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Ventilation - a Work in Progress

January 17, 2012. This is an effort to compile some of the many inputs we have received from owners on the very important subject of ventilation. Hopefully, it will inspire further commentary and good ideas we can share. We'll start with posts that began on the Forum back in July, 2007 from Eric Sorenson, Parakletos, Yankee #106. Here is the thread, heavily edited and modified with inserts..

Topic: Ventilation
Posted: 29 Jul 2007 at 3:29pm

Greetings fellow Dolphinites:

I've noticed my boat is great performer when it comes to drawing moisture from the air and pooling it in the bilge. It's easy to see how this can happen: Parakletos is in the 52 F waters of Puget Sound and surrounded by moist air that's just dying to find a dew point.

When I got the boat a few months ago the sole source of ventilation was three slots in the companionway drop boards. I've since installed a solar vent to one side of the mast and yesterday sawed out a three-inch hole in the foredeck for a dome vent that can be screwed closed during heavy-weather sailing. I'm also thinking of putting some small stainless vents on each cockpit seat.

Which is all by way of asking: What are the other Dolphin owners doing towards achieving the elusive ideal of a dry boat?

Fair winds,


Posted: 29 Jul 2007 at 8:08pm

Hi Eric

On Long Island Sound we don't have the (water/air) temp differentials you have but we have the problem too. The primary fight is against mildew.

Like your boat, Marionette has a 4' dia screw type mushroom vent in the deck at the bow (beween dock lines in photo at left). In combination with an 8" x 10" wood louver in the bulkhead (below left) that separates anchor locker from the V-berth, this system ventilates the anchor locker.

There is another vent below the V-berth (above right) that facilitates airflow around the spaces that contain the head, holding tank, hoses, and pump fittings. Here is a link to Marionette's vents in the V-Berth

A short detour here - Maine is infamous for fog and rain to go with its contrasting unbelievably beautiful days. If you have to leave your boat for several days buttoned up ventilation is critical. Marionette's 'maine tested' ventilation system consists of 1) a solar powered/rechargeable battery ventilation fan (below top left) that runs 24 hrs a day - a super piece of equipment now 16 years old -2 battery replacements in that time! NOTE: Make sure that the reversible fan is loaded so the air flow is exhausting! - otherwise you draw rainwater into the boat!!, and 2) a main hatch cover that has a flap to allow air to flow through the louvered top companionway panel. Here are some photos.

The hatch cover was originally designed to protect varnish but unintentionally blocked air flow. The 'flap' works. This system is the workhorse of Marionette's ventilation. Here is a link about covers and their effect on ventilation - click to go there)

In a few lockers (seat backs, galley) that back up directly to the hull, and that have books or other items better off not damp, I lined the hull with a fitted, non perforated headliner foam backed material so these lockers do not "sweat" on the hull surface. I was thinking of lining the entire hull above the waterline with this material (great/bad idea?, not done). This material is vinyl covered so clean up is easy.

Marionette has no opening ports, and her 7 fixed portlights do not leak....

I think that continuous fan operation plus insulating the hull (in critical places), and regular spray/wipe downs with a bleach/water solution is a good way to go. On the other hand, I know a guy who has a small dehumidifier and swears by it.

Marionette, #12


Posted: 03 Aug 2007 at 11:53am

I just posted this in the 'General' area replying to a post about portlights: I decided to put the round ports on Recovery because I had to replace the originals..... All of the ports on the sides are non-opening, the one on the forward is opening. They were surprisingly inexpensive.

As far as ventilation, I leave the forward port slightly open all the time and when I leave the boat, I put a bucket on the berth directly under it. Whenever it rains, the water drips into the bucket. For my uppermost companionway slat, I have a wood-framed bronze screen that I leave in whenever the boat's on a mooring or anchor. I only use the solid teak one when I'm at a dock not facing into the wind or when the boat's out of the water.

I also have two cowl vents on either side of the lazarette hatch that are attached to ducts that lead to either side of the inboard engine under the companionway. One cowl faces forward and the other aft and they provide an unbelievable amount of ventilation.

In the slightest breeze if you put your hand in front of the duct inside the cabin you'll be amazed at how it blows in. The other duct sucks it out.

Even if I had an outboard, I would continue to use the cowls and ducts.

I looked into some small dorade boxes with cowl vents on the cabin top (as I've seen on some dolphins) but as my halyards are led aft to the cockpit and there is precious little deck space on our little boats, there really wasn't room and frankly, I don't think I need them.

Even with all of the ventilation, I still get some mildew here and there and for that I keep a small spray bottle of cleanser with bleach and I spray and wipe as necessary.

Jay Picotte, Recovery


Since Jay brought up Dorade boxes and cowl vents lets check a few. Here's Arion's, Charlie Drew's Yankee #71

Dorade boxes - and a main hatch cover

Anne Bonny's Dorade Vents
Anne Bonny's Cowl Vents

Stay tuned








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