884-B606-03 R0 Propeller Design.pdf

REV ZONE DRAWN CHKD

GENERAL NOTES

NO.

SIZE REV

A 0

DATE: SCALE: SHEET 1 OF 13NTS

APP'D BY: PROJECT NO. DWG. NO.

3189 884-B606-03

DATE: BHGI PROJ #:

Propeller Calculations20-Oct-22 22705

MARINE DESIGN CENTER

REFERENCES

Bienville Replacement

DRAWN BY: CHECKED BY:

Towboat

JE DPE

DESCRIPTION DWG NO. REV.

REVISION HISTORY

DESCRIPTION DATE

HSMarinePropulsion, LLC 2113 Government St, Bldg G Ocean Springs, MS 39564

(228) 875-6611

10/20/2022

Document: 884-B606-03 Propeller Calculations

Propeller Design The propeller has been designed to meet the project goals of maximum thrust at 4 knots while minimizing unsteady forces and moments. The wake developed in the Hydrodynamic Optimization have been used to create a propeller design to meet these requirements. The design constraints on the propeller were to be a four bladed propeller that allowed for a minimum 15% tip clearance, which limited diameter to 70” and thickness to meet ABS Ice Class C0 and cavitation not to exceed 10% by the Burrill Chart. The propeller material is Nickel-Aluminum-Bronze, ABS Type 4.

The basic propeller parameters are as follows:

Diameter 70 in

Pitch (0.70R) 50 in

DAR 0.80

Z 4

Weight 1770 Lbs

WR2 3620 lb-ft2 (in air)

GD2 5720 lb-ft2 (in water)

The 70 in diameter is less than the optimal diameter for efficiency for this power, speed and RPM. The optimal diameter would be about 80”, but the tip speed could become an issue for cavitation and vibration if the diameter were made larger. The requirement for 15% tip clearance also limits the diameter to 70 in.

Figure 1 – Diameter Optimization

10,000

12,000

14,000

16,000

18,000

20,000

22,000

50 55 60 65 70 75 80 85 90

T h ru s t (l b s

Diameter (in)

Efficiency VS Diam 800 BHP / 323 RPM / 4 Kts

The image below shows the propeller with a circle drawn with a radius corresponding to the required 15% tip clearance. The higher buttock line is the propeller tunnel and the lower buttock line, the chine.

Figure 2 Propeller Tip Clearance

The propeller design process involves selecting the basic design variables of diameter, DAR, number of blades. Then determining appropriate distributions of radial geometry, chordlength, rake and skew and then finding the optimal pitch and camber to meet a specific design point. In this case, the chordlength distribution and skew distribution were optimized during the process to attempt to minimize cavitation and vibration at the design point while not degrading the astern thrust. This was accomplished through an iterative process using experience and analysis to arrive an optimal design.

The requirement to provide good backing characteristics as well as good ahead performance limits the design features that can be incorporated to enhance the ahead cavitation and vibration characteristics.

The propeller has been designed with some aft skew and rake to provide the best possible interaction of the blade leading edge with the wake field. The outboard and centerline shaft wakes are quite similar due to the tunnel configuration, and this allows a single design to work effectively in the imposed wake. The blade also has some pitch reduction at the outer radii to reduce cavitation and hull pressure pulses. Both these features must be applied carefully as they tend to reduce backing effectiveness. Camber has also been reduced from the optimal for ahead efficiency as camber also greatly reduces backing thrust.

The requirement for ABS Ice Class C0 thickness also adversely affects the performance both ahead and astern. The thickness to chord ratio at the root is over 20%, resulting in large viscous losses and increasing the potential for damaging cavitation at the aft end of the suction face. The thick edges and tip increase frictional losses and reduce efficiency.

Cavitation based on the Burrill Chart is well below the 10% line in a bollard condition and below the 5% line at a 4 kt operating condition. The 5% line is typically used for heavily loaded tow boat propellers to ensure low cavitation induced vibration levels. This chart is based on standard, constant pitch propellers design from the 1940’s so actual cavitation for a modern optimized design is typically somewhat less. CFD calculations show cavitation is no more than 5-7% of blade area in all conditions.

Figure 3 – Burrill Cavitation Chart

The basic radial geometry of the propeller is provided in the following table.

Geom

Proj. Design r/R Pitch Chord Skewº Drake Tmax Fmx TE thk LE Rad

0.140 50.52 15.990 -0.840 -0.720 4.100 0.372 0.250 1.051

0.200 51.13 18.778 -1.001 -0.857 3.610 0.794 0.250 0.698

0.250 51.60 20.936 -1.137 -0.971 3.351 0.975 0.250 0.545

0.300 52.02 22.626 -1.254 -1.067 3.119 1.063 0.250 0.445

0.400 52.57 25.180 -1.222 -1.177 2.686 1.114 0.235 0.313

0.500 52.45 27.180 -0.799 -1.196 2.279 1.072 0.235 0.224

0.600 51.57 28.805 -0.010 -1.108 1.902 0.966 0.235 0.162

0.700 50.06 29.873 1.150 -0.870 1.565 0.819 0.235 0.117

0.750 49.06 30.030 1.975 -0.670 1.414 0.730 0.235 0.100

0.800 47.87 29.816 2.948 -0.386 1.270 0.617 0.235 0.086

0.850 46.46 29.065 4.088 0.010 1.122 0.471 0.235 0.073

0.900 44.78 27.084 5.427 0.549 0.968 0.315 0.235 0.062

0.950 42.76 22.723 6.926 1.202 0.791 0.150 0.235 0.052

0.975 41.62 18.770 7.720 1.573 0.674 0.070 0.235 0.047

1.000 40.37 8.190 8.540 1.980 0.287 0.000 0.204 0.020

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.0500 0.1500 0.2500 0.3500 0.4500 0.5500 0.6500 0.7500 0.8500

T a u

C

Sigma (0.70R)

BURRILL CAVITATION DIAGRAM

Bollard

DESIGN

5%Back

10%Back

20%Back

Table 1 – Radial Geometry

Figure 4 – Views of Propeller

The thickness distribution was made to meet ABS Inland River Rules and ABS ice class C0. The thickness required by the ice class rules are far in excess of that required by the Inland River Rules, so the ice class rules have been used. ABS Ice Class blade thickness calculations are provided in Appendix A.

Open water characteristics for this propeller have been developed using a potential flow code. The high thickness to chord ratios and the thick edges and tip create problems for the panel code’s accuracy. A

RANS code has been used to verify the calculations and data from the code was used to adjust section drag coefficients for the panel code. The expected range of the advance coefficient, j, in ahead operations is 0 to 0.55. Open water curves have been developed over that range and are shown in the following table and figure. These open water curves are for fully wetted flow and do not account for cavitation. Cavitation was assessed using the RANS code with the propellers operating behind the vessel.

Kt 10Kq ETAo

0 0.352 0.3763 -

0.1 0.3165 0.3538 0.14

0.2 0.2761 0.3222 0.275

0.3 0.2286 0.2826 0.385

0.4 0.1857 0.2467 0.475

0.5 0.1444 0.2118 0.537

0.6 0.1015 0.175 0.552

0.7 0.0579 0.1359 0.472

Table 2 – Open Water Data

Figure 5 – Open Water Curves

The guidance from Cummins for this engine is to make sure that the engine can get above 1700 RPM in a bollard condition. The predictions for this propeller in the design condition, bollard and free run are provided below. The design is predicted to achieve 1720 RPM at bollard using 800 HP with a 5% transmission loss factor.

Figure 6 Engine Limit and Propeller Demand

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

K t, *K q

, E

TA

o

Ja

Propeller Open Water Curves 70X50(var), 4 Blades, 0.80 DAR

Kt 10Kq ETAo

400 600 800 1000 1200 1400 1600 1800

P o w er

B

H P

Engine RPM

Engine Limit 4 kts Bollard Free Run

The key design points were simulated using fully unsteady cavitating analysis. The conditions run include the design point of 4 knots using maximum power, bollard ahead at maximum power and bollard astern.

Net thrust predictions are as follows:

Condition Thrust Gross Net

(kN) (kN)

4 kts, full power 240 193

Ahead bollard 281 252

Astern Bollard 183 172

The net ahead bollard is 140.8 N/Kw (23.6 lbs/HP), the astern bollard is 64.3% of ahead. The thrust deduction factor is in the ahead direction is 10.3% and 6.4% astern. Images of the free surface and the slipstream from the propellers are provided in the following figures. The astern thrust is about 68% of the ahead thrust in the bollard condition.

Bollard Ahead

Bollard Astern

Appendix A - ABS Ice Class Calculations

Shipyard Name NA

Hull No NA

Reference Bienville

Date 10/18/20

Propeller Blade Width and Thickness

[Marine Vessel Rule 6-1-5/51.3.1, 6-1-5/51.3.2 and 6-1-5/51.5.3] [Steel Vessel Rule 6-1-5/51.3.1, 6-1-5/51.3.2 and 6- 1-5/51.5.3]

Unit

US

Blade Width and Thickness

Blade Bolts

Type of propeller Solid propeller w ith hub not larger than 0.25D

Explanation Notes On Off

Width and Thickness (According to [6-1-5/51.3.1])

• The thickness T and width W of propeller blade sections are to be determined so that the WT2 calculated by the actual designed W and T is not less than that required by the following equations::

Where:

a1 = 27000.0 a2 = 176.0 a3 = 59.13 a6 = 9500.0 a7 = 75.26

W = expanded width of a cylindrical section at the appropriate radius, cm (in) T = maximum thickness at the appropriate radius from propeller drawing, cm (in) U = tensile strength of the propeller material, N/mm2 (kgf/mm2, psi) P0.25 = pitch at 0.25 radius, mm (in).

P0.6 = pitch at 0.6 radius, mm (in).

D = propeller diameter, mm (in) https://www.eagle.org/rulescalcp4/jsp/GeneralIceProp_615/GeneralIcePropeller.jsp?kindofshaft=propeller https://www.eagle.org/rulescalcp4/jsp/GeneralIceProp_615/GeneralIcePropellerBolt.jsp

C = 1.0

N = maxiumum continuous power, kW (mhp(ps), hp) n = number of blades R = rpm at the maximum continuous rating M = ice torque, as defined in [6-1-5/51]

Ice Torque (According to [6-1-5/51])

• The Ice Torque M for determining the dimensions of propellers is to be in accordance with the following table and associated notes.

Value of Ice Torque M

Location of Propeller Centerline Off Centerline

Propellers protected by nozzle Nozzle protected (see Note 1) class A0-B0 class C0-E0

0.75M1 (see Note 2)

0.85M1 (see Note 2)

0.85M1 0.9M1

Nozzle unprotected class A0-C0 class D0 and E0

0.9M1 (see Note 3)

0.9M1 (see Note 3)

0.9M1 0.9M1

Open propellers class A0-E0

M1 M1

M1 = mD2/k1, kN-m (tf-m, Ltf-ft) D = propeller diameter, mm (in) k1 = 144.0 m = 0.37

Notes

1. These requirements apply where the nozzle is well protected by ice knives, fins or other adequate stern arrangement, from large ice fragments entering into nozzle from forward or backward motion of the vessel. These reductions are subject to special consideration.

2. To be not less than required for the second lower ice class.

3. To be not less than required for the next lower ice class.

4. Need not be greater than required for the next higher ice class.

Blade Tip Thickness (According to [6-1-5/51.3.2])

• The minimum blade thickness ta, in mm(in), at the tip of the blade (D/2) is to be determined from the following formula:

a2 = 0.024 a3 = 71000.0 a4 = 0.591 k = 12.0

D = propeller diameter, mmk (in) U = tensile strength of the propeller material, N/mm2(kgf/mm2, psi)

Blade Edges (According to [6-1-5/51.5.3])

• The thickness of blade edges is not to be less than 50% of the required tip thickness ta, measured at a point 1.25ta from the leading edge for controllable-pitch propellers, and from each edge for solid propellers.

Input Data

Ice Class First-year ice: Ice Class C0

Propeller protecting structure and location Open Propellers: Off Centerline

Tensile Strength of the propeller material (U) 86000 psi

Pitch at R0.25 (P0.25)

51.60 in

Pitch at R0.6 (P0.6) 51.57

Maximum continuous power (N) 800 hp rpm at the maximum continuous rating (R) 323

Number of blades (n) 4

Propeller diameter (D) 70

Actual expanded blade width at R0.25 (W0.25)

20.94

Actual expanded blade width at R0.6 (W0.6) 28.81

Actual blade thickness at R0.25 (T0.25)

3.35

Actual blade thickness at R0.6 (T0.6) 1.90

Actual blade thickness at the tip of the blade (D/2) .66

Actual minimum thickness of blade edges, measured at a point 1.25ta* from each edge (te)

.33

* ta is the required minimum blade thickness at the tip of the blade (D/2) [6-1-5/51.3.2]

Calculation Result

Notes:

In addition to the following calculated results, blade thickness should also satisfy the following additional requirements.

1. In accordance with 6-1-5/51.5.1, the blade thickness at 0.25 radius should not be less than the required thickness detailed in 4-3-3/5.1.

Link to 4-3-3/5.1 Blade Thickness - Fixed Pitch Propeller

2. In accordance with 6-1-5/51.5.2, the thicknesses of propeller sections at radii intermediate to those specified are to be determined from fair curves connecting the required section thicknesses.

https://www.eagle.org/rulescalcp4/jsp/Propeller/PropellerFixedPitchPage.jsp

3. In accordance with 6-1-5/51.5.5, where highly skewed propellers are utilized, stress calculations considering both the ahead and astern operating conditions as well as the above ice loads are to be submitted for review.

Ice torque, as defined in 6-1-5/51 (M) 12.59

Ltf-ft

Required WT2 at R0.25

229.79 in3

Actual WT2 at R0.25

235.00

Acceptable

Required WT2 at R0.6 100.12

Actual WT2 at R0.6 104.00

Required minimum blade thickness at the tip of the blade (D/2) .66

Actual minimum blade thickness at the tip of the blade (D/2) .67

Required minimum thickness of blade edges, measured at a point 1.25ta from each edge

.33

Actual minimum thickness of blade edges, measured at a point 1.25ta from each edge

.34

Calculate