Ken,

If the system has worked well for you, I would suggest making as few changes as possible. There are many complexities in using a seachest to feed multiple consumers, some of them rather subtle.

Here is what we did with our SM raw water manifold.  It has worked out very well for us, and there is nothing about it I would change: https://fetchinketch.net/boat-projects/upgrading-the-amel-raw-water-manifold/

I am not familiar with the exact geography of a Maramu, so forgive me if some of my comments are off base, but be very careful moving the AC and watermaker pumps.  The  March pump, especially, requires positive head at its inlet at all times. It is absolutely not self-priming! If you move it above the external water level it will not work well, or at all. The further below the waterline this pump can go, the better. How well your watermaker would tolerate this depends on the specific hardware.  Check the installation instructions from the manufacturer.

For any centrifugal pump you must have a continuously downward run of pipe from the strainer that can not trap air. Make sure the outlet of the strainer is below the normal waterline if you are connecting the AC pump to it.

Consider the possibility of reverse flow.  In any of the systems that have an outlet that is open, and above the waterline, air can be sucked backwards reducing the effective flow rate.  The most likely issue here is your engine potentially pulling air back through your AC cooling circuit.  I am not sure about the head connection.  That will depend on the exact type of toilet involved. You might need check valves to stop this.

Bill Kinney
SM160, Harmonie
Simpson Bay, Sint Maarten 
http://www.cruisingconsulting.com

The current Sea chest needs to be replaced (See pic) and your insight on the best approach for the aft saltwater consumers is greatly appreciated.

AFT Seawater consumers:

• Aft Head
• Engine
• Cockpit Washdown 
• Galley Sink
• March AC-5C-MD AC Pump for Aft AC and Saloon AC
• Water Maker

The current sea chest (pic 1) provides for the engine, aft head, cockpit washdown and galley sink. The AC pump and Watermaker are being relocated to the port cockpit lazarette.  What is your recommendation? Of note, the thru hull for the aft sea chest is smaller (pic 2) at 32mm than the 52mm on a SM.  Should I build a Sea Chest and manifold for all aft consumers based on the SM design in Bill's book. Should I add an additional thru hull and if so, where (considering port lazarette)?  If adding a thru hull, what sea water consumers would you recommend on the new thru hull?

Your insights are greatly appreciated as we work through a winter refit.

Best Regards, Ken
M202 Bon Edda