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CS36 Merlin - O Pato
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Discussion Starter · #1 ·
Hi,

I recently purchased a 1989 CS36 Merlin. I've been working on it throughout the summer, fixing various problems and undoing some of the less desirable customization the previous owner had made.

One thing that has bothered me is the lack of ventilation. There is one cowl vent on the coach roof and the companionway door has a passive vent, but that's it.

I had considered installing a day/night solar vent in the forward cabin hatch to draw air out of the cabin in order to encourage circulation... and I've seen many many boats with a similar configuration, but the few people I've spoken to about this looked at me as if I were planning to douse the boat in gasoline and use it to roast weenies.

Am I taking the wrong approach? If I'm looking to improve ventilation in my boat by adding an active vent, what's the best solution?

Cheers!

G
 

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I have allergies and asthma. We installed a solar vent and I have had zero problems breathing and there is hardly any mold at the beginning of the season.

So, it works for us.
 
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CS36 Merlin - O Pato
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Discussion Starter · #3 ·
Thanks DR.

If I may ask, WHERE did you install the vent? Did you mount it on a hatch or on the coach roof itself?

I'm concerned that once I cut a hole in the roof, that's it.... but if I don't like the vent on a hatch, I can replace the hatch and I'm back to where I started. Am I wrong to be concerned about putting a hole in my boat? Is using a hatch opening that bad an idea?

Cheers!

G
 

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We put it through the deck where the surveyor detected a soft spot. It had to come out anyway so we just used that location for the vent. It happened to be just in front of the V berth and outside of the head.

It makes a little hum when it's running. I tune it out but my SO can't sleep with it on so he shuts it down at night when we're on the boat. Otherwise, it runs 24/7 and through the winter when the boat is on blocks.

I don't particularly like them through the hatches. Just a personal aesthetic preference. Can't explain why. It's a perfectly acceptable place to put it as far as I know.

Another point is that we don't take this boat offshore. I'd have reservations about adding one anywhere if we were regular offshore sailors.
 

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Tartan 37
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I have two solar day/night vents, one in each hatch, one for exhaust and one intake. I also have four cowl vents so ventilation is great. If we're not on the boat for more than a couple of weeks I pull the floor boards as well. I have also vented my air cooled fridge into the bilge to help keep some air moving. Lastly, I have three cans of Kanbera Gel on board, one large in the bilge and two smaller ones in the cabin. Boat has only a slight smell from the teak but no mold. A well ventilated head tank also with a filter on the vent hose ;-)
 

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Mermaid Hunter
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I had considered installing a day/night solar vent in the forward cabin hatch to draw air out of the cabin in order to encourage circulation... and I've seen many many boats with a similar configuration, but the few people I've spoken to about this looked at me as if I were planning to douse the boat in gasoline and use it to roast weenies.
This is a perfectly reasonable thing to do. It's easy, straightforward, simpler than going through the deck (especially if cored), and likely to be effective.

I'd like sauerkraut and relish on my hot dogs please.
 

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I don't think you're taking the wrong approach at all, unless the vents are installed in a spot that might get in the way of your lines.

I just installed two nicor 4" day/night solar vents in my forward and aft cabin hatches. Thick lexan hatches, so used a roto-zip with the circular cut attachment and it was an incredibly simple process. The toughest part was cleaning up all the little shavings afterwards. I had a dropsheet laid out in the cabin below to catch the shavings, but they still managed to fly around a bit!

The forward vent is set to intake and the aft vent is set to exhaust.

For adhesive/sealant, I used 4200. No screws used. The vents look fine to me and the added ventilation, especially when I'm away from the boat, is more than worth the investment.
 

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CS36 Merlin - O Pato
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Discussion Starter · #8 · (Edited)
Thanks everyone for your input on this. I have another question related to this....

As I said, I plan to put a solar vent in the forward cabin hatch to draw air through the boat from the two passive vents in the salon. I was also considering putting a smaller solar vent in the head to draw out the nasty air in there.

If I have two solar vents drawing air out of the boat, do I need one pushing air in, or will the two passive vents in the salon be sufficient? I would think the two solar vents would create a vacuum, and air would naturally be drawn in through the passive vents to compensate.
 

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We put it through the deck where the surveyor detected a soft spot. It had to come out anyway so we just used that location for the vent.
Brilliant way to kill two birds with one stone.

To the OP, sounds to me like you have enough passive ventilation that you don't need an active intake to balance the active exhaust. Two exhaust vents should work fine.
 

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Thanks everyone for your input on this. I have another question related to this....

...will the two passive vents in the salon be sufficient?
I think this plan will work fine. Air will be drawn in through your passive vents, so no need for an active intake.

If ventilation doesn't seem optimal after installation, you always have the option of temporarily sealing your passive vents and reversing the flow on one of the active vents to see if that works better.

I have a couple of ankle level cockpit hatches that I used to leave open for marginal ventilation improvement, but they now remain closed because they would have interfered with the flow of fresh air from bow to stern. If my current setup isn't optimal, I may reverse the airflow on my forward nicor vent to exhaust and then leave the cockpit hatches open as the intake.
 

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CS36 Merlin - O Pato
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Discussion Starter · #11 ·
Should the air always flow bow to stern? The two passive vents in my boat are in the salon... (cowl vent behind the mast and vent in the companionway hatch) so my intent was to move air forward from the salon up to the head (which is forward of the mast) and the forward cabin, where the solar vents would draw the air out.

Basically, I'd be pushing air out the bow instead of the stern... which appears to be the opposite of what most people do. Does it matter?
 

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My thinking was that I'd want to have the shortest route for the stinkiest air to leave the boat. Since my engine and head are aft, the exhaust is there. With your configuration it would make sense to have the exhaust forward.
 

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It really doesn't matter which way you move the air as long as it's moving.

I have a solar vent in the head - it really does not move very much air at all. At best, it's not much better than a vent without a fan.

I'm in the process of installing a couple computer fans in the boat, fans that move lots of air, draw almost no electricity, and cost next to nothing. I purchased a pair of 72-mm PC fans with led lights and they only cost $8 each at Amazon.com. They move a huge volume of air, they are stone quiet, and the current drain is just .04 amps.

In your case I would place one at the bottom of each of your current air locations - I sincerely believe you will be amazed at just how effective these tiny fans are. For the price of a single solar powered fan, you could buy a dozen PC fans and have money left over for a bottle of rum to celebrate.

Good luck,

Gary :cool:
 

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That's a great idea Gary, I just wasn't interested in running any wiring which is why I went with the solar vents. Although once the motors or batteries eventually die I'm sure I could retrofit the vents with wired computer fans quite easily.

Do you have a some type of case or pre-existing passive vent that you're mounting the fans inside? I'd be very interested to see pics of the fans installed.
 

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CS36 Merlin - O Pato
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Discussion Starter · #15 ·
It really doesn't matter which way you move the air as long as it's moving.

I have a solar vent in the head - it really does not move very much air at all. At best, it's not much better than a vent without a fan.
Due to the way the boat is configured, I can have the door to the forward cabin open or the door to the head open but not both at the same time. Given that I have a limited capacity for logic, my plan is that no matter which door is open, I have a fan actively drawing air out of the boat.

This is, as you might have guessed, my first boat so I'm relying heavily on guesswork for configuration. Ask me sometime about my adventures trying to find a reasonable way to render the boat dog-friendly. By comparison this ventilation thing is a breeze.... (breeze, get it? damn, I'm funny)
 

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Just make sure the vent in the forward hatch can't snag your jib sheets while taking. And won't get tripped on. You might need to put a guard bar over it.

And of course make sure it can be secured shut, so that green water coming on deck won't promptly go below.
 

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Don't call me a "senior"!
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I have a day/night solar vent, mounted on the forward hatch, on my 27' boat. One advantage to that location is that the hatch is a bit recessed when looking at it from the inside. So the inch or two of vent hardware that sticks down into the boat doesn't catch the top of anyones head very easily.

I set the vent up as an "intake" fan so that it creates a very slight positive pressure in the cabin. This forces forces air down into the bilge and out through the engine compartment (and ultimately out via the cowlings at the stern, which I keep pointed away from the prevailing wind direction), and keeps most of the diesel and motor oil fumes from making their way into the cabin via both the bilge and the galley cabinetry. Some slits in the drop boards of the companionway act as a passive exhaust vent. There is also a vent with a cowl in the "chain locker" in the bow of the boat; while at the dock, I point this into the prevailing winds to help keep flow going aft.

Keeping the cabin slightly pressurized via the day/night solar vent and the passive cowlings noticeably reduced the "old boat smell" right away (washing the cushions didn't hurt either). And having a bit of air flowing 24/7, even on dead calm nights, has significantly reduced the mold and mildew problems.
 
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How about a middle road.

I just installed an "Air-only vent". It is a small footprint dorade for passive ventilation, and then has a fan option that you can run for active. I installed two of them, and they work pretty well.

Details and pics on my blog in sig.
 

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CS36 Merlin - O Pato
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Discussion Starter · #19 ·
Thanks everyone for all your suggestions. I appreciate all the input. I especially liked the idea of using PC fans, and may try that once I have a bit more experience with the electrical systems.

I haven't exactly decided what the configuration will be yet, but I now have a lot more confidence about using these day/night solar vents in the hatches. I'm definitely going to install one in the forward cabin hatch and one in the head. The only question is which way I'll direct them.

Again, great input. Thanks!
 

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... The only question is which way I'll direct them.

Again, great input. Thanks!
If you mean air in or air out, that's easy to change even after you install the vents. Ours came with two fan blades. Blades are facing different directions. Easy to pop out and put in the other if we want.
 
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