Thru-hull replacement and hull thickness

Apr 8, 2010
1,942
Ericson Yachts Olson 34 28400 Portland OR
Our Groco raw water strainer is mounted on a piece of 90 degree angle G10. Please do not keep that long "lever arm" on a pipe on your sea-cock valve. Short piece of wire-reinforced hose is appropriate.
Pix here: O34 - Coupler, Shaft Seal, and Antifreeze

Our boat did not come with a strainer and I originally added a plastic one. Later noticed some small cracks in the housing and replaced it with a "proper" bronze Groco version. Lifting the basket out for cleaning is easy.
 
Jun 21, 2004
2,532
Beneteau 343 Slidell, LA
I replaced all of the plywood backing plates on my '88 Hunter 33.5 after approximately 15 years. The plywood appeared to be deteriorating and delaminating. I took the "El Cheapo" route and simply made new plywood plates and thoroughly coated them with resin before reinstalling with 4200. The original plates were not coated and were not epoxied to the hull. I used a piece of 3/4" plywood and two hole saw blades of proper diameter to fabricate them. As in most production boats, these were not seacocks, only a thru hull fitting with a straight ball valve. Probably cost less than $20 to fabricate all of the plates. I theorized that the original uncoated plates lasted 15 years; therefore, the coated plates would have lasted much longer. I am sure that G10 would be a better material from which to fab the plates; however, the cost would have been much greater and much more difficult to cut and drill.

Interestingly, on my current Beneteau, there are no backing plates. In my opinion, this is not a good place to cut costs. Many of the locations of the thru hulls are places that would entail cutting the liner/grid to allow placement of backing plates and I am not doing that.
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
Our Groco raw water strainer is mounted on a piece of 90 degree angle G10. Please do not keep that long "lever arm" on a pipe on your sea-cock valve. Short piece of wire-reinforced hose is appropriate.
Pix here: O34 - Coupler, Shaft Seal, and Antifreeze

Our boat did not come with a strainer and I originally added a plastic one. Later noticed some small cracks in the housing and replaced it with a "proper" bronze Groco version. Lifting the basket out for cleaning is easy.
Yeah: as I've thought more about it, I think I will not replicate the old strainer-hanging-off-pipe installation. I had bought a new Sherwood strainer (maybe $44), but there's no way to mount it without buying a bracket too, and the brackets look flimsy. So I'll probably return it and buy a Groco strainer, which has a bronze body and comes with a mounting bracket. It's only money, after all...

It looks like the cleaning the basket on the Groco is very convenient too, as you say. The old installation wasn't too hard to clean, either: I'd slip a Pyrex glass measuring cup underneath the plastic strainer to catch the water, unscrew the strainer by hand, and move the whole mess to the sink. But a lift-out basket looks even better, given that I have very good access from the top.
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
Yesterday, I played around with how to mount/orient the new strainer. On the one hand, I have "lots" of room and good access. On the other hand, using bronze 90 degree elbows, you quickly run out of room. My first thought was to mount the strainer to the side of the engine pan, b/c it's a good solid location and I have plenty of room. But the hose routing may be awkward: lots of 90 degree bends in a short space. My second thought is to mount it roughly where the old strainer was located, but fashion a mounting bracket which projects out into the pan as drawn onto the next photo (Here, I'm holding the Sherwood strainer, which I've since returned and ordered a Groco ARG-750):
strainer_bracket.jpeg


This location would be very easy w.r.t. hose routing, but has the disadvantage that it involves a weird cantilevered mounting bracket projecting out into the engine pan. If I use very stiff steel (something like square tubing w/ holes, or an L angle), it would work, but is still a bit weird.

My third thought is to go back to my first thought, and see if I can just mount it on the front of the engine pan (the left side of the photo) and see if I can make the hose routing work. Or possibly on the starboard side (top of photo). The head of the strainer would be considerably above the top of the engine pan, but that first run of hose from the seacock to the strainer would be very tight. Leaning towards trying to make this work to avoid the odd cantilevered bracket.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
It is best to have the strainer below the water line. That will make it easier for the pump and reduce the time it runs dry at launch. If you do mount the strainer above the waterline, add water to strainer and fill the intake hose with water before starting the engine.

Locating the filter higher may give you more options. Sweeping turns with hose allows better water flow than 90° elbows.
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
It is best to have the strainer below the water line. That will make it easier for the pump and reduce the time it runs dry at launch. If you do mount the strainer above the waterline, add water to strainer and fill the intake hose with water before starting the engine.

Locating the filter higher may give you more options. Sweeping turns with hose allows better water flow than 90° elbows.
Any of these locations are without a doubt below the waterline. The thru-hull is at the hull, and the strainer will be at most a couple of inches above the hull.
 
Apr 8, 2010
1,942
Ericson Yachts Olson 34 28400 Portland OR
Presented strictly in the "FWIW" vein, I did not like the factory location for the raw water intake on our model boat. I moved it about 5 feet and rerouted the hose. Eliminated some sharp bends and some length. Lots more room to install a proper strainer. Sometimes it helps to step back and (where possible...) 'think outside the box' a little.
That picture in my blog of the strainer is the new location. Better access, too. As for the height, the top on the strainer is right at the waterline level, due mostly to luck. :)
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
Presented strictly in the "FWIW" vein, I did not like the factory location for the raw water intake on our model boat. I moved it about 5 feet and rerouted the hose. Eliminated some sharp bends and some length. Lots more room to install a proper strainer. Sometimes it helps to step back and (where possible...) 'think outside the box' a little.
That picture in my blog of the strainer is the new location. Better access, too. As for the height, the top on the strainer is right at the waterline level, due mostly to luck. :)
Well thanks for your comments, and for including the pictures of your installation. Looks like you have a Marelon seacock with a hose fitting on it for winterizing. I saw that there's an aftermarket fitting to replace the top fitting on the Groco strainer with one that takes a garden hose to accomplish the same thing. So I'll probably buy one of those to eliminate having to remove hoses to winterize. I'll figure out exactly how to mount the new strainer after it arrives.
 
Apr 8, 2010
1,942
Ericson Yachts Olson 34 28400 Portland OR
Yup. That three-way valve seacock is really the 'bee's knees'. We screw a short hose on it in the late fall and drop the other end into a gallon of pink RV antifreeze. Rotate the valve over to the position that opens to the standard "garden hose fitting" and then start the engine. When the exhaust burps out pink at about the 3 quart point in the jug we push the stop button. Takes care of winterizing from thru hull all the way to the outlet side of the water lift muffler. One of the most useful upgrades every added to our boat.
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
So fiberglassing the backing blocks is done. I epoxied the brass threaded inserts into all the backing blocks first. Here they are dry-fitted to the seacocks, showing how much bolt I need to cut off. I put small bits of tape on the underside of the inserts, to keep the fiberglass out, and then masked off the whole area before fiberglassing. The third picture is one of the (three) finished backing blocks. As you can see, I left the old ones in for now, as an aid to trying to keep the block perp to the thru-hull. Except for that part, this is exactly the same method as in Mainesail's article Replacing Thru-Hulls and Seacocks - Marine How To.

backing_block.jpegtape.jpeghead_pickup.jpeg

I've never done fiberglass before, so I was a bit surprised at how fast it sets up. It's really sensitive to how much hardener you add:
kitty_hair.jpegplus_hardener.jpeg
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
Did you use epoxy resin or polyester resin?

Polyester resin will set up faster with more hardener (catalyst) and with higher temperatures. Epoxy resin is very sensitive to the resin/hardener ratio. Adding more hardener will not yield a faster cure, but will yield a weaker cure. Warmer temperatures will cause epoxy to set up faster.
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
Did you use epoxy resin or polyester resin?

Polyester resin will set up faster with more hardener (catalyst) and with higher temperatures. Epoxy resin is very sensitive to the resin/hardener ratio. Adding more hardener will not yield a faster cure, but will yield a weaker cure. Warmer temperatures will cause epoxy to set up faster.
I really don't know a thing about fiberglass, so I used Evercoat Kitty Hair as mentioned in the Mainesail article. It is apparently a polyester resin mixed with long glass fibers. It's pretty gnarly stuff: not too hard to mix, but you really have to work quickly. I was getting a max of 4-5 minutes of working time after mixing it with a small (throwaway) paddle for less than a minute. It was maybe 62 degrees out. Once it starts to set up, you pretty much have to stop working. If I had to do it over again, I might use one of the products with shorter fibers (Glass-lite, from the same maker).

The first one I did, I barely got the backing block on and screwed down, and when I tried to smear the extra around the edge of the block, it was setting up too much. So I had to mix a second batch, which I used just to feather around the perimeter. With the 2nd and 3rd blocks, I knew I had to work fast, and I managed to get it all done before it set up, peeled off the protective masking tape really quickly, and gave it one more smoothing with my gloved fingers. All in all, it went better than I could have feared. I won't be able to tell to what extent I messed up on keeping them perpendicular to the thru-hulls until I take the old ones off and try to dry fit the new ones, but I think it will work out ok.

In any case, they sure as heck aren't coming off any time soon. I think I'll try to sand and gelcoat the blue part, b/c it's all full of nasty fibers that want to embed themselves in the unwary hand. Here are the other 2. For 2 of the 3 (the 2 I trimmed), I had to be extremely strategic about how the fitting sits so that I'll be able to close the seacock without interference. (BTW: the part underneath the fiberglass was very clean and roughed up. It's just the rest of the bilge that looks filthy...)

num_1.jpegnum_3.jpeg
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
The new strainer bracket is done and more-or-less installed:

strainer3.jpeg


Yeah: there are no hose clamps yet, the raw water pump isn't reinstalled, and I still need to glue down (4200) the seacocks and thru-hulls. I think the new sea strainer is probably a bit of over-kill for a 2GM20F (the 3/4" thru-hull and strainer fitting necks down to a 5/8" hose to go into the raw water pump). But it should be much easier to clean out, and safer than the plastic Sherwood strainer hanging off a pipe from the old factory thru-hull (shown in #20 of this thread). I had the new bracket all pre-drilled and ready to go, and thought I'd just be able to drill pilot holes in the fiberglass and put in (essentially) wood screws, which is mostly what the builder used. The first screw twisted in half in the pilot hole (see lower RHS of bracket). I had to go the the store for a tap set, and tap threads in the rest of the holes. Who knew fiberglass was that hard?
 
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Blitz

.
Jul 10, 2007
672
Seidelmann 34 Atlantic Highlands, NJ
BTW, Groco recommends the strainer above the waterline.
Groco.jpg
 
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CarlN

.
Jan 4, 2009
603
Ketch 55 Bristol, RI
If you find foam core, dig it out at least 1/2" back, clean the inside fiberglass well and then pack with epoxy filler. A good way to dig foam out is to chuck an Allen wrench in a drill and use it to whack away the foam. Below the waterline, water leaking past a thruhull into a foam core is pushed into a foam core under pressure and will travel a long way through the hull making for a most expensive repair project years down the road.

As someone else said, if you decide to replace the thru-hulls consider going with the Forespar Series 93 valves. They require no bolts although you should use a backing plate if the hull isn't flat. Forespar suggests white oak for the backing plate - a much better choice than plywood. It's rot resistant - just paint or stain it - and much easier to work than G10. It's really important that the backing plate be shaped to the hull curve on the back but be flat on the top. This is easy to do in a wood like oak. While there are lousy plastic seacocks, the Series 93 passes the ABYC side loading test. I've had them for over 15 years in two different boats and never had a Series 93 stick, break, or even need lubrication. I just exercise them twice a year. Here's Maine Sail's loading test -
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
BTW, Groco recommends the strainer above the waterline.
Well, the original was in the same place, which is below the waterline, and the new one is where it's going to be for the rest of eternity. Don't know where the heck I could have put it other than where it is, anyway.I imagine Groco either doesn't want to be blamed if some plastic part on the strainer breaks and floods your boat, or perhaps it's convenient to be able to stop the engine and clean the strainer without shutting off the seacock(!?). Anyway, I've been closing all thru-hulls every time I leave the boat for 15 years, so I think the "small leak in a plastic part" thing isn't something I worry about.
 

Blitz

.
Jul 10, 2007
672
Seidelmann 34 Atlantic Highlands, NJ
Well, the original was in the same place, which is below the waterline, and the new one is where it's going to be for the rest of eternity. Don't know where the heck I could have put it other than where it is, anyway.I imagine Groco either doesn't want to be blamed if some plastic part on the strainer breaks and floods your boat, or perhaps it's convenient to be able to stop the engine and clean the strainer without shutting off the seacock(!?). Anyway, I've been closing all thru-hulls every time I leave the boat for 15 years, so I think the "small leak in a plastic part" thing isn't something I worry about.
I agree with you on this that it probably was put in there for the lawyers. I also have made it a habit to close the sea cocks whenever you leave the boat.

I've been using the same 3/4" Sherwood strainer below the waterline that you noted for over 30 years and had recently upgraded to the Groco ARG-755-S (little shorter than the 750 since I had space limitations) on my Yanmar 3GM. I was troubled by the Groco instructions of requiring mounting above the waterline. I checked my waterline inside the boat and mounted it so that the top cap is less than an inch above the waterline. I won't know how well it will work until I launch in a week or so but my height is easily adjusted with just changing the intake and outlet hose lengths.

Thanks for sharing you installation details.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
If you mount the strainer above the water line, fill the strainer and hoses with water before launch. This will reduce the water pump's dry run time. Or just leave the antifreeze in the strainer.
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
If you find foam core, dig it out at least 1/2" back, clean the inside fiberglass well and then pack with epoxy filler. A good way to dig foam out is to chuck an Allen wrench in a drill and use it to whack away the foam. Below the waterline, water leaking past a thruhull into a foam core is pushed into a foam core under pressure and will travel a long way through the hull making for a most expensive repair project years down the road.

As someone else said, if you decide to replace the thru-hulls consider going with the Forespar Series 93 valves. They require no bolts although you should use a backing plate if the hull isn't flat. Forespar suggests white oak for the backing plate - a much better choice than plywood. It's rot resistant - just paint or stain it - and much easier to work than G10. It's really important that the backing plate be shaped to the hull curve on the back but be flat on the top. This is easy to do in a wood like oak. While there are lousy plastic seacocks, the Series 93 passes the ABYC side loading test. I've had them for over 15 years in two different boats and never had a Series 93 stick, break, or even need lubrication. I just exercise them twice a year. Here's Maine Sail's loading test -
I don't see any signs of foam in the holes (thank God), and the 3 thru-hulls I'm replacing are already pretty much all done but the 4200. If you look in the pictures, I'm using the Groco flanged seacocks. I did consider using the separate flanged base plus ball valve, but decided that the 1-piece looked more solid. I strongly suspect that Hell will be freezing over before I ever replace these 3 again. The galley and head sink thru-hulls still date back to 1 or 2 years after we bought the boat, but they aren't located where the plywood backing plates ever get wet, so they're in good shape.
 
Jun 25, 2004
475
Hunter 306 Pasadena MD
If you mount the strainer above the water line, fill the strainer and hoses with water before launch. This will reduce the water pump's dry run time. Or just leave the antifreeze in the strainer.
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.)