A New Raw Water Intake

The raw water intake for Wing's old engine used a 1/2" ID hose while the new Beta 14 requires a 3/4" hose and comes with the appropriate hose barb installed.  I also discovered that the "seacock" on the old raw water intake was a hardware store gas valve that had been bodged on to the old thru-hull with what looked like transparent silicon bathroom sealant: a complete new raw water intake system was in order!

I started by removing the old thru-hull and enlarging the hole to accommodate a thru-hull threaded for 1" NTP.  I decided to go with a 1" thru-hull in order to reduce the suction at the intake and to ensure that I am over-capacity for cooling water.

Here is the enlarged hole

The old thru-hull was a scoop-type and dark area around the hole shows its outline.  The Beta manual specifically recommends against scoop-type fittings on the intake and I decided to replace it with a simple Groco open bronze thru-hull.  There seems to be some debate on the merits of fitting a strainer on the outside of the hull: one camp feels it is best to keep detritus out of the system entirely at the risk of having a blockage outside the hull below the waterline that can be difficult to clear while underway; another camp thinks that it is best to accept some detritus getting into the system and up to the internal strainer where it can be more easily cleaned out while underway.  I don't have enough experience to have a strong opinion so at this point I have decided not to fit a strainer on the outside of the hull; I can always add one later if it is needed.

With the hole enlarged I proceeded to add a backing block on the inside of the hull to support the new seacock.  I made the block out of African Mahogany- the same wood that Wing is planked with.  The block is actually two planks laminated together with epoxy to get the required thickness.  Once I cut it to size I roughly backed it out with a gouge (sadly I don't have a proper backing-out plane) to match the curve of the planking and then did a final fitting it by laying some 60 grit sandpaper on the hull and rubbing the block back and forth against it.  This was a bit of a tedious job because, as you can see in the picture below, the block sits between two frames and there was not much space in which to move it.

Once the block was fitted I painted it with Interlux Bilgekote, bedded it with Sikaflex 291 LOT, and used the new thru-hull fitting to exactly align the hole in the backing block with the hole in the hull.  I wrapped the thru-hull fitting in plastic wrap so that I could remove it again and then used the nut provided with the thru-hull fitting to clamp the whole assembly in place.

I also attached the block to the planking from the outside with four screws that I countersunk and plugged in exactly the same way as the screws that attach the planking to the frames: there should be no leaks!

(The above photo of the thur-hull was taken after I had applied a coat of anti fouling but the plugs for the four screws can be seen telegraphing through.) 

Once the bedding had set on the backing block I remove the nut and plastic wrap from the thru-hull fitting, added more Sikaflex to the outside flange, and re-inserted the fitting.  I threaded the new Buck Algonquin seacock, again bedded with Sikaflex, onto the fitting from the inside and, with a friend bracing the fitting from the outside, I screwed the seacock down tight.

The seacock is prevented from rotating on the block by three 5/16" lag bolts.  I chose the length such that they go all the way through the backing block and partway into the planking.  This adds additional support to the whole structure and prevents it from rotating while at the same time reducing the potential for leaks that would arise if I chose to thru-bolt the seacock all the way through the hull.  The seacock is 1" NTP on both ends so I have added a 1" NTP to 1" ID hose adapter and sealed it to the seacock with Permatex thread sealant.

For the raw water strainer I chose a Groco ARG-750-S with a monel basket.  I have installed the strainer just above the waterline and positioned it such that I have plenty of clearance to lift the basket out of the strainer without detaching it from its supports.  This means I should be able to remove the basket in order to clear any blockages while underway without any fear of flooding.

This strainer has 3/4" NPT threads.  On the intake side I have used a bronze 1" hose barb to 3/4" NTP elbow to connect to the hose from the seacock while on the engine side I have used a 3/4" NTP to 3/4" hose barb elbow to connect a hose to the pump on the engine.  I connected the strainer to the seacock with a 1" ID Shieldsflex wire re-enforced hose.  The final assembly is shown below.

Both elbows are sealed with permatex thread sealant.  The strainer is thru-bolted to the plywood wall and, since the plywood is fairly thin, I added a backing panel for extra support.  The strainer supports and the backing panel are shown below:

The plywood wall to which the strainer is attached forms the inner wall of the quarter berth so the panel won't be very visible and won't get in the way of anything.

Now all I need to do is connect the raw water strainer to the engine once it is installed.