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Old 06-13-2020, 11:38 AM   #41
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City: Lagrange, IL
Vessel Name: Moondance
Vessel Model: Grand Banks CL 42
Join Date: Sep 2019
Posts: 172
So thanks again all. I am learning more. I feel a little better about the possibilities of this boat but you understand the feeling about forking over big $$ - you want to be sure as can be. I will go back for another look at this boat soon.
I have inquired about getting engine surveyor and have talked with a supposedly certified CAT guy and they did mention oil & coolant analysis as well as blowby. And yes using photo tach for rpm.
BTW John, engine serial # prefix is 4KG on one engine and 1SK on other - I am hoping that the governor setting is a little low as you and others mention. You also mention high idle spec - If high idle is 3075 and these engines hit 3000 then they are missing by approx. 2.5% so maybe again a setting that can be adjusted? And this is what last survey had for coolant temp at 2700 rpm - 180 degrees port, 187 degrees stb.
Keep those comments coming!
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Old 06-13-2020, 03:07 PM   #42
Join Date: Oct 2013
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I have 3126s and the load/rpm youíve described is well within tolerance. While 2800rpm should be the target, there are many variables that would affect that number. In order...check/verify the tachs as being accurate(most are not). Next is the load...donít know your fuel quantity at full but itís probably in the 2500-2800lb range and with 7 adults...itís a lot of weight. Next is the environmental conditions...wind? chop? Next is you have a big flybridge enclosure? Next is bottom paint condition...a few barnacles go a long way in destroying performance. Next is fuel filters...clean filters-better fuel flow- better performance. Bottom line...check those items before you ever start tweaking props.
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Old 06-13-2020, 03:33 PM   #43
City: Carefree, Arizona
Vessel Name: sunchaser V
Vessel Model: DeFever 48
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The Cat 3116s have some interesting histories. Check boat diesel .com. Personally, being able to achieve rated RPM plus 25-50 is desirable IMHO. These engines do not tolerate an over heat well, which could arise from the vessel having a dirty bottom, too much weight or too "big" of props.
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Old 07-07-2020, 03:53 PM   #44
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Vessel Name: Yankee Peddler
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Cat engine surveys

Your engines probably came off the assembly line in Mossville IL and were run at wide open for at least an hour under load. A cat marine engine dealer can get the history if you give him the serial numbers. If you want a really good survey contact Tim Caruso in Stuart, FL who is the best in the world and ONLY does Cat marine engines. His company is Diesel Engine Analysts (771 285-6770). In most cases a good engine survey pays for itself and it is a wonderful learning opportunity. The high idle is on the engine tag and the engines should meet this number since the load and hull condition are not a factor, but the throttle control is a factor. If your surveyor did not use a photo tach you had the wrong guy.
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Old 07-12-2020, 08:04 AM   #45
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Interesting stuff. Failing to hit a number could be indicative of a problem. Would need to be > 10% for me to be concerned. Good responses by many folks here. I'll suggest WOT performance is mostly about understanding if your boat (hull, prop or engine) has degraded performance (which'll cost you $ later.)
I specifically added 2" of pitch when I replaced my props and very happy about it. Yes, I did lose a little top speed but couldn't even tell you how much. Why? Because I would never run my engines at that RPM anyway. Across the rest of the operating range, I gained a knot. That's because the available power curve (look up any engine) is substantially linear, a ramp that flattens off at high RPM while the power demand curve (what you need for each speed) takes off exponentially; power demand is essentially cubic in speed & disregarding slip that means RPM. Maybe I should make a sketch but you're probably picturing it: below WOT, the engine is loafing. That can even be "bad" in that you don't run warm enough. This hit me when, running at 1900, I calculated 90HP (total) to move the boat (near hull speed) based on fuel consumption. I was way WAY under rated power: 2 Lehmans rated at 120HP/2500rpm. Of course: it was dialed to hit max rated power at 2500 at speeds where the boat drag would be way higher. At lower speed, power demand falls of exponentially, *way faster than available power.* For instance, 1650RPM instead of 2500RPM? 50% less RPM and boat speed but that's more than a 3x reduction in power. Engines loafing at 40hp each. I wanted more efficiency and therefore to operate closer to rated power in the heart of my speed range (1500-1800). Prop guy argued. Shop guy argued. "You'll never hit WOT." Did it anyway & very happy. A bit overpropped maybe but cruising faster at lower RPM. top of the power curve is flat. You won't hit WOT but very close to wide open Power, so you won't even lose much speed. Just like on the freeway, just like a long bike ride: if you're not running flat out, consider a taller gear.
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Old 07-12-2020, 08:35 AM   #46
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Vessel Model: Milkraft 60 converted timber prawn trawler
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Have never taken ours to WOT
Why would I?
WOT just burns a shittonne of fuel for no real speed benefit
She does 8 knots at a fast idle - mission accomplished.
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Old 07-12-2020, 09:11 AM   #47
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CAT 3126 Engines

I have owned two trawlers with 3126 Cats and both ran flawlessly. I never cruised over 1300 RPMs except at least once a month I ran them up to WOT for 20 minutes to test the change in cooling temperatures and kept a very accurate record. I wanted to purposely stress the engines to see if the cooling system was in good condition which is critical on the 31xx series. In some ways these are fragile engines and they must never be allowed to overheat. Anyone buying a boat with these engines in my opinion should hire the best Cat mechanic he can find. CAT has specially trained and certified mechanics for marine engine surveys and they have to re-certify annually. The 32xx engines did not do well with high speed boats.
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Old 07-12-2020, 09:30 AM   #48
City: Northport
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Originally Posted by Simi 60 View Post
Have never taken ours to WOT
Why would I?
WOT just burns a shittonne of fuel for no real speed benefit
She does 8 knots at a fast idle - mission accomplished.
We never ran at WOT either.
But a short WOT test does give a baseline when you might want to help determine things like hull condition, and prop running gear condition.
Of course on boats that have faster speed WOT is more of a concern.
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Old 07-12-2020, 01:25 PM   #49
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Why WOT?

Cat says you can run at WOT for one hour out of 10 - it is in the engine manual. By running at WOT you will stress (not damage) the engine to see if there is a weakness that is just waiting to happen. As an example one time when I did this it blew a water hose off the engine due to a broken hose clamp. Sometimes I get a slight increase in water temperature informing me the coolant system needed cleaning. I prefer to find the weaknesses under my control then when I am not 50 miles out in the Gulf.
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