can someone tell me what these two hoses/ducts are for?
- Thread starter Ted10028
- Start date
Builders make lots of compromises when putting a boat together. A blower for a diesel is not a safety critical feature the way it is for gas. My guess is a designer spec’d the boat to have an inlet and exhaust, and Catalina ran both ducts in the way that was most convenient for them at build time.
I tend to agree with you. Catalina makes good boats, but they have to make a certain price point. I'm not throwing stones. My Hunter has some irritating "why would they do that?" features too.
One of them runs straight back through the transom to a clamshell vent. The other I cannot trace. Do you know where the blower is? perhaps if I can find that I will be able to trace the hoses from it
that's an interesting idea. But it is very thin thin old old dryer hose or the equivalent. i'm sure it would poke through. Maybe I could put a ping-pong ball on the end of it. I really got interested because where it makes the right angle out the back of the boat it's all ripped. When I saw the ripping I figured I ld better check the whole system which I am trying to do.
If it turns out to be a powered vent, I would extend one of the hose ends further away from the other. But that's me.
Yep, on the inside of transom, port side, near the clam shell vent, under the lift up seat on port transom.
Sorry but I am not a fan of bronze seacocks. I have seen too many of them that turn to dust from electrolosis. The Marlon Seacocks meet all of the strength of the ABYC and do not corrode.
Use your portable wet/dry vac to push air into each vent separately to find out where it goes by listening for the air flow. This will give you a chance to decide where you want to put inside ductwork for low temperature outside air or exhaust hot engine air it will also give you a chance to look for an orphan blower disconnected from everything.
I think you are right. I have one bronze seacock on my boat and it is the only seacock that gives me trouble.
Nice clean looking engine bilge @Ted10028,
what kind of shaft seal is that? It looks like the “Johnson”:seal I looked at a few years ago, but never purchased…went with a Volvo/Penta seal instead.
How do you like it?
Greg
yes one runs to the port side aft
and the other runs to the starboard side aft clam shells. I do not see a blower attached anywhere?
Thanks, I will try the wet/dry vac if I can get a hose to reach back there. I guess I should try engine blower switch first and feel for air coming out both clam shell vents on transom. Perhaps Catalina used 2, 3" hoses because one 6" hose would not fit? Not sure why ventilation is so low and under mattresses and floor boards. Seems fumes and heat from engine would mostly be up higher where there is no ventilation that I know of? Thanks again!
I don't think you really need to worry about this very much but it is interesting that you are looking into it. Most folks probably never even give these 2 ducts a second thought. I know that I don't. But I am getting more curious based on your observations. These are my thoughts ...
You have 2 cowls on your stern. One duct is probably for passive ventilation and the other for the blower. It doesn't really matter that they come into the compartment low and together. They don't really have to function whatsoever. Some boats don't put any duct ventilation in at all. I had a boat with a diesel engine that had no ducts or blowers, just a lot of empty space under the cockpit that provided all the air and ventilation necessary. Diesel fumes, while annoying, are not volatile like gasoline fumes. I ran my engine for a 1.5 seasons before even noticing that I had a blower switch (it is down around shin level). Every once in a while I turn it on, but I find the blower loud and annoying. Passive ventilation seems to be enough because I rarely run the blower when motoring (I usually turn it off before very long) and I don't find any objectionable smells in the berth down below. I'm fairly sensitive to objectionable odors.
To be sure, it's good practice to run your blower when motoring. It does a good job for ventilation and helps to keep the motor cool, I suppose, but I've never noticed any difference. The other duct is probably passive and provided just for redundancy, I suppose. Sure, the fact that they enter the engine compartment in the same location is a little stupid maybe, but it doesn't matter and there is limited space under the berth, so who is going to bother trying to make another passage? When the boat is moving forward (either motoring or sailing), there is slightly negative air pressure surrounding those cowls and the passive duct is still drawing air out of the engine compartment. A better design for passive ventilation would be to have a cowl facing forward where the air pressure is positive and a duct coming into a high area in the engine compartment. That would work similar to the way attic ventilation is designed where air comes in at a ridge vent and leaves through a soffit vent. I'll bet some high-end boats have this thought out, with a dorade and duct providing some positive air flow.
It's good that you are looking into it. By all means, if you have ripped or damaged ducts, it would be a good idea to replace them. As you may be able to tell from a lot of vague responses, not many people put a lot of thought into these features. They are pretty much out of sight, out of mind and don't often lead to troubles that cause people to dwell on the ventilation. If you are able to trace those ducts, I'd be interested to know your findings. You've stimulated my curiosity, so I think I'll pay attention the next time I'm crouched inside the rear lockers chasing cables!
You have 2 cowls on your stern. One duct is probably for passive ventilation and the other for the blower. It doesn't really matter that they come into the compartment low and together. They don't really have to function whatsoever. Some boats don't put any duct ventilation in at all. I had a boat with a diesel engine that had no ducts or blowers, just a lot of empty space under the cockpit that provided all the air and ventilation necessary. Diesel fumes, while annoying, are not volatile like gasoline fumes. I ran my engine for a 1.5 seasons before even noticing that I had a blower switch (it is down around shin level). Every once in a while I turn it on, but I find the blower loud and annoying. Passive ventilation seems to be enough because I rarely run the blower when motoring (I usually turn it off before very long) and I don't find any objectionable smells in the berth down below. I'm fairly sensitive to objectionable odors.
To be sure, it's good practice to run your blower when motoring. It does a good job for ventilation and helps to keep the motor cool, I suppose, but I've never noticed any difference. The other duct is probably passive and provided just for redundancy, I suppose. Sure, the fact that they enter the engine compartment in the same location is a little stupid maybe, but it doesn't matter and there is limited space under the berth, so who is going to bother trying to make another passage? When the boat is moving forward (either motoring or sailing), there is slightly negative air pressure surrounding those cowls and the passive duct is still drawing air out of the engine compartment. A better design for passive ventilation would be to have a cowl facing forward where the air pressure is positive and a duct coming into a high area in the engine compartment. That would work similar to the way attic ventilation is designed where air comes in at a ridge vent and leaves through a soffit vent. I'll bet some high-end boats have this thought out, with a dorade and duct providing some positive air flow.
It's good that you are looking into it. By all means, if you have ripped or damaged ducts, it would be a good idea to replace them. As you may be able to tell from a lot of vague responses, not many people put a lot of thought into these features. They are pretty much out of sight, out of mind and don't often lead to troubles that cause people to dwell on the ventilation. If you are able to trace those ducts, I'd be interested to know your findings. You've stimulated my curiosity, so I think I'll pay attention the next time I'm crouched inside the rear lockers chasing cables!
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I think there is a general principle involved. The boat I have now is my first boat in 30 years. When the broker was showing it to me she raced onto the boat and opened the hatches to air it out before i went below. it immediately occurred to me that nothing had changed in 30 years. But today you can buy little 12v computer fans for $10. Why doesn't every manufacturer just put one or two of them on every boat so that every boat won't stink or smell for no reason? In any case I am sure I am tilting at windmills but in this case a victory is guaranteed by a $10 fan. I mean gee whiz, if you are sleeping on my boat in the aft cabin you are sleeping between the engine and the diesel fuel tank. back on land that
arrangement wouldn't meet any building codes that I know of. I will feel a lot more comfortable falling to sleep as I listen to a tiny little fan cycling fresh air through my bedroom.
arrangement wouldn't meet any building codes that I know of. I will feel a lot more comfortable falling to sleep as I listen to a tiny little fan cycling fresh air through my bedroom.
My thinking is that the blower exhausts air from one duct and the other brings in fresh air to the engine compartment. However, under sail, they both act as passive exhausts allowing cabin air to vent out.
Tom
Keep in mind that those vents are under the floor boards and under the mattresses. Although, the engine has a removable cover cabinet in front in the main cabin and another in the aft cabin which may seal up the engine pretty tight meaning it does draw air and exhaust air through those hoses
"If you move a few decades forward in time, the law was amended in 1982 to make a distinction between powered ventilation and natural ventilation. Every closed compartment containing a gas engine or gas tank must be ventilated by at least two ventilator ducts, and engine compartments containing a gas engine with a cranking motor must be ventilated by powered exhaust blowers operated from the instrument panel. This latter requirement applies to virtually all gas-powered inboard and sterndrive boats."