Can get close, but no cigar.

Does your boat have a U-shaped dinette or the L-shape dinette?

I think a rectangular duct just inboard of the holding tank would get you to the salon/head bulkhead, but getting a 6-inch diameter duct through the head compartment might be a bear of a job. If you had an outlet in the salon forward, at night you could attach a flexible duct that would route sufficient cool air to the V-berth. In the morning you would disconnect it and stow it away. Not an elegant solution but it might get you an enjoyable a/c season while you strategized about a final fix.

If you look in the Maintenance Upgrades library you'll find an article by Chic Lasser that utilizes this temporary flexible duct idea.

BTW, could we ask that you create an automated signature so that we know a little more about you and your boat? It's easy to create a signature. Use my signature below as a model.

I'm having diesel heat installed in my C36 and planned on using the same ducts for A/C when I added it later. The tech told me that you can't do that; the A/C requires a 6" duct, and the heater uses 3-4". If the A/C unit doesn't get enough airflow, the compressor ices up. So back to the drawing board on that.

We discussed my plan for putting the A/C unit under the settee just forward of the galley sink, with a big return ducted to the unit and a 6" duct somewhere in the dinette area. If that makes the compressor happy, I might just hook the heater duct system too, just to distribute additional cool air to the forward cabin, head and aft cabin. I haven't discussed that with the tech yet, but can't see how it would hurt anything.

Running 6" ducts through the boat seems impossible without compromising structure, something I'm not willing to do. I wonder how Catalina does it at the factory????

Gary, if 6" ducts for the AC are approved for the high internal temps of the forced air furnace then you can use the AC ducting for the heater.

The 3" ducts for the heater flow is a minimum diameter, and 6" would be just fine for the heater...the larger the better, in fact. If the furnace doesn't get enough airflow it overtemps, and reduces its life. What the furnace most wants is minimum internal air resistance (drag, in aeronautical terms), and drag is caused by air restrictions due to diameter, length of the duct routing, and corners in ducting. But whatever duct material you use MUST be capable of handling the *very high* temperature that the diesel forced air furnace puts out.

Agreed that 6" dia ducting will be a challenge to route. And you're right about avoiding cutting holes that might compromise structural integrity.

Gary, have you considered mounting the furnace in the hellhole?

Mark M,

First we have to clear up a semantic issue: When you say "lazarette" on the Mk II do you mean the lazarette that is behind your left shoulder when you're standing at the helm...the opening whose lid your feet would rest on if you were sitting in the portside sternrail seat? This is the true portside lazarette. Please do not confuse this opening with the "cockpit locker", which is the locker portside of the cockpit table, underneath the portside bench seating.

Mounting a furnace or AC in the cockpit locker is not advised because there is no routing path either down or forward from the cockpit locker, because the fridge, or the galley, or the fuel tank will be in the way. The only route from the cockpit locker is, first, to go AFT into the portside lazarette, then downward aft of the propane locker to the bilge, and only then forward beneath the aft cabin floor portside. (There is a compartment on portside beneath the cabin floor called "the hellhole".)

But...if you mount the AC in the portside lazarette, then you're in the best position to route forward, via the hellhole, then underneath the fridge, then underneath the stove, to the compartment just forward of the sink. To go any more forward from there will require a smaller or even rectangular duct to squeeze by the holding tank. Once forward of the holding tank, it's your call depending on whether you have the U-shaped or L-shaped dinette. The L-shaped dinette runs out of options. But if you have the U-shaped dinette, your ducting could turn right in the Y-valve compartment (just forward of the holding tank) and then head towards the mast. You could, somewhere in that area, route down through the floor and across the boat via the bilge, then up through or behind the drawers under the TV cabinet, then forward into the V-berth.

That's a long run.

In my part of the world, fortunately (unfortunately???) we don't have to deal with AC. And since we like it cold when sleeping aboard at night, we wouldn't need any heater ducting to the V-berth. Heater ducting - of smaller diameter, anyway - could terminate in the head compartment, so a furnace installation wouldn't have near the same challenges.

I hope this helps.

I have a reverse cycle Cruisair mounted alongside the battery charger under the setee just forward of the galley. A large duct runs to a vent between the two port cabinets. Another duct snakes its way behind the galley into the aft cabin and has a vent below the fuel tank on the port side. The third duct snakes its way behind the port setee up and through the upper part of the head cabinets and has a vent just above the shelf on the port side of the forward cabin. The thru hull is by the keel and the exit is about 12 inches above the port waterline. The return vent is by the unit under the seat just forwad of the Galley. Hope this helps, we have been happy with the setup.
John Meyer

Thanks for the reply. I'm having the heater installed by the dealer in Annapolis (don't recall the name offhand), and all ducting is part of the Espar 'kit'. So the diameter and duct type should satisfy the needs of the heater (or that's the plan).

As to A/C; that's a secondary consideration. I would only use A/C at night and I'd be anchored out during the day and trying to stay cool in the water. I'd return to the dock at night to use the A/C. I'd be curious if one of those cruise and carry units would be sufficient for the main and forward cabins just at night??

Seeing your reply to Mark (which I passed along to the installer); if the ducting comes from the 'hellhole', and a Y can be put there, it may be possible to run additional ductwork down the starboard side to compliment the heater run down the port side and get enough flow to make the A/C happy. Again, the heater is my primary consideration at this time, I'll tackle the A/C in a year or two (if ever).

Thanks again for the reply.

Gary, on a Mk II there is no reasonable way for ducting to cross the boat from the hellhole over to the starboard side because either the water tanks or the engine compartment are in the way. And if you did the split in the lazarette, there would be no route down the starboard side of the boat for a 3" duct. I think any ducting must be confined to the portside of the boat.

(Added later: Maybe I shouldn't have sounded so sure of myself. There 'may' be a way to cross from the hellhole via the engine compartment, about the present location of the raw water intake. But once on the starboard side, you would have the power distribution panel to contend with, and then there is no reasonable way forward from there. Getting wiring from one starboard game table seat to the other is a real bear, so a 3" duct would be nigh on impossible, it seems to me.)