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How to make a 1/2 through hole a 1 1/2 through hole?

6K views 44 replies 23 participants last post by  oaklandsailor 
#1 ·
Hi,
We have a ½” through hole and it is above the water line. It is for waste discharge. We want to replace it with a 1 ½ inch through hole.
How would be the best way to make the new hole?
Remove original through hole.
It leaves a hole in the boat.
Now how to make it the right size for a 1 ½ through hole?
Use a hole saw, but how to get it started? Need a drill bit in center but nothing to sink the drill bit into.
Maybe put a small piece of plywood over hole and fasten with screws then use hole saw?
Which side to drill from so it does not wreck the gelcoat?
Any better ideas please?
Thanks,
Chip
 
#2 · (Edited by Moderator)
I have used your idea of putting a backing plate behind the hole I want to enlarge. It works pretty well. I would start the hold from the side you want to protect. After getting the drill bit started and through the backing plate run the hold saw in reverse until you get through the gel coat. This should keep the gel coat from chipping.

The other option (if you don't care how clean the hole looks) is to use a RotoZip or Dremel and free hand the hole enlargement. This will create lots of dust so I would tape a box over the hole on the inside of the hull to catch most of it.
 
#4 ·
Maybe put a small piece of plywood over hole and fasten with screws then use hole saw?
I would try this

Which side to drill from so it does not wreck the gelcoat?
from outside in just enough to start the new hole, then remove the ply backer and finish it off
 
#5 ·
I would probably just drive a plug in the hole. Just something to hold the bit while you get it started. Wood or plastic will work OK. If you have time you could use thickened epoxy but that is overkill. Depends on what you have handy.Drill from both sides, just a little from the inside and finish from the outside.
 
#6 ·
I second offsetting the hole center to cover the existing hole yet bite the centering bit into material. With 1 1/2" hole ... center at 3/4" and a pre-existing hole of 1/2" you should have a good 1/4" of wiggle room.

Also, I agree with running the hole saw in reverse for a thickness to get through gel coat (and even first layer of cloth would help). Also, applying tape (ie painters tape) over the surface and cutting the hole through it may help.
 
#11 ·
What he said
 
#10 ·
A couple of questions first—

What do you mean the through-hull is for waste discharge? Is it a bilge pump through-hull or a black water tank pumpout through-hull?

Where on the boat is it located—the transom, the hull topsides?

As for drilling the hole... filling it and then drilling the new hole is one way. Another is to drill a hole through a piece of 3/8" plywood and then attach the plywood to the hull and use it as a "guide" for the hole saw.

Running the holesaw in reverse will allow you to cut the gelcoat without chipping it much.
 
#12 ·
It is the holding tank pup out through hole for the macerator

A couple of questions first-

What do you mean the through-hull is for waste discharge? Is it a bilge pump through-hull or a black water tank pumpout through-hull?
It is the holding tank pup out through hole for the macerator.

A couple of questions first-
Where on the boat is it located-the transom, the hull topsides?
Just above the water line on the port side by the salon.

For seating the through on the out side should I use 3M 5200?
I used 3M 5200? before on a through hole but am thinking of something a little less permanent.
Thanks,
Chip
 
#13 · (Edited)
There are very few places I would use 5200 on a boat this is not one of them...I think you should have to have a licence to buy the junk...:D

Maybe for mounting your seacock backing plate but not for bedding the mushroom head through hull fitting itself.
 
#15 ·
using a small hole saw inside a big hole saw on the same mandrel is fine, except that a) depending upon the quality of your hole saw set, the mandrel may not accept two saws at once, and b) if you size them carefully, you may find that the small hole saw will not be proud of the larger hole saw, which leaves you right back at square one.
 
#17 ·
Saildog...too funny...your red and blue oversize writing is exactly what I though when I read the discharge was above the water line. I was picturing Wile E Coyote with a clothespin on his nose hitting the Acme switch and discharging wondering why it still smelled when he sailed away from the mess.

Best scenerio....head to holding tank..at the bottom of the tank where your out put usually is put brass valve which closes so the s...t stays in your tank and doesnt sit in your lines until you want to pump out ...after that a Y valve..one side goes to the deck pump out and the other to the macerator and then to the thru hole under the waterline.

The trick with the valve at the bottom keeps your lines clear and will help them last longer ( Its a ***** bending and replacing the good sanitation hose).

Dave
 
#18 ·
There was a article in one of my sailing mags recently, I think it was Good Old Boat? IF, a big if, I remember right, the suggestion was to cut a hole in a piece of plywood using the old size, in your case the 1/2", then put the cut piece in the new hole saw, I guess it acts as a guide. I have not done this, and would be scared sh&tless doing to a hull of any boat (except a maybe a Telstar 28) so maybe try it several times on something else first or do what others have suggested. BUT I have to echo Sailing Dog...why the heck would you want it above the waterline? So much for lunch ;)
 
#20 · (Edited)
Hi,
Made a mistake.
The hole size is 1” not ½”.
The through hole is still in the boat so I am not exactly sure of the size. A 1” hose fits over it.

The new hole size will need to fit a through hole that a 1 ½ inch hose fits over so I am thinking a 1 ½ through hole.

The same situation still exists and all the ideas are still the same I think.

The macerator through hole is located at the waterline. I can bend over the dock and put my hand up against it, as I have done it when checking the macerator. No waste would run down the side or at least only an inch if it did. I cannot remember if it is at the waterline or part is under water. It may even be under water after we get to cruising with all the gear. We macerate when sailing. We are moving so it does not catch up with us. We did it once heaved to and never again, that was on our old Catalina 30 and the through hole was under water but still the odor was bad.

So I could see that when cruising we may be at anchor and need to pump out so underwater would be better.

To move the through hole below the water line I would need to drill yet another hole in the boat. Leave the one that is there because to take out the through hole and fill the hole and re-do the waterline is a lot of time\work and we have way to many other projects going to take that on. Besides our sh… don’t stink!

The toilet out through hole is in a bad location, under the master bunk and hard to get at. We do not use it. We put in all new waste plumbing and holding tank and toilet. We use fresh water and the holding tank.

I had never heard of the “Oops Arbor” but just looked at one on Amazon and looks like it will do the trick. I am definitely getting that tool. Seems like the answer. I am not sure if my hole saws will work with two together.

There have been a lot of good ideas and I am glad I asked.
Thanks,
Chip
 
#23 ·
Not kidding

You must be talking about the through hole under water?
Not kidding.
I have changed a few or more through hole valves that are below the water line, no problem. I also know some dock mates that have installed some through holes below the water line while in the water. I do not see the big deal? You're not going to sink. Ok the insurance company may not like it.
Chip
 
#26 ·
I would highly recommend hauling the boat if you're going to be putting in a new 1-1/2" through-hull.
 
#27 ·
I would be very interested in a Video!
 
#28 ·
sailingdog said:
Why would you want a holding tank macerator pump out ABOVE THE WATERLINE... Do you really want/like having a stream of **** running down the side of your boat???
I hear ya, you don't want to pollute. That's why on my boat, I ran a hose from the macerator up to spreader-level on my mast, with an aft-facing shower head attachment. Keeps it all in the cockpit.
 
#29 ·
That certainly explains why you smell the way you do.... :D :laugher :laugher :laugher :laugher
 
#32 ·
OK I asked at the dock last night

OK I asked at the dock last night.
There are two people on my dock who have put under water through holes in their boat while in the water. One a power boat the other a sail boat. They said it is no problem.
You need two people.
One in the water one in the boat.
Persons in the boat drills a pilot hole.
Person in the water puts a plunger or other suction cup over the area.
Person in boat drills the hole.
Person in water puts in through hole.
Done
Add valve etc.
Hope this helps,
Chip
 
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