Vessel Modification and Hull Maintenance Considerations Options & Pay Back Period or Return On Investments By Dag Friis Christian Knapp Bob McGrath Ocean Engineering Research Centre MUN Engineering 1
Overview: Energy Efficiency Related Hull Form problems commonly found in Length Restricted vessels Hull Maintenance Ghost Weights Hull Surface Fouling Appendages Lengthening Bow Half Angle Transom Immersion Anti-Roll Systems Bulbous Bows 2
Vessel/Hull Maintenance: Ghost Weights: The ever increasing weight! Excess Cargo, Gear and Miscellaneous Equipment Left On-Board unnecessary weight = Increased Fuel Consumption Hull Surface Roughness has a significant influence on resistance. Hull surface should be as smooth, even and fair as possible. ROUGH AND FOULED HULLS IMPROPERLY FAIRED FIBREGLASS HULL 3
Percentage Difference [%] Estimated Hull Surface Roughness Efficiency: 14.00% Comparison of Percentage Increase in Fuel Consumption due to Hull Fouling over that of a Clean Hull 12.00% 10.00% Effects More Pronounced at Slower Speeds 8.00% 6.00% 35 Footer 65 Footer 4.00% 2.00% 0.00% 0 2 4 6 8 10 12 Speed [knts] 4
Hull Surface Treatments: Possible Actions: Clean off Marine Growth on a regular basis Apply Fairing compound, sand and finish with a smooth coating to a clean hull. Paint for Surface Protection Especially Steel Against Corrosion ROUGH AND FOULED PlANING HULLS REFLECTIONS = PROPER LOOK OF A CLEAN & FAIR HULL! Moulded Fibreglass Planing Craft with good surface finish, Could be cleaned and scratches filled 5
Small Boat Surface Roughness Steel should be painted against Fouling and Corrosion Fibreglass Surface Roughness easily Faired with Sandpaper, Epoxy, Anti- Fouling Paint and Filler compound ROUGH AND FOULED HULLS Moulded Fibreglass Planing Craft with good surface finish, could be cleaned and scratches filled 6
Hull Appendages : Sonar Domes: Design should be faired into hull during installation to reduce drag IMPROPERLY FAIRED ICE DEFLECTORS CONSIDER USING A SEACHEST Proper Strut or Cavitation Plate Position = Immersed to minimise Cavitation! Additional Appendages such as Struts, Trunks, Heat Exchanger Pipes, Ice Deflectors, etc All Affect flow along hull as well as inflow conditions to the propeller, thereby increasing stern pressure, hull drag and reducing propeller 7 efficiency
Effect of Stern Tube and Skeg Shape on Design: Stern Tube, Skeg and Rudder and Rudder Post Faring Abrupt Changes in Shape Result in poor Flow to the Propeller Poor In-Flow Conditions Significantly Reduce Propeller Efficiency CLEANER PROP IN- FLOW ABRUPT PROP IN-FLOW ASYMMETRIC PROP IN-FLOW 8
Rudders: Rudders: The Common flat plate variety produce less Lift Force which is required to steer the vessel compared with Foil types requiring increased helm motion Increases the drag force produced when rudder angle is applied relative to the airfoil type slows vessel Incorrect Design of Rudder supports such as heel, trunk and struts can contribute: Significantly Increased Drag and Flow Turbulence Worse propeller outflow conditions and lower propeller efficiency and loss of manoeuvrability Potential Rudder Cavitation Erosion Foil Half Spade Rudder - Faired Trunk & Stock Plate Rudder with Heel Un Faired Rudder Cavitation Erosion 9
Percentage Difference [%] Estimated Hull Appendage Efficiency: 14.00% Percentage Increase in Fuel Consumption for a Non-Faired Hull Appendages Over Faired Appendages 12.00% 10.00% 8.00% Effects More Pronounced at Slower Speeds and Smaller Vessel Size 6.00% 4.00% 64'11" 34'11" 2.00% 0.00% 0 2 4 6 8 10 12 14 Speed [knts] 10
Rudder Selection: Rudders: Proper Rudder Selection can Decrease Thrust losses attributed to Propeller Rotational Flow and Cavitation, Reduce vibration & Noise Increase Propeller Fuel Efficiency and Vessel Manoeuvrability Reduce Necessary Helm Motion Affect Overall Vessel Performance Reduce Fuel Consumption High Lift Shilling Rudder 70 Deg max. Angle & Low Drag Twisted Rudder- Asymmetric Design Uses Swirl to Generate Added Lift & Reduce Cavitation Flap Rudder with Heel Increased Manoeuvrability & Course Keeping 11
Vessel Lengthening: The 35, 45, and 55 vessels may be lengthened by 5 ft The 65 vessels may be lengthened by 25 ft Note: New Small Fishing Vessel Regulations < 24m (78.74 ft) Lengthening will generally reduce the amount of power required to cruise at a given speed Allow for partial re-design of submerged hull Form Will likely improve directional stability, i.e. the Vessel is more likely to be able to go in a straight line. Staying on course reduces the total sailing distance reduced fuel consumption & Rudder Drag 12
Lengthening: For Fibreglass or Fibreglass-over-Wood hulls one may require the whole hull to be glassed over depending on how the lengthening is done. If the boat is cut at amidships and a piece added in the middle the hull will need to be fully glassed over If a piece is added at the stern one may not need to glass over the entire hull if one can prove that the connection is strong enough to remain intact even in extreme conditions. 13
Lengthening: For steel and Aluminum hulls lengthening is a much more straight forward thing regardless of whether the lengthening takes place at amidships or at the stern or the bow. The joining of the new to the old structure is done by welding. Steel or Aluminum hulls will make it possible to cut off the bow and replace it with one with a more suitable angle of entrance 14
Lengthening: Lengthening should be done using a well qualified Naval Architectural Engineer that will evaluate what additional vessel modifications may be needed in order to make the boat as safe and economic to operate as possible. 15
Stern Lengthening: Increase in Working Deck Area Increase In Directional Stability & Hydrodynamic Efficiency Better Course Keeping & Reduction in Service Power Moving Skeg & Stern Tube Aft = Increase in Propeller Clearance 16
Effect Of Transom Immersion & Abrupt Changes in Hull Shape: Larger Low Pressure Area Sucking in Water, Creating Vortices and a Resultant forward water motion Substantial Energy Loss & Inefficiency Creates a boxier profile No change in waterline Length Less clearance available for Propeller installation Generally means a greater interference in flow through Propeller Disc RISING STERN = Transom Immersion Varies with Displacement = More Efficient BOX LIKE = Always Max Submerged Area & Large Pressure Drop A CONTAINER VESSEL ONLY AT MOST EXTREME LOADING IS THE TRANSOM SUBMERGED! 17
Service Power [kw] ~48% Reduction Estimated Service Power with Transom Immersion for a 35 : 100 90 Estimated Service Power (No Genset) Variation with Immersed Transom: As Percentage of the Midship Draught for a 35' (L/B = 2.33) ~52% Reduction 80 70 60 50 40 100% Midship Draught Immersion 90% of Midship draught Immersion 80% of Midship draught Immersion 70% of Midship draught Immersion 60% of Midship draught Immersion 50% of Midship draught Immersion 40% of Midship draught Immersion 30% of Midship Draught Immersion (As-Built) 20% of Midship Draught Immersion 10% of Midship draught Immersion 30 20 10 0 0 1 2 3 4 5 6 7 8 9 Speed [knts] 18
Bow Lengthening: Reduction in Half Angle More Gradual Change in Hull Submerged Area 19
Fuel Volume [l] Lengthening: Decreasing Half Angle 20.00% Percentage Difference in Hourly Fuel Consumption with Variation In Bow Half Angle over As Built Case ( for L/B = 2.89) 15.00% 10.00% 5.00% 0.00% -5.00% -10.00% -15.00% -20.00% -25.00% 1 2 3 4 5 6 7 8 9 10 11 110% As-Built Half Angle (60.5 Deg) 105% As-Built Half Angle (57.75 Deg) 95% As-Built Half Angle (52.25 Deg) 90% As-Built Half Angle (49.5 Deg) 85% As-Built Half Angle (46.75 Deg) 80% As-Built Half Angle (44 Deg) 75% As-Built Half Angle (41.25 Deg) 70% As-Built Half Angle (38.5 Deg) As-Built Half Angle (55 Deg) -30.00% Speed [knts] 20
Case Studies Simulated : 65 @ Cruising Speeds (25% Sea Margin, 100 nautical miles) 65 Base (10 knots ): 1583 Litres 1923.9 Engine RPM 65 Optimised Speed (7.5 knots): 520 Litres 1025 Engine RPM 65 Lengthened to 75 (10 knots): 692 Litres 1340 Engine RPM 35 @ Cruising Speeds (15% Sea Margin, 100 nautical miles) 35 Base (8 knots ): 250 Litres 1989 Engine RPM 35 Optimised Speed (6 knots): 75 Litres 940 Engine RPM 35 Lengthened to 40 (8 knots): ~100 Litres 1439 Engine RPM 21
Anti-Roll-Devices and Energy Efficiency: Paravanes, Active Fin Stabilizers and Batwings: add significantly to vessel resistance and are more efficient in stabilizing the vessel at cruising than fishing speed Anti-Roll-Tank very effective at all operating speeds Can be installed away from work and hold areas Must be tuned and designed to specific vessel s parameters 22
EFFECT OF ANTI-ROLL TANKS ON SEAKEEPING TESTS Bulb B (L/B = 3) Irregular Waves Bulb B with ART (L/B =3) Irregular Waves CAUTION: ANTI-ROLL TANKS MUST BE PROPERLY DESIGNED AND FITTED FOR EACH INDIVIDUAL VESSEL
Roll (Deg) Anti-Roll-Tanks: Properly Designed and Tuned Anti-Roll-Tanks will reduce roll motions in normal conditions by the order of 55% 60% is likely a reasonable expectation. This will allow one to fish in worse conditions and likely reduce fishing time even in good conditions. Roll for Model with Bulb B with and without an ART 40 30 20 10 0-10 -20 0 5 10 15 20 ART No ART -30-40 Time (s) 24
Bulbous Bows: Reduces resistance by creating a wave that is sufficiently out of phase with the wave generated by the bow that it reduces the resulting combined wave Reduces pitch motion and phasing relative to waves if properly designed and significantly reduces the added resistance in waves WARNING: Bulbs can amplify pitch motion and increase the added resistance in waves if not properly designed OBTAIN PROFESSIONAL DESIGN SERVICES Properly designed bulbous bows have proven to reduce resistance by 15% to 40% depending on steaming speed and overall hull proportions etc 25
EFFECT OF BOW TYPE ON SEAKEEPING TESTS Standard Bow (L/B = 3) Irregular Waves Bulb A (L/B =3) Irregular Waves
Pitch Angle (Degrees) Effect of Bow Type on Pitch 12 Motion Comparison of Pitch Motion for Conventional and Bulbous Bows at Design Draught (L/B=3) in 2m Significant Waves 10 Bulb A 8 Standard Bow 6 4 2 0 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 Wave Frequency [rad/s]
Fuel Rate [l/h] Bow Type Fuel Rate : 700 Comparison of Estimated Hourly Fuel Consumption for a Design Draught for L/B = 3 and 25% Sea Margin 600 500 Standard Bow 0 Deg Trim Standard Bow 3 Deg Trim ~66% Reduction 400 Bulb A 0 Deg Trim Bulb A 3 Deg Trim 300 200 100 0 0 2 4 6 8 10 12 28 14 Speed [knts] ~40% Reduction
Advantages of Bulbous Bows: Bulbous Bows are effective in reducing resistance at cruising speeds : Roughly 4.5 7.5 knots for a 35 vessel (Estimated) 35 with bulbs exist, however, we have not currently tested them. Likely the payback period will be longer for smaller vessels Roughly 5.0 8.5 knots for a 45 vessel Roughly 5.5 9.5 knots for a 55 vessel Roughly 6 10 knots for a 65 vessel Economics Depend on Vessel Size, Construction Material, Operational Life, Steaming Distance and Frequency of Trips to determine IRR and Payback period 29
ECONOMIC COSTS: ART s : ~ $3000 For Professional Design + Construction and Trials ($25,000+ total estimate) Paravanes : ~10% Increase in resistance equivalent to the loss of 1 knot at steaming speeds (for Paravanes = 0.3-0.4 m 2 ) Require a few knots ahead Speed to gain dampening effect Alternate Rudders & Additions: Can Deliver 3-6% increase in Fuel Efficiency Increased Manoeuvrability and Course Keeping Increased Lift and Lower Drag Less Cavitation Erosion, Fewer Vibrations and Reduced Noise Bulbous Bows: Steel: ~$50,000 $120,000+ Depending on Vessel Length and Type (Cylindrical or Faired: Less for smaller vessels) Fibreglass: Significantly less as it is easier to Retro-fit 30
Percentage Difference [%] Estimated % Power Variation 65 : 100.00% Estimated Effect of Hull Fouling, Appendage, Immersed Transom and Half Angle on Service Power (L/B ~ 2.89) Appendage Drag 80.00% Fouling Drag 33% Increase in Transom Draught 60.00% 40.00% 20.00% 66.7% Increase in Transom Draught 100% Increase in Transom Draught 33% Reduction in Transom Draught 66.7% Reduction in Transom Draught 10% Increase in Half Angle 10% Reduction in Half Angle 25% Reductio in Half Angle 0.00% 4 6 8 10 10.5-20.00% -40.00% Speed [knts] 31
A CONCLUDING SLIDE Remember: COST vs. BENEFIT! 32