"new" oem props/clean bottom/clean HEs

[MikeP]

Dr Jim and I took Brigadoon out for quick cruise to see what difference the new painted bottom, brand new oem Hatt props (spares that came with the boat in 1980 - never unwrapped) , and clean HEs did.

The boat hit 17.8K against the current which was about a knot so it should be an honest 18K boat again for the first time since the sea trial when we bought it 6 years ago. RPM was around 2250 which is close enough to spec for me. Temps on the starboard engine never rose above the low 180s per the manual gauge. The port was indicating close to 190. However, I'm not sure these temps are correct.

I shot the Tstat boxes with an IR gun while at WOT. The starboard engine's manual gauge agreed with the temps on the IR gun; the port engs manual gauge showed about 7-8 degrees hotter than the IR gun which shot the same Tstat boxes from the same range (about 2"). All 4 Tstat boxes are painted the same color white so the heat gun should NOT be seeing something different based on the material/color of the surface.

So...The manual gauges show there was nearly a 10 degree difference in temps between the two engines (P-190, S 182); the IR gun shows they were within 2 degrees (P-184, S-182). Either the manual gauge is wrong or the IR gun is wrong. Can't think of a definitive test that could tell me which...

Any suggestions?

[JLR]

Mike - swap the gauges from one engine to the other. I am in the same boat and did the same thing but the spare gauge I had on hand was bogus. Back to the actual swap of the existing gauges. Really easy to do without removing the actual gauge. There should be enough wire on the probe.

[SKYCHENEY]

How new are the impellers? How do the cover plates look?

[MikeP]

Cover plates are fine, both impellors are new ( I install new Imps every season).

The temp gauges are manual (thermocouple and tube - can't remember what the tube is called.) No elec involved at all so could be thermocouple, could be gauge, could be IR gun... I can swap them though it's a bit tougher than it would be with elec. Both gauges read the same at displacement speeds - around 165, same as the IR gun. So it SEEMS that if the IR gun agrees with 3 out of 4 (both engines/gauges at around 165, one engine gauge at around 180, it's more likely an issue with the port gauge or BOURDIN () tube.

But I wish I could think of a way to positively "calibrate" the IR gun...

[JLR]

Mike - FWIW, when I swapped in my spare mechanical gauge last weekend to check the existing mechanical gauge, the spare read that the engine was running at 160 degrees and I knew/know that number was low. I always thought that the mechanicals were virtually bullet proof. I guess not. This weekend I head out with the IR gun to verify what the actual readings are (or at least what the difference in OT is between the two engines). After having been through everything you are now going through, my last alternative is to pull the stats and check them but there too, I have been told that they are pretty bullet proof. They were replaced (by me) ten years ago.

[MikeP]

Yeah...my bulletproof faith in mechanical gauges is being rather shaken. A fellow HOF-er who has his boat here at the marina said he ran into the same sort of problem with mechanical gauges and the folks at the gauge manufacturer (can't recall which one) told him that depending on the amount of liquid in the tube, the gauge could read dramatically differently. Doesn't sound to encouraging and now makes me wonder if electrical gauges might not be more accurate. After all, there is no thermocuple plus "tube" with (apparently, varying amounts of liquid). There are just two wires.

Now I'm wondering if my "By God, you have to install manual gauges in the engine rooms" mantra may be misplaced...

[J's Dream]

But I wish I could think of a way to positively "calibrate" the IR gun...

Why couldn't you get a bowl of ice and water, put something metal in it, let it sit a few minutes and shoot it with the IR gun? Theoretically, you should see 32 degrees. Same with a pot of boiling water...should read 212, right?

Jason

[MikeP]

Well, I guess it "should" but you then you have to deal with the emissivity involved with the material/color of the surface of whatever you are trying to measure. I have seen chrome surfaces read dramatically different surfaces than flat black at the same temp. As an example, I just measured the Heat exchanger, a chrome pipe that connects to it, and the black rubber hose that connects to that. The IR gun shows:

HE (painted white) 120 degrees, chrome pipe - 90 degrees, Black rubber hose connected to chrome pipe - 128 degrees. The same water is all three spots... If you were to believe the heat gun, you would conclude that the water drops 30 degrees when it enters the chrome pipe, and then rises 38 degrees when it enters the rubber hose. Obviously, this is impossible and makes IR guns rather questionable for any meaningful use OTHER than determining changes at the same location. There are IR guns that can be properly calibrated to handle different materials but they cost north of 1k dollars.

Heck, at the moment, I don't know WHAT to believe.

[SportFishCruising]

..... But I wish I could think of a way to positively "calibrate" the IR gun...

Infrared detectors require calibration & re-calibration, even spot radiometers. Overtime, sensors and electronics may drift effecting accuracy and repeatability.

Having said that, some work only requires a simple calibration 'VERIFICATION' be preformed. I suggest you do this each time you use your equipment. You can Verify calibration by looking at a person's tear duct. The tear duct's temperature is regulated by the body very well, remember some people may have cold fingers or noses but the tear duct is very consistent with the internal body temperature. The tear duct is located in the corner of the eye next to your nose.

The procedure,

1 safety first, if you have a laser turn it off before looking at someones face

2 set your emissivity to .98 (human skin),

3 set a standard distance to use during this test depending on spot size to distance resolution on your instrument, I suggest 6-8" and look at a person's tear duct.

4 record the temperature, it should be between 92-95 degrees F.

If it is in this range and all of your setting are correct then your IR-Instrument is ok to use.

If the temperature reading is above or below by more than a few degrees F then you have cause to worry.

1 Start by checking all of your settings that effect temperature readings, double check emissivity setting

2 check another person to make sure the person is not the problem, being sick elevates a person temperature as will extreme environmental conditions

3 if you do all of this and the unit shows "odd" temperature readings then you have a concern and may need re-calibration of the instrument which means it goes back to the manufacture.