Drilling 3/4" hole in side of boat....Tips/Advice

Tin Man

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Preparing to install a 3/4" 90 degree through hull at rear of boat...... port side, 1-2" from transom, and just below gunnel.
This will be for my 3/4" bilge pump discharge hose.

I am accustomed to drilling holes in fiberglass and wood boats....but not in aluminum boats. I feel as though with wood and fiberglass the repairs are easy for me (if holes needed to be plugged) as I worked with these materials for many years on several boats. No stresss with drilling these holes.
Alum....requires welding for repairs....with which I do not have any experience. This is has led to some anxiousness. I don't plan on making any mistakes, but I guess it's just the thought.

My 79yo dad says not to worry and just drill it, and if there's a mistake, just stop by his place as he has several beer cans and some JB Weld!! :mrgreen:

Any tips or suggestions?
Plan on using a bi-metal 3/4" hole saw on my drill motor.
I will be drilling from outside the hull as there is no way to access from inside.
 

maintenanceguy

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I's prefer a hole saw but a 3/4" standard twist drill will make a perfectly fine hole.

Instead of discharging 2" below the gunnel, why not just discharge over the top of the transom. My bilge pump hose runs up to the top of the transom where I have a 90 degree barbed fitting that points over the top of the transom. Everything is strapped to the inside of the transom with pipe hangers so it doesn't move.
 

MN Fisher

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Tin Man said:
Any tips or suggestions?
Plan on using a bi-metal 3/4" hole saw on my drill motor.
I will be drilling from outside the hull as there is no way to access from inside.

The bi-metal hole saw is a good idea - I actually used a carbide-tipped forstner bit to drill the holes I needed in the F-9 for the live-well inlet/outlet and the bilge outlet.

Use some thin machine oil to lubricate the hole-saw...ya, it helps cut a smoother hole and keeps the hole-saw cooler. 3-in-1 Multipurpose works fine for this.
 

GTS225

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STOP! [-X We're talking about thin gauge aluminum, here. DO NOT use a standard twist drill bit, or a hole saw. Go get yourself a "uni-bit", or what I call a step bit, that covers the hole size you need. Those work quite well drilling holes in sheet metal products. If you want to drill a small pilot hole with a standard drill bit, that's ok, but a hole saw or large twist bit will give you an out-of-round hole, or the twist bit will grab and tear as it goes through.
(As a personal observation, it seems that with all our technology, "they" could make a hole saw that runs true. :x )

Uni-bit-----> https://www.harborfreight.com/2-piece-titanium-nitride-coated-high-speed-steel-step-drills-96275.html?ccdenc=eyJjb2RlIjoiMzMzMzczNDYiLCJza3UiOiI5NjI3NSIsImlzIjoiMTMuOTkifQ%3D%3D&utm_source=google&utm_medium=cpc&utm_campaign=17426843902&campaignid=17426843902&utm_content=136172011126&adsetid=136172011126&product=96275&store=&gclid=EAIaIQobChMIgN_vqe-i-AIVrXxvBB3Q3Q6REAQYASABEgLG_PD_BwE


You can thank me later.....Roger
 

DaleH

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Just use the hole saw ... I've cut literally 100s of holes in tin boats using such a tool and NEVER got an out of round hole!
 

MrGiggles

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Keep in mind that your 3/4" thru hull likely has an OD of 1". A 1" twist drill is a pretty rare bird, and many step bits do not go up that big either.

A hole saw will work just fine, aluminum cuts easily. If by chance you have a step bit of the appropriate size, they work exceptionally well in sheet metal.
 

FuzzyGrub

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As mentioned, it is probably 1" diameter where the threads and washer are. In tight locations, make sure you will be able to access to tighten the nut down and to a lesser degree tighten the hose clamp.

I think you will be fine with a bi-metal hole saw. I have used "recessed" spade bits, with a small pilot hole. You end up making an aluminum washer. By "recessed", I mean it cuts at the outter edge and tapers away. Do not use the flat, straight style.
 

MN Fisher

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MrGiggles said:
Keep in mind that your 3/4" thru hull likely has an OD of 1". A 1" twist drill is a pretty rare bird, and many step bits do not go up that big either.

A hole saw will work just fine, aluminum cuts easily. If by chance you have a step bit of the appropriate size, they work exceptionally well in sheet metal.

Ya - If it's 3/4" tubing - it's a 1" external diameter...so you need to cut a 1" hole.
 

Tin Man

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Thanks for the suggestions.

I will do so measuring since I just received the through hull. It could very well be a 1" hole that is needed.

I do have a step bit. It would cover the 3/4"-1" hole. I am considering using it, but thought the Bi-Metal hole saw would be more accurate.

I'll have to decide on which to use.

Yes, I will haver a beer....but maybe after.....so I don't %$#$ it up! :mrgreen:
 

Tin Man

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After running hose up to where the through hull would be placed, running the discharge over the transom would work nicely. It's about 6-8" from where the through hull was going to be.

Now just considering these two options......through hull VS over the transom (as suggested by maintenanceguy).

Maybe decision will come to me after a few cold ones...then it won't matter so much! :mrgreen: Hell, it's 11:05AM and already 93F!!
 

DaleH

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You're talking adding ~" more of head to the pump, wher any head reduces efficiency, but that really isn't much.

The thru-hull option is the significantly more elegant or 'Bristol' approach, less 'Bubba'd' (no offense to any Bubbas intended, LOL), but that's just my opinion.
 

MN Fisher

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DaleH said:
You're talking adding ~" more of head to the pump, wher any head reduces efficiency, but that really isn't much.

The thru-hull option is the significantly more elegant or 'Bristol' approach, less 'Bubba'd' (no offense to any Bubbas intended, LOL), but that's just my opinion.

thumbs-up-25607__340.png
 

Tin Man

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DaleH said:
You're talking adding ~" more of head to the pump, wher any head reduces efficiency, but that really isn't much.

The thru-hull option is the significantly more elegant or 'Bristol' approach, less 'Bubba'd' (no offense to any Bubbas intended, LOL), but that's just my opinion.

I agree 100%!!
I drilled it out using my step drill bit. Worked great.

NOTE: Through hull was just set in the hole for measuring purposes...final install not yet completed.

I purchased a low profile Rule pump so that it would fit below floorboards. Hose and wiring will run up against transom, head to port side, and then hose will head up a few inches to through hull.

Pump wiring is headed over to port side as well, as I plan on building a box (will sit on top of rear/port corner seat decks) to house my 9"FF and a small electrical panel with a few switches and a 12V plug. The box idea I found on the new Crestliner tiller models.
 

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FuzzyGrub

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Looks good! Drilling holes in a perfectly good boat can get you nervous.

I'd make an access plate for the pump. Debris always finds its way to it. For me, it is silt and pine needles.

FWIW: I had to bubba style it on a 1448 grizzly. The welded corners and sides made it impossible to get my hand in there, let alone get the nut on and tightened.
 

JL8Jeff

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Make sure you test the final setup with the boat on the trailer. Run the hose until the pump kicks on and you can verify it pumps the water out properly. I've had some setups get airlocked and the water didn't make it up and out of the boat, but the pump just kept running. The angle of the hose could cause that problem so definitely test it out before you're on the water.
 

Tin Man

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FuzzyGrub said:
Looks good! Drilling holes in a perfectly good boat can get you nervous.

I'd make an access plate for the pump. Debris always finds its way to it. For me, it is silt and pine needles.

FWIW: I had to bubba style it on a 1448 grizzly. The welded corners and sides made it impossible to get my hand in there, let alone get the nut on and tightened.

Thanks! It was a little anxious drilling into the hull...I was even considering putting hose over transom, but I said what the heck!!
Glad I did because the hose will exit properly and look much more elegant and bristol, as DaleH suggested!

The floor has a cut out section right above pump...something like 6"x6" cut out. This allows for pump hose and electrical to exit as well as to check on bilge water.
 

Tin Man

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JL8Jeff said:
Make sure you test the final setup with the boat on the trailer. Run the hose until the pump kicks on and you can verify it pumps the water out properly. I've had some setups get airlocked and the water didn't make it up and out of the boat, but the pump just kept running. The angle of the hose could cause that problem so definitely test it out before you're on the water.

Great idea!!
 

1960 yellowboat

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Preparing to install a 3/4" 90 degree through hull at rear of boat...... port side, 1-2" from transom, and just below gunnel.
This will be for my 3/4" bilge pump discharge hose.

I am accustomed to drilling holes in fiberglass and wood boats....but not in aluminum boats. I feel as though with wood and fiberglass the repairs are easy for me (if holes needed to be plugged) as I worked with these materials for many years on several boats. No stresss with drilling these holes.
Alum....requires welding for repairs....with which I do not have any experience. This is has led to some anxiousness. I don't plan on making any mistakes, but I guess it's just the thought.

My 79yo dad says not to worry and just drill it, and if there's a mistake, just stop by his place as he has several beer cans and some JB Weld!! :mrgreen:

Any tips or suggestions?
Plan on using a bi-metal 3/4" hole saw on my drill motor.
I will be drilling from outside the hull as there is no way to access from inside.
Why put yourself through all this grief? attach the bilge outlet to some PVC and route it over the transome. Easy Peasy
 

Vol423

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A couple of ideas and observations:

I use a hole saw to cut through the hull for the through hull. Dozens done and never a problem. Use silicone sealer and stainless hose clamps. Screw the pump to a piece of cutting board (or HDPE), to keep the pump upright and out of the debris. Replacement will be a breeze. If you get vibration, glue the HDPE to the hull with a dollop of silicone sealant.
 
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