1. This past long weekend I had an incident that has been bothering me. It has been a consistent one for me that seems to be happening more frequently. My raw water intake has a tendency to get clogged while I'm sitting still and running. either while idling or at higher RPM's while charging my batteries. I don't have any straining device over my raw water intake thru-hull (e.g. clamshell strainer). I do have my internal strainer, but the 1/2" hull intake is where the blockage usually happens. Seaweed, eel grass, etc tend to be pulled in. My question: Is this normal? Or should I have the clamshell strainer on the hull? My dock mates' consensus is that I should have the hull strainer to avoid sucking up any material. What do you readers have over your intake thru-hull? 2. How high on the inside bulkhead should a raw water strainer be mounted? Should it overflow fast or slow when the cap is removed and the seacock is open? Or should it overflow at all? These are factory-installed conditions, so it has been my tendency to assume that they are OK. But...you never know. Thanks, in advance, to everyone. This site has always been and excellent source of information.
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What's the point?
If you had a clam shell strainer, are you going to dive under the boat to clear it? It's easier and safer to clean the strainer inside the boat, especially in bad conditions, which is when things like that seem to happen. There should be a sea cock at the thru-hull that you can close to keep sea water out when cleaning--if not, you should install one.
If you had a clam shell strainer, are you going to dive under the boat to clear it? It's easier and safer to clean the strainer inside the boat, especially in bad conditions, which is when things like that seem to happen. There should be a sea cock at the thru-hull that you can close to keep sea water out when cleaning--if not, you should install one.
Close de valve
As a matter of interest to this thread. I close the engine (Yanmar 3GM) sea water feed through hull valve every time I shut down the engine. I can just imagine the nice warm dark engine sea water feed tube being a place that sea crittes would love to set up housekeeping. Here in the warm waters of the Gulf (86F)crtters do grow. I also remove the through hull speed wheel every time I dock. If not,it may not turn next time out because of the sea critter growth. I understand there are chemical applications that can be used to cover the wheel itself and the housing - but I find it hard to believe that there is anything that will deter critter growth - except removal of the unit from the water. RD
As a matter of interest to this thread. I close the engine (Yanmar 3GM) sea water feed through hull valve every time I shut down the engine. I can just imagine the nice warm dark engine sea water feed tube being a place that sea crittes would love to set up housekeeping. Here in the warm waters of the Gulf (86F)crtters do grow. I also remove the through hull speed wheel every time I dock. If not,it may not turn next time out because of the sea critter growth. I understand there are chemical applications that can be used to cover the wheel itself and the housing - but I find it hard to believe that there is anything that will deter critter growth - except removal of the unit from the water. RD
Here's the point!
I've been told that the raw water hull strainer (clam shell) is less likely to become fouled than the thru-hull. If the strainer gets clogged with seaweed, it may just wash off when the motor is shut down. Or the entire strainer won't get covered in most cases (except for a plastic bag). Currently, anything large completely clogs the hole/thru-hull.
I've been told that the raw water hull strainer (clam shell) is less likely to become fouled than the thru-hull. If the strainer gets clogged with seaweed, it may just wash off when the motor is shut down. Or the entire strainer won't get covered in most cases (except for a plastic bag). Currently, anything large completely clogs the hole/thru-hull.
Confusing terminology.
Is your engine thru-hull just a flat mushroom type? If yes then you should have a strainer like you see in the Related Link. Most boats that I look at in my marina have the type of engine thru-hull that has the slotted strainer. Mine is like that and the slots are even large enough for zebra mussels to get sucked in. But the big Perko water strainer takes care of that. If we had a lot of grass I would probably add the outside strainer. Where we sail on Lake Erie there is little grass to deal with. If the outside strainer did get clogged I would hope it would clear by sailing away from the source. If not I would clean it from inside by removing the hose and going down through the valve. Yes, water would come in but I am not diving on it.
Is your engine thru-hull just a flat mushroom type? If yes then you should have a strainer like you see in the Related Link. Most boats that I look at in my marina have the type of engine thru-hull that has the slotted strainer. Mine is like that and the slots are even large enough for zebra mussels to get sucked in. But the big Perko water strainer takes care of that. If we had a lot of grass I would probably add the outside strainer. Where we sail on Lake Erie there is little grass to deal with. If the outside strainer did get clogged I would hope it would clear by sailing away from the source. If not I would clean it from inside by removing the hose and going down through the valve. Yes, water would come in but I am not diving on it.
Thanks, Ed
Yes, mine is a mushroom type of thru-hull. And it is entirely exposed. I have a strainer basket between ther thru-hull and the raw water pump. But it doesn't help when the mushroom gets clogged. If too much debris is introduced thru the mushroom, then the elbow on the inside of the hull at the shutoff valve becomes clogged. I hope this is less confusing. Thanks for the diagram. It will be very helpful. I am leaning toward the slotted hull strainer as a remedy to this problem.
Yes, mine is a mushroom type of thru-hull. And it is entirely exposed. I have a strainer basket between ther thru-hull and the raw water pump. But it doesn't help when the mushroom gets clogged. If too much debris is introduced thru the mushroom, then the elbow on the inside of the hull at the shutoff valve becomes clogged. I hope this is less confusing. Thanks for the diagram. It will be very helpful. I am leaning toward the slotted hull strainer as a remedy to this problem.
Here's a tip
I've had the same problem. I was talking to a commercial fisherman. He told me that they have two one inch through hulls at least two feet apart or more that go into a tee then into the strainer. There is very little suction but volume going into the strainer so you don't suck seaweed. Next haul out put in a 1" through hull with a vent on it then run a 1" hose to your strainer with an 1" adapter fitting for the strainer. This might do the trick.
I've had the same problem. I was talking to a commercial fisherman. He told me that they have two one inch through hulls at least two feet apart or more that go into a tee then into the strainer. There is very little suction but volume going into the strainer so you don't suck seaweed. Next haul out put in a 1" through hull with a vent on it then run a 1" hose to your strainer with an 1" adapter fitting for the strainer. This might do the trick.
Nice idea Ken.
Except for the additional hole in the boat with another expensive seacock. But I would still want external strainers over both inlets. Paul, having an elbow on the shutoff valve makes it hard to clean from the inside. A real seacock with the hose coming straight off the top is a better option. This assumes there is bilge room to do that.
Except for the additional hole in the boat with another expensive seacock.
But I would still want external strainers over both inlets. Paul, having an elbow on the shutoff valve makes it hard to clean from the inside. A real seacock with the hose coming straight off the top is a better option. This assumes there is bilge room to do that.Elbow, Ed
Ed. The elbow is a 90 degree radius elbow that's threaded onto the thru-hull. Then the seacock valve is threaded into the elbow. This keeps it parallel to the deck and below the floorboard. A barbed nipple is threaded into the valve and leads (via water hose) to the Perko strainer. It usually clogs at the nipple since the opening is too small (3/8"). To clean, I shut the valve off and remove the hose. I open the valve to determine how much water passes thru. There must be a solid shot of water for a clear opening. I will then use a heavy wire to "ream out" the valve/thru-hull and loosen the clog. Sometimes that is all that I have to do. Other times for a more heavy clog, I will also take my Avon foot pump and place it over the nipple and give it a good backflush of air pressure. That usually does the trick.
Ed. The elbow is a 90 degree radius elbow that's threaded onto the thru-hull. Then the seacock valve is threaded into the elbow. This keeps it parallel to the deck and below the floorboard. A barbed nipple is threaded into the valve and leads (via water hose) to the Perko strainer. It usually clogs at the nipple since the opening is too small (3/8"). To clean, I shut the valve off and remove the hose. I open the valve to determine how much water passes thru. There must be a solid shot of water for a clear opening. I will then use a heavy wire to "ream out" the valve/thru-hull and loosen the clog. Sometimes that is all that I have to do. Other times for a more heavy clog, I will also take my Avon foot pump and place it over the nipple and give it a good backflush of air pressure. That usually does the trick.
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