Questions regarding boat survey

[Mark Redmon]

My survey includes three issues I'm not sure how to remedy-
1: generator space does not have forced ventilation.  How should the blower be routed?  I assume the pickup should be at the lowest point; where should the generator space ventilation be vented to?  
2: There are no 'discharge of oil' or 'pollution' placards mounted.  Where is the standard location for these required placards?
3: "Generator seacock was not bonded.  Service all bonding wire connections and install bonding wire for generator seacock."  What does that mean?
Thanks for helping me get my boat seaworthy.
Mark Redmon
Melbourne FL

[Capt. Bob]

Here's the answer, from the "horse's mouth" to #2.

http://www.uscgboating.org/SAFETY/fedreqs/equ_pollution.htm

Here's a link to #3 explaining the theory behind your question.
http://books.google.com/books?id=kdHyM6_egMwC&pg=RA1-PA561&lpg=RA1-PA561&dq=bonding+generator+seacock&source=bl&ots=uR8QHIs0G1&sig=rTtCV1GO204Q6-FoVH_inTqAS-w&hl=en&ei=S5eOSpU8zam2B-XgzM4E&sa=X&oi=book_result&ct=result&resnum=1#v=onepage&q=&f=false

[GoneFission]

None of those are show-stoppers.  All 3 are easy to fix.  The blower blows air INTO the space; it does not draw it out.  Yes, you want the outlet low in the compartment.  

Also, seacock bonding may not have been required when your boat was built.  

If that's all a surveyor could find, you got a pretty solid boat there...  

[LilRichard]

Really?  My inboard ski boat always had the blower pulling air OUT of the space, at the lowest part of the chamber (to remove gas vapors)... as did my buddy's inboard go-fast.

???

[LilRichard]

More thoughts:

http://www.rule-industries.com/files/itemdoc12671.pdf

[GoneFission]

OK, here's the problem with sucking air out versus blowing it in - (the old sucking versus blowing issue   )  Yacht building codes (AYBC) have always required positive displacement (blowing in) ventilation for gas-powered devices in enclosed spaces.  Negative displacement (sucking out) ventilation is not the preferred (IMHO acceptable) option.  Some small boats are not built to AYBC (Amercian Yacht & Boat Council) code, but all craft over 200 feet must meet the code by law.  

Here's why the compartment should have positive pressure (blowing in) versus negative pressure (sucking out):  Say you have an explosive mixture in the compartment (above 100% LFL) - the blower motor sucking out of the compartment is SUPPOSED to be intrinsically safe - no potential for spark - but, if it's not, or if there might be a little-bitty short in the wiring - BOOM!  In a vacuum system, the air through the blower is likely to be explosive.  

On the other hand, if the blower is pushing fresh air INTO the compartment, the air over the blower is not explosive, and displaces and dilutes the potentially explosive air in the compartment out through the vents.   The blower outlet should be at the bottom of the compartment, since vapors tend to be heavier than clean air and accumulate in the lower compartment areas.  The blowing in option is much safer and more reliable than the sucking out option.   If anyone reading this has their blower set up to suck out versus blow in, my suggestion would be to reverse the situation ASAP.  The downside is very bad.  

Hope this helps - see ya on the water!

[LilRichard]

Ok, so one other question - if you're blowing in fresh air that is (assuming) lighter than the gas fumes - even if it's at the bottom of the bilge, how do the fumes ever make their way out?  More or less you're just diluting them.  It seems like it would make more sense to have it sucking the bad air out.  I do understand your point about the possibility of explosion should the "safe" blower create a spark.  

As you can tell - my experience with inboards is limited - never had a big one.

[GoneFission]

All bilges and compartments with gas-powered devices require vents.  The blower pushes the bad air out as it pushes good air in.  That's why you MUST run the blower for 5 minutes before starting the engine/generator - the blower is sized to have at least 5 full exchanges of air based on the volume of the compartment in the 5 minute pre-start time.  That takes the potential LFL (lower flammable limit) of the atomsphere from 100% to under 20%, which will not flash or explode.  

Almost all I/O and inboard boat fires on gas-powered boats are caused by fume accumulation. Get the blower right, use the proper procedures, and it won't happen.  The AYBC code was  developed through experience - you could even say it was developed - by accidents!  When it comes to bilge blowers, blow is good - suck is bad.

[Mark Redmon]

Ok, I see the value of positive pressure in the generator space.  The added benefit is drawing fresh air in is a simpler issue than where to vent fuel vapor.  So, new question: where should I draw fresh air from on my Explorer 275?
Thanks,
Mark Redmon
Melbourne FL

[Double Trouble]

My ventis on the starboard side of the gunnel in line with the hatch a few inches off the floor.