Well what a great summer we are having and it looks like its sticking around. We have had a high number of breakdowns, related to overheating, due to seaweed causing blockages in raw water intakes. Now not only is this in hull fittings it is also in Saildrives and Sterndrives. There are a few tricks to clear the blockages but also ways to try to prevent it in the first place.
Firstly before starting your engine you must check around the boat for seaweed and under your rear bathing platform, if you have one. If there is simply push it away with a boat hook. If you are running the engine or generator without moving you must do regular checks to make sure seaweed is not accumulating around the boat where it may get sucked into the water intake.
Secondly if you already have a blockage you can try a couple of tricks to clear it. If you have a raw water strainer you can remove the lid and fit a dingy/foot pump on the end of the pipe as it comes into the boat and apply air pressure to unblock the intake, once unblocked you will hear the air bubbles under the boat hull. If you have a sail or sterndrive and this is not successful you can use a stiff brush and scrub the side, just above the level of the propeller close to the front edge of the drive, and this will break up the seaweed so when the engine is run the smaller bits will make it to the sea water strainer to be then emptied out.
Thirdly your impeller and exhaust pipework can be severely damaged due to overheating so should also be checked carefully before and after starting the engine again. Once the engine is running the impeller cover and exhaust elbow, where the raw water is injected into it, should be cool to the to the touch. If they are not you either still have a blockage or the impeller needs replacing.
Lastly its always wise to try and avoid going through it when possible because not only does the seaweed itself cause issues it will hold within it debris such as plastic bags, netting, rope and any wood or other floating objects which will cause fouled propellers or in the worst cases damage to you hull.
I hope this information is useful to you and have a great rest of the season.