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Old 13-01-2014, 11:39   #1
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chimney hole angst!

Okay, I am going to put a five-inch chimney hole into my cabin roof. I am. I mean it this time. I have a jigsaw, removed the headliner and drawn a circle on the fibreglass... I am...

But if anyone can anyone suggest a website to give me more confidence in what I am about to do it would be appreciated.
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Old 13-01-2014, 12:22   #2
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Re: chimney hole angst!

Exactly what are you worried about? Doing the cutting, installing the heat dam, sealing up the core... tell us your thoughts.

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Old 13-01-2014, 13:08   #3
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Re: chimney hole angst!

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Originally Posted by Jim Cate View Post
Exactly what are you worried about? Doing the cutting, installing the heat dam, sealing up the core... tell us your thoughts.
The cutting. It appears fairly straight forward, cutting the hole in flawless glass. But once done, it is very much done.

I'm not sure to what you are referring by a "heat dam", though sealing the wood deck core seems single enough.

My plan is make a series of drill holes at right angles around the circle, connecting them as smoothly as I am able with a jigsaw... once I get over the fear I will discover too late there was something simple I should have done.
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Old 13-01-2014, 13:22   #4
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Re: chimney hole angst!

A website! Really?.............5 inches....You must want to burn wood! I did that once....watch for ants that made homes in your transom, and other ant appealing homesteads within your boats dimensions in the colorful 2014 season to come!
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Old 13-01-2014, 14:02   #5
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Re: chimney hole angst!

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The cutting. It appears fairly straight forward, cutting the hole in flawless glass. But once done, it is very much done.

I'm not sure to what you are referring by a "heat dam", though sealing the wood deck core seems single enough.

My plan is make a series of drill holes at right angles around the circle, connecting them as smoothly as I am able with a jigsaw... once I get over the fear I will discover too late there was something simple I should have done.
A heat dam is some means of insulating the flue from the deck material. Sometimes just an air space, sometimes some form of solid insulation.

With a five inch diameter, you should not need to drill but one hole... then following the circumference around with the jig saw. Likely get a smoother cutout that way IMO.

But you still have not told us what about the project is worrying you... why you want a link to some internet advice?

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Old 13-01-2014, 14:17   #6
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Re: chimney hole angst!

I have a wood/charcoal heater. 3" flue, it is a very straight forward installation. And well worth it for heat and ambiance. The section that goes through the roof is a special section that insulates the heat from the deck, vis air space. I think that part of my flue is 5" I think boring holes in our boat is a terrifying prospect in any case. Goes against keeping the water out. I would use a 5" hole saw, easier to keep vertical and a cleaner hole. Just close your eyes and go for it, well don't actually close your eyes.
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Old 13-01-2014, 14:41   #7
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Re: chimney hole angst!

A hole saw is definitely the way to go. I had to cut a 6"-diameter hole in my cabin top to install a Paul Luke tile fireplace in my prior boat.

Beware, though... you'll need a powerful 1/2"-chuck drill with an auxiliary side handle to cut a hole that size. If the saw "grabs" it can break your wrist if you are not ready for the sudden torque.
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Old 13-01-2014, 15:09   #8
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Re: chimney hole angst!

Hole saw is nice. They seem expensive, but you tend to collect them over the years and they get a lot of use. You will need a 1/2-inch drill. Go slow.

If you use a jig saw, tape the deck to prevent scratching.

My heater experience. It's still doing great.
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I understand the angst. I sailed a whole summer with a cardboard mock-up to make certain I like the location.
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Old 13-01-2014, 15:17   #9
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Re: chimney hole angst!

I triple the hole saw, best way to get an absolutely round / square hole!
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Old 13-01-2014, 15:21   #10
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Re: chimney hole angst!

BTDT. Used a hole saw with so large 1/2" drill but with aide handle. Might be willing to make a deal on the hole saw as I doubt that I'll ever need it again.

Be sure that you want the hole where you've planned. Changed the location of the hole at the last minute and saved myself grief from fitting on the deck.
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Old 13-01-2014, 15:26   #11
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Re: chimney hole angst!

If you use a hole saw, it is almost impossible to keep the bit vertical on a non-horizontal deck. You will have to either put the hole thru a horizontal part of the deck, or build up the deck with a tapered block so that the surface you start the hole saw in is horizontal. If the surface is sloped, then you have to project a circle onto the inclined deck which will not be round viewed from above. So, if the deck is sloped very much, then use the hole saw but be ready to enlarge it with a saw.
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Old 13-01-2014, 15:31   #12
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Re: chimney hole angst!

The hole saw is the way to go if you have or can borrow a big drill. But if you think you're nervous drilling a series of small holes imagine how a five inch bit will twist you into knots! Scary.
If you don't go for the hole saw I suggest going real slow - start with a small hole in the center of the cutout, inspect from above, inspect from below, think on it a while, etc.
Tape up the top and bottom and make sure to catch the fiberglass dust inside the boat with some plastic or a shopvac.
Lots of small holes on the circumference will take time but require less jigsaw work in the end. Take your time.
My opinion - the saw can get you into more trouble than the drill.
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Old 13-01-2014, 15:35   #13
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Re: chimney hole angst!

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Originally Posted by carlylelk View Post
If you use a hole saw, it is almost impossible to keep the bit vertical on a non-horizontal deck. You will have to either put the hole thru a horizontal part of the deck, or build up the deck with a tapered block so that the surface you start the hole saw in is horizontal. If the surface is sloped, then you have to project a circle onto the inclined deck which will not be round viewed from above. So, if the deck is sloped very much, then use the hole saw but be ready to enlarge it with a saw.
It's not THAT difficult unless the slope is extreme. The area of the cabin top where I drilled my 6" hole probably sloped 15 degrees or so. You just need to make sure your pilot drill bit is long enough and that the sides of the hole saw are deep enough to handle the slope. You also have to go very slowly until most of the circumference of the saw is in the kerf.

If there is any significant slope, your insulating fitting isn't going to work anyway without some sort of compensating pad.
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Old 13-01-2014, 17:26   #14
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Re: chimney hole angst!

What Ukeluthier said. Deck would have to have a severe slope before you had to worry about the pilot bit needing to be extended. Don't have to be that careful getting the hole vertical as there will be an 1" of airspace all around.

Deck slopes where the flue is mounted. Had to make up a fairing pad out of 2x teak. Bought a piece of scrap from a local boatwright and then used a belt sander to grind the pad to fit the slope of the deck.
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Old 13-01-2014, 17:33   #15
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Re: chimney hole angst!

While I have no experience with a hole saw in glass, in wood, its extremely important to drill a hole just inside the expected kerf, which will allow the chips and dust to fall through, and prevent the material from clogging the kerf, and dulling the saw before you get through the material you are cutting.
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