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View Full Version : Tips for boring out 3/4" drain thru-hull to fit a 1" thru-hull



mnpracing
08-15-2011, 01:30 PM
I currently have 1" drain lines on my rear bags but still have the 3/4 in thru-hulls. I have two questions that I'm pondering: 1) how to enlarge the hole to accept the 1" thru-hull. Since there's already a hole there, the pilot bit for a hole saw has nothing to guide it. 2) It is currently 3/4" for only 6 inches right at the fitting itself. Is this really restricting flow significantly?

jmvotto
08-15-2011, 01:53 PM
its for a drain line i would not mess with it. or wake makers has a commonsize thru hull, they may work for ya.

http://www.wakemakers.com/common-thru-hull-1-inch-fitting-ss.html

cab13367
08-15-2011, 03:05 PM
I currently have 1" drain lines on my rear bags but still have the 3/4 in thru-hulls. I have two questions that I'm pondering: 1) how to enlarge the hole to accept the 1" thru-hull. Since there's already a hole there, the pilot bit for a hole saw has nothing to guide it. 2) It is currently 3/4" for only 6 inches right at the fitting itself. Is this really restricting flow significantly?

Mike,

So you have a 1" drain hose that mates up to a 3/4" thru hull? I would run a simple test to see how much the difference really is. I would do this:

1. Disconnect the hose at the thru hull and remove the thru hull. Fill the rear sac full.
2. Drape the drain hose over the transom and reconnect the thru hull to it.
3. Get a 5 gallon bucket or a cooler of known capacity and place it on the swim platform.
4. Hit your empty switch and time how long it takes to fill the bucket or cooler.
5. Refill the rear sac and remove the thru hull so your 1" hose is emptying directly into the bucket or cooler. Time how long it takes to fill.

Make sure you keep everything the same other than the thru hull on and the thru hull off. Now extrapolate the results for the capacity of your rear sac - how much time is saved with the 1" hose vs the 3/4" thru hull? Then you can decide if the extra time is worth the time and effort to change out the thru hull with 1".

And post your findings here!

Al

mnpracing
08-15-2011, 03:27 PM
Mike,

So you have a 1" drain hose that mates up to a 3/4" thru hull? I would run a simple test to see how much the difference really is. I would do this:

1. Disconnect the hose at the thru hull and remove the thru hull. Fill the rear sac full.
2. Drape the drain hose over the transom and reconnect the thru hull to it.
3. Get a 5 gallon bucket or a cooler of known capacity.
4. Hit your empty switch and time how long it takes to fill the bucket or cooler.
5. Refill the rear sac and remove the thru hull so your 1" hose is emptying directly into the bucket or cooler. Time how long it takes to fill.

Now extrapolate the results for the capacity of your rear sac - how much time is saved with the 1" hose vs the 3/4" thru hull? Then you can decide if the extra time is worth the time and effort to change out the thru hull with 1".

And post your findings here!

Al

Al, thanks for the idea. I'm going to try that next time out. Right now it's 1" up to the thru-hull, then I have a reducer on it to mate the hose to the thru-hull.

moombadaze
08-15-2011, 07:12 PM
I was able to just replace the 3/4 with a 1" thru hull fitting--no grinding or anything

maxpower220
08-15-2011, 09:58 PM
You can "fill" the hole with a piece of cork. Then, start your hole with your saw and you have material to set your centerpoint. The cork grinds away easily and "perfect" center isn't needed in this case.

NCSUmoomba
08-15-2011, 10:13 PM
You might could try using a step drill bit, but it may not work in fiberglass. The cork sounds like good idea.

mnpracing
08-15-2011, 11:04 PM
I was able to just replace the 3/4 with a 1" thru hull fitting--no grinding or anything

haha, I guess I should try that first....

kaneboats
08-16-2011, 01:18 PM
You can "fill" the hole with a piece of cork. Then, start your hole with your saw and you have material to set your centerpoint. The cork grinds away easily and "perfect" center isn't needed in this case.

Somebody took my answer already. Lots of smart folks on here.

mnpracing
08-18-2011, 10:03 AM
I removed the 3/4" drain thruhull from the port side, and the 1" won't fit unless I enlarge the hole. The odd (frustrating) thing is the the edges of the hole were very jagged. It took about 20 seconds with a piece of 100 grit to smooth down the gelcoat and chamfer the edges. Not sure yet whether I'll enlarge the hole. The 1" thru-hull I have is almost 1" ID, where the 3/4" stock thru-hull is barely 1/2" ID, so the difference in flow should be substantial. I'll probably test the times next time I'm out to see if it makes enough difference to me.

mnpracing
08-19-2011, 02:17 AM
Well I did it tonight. I was tinkering in the garage and was looking at the drain thru-hull on the port side and was thinking about how to bore that hole out. I used Maxpower220's advice and put a cork in the hole, which was about a 1-1/4" hole. I needed 1-3/8" to fit the 1" thru-hull, so really not much, just a 1/16th around the whole hole.....

I cut the stopper so that only about 1/4" stuck out of the hole, then started the hole saw (a carbide type with abrasive teeth, vs the cutting teeth) by hand. It fit snugly over the stopper so I twisted it a bit more until it met with the gelcoat. While holding a beer in one hand I just turned the hole saw by hand until I was through the gelcoat. I kept turning by hand until I was probably 1/16th into the fiberglass. Then I pulled out the hole saw and the stopper, and used sandpaper to chamfer the edges of the gelcoat. Then I reinserted the stopper, and put the hole saw in my cordless drill, and drilled very slowly until I went through. I was surprised at how thin the fiberglass was, only about 1/4". The gelcoat was about 1-1.5mm thick. Then I trimmed the carpet fibers back and that was it. Here's some pics:
http://i848.photobucket.com/albums/ab49/mnpracing/IMG_3762.jpg

http://i848.photobucket.com/albums/ab49/mnpracing/IMG_3759.jpg

http://i848.photobucket.com/albums/ab49/mnpracing/IMG_3755.jpg

http://i848.photobucket.com/albums/ab49/mnpracing/IMG_3760.jpg

jmvotto
08-19-2011, 08:28 AM
Great way to do that... where is the pic of the one inch thru hull finally installled?

wolfeman131
08-19-2011, 08:31 AM
Where is the pic of the beer?

mnpracing
08-19-2011, 08:49 AM
Great way to do that... where is the pic of the one inch thru hull finally installled?

the last picture above is the 1" thru hull. I should have stuck the 3/4" inside the 1" for the picture. The ID of the 3/4" was actually 1/2", and the ID of the 1" is 7/8", so quite a difference.

jmvotto
08-19-2011, 09:50 AM
the last picture above is the 1" thru hull. I should have stuck the 3/4" inside the 1" for the picture. The ID of the 3/4" was actually 1/2", and the ID of the 1" is 7/8", so quite a difference.

i was expecting the chrome pic 1" looks great though. i would not have had the patience to hand turn, full power tools here.

maxpower220
08-19-2011, 11:20 AM
Wait..... that really worked????? That's just something I made up.


Glad it worked out. Work smarter, not harder!

mnpracing
08-19-2011, 11:33 AM
Wait..... that really worked????? That's just something I made up.


Glad it worked out. Work smarter, not harder!

haha, it worked really well in fact.....