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Old 10-13-2020, 09:29 PM   #1
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Nordic tugs 37 prop choice

Hi,
I just recently purchased a NT37 that doesn't have a spare prop. I figured I might get a new prop and keep the old one as a spare. The boat has a 330 hp cummins engine. It came with a 28" x 24 michigan wheel prop. As I look at props I have been considering a dyna quad and DQX. The DQX is a bit more expensive. Anyone with a NT37 try either?
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Old 10-13-2020, 09:41 PM   #2
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Why do you think you need a spare? Most boats in this class do not carry one, mostly due to the single screw and protective keel.

For WESTERLY, we carry the name of a prop shop who can prepare and ship a replacement on short notice. Never had to do that, however.

The original prop dated 1973 works very well, it has accumulated thousands of miles on it without a need for repair.
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Old 10-13-2020, 09:42 PM   #3
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Good point.
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Old 10-13-2020, 11:12 PM   #4
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I agree with Jay based on the 4000 hours I put on my NT37 in the PNW, including plenty of time in ice in front of glaciers. Jay has a lot more time underway than I do. It just doesn’t seem easy to damage these props.

I did have an inch or two of pitch removed so I could hit rated RPM or a bit more when loaded for cruising. But at hull speed I doubt it matters.
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Old 10-14-2020, 02:37 AM   #5
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Quote:
Originally Posted by Retriever View Post
I agree with Jay based on the 4000 hours I put on my NT37 in the PNW, including plenty of time in ice in front of glaciers. Jay has a lot more time underway than I do. It just doesnít seem easy to damage these props.

I did have an inch or two of pitch removed so I could hit rated RPM or a bit more when loaded for cruising. But at hull speed I doubt it matters.
I am glad to hear that you had the prop pitch changed, Sam! I did the exact same thing this last December. People looked at me funny when I told them what I did!
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Old 10-14-2020, 08:02 AM   #6
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What were the results of reducing your prop pitch? This is something I am also interested in. When the boat has full fuel and water it is about 200 rpms low and slow.
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Old 10-14-2020, 10:56 AM   #7
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For my boat, I did it for the long-term health of the engine. It lets me get up to wot at 2600 rpm. At low speeds, I haven’t seen much change
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Old 10-14-2020, 11:35 AM   #8
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Spinner, What is your rated rpm?
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Old 10-14-2020, 11:58 AM   #9
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Eric, the engine is a Cummins 6CAT8.3, 450 hp. Rated rpm is 2600.
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Old 10-14-2020, 02:08 PM   #10
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For my boat, I did it for the long-term health of the engine. It lets me get up to wot at 2600 rpm. At low speeds, I havenít seen much change
Same here. Apparently the 6BTA and QSB donít like being overloaded, and thatís what happens when the engine wonít turn to rated WOT RPM. Given that I seldom cruised at higher than hull speed (1300-1400 rpm) I doubt it really mattered, but I wanted to be kind to the engine in the rare instances Iíd run at higher speeds.
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Old 10-14-2020, 02:49 PM   #11
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Exactly! I do every so often run at high rpms, and want to know that my engine is not being strained! I had previously noticed that I couldn’t get above 2500 rpm, even with a freshly cleaned hull....
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Old 10-14-2020, 05:12 PM   #12
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You guy’s are right onto it.
Fewer strokes with less force is preferable.
And when/if you run at higher speeds you’ll go faster with less load, more oil and more coolant will take away more heat.
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Old 10-14-2020, 07:14 PM   #13
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I also took 2 inches of pitch out of my prop. I have the 6BTA engine with a rated RPM of 2800. Before the 'tune up" fully loaded Pilitak would only reach 2650, but with no black smoke (which is a good thing). Likewise, I run around 12-1400 RPM for cruising, and periodically run her up to 2200 RPM for 10 minutes and to WOT for 1 minute to burn out any carbon buildup and to ensure that "all is well". Now with a clean bottom, and the boat loaded, we reach 2850-2900 RPM at WOT, which according to Tony Athens, is right where we should be. I did this for the same reasons Sue described.
To the OP, I don't carry a spare prop. Lots of other spares, but not a prop, and we are often "far afield".
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Old 10-14-2020, 07:25 PM   #14
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Firehoser75,
Did your wot speed go up or stay the same after you took 2 inches out of the prop? Just curious. I know its better for the engine.

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Old 10-14-2020, 07:28 PM   #15
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Packer,
Personally, as I don't travel at that speed (only use it to check engine health and to "clean out the carbon'), I don't follow the speed that much, so I am not really sure
However, I think the "top speed" actually dropped a bit, but not much.
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Old 10-14-2020, 08:54 PM   #16
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Tom, Sue and Sam, Did you notice any change in fuel consumption at cruising rpm after you shaved the prop? Did cruising RPM change or just WOT?

And to the original question: I’ve never dinged the prop on my previous NT32 or current NT37. So carrying a spare prop, although not unheard of, is low priority for me.

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Old 10-14-2020, 09:23 PM   #17
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Waterford,
If you run the same rpm w less pitch sure you will burn less fuel.
And at the same speed (that would require more rpm) one may burn less but it would depend on many variables. But if you were coming from an overpropped boat better fuel economy will probably result ... IMO.. from a pitch reduction.
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Old 10-15-2020, 04:28 AM   #18
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My fuel consumption is about the same or maybe a tad lower at normal (less than hull speed) rates. I recently had to run fast (2000 to 2200 rpm) to try and get in before dark (long story) and yes I think the engine used less fuel.
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Old 10-15-2020, 09:29 AM   #19
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Doug,
As you know, Pilitak is an older boat, before the fuel scan and all the electronics, so my fuel monitoring (which I do) is done by monitoring hours, the "pump type" tank tender, sight tubes, and mainly how much fuel I need to refill. So, it is not completely accurate. Based on this, I would agree with Sue, and state that I have not noticed any increase in fuel consumption.
However, unless I am envisioning all of this incorrectly, pitch is basically the distance that the prop "screws itself" through the water for each rotation. With a pitch reduction, that distance would be less, therefore, at the same RPM, in theory you would travel a bit less distance per minute. As Eric stated, there is probably a lot more involved than that as far as actual fuel consumption goes.
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Old 10-15-2020, 09:36 AM   #20
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Less pitch should mean lower speed at a given RPM, but it doesn't always. There's always prop slip as a factor, and sometimes reducing pitch will reduce slip.
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