Furuno 525T-BSC, 525T-BSD Installation Instructions

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OWNER’S GUIDE & INSTALLATION INSTRUCTIONS

Thru-hull Metal Stem Depth Transducer

Models: B39, B45, B46, B49, B240,

B250, B256, B260, SS505

IMPORTANT : Please read these instructions

completely before proceeding with the installation.
These instructions supersede any other instructions in
your instrument manual if they differ.

CAUTION : NEVER USE SOLVENTS

Cleaners, fuels, paint, sealants, and other products may
contain strong solvents, such as acetone, which can attack

17-008-05 rev. 04 12/01

many plastics greatly reducing their strength.

Applications

•

Bronze housing

Caution

electrolytic corrosion will occur.

•

Stainless steel housing

•

Aluminum or steel hull

prevent electrolytic corrosion.

Caution

stainless steel sensor from a metal hull.

•

Caution

positive ground system

: Ne ver mount a bronz e housing in a metal hull, because

: Installation requires using a fairing kit to isolate the

: Never install a metal housing on a vessel with a

Tools and Materials

Fairing (
Digital level
Safety goggles
Dust mask
Band saw
Rasp
Electric drill
Drill bits:

Sandpaper
Mild household detergent
Marine sealant
Slip-joint pliers
Zip-ties
Water-based antifouling paint (
Installation in a cored fiberglass hull: (see page 3)

mandatory for SS505

or

power tool (installation with a fairing)

Pilot hole 3mm
B39, B49 26mm or 1"
B45, B46, SS505 22mm
B240, B250, B260 33mm
B256 30mm

Drill bit for hull interior:
B39, B49 37mm, 38mm,
B45, B46, SS505 35mm
B240, B250, B260 42mm
B256 40mm, 41mm,
Cylinder, wax, tape, and casting epoxy

recommended for fiberglass or wood hulls only.

is compatible with all hull materials.

—Use a stainless steel housing to

.

)

or

bubble level & protractor (installation w/ fairing)

or

hand saw (installation with a fairing)

or

1/8"

7/8"
1-5/16"

or 1-3/16"

weak solvent (alcohol)

mandatory in salt water )

1-1/2"
1-3/8"
1-5/8"

1-5/8"

Record the information found on the cable tag f or future reverence.

Part No._________________Date___________Frequency________kHz

B45

standard fairing

Identify Y our Model

The model name is printed on the cable tag.

Mounting Location

Acoustic Noise

Acoustic noise is always present and these sound waves can
interfere with the operation of the transducer. Background noise
from sources such as: waves, fish, and other vessels cannot be
controlled. However, carefully selecting the transducer mounting
location can minimize the affect of vessel generated noise from
the propeller(s) and shaft(s), other machinery, and other echo­sounders. The lower the noise level, the higher the echosounder
gain setting that can be used.

Placement

Choose a location where:

• The water flowing across the hull is smoothest with a minimum
of bubbles and turbulence (especially at high speeds).

• The transducer will be continuously immersed in water.

• The transducer beam is unobstructed by the keel or propeller
shaft(s).

• There is a minimum deadrise angle.

• There is adequate headroom inside the vessel for the height of
the housing and tightening the nut.

Caution : Do not mount the sensor:

Near water intake or discharge openings
Behind strakes, fittings, or hull irregularities
Behind eroding paint (an indication of turbulence)

Boat Types

•

Displacement hull powerboat —Locate 1/3 aft LWL and

150–300mm (6–12") off the centerline on the side of the hull
where the propeller is moving downward.

•

Planing hull powerboat —Mount well aft, on or near the

centerline, and
insure that the transducer is in contact with the water at high
speeds. Mount on the side of the hull where the propeller is
moving downward.

Outboard and I/O —Mount just forward of the engine(s).
Inboard —Mount well ahead of the propeller(s) and shaft(s).
Step-hull —Mount just ahead of the first step.
Boat capable of speeds above 25kn (29MPH)—Review

sensor location and operating results of similar boats before
proceeding.

•

Fin keel sailboat —Mount to the side of the centerline and

forward of the fin keel 300–600mm (1–2').

•

Full keel sailboat —Locate amidships and away from the keel

at the point of minimum deadrise angle.

(see Figure 1)

well inboard of the first set of lifting strakes to

1/3 aft

LWL

(Load Waterline Length)

outboard and I/O

step-hull

displacement hull

planning hulls

fin keel sailboat

pressure waves

150-300mm
(6-12")

inboard

Hull Thickness

(measured perpendicular to the waterline)

Minimum Maximum Maximum
Model
B39, B49 19mm (
B45 6mm (
B46 19mm (
B240 32mm (1
B250, B256, B26019mm (
SS505 6mm (

Installation

no fairing no fairing with fairing

3

⁄

4

") 98mm (3

1

⁄

4

") 92mm (2

3

⁄

4

") 88mm (3

1

⁄

4

") 152mm (6") 83mm (3

3

⁄

4

") 114mm (4

1

⁄

4

") 104mm (4

7

⁄

8

") 50mm (2")

5

⁄

8

") 50mm (2")

1

⁄

2

") 40mm (1

1

⁄

2

1

⁄

8

") 45mm (1
") 56mm (2

(no fairing or standard fairing only)

5

⁄

8

1

⁄

4

3

⁄

4

1

⁄

4

WARNING : High-speed fairing must be installed following the

Installation Instruction Supplement that comes with the fairing.
The high-speed fairing requires an anti-rotation bolt. Failure to
install the anti-rotation bolt may result in the fairing rotating while
the boat is underway. The effect may be violent movement and
loss of steering. This could result in serious injury or death to
passengers and/or damage to the boat or other property.

Metal hull —The SS505 must be isolated from a metal hull. For

your safety you m ust follo w the Installation Instruction Supplement
provided with the fairing.

Cored fiberglass hull —Follow separate instructions on page 4.
No fairing —If you are installing a transducer without a fairing,

disregard all references to a fairing.

")
")
")
")

full keel sailboat

Figure 1.

Best location for the transducer

About Fairings

Nearly all vessels have some deadrise angle at the mounting
location. If the transducer is mounted directly to the hull, the
sound beam will be tilted off the vertical at the same angle as the
deadrise. A fairing is strongly recommended if the deadrise angle
exceeds 10 °

• Orients the sound beam straight down by mounting the
transducer parallel to the water surface

• Minimizes aerated water flowing over the transducer’s face by
mounting it deeper in the water

Airmar Urethane Fairing

Made of a high impact urethane with an integrated cutting guide,
an Airmar fairing is safer and easier to cut with a band saw and
shape with hand tools than custom fairings. It can be shaped to
accommodate a deadrise angle of up to 25 °
numbers, see “Replacement Parts” on page 4.)

Backing Block

(see Figure 2).

. (For fairing part

Cutting the Fairing

High speed fairing —For your safety it is mandatory to follow the

Installation Instruction Supplement that comes with the fairing.

1.Measure the deadrise angle of the hull at the selected location
using a digital level, or b ubb le le vel and protr actor (see Figure 2)

2.Tilt the band saw table to the measured angle and secure the
cutting fence (see Figure 3).

3.Place the fairing on the table so the cutting guide rests against
the fence. The arrow will be pointing toward you for installation
on the port side and away from you for installation on the
starboard side of the boat (see Figures 3 and 4).

Notice : The ARROW always points forward toward the bow.

(A symmetrical fairing can be oriented either way.) Be sure to
orient the fairing on the band saw so the angle cut matches the
intended side of the hull and not the mirror image.

cable

stem

hull nut

backing block

fairing thickness

6–12mm (1/4–1/2")

Aft View

hull

slope of hull

parallel to
waterline

deadrise
angle

A backing block is mounted inside the hull to provide a level
surface for the hull nut to seat against (see Figure 2). It is
fabricated matching the interior deadrise angle of the boat. After
cutting an Airmar fairing, use the remaining section as the backing
block.

2

marine

standard fairing

sealant

Figure 2. Bedding and installing (B45 with std. fairing shown)

band saw
table

deadrise
angle

arrow end
for installation
on port side

cutting
guide

fence

Figure 3. Cutting the standard fairing

4.The fairing must be between 6–12mm (1/4–1/2") at its thinnest
dimension (see Figure 2).

Warning : Always wear safety goggles and a dust mask.

5.Recheck steps 1 through 4; then cut the fairing.

6.Shape the fairing to the hull as precisely as possible with a rasp
or power tool.

Hole Drilling

Warning : Always wear safety goggles and a dust mask.

1.Drill a 3mm or 1/8" pilot hole perpendicular to the waterline from
inside the hull (see Figure 2). If there is a rib, strut or other hull
irregularity near the selected mounting location, drill from the
outside. (If the pilot hole is drilled in the wrong location, drill a
second hole in a better location. Apply masking tape to the
outside of the hull over the incorrect hole and fill it with epoxy.)

2.Using the appropriate drill bit, cut a hole from outside the hull.

Be sure to hold the drill plumb, so the hole will be perpendicular

to the water surface.

3.Sand and clean the area around the hole, inside and outside, to
ensure that the sealant will adhere properly to the hull. If there
is any petroleum residue inside the hull, remove it with either a
mild household detergent or a weak solvent (alcohol) before
sanding.

Bedding

Caution : Never pull, carry, or hold the transducer by the cable as

this may sever internal connections.

1.Thread the transducer cable through the fairing (if used).

2.Apply a 2mm (1/16") thick layer of marine sealant around the
sides of the housing that will contact the fairing (or hull if no
fairing is used). Apply a 2mm (1/16") thick layer of marine
sealant to the stem of the housing, 6mm (1/4") higher than the
combined thickness of the fairing, hull, backing block, and hull
nut. This will ensure that there is marine sealant in the threads
to seal the hull and hold the hull nut securely in place.

3.If a fairing is used, seat the transducer firmly in/against the
fairing with a pushing twisting motion (see Figures 2 or 5).

4.Apply a 2mm (1/16") thick layer of marine sealant to the surface
of the fairing that will contact the hull.

5.Apply a 2mm (1/16") thick layer of marine sealant to the surface
of the backing block that will contact the hull

Installing

1.From outside the boat, thread the cable through the mounting hole.

2.With the fairing in place and arrow facing forward toward the bo w
(if used), push the stem of the transducer into the mounting hole.
(A symmetrical fairing can be oriented either way.) Squeeze out
any excess sealant.

the centerline of the boat

3.From inside the hull, slide the backing block (if used) and hull
nut onto the cable. Seat the backing block against the hull.
Screw the hull nut in place and tighten it with slip-joint pliers
(see Figure 2 or 5).

Wood hul l—Allow for the wood to swell.

4.Remove excess marine sealant on the outside of the hull and
fairing to ensure smooth water flow over the transducer.

Caution : If the transducer came with a connector, do not

remove it to ease cable routing. If the cable must be cut and
spliced, use Airmar’s splash-proof Junction Box 33-035 and
follow the instructions provided. Cutting the cable or removing
the connector, except when using Airmar’s junction box, will
void the warranty.

5.Route the cable to the instrument being carefu l not to tear the
cable jacket when passing it through the bulkhead and other
parts of the boat. To reduce electrical interference, separate the
transducer cable from other electrical wiring and the engine.
Coil any excess cable and secure it in place with zip-ties to
prevent damage.

6.Refer to the instrument owner’s manual to connect the
transducer to the instrument.

hull nut

backing
block

hull

fairing

marine
sealant

Figure 5. Bedding and installing (B240 with std. fairing shown)

T ake care to align the assembly parallel to

(see Figure 4).

stem

BOW ➤

std. fairing std. fairing std. fairing std. fairing

B45 B250, B260B240B39 B46 B256

(symmetrical)

B49

std. fairing

(symmetrical)

std. fairing std. fairing

Figure 4. Transducer and fairing orientation

SS505

std. fairing

BOW ➤

3

Checking for Leaks

Warning : Ne ver install a thru-hull transducer and lea ve the boat in

the water unchecked for several days.

When the boat is placed in the water, immediately check around
the thru-hull transducer for leaks. Note that very small leaks may
not be readily observed. It is best not to leave the boat in the
water for more than 3 hours before checking it again. If there is a
small leak, there may be considerable bilge water accumulation
after 24 hours. If a leak is observed, repeat “Bedding” and
“Installing” on page 3

immediately .

Preparing a Cored Fiberglass Hull

The core (wood or foam) must be cut and sealed carefully. The
core

must be protected from water seepage, and the hull must be

reinforced to prevent it from crushing under the hull nut allowing
the housing to become loose.

Warning : Always wear safety goggles and a dust mask.

1.Drill a 3mm or 1/8" pilot hole perpendicular to the waterline from
inside the hull (see Figure 6). If there is a rib, strut, or other hull
irregularity near the selected mounting location, drill from the
outside. (If the hole is drilled in the wrong location, drill a second
hole in a better location. Apply masking tape to the outside of the
hull over the incorrect hole and fill it with epoxy.)

2.Using the appropriate drill bit, cut a hole from outside the hull
through the
the hole will be perpendicular to the water surface.

3.The optimal interior hole diameter is affected by the hull’s
thickness and deadrise angle. It must be large enough in
diameter to allow the core to be completely sealed.

Using the appropriate drill bit for the hull interior, cut through the

inner skin and most of the core from inside the hull keeping the

drill perpendicular to the hull. The core material can be v ery soft.
Apply only light pressure to the drill bit after cutting through the

inner skin to avoid accidentally cutting the outer skin.

4.Remove the plug of core material so the
and the inner core of the hull is fully exposed. Sand and clean
the inner skin, core, and the outer skin around the hole.

outer skin only. Be sure to hold the drill plumb, so

inside of the outer skin

dimension equal to
the thickness of the
hull’s outer skin to
ensure adequate
clearance

pour in
casting
epoxy

hull

solid or hollow
cylinder

inner skin

core

outer skin

Caution : Completely seal the hull to prevent water seepage

into the core.

5.Coat a hollow or solid cylinder of the correct diameter with wax
and tape it in place. Fill the gap between the cylinder and hull
with casting epoxy. After the epo xy has set, remo v e the cylinder.

6.Sand and clean the area around the hole, inside and outside, to
ensure that the sealant will adhere properly to the hull. If there
is any petroleum residue inside the hull, remove it with either
mild household detergent or a weak solvent (alcohol) before
sanding.

7.Proceed with “Bedding” and “Installing” on page 3.

Antifouling Paint

Surfaces exposed to salt water must
be coated with antifouling paint (see
Figure 7). Use
antifouling paint only.
ketone-based paint since ketones
can attack many plastics possibly
damaging the transducer. Reapply
antifouling paint ev ery 6 months or at
the beginning of each boating
season.

Maintenance ,

Aquatic growth can accumulate rapidly on the transducer’s
surface reducing its performance within weeks. Clean the surface
with a soft cloth and mild household detergent. If f ouling is se v ere,
use a stiff brush or putty knife to remove the gro wth taking care to
avoid making scratches. Wet sanding is permissible with fine
grade wet/dry paper.

Replacement Parts

Lost, broken, and worn parts should be replaced immediately and
can be obtained through your marine dealer or instrument
manufacturer.

Model
B39 02-222 33-162 (standard)
B45 02-031-3 33-351-01 (standard)

B46 02-031-3 33-020 (standard)
B49 02-222 33-032 (standard)

B240 02-036-2 33-146 (standard)
B250, B260 02-036-2 33-030 (standard)
B256 02-222-03 33-226-01 (standard)

B260 02-036-2 33-391-01 (high-speed)
SS505 02-111-01 33-355-01 (high speed)

Transducer Replacement

The information needed to order a replacement Airmar transducer
is printed on the cable tag.
this tag. When ordering, specify the part number, date, and
frequency in kHz.

water-based

Never use

Figure 7. SS505 shown

Repair, and Replacement

Hull Nut Fairing

33-352-01 (high-speed)
33-359-01 (high-speed)

33-357-01 (high-speed)

Do not

abrade the marking or remove

antifouling paint

Figure 6. Preparing a cored fiberglass hull

AIRMAR

TECHNOLOGY CORPORATION

35 Meadowbrook Drive, Milford, New Hampshire 03055-4613, USA

■

www.airmar.com

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