All 355/356 Owners Must Read - Rear Deck Core Failures

[Adaptel]

Hello All,

Three seasons ago I purchased a 2001 356 aft cabin which I absolutely love. I got an incredible deal on this gorgeous boat because of a soft spot in the rear swim deck which is not a quick and easy problem to rectify. I learned that this was a VERY COMMON problem with this model of boat and was told the failure was caused by the installation of a grab handle installed in the rear deck on most of these boats to compensate for the AWFUL factory swim ladder which makes in nearly impossible to get back onboard from the water without it.

I tackled this gigantic project this spring and have to share the shocking thing I found in the process. My failure was not caused by the poorly installed grab handle in the platform BUT WAS CAUSED BY A HUUUUUUUGE MANUFACTURING DEFECT RELATED TO THE ATTACHMENT OF THE OPTIONAL FACTORY DECK STORAGE BOX THAT PRETTY MUCH GUARANTEED THAT THIS PLATFORM WOULD FAIL. I am writing this post because I am not sure how many 355s & 356s with storage boxes have this defect, but any boats that were built like mine WILL HAVE A PROBLEM (weather you realize it yet or not).

Here's the story:
I mapped out the part of the deck that I believed had failed by using a hammer and listening for the areas were there was a solid thud, compared to a hollow bounce. I believed that the rotted portion of the deck was as follows:

Percieved Damage.jpg

Although my map of the rotted core was pretty accurate, I learned after I started cutting into the deck that the balsa was very wet extending far past the places where the balsa was completely rotted.

CoreDamage.jpg

I ended up removing pretty much the entire swim platform because even though the balsa that was still structurally sound was completely saturated with water. This is were things got interesting and I discovered what the real failure was caused by. Amongst the balsa core, there are sections of marine plywood in the shape of the storage box, to give a more substantial material for the deck box screws to "bite" into. If you look at the photo below, I have marked the approximate locations of the screws holding the storage box to the swim platform. The circles in green are locations where the screws come through the outer skin and into the marine plywood. The circles in red are locations where the mounting screws "missed" the plywood frame and went directly into the balsa core.

BoxHoleLocations.jpg

THE FRAME THAT WAS MEANT TO PROVIDE A DENSE MEDIUM FOR THE SCREWS TO ATTACH TO WAS MADE TOO BIG AND MOST OF THE SCREWS MISSED IT!!!!!!! Carver simply put some butyl sealant on the screws and sank them through the skin thinking that they were biting hard into the marine plywood....but most of them were not. Over the years of boat flexing (from use and storage on land) caused these screws to turn into a "file" which made the holes through the deck quite large. I was actually able to pull 3 of these screws straight out of the platform without tools! With the way the rain flowed on the back of this boat, it streamed around the port side of the box and under the left forward and bottom areas where these enlarged holes existed.

I ended up rebuilding and replacing the entire swim deck balsa and marine plywood sections, I made the plywood underlayment in the correct size/shape so that all the screws went into the plywood. As an added measure of protection, I drilled a 1" round hole in all the mounting locations and filled them with Resin to that even future leaks through the holes have no path to the wooden portions of the platform.

NewBalsz.jpg

I deleted the plastic grab handle and replaced the terrible swim ladder with an awesome unit with retractable handles made by an Italian company called Nautix.

SwimLadder.jpg

Then got it all re-glassed and gelcoated back up where it was almost ready to hit the water again:

NewFiberglass.jpg

After re-installing deck box, finishing touches, and installing Seadek flooring to provide a non-skid surface for the platform, I am fairly happy with the way this all turned out....even though it was WAAAAAAY more work than I anticipated.

Done.jpg

So, I wanted to share this for anyone who might have one of these boats. Not sure if they ever offered a larger box, but the frame under the outer skin is simply too large to do what it was intended to do...which was to provide a solid material to accept screws though the skin. Total fail here. Also remember that even if your swim deck might appear to be solid, it could be completely soaked and has just not rotted yet. I would recommend anyone with one of these boats and a deck box check their platform with a moisture meter to see if your boat is slowly getting really sick. Dealing with this problem sooner rather than later could save you lots of headache and $$$.

[g36]

Yep I ve made some posts on this in the past. My 405 has the same dock box but I caught my issue waaaay before it got bad. Luckily I was able to dig out the rot around the screw holes until I hit solid core. Over sized them and filled them with epoxy and redrilled for the screws. Now totally in cased in epoxy. No other areas of the core was damaged on my boat. Looks like you did a nice job of repair but it's a shame carver did such a crappy job on sealing this. By the way you should check the anchor windlass foot controls on the foredeck and rebed them too. I've gotten to where if I mount anything into core I will epoxy the edges or if a hole will over size it and epoxy it before the final screws and sealant is installed to help avoid any issues

[Viper]

Great post. There are several threads on here about that very problem regarding box installs from factory but anything fastened to the platform or anywhere else for that matter that is cored is suspect.

BTW, it's too late now but this would have been the perfect opportunity to cut right through and remove the fuel tank to inspect its bottom and take preventive measures for the other major issue with these models which is a leaking aux tank.

[Midnightsun]

Awesome post, thanks for going to all the trouble of writing that up. Got to ask, where did you get the ladder, nice looking and functional addition.

[Adaptel]

Source of the post Got to ask, where did you get the ladder, nice looking and functional addition.

I ordered it directly from the manufacturer:
https://www.nautinox.it/en/product-category/ladders-for-boats-and-rib-boats/

[Drspikes355]

Dry nice work, my 355 has fender rack and an igloo large ice chest with corner holders, I’ll inspect those screws and that hand grab.

I was trying to see how the new ladder was attaching to the platform? Any new dress/ backing plates needed? Thanks again for the post.

[Adaptel]

Source of the post
I was trying to see how the new ladder was attaching to the platform? Any new dress/ backing plates needed? Thanks again for the post.

If you want to install one of these ladders, here is a few notes & tips.

The screws holding the factory ladder will not come out normally, and will need to have the heads cut off with an angle grinder...then ground flush to the boat.

The Nautuax ladder has a mounting plate with about 14 countersunk holes on it (for fastening to boat) and studs to attach ladder. Most of the holes in the rearward part of the mounting plate (that takes 90% of the load) cut though an aluminum plate that is embedded into the fiberglass of the carver (for the factory swim ladder)

I used M6 stainless bolts through all the holes, with fender washers and nylon lock nuts on the backside) after drilling them oversized, filling with strengthened epoxy, and using marine silicone sealant. I was only able to do this with access through the old swim platform handle hole (fiber glassed over when done). You may be able to get access by disassembling rear interior wall in bedroom. I would not trust screws in this installation

After using this ladder for the past month... I am extremely happy with it and getting back onto the boat is super easy and effortless

[KyleR]

Same on the 396...