Attaching Clamshell
- Thread starter jviss
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I would tend to look here for external strainer advice ................................ Really, just simple logic.
Why I Dislike Like External Strainers
Over the years I have really grown to distrust and dislike external intake strainers of either the scoop type or the non directional round type. The real danger in these devices comes when you have a blockage and can't get to the crud to clean it. They often require a dive over the side with a...
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Thanks, Ralph, but I've read that before and vehemently disagree. He obviously is unfamiliar with the conditions with which I deal, and have dealt with for 22 years.
I've done both, and no external screen sucks where I am. I am tired of cleaning my strainer, at least weekly, of grass, minnows, jellyfish, and other things, which I never had to do with the previous boat which had an external strainer.
I asked for "how to attach," not "should I do this."
As someone on here once said, "Your boat, your choice". Dunno who though 
.
If I HAD to install one, I'd use bronze screws to eliminate galvanic action and lots of 4200 in the holes just for peace of mind. And then wait for the first dry cleaner's plastic bag to come by.
.If I HAD to install one, I'd use bronze screws to eliminate galvanic action and lots of 4200 in the holes just for peace of mind. And then wait for the first dry cleaner's plastic bag to come by.
That's what I was thinking, 'though I'm not sure I'd use 4200. I haven't even seen that around lately!As someone on here once said, "Your boat, your choice". Dunno who though
If I HAD to install one, I'd use bronze screws to eliminate galvanic action and lots of 4200 in the holes just for peace of mind. And then wait for the first dry cleaner's plastic bag to come by.
I was thinking I'd use a drill bit collar and drill for a tap, then use a bottoming tap bronze oval head machine screws. I've tapped FRP before, it works quite well.
By the way, I think I know to whom you refer here. I always took that phrase to be insulting, a snide remark, as if to say, indirectly, "you're a jerk, but do what you want."As someone on here once said, "Your boat, your choice". Dunno who though
Snide:
"A snide comment or remark is one which criticizes someone in an unkind and often indirect way. "
Ouch. Don't know if I'd try to cut machine screw threads in FG. Just too shallow for my liking. If you do feel so compelled, go for a coarse thread to be sure you have something to grab on to. Also, be sure to use a longer (rather than shorter) screw, so you're increasing the grabbing surface area.
Haven't bought any in quite some time but I always see it in the big box stores along with all of 3M's other potions so it's still out there.
Never had a need to get that fancy. Always used nutted machine screws right through the FG above the water line.
I installed one using screws and butyl while snorkeling once. That was a decade ago.
I think the strainer/no strainer is both regional and application specific.
(I have done a LOT of strainer and bar grate design in refinery and waste processing applications. Cleanability is always key. Bar grates are best for rought straining and any application where self-cleaning is needed.)
I think the strainer/no strainer is both regional and application specific.
- Grass and jellies can clog internal strainers every 5 minutes in some places, where they will just slide off an external strainer.
- Some places minnows will swim in and get stuck at the first turn. Been there, done that.
- It depends on whether it is underway or at the dock, continuous vs. intermittent. Underway doesn't generally need one; the flow keeps the debris out. Intermittent, like a head intake, isn't a big deal either way. But continuous at the dock (AC) can be a bugger in grass/jelly areas, particularly if the wind or current stack the grass in your corner.
(I have done a LOT of strainer and bar grate design in refinery and waste processing applications. Cleanability is always key. Bar grates are best for rought straining and any application where self-cleaning is needed.)
My slotted screen is integral to my through-hull. If I was installing this over an existing through-hull, I would not be thrilled about putting six screw holes my hull.
This may be unconventional, but why not glue it in place with Fast Cure GM 5200? It’s actually an adhesive with sealant properties. Sand off any bottom paint under the flange for solid adhesion, clean both surfaces with acetone and hold it in place with strong tape until the 5200 cures. I usually very adamantly say never use 5200 for anything you might ever want to remove, but surface mounted on the underside of the hull, you should be able to get a knife edge under the flange if you ever need to remove it.
If you go with screws, bronze makes sense, with lots of 4200, and think about whether you really need six of them.
This may be unconventional, but why not glue it in place with Fast Cure GM 5200? It’s actually an adhesive with sealant properties. Sand off any bottom paint under the flange for solid adhesion, clean both surfaces with acetone and hold it in place with strong tape until the 5200 cures. I usually very adamantly say never use 5200 for anything you might ever want to remove, but surface mounted on the underside of the hull, you should be able to get a knife edge under the flange if you ever need to remove it.
If you go with screws, bronze makes sense, with lots of 4200, and think about whether you really need six of them.
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I never took it that way. I took it as an acknowledgement that “opinions on this topic differ”
You can just drill through the hull and use nuts and bolts with sealant. There is another model external strainer that opens for cleaning. That is probably overkill. One issue with installing these separate strainers that go over the standard thru-hull is that the hull is seldom flat creating fitting issues. I like the one piece thru-hull and small strainer model best, but I have the type you are contemplating with the nuts and bolt fasteners. It will not leak if installed correctly.
I'll give you a quick lesson. My sailing buddy and I on different boats transiting the Fox River, WI locks, (when you could) had to wait for the lock to open. On one particular lock he got an engine overheating alarm. Shut down his engine and in the meantime was slowly being swept to the lock overflow, not a great position to be in. He found fresh water snails in his engine intake and was able to clear in time to not get pulled into the overflow. Lesson learned. We both installed the strainer you've shown at our next winter haul out. That was 30 years ago.
Now it gets fuzzy, do you face the strainer into the prevailing flow of water or away from? I've seen and read many accounts, no one unequivocally says one way or the other. I choose away, thinking the water pressure would assure water flow into the engine water inlet and nothing would have a tendency to stay on the filter long enough to embed. I also filled the screw openings with screws, I've seen some that don't. Here it is many years later, I've never had a problem with my intake water. Hope this helps.
Now it gets fuzzy, do you face the strainer into the prevailing flow of water or away from? I've seen and read many accounts, no one unequivocally says one way or the other. I choose away, thinking the water pressure would assure water flow into the engine water inlet and nothing would have a tendency to stay on the filter long enough to embed. I also filled the screw openings with screws, I've seen some that don't. Here it is many years later, I've never had a problem with my intake water. Hope this helps.
Sorry, I should have added that I purchased the strainer that had the through hull treaded section and strainer. The logic is the same if you purchased just the strainer portion.
That's the way I did it. You need really top quality screws because you will probably want to remove this once in a while to clean the volume. Actually a screw with a hex cap so you can put a small wrench on them would be good.
This is from MaineSails Marine How to site:
HYDROLOCK! Cause = Improper Orientation of Scoop Strainer
This owner was the lucky recipient of an engine hydrolock event while under sail. When he went to start the engine a cylinder was filled with water, and water is not-compressible. He though something was wrong with the starter motor, so kept trying, and he eventually burned it up. A dead starter motor on top of a hydrolock.. Cha-ching $$$$$….
“But RC it worked for 6 years with no issues.”
Another way to look at that statement:
“You got lucky for 6 years.”
Yes, a “professional” boatyard did this installation… Apparently no one explained to them that when sailing a scoop-strainer can potentially force water up and over the siphon break, into the water lift muffler, and can eventually back fill a cylinder and cause a hydrolock..
Please let me be very clear on this point:
Raw water pump impellers are not shut off valves!
Impellers do and can leak water past them. Facing a scoop-strainer forward is simply an incorrect installation/orientation for a sailboat. Please, if your scoop strainer faces forward consider;
1- Removing it entirely
2- Installing a non-directional sailboat strainer
3- Reversing it
If you’ve not filled your engine with sea-water, and experienced a hydrolock, consider yourself lucky.
When I put on my clam shells I had the same question. So I visited several boat yards until I found a Hinckley on the hard. All her clam shells faced aft. So I installed mine thusly and never looked back.