Where to drill thru-hulls

[alanmoor]

Maybe I'm terrible at searching, or maybe people don't drill holes in the bottom of their boat.

I have two projects (that might start as soon as this weekend if parts arrive). One is to install a "Clipper Duet Instrument" which is a combo depth/speed meter. I have both of these now but neither work. The sensors are attached to the transom. The meter I'm getting has thru-hull transducers.

The second project is to install a washdown pump and plumb it to an alternate connection on my kitchen sink and the head, plus make a connection to a hose fitting on the transom.

I hear that drilling holes below the water line can cause a problem on boats, something about letting lake/sea water inside the boat. However, I talked to my brother-in-law about it, who has been a professional captain for years and even was a project manager for a boat builder, and he said it's no problem as long as you use the right sealant. He said since it was in the barn I should drill a few extra holes just for the heck of it. Anyway, I think I'm over the fear of drilling holes in the bottom of my boat. I'm potentially looking at 3 thru-hulls, one for each sensor, and one for the washdown. I believe I can drill them under the sink right next to the ballast tank, below the grey water discharge.

Realistically, I doubt I'm drilling anything this weekend, so I'm seeking advice on placement of my future leaks (ok, so I'm not over it).

This is on a 1996 26X.

[Québec 1]

The most wonderful thing about my 26M is that there are no holes under the hull for water to leak in! Last summer I watch a real sailboat sink in the marina cause his bilge pumps stopped working also was docked by a guy with a 22 catalina who got water in his cabin cause his swing keel thing started leaking.
Q1

[RobertB]

I installed a washdown on my under the aft table seat about 6-10 inches outboard of the water ballast tank. The hull here was close to 3/4 inches thick (no need for doubler). Used a plastic thru hull from West Marine with a ball valve on top. This is the location that Mike Inmon's shop recommended.

As far as the sensor holes go, do the sensors need thru hull holes or just the wires?

[mastreb]

Yeah, I very nearly sank my Columbia Sabre when a passenger in the cabin somehow opened a valve to a through-hull. If my brother-in-law hadn't found the valve and figured out what needed to happen, we would've sunk about 20' from shore. As it was we only had about six inches of aboveboard left when he got it figured out.

I'm sure it can be done correctly and safely, but no through-hulls for me, thanks.

[RobertB]

I thought the washdown installed is pretty safe - through-hull fitting to valve (kept closed when not in use), to pump, to fitting high in motor well (way above water line). As long as ystem is intact, no chance of flood. If anything after through hull is open/broken, valve should address issue. If valve breaks off, plug it or get wet (the boat is supposed to float if flooded - right ). Actually, way it is installed, even if hose comes off valve and valve is open, should be above the water line.

Besides, the dang boat leaks more thru the rudder posts than it is ever likely to thru the washdown setup.

In light of leaking thru rudder posts, I just bought some Coreplast sheets I plan to make false floors in the side compartments (kitchenette side primarily). This is a lightweight 1/4 inch thick corrugated plastic sheets and affordable at only $18 per 4x6 foot sheet.

[davidbourne]

I don't think I will be drilling any below water line holes. If it works well, let us know.

I googled coreplast and it seems like good stuff. Especially if you need a board, vs a more flexible material.

http://www.google.com/search?q=Coreplast%20sheets

But there is another material that's often used to help things dry out. More of a weave pattern with holes, like some garage flooring.

What's that stuff called?

[Kittiwake]

I'm 100% with Québec 1 and mastreb!
One of the nice features about the Mac is that it has essentially no thru-hulls below the waterline. It is true that, if all goes according to plan, thru-hulls can be OK below the waterline ... but in this world it is pretty darn common for things not all to go according to plan.
I worry quite enough about the thru-hull in the 26M transom (sink and motor-well drain) which is just above the waterline. To me it seems madness to add a below-waterline thru-hull to a Mac unless there is some awfully compelling reason for doing so ... and for me, wash-down pumps and depth sounders are not in the category of awfully compelling on a Mac.
Of course some of us worry more than others ....
Kittiwake

[Herschel]

I bought my 1998 26X used and the previous owner drilled three "through hulls", one for each transducer and one for a wash down "blaster" pump system. The inlet for the wash down is fitted with a Y valve internally to also flush the electric toilet, which then goes to a holding tank. That intake is on the starboard side amidships under the table with access from aft seat. Shortly after I got the boat, I noticed that when I motored at cruising speed, there was a small leak at the inlet when the valve was opened, and water would slowly build up in the bilge. I have since just shut the valve and never open it. I use fresh water from the head faucet to flush the toilet, instead, and I never use the wash down pump. It never worked so I never got used to using it. The two transducers are placed directly under the main aft ballast tank, one to port and one to starboard, with PVC conduits glued in the ballast tank. I have had problems with one of the PVC conduit connections leaking water from the ballast tank into the bilge. 5200 sealant applied to the area has stopped the leak for the past two years. I would not recommend the technique used by my previous owner for the transducers. I think it is an inherently weak system that will periodically need to be addressed as the years go by. Since the through hull for the blaster/toilet combo is never opened anymore, that too seems superfluous for me. I think, if I had it to do over, I would just get the type of transducers that hang off the stern and avoid the potential for trouble.

[yukonbob]

Water will ALWAYS find a way. May take time but it will eventually find a way. It is the most destructive force of nature.

[Divecoz]

I Have 2 neither has ever leaked .. Both are bronze ...both have ball valves inside . To each his own..

[Catigale]

The reasonable candidates for through hulls on a Mac are intakes for raw water...wash down, head, etc...

For the wash down, insider a transom mount with a pipe that could be simply dipped below the surface for pick up.

Putting in a through hull safely isn't that difficult.....double hose clamps on hoses, inspection protocol, ball valve shut off, and an appropriate size peg to plug it in case of failure.

[Chief Yeoman]

I installed an "inside the haul" depth sounder sensor for my Garmin 421 and it works perfectly.

Drilling holes below the water line is something I would not do unless my life depended on it. No holes - no bilge pumps.

[Gazmn]

Hi Alan,

I've drilled A Lot of holes in my boat. I respect that you're a grown man, Capt of your own ship & destiny; but regarding any holes below the water line, I only have one word of advice...

DON"T

[Russ]

My washdown pump uses a hose that I toss over the back by the engine when I need it. Works great. I put the strainer on the end for weight. No holes.

I wouldn't mount a depth finder transducer through hull. I've installed MANY inside the hull with silicone caulk. Works great.

[ronacarme]

On our 26X, we mounted the depth transducer on the transom with the cable led into the cabin above the waterline. At first it did not work but in time slime built up on the transducer, apparently improving the coupling to the water, and it has worked perfectly ever since!
If I needed a washdown unit, I would get one with an intake hose I could throw over the side.
I would not, repeat not, drill holes or install a thru hull below the waterline on this boat. Not needed and why risk flooding the boat and giving your insurance company a reason not to pay a claim.
Ron