80 M34 possible structural issue

Folks of older mainships,

I have an 80 mkll the one with the flybridge overhang. Last week I embarked on fixing the rollers on my sliding glass door, only to discover that I had about an inch of deflection at the center of the door frame which seemd to effect the screen door more than the glass door. Which door was effected more was not the issus as much as, I'm sure my issue goes far beyond my simple door fix. Another thing I noticed while I was rolling around on the cockpit floor like a farm animal was that the entire frame is bending from left to right as the boat rolls in the slip. Just a few other points to mention here. As I was sussing out a fuel pickup tube issue this summer, I noticed that the salon floor on the inside of the slider was rotted just where it meets the wall that the slider is attached to. The outside mouldings are also rotted out and it was one of those things that was on my list to repair.

I have since jacked up the ceiling just behind the door and the screen seems happy now but what am I looking at to get this right. Is it possible that the floor above is water logged and putting a boatload (no pun intended) of pressure on the door frame. Or is it just a matter of reframing the door on that wall to get the superstructure to stop swaying in the wind.When I first noticed this I got myself positioned under the floor next to the frame to see if I could move the center of the frame up with my head, and it didnt budge. Only the gentle push of my hydraulic floor jack did what I ultimately needed to get this back to spec.

Now I know I cant be the only one that been bit by this dog but I am open to suggestions on how to solve the said problem. I checked the wood underneath and that looks solid. I am going to grab some pictures this week to show where the current rot is located to possibly shed some light on what I am dealing with. See the attached for my makeshift ceiling support.

Problems with water intruding into the core of the fiberglass laminate in the cockpit are well known to this boat. Search this forum and you will find pics of a complete cockpit floor redo.

It is not really the weight of the water that is the problem. The water rots the core and the whole laminate/core structure loses strength. The only solution is to remove the top layer of fiberglass, remove the rotted core, replace with marine plywood or balsa and reglass the top. It can be quite a job.

David

It's hard to compare a boat to a house. But, this is like a load bearing wall that is at the center of the problem. You found the rot on the deck from cockpit into the cabin.It likely includes the decking and the wall. If you can find any places on the upper deck that allow water in, that's where you need to investigate further. It could be screws from a railing above the slider. Typical place for leaks to start. Many folks rebed these screws as preventative maintenance. Your skill level will decide if you tackle this on your own. But having a pro come in to diagnose the extent of water intrusion and damage is a smart move.

We had all of the issues you have described on our 34 and more! The flexing of the hull in a beam sea that you noticed at the bulkhead is ,to a very slight degree and unfortunately, normal for our boats. Please take notice of the "slight" part. All boats flex in seas a little. I noticed ours flexing at the salon door the very first day we brought her home. It wasn't flexing what I would call a little though! I could stick my finger in the gap that was opening and closing at the aft salon door!
We bought the boat with the full knowledge that the decks and flybridge were severely waterlogged and that the structural integrity was gone and that they were going to need replacing if we wanted the boat to be right.
The first year we removed the bridge and completely replaced the bridge floor with 3/4" marine plywood & multiple layers of biaxial fiberglass. In the process, I pulled the entire aluminum door frame out & discovered that the pitiful "support" mainship came up with for the door threshold had completely rotted away too. For that , I cut out the fiberglass that was under the threshold, sandwiched 2 treated 2x4's together with epoxy & SS carriage bolts & reglassed the threshold. I also added 2- 2x4 supports under the deck beneath the threshold where mainship had no vertical supports.
After launching, the first thing I looked for when we got in a beam sea was to see if the flexing was cured. Better but not perfect. I cant say I wasn't disappointed but I can say I wasn't surprised.
The next year was the deck year. Same drill, cutting out the old ,rotten decks and replacing with more 3/4 marine ply & fiberglass. Once again, after launching, I checked the doors in a beam sea. Much much better but still a very slight flexing is noticeable in heavier seas.
The new decks made a huge difference in the overall stiffness of the boat but I've come to the realization that if I want to really stiffen the boat up, I would have to add gussets to the athwartships bulkheads at each end where they meet the hull. It's doubtful I'll ever do that because these boats weren't built as offshore cruisers but serve us just fine as a 2 person inshore one!

Not all that uncommon on the 70's and 80's 34.

https://mainship34.com/

Go to Interior and sliding door.
Also the cockpit under the ladder is suspect.

boomerang said:

We had all of the issues you have described on our 34 and more! The flexing of the hull in a beam sea that you noticed at the bulkhead is ,to a very slight degree and unfortunately, normal for our boats. Please take notice of the "slight" part. All boats flex in seas a little. I noticed ours flexing at the salon door the very first day we brought her home. It wasn't flexing what I would call a little though! I could stick my finger in the gap that was opening and closing at the aft salon door!
We bought the boat with the full knowledge that the decks and flybridge were severely waterlogged and that the structural integrity was gone and that they were going to need replacing if we wanted the boat to be right.
The first year we removed the bridge and completely replaced the bridge floor with 3/4" marine plywood & multiple layers of biaxial fiberglass. In the process, I pulled the entire aluminum door frame out & discovered that the pitiful "support" mainship came up with for the door threshold had completely rotted away too. For that , I cut out the fiberglass that was under the threshold, sandwiched 2 treated 2x4's together with epoxy & SS carriage bolts & reglassed the threshold. I also added 2- 2x4 supports under the deck beneath the threshold where mainship had no vertical supports.
After launching, the first thing I looked for when we got in a beam sea was to see if the flexing was cured. Better but not perfect. I cant say I wasn't disappointed but I can say I wasn't surprised.
The next year was the deck year. Same drill, cutting out the old ,rotten decks and replacing with more 3/4 marine ply & fiberglass. Once again, after launching, I checked the doors in a beam sea. Much much better but still a very slight flexing is noticeable in heavier seas.
The new decks made a huge difference in the overall stiffness of the boat but I've come to the realization that if I want to really stiffen the boat up, I would have to add gussets to the athwartships bulkheads at each end where they meet the hull. It's doubtful I'll ever do that because these boats weren't built as offshore cruisers but serve us just fine as a 2 person inshore one!

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Swawn,


Thanks for the info. Couple of questions:


I am wondering if you had to do it again would you have used 3/4 ply or possibly something lighter to minimize the weight up up that high.


I also need to do decks , side and bow and I guess the best plan would be to start up high (flybridge) and work my way down.


When you did your flybridge did you remove the actual control station from up top or just tackle wet areas?


I need to get a moisture meter and see where the issues exist. Any suggestions would be great. On the lower side decks its very obvious as theirs brown gew oozing as well as swollen areas. But the upper looks pretty good from above. Except where the ladder passes through from the cockpit, that area has separated. I will get pictures today as I need to go down there.


Chris

John, you have a MKI. The MKII had the shorter cabin, larger cockpit, and no Flybridge deck over the cockpit.
The MKII is often considered the "fishing" version Mainship.
The MKIII had a bigger cabin than MKI, smaller cockpit, same overhang

John E Holden said:

Folks of older mainships,
I have an 80 mkll the one with the flybridge overhang.

Click to expand...

Mk l it is, thanks for the clarification.

So, in addition to rotten cockpit deck you have rot in the side decks and bow. How about the flybridge deck and the boat deck aft of it? Any rot in the superstructure? Older T/Ts sometime had this as they were built with just a thin layer of glass over crappy plywood.

In general Mainship built them decently but poorly sealed fittings leaked water into the core over the years. You have to re seal these fittings every ten years or so to be sure that the water stays out.

You can either use marine plywood for core or balsa or proprietary synthetic foams. Each have their +/- but don't worry so much about weight, worry about strength and durability. Marine ply is usually used in high stress areas and will last forever if you keep it sealed up tight.

That sounds like a huge job. I hope that you are a serious DIYer. If you hire a yard to do it, the cost could be more than the repaired boat is worth.

David

Further info

So I went to the boat today to dig a little deeper heres what I found:
I currently dont have a moisture meter so I tapped with a small hammer on the suspect areas and found that the majority of the floor of the flybridge is rock hard and sounds solid as well, however underneath till about 33 inches out from the door sounds hollow and gives when you push it up. Look at the attached photos to see the seperation at the ladder access hole. Is this supposed to be solid across the span or is there supposed to be a void in there?
Another thing I found that maybe is supposed to be is that the lower slidiing door track in on an 11 degree angle sloping towards the cockpit. Is that for shedding water or is something doing underneath?

David,
cockpit sole and flybridge seem solid, I am wondering what gives with the underside of the aft flybridge deck. Re framing the door isnt so scary and honestly the lower decks have been screaming my name for a few years so yea I would never pay a yard to do it as like you said we are getting into value of the actual boat numbers. So I will see if anyone has any tips about how to proceed aside from ripping the entire flybridge off and re doing that deck but from todays initial findings I am being optimistic. For now I think i'm gonna go for a moisture meter and see what kind of light that sheds on things.

DavidM said:

So, in addition to rotten cockpit deck you have rot in the side decks and bow. How about the flybridge deck and the boat deck aft of it? Any rot in the superstructure? Older T/Ts sometime had this as they were built with just a thin layer of glass over crappy plywood.

In general Mainship built them decently but poorly sealed fittings leaked water into the core over the years. You have to re seal these fittings every ten years or so to be sure that the water stays out.

You can either use marine plywood for core or balsa or proprietary synthetic foams. Each have their +/- but don't worry so much about weight, worry about strength and durability. Marine ply is usually used in high stress areas and will last forever if you keep it sealed up tight.

That sounds like a huge job. I hope that you are a serious DIYer. If you hire a yard to do it, the cost could be more than the repaired boat is worth.

David

Click to expand...

John E Holden said:

Swawn,


Thanks for the info. Couple of questions:


I am wondering if you had to do it again would you have used 3/4 ply or possibly something lighter to minimize the weight up up that high.


I also need to do decks , side and bow and I guess the best plan would be to start up high (flybridge) and work my way down.


When you did your flybridge did you remove the actual control station from up top or just tackle wet areas?


I need to get a moisture meter and see where the issues exist. Any suggestions would be great. On the lower side decks its very obvious as theirs brown gew oozing as well as swollen areas. But the upper looks pretty good from above. Except where the ladder passes through from the cockpit, that area has separated. I will get pictures today as I need to go down there.


Chris

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You won't know the scope of your repairs until you tear up the fiberglass and see exactly where the water damage has gotten. Even though the balsa core still feels solid in a lot of areas, it's probably still gotten wet and rather than trying to dry it, you would want to remove it too, for fear of future rot. Ours was completely water damaged so we removed the entire bridge, which really wasn't a big deal.
I actually bought a composite material called Nidacore to use in place of the balsa in the areas that weren't going to have a fastener or hole drilled in it with the idea of to keeping the weight aloft to a minimum. When I got into the repairs, I realized that most of the bridge was going to have a fastener put through it or more importantly, in it ,with a screw and not through bolted. The plywood was definitely needed for something for the screws to bite into. One difference between our Mainship flybridge and a lot of the others is that we have the molded fiberglass seating with storage underneath. A feature we looked for in a model 1 but it does have additional bolts towards the center of the bridge, hence the need for more plywood. I ended up giving several sheets of unused Nidacore to the yard owner because I used about 95% plywood on the entire bridge floor.
My biggest regret is not going with ply for the entire floor. The Nidacore thickness is a true 3/4" but the marine plywood was actually 21/32".
it was a HUGE pain trying to fair in the areas where we used Nidacore! You can still see the difference in thickness today but honestly, my lovely wife was a trooper and we stayed on the project for the entire summer working almost every weekend and evening trying to get it completed. We were really getting tired of working on it by the end of summer so the fairing of the different thickness isn't as perfect as it could be. I take comfort in know it is structurally sound now with no more "Mainship tea" brown water dripping from the rotten floor/roof!
I really can't say that I notice any adverse handling of the boat with the extra weight of the wood but then again, I didn't own it when it was new without a waterlogged roof so we have nothing to compare.
The decks were a no-brainer for me using all plywood, since I needed them to be solid with the addition of 4-10" spring cleats instead of the 2 Mainship ones, 2-12" bow cleats instead of the 1 Mainship bit and the addition on a glassed-in platform to support the anchor windlass and a cleat centerline for the anchor rode. Additionally, we elected to not replace the side railing stanchions, which were a major cause of leaking and ultimately rot, plus needed a solid bedding for the bow railing forward.
I'm sure the boat is heavier than it was when new but it's probably stronger than it was ,too.

John E Holden said:

Another thing I found that maybe is supposed to be is that the lower slidiing door track in on an 11 degree angle sloping towards the cockpit. Is that for shedding water or is something doing underneath?

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Nope. It's supposed to be flat. You'll want to remove the doors and the frame to get the decayed wood out from underneath and rebuild it. Not a big job but one more pain in the butt thing that you'll need to do BEFORE you reglass the roof. You'll want to get everything back into shape before reglassing or your roof and cockpit floor will have a permanent sag in them.

I'm attaching a link to the blog my wife started. It's no longer updated (I knew she would get tired of blogging!) but I think you'll find it helpful. You'll just need to dig through the posts , mostly april-october of 2017, to find the repairs we did similar to the ones you'll need to do.
My wife did a lot of venting when realized the project was going to take more than a few weekends! Sorry, too, but it's a rather confusing blog format to navigate through but like I said, I'm sure you'll find the pictures helpful.

Boating With Shawn and Liz

I had a 78 model I and rebuilt/recored most of the flybridge deck doing it all from above.
I did the side decks from below, and it's doable, but much much easier from above.
That's how I would recommend repairing the cockpit deck. From above.
If you want details send a private messsage to me with your e mail address and I'll send some pictures. the files are to big to post here.
Basically I cut the skin off, threw it away and laid plywood and mat and resin.
It came out very well, a friend ground the crown back by eye and the railing fit back perfectly.

Jay,
Grecoaudio@gmail.com

Shawn,
Thanks for the link, is the ceiling above your cockpit to the right of the laddar hole solid sounding or is there a cavity there?

On ours, the small section on the port side of the ladder hole was the only section of the roof we didn't take up. A 4" x 18" strip. I honestly can't remember what it was/is filled with but there must've been no water in it or I would've cut it out, too. When I tap on it, it sounds hollow.

Any troubles I have had with my doors, the culprit has always been the floor, not the fly bridge deck or top of the door. When you look at the door, visually it always seems like its the ceiling / flybridge deck that is sagging, an optical delusion as they say.

I would firm up the bottom of the door first, get it level and see how much that helps. For me that meant pulling the water tank out and bracing things up right underneath the door and just aft of it.