An instrumentation rake assembly comprising: a lead carrier; and a rake tower for immersion in a sensed environment, the rake tower having a base end and an immersed end, the rake tower being capped at the immersed end and mated at the base end to the lead carrier; wherein the rake tower comprises a curved wall oriented along and curved about a longitudinal axis of the rake assembly the curved wall supporting a plurality of probe holders wherein the rake tower is formed of a ceramic material, the lead carrier defines a lead carrier internal passage that is disposed within the lead carrier, that extends along the lead carrier and that is disposed about the longitudinal axis of the rake assembly where the lead carrier is mated to the rake tower, the curved wall of the rake tower having an inner surface that defines a rake tower internal passage that is uncooled and extends along the longitudinal axis of the rake assembly from the immersed end of the rake tower through the base end of the rake tower, the rake tower internal passage is configured for carrying instrumentation within the rake tower internal passage and along the longitudinal axis of the rake assembly from the plurality of probe holders to the lead carrier internal passage, the internal passage of the rake tower and the lead carrier internal passage are sealed from the sensed environment; said instrumentation rake assembly being characterised in that the curved wall defines a lengthwise gap positioned along an access side of the rake tower and oriented parallel to the longitudinal axis, and the lengthwise gap contains a ceramic filler. a lead carrier; and a rake tower for immersion in a sensed environment, the rake tower having a base end and an immersed end, the rake tower being capped at the immersed end and mated at the base end to the lead carrier; wherein the rake tower comprises a curved wall oriented along and curved about a longitudinal axis of the rake assembly the curved wall supporting a plurality of probe holders wherein the rake tower is formed of a ceramic material, the lead carrier defines a lead carrier internal passage that is disposed within the lead carrier, that extends along the lead carrier and that is disposed about the longitudinal axis of the rake assembly where the lead carrier is mated to the rake tower, the curved wall of the rake tower having an inner surface that defines a rake tower internal passage that is uncooled and extends along the longitudinal axis of the rake assembly from the immersed end of the rake tower through the base end of the rake tower, the rake tower internal passage is configured for carrying instrumentation within the rake tower internal passage and along the longitudinal axis of the rake assembly from the plurality of probe holders to the lead carrier internal passage, the internal passage of the rake tower and the lead carrier internal passage are sealed from the sensed environment; said instrumentation rake assembly being characterised in that the curved wall defines a lengthwise gap positioned along an access side of the rake tower and oriented parallel to the longitudinal axis, and the lengthwise gap contains a ceramic filler.