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Old 15-02-2013, 21:11   #1
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Seeking structural details of hull adjacent to the sail drive pod.

I am needing information on the hull structure specifically around the sail-drive pod (Yanmar SD-40) on my 440.

In November the boat came out for antifoul and sail drive maintenence. There were no specific issues with the sail-drives and specifically there was no water in the recess between inner and outer seals (where the water sensor monitors). We did see some persistent weeping of sea water coming from one or two screw holes on the hull curvature just forward of the recess in which the sail-drive sits. The shipwright inspected these and they were covered with epoxy. The bilge, by the way has always been dry. We assumed that the holes in a previous time permitted screw fixation a boot for the drive leg (long since removed) and perhaps the holes were drilled a little too deep into some "space" between the inner and outer fibreglass skins.

Come February and the water alarm to the port sail-drive indicates water in the space between inner and outer seals of the sail-drive. I initially thought that either by age (late 2004 build) or though some drying out with the last haulout, the outer seal had simply failed in an untimely manner.

So the boat come out yesterday and the legs will come off Monday and new seals, no doubt will be fitted, both to the offending port side but prophylactically to the starboard side too.

However, I remain troubled by the former issue and wonder if there is some inter-relationship. For instance, the inter-seal space also includes that hull thickness at the pod mount and any water that might seep though at that point (through the mount thickness) could mimick a seal failure. As a corollary, fixing the seal would then not fix the problem.

So, I am in need of any information the forum might have on the hull structure in and around the pod. I had assumed the hull would be solid below the waterline. Could it have a foam core. How is the mounting frame for the sail drive fixed to the hull and what is its construction. Are there "spaces" in and around this area where water could sit.

I don't want to have to grind back the epoxy, cut a hole in the hull to inspect this area just to see and then be faced with a complex repair without some good planning and risk analysis.

So does anyone have knowledge of the schematics? I have sent an e-mail to Lagoon (Beneteau) in France (Technical support) and await their response (hopefully).

"Second Wind"
Lagoon 440 Hull #30
Brisbane, Australia.
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Old 20-02-2013, 14:13   #2
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Re: Seeking structural details of hull adjacent to the sail drive pod.

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....

"Second Wind"
Lagoon 440 Hull #30
Brisbane, Australia.
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Old 20-02-2013, 14:22   #3
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Location: Innisfail, North Queensland, Australia
Boat: Lagoon 380 #241
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Re: Seeking structural details of hull adjacent to the sail drive pod.

Thanks for that detailed description of the saildrive structure. We are due to haul out shortly & this will make it easier to understand what I'm looking at.

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