Reply
 
Thread Tools Search this Thread
 
Old 10 January 2006, 15:23   #1
Member
 
Country: UK - Wales
Town: Southampton
Boat name: DynaMoHumm/ SRV/deja
Make: Avon8.4, 5.4 & 4.777
Length: 8m +
Engine: Cat3126 Yam 90 &70
MMSI: 42
Join Date: Dec 2003
Posts: 6,556
One benefit of the cold

I've been out and about a bit on Stevie lately and I must say the cold weather definitely has a pleasing effect on my outboard. Has any body else noted this

I presume it's cos the air is denser but it definitely seems to have more whumfff
__________________

__________________
Here it comes again, I don't stand a chance
Soul possession, Got me in a trance
Pullin' me back to you - Deja Voodoo
Rogue Wave is offline   Reply With Quote
Old 10 January 2006, 15:57   #2
Member
 
Country: Ireland
Town: Dublin & Enniscrone
Boat name: K'adó
Make: Redbay
Length: 7m +
Engine: Suzuki 300
Join Date: Oct 2004
Posts: 613
cool engines

Is it because the engines are cooler that they appear to be able to run for longer and appear crisper?

Is this a real effect?
__________________

__________________
Take it easy ....but, take it all the way.
Ezgoing is offline   Reply With Quote
Old 10 January 2006, 16:08   #3
ADS
Member
 
Country: UK - England
Town: Dorset
Length: 4m +
Join Date: Oct 2003
Posts: 1,410
Quote:
Originally Posted by Rogue Wave
I've been out and about a bit on Stevie lately and I must say the cold weather definitely has a pleasing effect on my outboard. Has any body else noted this

I presume it's cos the air is denser but it definitely seems to have more whumfff

My dad reckons that beacause its colder the spark is bigger and produces a bigger bang, therefore more power and it goes better. In the winter though I dont use the boat as often because of the weather therefore the time gap between each trip gets bigger, so if i dont use the boat for a month and then take it out I think this feels quick! When in reality its the same.


Alex
__________________
ADS is offline   Reply With Quote
Old 10 January 2006, 16:22   #4
Member
 
Country: UK - England
Town: Mighty Penryn
Boat name: Little Joe.
Make: Avon Searider
Length: 4m +
Engine: Honda BF50
Join Date: Aug 2005
Posts: 8,841
Diesels run better in cooler weather hence " intercoolers". Engine room temperatures on a boat with non-intercooled diesels are critical. If the engines are "breathing" hot air it can cause dramatic power loss.The air is less dense, less oxygen = less bang etc.
__________________
Mollers is offline   Reply With Quote
Old 10 January 2006, 16:39   #5
Member
 
Country: Other
Length: no boat
Join Date: Aug 2005
Posts: 623
My 4X4 not only goes better in cold damp weather, it goes much better when I clean it too...

Same for the boat....
__________________
hard1 is offline   Reply With Quote
Old 10 January 2006, 20:59   #6
Member
 
Country: UK - Wales
Town: swansea
Boat name: Too Blue
Make: BLANK
Length: 8m +
Engine: Suzuki DT225
Join Date: Mar 2004
Posts: 12,791
Just have a look at any aircraft operators manual - hot and high takeoff much longer than cold and low. Airliners can carry far more cargo/pax in colder conditions.
__________________
codprawn is offline   Reply With Quote
Old 11 January 2006, 00:30   #7
Member
 
Country: USA
Town: Oakland CA
Length: 3m +
Join Date: Feb 2005
Posts: 6,653
Quote:
Originally Posted by codprawn
Just have a look at any aircraft operators manual - hot and high takeoff much longer than cold and low. Airliners can carry far more cargo/pax in colder conditions.
That, however, is a function of the airflow over the wings, rather than engine power. Denser air over the chord creates more lift than warmer, less dense air for a given airspeed.

jky
__________________
jyasaki is offline   Reply With Quote
Old 11 January 2006, 04:13   #8
Member
 
Country: UK - England
Town: nr Lymington
Boat name: JU-JU
Make: Halmatic PAC22
Length: 6m +
Engine: 140.5 Mermaid
Join Date: Sep 2003
Posts: 1,400
Quote:
Originally Posted by Rogue Wave
.....I presume it's cos the air is denser .......
Yep, cold air gives you greater volumetric efficiency which is what an intercooler is trying to do.
Better still is cold air and fog (and no air filter) = whumfff whumfff whumfff Des
__________________
Scary Des is offline   Reply With Quote
Old 11 January 2006, 07:59   #9
Member
 
MikeH's Avatar
 
Country: UK - England
Town: blackburn
Boat name: Hornet
Make: XS Ribs
Length: 6m +
Engine: Optimax 150
Join Date: Jun 2005
Posts: 55
Found this after a quick search but I once found something a bit more detailed.

Quote:
Ever wonder why your boat seems like it runs better some days than others? Rest easy, friend. It’s not your imagination. Just as weather patterns have a direct effect on the feeding habits of fish, changes in air temperature, humidity and barometric pressure affect an engine’s performance — be it an outboard, inboard, two-stroke or four-stroke. Such weather-related performance issues stem from the fact that internal combustion engines are, essentially, air pumps — and in order to run at peak efficiency, they depend on a specific ratio of air mixed with fuel.

“In turn, the horsepower and torque available from a normally aspirated engine depend upon the density of that air,” says Richard Shelquist, an expert in engine mechanics and owner of Shelquist Engineering in Longmont, Colorado. “Higher air density means more oxygen molecules are available for combustion and, hence, more power. Lower air density means less oxygen and less power.”

Change any of the three factors — temperature, humidity or atmospheric pressure — and the amount of oxygen available to “stoke” your outboard changes proportionately. Altitude also plays a major role in how an engine will run. But altitude isn’t weather.

Lots of similar stuff if you look araound the web. If you ever plan to run a boat on a lake at altitude then you need to re-jet the carbs. I think they mean anything aver about 5000 feet so not applicable to the UK.

I was once told that the best day to run a boat is cold, damp during high pressure - Typical grey still winters day
__________________
MikeH is offline   Reply With Quote
Old 11 January 2006, 08:03   #10
Member
 
MikeH's Avatar
 
Country: UK - England
Town: blackburn
Boat name: Hornet
Make: XS Ribs
Length: 6m +
Engine: Optimax 150
Join Date: Jun 2005
Posts: 55
A bit more

[quote

All three engineers gave some weather-related examples using a 200 hp engine as a baseline. On a 77-degree day, with the barometer sitting at 29.53 in.-Hg, and 30 percent humidity, power output is 100 percent.

If humidity remains constant, but air temperature drops to 70 degrees and the barometer to 29.20 in.-Hg, power is down to 198.6 hp — a loss of 1.4 horses.

Run the same engine on a 100-degree day, with the barometer at 29.53 in.-Hg and the humidity a steamy 80 percent, and power is now down to 185 hp — a whopping 15 hp loss.

Conversely, if barometric pressure remains 29.53 in.-Hg, but air temps drop to 50 degrees and humidity plunges to 20 percent, power output jumps to 205.8 hp.

Drop the temperature to an ice-fishing 20 degrees, raise the bar to 29.7 in.-Hg, and cut humidity to 0 percent, and that 200 is now making 211.4 hp. Of course, it’s too cold to do anything with all that horsepower, but it’s nice to know it’s there, all the same.

’TUDES AND TEMPS

Even though altitude is a matter of geography, not weather, elevation plays the biggest single role in the horsepower/performance equation. For every 1000 feet you climb above sea level, there is a reduction in air density of approximately 4.5 percent, according to Marcellis. So, for every 1000-foot gain in altitude, there is a corresponding loss of horsepower, which means our 200 hp outboard gives up 9 ponies.

Water temperature also plays a role — although it’s miniscule in the grand scheme of the performance game. “Water temperature can impact power, depending on the way the cooling system is set up,” Marcellis says. “But the effect is minimal. If you have a closed cooling system with a thermostat, the thermostat will keep the engine’s operating conditions close to constant.

“On open cooling systems — like those found in our Merc 2.5 Drag — the lake water has a direct effect on cylinder-head temperature. The cooler the temperature, the denser the intake charge and the greater the power produced. However, the amount of the power change is difficult to establish, because you don’t know how much temperature change is involved.” Yamaha’s Hoshiba puts it in layman’s terms, saying, “Cool water keeps the engine cool, and allows it to draw in more air.”

[/unquote]
__________________

__________________
MikeH is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

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





Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -5. The time now is 02:30.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.