Performance of In-Hull Transducers in Fiberglass Hulls

In-Hull Transducers and Fiberglass Hull Thickness

•Performance of in-hull transducers like the M260 and R199 varies with hull thickness and operating frequency. There is no maximum allowable hull thickness.

•The optimum combination of hull thickness and operating frequency offers deeper target detection. The difference in depth detection can be up to 11% at 50 kHz and 7% at 200 kHz.

• Alternately, for a given hull thickness there will be one or more optimum operating frequencies to achieve maximum target detection.

• Broadband transducers offer the capability of tuning the sonar frequency to minimize transmission losses through the hull

• A sounder, using a broadband transducer, could be programmed to perform automatic tuning to find the optimum frequencies.

In-Hull Transducers and Fiberglass Hull Thickness

Transmission losses through the hull are due to two factors:

1. Absorption of the ultrasonic energy by the fiberglass hull. The thicker the hull, the greater the absorption.

2. “Impedance mismatch”:the thickness of the hull in wavelengths at the operating frequencies can cause transmission loss and shift the transducer frequency

– For hull thicknesses of 1/4, 3/4, 5/4, etc…, hull losses due to impedance mismatch will be lowest

– For hull thicknesses of 1/2, 1 and 1.5 wavelengths, losses will be highest.

– For a hull thickness (in wavelengths) that is not 1/4, 3/4, 5/4, etc…, the operating frequency of the transducer will be shifted.

In-Hull Transducers and Fiberglass Hull Thickness

M260 Specifications No Fiberglass

50 kHz 200 kHz

The following graphs show the loss and frequency shift when an in-hull transducer is transmitting through:

• No Fiberglass• 3/8” Fiberglass• 1/2” Fiberglass• 3/4” Fiberglass• 1” Fiberglass

• Note: In Hull transducers will not work with cored fiberglass, wood, or aluminum hulls due to excessive signal loss.

In-Hull Transducers and Fiberglass Hull Thickness

155

156

157

158

159

160

161

162

163

164

0" FIBERGLASS 3/8" FIBERGLASS 1/2" FIBERGLASS 3/4" FIBERGLASS 1" FIBERGLASS

HULL THICKNESS

TVR

(dB

)

0% Loss in Range

10% Loss in Range

5% Loss in Range

3% Loss in Range

7% Loss in Range

M260 50 kHz TVR CHANGE(RANGE LOSS)vs. HULL THICKNESS

40

42

44

46

48

50

52

54

56

0" FIBERGLASS 3/8" FIBERGLASS 1/2" FIBERGLASS 3/4" FIBERGLASS 1" FIBERGLASS

HULL THICKNESS

kHz

M260 50 kHz FREQUENCY SHIFTvs. HULL THICKNESS

50 kHz

53.5 kHz

51 kHz

53 kHz

45.5 kHz

M260 Max depth @ 50 kHz 1kW Input power

• No fiberglass- 3333’ (1015m)• 3/8” fiberglass- 3100’ (944m)• ½” fiberglass- 2850’ (868m)• ¾” fiberglass- 3190’ (972m)• 1” fiberglass- 3000’ (914m)

164

165

166

167

168

169

170

171

172

0" FIBERGLASS 3/8" FIBERGLASS 1/2" FIBERGLASS 3/4" FIBERGLASS 1" FIBERGLASS

HULL THICKNESS

TVR

, (dB

)

7% Loss in Range

3% Loss in Range

5% Loss in Range

4% Loss in Range

0% Loss in Range

M260 200 kHz TVR CHANGE & RANGE LOSSvs. HULL THICKNESS

M260 200 kHz FREQUENCY SHIFT vs. HULL THICKNESS

180

185

190

195

200

205

210

215

0" FIBERGLASS 3/8" FIBERGLASS 1/2" FIBERGLASS 3/4" FIBERGLASS 1" FIBERGLASS

HULL THICKNESS

kHz

200 kHz

210 kHz

190 kHz

210 kHz

191 kHz

M260 Max depth @ 200 kHz 1kW Input Power • No fiberglass- 1305’ (397m)• 3/8” fiberglass- 1165’(355m) • ½” fiberglass- 1255’ (382m) • ¾” fiberglass- 1200’ (365m) • 1” fiberglass- 1225’ (373m)

50kHz Maximum Depth RangeM260 In-Hull - 1kW Input Power

500 1000 1500 2000 2500 3000 3500 4000

0

20

40

60

80

100

120

Depth, feet

Sig

nal E

xces

s, d

B

50 k Hz Thru Hull Range B ehavior

no hull3/8" hull1/2" hull3/4" hull1" hull+ 6 dB detec tion thres hold

Area of Detail – (Next Slide)

Maximum Depth Line

Maximum Depth Line

50 kHz Maximum Depth RangeM260 In-Hull - 1kW Input Power

Depending on hull thickness,340 feet of depth sensing(11%) can be gained (or lost)

Maximum Depth Line

200 kHz Maximum Depth RangeM260 In-Hull - 1kW Input Power

200 400 600 800 1000 1200 1400 16000

20

40

60

80

100

120

Depth, feet

Sig

nal E

xces

s, d

B

200 k Hz Thru Hull Range B ehavior

no hull3/8" hull1/2" hull3/4" hull1" hull+ 6 dB detec t ion thres hold

Area of Detail – (Next Slide)

Maximum Depth Line

Maximum Depth Line

200 kHz Maximum Depth RangeM260 In-Hull - 1kW Input Power

Depending on hull thickness,90 feet of depth sensing (7%) can be gained (or lost)

Maximum Depth Line

R199 2kW Specifications No Fiberglass

50 kHz 200 kHz

200kHz Q = 2 200kHz Q = 4.5No Fiberglass ¾” Fiberglass

Flat response: any frequency between 160 to 240 kHz is an efficient operating frequency

Transmitting through the hull reduces bandwidth and shifts frequency - 180 kHz is now

the best operating frequency

R199 2kW @ 200 kHz

50kHz Q = 3 50kHz Q = 4.1No Fiberglass ¾” Fiberglass

Flat response: any frequency between 46 to 55 kHz is an

efficient operating frequency

Transmitting through the hull reduces bandwidth and shifts

frequency - 43 kHz is now the best operating frequency

R199 2kW @ 50 kHz

• On the high frequency ceramic, the best resonant frequency has shifted to 180 kHz. The bandwidth of the transducer installation is reduced.

• Stated another way, 180 kHz is the best operating frequency. While 200 kHz operation will work well, there will be an 11% loss in range.

• On the low frequency ceramic, the best resonant frequency has shifted to 43 kHz. The bandwidth of the transducer installation is reduced.

• For a 3/4” thick hull, 43 kHz is the best operating frequency. Operating at 50 kHz will result in a range loss of 7%

R199 2kW Summary