Furuno 235DST-MSE, 235DHT-MSE, 235DST-PSE, 235DT-MSE, 235DT-PSE Installation Instructions

INSTALLATION INSTRUCTIONSOWNER’S GUIDE &

Thru-Hull, Depth

Transducer

Low Profile, Flush, and Retractable Models

WARNING: Always wear safety goggles and a dust
mask when installing to avoid personal injury.

WARNING: Immediately check for leaks when the
boat is placed in the water. Do not leave the boat
unchecked for more than three hours. Even a small

17-006-01 rev. 11 01/26/11

leak may allow considerable water to accumulate.

WARNING: Retractable models—The O-rings must
be intact and well lubricated to make a watertight seal.

WARNING: Retractable models—Always attach the
safety wire to prevent the insert or blanking plug from
backing out in the unlikely event that the cap nut fails
or is screwed on incorrectly.

WARNING: B117 and P319—Do not use the spacer
if there is insufficient space to tighten the nut or it is
within 11mm (1/2") of the top of the housing.

WARNING: Stainless steel housing in metal hull—
Be sure the washer contacts the hull. Do not tighten
the hull nut with the washer against the isolation
bushing, as the housing will not be firmly installed. If
necessary, sand the isolation bushing until the washer
rests against the hull.

CAUTION: Never pull, carry, or hold the transducer by
its cable; this may sever internal connections.

CAUTION: Never use solvents. Cleaners, fuel,
sealants, paint, and other products may contain strong
solvents, such as acetone, which attack many
plastics, greatly reducing their strength.

CAUTION: Plastic housing—Never use a fairing with
a plastic housing; the protruding sensor would be
vulnerable to damage from impact.

CAUTION: Metal housing—Never install a metal
housing on a vessel with a positive ground system.

CAUTION: Stainless steel housing in metal hull—
Stainless steel must be isolated from a metal hull to
prevent electrolytic corrosion. Use the isolation
bushing supplied.

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

Record the information found on the cable tag for future reference.

Part No._________________Date___________Frequency________kHz

low profile
P319

retractable
low profile
B17

flush
P219

Applications

• Plastic housing recommended for fiberglass or metal hull only.

Never install a plastic transducer in a wood hull, since swelling
of the wood can possibly fracture the plastic.

• Bronze housing recommended for fiberglass or wood hull.
Never install a bronze housing in an aluminum hull, because
electrolytic corrosion will occur.

• Stainless steel housing compatible with all hull materials.
Recommended for aluminum hull to prevent electrolytic corrosion

provided the stainless steel housing is isolated from the metal hull.

• Accommodates up to a 20° deadrise angle.

Tools & Materials

Safety goggles
Dust mask
Electric drill with 10mm (3/8") or larger chuck capacity
Drill bit: 3mm or 1/8"
Hole saw (see table opposite)
Countersink tool (installing a flush housing)
Sandpaper
Mild household detergent or weak solvent (such as alcohol)
File (installation in a metal hull)
Marine sealant (suitable for below waterline)
Additional washer [for aluminum hull less than 6mm (1/4") thick]
Slip-joint pliers (installing a metal housing)
Grommet(s) (some installations)
Cable ties
Water-based anti-fouling paint (mandatory in salt water)
Installation in a cored fiberglass hull (see page 4):

Hole saw for hull interior: (see table on this page)
Fiberglass cloth and resin
or Cylinder, wax, tape, and casting epoxy

Identify Your Model

The model name is printed on the cable tag.

Model

(Housing)

Low Profile:
B22, B117,
P19, P319

P5 161mm 6-3/8”) 51 mm or 2" 60 mm or 2-3/8"

Flush:
B21, P219, P269

Retractable:
B17, B21
P17, P217, P314

Retractable:
SS577

Minimum

Headroom

95 mm (3-3/4") 51 mm or 2" 60 mm or 2-3/8"

100 mm (4") 51 mm or 2" 60 mm or 2-3/8"

200 mm (8") 51 mm or 2" 60 mm or 2-3/8"

200 mm (8")

Outside Hull

Hole Saw Size

51 mm or 2"

in a fiberglass or
wood hull

57 mm or 2-1/4"

in a metal hull

Cored Fiberglass Hull

Hull Interior

Hole Saw Size

60 mm or 2-3/8"

large displacement hulls

outboard and I/O

fin keel sailboats

planing hulls

small displacement hulls

stepped hull

Installation

Hole Drilling

Cored fiberglass hull—Follow separate instructions on page 4.

1. Drill a 3 mm or 1/8" pilot hole from inside the hull. If there is a rib,
strut, or other hull irregularity near the selected mounting
location, drill from the outside.

2. Using the appropriate size outside hull hole saw, cut a hole
perpendicular to the hull from outside the boat (see table on page 1).
Flush housing—Use a countersink tool to make a “seat” in the hull.

3. Sand and clean the area around the hole, inside and outside, to
ensure that the marine 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.
Metal hull—Remove all burrs with a file and sandpaper.

full keel sailboats

Figure 1.

Best location for transducer

Copyright © 2005 Airmar Technolog y Corp.

Mounting Location

CAUTION: Do not mount near water intake or discharge openings

or behind strakes, fittings, or hull irregularities.

• The water flowing under the hull must be smooth with a
minimum of bubbles and turbulence (especially at high speeds).

• The transducer must be continuously immersed in water.

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

• Choose a location away from interference caused by power and
radiation sources such as: the propeller(s) and shaft(s), other
machinery, other echosounders, and other cables. The lower
the noise level, the higher the echosounder gain setting that
can be used.

• Choose a location with a minimal deadrise angle, so the
transducer beam will be aimed at the bottom.

• Choose an accessible spot inside the vessel with adequate
headroom for the height of the housing, tightening the nuts, and
removing any insert (see the table below).

Hull Types (see Figure 1)

• Displacement hull powerboats—Locate amidships near the
centerline. The starboard side of the hull where the propeller
blades are moving downward is preferred.

• Planing hull powerboats—Mount well aft, on or near the
centerline, and well inboard of the first set of lifting strakes to
ensure that the transducer will be in contact with the water at
high speeds. The starboard side of the hull where the propeller
blades are moving downward is preferred.

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

installation location and operating results of similar boats before
proceeding.

• Fin keel sailboats—Mount on or near the centerline and
forward of the fin keel 300 – 600 mm (1–2').

• Full keel sailboats—Locate amidships and away from the keel
at the point of minimum deadrise.

2

Bedding

CAUTION; Be sure the surfaces to be bedded are clean and dry.

Apply a 2mm (1/16") thick layer of marine sealant around the
flange of the housing that will contact the hull and up the sidewall
of the housing (see Figure 2). The sealant must extend 6mm
(1/4") higher than the combined thickness of the hull, washer, any
spacer, and the hull nut. This will ensure there is sealant in the
threads to seal the hull and to hold the hull nut securely in place.

Stainless steel housing in a metal hull—The stainless steel
housing must be isolated from the metal hull to prevent electrolytic
corrosion. Slide the isolation bushing onto the housing (see
Figure 3). Apply additional marine sealant to the surfaces of the
bushing that will contact the hull, filling any cavities in and around
the bushing.

Installing

NOTE: Ignore any arrows on the housing, insert, and blanking plug.

1. From outside the hull, push the housing into the mounting hole
using a twisting motion to squeeze out excess marine sealant.

2. From inside the hull, slide the washer onto the housing (see
Figure 2).

B117 and P319—Also slide the spacer onto the housing and
rest it against the washer. Do not use the spacer if there is
insufficient space to tighten the nut or it is within 11 mm (1/2") of
the top of the housing.

Aluminum hull less than 6mm (1/4") thick—If necessary, use
an additional rubbery, fiberglass, or plastic washer. Never use
bronze since electrolytic corrosion will occur. Never use wood
since it will swell, possibly fracturing the plastic housing.

Stainless steel transducer in metal hull—Be sure the washer
contacts the hull. Do not tighten the hull nut with the washer
against the isolation bushing, as the housing will not be firmly
installed. If necessary, sand the isolation bushing until the
washer rests against the hull (see Figure 3).

3. Screw the hull nut in place.
Plastic housing—If your housing has wrenching flats, do not
clamp tightly possibly causing the housing to fracture.

Plastic hull nut—Hand tighten only. Do not over tighten.
Metal hull nut—Tighten with slip-joint pliers.
Cored Fiberglass Hull—Do not over tighten, crushing the hull.
Wood hull—Allow the wood to swell before tightening the hull nut.

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