Engine Compartment Vent ("Blower hose") and clam-shell vent cover

[c34no1471]

In a 2003 post on this forum, Roc asked about the y-fitting just forward of the starboard engine compartment vent opening on the transom. This y-fitting is just above the refrigerator compressor shelf.  The answering posts didn't seem to clear up the question--what's the y-fitting for?   I have the same question.  One end accepts the 3" hose from the engine compartment, one end feeds from the y-fitting to the the opening on the transom (which is covered by a metal clam shell--more on that later).  The third opening has no connection.

As described in his post, the port side vent hose houses the blower, in line in a three inch hose feed from the engine compartment, and the port side hose exits the transom through the same style and size clam shell vent cover. There is no y-fitting on the port side vent hose assembly.

Two weeks ago I managed to bump the starboard metal clam shell cover off (got too close to a pier,exiting a transient slip in high winds, and a wave bounced the transom up). The cover sank, of course.  So I improvised a vent cover (another good use for duct tape) and headed home.  I then talked with Catalina parts, and learned that they don't have the low-profile clam shell cover that was installed originally on the boat (Hull number 1471).  So I ordered a matching set of replacement clam-shell covers, slightly larger than my originals.

I removed the remains of the broken starboard cover and (plastic) vent-hole fitting, and learned that the opening was just slightly too small to accept the new cover (metal) vent-hole fitting.  After considerable filing and sanding I got the new fitting/cover to slide in, fixed it in place, and refastened the three-inch hose to the cover/fitting.  I then puzzled over the y-fitting.

I will tackle the port side vent cover replacement later.  Enough for today.  But I'm still puzzled about the y-fitting.  Any thoughts? 

George Alberts
Breezing Up
Catalina 34 MK II
Hull number 1471

[Wayne]

I always just assumed that the stb side hose was an air inlet hose running into the engine compartment (bringing fresh air in for combustion and to provide flow for the port side blower hose assembly).  I'm not sure that it is really of much value . . . but I'd sure like to hear other's opinions!

[Ron Hill]

Not too sure about a MKII, but in the earlier C34s the port side has the blower exhausting air thru that side port. 
Maybe the starboard "Y" is for the refrig compressor heat to escape thru convection?  A thought

[Roc]

George,
Yes it is puzzling.  I think the blower does not blow air in, I think it exhausts out and the port vent is a line that allows fresh air to draw into the engine compartment from the movement of air out of the blower.  I'm trying to think what I've noticed with the blower air flow, and I think I've felt air coming OUT of the cowl vent on the stb side.  The Y fitting doesn't make sense because the blower would be venting air out of the lazarette and not totally from the engine compartment.  Next time I'm down at my boat, I'll have to turn on the blower and feel which way the air moves.

[Wayne]

The blower exhausts air.

[c34no1471]

I think Ron Hill may well be right--the open leg of the Y sits above the refrigeration compressor.  It would make sense to provide this path for warm air to exit the compartment out the transom vent. The three inch hose segment from the Y to the vent outlet drops a bit between the Y and the vent outlet, but the warm air rising from the compressor would still vent through the Y to the transom rather than drop back into the engine compartment, right? So with the refrigeration compressor running, for example when I am at the slip and haven't run the engine for some time, I should feel the warm air venting from the compressor out the starboard transom vent.

Now, if the refrigerator isn't running, I can imagine how the starboard setup works as a vent from the engine compartment.  With the engine running, the air from near the engine would be warmer than the air near the transom, inside the compartment, so it would also convect out through the vent, bypassing the open end of the Y, as long as it is lower than the vent outlet? So I should feel warm air coming out the starboard transom vent while the engine is running....

George Alberts
Breezing Up
Catalina 34 MK II
Hull No. 1471
(on the Chesapeake Bay)