MRA.Report.ESSAYONS.Thruster.18DEC2024.pdf

USACE ESSAYONS Bow Thruster CFD Analysis

Brant R. Savander, Ph.D., P.E.

Principal Research Scientist Maritime Research Associates for

Technical Point of Contact:

Mr. T.J. Brackin, P.E.

Bruce S. Rosenblatt & Associates, LLC

Program Sponsor:

USACE

Revision History:

Initial Release: 18 December 2024

Table of Contents

Page Number

1.0 Abstract 6

2.0 Definitions 6

3.0 Hullform Geometry & Load Case Definition 7

4.0 Thruster Fairing Baseline Analysis 11

4.1 Geometry 11

4.2 CFD Analysis 12

5.0 Thruster Fairing Redesign 20

5.1 Geometry 20

5.2 CFD Analysis 22

6.0 Thruster Baseline Rotor 27

7.0 Thruster Rotor Redesign 37

7.1 Geometry 37

7.2 ABS 45

7.3 CFD Analysis 46

8.0 Summary & Conclusions 52

9.0 References 53

List of Figures

Page Number

Figure 3.0.1: US Army Corps of Engineers Dredge - ESSAYONS, constructed in 1981 at Sun Ship-building & Dry Dock Company. 8

Figure 3.0.2: Frame images from the GHS file (*.GF) provided by Bruce S. Rosenblatt & Associ-ates, for the ESSAYONS. The GHS file frames provided the basis for the three dimensional surface model developed for the RANS analysis contained in this report. 8

Figure 3.0.3: Three dimensional surface model generated from the *.GF file as shown in

Figure 3.0.2. This surface model was used for all baseline analyses. 9

Figure 3.0.4: Modified hullform with a larger bow thruster fairing on both the PORT and STBD sides of the vessel. 10

Figure 4.1.1: Baseline bow fairing detail, and baseline thruster rotor, on the ESSAYONS, as estimat-ed from the GHS file shown in Figure 3.0.2. Lower forward quadrant areas highlighted in red show portions of the tunnel inlet with poor inflow characteristics. 11

Figure 4.2.1: Overview of the meshing strategy and computational domain used for all RANS cas-

es. 13

Figure 4.2.2: Meshing strategy used for all RANS runs in way of the bow thruster fairing and bow thruster rotor. 14

Figure 4.2.3: Pressure and velocity contours in the baseline rotor and baseline thruster fairing case at 1450 rpm with a forward speed of 3 knots, while pushing to PORT. 15

Figure 4.2.4: Pressure and velocity contours, along with 3D velocity vectors, in the baseline rotor and baseline thruster fairing case at 1450 rpm with a forward speed of 3 knots, while pushing to

PORT. 16

Figure 4.2.5: RANS results for the baseline thruster fairing and baseline rotor case at 1450 rpm pushing to PORT, with a forward speed of 3 knots. 17

Figure 4.2.6: RANS results for the baseline thruster fairing and baseline rotor case at 1450 rpm pushing to STBD, with a forward speed of 3 knots. 17

Figure 5.1.1: HRP structural arrangement drawing showing the housing for the rotor and pod as-sembly. 20

Figure 5.1.2: The light green box is showing the structural housing bounding box for the HRP thruster shown in Figure 5.1.1 21

Figure 5.1.3: Redesigned bow thruster fairing (MRAD-03) to improve inflow in the lower forward area of the thruster inlet, both PORT and STBD. The redesigned rotor (Rotor-07) is also shown above. 22

Figure 5.2.1: Pressure and velocity contours in the baseline rotor and redesigned thruster fairing case at 1450 rpm with a forward speed of 3 knots while pushing to PORT. 23

Figure 5.2.2: Pressure and velocity contours, along with 3D velocity vectors, in the baseline rotor and redesign thruster fairing case at 1450 rpm with a forward speed of 3 knots, while pushing to

PORT. 24

Figure 5.2.3: RANS results for the redesign thruster fairing and baseline rotor case at 1450 rpm pushing to PORT, with a forward speed of 3 knots. 25

Figure 5.2.4: RANS results for the redesign thruster fairing and baseline rotor case at 1450 rpm pushing to STBD, with a forward speed of 3 knots. 25

Figure 6.0.1: Baseline thruster rotor photograph from Hanna, etal. (2011), a bow thruster vibra-tion report. 27

Figure 6.0.3: Isometric views of the HRP baseline rotor. 29

Figure 6.0.4: Comparison of the tip geometry and section thickness at the tip between the base-line HRP rotor and the redesigned rotor. 30

Figure 6.0.5: Spanwise HRP rotor distributions estimated from image shown in Figure 6.0.1, and the propeller shop report, Remsing (2011). 31

Figure 6.0.6: Spanwise HRP foil section information estimated from image shown in Figure 6.0.1, and the discussion from the original noise and vibration report, Hanna, etal (2011). 32

Figure 6.0.7: HRP foil section information estimated from image shown in Figure 6.0.1, and the dis-cussion from the original noise and vibration report, Hanna, etal (2011). 33

Figure 6.0.8: HRP foil section information estimated from image shown in Figure 6.0.1, and the dis-cussion from the original noise and vibration report, Hanna, etal (2011). 34

Figure 6.0.9: HRP foil section information estimated from image shown in Figure 6.0.1, and the dis-cussion from the original noise and vibration report, Hanna, etal (2011). 35

Figure 6.0.10: HRP foil section information estimated from image shown in Figure 6.0.1, and the discussion from the original noise and vibration report, Hanna, etal (2011). 36

Figure 7.1.2: Isometric views of the redesigned rotor. 38

Figure 7.1.3: Spanwise redesign rotor distributions. 39

Figure 7.1.4: Spanwise foil section information for the redesigned rotor. 40

Figure 7.1.5: Redesigned rotor foil section information. 41

Figure 7.1.6: Redesigned rotor foil section information. 42

Figure 7.1.7: Redesigned rotor foil section information. 43

Figure 7.1.8: Redesigned rotor foil section information. 44

Figure 7.3.1: Pressure and velocity contours in the redesigned rotor and redesigned thruster fairing case at 1450 rpm with a forward speed of 3 knots while pushing to PORT. 47

Figure 7.3.2: Pressure and velocity contours, along with velocity vectors, in the redesigned rotor and redesigned thruster fairing case at 1450 rpm with a forward speed of 3 knots while pushing to

PORT. 48

Figure 7.3.3: RANS results for the redesign thruster fairing and redesigned rotor case at 1450 rpm pushing to PORT, with a forward speed of 3 knots. 49

Figure 7.3.4: RANS results for the redesign thruster fairing and baseline rotor case at 1450 rpm pushing to PORT, with a forward speed of 3 knots. 49

List of Tables

Page Number

Table 4.2.G: Baseline thruster fairing and baseline rotor RANS results at zero forward speed. RPM range considered as denoted in noise and vibration sea trials, Hanna, etal. (2011). 18

Table 4.2.H: Baseline thruster fairing and baseline rotor RANS results at 3 knots forward speed.

RPM range considered as denoted in noise and vibration sea trials, Hanna, etal. (2011). Maxi-mum operational RPM (1270 RPM) also considered. 19

Table 5.2.E: Thruster fairing design iterations and baseline rotor RANS results at 3 knots forward speed. 26

Table 6.0.B: Baseline HRP thruster rotor design summary. 27

Table 7.1.A: Redesign rotor, Rotor-07, design summary. 37

Table 7.2.A: ABS Steel Vessel Rules calculation for the redesigned thruster rotor. 45

Table 7.3.E: RANS results showing the rotor design iterations using the final thruster fairing de-sign (MRAD-03). The final rotor design ID is Rotor-07. 50

Table 7.3.F: RANS results over the RPM range defined in Hanna, etal (2011) with the final thrust-er fairing design, MRAD-03, and the final rotor design, Rotor-07. 51

USACE ESSAYONS Thruster Analysis

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1.0 Abstract

Contained herein is the Maritime Research Associates, LLC (MRA) report documenting the computational analysis and related redesigns of the bow thruster fairing and bow thruster rotor on the USACE dredge, ESSAYONS.

The ESSAYONS bow thruster motor was increased from 600 hp to just under 1000 hp at a time prior to 2011. The bow thruster fairing and bow thruster rotor were not changed when the larger power motor was installed. The bow thruster noise and vibration were excessive when operating at power levels above 600 hp.

A Noise Control Engineering (NCE) report, Hanna, etal (2011) documented an instrumented sea trial program to measure the noise and vibration levels in way of the bow thruster area on the ESSAYONS. Hanna, etal (2011) theorized that the primary cause of the excessive noise and vibration was poor bow thruster rotor design, especially from a cavitation inception per-spective. Hanna, etal (2011) goes onto highlight the importance of determining the hydrody-namic inflow characteristics to the rotor in order to conduct a proper rotor redesign. Notably, Hanna, etal (2011) makes no mention of the potential for poor inflow to be a significant con-tributor to the excessive noise and vibration.

The baseline RANS analysis of the entire vessel, with a full rotating thruster rotor, and com-plete bow thruster assembly clearly shows the primary cause of the excessive noise and vibration is poor hydrodynamic inflow in way of the forward lower quadrant on the bow thruster tunnel. If on PORT and looking to STBD, the area of concern is between 6 and 9 o’clock on a clock face. As a result, a new bow thruster fairing was designed to mitigate the strong vortical content and flow reversal in this region of the bow thruster inlets, PORT and

STBD.

Subsequent to the bow fairing redesign effort, the bow thruster rotor was redesigned to improve cavitation inception characteristics, improve overall noise and vibration performance, and utilize as much of the available 986 brake horsepower as possible.

The ESSAYONS currently limits bow thruster power, down from 986 hp, to 600 hp at a maxi-mum rotor speed of 1270 rpm to avoid excessive noise and vibration.

The new rotor and bow thruster fairing designs improve the push to PORT performance by

19% and the push to STBD performance by 11% when compared to the current 1270 rpm baseline case. The new rotor and bow thruster fairing designs also substantially reduce noise and vibration, which includes a 50% reduction in the thrust first blade rate harmonic ampli-tude, and a 40% reduction in the shaft torque first blade rate harmonic amplitude, again when compared to the 1270 rpm baseline case.

2.0 Definitions

, (1)T Thrust=

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(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

3.0 Hullform Geometry & Load Case Definition

The USACE dredge ESSAYONS was built in 1981 by Sun Ship Building Company. Various pictures of the ESSAY-

ONS in service are provided in Figure 3.0.1

The hull surface model used for all RANS cases in this report were derived from the GHS file provided by Bruce

S. Rosenblatt & Associates for the ESSAYONS. The GHS file sections are shown in Figure 3.0.2.

The hull surface model for the baseline geometry case is shown in Figure 3.0.3. Figure 3.0.4 shows an overview image of the hull surface model with the redesigned bow thruster fairing and redesigned bow thruster rotor.

Additional close-up views of the redesigned rotor and fairing are provided in subsequent sections of this report.

The operational draft used for all analysis cases was 32 feet 4 inches (32’4’’). The under keel clearance for all computational models was 2 feet.

Q Shaft Torque=

Pb Brake Power=

FH Horizontal Force=

FV Vertical Force=

MH Horizontal Moment=

MV Vertical Moment=

Sigma Bollard

TD

2Q

D Diameter=

RANS Reynolds Average Navier Stokes=

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Figure 3.0.1: US Army Corps of Engineers Dredge - ESSAYONS, constructed in 1981 at Sun Shipbuilding & Dry Dock Company.

Figure 3.0.2: Frame images from the GHS file (*.GF) provided by Bruce S. Rosenblatt & Associates, for the ESSAYONS. The GHS file frames provided the basis for the three dimensional surface model developed for the RANS analysis contained in this report.

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Figure 3.0.3: Three dimensional surface model generated from the *.GF file as shown in Figure 3.0.2. This surface model was used for all baseline analyses.

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Figure 3.0.4: Modified hullform with a larger bow thruster fairing on both the PORT and STBD sides of the vessel.

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4.0 Thruster Fairing Baseline Analysis

4.1 Geometry

The bow thruster inlet fairing for the baseline case is shown in Figure 4.1.1. The fairing was derived from the

GHS file provided for the ESSAYONS. Note, the RANS analysis clearly shows poor inflow in way of the forward, lower quadrants of the tunnels as highlighted in red in Figure 4.1.1.

The redesigned thruster inlet to improve inflow is shown in Figure 5.1.3.

PORT

STBD

Figure 4.1.1: Baseline bow fairing detail, and baseline thruster rotor, on the ESSAYONS, as estimated from the GHS file shown in Figure 3.0.2. Lower forward quadrant areas highlighted in red show portions of the tunnel inlet with poor inflow characteristics.

Area of Poor Inflow

Area of Poor Inflow

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4.2 CFD Analysis

The computational models, and meshing strategy used for RANS based bow thruster performance analysis, is shown in Figure 4.2.1, from a far field perspective. Figure 4.2.2 shows the meshing strategy, in way of the bow thruster fairing and rotor assembly.

The poor thruster inflow characteristics are revealed in Figure 4.2.3, for the baseline rotor and baseline thruster fairing case. This is a pushing to PORT case at 1450 rpm and a vessel forward speed of 3 knots. The strong wake deficit produces larger suction side cavitation shown in the upper image while the blade is located in the lower forward quadrant of the tunnel. The bottom image shows the actual flow reversal in this lower quadrant with the yellow to orange color contours.

Figure 4.2.4 also shows the velocity vectors for the case discussed in Figure 4.2.3. The forward quadrant, at roughly the 6 o’clock position, shows a strong vortical structure that is a large contributor to the flow reversal which creates an incredibly challenging environment for rotor operation.

Figure 4.2.5 shows a streamline, pressure contour, and cavitation pattern for the pushing to PORT case at 1450 rpm and a 3-knot forward speed. Figure 4.2.6 shows a streamline, pressure contour, and cavitation pattern for the pushing to STBD case at 1450 rpm and a 3-knot forward speed.

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Figure 4.2.1: Overview of the meshing strategy and computational domain used for all RANS cases.

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Figure 4.2.2: Meshing strategy used for all RANS runs in way of the bow thruster fairing and bow thruster rotor.

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Figure 4.2.3: Pressure and velocity contours in the baseline rotor and baseline thruster fairing case at 1450 rpm with a forward speed of 3 knots, while pushing to PORT.

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Figure 4.2.4: Pressure and velocity contours, along with 3D velocity vectors, in the baseline rotor and baseline thruster fairing case at 1450 rpm with a for-ward speed of 3 knots, while pushing to PORT.

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Figure 4.2.5: RANS results for the baseline thruster fairing and baseline rotor case at 1450 rpm pushing to PORT, with a forward speed of 3 knots.

Figure 4.2.6: RANS results for the baseline thruster fairing and baseline rotor case at 1450 rpm pushing to STBD, with a forward speed of 3 knots.

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Table 4.2.G provides a tabular summary of the baseline rotor performance with the baseline rotor over the rpm range of 800, 1000, 1200, and 1450, in the zero forward speed case. All tabular definitions can be found in

Section 2.0: Definitions. One highlight from this table is how quickly the first blade rate harmonic on thrust approaches and exceeds 10% of the mean thrust value. Normal propulsor design would target a value of less than 5% for the ratio. Hence, 10% is notable, and 20% is excessive.

Further, once forward speed is introduced, these ratios even more quickly approach the 20% area, as shown in

Table 4.2.H. As a result, all subsequent RANS cases focus on the more challenging 3-knot forward speed sce-nario.

T1BR Tmean

Design Push Vs ERPM Sigma Max

ID Dir. T Q Pb FH FV T MH MV Q Bollard P_tap

(P/S) (kts) (rpm) (lbs) (ft-lbs) (hp) (lbs) (lbs) (lbs) (ft-lbs) (ft-lbs) (ft-lbs) (psi)

Base PORT 0 800 3,133 3,231 130 33 22 263 234 204 173 0.81 0.52

Percentage of Mean: 1% 1% 8% 7% 6% 5%

Base STBD 0 800 5,536 3,045 123 35 34 536 442 487 322 1.52 0.88

Percentage of Mean: 1% 1% 10% 15% 16% 11%

Base PORT 0 1,000 5,731 5,040 254 44 68 355 381 536 249 0.95 0.9

Percentage of Mean: 1% 1% 6% 8% 11% 5%

Base STBD 0 1,000 7,846 4,756 239 106 82 1,260 1,060 1,145 758 1.38 2.3

Percentage of Mean: 1% 1% 16% 22% 24% 16%

Base PORT 0 1,200 8,843 7,223 436 210 151 780 517 1,423 512 1.02 1.7

Percentage of Mean: 2% 2% 9% 7% 20% 7%

Base STBD 0 1,200 10,705 6,885 416 245 107 1,946 1,679 1,621 1,214 1.30 3.9

Percentage of Mean: 2% 1% 18% 24% 24% 18%

Base PORT 0 1,450 13,583 10,580 772 275 244 1,056 572 484 698 1.07 2.3

Percentage of Mean: 2% 2% 8% 5% 5% 7%

Base STBD 0 1,450 15,004 10,122 739 783 257 3,033 2,542 2,354 2,027 1.24 6.6

Percentage of Mean: 5% 2% 20% 25% 23% 20%

First Blade Rate Harmonic AmplitudeMean Values

Table 4.2.G: Baseline thruster fairing and baseline rotor RANS results at zero forward speed. RPM range considered as denoted in noise and vibration sea trials, Hanna, etal. (2011).

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Design Push Vs ERPM Sigma Max

ID Dir. T Q Pb FH FV T MH MV Q Bollard P_tap

(P/S) (kts) (rpm) (lbs) (ft-lbs) (hp) (lbs) (lbs) (lbs) (ft-lbs) (ft-lbs) (ft-lbs) (psi)

Base PORT 3 800 3,366 3,319 134 16 32 516 442 526 314 0.85 0.6

Percentage of Mean: 0% 1% 15% 13% 16% 9%

Base STBD 3 800 6,129 3,396 137 120 180 1,124 1,070 1,186 314 1.51 1.7

Percentage of Mean: 2% 3% 18% 32% 35% 9%

Base PORT 3 1,000 6,055 5,179 261 160 53 975 813 854 570 0.98 1.0

Percentage of Mean: 3% 1% 16% 16% 16% 11%

Base STBD 3 1,000 8,573 5,195 262 279 240 1,701 1,082 1,670 1,082 1.40 2.9

Percentage of Mean: 3% 3% 20% 21% 32% 21%

Base PORT 3 1,200 9,265 7,418 448 318 115 1,410 1,054 1,203 882 1.00 1.7

Percentage of Mean: 3% 1% 15% 14% 16% 12%

Base STBD 3 1,200 11,550 7,417 448 489 344 2,242 1,972 2,198 1,311 1.30 4.5

Percentage of Mean: 4% 3% 19% 27% 30% 18%

Base PORT 3 1,450 14,135 10,838 791 603 32 1,529 2,400 3,083 61 1.09 3.1

Percentage of Mean: 4% 0% 11% 22% 28% 1%

Base STBD 3 1,450 16,046 10,828 790 935 668 3,403 3,636 2,988 1,797 1.24 8.2

Percentage of Mean: 6% 4% 21% 34% 28% 17%

MAX. CURRENT OPERATIONAL RPM:

Base PORT 3 1,270 10,269 8,096 518 364 142 1,529 983 1,325 981 1.06 2.0

Percentage of Mean: 4% 1% 15% 10% 13% 10%

Base STBD 3 1,270 11,889 7,758 496 496 376 2,142 1,992 2,156 1,185 1.28 4.8

Percentage of Mean: 4% 3% 18% 17% 18% 10%

Mean Values First Blade Rate Harmonic Amplitude

Table 4.2.H: Baseline thruster fairing and baseline rotor RANS results at 3 knots forward speed. RPM range considered as denoted in noise and vibration sea trials, Hanna, etal. (2011). Maxi-mum operational RPM (1270 RPM) also considered.

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5.0 Thruster Fairing Redesign

5.1 Geometry

The thruster fairing redesign objective was to smooth the transition from the hull exterior shell to the interior tunnel volume in way of the lower forward corner of the tunnel inlet. The bounding constraint was to make sure the new fairing did not overlap with structural housing of the HRP thruster shown in Figure 5.1.1 The surface models used for the RANS analysis also show a green box denoting the HRP structural housing, Figure 5.1.2.

Figure 5.1.3 shows near field images of the redesigned thruster fairing.

Figure 5.1.1: HRP structural arrangement drawing showing the housing for the rotor and pod assembly.

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PORT

STBD

HRP

Bounding Structural Housing

HRP

Bounding Structural Housing

PORT

Fairing Boundary

STBD

Fairing Boundary

Figure 5.1.2: The light green box is showing the structural housing bounding box for the HRP thruster shown in Figure 5.1.1

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5.2 CFD Analysis

Figure 5.2.1 shows pressure and velocity contours for the 3-knot forward speed, 1450 rpm, pushing to PORT case with the baseline rotor and redesigned thruster. The more uniform velocity contours are clearly evident when compared to the baseline fairing results. Figure 5.2.2 show the velocity vector results for this same case.

Notably, the strong vortical content and flow reversal characteristics are no longer present.

The pushing to PORT and STBD streamline and pressure contour results are shown in Figure 5.2.3 and

Figure 5.2.4, respectively, for the 1450 rpm, 3-knot forward speed case. These images show a notable reduc-tion in suction side cavitation volume when compared with the baseline fairing, baseline rotor case.

PORT

STBD

Figure 5.1.3: Redesigned bow thruster fairing (MRAD-03) to improve inflow in the lower forward area of the thruster inlet, both PORT and STBD. The redesigned rotor (Rotor-07) is also shown above.

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Figure 5.2.1: Pressure and velocity contours in the baseline rotor and redesigned thruster fairing case at 1450 rpm with a forward speed of 3 knots while pushing to PORT.

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Figure 5.2.2: Pressure and velocity contours, along with 3D velocity vectors, in the baseline rotor and redesign thruster fairing case at 1450 rpm with a forward speed of 3 knots, while pushing to PORT.

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Figure 5.2.3: RANS results for the redesign thruster fairing and baseline rotor case at 1450 rpm pushing to PORT, with a forward speed of 3 knots.

Figure 5.2.4: RANS results for the redesign thruster fairing and baseline rotor case at 1450 rpm pushing to STBD, with a forward speed of 3 knots.

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Table 5.2.E gives the tabular results for the baseline rotor with the redesigned fairing iterations at 1450 rpm and a 3-knot vessel forward speed. The ratio is shown to now be below 10% range.T1BR Tmean

Design Push Vs ERPM Sigma Max

ID Dir. T Q Pb FH FV T MH MV Q Bollard P_tap

(P/S) (kts) (rpm) (lbs) (ft-lbs) (hp) (lbs) (lbs) (lbs) (ft-lbs) (ft-lbs) (ft-lbs) (psi)

Base PORT 3 1,450 14,135 10,838 791 603 32 1,529 2,400 3,083 61 1.09 3.1

Percentage of Mean: 4% 0% 11% 22% 28% 1%

Base STBD 3 1,450 16,046 10,828 790 935 668 3,403 3,636 2,988 1,797 1.24 8.2

Percentage of Mean: 6% 4% 21% 34% 28% 17%

MRAD01A PORT 3 1,450 10,892 9,002 657 270 173 606 892 1,865 326 1.01 2.2

Percentage of Mean: 2% 2% 6% 10% 21% 4%

MRAD01A STBD 3 1,450 12,002 8,276 604 277 308 1,298 3,991 4,983 740 1.21 7.0

Percentage of Mean: 2% 3% 11% 48% 60% 9%

MRAD02 PORT 3 1,450 9,989 8,399 613 207 277 345 848 832 207 0.99 2.2

Percentage of Mean: 2% 3% 3% 10% 10% 2%

MRAD02 STBD 3 1,450 11,713 8,125 593 374 215 212 2,478 4,179 250 1.21 5.7

Percentage of Mean: 3% 2% 2% 30% 51% 3%

MRAD03 PORT 3 1,450 10,378 8,623 630 121 163 519 497 499 353 1.01 1.6

Percentage of Mean: 1% 2% 5% 6% 6% 4%

MRAD03 STBD 3 1,450 11,674 8,121 593 454 309 934 1,494 3,565 586 1.20 4.7

Percentage of Mean: 4% 3% 8% 18% 44% 7%

Mean Values First Blade Rate Harmonic Amplitude

Table 5.2.E: Thruster fairing design iterations and baseline rotor RANS results at 3 knots forward speed.

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6.0 Thruster Baseline Rotor

The baseline thruster rotor geometry has been estimated from the picture provided in Table 6.0.1 and the report data from Remsing (2011). Table 6.0.B shows the principal characteristics for the baseline rotor.

Figure 6.0.1: Baseline thruster rotor photograph from Hanna, etal.

(2011), a bow thruster vibration report.

ESSAYONS

Engine HRP Engine Rating 986 bhp at 1500 rpm Gear Ratio 3.938 : 1 Design RPM 1500

Propeller Characteristics Diameter 63.0 in. Material NiBrAl Mean Pitch 53.0 in. Number of Blades 5 EAR 1.034 Section Shape Custom Skew 0.00 deg. Camber Zero Hub

Aft End Dia. 9.173 in. Weight 1,478 lbs Fwd End Dia. 16.541 in. WR2, Air 363,011 lb-in2

Length 15.669 in. WR2, Water 484,711 lb-in2

Propeller Design Summary

Table 6.0.B: Baseline HRP thruster rotor design summary.

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Isometric views of the baseline rotor surface geometry are shown in Figure 6.0.3. Tip views of the baseline rotor and the redesigned rotor are given in Figure 6.0.4. Spanwise blade surface distributions are given in

Figure 6.0.5 and Figure 6.0.6.

The blade sections are symmetric from leading to trailing edge and zero camber. These sections are shown in

Figure 6.0.7 through to Figure 6.0.10.

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Figure 6.0.3: Isometric views of the HRP baseline rotor.

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Figure 6.0.4: Comparison of the tip geometry and section thickness at the tip between the baseline HRP rotor and the redesigned rotor.

Baseline HRP Rotor

Redesigned Rotor

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Figure 6.0.5: Spanwise HRP rotor distributions estimated from image shown in Figure 6.0.1, and the propeller shop report, Remsing (2011).

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Figure 6.0.6: Spanwise HRP foil section information estimated from image shown in Figure 6.0.1, and the discussion from the original noise and vibration report, Hanna, etal (2011).

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Figure 6.0.7: HRP foil section information estimated from image shown in Figure 6.0.1, and the discussion from the original noise and vibration report, Hanna, etal (2011).

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Figure 6.0.8: HRP foil section information estimated from image shown in Figure 6.0.1, and the

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Figure 6.0.9: HRP foil section information estimated from image shown in Figure 6.0.1, and the

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Figure 6.0.10: HRP foil section information estimated from image shown in Figure 6.0.1, and the discussion from the original noise and vibration report, Hanna, etal (2011).

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7.0 Thruster Rotor Redesign

7.1 Geometry

Table 7.1.A shows the principal characteristics for the redesigned rotor.

Isometric views of the redesigned rotor surface geometry are shown in Figure 7.1.2. Tip views of the baseline rotor and the redesigned rotor are given in Figure 6.0.4. Spanwise blade surface distributions are given in

Figure 7.1.3 and Figure 7.1.4.

The blade sections are again, symmetric from leading to trailing edge with zero camber. These sections are shown in Figure 7.1.5 through to Figure 7.1.8.

ESSAYONS

Engine HRP Engine Rating 986 bhp at 1500 rpm Gear Ratio 3.938 : 1 Design RPM 1450

Propeller Characteristics Diameter 63.0 in. Material NiBrAl Mean Pitch 59.5 in. Number of Blades 5 EAR 1.191 Section Shape Custom Skew 5.00 deg. Camber Custom Hub Bore 4.00 in.

Aft End Dia. 9.173 in. Weight 2,142 lbs Fwd End Dia. 16.541 in. WR2, Air 734,365 lb-in2

Length 15.669 in. WR2, Water 999,549 lb-in2

Propeller Design Summary

Table 7.1.A: Redesign rotor, Rotor-07, design summary.

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Figure 7.1.2: Isometric views of the redesigned rotor.

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Figure 7.1.3: Spanwise redesign rotor distributions.

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Figure 7.1.4: Spanwise foil section information for the redesigned rotor.

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Figure 7.1.5: Redesigned rotor foil section information.

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Figure 7.1.6: Redesigned rotor foil section information.

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Figure 7.1.7: Redesigned rotor foil section information.

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Figure 7.1.8: Redesigned rotor foil section information.

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7.2 ABS

The redesigned rotor meets the ABS criteria for Steel Vessels, Thrusters section, with the results showing the compliance in Table 7.2.A.

ABS Rules for Building and Classing Steel Vessels, 2017 Part 4, Chapter 3, Section 5 5.3.2(c) Thrusters

Vessel Data Variables

Vessel Engine HP 986 H = 986 hp Engine RPM 1500 Gear Ratio 3.938 : 1 R = 381 rpm

Propeller Data

Diameter 63.0 inches D = 5.250 ft Pitch at 0.35 r / R 61.2 inches P 0.25 = 0.971 Pitch at 0.70 r / R 61.4 inches P 0.70 = 0.974 Number of blades 5 N = 5 EAR 1.191 a = 1.191 Chord length at 0.35 r / R 21.08 inches W = 21.08 Tmax at 0.35 r / R 2.092 inches T = 2.09 Rake at the tip (+ aft) 2.63 inches K = 2.63 Material NiBrAl S = 1.0

Calculations Section Properties Material constant, f 85 a s = 34.550 Material constant, w 0.27 I o = 9.795 Coefficient A athwartship 11.972 U f = 1.046 Coefficient B 78.084 Coefficient C 2,712 Section modulus coefficient, Cn 0.102 As calculated Section modulus coefficient, Cn 0.100 Used Section area coefficient, Cs 0.784 K3 Coefficient 11.1

Thickness required at 0.35 r / R 1.784 *** MODIFIED FOR ATHWARTSHIP THRUSTING ***

Input Data

ESSAYONS

Table 7.2.A: ABS Steel Vessel Rules calculation for the redesigned thruster rotor.

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7.3 CFD Analysis

Figure 7.3.1 shows pressure and velocity contours for the 3-knot forward speed, 1450 rpm, pushing to PORT case with the redesigned rotor and redesigned thruster. The more uniform velocity contours are clearly evident when compared to the baseline fairing and baseline rotor results. Figure 7.3.2 show the velocity vector results for this same case. Notably, the strong vortical content and flow reversal characteristics are again, no longer present.

The pushing to PORT and STBD streamline and pressure contour results are shown in Figure 7.3.4 and

Figure 7.3.3, respectively, for the 1450 rpm, 3-knot forward speed case. These images show a notable reduc-tion in suction side cavitation volume when compared with the baseline fairing, baseline rotor case.

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Figure 7.3.1: Pressure and velocity contours in the redesigned rotor and rede-signed thruster fairing case at 1450 rpm with a forward speed of 3 knots while pushing to PORT.

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Figure 7.3.2: Pressure and velocity contours, along with velocity vectors, in the rede-signed rotor and redesigned thruster fairing case at 1450 rpm with a forward speed of 3 knots while pushing to PORT.

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Figure 7.3.3: RANS results for the redesign thruster fairing and redesigned rotor case at 1450 rpm pushing to PORT, with a forward speed of 3 knots.

Figure 7.3.4: RANS results for the redesign thruster fairing and baseline rotor case at 1450 rpm pushing to PORT, with a forward speed of 3 knots.

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Table 7.3.E gives the tabular results for the redesigned rotor iterations with the redesigned fairing at 1450 rpm and a 3-knot vessel forward speed. The ratio is shown to again be at or below the 10% range.T1BR Tmean

Design Push Vs ERPM Sigma Max

ID Dir. T Q Pb FH FV T MH MV Q Bollard P_tap

(P/S) (kts) (rpm) (lbs) (ft-lbs) (hp) (lbs) (lbs) (lbs) (ft-lbs) (ft-lbs) (ft-lbs) (psi)

MRAD03 PORT 3 1,450 10,378 8,623 630 121 163 519 497 499 353 1.01 1.6

Base Percentage of Mean: 1% 2% 5% 6% 6% 4%

MRAD03 STBD 3 1,450 11,674 8,121 593 454 309 934 1,494 3,565 586 1.20 4.7

Base Percentage of Mean: 4% 3% 8% 18% 44% 7%

MRAD03 PORT 3 1,450 9,465 8,081 590 137 55 477 305 978 369 0.98 2.9

Rotor03 Percentage of Mean: 1% 1% 5% 4% 12% 5%

MRAD03 STBD 3 1,450 10,833 7,625 557 263 108 721 1,559 3,551 450 1.19 5.3

Rotor03 Percentage of Mean: 2% 1% 7% 20% 47% 6%

MRAD03 PORT 3 1,450 9,846 8,432 616 139 58 505 334 1,006 392 0.98 3.0

Rotor04 Percentage of Mean: 1% 1% 5% 4% 12% 5%

MRAD03 STBD 3 1,450 11,168 7,958 581 284 147 758 1,618 3,687 488 1.17 5.7

Rotor04 Percentage of Mean: 3% 1% 7% 20% 46% 6%

MRAD03 PORT 3 1,450 11,213 9,671 706 183 77 620 347 1,260 451 0.97 3.0

Rotor05 Percentage of Mean: 2% 1% 6% 4% 13% 5%

MRAD03 STBD 3 1,450 12,327 9,127 666 462 250 1,075 1,740 4,280 731 1.13 6.5

Rotor05 Percentage of Mean: 4% 2% 9% 19% 47% 8%

MRAD03 PORT 3 1,450 11,841 10,292 751 225 92 688 334 1,432 537 0.96 3.2

Rotor06 Percentage of Mean: 2% 1% 6% 3% 14% 5%

MRAD03 STBD 3 1,450 12,856 9,717 709 584 327 1,233 1,928 4,771 867 1.11 7.3

Rotor06 Percentage of Mean: 5% 3% 10% 20% 49% 9%

MRAD03 PORT 3 1,450 12,187 10,659 778 207 105 553 315 1,511 444 0.96 2.6

Rotor07 Percentage of Mean: 2% 1% 5% 3% 14% 4%

MRAD03 STBD 3 1,450 13,209 10,108 738 509 301 1,240 1,855 4,368 870 1.09 6.7

Rotor07 Percentage of Mean: 4% 2% 9% 18% 43% 9%

Mean Values First Blade Rate Harmonic Amplitude

Table 7.3.E: RANS results showing the rotor design iterations using the final thruster fairing design (MRAD-03). The final rotor design ID is Rotor-07.

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Table 7.3.F provides the results for the redesigned rotor and redesigned fairing combination over the rpm range of 800, 1000, 1200, and 1450, all in the 3-knot forward speed case.

The ESSAYONS currently limits bow thruster power, down from 986 hp, to 600 hp at a maximum rotor speed of

1270 rpm to avoid excessive noise and vibration. The 1270 results are shown at the bottom of Table 7.3.F.

The new rotor and bow thruster fairing designs improve the push to PORT performance by 19% and the push to

STBD performance by 11% when compared to the current 1270 rpm baseline case. The new rotor and bow thruster fairing designs also substantially reduce noise and vibration, which includes a 54% PORT + 42% STBD, reduction in the thrust first blade rate harmonic amplitude, and a 55% PORT + 27% STBD reduction in the shaft torque first blade rate harmonic amplitude, again when compared to the 1270 rpm baseline case.

Design Push Vs ERPM Sigma Max

ID Dir. T Q Pb FH FV T MH MV Q Bollard P_tap

(P/S) (kts) (rpm) (lbs) (ft-lbs) (hp) (lbs) (lbs) (lbs) (ft-lbs) (ft-lbs) (ft-lbs) (psi)

MRAD03 PORT 3 800 2,694 3,302 133 28 30 125 54 250 108 0.68 0.6

Rotor07 Percentage of Mean: 1% 1% 5% 2% 8% 3%

MRAD03 STBD 3 800 5,145 3,172 128 27 80 554 612 988 380 1.36 1.6

Rotor07 Percentage of Mean: 1% 2% 11% 19% 31% 12%

MRAD03 PORT 3 1,000 5,044 5,135 259 66 61 289 139 595 249 0.82 1.3

Rotor07 Percentage of Mean: 1% 1% 6% 3% 12% 5%

MRAD03 STBD 3 1,000 7,099 4,852 244 93 144 613 884 1,934 428 1.22 2.5

Rotor07 Percentage of Mean: 1% 2% 9% 18% 40% 9%

MRAD03 PORT 3 1,200 7,887 7,351 444 81 77 358 201 854 300 0.90 1.7

Rotor07 Percentage of Mean: 1% 1% 5% 3% 12% 4%

MRAD03 STBD 3 1,200 9,503 6,916 418 146 123 649 1,194 2,845 449 1.15 3.9

Rotor07 Percentage of Mean: 2% 1% 7% 17% 41% 6%

MRAD03 PORT 3 1,450 12,187 10,659 778 207 105 553 315 1,511 444 0.96 2.6

Rotor07 Percentage of Mean: 2% 1% 5% 3% 14% 4%

MRAD03 STBD 3 1,450 13,209 10,108 738 509 301 1,240 1,855 4,368 870 1.09 6.7

Rotor07 Percentage of Mean: 4% 2% 9% 18% 43% 9%

Base PORT 3 1,270 10,269 8,096 518 364 142 1,529 983 1,325 981 1.06 2.0

Rotor07(1450)/Base(1270): 119% 57% 74% 36% 32% 114% 45%

Base STBD 3 1,270 11,889 7,758 496 496 376 2,142 1,992 2,156 1,185 1.28 4.8

Rotor07(1450)/Base(1270): 111% 103% 80% 58% 93% 203% 73%

Mean Values First Blade Rate Harmonic Amplitude

Table 7.3.F: RANS results over the RPM range defined in Hanna, etal (2011) with the final thruster fairing design, MRAD-03, and the final rotor design, Rotor-07.

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8.0 Summary & Conclusions

As discussed in Section 1.0: Abstract, the following conclusions are again noted as:

1) The ESSAYONS bow thruster motor was increased from 600 hp to just under 1000 hp at a time prior to 2011. The bow thruster fairing and bow thruster rotor were not changed when the larger power motor was installed. The bow thruster noise and vibration were excessive when operating at power levels above 600 hp.

2) A Noise Control Engineering (NCE) report, Hanna, etal (2011) documented an instrumented sea trial program to measure the noise and vibration levels in way of the bow thruster area on the

ESSAYONS. Hanna, etal (2011) theorized that the primary cause of the excessive noise and vibra-tion was poor bow thruster rotor design, especially from a cavitation inception perspective.

Hanna, etal (2011) goes onto highlight the importance of determining the hydrodynamic inflow characteristics to the rotor in order to conduct a proper rotor redesign. Notably, Hanna, etal

(2011) makes no mention of the potential for poor inflow to be a significant contributor to the excessive noise and vibration.

3) The baseline RANS analysis of the entire vessel, with a full rotating thruster rotor, and complete bow thruster assembly clearly shows the primary cause of the excessive noise and vibration is poor hydrodynamic inflow in way of the forward lower quadrant on the bow thruster tunnel. If on

PORT and looking to STBD, the area of concern is between 6 and 9 o’clock on a clock face. As a result, a new bow thruster fairing was designed to mitigate the strong vortical content and flow reversal in this region of the bow thruster inlets, PORT and STBD.

4) Subsequent to the bow fairing redesign effort, the bow thruster rotor was redesigned to improve cavitation inception characteristics, improve overall noise and vibration performance, and utilize as much of the available 986 brake horsepower as possible.

5) The ESSAYONS currently limits bow thruster power, down from 986 hp, to 600 hp at a maximum rotor speed of 1270 rpm to avoid excessive noise and vibration.

6) The new rotor and bow thruster fairing designs improve the push to PORT performance by 19% and the push to STBD performance by 11% when compared to the current 1270 rpm baseline case. The new rotor and bow thruster fairing designs also substantially reduce noise and vibra-tion, which includes a 50% reduction in the thrust first blade rate harmonic amplitude, and a 40% reduction in the shaft torque first blade rate harmonic amplitude, again when compared to the

1270 rpm baseline case.

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9.0 References

Bruce S. Rosenblatt & Associates (2020) GHS file for ESSAYONS. ESSAYONS.GF.

Hanna, J., Patterson, A., Bahtiarian, M., and Brown, N. (2011) Army Corps of Engineers Dredge ESSAYONS:

Bow Thruster Survey. Noise Control Engineering, Inc. Report. Technical Memo 2011-064. 15 December 2011.

HRP Thruster Systems Drawing (2004) General Arrangement HRP 500TT. Drawing Number 60012004018500.

Kongsberg Simrad, AS (2003) DP Capability Analysis for ESSAYONS.

Remsing, D. (2011) ESSAYON Bow Thruster Report. Sheffield Marine Propeller, Inc. Report.

Sun Ship, Inc. (1981) Drawing - Hull Outfitting for Unit Assembly 5211. Drawing No. 354-H250-0032.

Sun Ship, Inc. (1980) Drawing - General Arrangement, Outboard Profile. Drawing No. 354-H150-0001.

Sun Shipbuilding & Dry Dock Company (1981) Lines Plan - FWD. Drawing No. 354-H100-002.

Sun Shipbuilding & Dry Dock Company (1981) Lines Plan - AFT. Drawing No. 354-H100-003.