Blowers

[dozerII]

I'm redoing a StarCraft Holiday and have a question about the bilge ventilation system. There are two clamshell vents facing forward on the gunwales and two on the rear deck facing rearwards.



The two forward ones I plan on ducting with 3" flex able line to the engine bay. Should I put a blower on each rear facing ones, or just one? I have two 130 cfm inline blowers?

Thanks

 

[Bob_VT]

Re: Blowers

Just one is sufficient

 

[smokeonthewater]

Re: Blowers

one or two... your choice... one works but two gives redundancy... blower need suction hoses to below the engine and above any likely bilge water level

the intake vents do not get ducts unless the air must be routed through a bulkhead

 

[UncleWillie]

Re: Blowers

To get technical....
The number of blower is properly determined by the size of the engine compartment and the capacity of the blowers. A single blower rated for 130 cfm is good for up to an 86 cu.ft. engine compartment.
For most recreational boats, One is sufficient.

Also remember that they Blow OUTWARD. From the Bilge point of view, they are Vacuum Suckers! :facepalm:

 

[jasoutside]

Re: Blowers

Wow, that boat is totally awesome!:thumb:

Is it made of metal?:becky:

 

[dozerII]

Re: Blowers

Thanks everyone, I will install one and keep the other for backup.

 

[Grandad]

Re: Blowers

Hi Glen. When I replaced the original in my boat, there was only one. I left the second rear facing vent without a blower. I told myself that if I had blowers in both and forgot to turn them on, the airflow would actually be restricted by the stationary blower blades. Mine also has ducts on the forward facing scoops directing air intake to the corner where the transom, bottom and each side meet. I figure both sucking and blowing the low spot is a good way to increase CFM where the fumes accumulate. - Grandad

 

[dozerII]

Re: Blowers

Hi Glen. When I replaced the original in my boat, there was only one. I left the second rear facing vent without a blower. I told myself that if I had blowers in both and forgot to turn them on, the airflow would actually be restricted by the stationary blower blades. Mine also has ducts on the forward facing scoops directing air intake to the corner where the transom, bottom and each side meet. I figure both sucking and blowing the low spot is a good way to increase CFM where the fumes accumulate. - Grandad

Thanks Grandad.

 

[Idlespeedonly]

Re: Blowers

Wow, that boat is totally awesome!:thumb:

Is it made of metal?:becky:

Ill answer ya. That is a good lookin boat. I see rivets on the sides so I think so. But it is neat looking.

 

[Ciscovet]

Re: Blowers

More pics please!!!!!

 

[smokeonthewater]

Re: Blowers

Mine also has ducts on the forward facing scoops directing air intake to the corner where the transom, bottom and each side meet. I figure both sucking and blowing the low spot is a good way to increase CFM where the fumes accumulate. - Grandad

This is actually a bad idea... by directing a stream of incoming air at the area most likely to collect fumes you will circulate and spread the fumes... you want to ONLY pull from down low and let incoming air flow from the top down so as to CONTAIN the explosive mixture near the exhaust intake for expulsion from the boat....

IF your boat is such that intake air MUST be ducted, route it to the top of the engine near the carburetor intake

 

[H20Rat]

Re: Blowers

Hi Glen. When I replaced the original in my boat, there was only one. I left the second rear facing vent without a blower. I told myself that if I had blowers in both and forgot to turn them on, the airflow would actually be restricted by the stationary blower blades. Mine also has ducts on the forward facing scoops directing air intake to the corner where the transom, bottom and each side meet. I figure both sucking and blowing the low spot is a good way to increase CFM where the fumes accumulate. - Grandad

In addition to what smokeonthewater said, keep in mind that a little old chevy 350 will draw in over 600 CFM through the carbs. Once you are above idle, the amount of air that a bilge blower can move is inconsequential. On plane, there is going to be NO air leaving through the exhaust vents, worst case, you actually might draw air in through them to feed the engine.

 

[Grandad]

Re: Blowers

Glen, you may find the PDF document at this link helpful. Ventilation in Section 6. It is available to freely copy and distribute. - Grandad
http://www.tc.gc.ca/publications/en/tp1332/pdf/hr/tp1332e.pdf

 

[dozerII]

Re: Blowers

This is actually a bad idea... by directing a stream of incoming air at the area most likely to collect fumes you will circulate and spread the fumes... you want to ONLY pull from down low and let incoming air flow from the top down so as to CONTAIN the explosive mixture near the exhaust intake for expulsion from the boat....

IF your boat is such that intake air MUST be ducted, route it to the top of the engine near the carburetor intake

In addition to what smokeonthewater said, keep in mind that a little old chevy 350 will draw in over 600 CFM through the carbs. Once you are above idle, the amount of air that a bilge blower can move is inconsequential. On plane, there is going to be NO air leaving through the exhaust vents, worst case, you actually might draw air in through them to feed the engine.

Glen, you may find the PDF document at this link helpful. Ventilation in Section 6. It is available to freely copy and distribute. - Grandad
http://www.tc.gc.ca/publications/en/tp1332/pdf/hr/tp1332e.pdf

All great info everyone, thanks. I will duct the side forward facing, one to the top outer corner of the transom and the other to the bottom outer corner, then leave one rear facing one open and the other with the blower hose run into the bilge.

Here's a couple more pics, the restore is here in the StarCraft section. http://forums.iboats.com/starcraft-boats/1976-holiday-18-mercruiser-120-a-619470.html

 

[smokeonthewater]

Re: Blowers

close... route both intakes to the top of the engine bay and route BOTH exhausts to the bilge below the engine... you can put a blower in only one but both need ducted

 

[dozerII]

Re: Blowers

close... route both intakes to the top of the engine bay and route BOTH exhausts to the bilge below the engine... you can put a blower in only one but both need ducted

Thanks smoke, will do.

 

[H20Rat]

Re: Blowers

close... route both intakes to the top of the engine bay ... but both need ducted

I know of no OEM's who duct the intake air. There really is no point to it other than to serve as a restriction for incoming air.

 

[smokeonthewater]

Re: Blowers

I know of no OEM's who duct the intake air. There really is no point to it other than to serve as a restriction for incoming air.

You are correct.... You misread and misquoted my statement.

As I said in my first post intake is ONLY ducted if it needs to be routed through a bulkhead.
I only suggested ducting intake to the top of the engine because the O/P seems determined to duct it.

The vents that BOTH need ducted are the EXHAUST vents.

 

[Grandad]

Re: Blowers

I certainly don?t want Glen?s thread to turn into an argument, but there is a safety issue here and the discussion so far could potentially mislead readers of this thread long after it expires. I usually say my piece and shut up, even if someone else says I?m wrong, but the technical points made here warrant more serious consideration.

Smokeonthewater has replied that ducting the intake air to the area that accumulates fumes is a bad idea and that ducting is unnecessary, but if used, the ducting should be directed to the carburetor intake. I understand the point that directing air flow toward the vapours could disperse them to other points. I suggest that this will reduce the hazardous concentration of vapours to below an explosive level. But hey, I?m no expert, so I went on a quest to find the answer.

I haven?t been able to find a regulation or a discussion by regulators on the merits of not ducting the intake air to the low point of the hazardous vapour location. On the contrary, I?ve found only regulations requiring that two ventilation supply ducts are required to extend to the lowest part of the space. Smoke, perhaps there is a conflict between the two regulations that I found and another regulation that you are promoting. Please provide us with some legal support for ducting intake air to other than the low point of the hazardous space and maybe we?ll save someone some heartache. - Grandad

HTTP://CFR.REGSTODAY.COM/46CFR182.ASPX#46_CFR_182P460
AUTHORITY: 46 U.S.C. 3306; E.O. 12234, 45 FR 58801, 3 CFR, 1980 Comp., p. 277; Department of Homeland Security Delegation No. 0170.1.
SOURCE: CGD 85-080, 61 FR 986, Jan. 10, 1996, unless otherwise noted.
?182.460 Ventilation of spaces containing machinery powered by, or fuel tanks for, gasoline.
(a) A space containing machinery powered by, or fuel tanks for, gasoline must have a ventilation system that complies with this section and consists of:
(1) For an enclosed space:
(i) At least two natural ventilation supply ducts located at one end of the space and that extend to the lowest part of the space or to the bilge on each side of the space; and
(ii) A mechanical exhaust system consisting of at least two ventilation exhaust ducts located at the end of the space opposite from where the supply ducts are fitted, which extend to the lowest part of the bilge of the space on each side of the space, and which are led to one or more powered exhaust blowers;

From http://www.tc.gc.ca/publications/en/...hr/tp1332e.pdf

 

[dozerII]

Re: Blowers

Okay, the only reason I am ducting the intake air is because the clamshell scoops will deposit the air into the side storage compartments. The ducting will only be long enough to get the air in to the top of the engine bay.