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Old 06-22-2017, 11:42 PM   #7
Lepke
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City: Between Oregon and Alaska
Vessel Name: Charlie Harper
Vessel Model: Wheeler Shipyard 83'
Join Date: Jun 2016
Posts: 3,023
Some hour meters count the minutes an engine runs and some have a factor that adds hours based on rpm.
My experience is in heavy duty engines not smaller yacht diesels. In my time I have personally overhauled or watched the overhaul of many engines that I knew the hours and operating conditions of the engines. Engines run near wot do not last as long as engines kept under 80% of max hp. In some engine makes that can mean twice or triple the span between overhauls. Turbo engines almost always have a short span compared to their non turbo models. Continuous wot can cause damage beyond normal wear. Sometimes in sleeved engines the waterjacket becomes distorted and has to be rebored requiring special sleeves. Why larger sport fishing boats often have very expensive overhaul. Going 25 kts instead of 30 saves more than fuel. Excessive heat also leads to cracks. Just because the coolant doesn't overheat isn't a sign of safe operation. At high hp, cavitation (small bubbles form on the water side of the waterjacket) causes deep pits that are not fixable.
Engine makers want to sell engines and adjust their max and continuous rpm on the market. Commercial engines have to last or no more engines would be sold. But yacht engines are used lightly and I believe the continuous rpm specs are given planning on the engines to be off warranty when they fail.
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