In my effort to splash the Roamer in October 2022, I’m closing up holes all over the boat. Installing the swim platform closed up 50+ underwater bolt holes on the transom. Installing the mast base on the salon roof and deck hardware on the mahogany toe rail closed up dozens of holes. But the biggest holes of them all are in the engine room: the raw water inlets for main engine and genset cooling and air conditioning.
I’ll be using the OEM Chris Craft/Groco strainer and seacock for the air conditioning system because it’s adequately sized for that application and I already have it. I could just install the strainer on the standpipe thru-hull and leave the seacock valve closed, but I suspect the insurance company will want hoses attached to the strainer, which means I should have the raw water pump installed, too. And while I’m at it, I might as well run the hoses from the pump to a manifold, then on to the air conditioners themselves.
Dometic P3000BXT raw water pump moves 3000gph
I bought two of these Dometic pumps at the Dania Marine Flea Market down in Florida about ten years ago, along with several NOS fuel and water tanks, washer/dryer combo units, and a bunch of NOS electrical cables of varying sizes. The key to getting the best deals at Dania is to do a buying spree on the last day, when sellers would rather let things go for cheap than to load them up and take them home again.
I serviced the pump and coated the bronze pump head
I’ve mentioned many times that the only place on this hull where I found significant corrosion was in the engine room in the vicinity of copper water and fuel lines, and anywhere bronze could interact with the aluminum. So one thing I didn’t like about the Dometic unit is the bronze pump head. I figured coating it with self-etching primer should help isolate the bronze and keep green copper oxide from flaking off and falling on my precious aluminum hull.
Putting a leftover sheet of aluminum to use
I kept all of the big pieces of leftover aluminum sheet from the aft deck enclosure build. They’ve been taking up space in my garage for a long time, so it’s nice to finally cut one of them down to size.
Laying out the raw water pump platform
Aluminum is much easier to work with than steel
Carbide-tipped woodworking tools cut through aluminum like butter. And my EZ-One tracksaw guides help keep the cuts straight.
The platform is wide enough to span the main engine stringers
My signature pile o’ dimes, nickels, & quarters TIG welding secures a vertical panel to the pump platform
The raw water manifold will attach to and be protected by the vertical panel.
Epoxy-coated and ready for installation…or not
The more I thought about that P3000BXT pump, the more I realized there was a better option. Reading through the spec sheets for the new Flagship Marine air conditioners I bought in 2017, they only need ~700gph of raw water, which is 1/4 of what this big Dometic pump can put out. Throttling back the output doesn’t hurt the pump, but the six amp draw is six times what a 1000gph pump requires.
So I decided to get a March BC-4C-MD raw water pump instead. That’s a blast cooled (internal fan that draws outside air through the motor) unit with a magnetically driven plastic pump head, so there’s no bronze or shaft seals to worry about.
Unfortunately, the output was opposite of the Dometic pump
There’s not enough room to the right of the manifold support for the March pump.
Ideal outlet orientation is at the top
This is a submerged-style pump. It has no ability to draw water up into it unless the pump head is naturally flooded. Having the outlet at the highest point AND below the waterline ensures that the pump will be full of water.
Less than ideal orientation points straight up
You can see that an air bubble will be in the pump if the outlet is pointed up. That can cause cavitation, but the bigger problem is that the raw water manifold would become a tower that would be vulnerable to being hit and possibly broken.
This orientation would work with the pump platform, using a hose to connect the pump to the manifold.
But a hose adds connections, which adds potential failure points.
This orientation also guarantees a large air bubble in the pump, cavitation, and no water pumping
This isn’t going to work. Gotta change the pump platform.
I cut off the welds holding the vertical panel in place
Flipping the platform over, I can weld the manifold panel back on with the proper orientation
The new epoxy coating is ground back, and the manifold panel and platform are clamped back together and ready to weld
3/8″ aluminum angle makes a great heat sink to clamp to and guarantees corner welds are 90°.
More pile o’ dimes, nickels, & quarters TIG welds secure the manifold panel in its new location
I applied the same Bar-Rust 235 epoxy coating to the weld areas and got busy making pipe straps while it cured.
Narrow strips of leftover 316 stainless make great pipe straps
After drilling screw holes on each end, I form each strap around the Schedule 80 PVC manifold Tee
Mark the strap for bends
4″ bench vise metal brake puts perfect bends in the straps
Peel off the protective plastic
The stainless straps are ready for a touch on the grinder to smooth sharp edges
Ready to install
Drill holes through the stringers, apply TefGel, then bolt together with stainless 1/4-20 hardware
Nylon washers separate the pump platform from the stringer. That leaves just enough of an air gap that water won’t condense and collect between the aluminum components. Granted, everything is epoxy-coated, but adding a few nylon washers is cheap insurance against sharp edges breaching the epoxy coating once the nuts are snugged up on the bolts.
Done!
I can install the hoses that supply raw water to each air conditioner, but first I need to install the AC units. At $10/foot, I don’t want to waste a bunch of hose by guessing how long they need to be. Conservative guesses (i.e. overly long) will result in more wasted hose, while guessing short will mean adding hose menders, more hose, and clamps, so it’s better to just cut them the exactly right length from the beginning.
But rather than bolting the AC units directly to plywood cabinetry, which can transmit noisy vibrations into the hull, I have an idea to make them super quiet.
Next up in our 1969 Chris Craft Roamer 46 Refit: Installing the Aft Stateroom AC Unit
1969chriscraftroamer46 