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?

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.

Good point.

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.

Retriever said:

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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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!

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.

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

Spinner, What is your rated rpm?

Eric, the engine is a Cummins 6CAT8.3, 450 hp. Rated rpm is 2600.

Spinner said:

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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Same here. Apparently the 6BTA and QSB don’t like being overloaded, and that’s what happens when the engine won’t 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 I’d run at higher speeds.

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....

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.

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".

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.

Thanks

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.

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.

-Doug

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.

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.

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.

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.

Has anyone tried the Michigan wheel DQX on the Nordic tugs?

With othe boats i have heard that it has an impressive increase in performance.

Sue,

What pitch did you end up with? I have a 28x28 4 blade prop that I can hit slightly over 2600 fully loaded with a 6CTA rated at 420hp.

Tom

A spare prop, as others have said, is a low priority for me, a single prop behind a large keel trawler owner. That said, there's been some very exciting developments in prop design in the past 2 years. Sharrow Engineering are producing a double bladed prop that is up to 15% better in terms of speed, fuel consumption, stability in turns, etc. Worth checking out. Disclaimer: I have no connection to Sharrow.

tpbrady said:

Sue,

What pitch did you end up with? I have a 28x28 4 blade prop that I can hit slightly over 2600 fully loaded with a 6CTA rated at 420hp.

Tom

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Hi Tom, it was 28 x 30, now it is 28 x 28.

We have a trawler built in 1964. We’ve travelled poorly charted waters over the last 15 years and guess what? Same prop!