Reply
 
Thread Tools Search this Thread Display Modes
 
Old 11-07-2017, 09:00 AM   #1
Guru
 
Tom.B's Avatar
 
City: Cary, NC
Country: USA
Vessel Name: Skinny Dippin'
Vessel Model: Navigator 4200 Classic
Join Date: Jul 2009
Posts: 5,708
Getting air to motors

So I was thinking the other week about how my motors get air. It all started when I was considering a cold air kit for my truck. Why do our boats just pull warm/hot air from the engine rooms with the only connection to the outside being slotted vents on the side of the hull? Wouldn’t motors run much better if we plumbed a path to grab cold air more directly from the outside? Maybe not a sealed system, but maybe just a draft of cooler outside air directed toward the motor’s intake.

It seems to me that a measurable gain in performance (HP or efficiency) could be had by doing something like that. Or am I missing something?

Discuss... and thanks!
Tom-
__________________
Advertisement

__________________
2000 Navigator 4200 Classic
(NOT a trawler)
Tom.B is offline   Reply With Quote
Old 11-07-2017, 09:21 AM   #2
Guru
 
caltexflanc's Avatar
 
City: North Carolina for now
Country: USA
Vessel Name: Small Incentive
Vessel Model: Boston Whaler 130 Sport
Join Date: Aug 2011
Posts: 5,255
The vents are a direct path to outside air. If designed properly by the OEM, no more is really needed. I suppose you could run blowers if really paranoid for some reason.
__________________

__________________
George

"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
caltexflanc is offline   Reply With Quote
Old 11-07-2017, 09:38 AM   #3
Guru
 
boathealer's Avatar
 
City: North Carolina
Country: US
Vessel Name: SCOUT
Vessel Model: Great Harbour N37
Join Date: Aug 2017
Posts: 630
Quote:
Originally Posted by caltexflanc View Post
The vents are a direct path to outside air. If designed properly by the OEM, no more is really needed. I suppose you could run blowers if really paranoid for some reason.
I think he may be referring to the fact that the outside air has to sit in, and travel through, the 115 degreeF engine room to get to the air cleaner intakes.
boathealer is online now   Reply With Quote
Old 11-07-2017, 10:17 AM   #4
Guru
 
Northern Spy's Avatar
 
City: Powell River, BC
Country: Canada
Vessel Name: Northern Spy
Vessel Model: Nordic Tug 26
Join Date: Feb 2012
Posts: 3,027
My boat and truck engines are turbo-diesels. Cold air wouldn't make a (noticable) difference.

Gasoline engines have a fixed stoichiometric ratio, that's why they benefit from cold air induction.
Northern Spy is online now   Reply With Quote
Old 11-07-2017, 10:31 AM   #5
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 5,393
At high power settings, there is so much air entering turbos that it is in fact rather cool at the actual air filter.

At low power settings, it does get hot at turbo suction, but at low power settings there is no downside to that air being warm.

At high power the turbo compressor is more efficient if the air entering is cool, but only by a small amount. It roughly follows the ratio of temps using an absolute scale. So comparing 80F to 115F is really comparing 540R to 575R, or about 6% reduction in mass air flow.

Actual cylinder charge air temp is mostly governed by the charge air cooler (aftercooler) and that is not very sensitive to turbo suction temps, maybe by a few degrees. The 6% loss of mass air flow due to turbo suction temp will be reflected in a little less flow and little less manifold pressure, but since diesels run with such a high amount of excess air, not worth fiddling with it in my opinion. If exhaust is clear of smoke, still plenty of excess air.

Cooler intake air is certainly better, but not worth clogging your tight engine room with all sorts of large diameter plumbing.

And if you route it outside, the noise would be nuts.

You would also need some provision to coalesce out any entrained sea mist.

Unless your ER blowers are like 3hp or more, they won't do diddly compared to the airflow going into a turbo at power.
Ski in NC is offline   Reply With Quote
Old 11-07-2017, 10:53 AM   #6
Guru
 
jleonard's Avatar
 
Join Date: Jun 2008
Posts: 3,520
The "general rule of thumb" is that the engine room temperature should be no more than 30 deg F above the ambient air temp.
If you are within that parameter, you should have enough air flow to maintain efficiency.
Take some measurements and see where you stand before adding anything.
__________________
Jay Leonard
Attitude Adjustment
40 Albin
Mystic,Ct. /New Port Richey,Fl
jleonard is offline   Reply With Quote
Old 11-07-2017, 11:50 AM   #7
Guru
 
djmarchand's Avatar
 
City: Litchfield, Ct/Punta Gorda, Fl
Country: USA
Vessel Model: Atlas Pompano 23
Join Date: Aug 2012
Posts: 4,890
Another caution is that the air intakes on boats are placed to limit downflooding under severe heel. Anything you do should not compromise that geometry.

In general I agree with Ski and others that it doesn't make enough difference as long a Jay's rule of thumb is met.

David
djmarchand is offline   Reply With Quote
Old 11-07-2017, 01:28 PM   #8
Guru
 
Benthic2's Avatar
 
City: Boston Area
Country: United States
Join Date: Feb 2017
Posts: 1,493
Go for a test run with your hatch covers off and see if you notice a difference.
Benthic2 is offline   Reply With Quote
Old 11-07-2017, 02:21 PM   #9
Guru
 
Tom.B's Avatar
 
City: Cary, NC
Country: USA
Vessel Name: Skinny Dippin'
Vessel Model: Navigator 4200 Classic
Join Date: Jul 2009
Posts: 5,708
So I WAS missing something. :-) Thanks for the education y’all. My thought was that cooler air might make a difference, but didn’t know most of the higher physics of the turbo motors.

Tom-
__________________
2000 Navigator 4200 Classic
(NOT a trawler)
Tom.B is offline   Reply With Quote
Old 11-07-2017, 03:06 PM   #10
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 19,833
"It seems to me that a measurable gain in performance (HP or efficiency) could be had by doing something like that. Or am I missing something?"


The HP gain from denser cold air comes at full throttle , nothing gained at modest cruising loads .
FF is offline   Reply With Quote
Old 11-07-2017, 03:57 PM   #11
Guru
 
Lepke's Avatar
 
City: Between Oregon and Alaska
Country: US
Vessel Name: Charlie Harper
Vessel Model: Wheeler Shipyard 83'
Join Date: Jun 2016
Posts: 1,632
Commercial tugs have large blowers to bring in large volumes of air. Usually a smaller exhaust blower to remove some of the air. Incoming air is dispersed right over the diesel intakes. Even with really big diesels at full power the engineroom is only slightly warmer than the rest of the inside.
As long as you have sufficient incoming air vents and you have a turbo diesel with an aftercooler, a cooler engineroom probably won't make a noticeable difference. But a turbo w/o an aftercooler or natural engine might benefit.
In a hot climate, a cooler engineroom makes less for the AC to overcome.
Lepke is offline   Reply With Quote
Old 11-07-2017, 04:49 PM   #12
Guru
 
Lou_tribal's Avatar
 
City: Quebec
Country: Canada
Vessel Name: Bleuvet
Vessel Model: Custom Built
Join Date: Jan 2016
Posts: 3,521
Quote:
Originally Posted by djmarchand View Post
Another caution is that the air intakes on boats are placed to limit downflooding under severe heel. Anything you do should not compromise that geometry.

In general I agree with Ski and others that it doesn't make enough difference as long a Jay's rule of thumb is met.

David


Indeed do not do what the PO of my boat did once... looking at the hull vents he had a sudden “bright” idea... why no to reverse them, being mouth open directly to the air flow will make more air coming in... until the first storm when he realized he was taking water in from rain and waves...



L
Lou_tribal is online now   Reply With Quote
Old 11-07-2017, 08:09 PM   #13
Guru
 
BruceK's Avatar
 
Join Date: Oct 2011
Posts: 10,042
My IG has a blower,it is near the vent on one side but not connected by tubing to the vent.
If I forget to run it, the ER will be noticeably hotter. At the vents I can feel air entering on one side and exiting the other, no great pressure but enough to be noticeable.
FLs, so no turbos to feed.
__________________
BruceK
Island Gypsy 36 Europa "Doriana"
Sydney Australia
BruceK is offline   Reply With Quote
Old 11-07-2017, 10:00 PM   #14
Guru
 
Moonfish's Avatar


 
City: Port Townsend, WA
Country: USA
Vessel Name: Traveler
Vessel Model: Cheoy Lee 46 LRC
Join Date: Nov 2011
Posts: 965
We are fortunate to have opening portlights port and starboard in the engine room. I typically have those open when underway. During the summer. When it's calm. Seriously, most of the time they are open when underway. I have only closed them on a few occasions when sea conditions were really nasty.
__________________
Darren
Port Townsend, WA
m/v Traveler - '79 Cheoy Lee 46 LRC
https://www.pacificnwboatertested.com
Moonfish is offline   Reply With Quote
Old 11-08-2017, 08:52 AM   #15
Guru
 
caltexflanc's Avatar
 
City: North Carolina for now
Country: USA
Vessel Name: Small Incentive
Vessel Model: Boston Whaler 130 Sport
Join Date: Aug 2011
Posts: 5,255
Quote:
Originally Posted by BruceK View Post
My IG has a blower,it is near the vent on one side but not connected by tubing to the vent.
If I forget to run it, the ER will be noticeably hotter. At the vents I can feel air entering on one side and exiting the other, no great pressure but enough to be noticeable.
FLs, so no turbos to feed.
Which way does it blow, in or out of the boat?

A little off topic: My Hatteras had two OEM sets in each ER, both of which sucked air out of the ER. One set was DC and vented the batteries, with intake low along the battery boxes. The operating manual said not to run these at or above "cruising speed" which meant about 80% throttle which we never did for extended periods of time. The other set were AC blowers specified for cooling the ER after the engines were turned off or to vacate CO2 if the fire system had discharged. These vented at the ceiling.

The engines, Detroit 8v92tti (twin turboed) were fed air from large side vents next to each engine. During the winter, we used to stuff towels in the intake vents so more of the the warmth generated by the block heaters would stay inside the boat.
A few times I forgot to remove the towels, until I put that on the checklist. At hull speed and below it didn't seem to make any difference and I don't recall running the engines up with them in, but if I did I didn't notice a difference then either. But then again they were never in there more than an hour or two .
So that there's my story, or most of it on that subject. I looked into putting a Delta T system in, but never could make a "business case" to do so.
__________________
George

"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"
caltexflanc is offline   Reply With Quote
Old 11-08-2017, 09:52 AM   #16
Guru
 
City: gulf coast
Country: pinellas
Join Date: Jun 2014
Posts: 2,817
if you have seawater cooled aftercoolers they will control charge air temp more than air temp IMO.
bayview is offline   Reply With Quote
Old 11-08-2017, 12:17 PM   #17
Guru
 
Tom.B's Avatar
 
City: Cary, NC
Country: USA
Vessel Name: Skinny Dippin'
Vessel Model: Navigator 4200 Classic
Join Date: Jul 2009
Posts: 5,708
Quote:
Originally Posted by bayview View Post
if you have seawater cooled aftercoolers they will control charge air temp more than air temp IMO.
That is, indeed, what we have. Thanks!
__________________
2000 Navigator 4200 Classic
(NOT a trawler)
Tom.B is offline   Reply With Quote
Old 11-08-2017, 12:46 PM   #18
Guru
 
HopCar's Avatar
 
City: Miami Florida
Vessel Name: Possum
Vessel Model: Ellis 28
Join Date: Aug 2011
Posts: 4,409
Along these lines I often wondered if the engine on Possum was getting enough air. I thought about putting a recording barograph in the engine compartment. If the pressure dropped when the engine was running it would indicate the compartment needed more ventilation. Never did get around to trying it.

What do you guys think of that idea?
__________________
Parks Masterson
HopCar is online now   Reply With Quote
Old 11-08-2017, 12:48 PM   #19
Guru
 
boathealer's Avatar
 
City: North Carolina
Country: US
Vessel Name: SCOUT
Vessel Model: Great Harbour N37
Join Date: Aug 2017
Posts: 630
Quote:
Originally Posted by HopCar View Post
Along these lines I often wondered if the engine on Possum was getting enough air. I thought about putting a recording barograph in the engine compartment. If the pressure dropped when the engine was running it would indicate the compartment needed more ventilation. Never did get around to trying it.

What do you guys think of that idea?
Your cellphone may already have a barometer in it.

https://www.phonegg.com/list/303-Cel...with-Barometer
boathealer is online now   Reply With Quote
Old 11-08-2017, 02:42 PM   #20
Guru
 
jleonard's Avatar
 
Join Date: Jun 2008
Posts: 3,520
Quote:
Originally Posted by HopCar View Post
Along these lines I often wondered if the engine on Possum was getting enough air. I thought about putting a recording barograph in the engine compartment. If the pressure dropped when the engine was running it would indicate the compartment needed more ventilation. Never did get around to trying it.

What do you guys think of that idea?
Just do the temperature measurements per my post above and that will tell you.
__________________

__________________
Jay Leonard
Attitude Adjustment
40 Albin
Mystic,Ct. /New Port Richey,Fl
jleonard is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 07:46 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012
×