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Old 12-11-2014, 02:18 PM   #1
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City: Holden,MA
Country: USA
Vessel Name: Diane Louise
Vessel Model: Sundowner Tug
Join Date: Mar 2014
Posts: 5
Propeller for 30' Sundowner Tug

I have a 30' Sundowner Tug with a 100hp Yanmar diesel engine (4JH4TX1) at 3200rpm. She has a 2.04 gear reduction.

I am looking for someone who has had experience with a similar tug, rpm and hp and what they are using for a propeller size.

Thanks.
Paul
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Old 12-11-2014, 10:23 PM   #2
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City: Kitimat, North Coast BC
Country: Canada
Vessel Name: Badger
Vessel Model: 30' Sundowner Tug
Join Date: Jul 2012
Posts: 3,331
Hi Paul, welcome aboard

I'm not too knowledgeable (bottom end of the learning curve) but we have a 30' Sundowner Tug as well, so I'll give you what information I have.

The previous owner (PO), who wasn't very diligent updating his maintenance log as his health deteriorated, put in a 100hp Yanmar 4JH2-UTE engine with a Yanmar/Hurth KM4A transmission...not sure of the gear ratio...will check next time down at the boat. The propeller is three blade 17x15.

We normally cruise at about 7 knots at 2700rpm, or a bit past where the turbo kicks in. Crunching the numbers after our first year showed we burned 1.2 gallons an hour overall.

The PO took good notes on a trip from Vancouver to Kitimat, running between 2900 and 3050rpm, and wrote that Badger used 2.2 gallons an hour overall.

Let me know if you need more clarification or have any other questions,

Murray
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Old 12-11-2014, 10:39 PM   #3
Al
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City: ketchikan, Alaska
Country: usa
Vessel Name: 'SLO'~BELLE
Vessel Model: 1978 Marben-27' Flybridge Trawler Pilothouse Pocket Cruiser[
Join Date: Apr 2012
Posts: 1,695
Hi Murry- Just popped in with the title of the subject.
we are in the preliminary stage of repowering our Marben from the current Perkins 4-154 to a newer (2003) Perkins 4-236 (No turbo). In our quest to gain similar results from neighboring boats I contacted a 30 Sundower owner in our harbor. He is running a Perkins 4-236 with a 1:9-1 Velvet drive. His wheel is 22x13 and he is claiming a steady 6 knots at 1800 RPM. I throw this into the mix knowing that it will or maybe apples and pears to the real world of Yanmars.
I know you are aware from earlier post that the discussion of how to determine wheel requirements brings forth the many suggestions and good that they come up. In that department for Paul I will include the formula that I use and it proves to be quite close.

Vicprop - Propeller Calculator

Still have you on our visit list Murry, it will happen.
Cheers,
Al
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Old 12-15-2014, 03:37 PM   #4
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City: Holden,MA
Country: USA
Vessel Name: Diane Louise
Vessel Model: Sundowner Tug
Join Date: Mar 2014
Posts: 5
Thanks Murry for your reply.
Sorry it took so long for me to get back to you. My 30' Sundowner has 85HP Pathfinder (VW) engine she has Borg-Warner 2:56 to 1 transmission turning a 3 blade 18x10 wheel. She will about make 7 knots at 2800 RPM
I am presently installing the Yanmar. I was hoping to go to a 4 blade prop. But maybe that is not realistic.

Thanks again for your info.

Paul
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Old 12-15-2014, 05:02 PM   #5
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City: Holden,MA
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Vessel Name: Diane Louise
Vessel Model: Sundowner Tug
Join Date: Mar 2014
Posts: 5
Al,
Thanks for your reply.
I used your link for sizing of a prop. Comes out to 18x13.5 four blade.
I am not able to swing as big of a wheel as the people that you know with the 30' Sundowner. I am presently turning an 18x10 3 blade with an 85 HP Pathfinder (VW) with a 2.56 to 1 reduction gear and I only have 1 1/2" clearance.
I am presently installing the Yanmar.
Good luck with your repowering of your Marben.
I would love to hear how you are making.
Thanks again,
Paul
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Old 12-15-2014, 09:13 PM   #6
Al
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City: ketchikan, Alaska
Country: usa
Vessel Name: 'SLO'~BELLE
Vessel Model: 1978 Marben-27' Flybridge Trawler Pilothouse Pocket Cruiser[
Join Date: Apr 2012
Posts: 1,695
Paul,
Wow!! that is the clearance? Here is the formula information I used at random for you boat. Errors may well be in attendance as I am estimating much.
Will keep you and the forum posted. My biggest concern is the requirement of raising the cabin floor 1 1/2 inches to accommodate the height. With duplicate boat having the bigger Perkins anticipated installing the floor must have been heighten at construction. This is said as the built in fiberglass exhaust tube installed is only the 2" allocated for the smaller present engine in our boat. Fortunately there is substantial headroom to allow the floor rebuild. We will have to run the exhaust out the side due to lack of being able to access the bulkhead to install a 3 inch exhaust required. Always challenges to a engine change as you may find with the Yanmar conversion. Good luck back to you.
Al






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Data Input

Waterline length in feet: 30 feet
Beam at the waterline in feet: 11 feet
Hull draft in feet (excluding keel): 3.6 feet
Vessel weight in pounds: 14500 lbs
Engine Horsepower: 85 HP
Number of engines: 1
Total Engine Horsepower: 85 HP

Engine R.P.M. (max): 3000 RPM
Gear Ratio: 2.5:1
Shaft R.P.M. (max): 1200 RPM

Number of shaft bearings (per shaft): 1
Desired speed in Knots: 8 knots
Horsepower Calculations

This will calculate the maximum horsepower and torque available at the prop(s).

Total available horsepower at the engine(s): 85 HP
Total available torque ft/lbs at the engine(s): 149 ft/lbs
Horsepower loss of 3% per gearbox: - 2.5 HP
Horsepower loss of 1.5% per shaft bearing: - 1.3 HP

Total horsepower available at the propeller(s): 81.2 HP
Total torque ft/lbs available at the propeller(s): 355 ft/lbs
Speed & Power Calculations

Basic displacement speed and horsepower required
Displacement hull speed (1.34 X sqrt of waterline length): 7.34 Knots
Minimum horsepower required at propeller(s) for Hull speed: 31.6 HP

Calculations based on desired speed and available HP
HP required at propeller(s) for desired 8 knots speed: 37 HP
Estimated maximum speed with existing 85 horsepower:
This is the speed we will use for the propeller size. 10.34 Knots

At this point it is important to note that all of the calculations above are based on full RPM and HP. Most engines are rated to run at a percentage of thier full RPM. This is what will determine your maximum cruising speed. The propeller sizing calculations below are based on 90% of full RPM. This gives the engine some reserve power to allow for variable loading in the vessel.

Propeller Size

Number of blades Diameter (inches) Pitch (inches)
2 Blade 22.9 X 15.6
3 Blade 21.8 X 15.5
4 Blade 20.5 X 15.2

The propeller sizes shown above do not contain calculations for cavitation or blade loading.
If you find that the recommended propeller is too large to fit your vessel, you can try increasing the shaft speed. Failing this, you can reduce the diameter and increase the pitch at the expense of your propeller efficiency. The rule of thumb is 1 inch of diameter is equal to 1 1/2 to 2 inches of pitch.
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Old 12-16-2014, 02:31 AM   #7
Al
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City: ketchikan, Alaska
Country: usa
Vessel Name: 'SLO'~BELLE
Vessel Model: 1978 Marben-27' Flybridge Trawler Pilothouse Pocket Cruiser[
Join Date: Apr 2012
Posts: 1,695
Paul- Noticed the discrepancy between your wheel clearance and that on the boat laying here in Ketchikan. I repeat that the local boat is swinging a 22x13 wheel which would be cutting into the hull based on your clearance. For sure the two engines and gear ratio will provide different results, yet the clearance is a fixed number. Not disputing the numbers as it makes no mind to me except for noticing. He and I have similar installations resulting in similar size on the wheels. I throw a 22x16 wheel with a 3:1 Anyway- On with the conversions and the posting as to progress.
Cheers,
Al
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Old 12-16-2014, 06:09 PM   #8
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City: Holden,MA
Country: USA
Vessel Name: Diane Louise
Vessel Model: Sundowner Tug
Join Date: Mar 2014
Posts: 5
Al,
Thanks for the propeller calculation.
I also have to change the exhaust from 2 1/2" to 3". Just picked up the 3" hose, muffler and thru hull fitting today. The galley area is disassembled to facilitate this installation.
The existing engine will come out first to make this installation easier. Time allowing maybe in the next few days,
wishful thinking.
Sorry to here that you have to raise your cabin floor. A big job I am sure.
I'll keep you posted on the progress.
Paul
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