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Old 05-09-2015, 20:14   #16
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Re: 165 hp cummins for 50ft roberts ketch

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Twin 500hp engines in a 24ft. Donzi-type powerboat. Yes, entirely different type of boat, but they still handle the weight and horsepower. 5.9 Cummins is a great engine and not that heavy.

Well YOU wont have trouble pushing against tide then!

It is not just the weight of the engine of course. I have 2" shafts and big tanks so it does stack up. In my case they are integral keel tanks and engine is low down in the bilges so acceptable. Actually the biggest negative for me is that my wife hates the noise of the engine. Does not help that the engine space has not been enclosed as yet - a work in progress.😩😩😩


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Old 06-09-2015, 05:22   #17
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Re: 165 hp cummins for 50ft roberts ketch

Discussed this issue at length with designer Eric Sponberg related to my 47' Alden ketch. 36,000 lbs displacement. Full keel drawing 6' 9". There is no real benefit to being overpowered like that. Like cars, people buy horsepower but they drive torque. I'm installing a 65 hp Cummins B 3.3. Low RPM high torque non-turbo. As you approach hull speed the HP needed to add speed goes way up as does your consumption of fuel. At lower speeds you are loading and the engine enough.

It wouldn't necessarily be a deal maker but I wouldn't choose to install such a machine in my boat.
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Old 06-09-2015, 06:32   #18
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Re: 165 hp cummins for 50ft roberts ketch

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Originally Posted by crazyoldboatguy View Post
Discussed this issue at length with designer Eric Sponberg related to my 47' Alden ketch. 36,000 lbs displacement. Full keel drawing 6' 9". There is no real benefit to being overpowered like that. Like cars, people buy horsepower but they drive torque. I'm installing a 65 hp Cummins B 3.3. Low RPM high torque non-turbo. As you approach hull speed the HP needed to add speed goes way up as does your consumption of fuel. At lower speeds you are loading and the engine enough.

It wouldn't necessarily be a deal maker but I wouldn't choose to install such a machine in my boat.
We have a Camper-Nicholson 58; 36 tons with a 6-cyl Westerbeke 115 HP; 2:1 reduction and Hundested 3-blade, 24-inch continuously variable pitch prop. As Crazyguy notes, you won't go over hull speed without a lot of fuel consumption. What you will be able to do is motor against swells and wind without a serious penalty of speed. We have been unable on a couple of occasions to motor out of harbor against incoming big stuff. -SO , I don't think 165 is too big. This will get you out of trouble when you need it.

The variable pitch came with the boat. Its expensive new but a great addition on a big heavy boat. It lets you match the prop to the speed and sea state to maximize the performance. If we stick the keel in the sand, We lower the prop pitch and speed up the engine. This gives huge thrust at zero speed. Likewise, motoring against wind and swell we flatten out the prop. In zero wind or light air motor sailing we stretch out the pitch.
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Old 06-09-2015, 06:38   #19
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Re: 165 hp cummins for 50ft roberts ketch

For my own boat, an old Pearson 30, the original engine is often replaced with a 10hp diesel. Thats apparently all the power it requires. I have an 18hp diesel. In theory, I have 80% more power than I need.

I think its fine, a benefit actually. I can run at lower rpm, which is both fuel efficient, and more comfortable (quieter, less vibration).

Aside from the greater initial cost, I can't see any downside. The engine size and wieght are about the same, as are the peripherals, like the alternator, pumps, exhaust, etc.

Did I mention my engine is 30 years old and still running strong...does not burn oil, and no issues to date. I expect it will outlive me.
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Old 06-09-2015, 08:09   #20
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Re: 165 hp cummins for 50ft roberts ketch

I have a 51 foot Gulfstar- 135 hp Perkins-- so my boat is not known to be a racer but it is comfortable. Have not regretted the large engine and just throttle down to keep fuel consumption lower. I carry 200 gallons of diesel so it is less of an issue but I have never been unhappy with the engine- i dont think the weight penalty is huge-- prop drag is a consideration but is not something that i would fret about too much.
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Old 06-09-2015, 14:27   #21
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Re: 165 hp cummins for 50ft roberts ketch

It used to be 1-2 HP/tonne... now it is 4-5 HP/tonne

On turbo charged diesel, running must be at a high rpm, or turbo will overheat and uses oil.

Extra power is available only with a bigger propeller, i.e. more drag
As many sailors motor a lot, they may love the idea that extra power is a safety measure.

I don't :-)
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Old 09-09-2015, 03:44   #22
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Re: 165 hp cummins for 50ft roberts ketch

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It used to be 1-2 HP/tonne... now it is 4-5 HP/tonne

On turbo charged diesel, running must be at a high rpm, or turbo will overheat and uses oil.

Extra power is available only with a bigger propeller, i.e. more drag
As many sailors motor a lot, they may love the idea that extra power is a safety measure.

I don't :-)
intersting

well running a 3.7 liter 4 cyl turbodiesel, intercooled,115hp at 2600rpm, running, 1400-1800 range would be ok acording to you? and sometimes, some minutes almost full throttle
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Old 09-09-2015, 19:02   #23
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Re: 165 hp cummins for 50ft roberts ketch

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intersting

well running a 3.7 liter 4 cyl turbodiesel, intercooled,115hp at 2600rpm, running, 1400-1800 range would be ok acording to you? and sometimes, some minutes almost full throttle
This is a heavy duty engine with just 30HP/litre

That range sounds good, for max torque and low specific consumption, gr/HP/hr.

Find out the engine curves and tune ears for best rpm
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Old 09-09-2015, 19:30   #24
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Re: 165 hp cummins for 50ft roberts ketch

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intersting

well running a 3.7 liter 4 cyl turbodiesel, intercooled,115hp at 2600rpm, running, 1400-1800 range would be ok acording to you? and sometimes, some minutes almost full throttle
Sounds ok to me. Ours is a 3.3 litre, 4 cylinder, conventionally aspirated 96HP, we run it from 1400 to 1600 rpm, and it loves it.
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