This was my first year with my newly acquired 1968 Commander, 35' twin 327f.

The engines start and run fantastic. I get a lot of fumes when under way. We have tried having the hatch in the front open when under way. We have tried the hatch and cabin windows open. We have tried having nothing open.

I had the boat pulled for the season this past week (sad day) and cleaned the boat out for winter storage. The clothing stored in the boat since the launch in July smell of exhaust fumes so strong you would not want to wear them.

My guess is the engines are running rich but I though maybe everyone has this issue.

Opinions please.

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Steve, given that information I think you might be having crankcase blowby.  The 327Fs on mine just vented through the breather cap and it doesn't take much of these fumes to be noted.  We may not have the nose of a dog but many alluring and awaring notes we detect in the the low ppm range.

I think there must be additional leakage, that may well be exhaust, for the fumes to be noticeable at the helm at those rpms.  The bilge will lose probably 400 to 800 cfm or more through the carbs.  Granted most of the make-up/intake air vents low into the bilge but the area above and surrounding the engines will probably be a bit turbulent.

After a good run while everything is warm, your at anchor or dock with the engines idling, run an IR temp gun over the full drive and exhaust train looking for temperature anomalies. Do you have water in the main bilge after these runs?  Drive train will be captured in the engine bilge but most of the exhaust train will end up in the central/keel bilge.  I don't know if it is necessary for exhaust leaks to also leak the cooling water but it is worth checking.

One more thought and question.  Are you running the generator?  If so is it the Kohler 6.5 that was optional for this boat?

Good luck, Tim

Another thought I had - just those intake scoops on the midship rails and clamshells on the transom to make sure they aren't clogged with anything.  

Another suggestion, get a handheld sniffer and walk around the boat while under way, even in the engine bay, and see where the CO is strongest.

I would not recommend that anyone turn off CO detectors in their boat (or house). I installed 2 Smoke/CO detectors on my 382, 1 in the saloon and 1 in the master stateroom, neither has ever gone off. I have witnessed the effects of CO exposures and have been to several CO related fatalities. We call it the silent killer. It is colorless, odorless and tasteless when coming from a clean burning engine. It is a by product of burning fossil fuels no matter how well tuned the engine (or furnace). CO bonds to hemoglobin 100 times more readily then oxygen. The only way to reverse the effects of CO poisoning is to get the patient to a hyperbaric chamber and force it out of the blood with pressure. The symptoms of CO poisoning mimic sea sickness. Our home CO detectors go into alarm at 16 PPM, this is enough to make you sick. Our meters go into alarm at 34 PPM, this is a potentially lethal exposure. Turning your CO detector off is treating the symptom, not the problem. As Tim mentioned, the "Station wagon" effect can be observed by looking at your ensign. If it is blowing in to the cockpit when running, exhaust fumes are blowing in. If it is blowing out, and your getting exhaust in the cabin, you have a leak. Bear in mind that our boats are not subject to the same emission standards as our cars, which is why we can get 350 horses out of a 7.4 Crusader that was only delivering 280 in the Chevy truck. Think back to the cars we drove in the late 60's and early 70's. That is what our boat exhaust should smell like. If it really stinks, it is a symptom, treat the problem, tune up? timing? mixture? Tim, My 382 has rubber flaps over the cockpit drains, I don't know if this is a possible retrofit on the 35. you can see them just above the swim platform, and you can see the exhaust pipe six inches below it.

Thanks for all the additional suggestions. A number of things to look at in the spring. I never did look at the clamshell and intake scoops for possible obstructions. The boat had been in storage, indoors, at the marina for 4 years. There certainly could be a nest built in there.

When I purchased the boat the fuel tanks were about 2/3's full of 4 year old fuel. The engines started and ran just fine. After we launched the boat I had to drive it about 2 miles to get to a fuel dock and top off the tanks. I am guessing stable must work well.

Nat, the 35 has a step to the hull nearly stem to stern that is around an inch.  In that step the cockpit drains are located so not only are they above the exhaust they have a head start on a venturi effect.

I agree with you ,Nat--100%

My 327F's had small pinhole sized leaks on the intake manifolds under the carbs.  We ended up tapping and filling.  I really don't think the forward air intakes on the 31' push much air into the engine compartments for ventilation.

I know this is an older discussion but I recently had exhaust issues so I looked this up.  

While running our CO alarm was going off. We would have readings of 20 to 30 on the CO monitor and if there was much wind it was much higher.  I bought a hand held to take readings and we  were getting very high readings (50 to 100) if we didn't have all the windows open and boat turned to allow wind in the cabin.  This does not work well in 3' to 4' seas because of wind blowing spray over the bow.  I checked for exhaust leaks, tried opening hatches, etc.  but still the problem persisted.  We really couldn't run very well when we would have to stop every couple of miles to air out the cabin.

What I discovered: we had our dingy tied on the swim step and leaned forward on to the cockpit transom rail.  The dingy was catching air when underway and forcing it back into the passive vent system at the stern of the boat.  We installed a proper dingy davit system, one with hold off bars that keep the dingy over two feet off the cockpit rail and our exhaust fumes went away.  The CO monitor registers zero all the time now while running.

However, I remain somewhat concerned and want an even better system.  Does any one have in-line fans on your bilge vents?  I am thinking about adding them to get even better airflow than I can from the purely passive system.

Richard, boats built after July 1, 1980, are required to have a power ventilation systems, AKA blowers, to remove fumes from the bilge. Prior to that, natural ventilation was all you needed. If you have read this thread, you will have seen blowers mentioned by members with older boats. Either they, or a previous owner, added a blower fan unit to the exhaust side of the natural ventilation to pull fumes out of the bilge. The P.O. of my Luhrs (1975) added an after market marine blower to the boat. Fairly simple installation. Locate the exhaust vent hose and find a good spot to mount the unit. While your there, check the hose for dry rot. this hose should extend to the lowest part of the bilge. 

Aside from CO, I run the blower for five minutes every time I fuel up. I stick my nose in the air stream and if I smell gas, I don't touch the key. Fun Fact, the fumes from one cup of gasoline have the explosive force of 16 sticks of dynamite. That's not a ride you want be on.

Nat,

My boat has a blower installed.  Even though it is a 1979 model it looks like a factory install.  I am considering adding more blowers.  I agree they should be fairly easy to install.  I was just wondering if there are any reasons or instances that this would not be a good idea.

Thank you for replying.

Richard



Nat Brady said:

Richard, boats built after July 1, 1980, are required to have a power ventilation systems, AKA blowers, to remove fumes from the bilge. Prior to that, natural ventilation was all you needed. If you have read this thread, you will have seen blowers mentioned by members with older boats. Either they, or a previous owner, added a blower fan unit to the exhaust side of the natural ventilation to pull fumes out of the bilge. The P.O. of my Luhrs (1975) added an after market marine blower to the boat. Fairly simple installation. Locate the exhaust vent hose and find a good spot to mount the unit. While your there, check the hose for dry rot. this hose should extend to the lowest part of the bilge. 

Aside from CO, I run the blower for five minutes every time I fuel up. I stick my nose in the air stream and if I smell gas, I don't touch the key. Fun Fact, the fumes from one cup of gasoline have the explosive force of 16 sticks of dynamite. That's not a ride you want be on.

Blower is not the answer, somewhere in the files is the answer I came up with,  Tennis balls in the corner scuppers.  The exhaust is immediately below the scupper drain on the 35 so you get the "station wagon" effect.  This will not totally eliminate the problem when going downwind at less than wind speed but it eliminates the problem in most instances.  The balls also will float clear enough of the scupper to allow water to flow overboard.

Tim

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