1. Hydrodynamic Design Aspects for Conventional Fast Ships Manfred Fritsch Volker Bertram

2. Focus on “conventional” fast vessels

3. Monohulls

4. Speed ranges tested at HSVA for MONOHULLS
There is considerable overlap in speed ranges
Speed ranges tested at HSVA for MONOHULLS

5. Displacement ships frigates, corvettes, ... 0.3 < Fn < 0.6
good seakeeping
good course-keeping
low dynamic trim
steep power increase
V-shaped section in forebody
slender waterlines
round bilge with decreasing R going aft

6. Planing hulls patrol boats, S&R boats, racing yachts,...
0.8 < Fn < 1.7
low resistance at high Fn
dynamic instability
poor seakeeping
straight sections and knuckle lines
slender waterlines
deadrise angle decreasing aft to L/2
then nearly constant > 10º
trim wedges with adjustable tabs frequent

7. Semi-Displacement ships
patrol boats, pilot boats, pleasure craft
0.6 < Fn < 1.2
good seakeeping
good course-keeping
dynamic instability

8. Simple HSVA power prediction available
planing hulls
PB = f(,B,V)
semi-displacement hulls:
PB=RT·V/(D·M)
RT = CT ·½ ·V2·2/3

9. (All) designs can be improved
spray rails
trim wedges
appendages

10. Spray rails effective and cheapPE
w/o with
Speed V [kn]

11. Sometimes considerable improvements
50 knot patrol boat with original trim wedge

12. Sometimes considerable improvements
50 knot patrol boat with modified trim wedge

13. Sometimes considerable improvements
50 knot patrol boat modified wedge + spray rails

14. Trim influences resistance
Influence of LCG

15. Recommendations for trim given
Recent
designs
have
lower trim

16. Trim wedges frequently employed
most effective for Fn =
(10% savings possible)
almost no effect for Fn>1.2

17. Interceptors allow speed-dependent trim
Height of interceptor

18. Appendages influence resistance strongly
RAPP = 6%-15%RT
avoid oversizing shaft brackets, bossings, rudder profiles
V-brackets may have 7% higher resistance than I-brackets
Align brackets with flow (CFD or experiment)
power changes by 3%-5%
depending on sense of propeller rotation for twin-screws
shaft inclination reduces efficiency
inward inclination of rudders for twin-rudder designs
can increase propulsive efficiency by 3%
keep strut barrels small; nose rounded or parabolic
Align bilge keels with flow
determine angle of attack of least resistance
for non-retractable stabilizers

19. (All) Designs can be improved...
History of fast vessel project at HSVA

20. Catamarans 70% more deck area 20-80% more resistance
high transverse stability
similar roll periods

21. Catamarans cover wide speed range
Displacement
Fn  0.5
large platform
Semi-displacement
Fn  1
round-bilge or hard-chine
Planing
50+ knots
hard-chine
waterjets

22. Simple design estimates possible
Froude number

23. Foil-assisted cats at high speeds
improved resistance
improved seakeeping
efficient ride-control system
controllable flaps forward and aft recommended

24. Foil-assisted cats often with aft immersed

25. Seakeeping tests are sometimes performed

26. Deep-V addition serves as anti-slam device
faired
knuckled

27. Longitudinal rails alternative ASD

28. Thank you
all
The