Hot Water (I think)

This project has been weighing on my mind ever since I decided to locate the IsoTemp 20l water heater underneath the starboard settee.  I really liked the location because everything is easily accessible and should actually be fun to service (type A fun), but running the coolant hoses from the engine was a bit of a head scratcher because despite of the easy access, getting the hoses into the compartment and ultimately to the tank to heat the water with excess engine heat is not easy.

I've spent the better part of 2 years since I installed the tank (Water System - Check (almost)) thinking about it, but ultimately holding off because I wasn't sure. Well, I don't have much time left and if I want hot water this summer when I launch I had to figure it out.  

The first problem I needed to overcome was the fact that the coolant ports on the engine (in and out) are located in such a way that they would need to basically turn 90 degrees.  After a ton of searching online I found prebent (90degree turn) 7/8" silicone coolant hoses at an automotive performance shop near me.  From here I added 2 7/8" couplers and found a 20 foot roll of 7/8" silicone coolant hose on amazon.com.

I fitted the prebent hoses onto the engine coolant ports sending them down toward the transmission, then added the couplers and after some searching found a decent route to the hot water tank. I ran the hoses down alongside the transmission and under the floorboards over to the nav station.

At this point I drilled 2 -1.25" holes with my holesaw in the bulkhead between the starboard settee and the nav station.  The bulkhead is 1/2" marine plywood with a layer of glass mat on both sides and was pretty sharp, so I needed to come up with a gland/grommet for each hole that would allow the hoses to pass through without chafe.  

I fired up the CAD system and designed a pass through grommet with rounded edges so the hoses wouldn't rub on the sharp fiberglass.  I printed them up with the 3d printer in safety orange (mainly because that was what was loaded into the machine) and printed them up.  Once finished I took them over to the boat, fitted them and then glued them in with 4200 sealant.  

I left them overnight so the sealant would cure and the next day came back and snaked the hoses underneath the nav station and through the holes into the water heater compartment.  The coolant hose ports on the water heater are 1/2" male npt, so I had to come up with a solution to make the connection to the 7/8" ID hose.  I finally came up with the following: 1/2" female npt to 3/4" female npt followed by a 3/4" male npt to 7/8" hose barb (I really hate pipe connections, it's never simple).  

Anyway, I taped and installed the fittings on the water tank side and finally connected the silicon hoses with hose clamps.  The last thing to do was fill up the hoses with coolant so there is no air in the lines to create an airlock. I did this by taking the hoses off the couplers just after the 90 degree elbows and pouring coolant in on one side until it came up to the top of the other hose and then reconnecting everything.  All told, the full circuit from the engine to the water tank is about 14' and should be within the limits of the coolant pump.  Hopefully this will work, but I won't know until I run the engine for a bit once it's in the water to see if the water heats up.  Crossing my fingers, but I can cross this job off my list for now.