[C320-list] Bilge blower

[Joe M]

Thanks for that, Jeff!

Joe 2002 C320 hull #902

On Wed, Dec 22, 2021 at 4:40 PM Jeff Hare <Catalina at thehares.com> wrote:

> Hi Joe,
>
> You've gotten a lot of info already on this.  This is a bit long, but
> hopefully it'll get you thinking more critically about reaching your goal...
>
> First, I'm sorry to say, your dealer wasn't correct about running it
> continuously so you can safely just forget he ever said that.  The blower
> wasn't intended for that purpose and really isn't doing what you would
> think it's doing, read on. :)
>
> Let's analyze this a bit using some info from Boat Mechanical Systems
> Handbook. I'm rounding up heavily in the math below.
>
> - The Yanmar engines in our boats are just under 30hp (27-29hp). The
> minimum intake airflow formula I believe Caterpillar Diesel uses is ~2.5 *
> HP for an engine at full throttle, but let's use 2.7 for giggles and extra
> margin. This says they would pull less than 85 CFM of air at full throttle.
>
> - So, this means the engine area needs about 9 sq inches of unobstructed
> ventilation area to meet its minimum air intake requirements into the
> engine area with passive airflow (no blower). (Formula for amount of
> sq/inches needed is roughly Engine HP / 3.3).
>
> - Catalina provided a pair of 4" holes cut into the shaft tunnel shared
> with the engine. When unobstructed, those 2 should easily supply 15-20sq
> inches of air intake area. There are other places where air will enter the
> engine area as well since it isn't a sealed compartment by any means. So,
> /without/ the 4" holes being obstructed, there's plenty of cool air for the
> engine.  REMEMBER: The engine is going to be both drawing cool air in and
> due to the position of the air intake port on the engine, it will also draw
> excess heat out of the upper part of the engine compartment, through the
> engine and out the exhaust.  You don't need an exhaust blower fighting that
> process when the engine is running. The engine will have far more power to
> draw air in than the blower has trying to draw hot air out.
>
> - The temp of the air being drawn from the bilge/below inner liner and aft
> locker is typically the coolest air around since it's being drawn across
> the area of the hull floor that's in the water.
>
> Now let's look at the blower system.
>
> - Problem 1: I don't really know what it's CFM rating is, but there is
> virtually zero chance that this will protect you against a propane leak.
> Let's assume that you had a leak in the propane locker AND ALSO the vent
> hose was broken and open into the aft locker instead of running out the
> drain. That would fill the aft locker and likely work its way into the
> bilge and under the floorboards in the main cabin and some of it would
> undoubtedly end up in the shaft tunnel where the engine is but only some of
> it. The Blower is pulling limited amounts of air to begin with AND only
> from the shaft tunnel area for the most part. That would remove only a tiny
> amount of propane that happened to find its way into that shaft tunnel
> squeezing around the hoses. You'd know you had a problem long before you
> went to start the engine because you'd be smelling it in the main cabin.  A
> leak in the hose leading to the stove would likely not even get into the
> engine tunnel until it backed up high enough to leak into that
> compartment.  The blower was designed to remove gasoline fumes due to a
> leak at the carburetor or fuel line at the engine. That simply isn't a
> thing on our diesel boats.
> To protect yourself from propane leaks, shut off the propane at the tank
> and install a propane alarm in the bilge.
>
> - Problem 2: The blower vent hoses are very heavily corrugated dryer vent
> hoses with loads of air resistance. They are practically useless for moving
> air by vacuum. They collapse if you just look at them and make lots of
> sharp bends further restricting airflow. The one connected to the blower
> draws very little air out in practice. The other one travels a crazy route
> winding all the way across the boat and is supposed to provide fresh air
> in. Total fail. LOL!  The result of all this is that they only serve to
> block the natural unobstructed airflow into the engine compartment through
> that pair of 4" vent holes.  When you RUN the blower when the engine is
> running, you're actually fighting the engine trying to draw air in and the
> engine will win every time.  So the blower running with the engine is doing
> nothing good whatsoever. Guaranteed.  Even when you run this blower with
> the engine off, it's unlikely to be removing enough heat to notice. You
> could prove this to yourself if you wanted to do some measurements and run
> an experiment.  Note that the hose in and the hose out are quite close to
> each other in the shaft tunnel. What do you think the airflow pattern
> really is going to be there?
>
> In Theory the STB side vent hose would draw air in for the engine when the
> engine is running and the PORT vent hose connected to the blower would draw
> gasoline fumes out when run before starting the engine. It doesn't work in
> practice. Neither hose moves sufficient air to serve the intended purpose
> so the engine happily pulls air from other sources and gets on with
> business.
>
> Solution:
> ==========
> - Remove every scrap of that white blower hose.
> - Add mesh/screen over the aft intake vents and let air get drawn in, or
> flow out naturally as needed by the engine, or when the engine isn't
> running, excess heat from the fridge will exit those vents and be replaced
> by air from the bilge and keep the fridge running a little more efficiently.
> - The engine compartment will cool down just fine after a long run with no
> help, but you can get nearly silent IP65 rated "computer" fans that will
> move more than 100cfm of air and run on 12vdc and just wire one up right at
> the port aft vent without being routed to the engine tunnel. That would
> make it cool the aft locker, keep the fridge from running so often and
> gradually draw air out of the bilge area. You can accomplish the same thing
> by cracking open the port aft locker over the fridge and letting the heat
> rise up out there.
>
> Best bet is to insulate the engine compartment like many have done using
> the heavy Sound Down dense foam and let a lot of the heat dissipate through
> the hull over time. It'll also be as quiet as it can be while running the
> engine.
>
> Crack a beer, don't over-think it and just have fun sailing.
>
> -Jeff Hare
> Formerly C320 #809 (Sailed 2001-2021)
> Currently C355 #17
>
> -----Original Message-----
> From: C320-list <c320-list-bounces at lists.catalina320.com> On Behalf Of
> Joe M
> Sent: Wednesday, December 15, 2021 2:23 PM
> To: C320-List at catalina320.com
> Subject: Re: [C320-list] Bilge blower
>
> I want to hot air out, fresh air being pulled in for engine as dealer told
> me to leave it on running when I bought it 3 years ago. My first diesel,
> first inboard, first sailboat. Previous boats of 30 years were all
> outboards.
>
> Joe 2002 C320 hull #902
>
> On Wed, Dec 15, 2021 at 11:09 AM Troy Dunn <troutwarrior at gmail.com> wrote:
>
> > Joe
> >
> > What is your goal for continuous operation?   Is it reduced engine room
> > temps, or something else?
> >
> > I have been studying this problem solely from the perspective of
> > getting cooler air to the alternator and subsequently removing the
> > heat from said alternator.
> >
> > I don’t think the original bilge blower was designed for continuous
> > operation nor does it seem to move much air and it’s noisy as all get
> > out…as you’ve stated.
> >
> > I think the solution is higher cfm 12V fans designed for quietly moving
> > more air.  Probably a squirrel cage centrifugal blower.    I haven’t got
> > past trying to design a duct system to get the air directed at the
> > alternator so I haven’t focused too much on the actual blower yet.
> >
> > Cheers
> >
> > Troy Dunn
> > Hull#514
> >
>
>