Repair log - wet transom core

[Ctarmigan]

I've discovered a crack in the fibreglass beneath the black plastic transom cap on my 2004 22 Cruiser. On removing the cap and inspecting further, it's clear that water's gotten into the wooden transom core.

I'll investigate further, and plan a repair. While it's a disappointing discovery for me, I can at least add something positive by keeping a record of my diagnoses and fixes here, in case they're of use to others. I'll also plumb the considerable collective intellect here for guidance.

My first, and perhaps most important, note to others - carefully examine your transom for potential separation of the cockpit and hull fibreglass skins. On my boat, anyhow, there was next to no material joining the two, but the adhesive used to attach the plastic transom cap partially obscured the crack that must have been steadily forming. No matter how much water intrusion I find, it would surely have been less (or prevented altogether) with more careful attention to this.

Photo below is of the cockpit side of my transom, after I scraped away some of the black adhesive to get a better look at the separation between the fibreglass skins, revealing the core.

 

[Ctarmigan]

My initial take was one of only moderate concern. While I could see core through the crack (bad), it appeared to be something other than wood (good?). It was a light-coloured material, that I could gouge out with a screwdriver blade. Foam? That would be good - perhaps I could get away with a gap fill and re-skin repair like mutski's (http://www.c-brats.com/viewtopic.php?t=31043).

Thinking this, my next step was to remove the black plastic transom cap. It proved to be attached with remarkably stout adhesive, and removing it took away chunks of gelcoat, and even down into the fibreglass itself. Quite a mess. The cap also snapped in two as I removed it.



Removing the cap also showed how large the crack was, and how little material was actually joining the inner and outer fibreglass skins. As others have found (with this particular vintage of C-Dory?), there was almost no material fixing the two skins together at this joint. I really like my boat, but this was a disappointing discovery - it's a pretty mission-critical spot to seal this flimsily.



The second bad surprise was beneath the motor mount. Poking into that section of crack, it was obvious there was wooden core in the transom, and it was definitely waterlogged and rotten.

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[Ctarmigan]

My next step was to evaluate how far along the transom top there was wet wooden core. I drilled a series of vertical test holes through the top of the transom, from left to right. While the worst rot was centred around the main motor mount, the core all the way along had at least some moisture (if not overt rot). This appeared to extend as deep as my drill bit (~2").

I left off last night having started to remove my kicker bracket (I'll need a second person for the lower bolts), and I've removed both fuel tanks. My next move will be to pull off the main motor. In aid of this, I'll set up a chain hoist above it, holding the load on a three laminated 2x4s bridging as many ceiling joists as I can span.

Side note - I was worried about successfully removing the fuel tanks, as disconnecting the fill hose is noted in many C-Brats posts to be a mightily difficult task. It certainly started that way, but then I changed approaches - I removed the brackets holding it in place, budged it away from the transom enough to give some overhead clearance beneath the splashwell, then levered it up and over the inset bolts that held the inner bracket in place. Once I'd done that, I could rotate the whole tank around into the cockpit while still attached to the fill hose. At that point, I could use gravity to assist me in removing the fill hose from the tank, which made the operation pretty easy.

 

[clayhubler]

Sorry to hear this news, especially as boating season is starting. I have a 2003 and I had to replace the core in the transom also but it was the lower part of transom.
One thing to consider, since it is may. I had a lot of rotten core in my hull and transom, but I did not have any soft spots or delamination. Really, I only started out to repair the problem with the gas tank holddowns not realizing the extent of the problem. There were no other symptoms indicating I had a problem.
What I’m getting at here is that it may be wise to pause and consider the extent of the damage. You might be able to defer the repairs until boating season is over. Obviously you’ll have to be the judge of this, but the fiberglass on these boats is thick and I don’t believe I would’ve had any problems relating to the rotten core for years to come. Since our boating season is so short on the West Coast, it’s something to think about.

 

[Ctarmigan]

Thanks Clay - that's a good option to consider now (before I dig any further and eliminate that possibility). I certainly haven't been noticing any flex or mushiness to the transom or elsewhere - I'll do a bit more careful checking to that end no matter which direction I go.

My initial repair plan (when wet core wasn't on the menu) was to epoxy up the crack, glass over the transition, and then have an aluminum transom cap fabricated to replace the (now-broken) black plastic one. I'd figured I'd also have it extended down in the centre of the splashwell side, so that it would span the upper bolts of the motor mount, spreading the weight. My motivation for this was two-fold - add some protection to an area where we do step from time to time, and also to hide what would inevitably be my serviceable but rough-looking epoxy/glass repair job beneath.

An option in this case (i.e. patch up for this season, do extensive core repairs this coming winter) could be to go ahead with installing such an aluminum cap, with copious adhesive-but-removable sealant, to get me through this season.

Being in Whitehorse, I am acutely aware of how long boating season lasts. Our bigger lakes are reliably ice-free the first week of June.

 

[ssobol]

IMO, I would think that the inner and outer skins are held together quite well by the engine mounting bolts, swim step bolts, kicker mounting bolts, etc. There only really needs to be enough FG at the top (under the cap) to seal against water intrusion.

 

[thataway]

First, the core of your transom is wood. The foam was some filler put under the "hull to deck joint" which is the transom outside for the hull, and the splash well being the deck. However there may be a space between the splash well pan and the inside glass on the transom.

Your repair is to remove the fiberglass on the tramson in one piece, cutting about 2" to 3" inside of the outer perimeter of the transom. All of the wood material removed and then decide if you want to use wood, or some material like Coosa which is basically very tough foam.

Putting caps of aluminum are a bandaid. It does not add structurally to the boat. I have observed that diamond plate seems to be a "cure all" in Alaska-it is not a real solution.

To check for the stability of the transom, put the outboard in the trailering position, and bounce your full weight on the lower unit. It will most likely show flex of the transom.

Can you save the season? Probably, if you are careful. There are aluminum bars which you can make or buy to spread out the motor load. I have also seen in 22's where the engine was put a risk as the transom broke.

The transom: inside and outside should have had continuous fiberglass over the wood in the core of the transom. What you found was first the aft laminate of the transom. There is then the core, and finally the inner layer of the hull/transom. Then the Hull to Deck joint, which is the splash well is glassed in to the top, and the plastic cap applied.

Fiberglass does flex. Be a little careful with too sharp corners, and it can cause some major issues if parts that are made to flex, are not allowed to do so.

If my discription is not clear, I wll try and find, or draw a diagram.

There is another way to deal with the transom. Some say you can take a chainsaw, and cut out all of the wood (tooth picks in some cases), all of the wood is removed and a high density material is poured into the space between the outer transom, and the inner laminate of the hull. To do a pourable transom, the fiberglass has to be much cleaner than you can get it with power files and chain saws. It can be done, but is not a proper repair--and will fail, perhaps sooner than later.

Let us know what you decide. Do not risk dunking the motor. I have seen it happen.

 

[DKennaC25]

I am doing my transom top right now .
It was solid , yet the corners had substantial cracks. So when taking the topper off it pulled up a lot of the gelcoat and some glass up.
I took a drimel and opened up the space between the top and the hull.
Then mixed poly resin filling the Crack and adding stran glass.
Took doing it several times over several days till the Crack was full.
Sanded and then covered the top of the transom with resin and cut pieces of stran mat. Doing fiberglass filler now. Next will be fairing compound the gel coat .
Also take your scuppers off and feel inside if it is solid. Mine were but I am going to sand and give them a coat of resin.

 

[Ctarmigan]

A few updates from last night's work:

I tried bouncing my full weight on the outboard leg in trailer mode. No detectable flex; felt very solid.

I did a deeper examination of core at the top of the transom, using a longer, larger-diameter drill bit. I did find solid, dry-seeming balsa all the way along the transom top, from about 2-2.5" down.



I also cleared away the fuel tanks, cleaned up the years' worth of grunge under them, and investigated the inside of the lower transom there. Tapping with a hammer, I could easily detect a dull-sounding area of hull behind where the starboard fuel tank had been (red circle in image below). The fiberglass there is not firm; it has a small amount of give when pressed, as if it's separated from the core. Tapping that area from the outside of the transom also gives a duller-sounding knock, though I struggle to feel confident in actually detecting a difference. Outer hull fiberglass in that area is firm - no difference from elsewhere on the hull.



I'm still in the investigation stage of all of this - there are a few more diagnostics I'd like to try before determining what my next move will be (such as drilling a few test holes in the cockpit-side fiberglass to determine state of the core beneath). I'll also be lifting the main motor regardless (I need to replace the tilt tube), so it won't be much more work to remove it from the transom entirely. Those larger-diameter bolt holes are well-situated to help me diagnose core state.

 

[thataway]

Your plan is solid. If it is localized to the top part, I would fill with micro balloons and epoxy. There are reasons to not use this for fairing, but for the upper few inches, and if the rest is good, just do that repair and move on. It sounds as if you should be able to use the boat for this year's season.

 

[Nancee]

Just as an inexperienced c brat, is it normal to have this much damage on this age of boat???

 

[Ctarmigan]

Some more investigations last night, to determine whether it is indeed just the top couple of inches of the transom that's wet/degraded, or if the issue pervades further down.

I removed a section of fibreglass at starboard top of the transom, which exposed the predictably-wet balsa core. From there, I bored out a couple of 4" deep sections, isolating a 1" wide section of core to pop out as a horizontal sample of the transom core. Easier said than done, but I did manage to extract a 3 3/4" piece to examine.





The core sample showed:
- top 2": wet, deteriorated balsa, with delamination from cockpit fiberglass
- 2" to ~3": damp but solid balsa, tight bond to fiberglass
- 3" and deeper; drier solid balsa, tight bond to fiberglass



I doubt a moisture meter would find this to bottom layer to be bone dry, but it feels solid to my prodding investigations, and I'm heartened by the rapid transition from soggy at the top layer.

I continued investigations of the lower transom, removing all kicker bracket hardware and one lower main motor bracket bolt. Good news - boring out the main motor bolt hole (starboard side) produced whiskery dry balsa shavings - no moisture here!



Less good - the lower kicker bracket bolt hole furthest to port produced soggy brown balsa when dremeled out. However, the lower kicker bracket bolt hole toward the centre of the boat was pretty good (though not perfect - some dampness). Moving up to the upper kicker bracket bolt holes, the port one was dry, the centremost damp. These uppermost bracket bolt holes would be addressed by removing balsa core from the top of the transom.




I'm reading my bolt hole findings in the lower transom as patchy damp related to poorly-sealed hardware installation - something could hopefully address with section-specific replacement of wet core patches with dry.

I also reapplied myself to the delaminated-sounding section of the lower transom behind the starboard fuel tank. On further inspection, this is perhaps a red herring - the layer that's delaminated feels papery-thin, and can be flexed with a stout finger press. It also protrudes a little from the surrounding fiberglass skin. Comparing to the thickness of the cockpit fiberglass skin visible at the top of the transom, what's going on here must be some kind of delamination of a thin layer of outer fiberglass from the thicker main cockpit skin. I'm not certain what the cause or implications of this are, but I'm (cautiously) less concerned about a catatrophic delamination between balsa core and cockpit fiberglass.

I really appreciate the feedback so far (and know I've been focusing on presenting the evidence rather than responding so far). I have a number of questions following up from what I can see so far, but I'll distill them a bit further in aid of specific requests rather than half-cooked pleas for assistance.

 

[thataway]

Just as an inexperienced c brat, is it normal to have this much damage on this age of boat???

Transom problems are relatively rare in C Dorys. If the boat is in a freeze thaw cycle winter environment and water somehow gets into a crack then this can occur. I would say that all in all, C Dory boats have a little less transom issues that most boats their age, if they are still in use.

Any hole drilled a cored fiberglass/wood/fiberglass laminate, should be sealed with epoxy. Just a dab of 5200 is not enough.

In this case it appears that the wet core is not far down into the transom, and the fix should be fairly easy.

 

[Ctarmigan]

Over the past couple of evenings, I’ve lifted off the main outboard, removed the transom cap and started pulling out wet balsa.

It’s not looking good.

I’ve worked by way 6” down in some places, and except for a couple of areas I’m still encountering wet balsa. In some cases, it seems moisture levels are increasing (to the point of pooling). This could be from bracket mounting holes in the fiberglass, which were not epoxy-sealed. Core bond to the fiberglass is poor or nonexistent. I can see several places where core discolouration follows sipes in the balsa core downward. I haven’t detected any epoxy in the sipes (but perhaps this is not out of the ordinary).

I’m considering my options. Informing them – I’m in a small, remote and landlocked city. Materials are hard to come by, and can take considerable time/expense to arrive. There’s one fiberglass shop in town, but others’ previous experience is he won’t tackle a job like this. I’ll need to do most/all of whatever the main steps are myself, and carefully plan in advance what I’ll need. I will be down south late next week and driving back up with a trailer, and so do have an opportunity for marine-supply shopping. I’m hoping to have a plan and a materials list by then.

Bob – I value your suggestion of going at a full-transom repair by removing the outer skin. I’m also very hesitant – I think I can make the repair, but suspect it would look awful once I was done with it. Before putting a saw to my boat, I’m doing a version of measuring twice – what other options do I have?

As one alternative, I’m considering doing this in two stages: 1) remedying lower transom core by removing the inner transom skin below the splashwell and re-coring from the inside, and then 2) repairing the top ~6” (splashwell and up) from the top, by sliding in some (well-slathered) core material and subsequent clamping to develop a consistent core-skin bond. I’m considerably less concerned about esthetics of the inner transom skin (below the splashwell) – this area’s mostly hidden by fuel tanks. Understanding outer transom removal is the go-to; are there reasons to abandon this alternative?

A second question – if indeed I’m removing all of the transom core (one way or another), is there strong reason to replace it with balsa again? Given I’m dealing with a flat plane rather than a curve, other options I believe I can get my hands on are marine plywood and Coosa Board. My preference is going to be on ease of use (in effecting repair) and reliability. I haven’t put much mind to SeaCast pourable transom repair, but happy to if that’s warranted.

I should also note – Clay, I suspect you were right; I could have waited on this until this coming winter. Digging into the transom, the majority of the balsa was still sound (if wet). That, combined with my inability to flex the transom when bouncing on the raised outboard leg suggests I could have deferred. This in mind, I plan to carefully examine the cockpit floor for moisture after this boating season. It’s showing no outward signs of failure.

Now, back to picking balsa shreds out of my hair…

 

[ssobol]

David at Cruising the Cut on YT is in the process of doing the same thing you are considering in replacing the wet core of a FG boat transom. The boat is a different brand, but the technique is the same. So far he has cut off the outer skin of his boat and removed the sodden core. David posts videos on different topics related to boating and you have to look through his videos to find the transom repair ones.

For information on all things FG and boats, check out the FishBumpTV YT channel.

 

[clayhubler]

One thing to keep in mind if you repair only the transom first is that there is no resin or epoxy barrier between the hull coring and the transom coring. So if you repair the transom, but the hull is still soggy and wet, it’s going to get the new transom coring wet unless you’re careful to seal it with epoxy when you are working on it. And unfortunately that probably means the hull coring is wet also.

I would probably do the repair from the inside because you don’t have to worry about making a perfect aesthetic repair and that’s how I did mine. But I didn’t have to repair mine above the splash well so I’m not sure the best way to go about that. Might actually be easier to do it on the outside. It is not easy working under the splash well. You could cut the entire back skin off and grind the backside of it and glue it back on with the new coring behind. I think I saw Andy on Boatworks Today do that.

I’ve not worked with Coosa board before, but I would consider it.

 

[thataway]

There is "Sea Cast" pourable material. Nida pour used to be available--not sure if it still is. Coosa, or Penske board (Baltek AIREX PXc foam board today) I like to rebuild with epoxy resin if not in the open--even if the back of the transom is pulled and core replaced from outside, I use Epoxy on the inside, and "glueing the old transom to the new core. But on the outside, when making the hull to transom (3" shelf is left around the transom when the aft outer surface is removed, and the old transom is also taper ground to get the strength back to the outer layer I use vinyl Ester or polyester resin. That is then sounded flush, and gelcoated to match the rest of the transom.

Although a chain saw is traditionally used to remove all of the core when outside and inside of the transom is retained, recently we used a 1 1/2" spade bit on a 25" extension (started with 14" shank and when that was done, went to a 25" extension.). Don't pour epoxy or polyester resins with fillers. They will get way too hot as they catalyze.

 

[Ctarmigan]

I've followed up with a call to SeaCast, to examine this option more thoroughly also. They're somewhat incredulous that the entire transom is not cored.

Perhaps I'm wrong; my understanding (before drilling any holes) is that the transom core in my boat is a 60" wide, 20" deep rectangle, which more or less corresponds with the transom cutout. The volume of the core is visible as the thicker area below the splashwell. The transom behind and below the lazarettes is not cored.



Before I start making confirmatory test holes, I'll check with the group.

 

[thataway]

I cannot speak to the various years of C Dory 22's. But the my C 2003 C Dory 25, had about what you described. As I recollect it did go down further. However I was amazed that it did not go all of the way to the sides of the transom. The core in the 25 was OK, but we had some issues as documented in my Album. I added several layers if 1708 with epoxy to take more of the load distributed out into the spashwell and down onto the bottom.

On the 2007 25 there was a space between the lamination of the spashwell, and the hull/transom. The bolts and even a plate on the inside had crushed the splashwell. This was discovered at the time of sale of the boat. I had not noted any issue, but the new owner brought it to my attention after he had taken it on several trips. (The boat was left at my home for over a year after purchase, and the buyer flew to Pensacola and used the Boat along the Gulf Coast and Eastern Sea Board.

I cleaned out the old bolt holes, then over drilled them, and put in glass and epoxy plugs into the transom. I also filled the space and about 3" in diameter around where the boat holes were, with solid 1708 circles. Then I made larger plates and used them under the motor bolts.

 

[clayhubler]

My 2003 had exactly what your illustration shows