...I added a swim platform to my N46 and presto, I was driving a 49 ft boat...
I really want to be eligible to join the Boat International owners club so I can hang out with outrageously rich people who wear white pants and navy blue blazers and ascots, but the eligibility for that club is a boat that's 24 meters or 78.7 feet. Somehow I need to figure out how to extend my 40' LOA by 38.7 more feet. Has crossed my mind to paint a big red 36" diameter "H" inside a circle on my bow and then use a drone to take what looks like high altitude shot of my helipad, but they'll probably see through it.
Planing will be more efficient than plowing. But if you compare planing to an efficient slow cruise of say 6.5 kts, slow will produce better mpg. On my boat, mpg at 6.5 - 7 kts is more than double what it gets on plane at 17 - 18.
I got a little sideways with the harbor master in our marina over my length. Like many I have a so called 34 CHB, a Puget Trawler. But from end to end with pulpit and swim step and the dinghy against the transom I was too long for my slip at 37', rear end into the fairway which for a time at least was a huge problem for some reason.
Not so much now but I moved into a longer, more expensive slip so I could avoid the issue altogether.
The 34 CHB is almost 34 on the waterline.
Of course that is true. My reply started around the post about a 34' boat running at 10 knots. My guess, that is not very effcient and not worth the extra fuel to go a little faster than hull speed.
That sort of depends on the next refueling dock and the credit limit on your bank card
*1Certainly the boat is happy cruising at 2200 RPMs. Is it fuel efficient? No! What is more important to you, fuel efficiency or time? I am not very sensitive to being fuel efficient so I would be happy with what you are doing. The boat probably rides better at 8.5kts than it would at 7kts.
I am not trying to hijack the thread - I have a 500hp Cummins with a turbo charger. Those of you running at lower speeds - if you don't kick on the turbo charger - aren't you simulating a "blown turbo" and isn't that bad for the engine?
Turbos don't really "kick in", they are running all the time thanks to the exhaust stream running over their turbine wheel. The more robust the exhaust stream (more pedal to the metal) the faster the turbo spins, and the more the boost pressure. A properly engineered turbo installation will intrinsically provide the appropriate inlet air pressure boost appropriate to the the fuel being burnt when the propeller ratio is correct. The principal time you will damage a turbo is when you are over-propped and the engine can't get the RPM and thus commensurate air intake/throughput for the correct fuel/air ratio thus giving a "dirty burn" with lots of black smoke and carbon. Generally, if the turbo is properly matched to the engine and the propeller pitch and diameter are correct, the engine will run clean at all reasonable RPM's. They are not engineered to have one, and one only "sweet spot".
I think we have 3 units. The engine, which is a constant, the gear box and the prop. The prop while very important, consider it a point for fine tuning the entire package. The engine mods, if drastic, might suggest the wrong engine was selected... IMO the only place mods would make sense is the gear box ratio. It can be designed for high speed, low speed or average, ignoring torque. Trawlers are pretty much designed for hull speed. Now given those parameters it is up to 'someone' in a higher pay grade to make the decisions on gearing recommendations. When all is done, the final tuning can be done with the prop.
Don't forget that the gearing vs prop diameter balance will also be limited by what size prop fits under the boat.
I think we have 3 units. The engine, which is a constant, the gear box and the prop. The prop while very important, consider it a point for fine tuning the entire package. The engine mods, if drastic, might suggest the wrong engine was selected... IMO the only place mods would make sense is the gear box ratio. It can be designed for high speed, low speed or average, ignoring torque. Trawlers are pretty much designed for hull speed. Now given those parameters it is up to 'someone' in a higher pay grade to make the decisions on gearing recommendations. When all is done, the final tuning can be done with the prop.
Hi Old Dan,
i have the same cummins as your AT. I have been asking the Cummins factory about this low engine load for long periods of use.
My questions:
"Hi,
I have a Cummins 5.9 qsb marine engine 2009 and it reaches max rmp 3065 which is perfect my Nordic Tug 37.
I have read a lot of conflicting opinions on the engine to run at low rmp a long time, because the machine may damage the carbon and etc. Some say it's ok to run this type engine at low rmp if the coolant remains in the correct slot.
The time i run my engine is most often 850-1300 rpm since the boat is most economical in this rmp area and temperature is ok. Cummins runs fine and does not smoke any, exhaust pipe mouth environment does not show any black carbon.
What is the manufacturer's view of low load low rmp almost always, whether it is ok or damaging the engine?
It would be great to have an expert answer, all the web instead of rumors."
And Cummins answers:
"This is fine for our engines. It is not suggested to Idle (650-750rpm) for long periods. Generally speaking, you can idle for about 20 minutes or so at this range and be okay. If you plan to idle longer than 20 minutes or so it is suggested that you ramp up your RPM to about 800-1000. Working the engine under a light load/rpm is fine. This is not uncommon for some our engines (like Generators which normally work at 1800 RPM or less) and will not cause any undue harm.
Thank you for contacting Cummins.
Katelyn
Customer Care Representative
If we have misunderstood the information in your communication or you have additional questions please feel free to respond to our support staff by e-mailing support.engineparts@cummins.com or 1-866-CUMMINS (286-6467). If you are located outside of North America, you can reach us at 1-615-871-5500.
Visit us at www.cummins.com or www.cumminsengines.com "
The Cummins qsb 380 is a fine and reliable marine diesel, I have now used it for 2700 hours, running 95% of the time from 830-1100 rmp and the remaining 5% around 1400-2500rmp and the machine does not smoke or black carbon exhaust around the gel goat.
NBs
Hi Old Dan,
i have the same cummins as your AT. I have been asking the Cummins factory about this low engine load for long periods of use.
NBs
Trolling valves are mated to the transmission, not the engine. Twin Disc in my NT 37 can have one. So can my friend's NT 42. No need unless you want to go really slow, like 1-2 knots.Maybe Cummins make a trolling valve for the engine
I do not know
I agree, time matters more, so I normally run about 16 knts!
And, that can change! Before I retired, I was happy to exchange money for time, when I had more money than time.
Now, retired, I have a lot more time than money, so I do just the opposite!