Hot weather and engine performance

N

nicho

RIP
Joined
19 Feb 2002
Messages
9,265
Location
Home - Midlands, Boat - South Coast
Visit site
We went out into the Solent yesterday, and whilst generally overcast, it was damned hot and very humid. These conditions seemed to cause a loss of power from the KAD300's we have. Nothing serious, but they certainly laboured more than normal. We were admittedly pretty well loaded, 75% fuel, 100% water. 4 good sized (!) adults and loads of kit on board (we are down for 6 weeks), but they normally cope better than they did. We were only out a few days before in "normal" temperatures, and performance was normal, so unlikely to be fouling, and everything else (t's and p's etc) were fine. I can only put it down to the heat/humidity.

Anyone else noticed this?
 
We was out in the solent on Sunday, and yes I thought my engine had to dig a little deeper to get us on to the plane. She seemed a bit more growley and laboured abit longer, but once up and running normal service resumed!! I but it down to a mixture of a little more fouling and the heat?? Like you too, all things in good shape and all gauges good......
 
That can be quite possible, I can manage 40.3 knts on an ABS 47 IPS 600's in the Solent when its less than 20 degrees, same boat, same fuel stores etc three weeks later in SoF and 32 degrees , humid and no way will she pull more than 37.5 knots.

There is a theroy/ rumor that all new Volvo engine models are tested in the colder waters and air temp of Scandinavia and dyno'd for their HP, so your 435 hp up there is more like 380-390 hp in the med.
 
Hi
I cannot say I have noticed it on my boat as I have been at work!. However I can confirm that the weather conditions will play about with the engine performance. We do not run engines on the test stand during the heat of the day as it up-sets the maximum power settings, so we run first thing in the morning before it gets too hot as it has been recently.
Hopefully this will put your mind at rest.
 
With turbo d's, the power loss at sea level should not be too major, as the air intake temp will be only a few degrees higher at 25-30 C ambient. So the I cannot see that the performance should change all that much. No loss of performance with my car this week, and that is a turbo D. Charge coolers are designed to optimise the air temps.
 
I think many people underestimate how high the temperature can be in an engine room/bay. It's cheap and easy to fit a gauge.

The manual for my engine says "for every 1°C rise in air temperature above 39.5°C there will be a power loss of approximately ½HP" . Maximum output of my engine is only 88HP so should the engine room temperature rise to 50°C there would be a significant power loss. I would imagine that the more HP an engine puts out the greater the loss would be. I use the blowers in hot weather to keep the engine room temperature down.
 
Hi
I understand your statement about not noticing any loss of power in your car, however please note the wording I used in my post

"We do not run engines on the test stand during the heat of the day as it up-sets the maximum power settings"
That is where you will have the loss of power, I totally agree with you that you would not notice any difference in your car apart from fuel consumption would be slightly higher.
As already mentioned in another post, please allow for the engine bay temperature as well.
I hope you can see the point I am trying to illustrate.
 
Blowers, would it be wise to be extracting more air out of the enging compartment, or should you have one blower to draw in extra air as well as the extractor one, creating more air (cooler) flow??
 
The RNLI Severn class lifeboats have two 1,200 hp Caterpillars down below which would give off serious kilowatts of heat when underway - yet I remember going out on trials on one in mid summer in conditions probably similar to what you are experiencing at the moment, and being amazed at how cool it was in the engine room, even when going at full chat.

But then they have large walk-around engine rooms with HUGE fans - almost like air conditioning!
 
[ QUOTE ]
[ QUOTE ]
I use the blowers in hot weather to keep the engine room temperature down.

[/ QUOTE ]

That's very good point - I'll do that in future. By the way it's absolutely stifling in the Hamble at present - where's the sea breeze?

[/ QUOTE ]

The blowers on your boat will be permanently on when the engines are running anyway, unless you've disconnected them. Also the engines are sucking such a volume that the air barely has time to warm up before it's used, so I don't think heat from the engines is a big issue, it's the ambient temperature of the air outside that will make the difference IMO.
 
You only need vent fans at inlet or outlet. Depends if you want to run the engine room at under pressure or over pressure. The engine will always take what it needs you can be sure of that!
All engines will be derated for ambient conditions based on a set of (usually) ISO standard conditions. I dont know what they are right now for the VP marine range or what their dreating factors are. Generally there is a derate for altitude (not a problem for marine engines of course!!) a derate for ambient temperature (in the engine room or more correctly combustion air inlet temperature) and intercooler water temperature. For shore based engines relative humidity is also considered as that will determone wet buld temperature if cooling tower cooling is used.
So depending what the starting point for derating is on VP marine engines the combustion air temperature could well be a factor as could sea water temperature for intercooloer efficiency. I noticed on one of the VP industrial diesels the derating on ambient was 2% for every 5 DegC above 40C but on a site for marine engines I also saw ISO conditions quoted as 25C, 100kPa and 30% RH so not sure what it is for your engines. If its 32C ambient you could easily have 40C in the engine room and if derating starts at 25C it could be a noticeable reduction in power!!
 
Simplifying the physics, the mass of gas drawn in by the engine will be inversely proportional to the abolute temperature. Absolute zero is -273 degrees C so 30C = 303 Abs. If we compare this with 15C = 288 Abs there would be about 5% less air. 5% reduction in power could make quite a difference to a boat, especially when getting onto the plane.

Intercoolers only cool the charge that has been drwan into the turbo at atmospheric pressure so the same loss of power would still apply.
 
All my experience is with large industrial diesels but as a general comment the intercooler water temperature is very definitely one of the factors in establishing "site output" along with ambient temperature, altitude and exhaust gas back pressure.
In the marine world the intercooler water temperature is not such an issue as the raw water will be relatively cold compared with engine low temperature circuit inlet requirement of perhaps 35 to 40C. But nonetheless intercooler water temperature is a factor in derating but more for land based installations that use radiator or cooling tower for cooling.
Anyhow just take a look in ISO 3046 its all in there but I dont have a copy at the moment.
 
Your comparison with the Med involves water density as well as temperature. The density of Med water is higher because of its greater salinity. I can't remember the figures now, but I'm sure a search will find it.

Strictly, for the very best performance, you need different props for the Med.
 
[ QUOTE ]


The blowers on your boat will be permanently on when the engines are running anyway, unless you've disconnected them.

[/ QUOTE ]

No, Nick, they are manually controlled from the helm. Every Sealine boat I've owned so far has been the same.
 
You must log in or register to reply here.

Share this page

Top