The Motorsailer Project

Project Log: Saturday, August 11, 2012

Next on the agenda was to complete the installation of the exhaust and air intake system for the diesel heating system. My plans in this direction had been stymied a bit earlier when I found that one of the fittings I'd ordered in advance was the wrong size, but with the correct fitting now on hand and no particular reason not to proceed, it was time to knock this off the list.

I'd oriented the boiler in such a way as to make the exhaust run in particular as straight and simple as possible, as I had the least leeway in its routing and design, and knew that the exhaust outlet would necessarily end up somewhere aft and high up on the hull. Exactly where would depend on many factors, all of which I had to now consider and take into account.

Practically speaking, the first consideration was access for installing the exhaust and intake fittings and piping as required. The exhaust fitting was a special double-walled fitting incorporating a 90° bend on the inside, which I'd specified since I planned to install the fitting in the space outboard of the cockpit coaming, where the angled fitting would provide the cleanest run for the exhaust piping. In addition, there were four rings of a special insulating material, two for outside and two for inside, plus a smaller spacer ring that would hold the fitting in the center of its slightly-oversized installation hole to prevent contact of the metal with the hull.

The intake fitting was nothing unusual; a plastic through hull would have worked fine, but I chose a nice stainless steel 1" through hull fitting instead. The piping included 22mm stainless steel flex pipe for the exhaust, and a double-walled fiber-type flex pipe for the intake.

The overriding consideration, however, was safety. The exhaust would be hot, and could damage things around it or burn people. So appropriate clearances from known or future installations were required. The exhaust piping itself would be protected with thick heat insulation, but even so I needed to ensure clearances around the pipe. Fortunately, my proposed run didn't require any passage through bulkheads or other obstructions, with a generally clear run from the heater to the general location of the outlet on the after part of the port hull. The intake had no special installation requirements, other than the piping needed to be basically the same length as the exhaust pipe to ensure proper combustion balance.

Finally, the intake and exhaust fittings were required to be a minimum of 20" apart from one another, and the exhaust at least 20" from any other opening.

With these significant considerations in mind, it was time to determine the exact location of the fittings and install them. I'd already selected the port quarter of the hull, forward of the transom, both for safety reasons and for access. With a 4" deck access plate already cut in the inside wall of the cockpit (I'd cut this long ago to provide necessary access to chainplate and mooring bit fasteners), I planned to install the heater fittings within reach of this opening. Otherwise, there was no access to this part of the inside of the hull. As it was, the installation would take me to the far reaches of the access afforded by this small opening, and the opening allowed me to either view the fittings or put an arm in, but not both at the same time.

Of course this brought with it related complications: namely the name. This section of the hull was where I expected to apply the name and port, sometime much later in the process, but the last thing I wanted to do was install a fitting where it'd be in the way of the graphics. So to help me sort out this small--yet important--issue, I decided to first figure out where the name was likely to end up, and how big it was going to be.

A little work online gave me some estimated overall lengths, depending on the letter height, but this was too abstract, so instead I made up a pair of full-sized mockups, choosing (somewhat randomly) a 4" height for the name (2.5" for the port) and a basic Times Roman font, both of which my sense told me were generally the appropriate choices. The actual lengths of the printed mockups were very close to the estimated measurements I'd received from some online graphics shop's software.

After eyeballing the space on the quarter, I made a few reference marks, beginning with marks 4" down from the caprail, which I thought would be about right for the top edge of the name. From the center of the transom, I marked a 10" space, randomly, to demark the end of the graphics, then taped them up. I had to start somewhere.

I thought the size seemed about right, but decided to print out a 5" height version as well for comparison. This was clearly too large: too long, too tall, too crammed-looking, and just too bold.

Returning to my 4" height, I made some minor adjustments to the position. I liked the 4" distance from the caprail, but the 10" spacing from the transom was too much, and forced the first letters too far forward. Spacing at the aft end was important, but I thought a better reference point at the forward end would be a vertical line extending from the end of the teak rubrail on the hull, so with that I repositioned the graphics a few inches further aft for consideration, repeating the process on the starboard side to give me as many views of the idea as possible. This was much better, to my eye.

With this somehow frivolous tangent aside, I could move on with the fittings' installation. To begin, I used the backing nut from the intake fitting to simulate its location on the hull, and located this as far forward as I could before running into the molded recess that would later accept the refinished bulwark planking. I chose to locate the intake forward of the exhaust since our typical usage of the boat, specifically that we tend to swing on moorings or anchors rather than slips, would mean that the intake was upwind of the exhaust under normal circumstances.

With a strip of masking tape cut to a strong 20", I located the exhaust fitting, using one of the rings of heat insulation as an analogue. This placed the exhaust in the 4" band above the name, and somewhat close to--but forward of--the location of the mooring bit on the caprail, which was a potential concern since I needed to ensure that I could later bolt that in place. I kept the centers of the dissimilarly-sized intake and exhaust fittings the same distance from the caprail.

After various considerations, I finalized the fittings' positions, and from outside drilled small pilot holes so I could ensure, from inside, that the fittings would run into no obstructions. Satisfied, I drilled a 2-1/4" hole for the exhaust, and a 1-1/4" hole for the intake, and dry-fit both fittings.

Here it is possible to see how the metal body of the double-walled exhaust fitting is held clear of the hull by the spacer.

After cleaning up the area and preparing the openings with masking tape, I installed both fittings, beginning with the intake. With no special requirements, I installed this fitting with polysulfide sealant, then went ahead and installed the intake piping right away, leaving the heater end's connection for later.

The exhaust fitting required a special high-heat RTV sealant, Permatex Ultra-Copper. The instructions called for beads of the sealant on both sides of all the heat-resistant insulating rings, and I applied some to the inside of the exhaust flange and caulking groove as well. I angled the neck of the fitting slightly up from vertical to provide better access and the straightest run to the heater down below in the engine room. I'd work on the exhaust piping later.

Afterwards, I cleaned up the excess sealant from both fittings, and reapplied my simulated graphics so I could continue to observe the appearance and settle on the final details as needed.

Normally, I might have waited to install fittings such as these till after the hull was painted. However, in this instance, with the hull paint still some time in the future, I felt that overall progress dictated their installation now, and I'd simply mask off and paint around them when the time came.

Similarly, I began to consider the engine exhaust outlet location. I'd selected 2" stainless steel fitting from Vetus, and with the fitting on hand it was time to install it, which would allow me to wrap up the exhaust hose installation--one of the final engine loose ends. I planned to have the outlet higher and farther aft in the hull than the original (which had been responsible for the boat's sinking under her previous ownership), which meant exiting from somewhere in the after steering room. Exactly where remained to be seen, but from inside and out I considered various options before taping the removable exhaust flange to the hull in one proposed location and letting things settle overnight before continuing.