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Old 04-20-2012, 07:40 AM
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Default Sharing a thru-hull for a bilge pump

After some reading this looks like it's frowned upon, but I wanted to get a sanity check to confirm.

One of my surveyor's findings was to install a second bilge pump. I picked up a hefty Rule 2k/GPH pump, but since my boat is going to be in the water at the marina before I can get to it, I'm not going to be able to install a dedicated thru-hull for it.

Right now, I have one thru-hull being used for a fish box, which I only plan to use as a cooler (throw some ice in there and then put the fish on ice when caught). I'm not expecting this to generate a whole lot of water, and certainly in terms of flow it'd be a trickle.

Am I wrong to consider sharing this thru-hull with the secondary bilge pump? I thought about adding a check valve too, just to be safe, but I'm not sure it's necessary.

At the end of the season I plan to add a dedicated thru-hull for it, as well as swap out some of my other thru-hulls that are plastic and starting to chalk up with either stainless or bronze. And if need be, I could always just use the fish box's thru-hull for the bilge pump and use a cooler to put fish on ice until the end of the season.

Has anyone shared a thru-hull for such a purpose? Am I off target?
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Old 04-20-2012, 07:51 AM
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You don't want to use a shared thruhull for a bilge pump. Not sure why you can't install while in the water, they outflow needs to be well above the waterline anyway.
A check valve could risk clogging and multiple connections.
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Old 04-20-2012, 08:23 AM
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You can't share a thru-hull for bildge pumps because some of the water will go overboard, the rest will get sent to the other pump just going back to the bildge.

If you use check valves, you will reduce the flow of the pumps and if they fail, you won't pump anything.

You can only share a thru-hull for intakes. For example, a 1" thru-hull feeding two pumps, one for a wash-down and the other for a live well. Some manufactures are not putting in a large intake with a manifold on it that services all intake needs, however all outputs must have their own output.

You didn't mention what kind of boat it was and what size. A lot of smaller boats only have 1 bildge pump and then a 2nd as backup, usually mounted a few inches higher than the first, purely as a safety margin in the event the primary pump fails.

For now, you can install your 2nd pump and have the hose discharge back by a scupper or over the gunwale if needed when you are away from the boat. This way if your primary fails, you will have a backup. When you are underway and don't want the extra hoses running, you can put a high water alarm in the bildge so in the event you start to take on water and the primary fails or can't keep up, you can turn on your secondary pump and toss the end of the hose back over the gunwale... Keep in mind- this is temporary until you have the boat on dry land to install a though hull.

Since it is above the water line, you might be able to get your boat alongside a dock that will give you the access you need to install the new fitting.
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Old 04-20-2012, 08:29 AM
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I cannot imagine scenario where the easiest thing isn't just to add another thru-hull outlet above the waterline.


Seems like the effort involved in avoiding that easy step is far more laborious.
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Old 04-20-2012, 08:44 AM
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Yeah - to caveat - I would definitely be adding it above the waterline, but since the boat would already be in a slip and this is my first boat, I'm not sure how keen I am on adding a thru-hull while the boat is in the water. I'd rather do it when the boat is blocked up at the end of the season, when I know my 5200 will have plenty of time to cure and I'll do as careful a job as humanly possible.

Justin - it's a 24' Grady White Explorer, well used but new to me. These boats apparently have issues with water intrusion and the survey came back that it was dry as can be, so I'd like to keep it that way. I already have one bilge pump down below, but the surveyor recommended that a second one be added if the boat was going to be stored in a slip. I think your suggestion might be the best one - keeping that pump as a reserve, really only to be used when at the dock with a hose that I just manually pull out over the gunwale. Either that, or I bite the bullet and plug off that fish box and use that thru-hull for the secondary pump until I get a chance to put in a proper thru hull for it.

Thanks for the feedback all!
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Old 04-20-2012, 08:52 AM
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Quote:
Originally Posted by Brooklyn Greenhorn View Post
I'd rather do it when the boat is blocked up at the end of the season, when I know my 5200 will have plenty of time to cure and I'll do as careful a job as humanly possible.
Use 4200. All you need is a sealant.
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Old 04-20-2012, 09:14 AM
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Quote:
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Use 4200. All you need is a sealant.

Both 5200 & 4200 are the wrong product for above the waterline thru-hull futtings. The correctproduct is 3M 4000
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Old 04-20-2012, 09:35 AM
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Quote:
Originally Posted by LI32 View Post
Both 5200 & 4200 are the wrong product for above the waterline thru-hull futtings. The correctproduct is 3M 4000
3Mô Marine Adhesive Sealant Fast Cure 4200
A one-part, general all-purpose polyurethane
that chemically reacts with moisture to
deliver flexible bonds with good adhesion to
wood, fiberglass, gelcoat, plastics and metals.
Forms watertight, weather-resistant seals on
joints and boat hardware above or below the
waterline. This product is approximately half
the strength of 3Mô Marine Adhesive Sealant
5200, which allows for disassembly of parts.
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Old 04-20-2012, 10:29 AM
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I still don't understand why the boat needs to be on dry ground at year's end for this.

Sorry, I don't think I am being dense.

The product you use will cure and the entire job risks you losing a drill into the drink, which you can easily avoid. Drill, add fittings, hose. Other options are just avoiding the drilling.

Right?
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Old 04-20-2012, 10:43 AM
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Pick a nice day with no wind or waves.
Research appropriate size thruhull and hose according to bilge pump manual specs.
Go to store, buy small tube 4200 (it may harden before you can use it all), sand paper 200 grit, acetone, a 2 part epoxy fast set, a plastic lid for mixing, plastic knives for spreading goo, thru hull and hose, and four stainless hose clamps, rags.
Bring with you: drill, hole saw size for thru hull maybe a tad bit bigger, shop vac, large adjustible wrench for thruhull nut or channel locks or something to turn tight.
Orient the boat in the slip so the side you choose is not subject to wake or waves.
Go to boat and pick a place high up on port side near transom. I think other bilge thru hull is stbd so I would do port for this one, in case boat lists to one side and makes pumping harder, you wouldn't want both pumps on both side in case it was listing to that side...
You need clearance under gunwale for the end of the thru hull and hose, so not too high and not to close to the transom. Choose the spot from the inside and drill from inside so you know you have enough room. You also want the glass to be thick there or have some wood in it, which I dont think it does anywhere there.
Drill the hole. Sand it out nice and clean. Clean the hole with acetone. Mix up the epoxy and coat the inside of the hole. Wait appropriate time for epoxy to harden. Hoover out (vacuum) the saw dust. Go to lunch.
Come back to boat and coat the thru hull in 4200 or whatever sealant you bought. Put it on the thickness of the hull plus a little extra on the threads as a threadlocking agent. Put it on the flat surface that mates to the outside of the hull.
Stick it in and crank it down. Put acetone on rag and go clean up around the outside of the hull where the sealant runs.
Now you have a dedicated thruhull installed properly.
Put 4200 in a ziploc in the fridge and dont tell wife. Double clamp hoses. Dont leave boat without attatching a hose to the thruhull and ziptying it high up.
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Old 04-20-2012, 11:17 AM
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Quote:
Originally Posted by miike View Post
Pick a nice day with no wind or waves.
Research appropriate size thruhull and hose according to bilge pump manual specs.
Go to store, buy small tube 4200 (it may harden before you can use it all), sand paper 200 grit, acetone, a 2 part epoxy fast set, a plastic lid for mixing, plastic knives for spreading goo, thru hull and hose, and four stainless hose clamps, rags.
Bring with you: drill, hole saw size for thru hull maybe a tad bit bigger, shop vac, large adjustible wrench for thruhull nut or channel locks or something to turn tight.
Orient the boat in the slip so the side you choose is not subject to wake or waves.
Go to boat and pick a place high up on port side near transom. I think other bilge thru hull is stbd so I would do port for this one, in case boat lists to one side and makes pumping harder, you wouldn't want both pumps on both side in case it was listing to that side...
You need clearance under gunwale for the end of the thru hull and hose, so not too high and not to close to the transom. Choose the spot from the inside and drill from inside so you know you have enough room. You also want the glass to be thick there or have some wood in it, which I dont think it does anywhere there.
Drill the hole. Sand it out nice and clean. Clean the hole with acetone. Mix up the epoxy and coat the inside of the hole. Wait appropriate time for epoxy to harden. Hoover out (vacuum) the saw dust. Go to lunch.
Come back to boat and coat the thru hull in 4200 or whatever sealant you bought. Put it on the thickness of the hull plus a little extra on the threads as a threadlocking agent. Put it on the flat surface that mates to the outside of the hull.
Stick it in and crank it down. Put acetone on rag and go clean up around the outside of the hull where the sealant runs.
Now you have a dedicated thruhull installed properly.
Put 4200 in a ziploc in the fridge and dont tell wife. Double clamp hoses. Dont leave boat without attatching a hose to the thruhull and ziptying it high up.
Thanks Mike! I still hate the thought of taking a saw to a boat (and I'm not afraid of taking a power tool to most anything, but I haven't even taken delivery of the boat yet and I'm talking about poking holes in it).

One question about the epoxy - that's not to bond the thru-hull to the boat, the 4200 will do that. Is the epoxy solely intended to cover up the wood that was exposed by the drilling? Is there any specific type of epoxy that I should use?

My problem is once I get the confidence to do it, I'm going to start poking too many holes back there. I want to add a battery charger (and thus far, I've been trying to find a way to mount it with a piece of plywood and glue), as well as a receptacle to hook up the shore power to (for said charger). Now, I'm poking three holes, before you know it there won't be any wood left
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Old 04-20-2012, 11:57 AM
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In case you are tempted to put two into one.

http://www.cgedwards.com/Rule/rule04.html
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Old 04-20-2012, 06:06 PM
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Any 2 part epoxy from the boat store should work. Most from the hardware store would work too. The epoxy is put on in order to seal the plywood or fiberglass from water intrusion in case the sealant fails. You may think this is unnecessary and I would bet most boaters wouldnt do it. Hell I might not even do it depending on the situation, ie thickness of the glass.

If you use plywood to mount something to, then you would want to coat that in epoxy too, so start buying the large quantity of epoxy. Without epoxy, plywood could get spongy in one season depending on your humidity and whether or not you clean your bilge often. Use all stainless hardware.

Shorepower receptacles are rarely a thruhull apparatus. There is no reason to risk hull integrity to install there. People would rather run wires up to the side of the console or cabin and install a receptacle there. Secure all wires every couple feet, maybe 18" is NMMA spec? Who cares just keep it from flopping around.
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Old 04-20-2012, 10:29 PM
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I doubt you'll find any wood in the sides of a 24' Grady ...
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Old 04-21-2012, 01:32 AM
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You got lots of bits of information but its incomplete , the outlet height isn't the critical thing, the height of the riser is and no-one has mentioned the riser, so you'd be doing it wrong so far.

Wooden backing is not needed, if there is any load placed on the connection the install is wrong and will fail, a plywood backing plate will not do anything.
The riser must be supported to keep loads from the connector.

The outlet is usually a 90deg connector on the back, it should point UP , not down.

http://www.yachtsurvey.com/bilge_pumps.htm
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Old 04-23-2012, 08:18 AM
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Thanks again guys - appreciate all the feedback. Like I said, I am REALLY new at this - first boat, and I don't know a whole lot about them. The point of this season was really just to take it slow and get to know the boat and figure my way around. I'm not in a full service marina, otherwise I would've just asked them to handle this one and let the future upgrades be the learning curve.

Mike - with regards to the shore power, I figured I'd keep the charger close to the batteries, but I guess it's not that difficult to just put the receptacle somewhere in the cabin and mount the charger nearby, just running four cables out to the battery terminals. I'm new to fiberglass but I know my electrical work, so aside from the added cost of longer cables I don't think I'll have a problem there.
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