General Info: Lagoon Hull - Deck movement

[robert sailor]

Originally Posted by HighTemp

A couple months back, I was approached by a Broker / Beneteau dealer to gauge my interest in a 2015 Sense 55 that was available and that had this issue. He stated that Beneteau had it repaired by factory techs and that all was well. Sounds as if this might not have been an isolated incident.

Sometimes I don't know what to think. Obviously its much cheaper to build boats that are glued together rather than introduce the high labor costs of nuts and bolts. When its been questioned in the past the naysayers all tell us how old fashion our thinking is as airplanes and cars are all held together with glue and its a much better solution than mechanical fasteners and adhesive together. I guess the people building cars and airplanes are either using different products or have a much higher level of quality control or both. The hull to deck joint on a mono hull is under a lot of stress when in a large seaway and some companies like HR and Amel go so far as to fiber glass the hull and deck together making them essentially a single component to ensure this area is completely bullet proof and could never leak or start opening up.

[MarkSF]

Originally Posted by robert sailor

Sometimes I don't know what to think. Obviously its much cheaper to build boats that are glued together rather than introduce the high labor costs of nuts and bolts. When its been questioned in the past the naysayers all tell us how old fashion our thinking is as airplanes and cars are all held together with glue and its a much better solution than mechanical fasteners and adhesive together. I guess the people building cars and airplanes are either using different products or have a much higher level of quality control or both. The hull to deck joint on a mono hull is under a lot of stress when in a large seaway and some companies like HR and Amel go so far as to fiber glass the hull and deck together making them essentially a single component to ensure this area is completely bullet proof and could never leak or start opening up.

Some monohull manufacturers, like Bristol, used to build the hull in two halves, allowing a fully encapsulated hull-deck joint. Just to make sure, they then through-bolted a 4" deep, 3" wide teak toerail, every few inches, right through the whole thing.

My Bristol is 32 years old this year, and there's never been a single drip from the joint. So it can be done properly, it just takes the builder to care.

[a64pilot]

I believe IP uses 5200 to join the flanges, then installs a .25" bolt every six inches, then screws the teak cap rail on with the screws extending through the joint, and the screws holding the stanchions go through the joint so you end up with a faster through the joint every couple of inches.
I believe putting the bolts through the joint here is a permanent fix, I'd be surprised if it is a problem in the field if the new boats haven't incorporated this fix in manufacturing.

I think hull to deck joint leaks are not all that uncommon in monos too?


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[PaulinOz]

My vessel L450 2013 sure-come to the Hull / deck joint leak, Port side same place as Dave's in the vicinity of the chain plate area. The leak was viewed through the top of the bathroom cabinet once the screwed in panels in the top had bee removed.



The repair necessitated the removal of the 1 meter toe rail both for and aft of the Port side stays.

The first job is to fully access the under side of the deck, removal of the cabinet in the bathroom should be straight forward. After the removal of screws in the left and right sides and cutting the sealant joint down the left side next to the wall. The right side was moving but the left side of the cabinet would not budge. With the use of torch an mirror found a small patch of glue from bulkhead installation had stuck to top left hand side once broken the cabinet came out completely. Would have been an easy job except for that glue.



Next was the removal of the toe rails and open up the joint. The joint is held together with two types of screws, counter sunk hex screws some under the toe rail and some visible on the deck. Plus the 6mm socket headed bolts holding the toe rail itself and the joint. The toe rail on my 2013 is a synthetic (read Plastic) imitation wood with plastic plugs covering the head of the screws. A small screw screwed into the plastic plug will enable it to be pulled out and as long as you do not go right through, they can be reversed and re-used, I only thought of this on the last one. Two man job one contortionist below to hold the nut and one above to undo. Would have been simple if when built the last socket head screw to be removed had not been replaced with a broken self tapping screw that would not come out even with an impact driver, 1 hour later the head was surgically removed from the screw, toe rail removed and the bent and broken stub removed from the deck.




Once the 2 x toe rails where removed it was obvious that the sealant, what there was of it in the joint had failed and this was the site of our water ingress. So area all cleaned up and a couple of extra screws added under the toe rails in the chain plate vicinity to add some extra mechanical strength as well as the new chemical bonding.

Reverse the whole procedure with new ny-lock nuts and larger washers under the deck and new sealant above and job done took two of us 5 hours but would have been a lot quicker if not for the bodged up toe rail bolt.



Only need to put bathroom back together now.

[Emerald Sea]

Dave & Paul. I haven't noticed any flex movement at the stays but will check next time were out.

But we do have a small leak on the portside deck joint seal and water behind the head cabinet where I replaced about 2m of the deck joint seal about 4 months back but Ive noticed its leaking again. I'll guess the next step to remove the toe rail as you've done (thanks for the photos and point above guys).

[PaulinOz]

Steve I had not seen any movement, but we had a significant rain event and bathroom floor was very wet. Water running down behind cabinet then across bench top onto floor.

[Boat Guy]

I'm surprised to learn how they are joined together....I thought they were glassed and the reinforced with screws....So basically the deck is just glued down to the hull with some bolts?.... Then finding boats with missing sealant areas makes me concerned about design and quality control...Not trying to be dramatic here, but I guess I took it for granted that structural integrity was of paramount concern...

[PaulinOz]

Further to the toe rail attachment, I was comparing my vessel Launched Feb 2013, to Steve's launched Nov 2011. His toe rail appears to be real wood. Also it has no plugs on the top to access screws to hold it down.

The assumption at this point is the earlier L450's had the deck/hull joint sealed and screwed then the toe rail glued on top.

Anybody had a toe rail off a L450 that was actual wood, how was it attached?

[Emerald Sea]

Originally Posted by PaulinOz

Steve I had not seen any movement, but we had a significant rain event and bathroom floor was very wet. Water running down behind cabinet then across bench top onto floor.

Yep, same! I have few days to spare now as we wait for a windlass so gotta get up the gumption to tackle this one properly. Our toenail is plastic wood (2014)

[PaulinOz]

Originally Posted by Emerald Sea

Yep, same! I have few days to spare now as we wait for a windlass so gotta get up the gumption to tackle this one properly. Our toenail is plastic wood (2014)

As I said before the plugs are plastic just use a small PK screw drill and insert, pull, then you can turn over and reuse. I have just had a dozen plugs made out of teak cost $5 for the lot at a teak deck shop, so now have real teak plugs in fake teak toe rail but looks original.

The 6mm bolts under the plugs had a smaller head and from memory used a 4mm Allen key. The original damaged bolt that we drilled out and replaced with a standard 6mm S/S Allen head bolt used 5mm Allen key, but still just fitted in hole in toe rail so all good.

Depending on how dexterous you are just the removal of the top and back insert panels of both sides of the cabinet and the Black Tank door may well give you enough access to the under side and the nuts to enable a socket to be fitted to the nuts under the deck for removal and re-install. If the Cupboard can stay in place makes the work load a lot less.

A mirror and torch helps to locate the nuts up under the lip.

A couple of extra bolts we added I believe will help in preventing this happening in the future.

[exitstrategy]

Wow!

Thanks guys.

This might be the best thread yet for me on CF! ;-)

On my STBD side I have the same problem. 2012 450 #161

At first I thought my stanchions were leaking. Indeed they had small smidgens of silicon sealant. Pulled and cleaned and re-fitted with Sikaflex. The leaking was definitely reduced - but not eliminated.

We anchor out almost exclusively. But one day we had a reason to be tied up in a marina, and then I noticed a large gap of about 12 inches on either side of the chainplate where the sealant failed between the hull and the deck.

Filled that with 5200 and my leaks ended for a few months. Now they are creeping back and I have been putting this off. Now I am inspired and will get those toe rails up and do this job again more properly.

Thanks!
-Erik