Dorade Dilemma

  Tuesday, November 18, 2014 / Stephanie / Projects  

Does anyone notice what is missing from Detour's dorade ventilation box? There are no boxes; hence "dorade box" a ventilation system designed by Sparkman and Stephens which enables air to flow freely into the cabin yet prevents water from entering the boat. A rectangular box is affixed to the deck. Within the box are two baffles (or alternatively, pipes); one extending upward from the deck and one extending downward from the box top. The baffles form two chambers within the box. Air enters the box from a forward facing, wide-mouthed cowl mounted at the box's top. Air flows through the cowl, into the box, around the baffles, and down into the boat's cabin. The baffles prevent any water which may have entered the cowl from entering the cabin. The base of the dorade box has openings to drain out onto the deck any water that may have entered. This is a simple idea and it works beautifully. We had only one dorade ventilation box on Rode Trip and it never took on water. On Detour's deck there are mushroom type vents through the deck that are covered by cowls. The mushroom vents have an interior knob that turns the exterior vent cap; either raising the exterior cap to allow air flow in or lowering the exterior cap to close it against the deck and stop air flow. A closed mushroom cap should theoretically prevent water from getting inside the boat's cabin. Atop the mushroom vent is a cowl which should facilitate air flow. The mushroom vents had corroded so badly, however, that we could not open or close them by using the interior knob. Brian and I removed each cowl from the deck and took out each mushroom vent. Not only were the cowls and vents filthy, they also housed some interesting spiders and other yet-to-be-defined insects.

We cleaned each cowl. We disassembled each mushroom vent, in some cases using WD-40 to get the vent knobs to turn. The vents were cleaned with soapy water and steel wool. The previous sealant was removed from the vents and the deck with acetone. Once everything was cleaned and lubed, Brian re-installed the mushroom vents. We could now open and close the vents from inside of the boat. As for the dilemma, I return to the fact that there are no dorade ventilation boxes atop the deck. The cowls mounted over the mushroom vents are simply screwed into the deck. First problem; the stainless screws had not been properly insulated from the aluminum deck. The screw holes were completely stripped where, over the previous 13 years, the stainless had interacted with the aluminum and caused it to corrode. So actually the cowls were not fastened to the deck at all because the screws no longer threaded into the holes and the entire cowl could be lifted by simply picking it up. Second problem; the corroded screw holes enable water to leak into the boat's ceiling. The holes are now exposed, not sealed, and the cowls provide no barrier to water whether the mushroom vents are opened or closed. A short-term solution was for Brian to seal each cowl's screw holes, which he did so that we will not have water leaking into the boat's ceiling. The proper solution, however, is to install dorade ventilation boxes. Brian has prepared the appropriate measurements for a dorade ventilation box and we are awaiting quotes from aluminum welders at the yard to build aluminum boxes and weld them directly to the deck. No more stainless screws, no more leaks, lots of air! Brian could of course do this project himself, which would require we purchase a welder and assemble all of the necessary materials. This proves difficult at our current location so while awaiting the welders' quotes we are also entertaining the idea of dropping this boat into the water and sailing directly to Florida.


  1. From Brian Grandjean on Nov 28, 2014
    Thanks, Mitch, for the tip. The steel wool was not used on or around aluminum, in fact we brought the vents off the boat in order to clean them. They are stainless. The vents were thoroughly washed with soapy water and the goal to not allow any steel wool aboard.

  2. From Mitch Brown on Nov 28, 2014
    You will want to be careful using steel wool on aluminum and stainless steel as the bits of steel get in-bedded and start corrosion/rust. have no first hand experience using it on aluminum but on stainless it definitely causes it to rust. It's best to use the green scotch bright pads.

  3. From Stephanie Grandjean on Nov 20, 2014
    Brian, wishful thinking...only wishful thinking ;) but we could probably cross the Atlantic faster than the French seem to work.

  4. From Stephanie Grandjean on Nov 20, 2014
    Janet, this would not be acceptable for USPS standards! I'll contact the designers to sign them up for a class :)

  5. From Stephanie Grandjean on Nov 20, 2014
    Ann, we did have a full report from a boat surveyor before we purchased the boat...there are always surprises! With so many considerations, I guess we missed the dorades during our initial inspection.

  6. From Brian Schmoyer on Nov 20, 2014

  7. From Ann Landau on Nov 19, 2014
    Are there boat inspectors like 'home inspectors' you hire as a buyer? If not I see a business opportunity there for you two !!!

  8. From Janet Cass on Nov 19, 2014
    I guess that's how the French set up dorade boxes!