Cal's Evals » HUGHES 71' TRI

Release Date: 1/3/2011

Hughes 71 Trimaran

 

Kurt Hughes has designed an impressive large cruising trimaran that is over 70 feet in length and nearly 60 feet in beam. Multihulls of this size come in either of two types; cruising boats with good predicted performance and stability or racing boats with extraordinary performance and less stability. This boat is one of the former. The Multihull Dynamics, Inc. database does not contain other trimarans of this size except for pure racers like Lakota and Castorama B&Q, so comparisons are not meaningful. However, there are five large cruising catamarans that provide a basis for evaluating the Hughes 71, as shown in the table below.

BOAT NAME

D

Loa

Lwl

B

SA

Bcl

Bh

Lwl/ Bh

SA/D

Perf Indx

Bruce No.

Texel No.

Base Spd

Stab

Spd

Units

tons

ft

ft

ft

ft2

ft

ft

ft/ft

ft2/ft3

knots

knots

HUGHES 71 TRI

19.95

70.90

70.00

58.80

1822

52.50

8.11

8.63

23.15

0.84

1.21

107

13.31

40.13

ALUMARINE 22

35.00

73.82

68.90

36.09

3229

31.12

7.02

9.81

28.21

0.84

1.33

106

14.01

25.58

BLUBAY 72

17.00

75.00

70.00

48.00

2809

43.15

4.85

14.42

39.71

1.14

1.58

89

16.14

23.82

ORAM 72 MERLIN

16.21

72.00

72.00

29.50

1604

24.83

4.67

15.41

23.41

0.89

1.21

110

13.60

27.70

AKASHA

33.00

75.80

72.00

38.00

2975

31.33

6.67

10.80

27.02

0.85

1.30

106

14.12

27.03

BIS 77

30.00

77.00

72.00

36.00

3100

29.64

6.36

11.32

30.01

0.91

1.37

101

14.68

24.33

The Hughes 71 is about the same displacement as the lighter of the catamarans. However, the sail area is quite low (except for Merlin). The Sail Area to Displacement ratio (SA/D) combines these factors to indicate why the Hughes 71 has the lowest predicted base speed, a respectable 13.31 knots. Hughes designs have a tendency toward lower than average sail area, so this is not a surprise.

One tri vs. cat element is the hull length to beam ratio, Lwl/Bh. Note that, since all of the displacement is credited to the main hull of a trimaran, the Hughes 71 has a lower Lwl/Bh ratio than the catamarans. This makes trimarans appear to have lower performance potential than equivalent catamarans, but in fast sailing, much of the displacement is carried by one of the sizeable amas (outriggers), so there doesn't seem to be a penalty here.

One specification that stands out is the considerably greater overall beam of the trimaran than the catamarans, resulting in the predicted stability speed that is approximately 15 knots higher. Some of this stability is also due to the tendency Kurt Hughes has toward lower than average sail area. One wonders why Kurt doesn't trade some of this stability for more performance.

For example, increasing the sail area to 2500 square feet would increase the predicted base speed to nearly 15 knots while maintaining a stability speed of over 30 knots, making it the fastest and most stable boat in the set.

Using Charles Kanter's rating system which is based on Lwl/Bh, this boat is in the Cruising category.

Kurt Hughes Sailing Designs

Calvin H. Markwood
Engineering Analyst
Multihull Dynamics, Inc.

Contact Cal: multihull.analysis@comcast.net