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    Tach question-gctid391734

    I have a 185 with the 3.0 and alph 1. It seems that the tach and what RPMS the engine is running at is very important to people. For example people always ask about WOT and cruising rpms. Why is this. Why is RPM so important in boating?

    #2
    Just my 2 cents on this.

    #1 Run your boat at WOT and the answer will cost about $3000. Blown engine. Rpm's are more important than speed because it tells where to run your engine for longevity of the engine. Would you run your car at 8000 rpm, probably not, unless you drive an Indy car, for the same reason, blown engine. It can also tell you how your engine is performing over the years. If, lets say, you run at 5000 rpm and get 43 mph consistently, then the following year at same rpm you are running at 30 mph, there is a great indicator of a problem. Either water logged boat, or your engine is out of breath (compression). RPM also serves as to tell the most economical spot for fuel consumption. If manu. rec's 4000 for cruising, this is probably the sweet spot for fuel consumption. Also if you cant hit WOT or cruising rpm, your engine is lugging and will run out of breath quickly, again a $3000 answer. Or if you are waaaaaaaay over wot rpm your piston rods are getting stretched beyond what they are meant to do. In short, it helps you maintain your engine performing at its peak for long periods of time. Consider the tach like a heartbeat monitor, too high and boom, too low, not good either. This is the one gauge i pay careful attention to ALL the time.

    Again, just my 2 cents. Others will chime in with their thoughts on this matter.

    Comment


      #3
      K townguy could'nt have said it any better!

      Comment


        #4
        k-townguy wrote:
        Just my 2 cents on this.

        #1 Run your boat at WOT and the answer will cost about $3000. Blown engine. Rpm's are more important than speed because it tells where to run your engine for longevity of the engine. Would you run your car at 8000 rpm, probably not, unless you drive an Indy car, for the same reason, blown engine. It can also tell you how your engine is performing over the years. If, lets say, you run at 5000 rpm and get 43 mph consistently, then the following year at same rpm you are running at 30 mph, there is a great indicator of a problem. Either water logged boat, or your engine is out of breath (compression). RPM also serves as to tell the most economical spot for fuel consumption. If manu. rec's 4000 for cruising, this is probably the sweet spot for fuel consumption. Also if you cant hit WOT or cruising rpm, your engine is lugging and will run out of breath quickly, again a $3000 answer. Or if you are waaaaaaaay over wot rpm your piston rods are getting stretched beyond what they are meant to do. In short, it helps you maintain your engine performing at its peak for long periods of time. Consider the tach like a heartbeat monitor, too high and boom, too low, not good either. This is the one gauge i pay careful attention to ALL the time.

        Again, just my 2 cents. Others will chime in with their thoughts on this matter.
        As per my bayliner owners manual; "If full throttle operation is below the recommended range (2004 bayliner 175br 3.0 is 4400-4800 rpm), the propeller must be changed to prevent loss of perfomance and possible engine damage. On the other hand, operating an engine above the recommended operating rpm range will cause higher than normal wear and/or damage."

        So according to the manual, running the boat at Wot (wide open throttle) is normal and is actually good for the boat, especially under load. obviously once you get to the speed you want to cruise at, then you back the throttle off and cruise for safety of the engine and mpg, but under load, you should be running the engine in the specified WOT range.

        Comment


          #5
          ok good info thanks - one thing - I do not have a owners manuel for my but - but its a 185 with a Alfa 1 and a 3.0 - what is a good cruising RPM to be at?

          Comment


            #6
            Bay-185 wrote:
            ok good info thanks - one thing - I do not have a owners manuel for my but - but its a 185 with a Alfa 1 and a 3.0 - what is a good cruising RPM to be at?
            Whatever feels comfortable, obviously like the other guy said, you dont want to be cruising around with the throttle mashed all the way down, but as long as you are under 4k rpms you should be fine, 3k rpms seems to be a comfortable cruising range for my boat, yours probably isnt much different, just keep in mind, the lower your rpms are while cruising, the less gas you are using

            Comment


              #7
              "So according to the manual, running the boat at Wot (wide open throttle) is normal and is actually good for the boat."

              When I was a kid, I had a job warming up all the engines on a used car lot every morning. Admittedly, that was a much different time, much different engines, but from the constant warnings I got in that job, I get very uncomfortable hearing a factory stock engine at high RPMs.

              Other's will differ in opinion and they're probably correct, but I would only run an engine at WOT in an emergency.

              Comment


                #8
                MikeRoss wrote:
                "So according to the manual, running the boat at Wot (wide open throttle) is normal and is actually good for the boat."

                When I was a kid, I had a job warming up all the engines on a used car lot every morning. Admittedly, that was a much different time, much different engines, but from the constant warnings I got in that job, I get very uncomfortable hearing a factory stock engine at high RPMs.

                Other's will differ in opinion and they're probably correct, but I would only run an engine at WOT in an emergency.
                As a mechanic, i know the engines that last the longest are the ones that are driven the hardest. Ask any mechanic, as long as you take care of the engine, running it at its peak operating range is perfectly fine, i have done it with every car i have ever owned and never once had an engine failure.

                Comment


                  #9
                  whitey382 wrote:
                  As a mechanic, i know the engines that last the longest are the ones that are driven the hardest. Ask any mechanic, as long as you take care of the engine, running it at its peak operating range is perfectly fine, i have done it with every car i have ever owned and never once had an engine failure.
                  Thats a good point, I was told by a mechanic after I had reconditioned the engine in my car to run it in the way I wanted to drive it. Obviously i was carefull for the first 30min but then took it on a run and gave it heaps. That turned out to be the best engine I ever had, it rev'd to the red line with ease and never let me done until the gearbox blew up... Thats another story.

                  It proved the old thinking of never going over a certain RPM and running the engine in is not always correct.

                  Comment


                    #10
                    Macca wrote:
                    That turned out to be the best engine I ever had, it rev'd to the red line with ease and never let me done until the gearbox blew up... Thats another story.

                    It proved the old thinking of never going over a certain RPM and running the engine in is not always correct.
                    Gear box being another term for transmission, so the transmission failed you. But thank you for backing me up. the engines that break down and have the most problems are the ones driven by old people. Old people drive like the engine is running on 2 cylinders, and if you constantly tell the dog he looks like a cat eventually he will act like a cat, engines that are driven like they are broken down will evetually break down, engines driven like theyre a race car will run like theyre a race car (within the limits of the engine, in this case wot which is 4400-4800 rpm)

                    Comment


                      #11
                      whitey382 wrote:
                      Gear box being another term for transmission, so the transmission failed you. But thank you for backing me up. the engines that break down and have the most problems are the ones driven by old people. Old people drive like the engine is running on 2 cylinders, and if you constantly tell the dog he looks like a cat eventually he will act like a cat, engines that are driven like they are broken down will evetually break down, engines driven like theyre a race car will run like theyre a race car (within the limits of the engine, in this case wot which is 4400-4800 rpm)
                      Probably in the best interests of the original poster to clarify definitions here while he still has an engine.

                      WOT is defined as follows: "Wide open throttle (WOT) refers to an internal combustion engine's maximum intake of air and fuel that occurs when the throttle plates inside the carburetor or throttle body are "wide open", providing the least resistance to the incoming air. In the case of an automobile, WOT is when the accelerator is depressed fully, sometimes referred to as "flooring it".

                      Based on your previous posts and your statement above, "........in this case wot which is 4400-4800 rpm." You're confusing WOT with Peak Operating Range. Big difference. Particularly for the engine.

                      Comment


                        #12
                        First of all, when WOT RPM is being discussed for a Marine application, this WOT RPM is targeted while under load.

                        If I understood him, I believe this is what Mike Ross is referring to.

                        This RPM is certainly not what the engine is capable of, but is rather what the OEM engineers wants us to use in order to determine if we a propped and geared correctly.

                        NO WHERE do they state that this is an RPM to be sustained for any duration!

                        whitey382 wrote:
                        As a mechanic, i know the engines that last the longest are the ones that are driven the hardest. Ask any mechanic, as long as you take care of the engine, running it at its peak operating range is perfectly fine, i have done it with every car i have ever owned and never once had an engine failure.
                        Macca wrote:
                        Thats a good point, I was told by a mechanic after I had reconditioned the engine in my car to run it in the way I wanted to drive it. Obviously i was carefull for the first 30min but then took it on a run and gave it heaps. That turned out to be the best engine I ever had, it rev'd to the red line with ease and never let me done until the gearbox blew up... Thats another story.

                        It proved the old thinking of never going over a certain RPM and running the engine in is not always correct.
                        This is where the Marine and Automotive mechanics must part ways..... Apples/Oranges! rod

                        When/if we do not understand Marine loads -vs- Automotive loads......, we should refrain from doing Marine engine work.

                        It's that simple!

                        .
                        Rick E. Gresham, Oregon
                        2850 Bounty Sedan Flybridge model
                        Twin 280 HP 5.7's w/ Closed Cooling
                        Volvo Penta DuoProp Drives
                        Kohler 4 CZ Gen Set

                        Comment


                          #13
                          2850Bounty wrote:
                          First of all, when WOT RPM is being discussed for a Marine application, this WOT RPM is targeted while under load.

                          If I understood him, I believe this is what Mike Ross is referring to.

                          This is where the Marine and Automotive mechanics must part ways..... Apples/Oranges! rod

                          When/if we do not understand Marine loads -vs- Automotive loads......, we should refrain from doing Marine engine work.

                          It's that simple!

                          .
                          I will make this my last post on the topic, because quite frankly this is getting old. In the statement above, you are actually supporting what I was originally telling the poster. Unless you are using a rotary engine (which to the best of my knowledge, no boat uses one), you do not want to spend all day at the top of your vehicles (boat or car) RPM range. The original poster asked about safe running conditions for your boat. Mikeross said unless you want to blow up your engine, don't run it at WOT. As quoted above, WOT is the optimum RPM range you want your boat to operate in when under load. In other words, when you are launching from your hole shot pulling a skier, you want to be in that RPM range to apply the most power to the prop without putting the engine in a dangerous range. That is all I have been saying since this post started. Use the WOT range the manufacturer gives to you and have fun with the boat. If every you pull a skier out of the water you use the WOT range are you somehow going to do more damage to your engine than you would if you launched at 3k rpm? No, in fact, as per the manual you will do more damage because the engine produces it peak power at WOT range and you are actually putting more strain on the engine when max loading it and not having the engine WOT range. As I told the originaly poster before, use WOT properly and have fun with the boat, but when you are out cruising don't have the engine pegged all the time.

                          One more thing I would like to add, while there are some obvious differences between a boat and car, in this specific case, the apples and oranges thing doesn't really apply. The 3.0 engine used in our boats is a GM produced engine from the early 70's if I'm correct. It was an engine used in cars first, boats second. So while the automotive field uses terms like redline, and the boating field uses terms like WOT (and no I am not saying that these terms mean the same thing) the same basic principles apply.

                          Comment


                            #14
                            whitey382 wrote:
                            I will make this my last post on the topic, because quite frankly this is getting old. In the statement above, you are actually supporting what I was originally telling the poster. Unless you are using a rotary engine (which to the best of my knowledge, no boat uses one), you do not want to spend all day at the top of your vehicles (boat or car) RPM range. The original poster asked about safe running conditions for your boat. Mikeross said unless you want to blow up your engine, don't run it at WOT.

                            1.... As quoted above, WOT is the optimum RPM range you want your boat to operate in when under load. In other words, when you are launching from your hole shot pulling a skier, you want to be in that RPM range to apply the most power to the prop without putting the engine in a dangerous range. That is all I have been saying since this post started. Use the WOT range the manufacturer gives to you and have fun with the boat. If every you pull a skier out of the water you use the WOT range are you somehow going to do more damage to your engine than you would if you launched at 3k rpm? No, in fact, as per the manual you will do more damage because the engine produces it peak power at WOT range and you are actually putting more strain on the engine when max loading it and not having the engine WOT range. As I told the originaly poster before, use WOT properly and have fun with the boat, but when you are out cruising don't have the engine pegged all the time.

                            2...... One more thing I would like to add, while there are some obvious differences between a boat and car, in this specific case, the apples and oranges thing doesn't really apply. The 3.0 engine used in our boats is a GM produced engine from the early 70's if I'm correct. It was an engine used in cars first, boats second.

                            3.... So while the automotive field uses terms like redline, and the boating field uses terms like WOT (and no I am not saying that these terms mean the same thing) the same basic principles apply.
                            1.... The OEM specified WOT RPM is an RPM calculated by the engineers that suits the engine's capabilities when propped and geared correctly.

                            This is to ensure that we are not over-burdening an engine at any RPM.... not just WOT.

                            We don't have the option of selecting different gear ratios, as we do with car/truck transmssions.

                            None-the-less, this is to be used as a TEST RPM ...... not a sustainable RPM.

                            I guess that you've covered it by suggesting to an OP; [COLOR]"#0000FF" wrote:
                            "use WOT properly and have fun with the boat, but when you are out cruising don't have the engine pegged all the time".[/COLOR]

                            I don't disagree if this is your bottom line!

                            2...... Agreed.

                            With exception to very few 4-stroke engines, most all gasoline Marine Engines began their lives under the hood of a car/truck.

                            Merc's aluminum block 470 is one exception. To my knowledge, this engine never saw a car/truck installation.

                            3... Automotive Red Line/Marine WOT RPM......... again, Apples/Oranges.

                            Take a marine engine with an OEM spec'd WOT RPM of 4,400-4,600 RPM.

                            I can almost assure you that this engine will do 5.5k RPM with a very mild propeller attached.

                            But now we've gone from a Marine Engineered WOT RPM, to a what may be a Red Line.

                            .
                            Rick E. Gresham, Oregon
                            2850 Bounty Sedan Flybridge model
                            Twin 280 HP 5.7's w/ Closed Cooling
                            Volvo Penta DuoProp Drives
                            Kohler 4 CZ Gen Set

                            Comment

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