Thru-hull replacement and hull thickness

Jan 11, 2014
11,321
Sabre 362 113 Fair Haven, NY
I'll either burp the strainer when I'm in the water, or (more likely) just pre-fill it with fresh water before launch. I still have lots of engine maintenance to do (clean out the heat exchanger, replace anti-freeze, etc.), so I may even fill the hoses up with water from the top. (Already cleaned and re-impellered the pump.)
Since your strainer is below the water line, as soon as the pump starts water will be flowing. Just the water pressure will flood the hose and most if not all the of the strainer. Once the pump starts spinning water will enter of its own accord. This is different when the strainer is above the water line. The pump has to suck a lot of air to pull the water up into the strainer and then down into the engine. In this case once the pump is flooded a siphon will form and the pump will always be pushing water.
 

Mr Fox

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Aug 31, 2017
204
Marshall 22 Portland, ME
BTW, Groco recommends the strainer above the waterline.View attachment 178311
Most definitely, less fittings below waterline means less potential boat sinking leaks. If it’s a unit designed for above the waterline installation I personally would follow the manufacturers instruction, or install one designed for below waterline use. Below waterline unit has to deal with water pressure from the seacock when the engine isn’t running.
 
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Jun 25, 2004
475
Hunter 306 Pasadena MD
Since your strainer is below the water line, as soon as the pump starts water will be flowing. Just the water pressure will flood the hose and most if not all the of the strainer. Once the pump starts spinning water will enter of its own accord. This is different when the strainer is above the water line. The pump has to suck a lot of air to pull the water up into the strainer and then down into the engine. In this case once the pump is flooded a siphon will form and the pump will always be pushing water.
Yep: the only reason I might pre-fill it with water is because I've got nothing better to do ahead of time. It's always a little hectic when we launch, so I prefer to have less to think about. Just have the engine seacock open, go in the water, quickly check everything to make sure nothing is letting water in that's not supposed to, start the engine, check again, and go.
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
Most definitely, less fittings below waterline means less potential boat sinking leaks. If it’s a unit designed for above the waterline installation I personally would follow the manufacturers instruction, or install one designed for below waterline use. Below waterline unit has to deal with water pressure from the seacock when the engine isn’t running.
When the engine isn't running, the seacock is closed. Always. I don't think this is rocket science: if this strainer couldn't handle the pressure of being 1 foot below the waterline, it wouldn't be worth much, would it? It's a _very_ solid piece of gear, unlike the plastic Sherwood strainer which came installed on the boat, hanging off 6" of brass pipe which was screwed directly into a ball valve which was mounted on the thru-hull using incompatible threads (straight screwed into tapered), which provided a wonderful lever arm for breaking off the thru-hull. And frankly, even the Sherwood strainer performed well for 15 years. I have confidence that the new installation will be fine.
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
Just for interest sake: here's the difference between the old brass fitting (5/8" hose barb to 1/2" MPT) used on the outlet of the strainer and a new bronze fitting by Buck Algonquin. BTW: this was pretty much the only bronze fitting I could find for these in/out sizes. The difference in thickness on the hose barb end is probably much more than it is on the MPT side.
fittings.jpeg
 

Mr Fox

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Aug 31, 2017
204
Marshall 22 Portland, ME
You are absolutely correct- it’s an unlikely risk of a leak; you’d have to say not tighten the plastic cap or drain plug quite enough and also forget to close the seacock to do any harm. I’m not meaning the basket is going to explode or the drain plug’s gonna launch across the engine bay :)

I personally like to eliminate as many of those what if (however unlikely) scenarios as possible, but I’m pretty uptight about safety as I have little kids (which means dealing with any situation on the boat becomes 50 times harder). If you are cool with that setup, which definitely seems reasonably safe, awesome and enjoy the sailing! Nice job on the install too btw, looks great.
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
You are absolutely correct- it’s an unlikely risk of a leak; you’d have to say not tighten the plastic cap or drain plug quite enough and also forget to close the seacock to do any harm. I’m not meaning the basket is going to explode or the drain plug’s gonna launch across the engine bay :)

I personally like to eliminate as many of those what if (however unlikely) scenarios as possible, but I’m pretty uptight about safety as I have little kids (which means dealing with any situation on the boat becomes 50 times harder). If you are cool with that setup, which definitely seems reasonably safe, awesome and enjoy the sailing! Nice job on the install too btw, looks great.
Well, "the basket is [not] going to explode or the drain plug’s gonna launch across the engine bay" was pretty much my point :). For every upgrade I'm making, I'm trying to think it through as carefully as I can, and vet it here on the site. But there comes a point where you need to decide and get it done. Looking at my engine room today, I don't think it would be possible to mount this above the waterline unless I put it in the companionway. Which would be... you know... awkward. So it is where it is. And thanks!
 
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