cape dory 25 outboard exhaust

[mccue04@optonline.net]

I am a new owner of a CD25.
When running the outboard I've found I have to leave the hatch open. Anyone ever try to install an exhaust fan to stop the engine from choking? Is running the engine with the hatch open something I'll have to learn to live with?

[winthrop fisher]

Hi...
in stall a two solar vents, (in and exhaust)
that will fix the proplem and you will not have to have the hatch open at all.
winthrop

I am a new owner of a CD25.
When running the outboard I've found I have to leave the hatch open. Anyone ever try to install an exhaust fan to stop the engine from choking? Is running the engine with the hatch open something I'll have to learn to live with?

[Scott MacCready]

Hello, and welcome to the world of Cape Dories.

You don't mention what engine you have but I've had Honda 4-strokes (5hp & 9.9hp) in my cape dory 25 & 26. The exhaust problem was solved in each of these cases by connecting a length of tubing to the engine's secondary exhaust and routing it straight down the back of the engine shaft under the waterline. It kept the exhaust out of the lazarette and by no means impeded engine performance. I could run all day with no problems.
The secondary exhaust is located on the back side of the engine shaft, above the water-line. I used a length of 3/8" copper tubing, just inserted it into the hole and used marine sealant to hold it in. A long plastic zip-tie around the shaft below the waterline held the bottom end in place. Never had another problem.
This has been discussed on here many times in the past so I'm sure other engine makes have similar set-ups.

[Mathias]

There is a lot of information on this if you do an archive search. One, albeit expensive, way to solve the problem is to buy the Nissan (built by Tohatsu) 4-stroke engines which exhaust through the prop. What a wonderful idea. I have one and it is quiet, works with hatch down, and no more smellies.

-Mathias
Sunset, CD25, #332
Lake Champlain

[Scott MacCready]

The honda's main exhaust is via the prop also. It's only the secondary exhaust (whatever that is) that exits above the waterline. On my 5hp, it was enough to choke the engine with the lazarette closed. On my 10hp, it was not a problem.

[Jim Leininger]

All outboard motors have some exhaust above the prop, albeit very small. At idle, cylinder pressure is insufficient to push exhaust through the prop (or deep underwater). I made an extension on my Yamaha 9.9 that gets the exhaust "just past the transom, just under the water". This is reasonably successful, but under the wrong wind conditions will still allow exhaust choking. See my website at http://home.earthlink.net/~leinfam/index.html to see how I set it up.

It is important to keep the extension at a minimal submersion. You'll get poor ring sealing and attendant oil fouling (soot) if the exhaust pressure is too high (on 4 strokes).

I find I'm going to need a ventilation fan that will run with the engine "on" to really solve the problem. On my previous boat (CD25) I made a fresh air intake for the carbs, with flexible hose routed through the outboard upper cover.....but that leaves a lot of intake noise in the cockpit.

Regards, JimL

[awatson72]

I solved the problem by mounting a cheap bilge blower on the underside of one of the vents. I experimented with both blowing air in and sucking air out by reversing the wires, and both ways worked fine and allowed me to run the engine with the cover closed without it starving for O2, or gassing us out of the cockpit. I'd recommend having your outboard supply a trickle charge to the battery though, since the blower would eventually drain it.

[Kurt]

When I owned my CD26 I solved the problem by routing a 1-1/2" hose from one of the motor well vents to the engine cowling...thereby giving the engine a chance to suck clean air into the carburetor...I also routed the idle relief exhaust port through the bottom aft end of the motor well. This was with a Honda 9.9. My modifications worked like a charm