CD 25 Outboard hatch opened or closed?

[dustintodd]

I purchased a CD 25 and the yard mechanic told me to always keep the outboard hatch open when running. The CD 25 came with a Yamaha 8hp. The outboard is practically in your lap with 25 configuration and really annoying. Do I really need to keep the hatch open to run the outboard? What is the issue?

[Paul Clayton]

My CD25 came with an obnoxiously loud and smoky Yamaha 6 horse two stroke. If you closed the cover all the way, it would choke itself on its own fumes. If you left the cover open, you were the one that choked on the fumes, as well as going deaf. With adequate ventilation, you can close the cover - I suggest that you try it and if the engine runs ok, don't worry about it. Some people can and some can't.

I replaced my engine with a new 4-stroke that runs fine with the cover down.

[dustintodd]

Which 4 stroke did your purchase?

[Paul Clayton]

I put in a Nissan 8, but I wouldn't do that again. I had to do some substantial modifications to the well to get it to fit. If I had to do it again, I would put in a 6 - I don't think it matters what brand, just buy from a reputable dealer. Also, you may want to get one with an alternator to keep your battery up. Be sure to get one with a long shaft or the prop will be out of the water half the time.

There are many, many posts on the board regarding repowering CD25s, you may want to run a search and look over them - lots of good information.

[Oswego John]

[quote="dustintodd" Do I really need to keep the hatch open to run the outboard? What is the issue?[/quote]

Dustin,

I don't own a CD25 so I can't speak with authority. However, I have spoken to and have read reports of CD25 owners who have commented on this problem. From what I gather, it is an either/or situation.

When motoring, it is much quiter with the engine hatch closed. While motoring with the hatch closed, I get the idea that there isn't adequate air entering the engine chamber to supply enough oxygen for efficient combustion, especially at higher RPMs. In effect, the engine is running rich, not good for an engine, especially so for a four cycle engine.

I suppose that somewhere there may be a happy medium of sorts. Keeping the engine hatch closed would make things much quiter. Maybe a louver could be installed to allow adequate air for proper combustion. There would be some noise, but certainly not as many decibels as there would be with the hatch open. Maybe a baffle setup could be incorporated in the airway to further reduce engine noise.

I have read where some boat owners have installed a sound deadening barrier in their engine compartments. So far, I think that this is only with diesels, maybe not.

At any rate, make sure that the motor you use has an underwater exhaust. Most of the larger engines do.

I hope that someone with realtime experience would go further with this. It seems to be a problem for many owners.

Good luck
O J

[Dick Emrich]

I can't take credit for it because my boat came this way, but with an old Johnson Seahorse 9.9 two-stroke I can run almost all the time with the hatch cover down because there are air intakes on the cover, one facing forward, one aft. The fumes problem was corrected by the previous owner who ran a plastic tube from the exhaust into the water. It all works perfectly. No fumes at all. When I do have to have the hatch open, for example when I need to get at the controls, the noise is, as you say, annoying. As to the motor, I've read here on the CD Board that people feel a 5 h.p. four-stroke is adequate. It would depend on the conditions where you sail.

[Doug Fallin]

I have a 6 hp 2-stroke Johnson that use to fill the lazarette with fumes and kill the engine if I closed the hatch. I tapped the exhaust port and ran a tube about 2 feet down. Now the exhaust exits below the water and out of the lazarette. I have zero fumes and can close the hatch. It made all the difference in the world.

[dustintodd]

No experience with outboards before this purchase. Where would the exhaust port be on my Yamaha? It's not below the water line normally? My CD 25 already has the ventilation ports on the hatch cover. I can orient one forward and one backwards.

[Doug Fallin]

On older, and some newer, two stroke motors the exhaust exits just below the motor base, at the top of the shaft on the aft side. When you run the motor, you will see smoke exiting. You can also see the outlet which looks like a 1/2 inch hole opening downward. Newer motors and most 4 stokes I belive have the exhaust exit thru the bottom of the shaft at the prop. I hope this helps. I don't have a lot of experience with newer outboards. My '76 johnson has worked perfectly for many years and I have not had reason to look elsewhere.

[Kilgore]

I have a couple of extra sheets of this stuff: http://www.secondskinaudio.com/vibratio ... er-pro.php leftover from an automotive install.
I may try sneaking some onto the engine compartment sides and front using the cockpit lockers for access.

I had briefly borrowed a 5hp 2stroke Merc before my Tohatsu 6 arrived. The new motor is noticeably quieter, even though the cover doesn't fully close. I presume this is mostly related to the prop exhaust. I'll be building a new transom board so that the cover will clear. My cover also has a pair of PVC cowl vents.

[Steve Zwicky]

I've got a CD26 with an outboard in the well. The 9.8 Tohatsu ran fine with the hatch closed except when I motored with the wind behind me. Then the cowl vents were sitting in still air and the motor would choke up. I connected a 12 volt fan to the exhaust (aft facing) vent and it works fine. Bit of a plumbing challenge with dryer hose and other fittings but saved my sanity.

[Gary M]

My friend solved this problem on a Columbia 26 MKI with an outboard well.

He used a bilge blower to keep the well supplied with clean air and he was very satisfied. Since the outboard supplied 12VDC, power usage was of little consern.

I think I would tackle the problem the same way but a bilge blower may be over kill. Maybe it can be slowed down or even controled with a resistored switch.

I did motor with him on this boat and it was amazingly quiet compared to befor the fix.

Gary

[seajunkie]

My 4HP Nissan 4 Stroke doesn't have a problem breathing with the hood down. There was a strange modification done to the boat at some point. You can see a cut out on the rear bottom of the well. Maybe it helps it breath? I was wondering if there was a long shaft motor that could actually tilt through that thing, but I can't imagine one that would.

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