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Experimental Strain Analysis of the Mastof a 420 Sailboat During Sailing

G. Pellicioli and N. Petrone

Dipartimento di Ingegneria Meccanica, Universita di Padova, Via Venezia, 1 35100 Padova, Italy

ABSTRACT: Aim of the work was the experimental strain analysis of a 420 sailboat mast during

sailing: this type of data is of great interest in the structural design of sailboat masts and hulls as well as

in the sail-making. The work involved the design, calibration and installation of strain gauge bridges at

seven sections of an instrumented mast and at the shrouds: this was followed by the collection of

strain data during simulated laboratory rigging tests and real sailing sessions with medium/strong

wind. Compression loads at the mast step were recorded with a customised load cell calibrated on a

force platform. On the basis of laboratory calibration constants, the strain measurements were

converted into structural loads and averaged over steady states during rigging and sailing either close

to the wind or beam reach: the longitudinal bending moment, the lateral bending moment and theaxial loads were analysed and plotted along the 6.20 m mast length. Highest values of lateral bending

(146 14.5 Nm) were recorded at the mast head, whereas longitudinal bending showed highest

values at the vang connection to the mast (229 29 Nm). Tension loads acting on the shrouds were

also measured with highest values of 2887 167 N. The knowledge of loads acting along the mast

will support the designers in improving the masts cross section profile, the material selection and the

validation of numerical structural analysis. Moreover, experimental data about the loads acting on the

standing rigging and on the mast-step during sailing will support the optimised design of the boat shell.

KEY WORDS: 420 sailboat, mast, sailing loads, shrouds, strain analysis

Introduction

Innovation in masts cross sections and appropriate

selection of materials oriented to the optimum

stiffness, strength and durability are possible only if

reliable data about the distribution of bending

moments acting along the mast during sailing are

available. In addition, the accurate knowledge of

loads acting on the standing rigging and on the

mast step supports a possible optimised design of

the boat shell. Furthermore, experimental data may

also be used to validate computational fluid

dynamics predictions of the sail behaviour and

numerical structural models of the redundant mast-

hull system [1]. Finally, from a sail designer point of

view, the knowledge of the masts deflection line in

the longitudinal and lateral planes is fundamental

for an efficient sail design: displacement measure-

ments are difficult to perform in a rough environ-

ment like a sail regatta, so an indirect structural

approach can be adopted to estimate the deflection

state of the mast.

Very few experimental data from real sailing ses-sions are available, or they are restricted to few

components and not to the whole mast-hull system:

in some cases, only laboratory tests under simplified

loading conditions were performed [1] and compared

with numerical structural simulations. Other

approaches to the problem such as numerical models

without experimental validations or scale models are

possibly characterised by high unreliability levels: at

present it is very difficult to predict numerically the

real load and displacement conditions during sailing

because of the complexity and variability of sea-

wind-sailboat dynamics.

Given these facts, the first objective of the work

was the development of an integrated system for

measuring the structural loads on the mast and the

standing rigging of a 420 dinghy. The main research

requirement was the minimum modification of the

real mast-hull system and the possibility of transfer-

ring the instrumented components and the adopted

methodology to other dinghies.

The second objective of the study was the measure

of bending moment diagrams in the longitudinal and

lateral planes corresponding to well defined states of

the rigging and to different point of sailing underknown wind and sea conditions.

2010 Blackwell Publishing Ltd j Strain (2010) 46, 482492482 doi: 10.1111/j.1475-1305.2009.00673.x


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Materials

The boat reference frame adopted is a system of three

orthogonal axes X, Y, Z. The origin of the coordinate

system is placed in correspondence of the centroid of

the masts cross section, at the mast step. Then, X

axis is oriented in the direction of the axis of sym-

metry of the section, that is the direction of thelongitudinal axis of the boat; Z axis develops in the

direction from the step to the head of the mast and Y

axis complete the triad (Figure 1).

The mast and the standing rigging measurement

systems were designed, calibrated and installed in

order to measure the dynamic structural loads during

sailing with minimum disturb effect: strain gauges

were directly applied to components such as the mast

and the shrouds, whereas a low profile two compo-

nent load cell was specifically designed to measure

the vertical and the longitudinal loads at the maststep, as described in what follows.

Instrumented mast

The mast used for this research project is produced by

Super Spars company (Fareham, New Hampshire,

England). It is made of aluminium alloy by extrusion,

cutting and welding. The surface is anodised to pre-

vent corrosion; linear density given by the con-

structor is 0.94 kg per meter of length. The mast is

6200 mm long, the main section measures 57.5

70.5 mm and it is uniform for about 4500 mm of the

total length, while the remaining part of the extru-

sion is tapered up to the top section that is 32.5

34.5 mm. In correspondence of the mast head and ofthe mast step there are two steel components that

respectively allow the movement of the mainsail

halyard and of running rigging.

After a preliminary study of the different possible

loading configurations and of the effects on the sys-

tem mast-hull generated by the combined action of

standing and running rigging, the seven measure-

ment sections were chosen as listed in Table 1 and

sketched in Figure 1.

Fundamental loads considered for the definition of

measuring systems were bending moments in thelateral (Mfx) and longitudinal planes (Mfy) together

with the axial load (N), as shown on Figures 2 and 3.

Against a structural analysis of the mast during the

navigation, the boat with sails hoisted was taken as

reference situation.

Wheatstone bridge circuits were used for the mea-

surement of resistance changes from strain gauges.

The types of connection used are: Quarter bridge,

Half bridge and Full bridge, depending on measured

loads [2]. The bending moment in the longitudinal

plane Mfy were measured at mast sections number 1,

2, 3, 4 and 5 (Figure 3) with four strain gauges at each

section connected with a Full Wheatstone bridge as

shown in Figure 4 (gauges from #1 to #4). Gauges

type HBM 0.6/120-LY43 were used having a 0.6 mm

measuring grid to match with the narrow available

planar surface (gauges #2 and #4) at the sides of the

mainsails head groove. The bending moment in

lateral plane Mfx was measured at sections 4 and 6

7

6

5

4

3

2

1

SR

MS

SL

Y

Z

X

Figure 1: Indication of measuring points along the mast andreference frame adopted on the sailboat

Table 1: List of measuring points, measured load components

and adopted names of measuring channels

Point Description

Measured

loads Measuring channels

7 Mast head Fz M7N

6 Above shrouds junction Mfx M6Mx

5 Under shrouds junction Fz, Mfx, Mfy M5My, M5eL, M5eR

4 Under cross-trees junction Mfx, Mfy M4My, M4Mx

3 Under the parrel Fz, Mfx, Mfy M3My, M3eL, M3eR

2 Mast hole Fz, Mfx, Mfy M2My, M2eL, M2eR

1 Above vangs connection

with the mast

Fz, Mfx, Mfy M1My, M1eL, M1eR

SR, SL Shrouds TL, TR S_SX, S_DX

MS Mast step Fz, Fx FX, FZ

2010 Blackwell Publishing Ltd j Strain (2010) 46, 482492doi: 10.1111/j.1475-1305.2009.00673.x 483

G. Pellicioli and N. Petrone : Experimental Analysis of a Sailing Mast


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(Figure 3) with two couples of strain gauges (#L and

#R) connected as Half bridge and placed exactly on

the cross section principal inertial axis (the neutral

axis of bending moment Mfy). At sections 1, 2, 3 and

5 both lateral bending moment and axial load were

measured, by means of lateral strain gauges #L and

#R in a three wires Quarter bridge configuration.

Assuming a linear elastic behaviour it was possible to

calculate lateral bending moment Mfx from the Left/

Right strain values difference and normal stress N

from the strain values average. Quarter bridges were

adopted to reduce the overall number of strain gau-

ges applied on the mast, and the three wire connec-

tion allowed for temperature compensation: for the

purpose of this work this approach was considered

effective for estimating the axial load trend across the

mast on the basis of the channels laboratory cali-

bration in bending and axial loads. On the other

hand, the axial load was measured with a Full

Wheatstone bridge at all sections where it was con-

sidered fundamental (at the mast head section 7 andat mast step).

To prevent damages or short circuit on the mea-

suring system, all strain gauges and their connectionswere insulated with silicone.

Mfx

6

5

4

3

Z

Y

2

1

Figure 2: Sketch of the lateral bending moments Mfx at thecorresponding measuring sections

Mfy

5

4

3

2

1

Z

X

Figure 3: Sketch of the longitudinal bending moments Mfy at

the corresponding measuring sections

3

L RCentroid

24

Y

X

1

Figure 4: Main cross section of the mast with indication of the

strain gauges positions


Experimental Analysis of a Sailing Mast : G. Pellicioli and N. Petrone


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Shrouds and mast step

Shrouds tension was measured with four strain gaugesconnected as Full bridge, installed directly applied

in correspondence of the chain-plates as shown in

Figure 5 and calibrated on a servohydraulic test

machine in tension. This ensured the possibility of

measuring loads without changing some important

parameters such as the length and stiffness of the

shroud, by preserving the possibility of fine tuning

given by different pin positions at the chain-plate.

For the measurement of loads at the mast step, a two

component load cell (Figure 6) was specifically de-

signed and calibrated. It consists in a stainless steel

block that was CNC machined in order to match

upwards with the mast step stud and downwards with

the standard connection rail fixed to the sailboat hull.

Themast step stud was hosted in the elongated hole of

anupperplateconnectedtothelowerplatebymeansof

two horizontal lamina (measuring the vertical load Fz)

andtwoverticallamina(measuringthehorizontalload

Fx). On each pair of laminas, four strain gauges con-

nectedasFullbridgeswereproperlyplacedtoobtainthe

two decoupled FX, FZ force channels [3]: strain gauges

measuringdeformation zduetoFZforcewereplacedat

the most external part of the upper and lower faces of

the horizontal laminas and strain gauges measuring zduetoFXforcewereplacedatthelowerpartoftheinner

and outer faces of the vertical laminas (Figure 7).

Data acquisition systems

A Somat 2300 CC data acquisition system was used

for data collection both during laboratory and sailing

tests: the system can record 16 strain channels and 16

Figure 5: Instrumented chain-plate at the left shroud

Figure 6: Top-side view of the instrumented load cell at the

mast step

Fz

Fx

x

MN

MX

XZ

Z

e1 = ez

e2 = ez

e3 = ez

e4 = ez

e7 = eze6 = eze5 = eze8 = ez

Figure 7: Placement of sensing strain gauges for FZ and FX Full bridges on the mast step load cell




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analog channels. Sampling rate of 40 Hz and 500 Hz

per channel were used respectively during laboratory

and sailing tests.

An inertial platform MTi Xsens (miniature Attitude

and Heading Reference System AHRS) was applied at

the mast hole for measuring the boat orientation

during sailing, synchronously connected to the Somat

2300 system: the boat roll, pitch andyaw anglesduringsailing were therefore available and allowed to recog-

nise the different point of sailing during a sailing

session. The sailing test was entirely filmed also via

commercial video camera from a motorboat.

Methods

Calibration tests

All measuring systems were calibrated in the labora-

tory. Strain gauge bridges installed on the mast were

calibrated with several static tests after applying canti-lever loads in the two bending planes at each sections.

Bythismethod,calibrationconstantsexpressedinNm/

mV/V were obtained at each mast section. These values

were used during data analysis to estimate bending

moments Mfx, Mfy and axial load N from the bridge

voltage output during the measurement tests [3].

The two chain-plates mounted on the shrouds were

calibrated on a servohydraulic machine at each po-

sition of the pin in the plate.

The mast step load cell was calibrated on a labora-

tory rig reproducing the bottom rail on a BERTECforceplatform fixed to the ground and the mast step stud for

load application with servohydraulic cylinders.

Full scale laboratory tests

In order to assess the complete system reliability

before putting to sea for the sailing tests, a restraint

system similar for dimensions and disposition to the

mast hole and the shrouds connections existing on

the 420 was accurately reproduced on a laboratory

bench. During the laboratory tests a BERTEC dyna-

mometric platform was used to measure forces Fx and

Fz acting at mast step and validate measurement

coming from the mast step load cell.

The laboratory tests aimed to reproduce the normal

procedure of boat manning and to evaluate the pureeffect of a man hanging on the trapeze. In particular,

several states were recorded in sequence correspond-

ing to typical rigging and manning states:

state A: jib joisted from resting state;

state B: from state A, applying loads at the

mainsail halyard;

state C: from state A, man of 75 kg at the right

trapeze;

state D: from state A, man of 75 kg at the left

trapeze.

The different states were maintained for at least 10 s

in order to stabilise and clearly distinguish the load-

ing configurations: each state was also repeated at

least three times to allow for estimating correspond-

ing average values.

Sailing tests

Navigation tests were performed in the Adriatic

sea with medium/strong wind conditions (about

68 m s)1), under expert coaching. The acquisition

system was positioned with its battery close to the

mast step into a protective case: the additional mass

of the data acquisition system with cables and battery

was around 10 kg.

Before putting out to sea, an important measure-

ment of the rigging state was made. This state was

named A being equivalent of state A simulated dur-

ing the laboratory tests (jib hoisted).

M N O P Q R

1908.55Time (s)0

Figure 8: Schematic overview of a navigation test lasted about 30 min. The red plot is a qualitative representation of yaw signalcoming from the inertial platform




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Several training and regatta operations (Figure 8)

were made with two expert sailors of total mass

135 kg. During this test the sailboat:

sailed close to the wind on starboard tack (M and

O) and on port tack (N and P) with bowman

(80 kg) at the trapeze;

sailed beam reach with the spinnaker on porttack (Q) and on starboard tack (R);

made several tacking and jibing between differ-

ent point of sailing.

Data analysis

Data collected from the strain signals were subse-

quently analysed introducing the static calibration

constants: bending moments Mfx, Mfy and axial load

N were calculated by direct linear transformation and

plotted on diagrams having the vertical axis coinci-dent with the Z coordinate along the mast and the

horizontal axis corresponding to the bending

moments under evaluation. It is worth noting that

the Mfx bending moment diagram will be plotted on

the side of fibres in tension, that means looking

at the sailboat mast from bow to aft (in the negative

X axis direction): likewise, the Mfy bending moment

diagrams will lay on the side of fibres in tension as if

looking at the boat from right to left (in the positive

Y axis direction).

Results

One of the major objectives of the work was to obtain

the bending moment diagrams in the longitudinal

and lateral planes corresponding to fundamental

states from the rigging action and the sailing events:

the results will then be presented in terms of plots

obtained from laboratory and sailing tests, high-

lighting noticeable differences to be further

addressed in the discussion.

Laboratory tests

A bent state of the mast in the lateral plane resulted

evident during state A (Figure 9), despite the maxi-

mum care in the rigging setup. In the further states

analysis, the subsequent additional bending

moments due to the man on a trapeze were referred

6

5

4

3

Z-coordinate(m)

2

1

06000 4000 2000 2000 4000

Axial load (C)

Axial load (A)

60000(N)

Figure 9: Results of laboratory tests. Values of the structural

bending moments along the mast axis in different states

170

240

130

130

180

120

180

3200 State M State N 426Time (s)

260M2Mx

(Nm)

M3Mx

(Nm)

M4Mx

(Nm)

M5Mx

(Nm)

M6Mx(Nm)

220

Figure 10: Results of laboratory tests. Diagram of lateral bending moments with man on the right (C) or left (D) trapeze




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to the state A bending diagram as a baseline. These

additional bending moments were named Mfx* and

showed a high degree of symmetry as expected

(Figure 10).

Highest peak values of bending moments Mfy onthe longitudinal plane were recorded in correspon-

dence of section 4 (Figure 9): the shift from state (A)

to the other two states of man on the right (C) and on

the left trapeze (D) causes small changes. On the

other plane, the effect of the trapeze on the lateral

bending moment Mfx* is much more evident

(Figure 10).

The differences between the longitudinal and

lateral bending moments are appreciable both in

terms of absolute values of peaks of bending

moments (Mfy peaks are more than twice higher than

Mfx peaks) and of location of peaks: section 4

experiences maximum longitudinal bending, section

2 experiences maximum lateral bending.

Shrouds tension loads recorded in state A were

1674 N at the right and 1190 N at the left side,

confirming an asymmetric mast rigging state. The

axial load curve along the mast axis had a maxi-

mum values between the shrouds connection and

the mast hole and showed the comparison of

additional loads due to the man on the trapeze

(Figure 11). In this last condition, the maximum

values of forces at the mast step, Fz =)

5090 N andFx = 370 N, were recorded.

Sailing tests

After sailing tests, strain data were again convertedby means of the calibration constants into bending

moments Mfx, Mfy and axial load N and studied in

the time domain. Due to the maximum available

number of 16 channels, the two quarter bridge

channels named M1eL and M1eR were not recorded

so that the lateral bending moment Mfx and the

axial load N at section 1 were only linearly esti-

mated from the values of the adjacent sections.

Moreover, some data at section 3 of moment Mfywere showing unrealistic patterns: the correspond-

ing values were linearly interpolated from the

adjacent sections 2 and 4.

The strain signal showed consistently a stable

mean value for each sailing state with a variable

superimposed oscillating signal due to the sea waves

and the wind gusts (Figure 12).

Considering the aim of the study, oriented to an

evaluation of steady state loading conditions, the

measured data were averaged over all the time

interval corresponding to a certain state: the mean

values of bending moments along the mast are

collected in Tables 2 and 3 with the corresponding

standard deviations. The bending moment curves ofmean values are presented in Figures 13 to 16.

6

5

4

3

Z-coordinate(m)

2

1

0250 150200 50100 15010050 200

Mx (A)

My (C)

My (A)

My (D)

2500(Nm)

Figure 11: Results of laboratory tests. Diagram of axial load

6

5

4

3

Z-coordinate(m)

2

1

0250 150200 50100 15010050 200

Mfx* (C)

Mfx* (D)

2500(Nm)

Figure 12: Example plots of the time series of five channels

from the strain measurements, showing the transition between

state M and N due to a tacking manoeuvre




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The first significant result from sailing test was the

correspondence of state A (Figure 13) with state A of

laboratory test (Figure 9), mainly in terms of Mfy: also

the Mfx curve from sailing tests is very similar to the

Mfx curve in the laboratory tests but much more

closer to the vertical axis in the case of sailing tests.

This was interpreted as due to a much more realistic

rigging state than in the laboratory simulation, to-

gether with a more accurate setup procedure followed

in the sailing session under the supervision of an

expert coach.

During sailing, the six significant sailing states

from letter M to letter R (Figure 8) were analysed, but

for the present discussion structural loads of only

three significant sailing states M, N, Q have beenplotted (Figures 14, 15 and 16).

The second evident result is the high negative peak

values of Mfy at sections 1 and 2 in state M (Fig-

ure 14), that is very different from Mfy in state A and

A (Figures 9 and 13): this is correlated with the ten-

sioning of the vang, acting between the boom and

the mast, that was not present neither in the labo-

ratory tests nor in the state A. The particular vang

configuration showed an unexpected major influence

on the mast stress condition, that should be consid-

ered both in the planning stage of an experimental

measurement and in the mast design.

A third evident difference between laboratory

(Figure 10) and sailing tests (Figures 1415) can be

observed in the Mfx diagrams with a man on the

trapeze: during sailing tests the effect of thewind clearly modifies moment diagrams: this is

Table 2: Lateral bending moments during sailing

Mfx (Nm)

Close to the wind Beam reach with spinnaker

On starboard tack (M)

(Wind angle = )35)

(Dt = 178 s)

On port tack (N)

(Wind angle = +35)

(Dt = 248 s)

On port tack (Q)

(Wind angle = +130)

(Dt = 447 s)

On starboard tack (R)

(Wind an-

gle = )140)

(Dt = 334 s)

Section Mean SD Mean SD Mean SD Mean SD

Mfx_7* 0.0 n.d. 0.0 n.d. 0.0 n.d. 0.0 n.d.

Mfx_6 )131.0 10.8 145.9 14.5 124.7 22.6 )97.7 17.8

Mfx_5 76.2 9.1 )97.1 12.0 )102.1 20.0 64.2 15.4

Mfx_4 23.8 17.5 )54.6 16.0 38.0 22.0 )3.9 19.3

Mfx_3 103.8 13.5 )41.0 16.7 15.7 23.6 99.6 20.4

Mfx_2 )5.0 29.5 13.1 29.4 124.4 37.6 )56.5 36.1

Mfx_1* )2.4 n.d. 6.4 n.d. 60.9 n.d. )27.6 n.d.

Mfx_0* 0.0 n.d. 0.0 n.d. 0.0 n.d. 0.0 n.d.

*Theoretically assumed values; Standard Deviations are not defined (n.d.).

Table 3: Longitudinal bending moments during sailing

Mfy (Nm)

Close to the wind Beam reach with spinnaker

On starboard tack (M)

(Wind angle = )35)

(Dt = 178 s)

On port tack (N)

(Wind angle = +35)

(Dt = 248 s)

On port tack (Q)

(Wind an-

gle = +130)

(Dt = 447 s)

On starboard tack (R)

(Wind angle = )140)

(Dt = 334 s)

Section Mean SD Mean SD Mean SD Mean SD

Mfy_7* 0.0 n.d. 0.0 n.d. 0.0 n.d. 0.0 n.d.

Mfy_6* 61.4 n.d. 64.3 n.d. 4.0 n.d. 14.7 n.d.

Mfy_5 71.9 14.2 75.3 10.5 4.7 10.9 17.2 11.0Mfy_4 205.2 20.1 214.9 16.7 204.8 21.3 204.8 23.2

Mfy_3* )102.6 n.d. )102.8 n.d. 2.6 n.d. )45.2 n.d.

Mfy_2 )225.0 19.0 )229.3 29.0 )77.8 32.3 )144.7 35.8

Mfy_1 )224.2 27.1 )228.1 10.5 )94.0 20.6 )127.7 22.9

Mfy_0* 0.0 n.d. 0.0 n.d. 0.0 n.d. 0.0 n.d.

*Theoretically assumed values; Standard Deviations are not defined (n.d.).




9/11

particularly evident at the mast head where the lat-

eral bending is due only to the wind pressure on themainsail.

Finally, when the point of sailing changes from M

(Figure 14) to N (Figure 15), the angle between thewind and the boat changes almost symmetrically and

6

5

4

3

Z-coordinate(m)

2

1

0250 150200 50100 15010050 200

My (A)

Mx (A)

2500(Nm)

Figure 13: Results of sailing tests. Diagram of lateral and lon-

gitudinal bending moments after hoisting the jib

6

5

4

3

Z-coordinate(m)

2

1

0250 150200 50100 15010050 200

Mx (M)

My (M)

2500(Nm)


gitudinal bending moments sailing close to the wind on star-

board tack (state M)

6

5

4

3

Z-coordinate(m)

2

1

0250 150200 50100 15010050 200

Mx (N)

My (N)

2500(Nm)


gitudinal bending moments sailing close to the wind on port

tack (state N)

6

5

4

3

Z-coordinate(m)

2

1

0250 150200 50100 15010050 200

Mx (Q)

My (Q)

2500(Nm)


gitudinal bending moments sailing beam reach on port tack

(state Q)




10/11

the two diagrams of Mfx show almost symmetric

changes in the curves, as expected. Major differences

are evident when state Q (Figure 16) is compared

with state N: in this case, state Q corresponds to the

hoisting of the spinnaker and the surging of the vang

that justify the great changes in the longitudinalbending moment diagrams both at the mast head

and at the mast step. On the other plane, the lateral

bending moment Mfx shows changes due to the effect

of the different mainsail orientation and the spin-

naker boom connected to the mast.

The values of shroud loads in the different points

of sailing (Figure 17) are justified by the upwind or

downwind position of each shroud during starboard

(M, O, R) and port tack (N, P, Q): sailing beam reach

gives highest tension values as expected due to the aft

wind sailing and the presence of the spinnaker.

Discussion

The rationale of the work was the development of an

experimental method to measure the bending and

axial loads acting on the mast and shrouds of a sail-

boat during sailing: this would allows the collection

of significant structural load data, useful for an opti-

mised design of innovative masts and hulls.

A first limitation of the present work can be found in

the maximum number of 16 synchronous strainchannels recorded during the tests; another limitation

is that reported results refer to a single sailing session,

with specific crew, wind and sea conditions. Further

activities such as the adoption of improved hardware

and the planning of additional sailing sessions will

help in overcoming the mentioned limitations.

Full scale laboratory tests were useful to analyse the

structural behaviour of the mast under simulated

realistic rigging conditions; further, these tests were

necessary to make the calibration procedures and to

check the measuring systems reliability. Results of

laboratory tests were important for a comparison

with corresponding data from sailing tests in order to

evaluate the effects of a correct simulated rigging

setup and the variation of the bending moment

diagrams due to the wind effect.

In sailing tests, the adopted approach to measure

the loading conditions on the mast was suitable to

give sufficiently reliable data that were not available

before to our knowledge for this class of sailboats.The bending moment diagrams in the longitudinal

plane (My) and the lateral plane (Mx) corresponding

to average values of steady states can be considered as

the main outcome of the work, both in terms of

average values and of data variability.

Several engineering analysis can be addressed and

carried out on the basis of the collected data, such as

(i) the estimation of the mast deflection line from the

combination of mast stiffness and bending diagrams,

(ii) the evaluation of mast safety factors with respect

to peak values in the two planes, (iii) the evaluationof mast axial behaviour and eulerian critical safety

factors, (iv) the analysis and redesign of the overall

hull structure, using the experimental data as load

conditions at the mast step and standing rigging

connections of a numerical model and (v) the local

hull strength verification at the shrouds fixation

points and at the mast step.

Conclusions

An instrumented mast developed for both laboratory

and sailing tests was used in combination with strain

gauged standing rigging components at the shrouds

and the mast step. After a first session of laboratory

tests when rigging loads were measured, strain data

were collected at seven mast sections during real

sailing with medium/strong wind in different point

of sailing.

The data were analysed to obtain the bending

moments along the mast in the lateral and longitu-

dinal planes as average values over steady states of

sailing either close to the wind or beam reach: lon-gitudinal and lateral bending moments were plotted

along the mast length. Highest values of lateral

bending (146 14.5 Nm) were recorded at the mast

head, whereas longitudinal bending showed highest

values at the vang connection to the mast

(229 29 Nm). Shrouds highest tension value of

2887 167 N was recorded during beam reach sail-

ing with spinnaker.

The collected data shall allow the sailboat designers

to improve the masts cross section profile and its

material selection or to perform the validation of

numerical models. Moreover, the accurate knowledge

3500

3000

2500

1500

500

0M N O P

Right shroud

2439

18432010

22752356

1924

2212

1998

2372

2746

2887

2230

Left shroud

Point of sailing

Shroudtension(N)

Q R

2000

1000

Figure 17: Results of sailing tests. Variation of the shroud

loads during sailing




11/11

of loads actingon thestanding rigging andon the mast

step will support an optimised design of theboat shell.

ACKNOWLEDGEMENTS

Compagnia della Vela Yacht Club (Venice, Italy); Super

Spars (Fareham, New Hampshire, England); Dr. Renato

Pellicioli.

REFERENCES

1. Bottacin, G., Meneghetti, G., Quaresimin, M. and Zordan,

A. (2004) Analysis and testing of a new composite sailing mast.

By Sea, Milano.

2. Dalley, J. W., Riley, W. F. and Meconnel, K. G. (1999)

Instrumentation for Engineering Measurement. John Wiley & S,

Hoboken.

3. Pellicioli, G. and Petrone, N. (2008) Acquisition of struc-

tural loads acting on the mast of a 420 during sailing. Pro-

ceedings of 7th International Conference on the Engineering of

Sport, Biarritz, 26 June 2008, Vol. 2, 499508, Springer.

ISBN 978-2-287-09412-5.



Carichi su albero

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