What did I do wrong with Transom?

[jdupree]

I replaced the transom 5 years ago. The boat has been sitting outside since then waiting for a deck. I went out the other day and noticed the transom is mush!!! Motor is barely hanging off the back. I used exterior plywood (not pressure treated) and coated with 2 coats of 3 to 1 epoxy resin. All holes were sealed up when I did the job.

I am not understanding this at all? Did I do something wrong on the chemistry side?

Here is the link to where I did it.

1975 Starcraft 16' SS

A couple of more pictures.

forums.iboats.com

 

[jbcurt00]

Left exposed?

Or well covered and free of damp & humid conditions under a boat cover?

Expansion/contraction probably created cracks in the epoxy allowing moisture in. Once in, it was likely trapped and you found the results..mm

 

[classiccat]

I replaced the transom 5 years ago. The boat has been sitting outside since then waiting for a deck. I went out the other day and noticed the transom is mush!!! Motor is barely hanging off the back. I used exterior plywood (not pressure treated) and coated with 2 coats of 3 to 1 epoxy resin. All holes were sealed up when I did the job.

I am not understanding this at all? Did I do something wrong on the chemistry side?

Here is the link to where I did it.

1975 Starcraft 16' SS

A couple of more pictures.

forums.iboats.com

Sorry to hear that jdupree .

Any other clues as to where the rot started? (top-to-bottom? around fasteners? z-bracket?, outer-PLY layers or completely through?)

I assume that you didn't use fiberglass with the epoxy. If that's the case, that could be your 1st issue; plywood grains have the tendency to check when coated with epoxy ...which exposes untreated wood to the elements.

How were the holes sealed? If you used 5200, were there fuel leaks by chance?

 

[jdupree]

I guess you can call it exposed. I did not have a cover on it. I went to great lenths (obviously not enough) to make sure the transom was sealed. I never figured that it would rot sitting in the yard!

All that work down the drain and I still have to put a deck in it

 

[jdupree]

Sorry to hear that jdupree .

Any other clues as to where the rot started? (top-to-bottom? around fasteners? z-bracket?, outer-PLY layers or completely through?)

I assume that you didn't use fiberglass with the epoxy. If that's the case, that could be your 1st issue; plywood grains have the tendency to check when coated with epoxy ...which exposes untreated wood to the elements.

How were the holes sealed? If you used 5200, were there fuel leaks by chance?

I have not had a chance to see where the rot started. I did not use fiberglass with the epoxy That sounds like my mistake based on what you are saying. Maybe I should have laid down some 1708 and then coated it with epoxy? If I remember correctly, I used 5200 especially below the waterline. I might have used 4000 above the waterline.

Well, what a lesson learned! I just cost myself a ton of extra work!

 

[classiccat]

I have not had a chance to see where the rot started. I did not use fiberglass with the epoxy That sounds like my mistake based on what you are saying. Maybe I should have laid down some 1708 and then coated it with epoxy? If I remember correctly, I used 5200 especially below the waterline. I might have used 4000 above the waterline.

Well, what a lesson learned! I just cost myself a ton of extra work!

I feel for ya man. Despite what many say on the old interweb, epoxy requires a bit more than mixing / spreading...along with the additional expense. If folks aren't going to go through all of the extra expense/prep/processing required with epoxy, I've been intrigued by the "Old Timer Formula"...applied after laminating transom pieces. Predrill all of the holes and make sure that all ply edges get the same OTF love!



If you insist on taking another crack at epoxy, I use 6oz cloth on all of my epoxy coated wood (you can flip through my resto thread for several examples). 1708 (17oz biaxial cloth) would probably make the transom too thick for the the aluminum "pocket".

if you relied solely on 4000 or 5200 for sealing the holes, they're not fuel resistant...another member recently came back to report a similar issue.

This is the process I use...that probably makes glasser-guys cringe:

1. figure out where all of the holes will go.
2. Drill oversized holes for epoxy plugs and chamfer (so plugs are locked in place).
3. cover the undersides of holes with painter's tape
4. backfill with epoxy+filler (cabosil)
5. cut cloth to size with 1-2" of overhang if possible.
6. prime coat plywood with 3:1 epoxy
7. lay cloth and wet it before prime coat of epoxy completely cures...a little tacky.
8. 2-3 additional epoxy coats to fill-in the cloth grains.
9. repeat on the other side and edges.
10. Drill final faster holes through epoxy plugs; all PLY edges are encapsulated.

Additional reading: Gougeon Brothers

 

[racerone]

One reason why I am not using any WOOD in my project boat.---All composite materials being used.---Carbon fiber / kevlar / foam core / West system Epoxy.---Takes longer and materials cost more coins.----But the results are " priceless " as they say.

 

[Decker83]

I agree with classiccat, I would add one thing more,
Try and round over any sharp edges on the transom before using
the cloth glass. This helps the glass lay down without as many
air bubbles. It doesn't take much. just break the edge.
There or several post where people used epoxy without the glass cloth
and had bad results with the plywood checking..

 

[Scott Danforth]

I have used rustoleum oul based paint for years on tinnys

 

[SHSU]

Bummer to hear, but think as mentioned @jbcurt00 left un protected the wood expanded and contracted, hence the failure of the epoxy.

I will say I did not use any fiberglass with my build, but that has been mentioned as a point of potential issue. That being said, I also keep the boat in a garage and not exposed to the elements. If I had the property to store a boat outside, trust me I would get a bigger boat and do that.

SHSU

 

[jdupree]

Thanks to all for the replies/suggestions. I wasn't trying to cut any corners due to money, I just didn't know any better about just using epoxy. I sure learned my lesson!

I think I will go ahead and tackle the deck. Any instructions on what kind of foam to use and where to get it, what size wood, and prep for the wood would be greatly appreciated.

I sure want to do this right!

 

[DLNorth]

Spend some time over on the WoodenBoat site/BB. There are lots of arguments against using epoxy to "seal" wood from water.

 

[racerone]

Visit -----boat building candy stores.------noah's-------Compositescanada----And I am sure many more for information on quality boat building materials.

 

[SHSU]

I think I will go ahead and tackle the deck. Any instructions on what kind of foam to use and where to get it, what size wood, and prep for the wood would be greatly appreciated.

Foam: closed cell is the recommended in the form of foam boards. Don't use the liquid form. Many projects start with shoveling (litteraly) out the old liquid foam that had absorbed water.

Wood for the deck: I think the standard is 1/2 inch from the factory. I went with ~3/4 as I am a bigger guy and didn't want any flex. You can go with marine grade but most don't say its needed. Just need to get BCX from your local hardware store and properly seal it.

Prep/sealing: That is back to what @DLNorth and @racerone mentioned. Lot of info out there. You just got to choose which you think is best for your project and go with it.

That said, I again just used straight epoxy to seal my decks. I think future projects will probably include fiberglass but for now, it is holding up and hope it will for awhile.

Hope that helps

SHSU

 

[Mark ofs]

My .02 cents...I replaced the wood decks on mine this past summer. The original plywood was 7/16", and replaced with the same. I used marine grade, as from what I understand, there are no "voids" in the interior lamination's and you get two good sanded sides you can work with. Standard plywood will usually have some "void" areas in the interior lamination's.

 

[classiccat]

Foam: closed cell is the recommended in the form of foam boards. Don't use the liquid form. Many projects start with shoveling (litteraly) out the old liquid foam that had absorbed water.

Wood for the deck: I think the standard is 1/2 inch from the factory. I went with ~3/4 as I am a bigger guy and didn't want any flex. You can go with marine grade but most don't say its needed. Just need to get BCX from your local hardware store and properly seal it.

Prep/sealing: That is back to what @DLNorth and @racerone mentioned. Lot of info out there. You just got to choose which you think is best for your project and go with it.

That said, I again just used straight epoxy to seal my decks. I think future projects will probably include fiberglass but for now, it is holding up and hope it will for awhile.

Hope that helps

SHSU

i think you'll be fine @SHSU . Your current boat is a garage/trailer queen so little exposure even if you had some checking. For someone planning to store outside or slipped, I'd reconsider.

Plywood sheathed in glass will make it considerably more rigid. I don't notice any flex in my 1/2" main deck. My raised bow deck I went with 3/4" (with reinforcement) due to large hatch cutouts.

this isn't an empirical result...but this is what ~ 180# looks like on my 1/2" glassed SW doors.

 

[racerone]

It is the glass that gives it the strength.-------Look up ----radius of gyration ------Part of structural engineering lingo.-----For the floor I am using 1/2" foam core material with carbon fiber on one side , perhaps kevlar on the other side.----Very strong because the FOAM seperates the strong materials.-----Just look at nature where birds have hollow bones but very strong they are !!

 

[Watermann]

Epoxy with cloth or not if left exposed without anything in the way UV protection will ruin the epoxy and allow water to rot the wood.

 

[jbcurt00]

Epoxy with cloth or not if left exposed without anything in the way UV protection will ruin the epoxy and allow water to rot the wood.

In this case, I think he painted it blue after epoxy

 

[Watermann]

In this case, I think he painted it blue after epoxy

And installed the SW too, must have partially filled with water and sat submerged for years then.