Sundowner Tug's propeller pitch (specs?)

[Kamehameha]

I’ve got a 30’ Sundowner Tug
with an 18" three blade bronze propeller
• upon survey: the actual pitch was 15”
• my Marine Surveyor suggests that the optimum propeller pitch is 13”
my question is: can any Sundowner tug owners direct me to the correct specs for the propeller pitch ?

 

[Nomad Willy]

What engine and power?

I have an 18” dia Prop w 2.57-1 red and 13” of pitch. Consider it ideal but you have a faster hull and w enough blade area 15” may be fine for you.

Also can you reach your rated rpm for max power? That’s needed information also.

 

[MurrayM]

Welcome aboard

The previous owner of our 30' Sundowner Tug repowered with a 100hp engine in the mid 1990's. I looked at photos from when we hauled out last, and 17x15 is stamped on the three blade prop.

 

[Nomad Willy]

Murray do you have 2-1 and a four blade?

 

[MurrayM]

Murray do you have 2-1 and a four blade?

Sorry...translation? I am but a repurposed sea kayaker.

 

[MurrayM]

Pretty sure the Kanzaki gear ratio is 2.83:1 (quick google search) and it's a three blade prop.

 

[High Wire]

Welcome aboard!
Some of the basics for determining if you have the right prop:
What is the engine hp at rated Wide Open Throttle WOT?
What is your rated WOT rpm?
What is your actual WOT rpm under load?
What is your transmission reduction ratio stamped into the data plate on the transmission?
Number of propeller blades?
Prop diameter in inches?
Prop pitch in inches?
Left or right hand rotation?
Prop material?
Shaft diameter?

 

[Kamehameha]

thanks,
you are correct...
WOT: At wide open throttle the engine turned 2900 RPM, below the manufacturer's
specification of 3250 RPM.

 

[Nomad Willy]

At 350rpm overpropped I’d take out 1” of pitch.
That may be close to 200rpm (or at least 200 IMO) and you’d still have 150rpm to go. See a good prop man or/and call Michigan Wheel. They are easy to talk to, knowledgeable and free. Find out about how many rpm you’ll gain from a 1” change in pitch.

FYI if it was mine I’d shoot for very close to 100rpm up “under propped” or 3350rpm. At that engine speed 100rpm isn’t much. Your rated rpm isn’t a red-line.
Not at all.

 

[Nomad Willy]

Murray I’m think’in there’s something in the closet here.
I think that because you are putting over three times the power to the shaft as I am. I suspect it’s the re-drive ratio. How can you be absorbing three times as much power through a smaller prop.

And not critical words as you’re one of my very favorite people here.

 

[MurrayM]

Murray I’m think’in there’s something in the closet here.
I think that because you are putting over three times the power to the shaft as I am. I suspect it’s the re-drive ratio. How can you be absorbing three times as much power through a smaller prop...

Can't help you. I have paid zero attention to that end of the engine, other than changing oil.

PO did the changes, so not sure of the rationale. I would have kept the original engine, or swapped it out with an equivalent hp Kubota.

 

[Nomad Willy]

Murray,
I had my own repower done and called all the moves. Got highly involved. But in my case the builder got it right and I re-installed the same amount of power.

But the Sundowner hull can use (if desired) more power. Can’t recall the original engine in the Sundowners but I’d think 65-75hp would be the norm so the 100hp Yanmar is good if faster speeds are needed at times .. or all the time. I steered away from Yanmar mostly because of the aluminum. Wanted to avoid the corrosion problems I had w the Yanmar in my first trawler. They’re a great engine for weight reduction. You must have a turbo’d JH series engine .. the best Yanmar of all I hear.

Is it winter yet? Just a bit chilly here.

 

[MurrayM]

Has snowed on the valley floor a couple times, but is only sticking in the shadows. Nothing serious so far and we haven’t had any cold northerly outflow winds yet.

Our summer was so rainy and cold this year, combined with lots of snow last winter, that there were some snow patches left on the mountains down to about 3000’ that just got snowed on...new glaciers in the making?

4JH2-UTE has been pretty much flawless, which is great for me. Our next door neighbour is a certified marine diesel mechanic. I’ve made it a point to get along with him really well! We’re going to give the engine a going over in the spring, and I’m going to get the “family rate”

When we apply too much power (anything past 8 knots) the arse end squats and Badger starts pushing a ridiculous wake.

You still tucked up in the mountains of Washington State?

 

[fgarriso]

I’ve got a 30’ Sundowner Tug
with an 18" three blade bronze propeller
• upon survey: the actual pitch was 15”
• my Marine Surveyor suggests that the optimum propeller pitch is 13”
my question is: can any Sundowner tug owners direct me to the correct specs for the propeller pitch ?

This will give you the true specs by the numbers.

https://vicprop.com/displacement_size_new.php