So,...either not much knowledge about the structures or not much interest in the topic I guess. No response from
Lagoon either!
For the sake of prosterity, this is what I have learnt.
The hull below the waterline is solid glass.
The
engine and sail-drive sit on a hollow fibreglass pod that essentially forms the floor of the
engine compartment extending forward towards the bulkhead and aft beyond the
saildrive. This is glassed into the hull structure. The through hull aperture for the sail drive is via the pod and it extends downward forming the sidewalls and base of the recess seen from below where the leg is fitted.
The top and bottom halves of the sail-drive are bolted into the pod with the
anchoring nuts (stainless) being glassed into the pod itself. The bolts from above are a Cad plated
steel, no doubt to avoid spalling. All OK so long as it remains dry.
There is an upper and lower seal to the
saildrive seaparated by a small space into which the water
sensor is mounted, so as to alert the
skipper to a potential breech that might threaten the vessel. The upper seal is mounted on the leg before fitting to the hull. It is held in place by a metal band that is located internally and out of sight once the halves are joined. It cannot be inspected insitu. This upper or internal seal represents the last line of defense against a failure of the larger lower or outer seal.
Out of the factory the external leg is fitted with a rubberised boot that fits to the recess in the lower curved hull and is designed to assist water flow/turbulence but is not a watertight element. It is generally glued in place. I suspect many are eventually discarded, particularly if they become loose. On my boat, some bright spark, in a former time had decided to screw the boot into place by drilling into the pod base. Unknowingly or otherwise, those holes were too long and created a communication from seawater to the hollow inside of the pod. The boot had long since been discarded by the time I bought the boat, although the holes remained, largely covered by antifoul etc. These I discovered by the appearance of some weaping when the boat was last out.
THe sea water within the pod had not entered the hull of course, but had managed to corrode the drive
anchoring nuts embeded in the pod, which I have had to
core out and reglass/anchor to the pod. A grind back to
gelcoat of the entire area has been required to find all offending holes (and a small crack as well) followed by
restoration of glass, epoxy and antifoul.
In the process, having finally removed the leg, I discovered that the
steel band that fixes the inner seal to the leg had long been broken providing for a very inadequate seal internally. Water from a clean down of the engine had simply run down and around the inadequately sealed top side of the leg and into the space between upper and lower seals, triggering the
alarm. New seal both sides now complete.
What is of concern, I think, is that the integrety of the seals is difficult to determine when in situ. You cannot see the anchoring steel band as it is internal. THe upper seal/looks to be fine and in place, but you really can't tell. Thus, the water detection sensor between the seal is mission critical.
So, the former owners of my boat, likely sailed across the Pacific with their three
children under age 6, in a boat with a failed inner seal, reliant on continued integrety of the outer seal alone. They or others had removed the water sensor for unknown reason, but perhaps because it appeared to give "false" alarms. It wasn't until i fitted new sensors after the last slipping in November that the issue was discovered.
So an expensive execise comes to an end, and I look forward to some sailing....
Cheers.
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