View Full Version : In Memoriam Ventilator Doradum
09-13-2001, 09:35 AM
My copy of Michael Illingworth's "Offshore" tells me that, in 1946, Rod Stephens was formally presented, by Michael Mason, the owner of the Fife yawl "Latifa", with a bottle containing a fish, preserved in spirit, which had come down a Dorade vent during an Atlantic crossing to take part in the Bermuda Race of that year. The bottle was inscribed as above.
Now, I have just had an heretical thought. I am abolishing both the Dorade box ventilators on the boat, although I remember building one, and rebuilding the other, a few years ago. I was so proud of their nicely dovetailed boxes and smartly painted cowls!
The penny has dropped. They were not much use as ventilators, but they were quite superb at catching ropes, bashing shins, occupying valuable deck space, and so on.
They were fashion statements - "Look at me, I am a real seagoing boat".
Now, IF I were offshore racing, with a big crew down below trying to get some kip as we thrashed through heavy weather, they would be worth while. But the truth is, I ain't. I go cruising with family and friends, and for most of her life the boat swings quietly round her mooring, in the summer, or is laid up under her winter cover, with the hatches wide open, in the winter.
I am replacing the offending rope and shin trappers with big high coaming mushroom vents, which can stay open on the mooring and for most of the time under way. And I shall get my foredeck back.
09-13-2001, 10:09 AM
Ain't nuttin sacred anymore?
Mirelle,sound like a dang good idea.
I know how the traditional way can become an end in itself sometimes,but improving a boats functioning just seems right.After all how often do you hear someone say,gosh we had fun today,tripping over that pretty wood thingy,and swearing at our hung up lines?
09-13-2001, 10:24 AM
The nice bronze mushrooms that can be screwed shut don't, in my experience, let in much air and will likely, if you mount them on the rail or deck, let in some water, even closed.
Regretably, the solar/battery fan inside units are butt ugly on a real boat.
Some folk I've known (and I may when I rebuild) have gone hog wild at finding cool new places to hide vents, like in the bitts or safety rails at the mast, and let the piping for at least some of these go into the bilge, both to improve ventilation and to make a hole in the deck that's no worry if it lets a little water in or if the boat's capsized.
You could reduce the amount of shin damage by combining a nice big vent over a mushroom, allow some weep holes, and perhaps a three legged bronze tube guard rail over all that.
Tell you crew that they look better bruised.
09-13-2001, 11:11 AM
Ian Nicholson says somewhere that a ventilator with less than 6 sq. inches opening is useless. I agree with him.
I found that the drain holes in the Dorade boxes caused the ventilators to perform poorly; most of the air escaped that way, and the pattern of high coaming mushroom with a rubber O ring seems quite tight when closed.
Now, let me explain. There's a lapstrake ply dinghy that lives almost permanently over the skylight, which is left open when I'm not on the boat. About 100 sq inch opening. The lee side can be left open under way in almost any conditions. The forehatch has side panels and can be left open about 3" - another 36 sq inch opening. 5" dia stove pipe with H head - 15" sq, three 4" dia mushrooms - 12"sq. each. Plus opening ports and the companion when under way, but my concern is the ventilation when I am not aboard and/or am aboard but not under way.
09-13-2001, 11:20 AM
Originally posted by Mirelle:
...I found that the drain holes in the Dorade boxes caused the ventilators to perform poorly; most of the air escaped that way,...
Sounds like an application for a float valve of some sort. No water, the drain is closed. Water gets in the float lifts and drain is opens.
If you incorporate this into your Dorade vents I expect a royalty payment.
09-13-2001, 11:39 AM
That's a Revon ventilator, Ian; found aboard RNLI lifeboats, (also USCG ones?) and the cowl ventilator with the mushroom underneath it is a Fairmile ventilator. So both your inventions work fine, but I fear I cannot offer you a royalty payment!
Seriously, the Revon, which uses a water seal, is really really clever, but they only seem to come in big sizes - or perhaps are only made for the RNLI.
09-13-2001, 11:42 AM
Well, I don't know anything about dorade vents, unless they're big enough for spies to hide in, and to my mind nothing less will do.
I do know, though, that it's good to see you back on the forum, ACB/Mirelle.
09-13-2001, 12:23 PM
There are no dorade ventilators on Ta'ana Mari as such.The hatch has a double baffle to eliminate the water below but have twin fans bringing air in, and a permanently mounted solar charger on the teak trrim of the hatch. There are similar arrangements elsewhere on the boat...but... the hatch inlet and outlets go to sealed tubes that extend to the cabin sole......the boat can turn turtle and now water will pour in the vents...
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