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Old 11-04-2020, 07:50 AM   #41
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"If you go for the boat MAKE ABSOLUTELY SURE to get the props adjusted/repitched so the engines make their RATED rpm plus another 100 or 2900 as already mentioned."


A reasonable plan B would be to run once to WOT , note the RPM and pull back 300 as your max usable RPM . Cruisinfg RPM may be slower , no black smoke should be seen at 300RPM down or at cruise.
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Old 11-04-2020, 08:15 AM   #42
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"If you go for the boat MAKE ABSOLUTELY SURE to get the props adjusted/repitched so the engines make their RATED rpm plus another 100 or 2900 as already mentioned."


A reasonable plan B would be to run once to WOT , note the RPM and pull back 300 as your max usable RPM . Cruisinfg RPM may be slower , no black smoke should be seen at 300RPM down or at cruise.

In a GB with 400+ hp engines, that's probably not the greatest idea. You'd end up moving very fast at idle if significantly overpropped, plus you'd lose the ability to run fast with the big engines. With that much power, even propped correctly, a below hull speed "slow cruise" should already be at pretty low RPM.
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Old 11-04-2020, 09:14 PM   #43
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25-50 over rated WOT RPM is a typical goal, it ensures the engines can't be over-loaded if they are ever run at WOT, and it provides some cushion for weight being added to the boat. That sea trial for WOT should occur with a full load, full fuel, full gear, full water. 100 over won't hurt, it simply means you are underloaded to a greater and probably unnecessary degree. I've never seen an engine manufacturer ding a boat builder at commissioning for making over rated RPM, underloading. Under-revving, i.e. over-loading, on the other hand is forbidden.

More on WOT here https://www.proboat.com/2010/09/wide-open-throttle/
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Old 11-04-2020, 10:52 PM   #44
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A question on after coolers on cat 3208 being bypassed: How did you by-pass? Are they still in place and the water loop coupled. I have two 3208TA 375 hp. I never use the rate power requiring the after cooler. Typically we run between 1300 to 1500 which is a 8.5 to 10 knot cruise with a clean bottom about 6 to 7 gal/hr total both engines. I have been thinking about by-pass as I have hear some leakage stories wiping out engines. I have had my AC out, cleaned and tested. They appear to be a robust design and I believe the tubing is a copper nickel composition. I also flush the engines with fresh water when leaving the boat no operable which lessens the corrosion issue.
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Old 11-05-2020, 06:02 AM   #45
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How to prevent? Monitoring long term trends, I have been working on a monitoring project for a while now. Currently running on a mini computer (raspberry pi). every 15 seconds it stores temps of sensors located around the engine. This data is stored in a database. Once in the database there is long term data and you can spot issues before them become major. I then display them as a webpage accessible from any device with internet access either onboard or remotely. Currently I manually average and graph the long term data in excel but am building to towards automatic alarming based on anomalous behaviour. When I get time.
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Old 11-05-2020, 08:14 AM   #46
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"In a GB with 400+ hp engines, that's probably not the greatest idea."


The 300 RPM down concept is not for selecting or installing a cruising prop, just to operate the boat with no harm till the owner decides how he will prop and cruise the boat. A get home for a new purchase.
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Old 11-05-2020, 08:21 AM   #47
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Quote:
Originally Posted by FF View Post
"In a GB with 400+ hp engines, that's probably not the greatest idea."


The 300 RPM down concept is not for selecting or installing a cruising prop, just to operate the boat with no harm till the owner decides how he will prop and cruise the boat. A get home for a new purchase.

Oh yeah, in that case, 100% agreed.
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Old 11-05-2020, 09:27 AM   #48
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Check out https://www.sbmar.com/

They mostly do Cummins but there are very good articles/advice by Tony Athens on what to look for in marine exhaust (plus other excellent articles not specific to Cummins). Using Tony's knowledge should give you a yardstick to evaluate your installation. The basic naturally aspirated 3208s are lifetime engines but by doubling the horsepower their longevity suffered. Some Cat blocks were not rebuildable but as I'm attached to a Cummins now, I have no idea which.
Check out Tony's stuff.
We used to have DD671 and then upgraded (we thought) to 3208 - loved anything naturally aspirated. When CAT decided to go turbo thus boosting the hp out of the same size engine, we went to 855 Cummins (now 8.3L). Red tops are indestructible. Can't say the same for 3208 t/a's. Plus they are noisy and don't get me started on the cost of ownership. I know of a guy who just bought an aluminum sportcruiser that had 3208 T/A's. I say had, because a month after purchasing - he had to repower it. He found a pair of remanned red tops and now he's very happy.
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