as well.

 

[Fr J Hackett]

Some holesaw spindles will allow you to mount two holesaw blades.

The inside one needs to match the existing hole size and will keep everything centred. The larger, outside, holesaw will cut a new hole.

That's a neat answer, I always bang in any old bit of wood in GRP, not much good for a kitchen.

Starrett hole saws make an arbour that you can mount two cutters the smaller one fits the hole and the larger cuts the new hole, I have done it several times.

 

[Motor_Sailor]

. . . so if I can avoid 3 to 4 hours on my back under the boat I would prefer it. . .

That's why you roughly shape a soft wooden plug, bang it in, trim it down if necessary and use your standard 51mm hole saw.

We did it day in, day out at the boatyard: it's cheap, simple and you will have it done in under 15mins from start to finish. You can also move the axis off centre if that helps position the new fitting.

 

[earlybird]

I don't have a file and the grp is well over an inch thick, so if I can avoid 3 to 4 hours on my back under the boat I would prefer it.

I thought of using a Dremmel, but I think that would be really slow going as well.

You're right dismissing a Dremel, wouldn't pull the skin off a rice pudding! However, a big, say 14", half round bastard file will shift GRP surprisingly quickly. Job would be minutes rather than hours.

 

[fisherman]

Blade type cutter, if big enough, dress the cutting edge first. Plug the hole, the blade cutter will simply cut all the plug away til it's in the grp and you are home and dry.

 

[strawbs]

When I did this I drilled through the center of the old log for the pilot hole. It wasn't working anyway and was easier than creating a plug of the same size

 

[peteK]

A jigsaw with a narrow blade and finish it off with a file or if no file 60 grit around some dowel.

 

[fisherman]

A jigsaw with a narrow blade and finish it off with a file or if no file 60 grit around some dowel.

Both difficult with inch thick GRP, as the OP has.