1973 Monark transom/stress crack repair

Bantou · Sep 8, 2024

Would you bother trying to get this crack fixed or just replace the wood and call it good?

If you would fix it, would you get it welded or just slap a piece of 1/8” aluminum angle over the whole transom cap? I’m leaning towards the aluminum angle. If I put it on the inside, I can bolt/rivet it so that it sandwiches the wood between it and the aluminum transom.

FuzzyGrub · Sep 8, 2024

I'd removve the transom wood before finalizing on a repair plan.

Is this for the 15HP in your other thread? What is max rating for HP on the boat?

Bantou · Sep 8, 2024

That's a really good question that I don't have the answer to. I can't find the plate on it anywhere and the title doesn't include a model number for me to locate a manual with. I went with the smallest motor recommended for a 16' Jon boat.

Edit to add: It looks like the max hp rating for a 16' 1973 Monark is between 20-35hp depending on the model.

Bantou · Sep 8, 2024

The boat is in pretty rough shape overall but still serviceable

Pictures for reference

FuzzyGrub · Sep 8, 2024

Yes, the typical 1648 would have a max hp more than 15. Probably 25-30. Mine has a 40hp max.

Yea, she has seen better days. If you haven't, do a leak check so you have a good overall assessment before diving into the transom.

Is the transom wood 1.5" thick?

My concern with the angle, is can you get it to sit flat on both edges? Putting a level to the edges will show how much "correction" might be needed. There is a transom angle, so the 90 degree wouldn't sit perfect.

Bantou · Sep 8, 2024

I did a float test with a 3.5 hp motor while deciding if it was worth moving forward on. It has an extremely slow leak from the drain hole but is otherwise water tight. The drain hole is mushroomed on the inside and slightly out of round on the outside. The drain plug was in pretty rough shape though. I’m going to get a new plug and see what that does before taking further action on the hole.

Edit: Given how this boat has been cared for, I suspect that it is currently undersized but I don't know for sure.

Would a C-channel work better than the angle? I ran across some other posts on here that used c-channel for a similar repair while researching.

FuzzyGrub · Sep 9, 2024

I think C channel would be harder to get a tight fit. Does the transom wood go all the way to the floor? It looks like it does from the pic, which is unusual, but I not familiar with our boat model. If it does, my guess it has been replaced by a prior owner.

LDUBS · Sep 9, 2024

Whether you use angle or channel, I would want to make sure the exposed edge of the new ply is covered. I kind of like the idea of channel covering the whole thing, but suspect finding a stock size that would fit will be a problem.

I'm like @FuzzyGrub . The transom wood going all the way to the floor seems unusual. I would hold the new transom wood back away from the bottom of the hull. Maybe about where that shadow line is from the strap in your first pic.

DaleH · Sep 9, 2024

FWIW I just replaced the transom wood in a sweet FRP hull and needed to replace the tin trim cap as I went with a thicker layup transom.

I just ordered a 5' long length of 1/8" thick wall 6061 channel, with a looooong 1-3/4" tall 'leg' on each side, to allow me to securely bolt it to the new transom layup (SS bolts properly insulated from the tin of course ...), for only $40. IMHO most trim caps eventually weep water into the wood from the rivets or aluminum trim nails driven vertically straight down into the underlying wood.

Now that piece is certainly overkill for most trim cap applications, LOL, but that's how I roll. Well hey, the wood was free and I had copious amounts of epoxy & glass mat/tape on hand.

Link = http://www.metalsupermarkets.com

Bantou · Sep 9, 2024

DaleH said:
I just ordered a 5' long length of 1/8" thick wall 6061 channel, with a looooong 1-3/4" tall 'leg'

Does the stainless not corrode the aluminum? the original plan was to just use a piece of angle iron but I've been told that, that would eat away the aluminum.

Whatever I do, I'm going to secure it through the top of the transom, not the cap. I will get more support that way, and sealing it up with marine grade sealant should prevent any leaks until long after I'm done with it.

Bantou · Sep 9, 2024

FuzzyGrub said:
Does the transom wood go all the way to the floor?

It stops about 1/2" above the floor. Looking at the picture of the drain hole, I'd be willing to bet a significant sum that the current transom is a replacement. The cut out for the drain hole does not line up well with the hole.

FuzzyGrub · Sep 9, 2024

Bantou said:
It stops about 1/2" above the floor. Looking at the picture of the drain hole, I'd be willing to bet a significant sum that the current transom is a replacement. The cut out for the drain hole does not line up well with the hole.

Yea, it is looking like it was a replacement.

Do you have a wood plate on the outside of the transom, where the motor mounts? If you do, it is likely that the inside is 3/4" and outside is 3/4", to make up the typical 1.5" transom. I have a lite 14' boat that the transom is like that.

Once you have the wood out, can determine if the part that is cracked, is structural or mainly a protective cap.

Bantou · Sep 9, 2024

The outside is bare aluminum, no wood.

It's going to be a hot minute before I get around to pulling the wood out. I need to get the motor working and get siding on a shed before I start on this project. The list of "quick and easy" fixes that aren't going to be nearly as quick and easy are stacking up quickly on this thing lol

FuzzyGrub · Sep 9, 2024

They never are.

DaleH · Sep 10, 2024

Bantou said:
Does the stainless not corrode the aluminum? the original plan was to just use a piece of angle iron but I've been told that, that would eat away the aluminum.

Yes, it could, and will (especially if used in saltwater!), if not properly isolated, but the hull I added this to was fiberglass, not tin ...

Simple isloation for anything SS to tin can be accomplished by layers of duct tape, heatshrink on bolt/fasteners bodies, or nylon washers, just for example. For bolts, the US Navy even developed a 'goop' made expressly for use when adding SS hardware or bolts to their aluminum hulled detroyers and frigates, called "Tef-Gel". Expen$ive, but works!

My 1st tin hull refurb done 30-years ago or more ... I just used layers of duct tape to isolate the SS panels and/or hardware from the tin hull. About 20-years later the guy I sold it too called me and asked for advice on how I particularly attached something. Long story shortened ... he brought the boat to my house, I took apart that feature ... and lo' and behold, the duct tape was still sound and there was ZERO evidence of any galvanic corrosion between the 2 dissimilar materials, even on the SS bolt bodies or the surround tin they pierced through!

Bantou said:
Whatever I do, I'm going to secure it through the top of the transom, not the cap. I will get more support that way, and sealing it up with marine grade sealant should prevent any leaks until long after I'm done with it.

I agree 110%, good thinkin'!

LDUBS · Sep 10, 2024

Bantou said:
Does the stainless not corrode the aluminum? the original plan was to just use a piece of angle iron but I've been told that, that would eat away the aluminum.

Beyond galvanic corrosion the other reason I would avoid using angle iron is simply that it will rust. Sure it can be protected, but it isn't worth it when there is a better option.

Bantou · Sep 10, 2024

LDUBS said:
Beyond galvanic corrosion the other reason I would avoid using angle iron is simply that it will rust. Sure it can be protected, but it isn't worth it when there is a better option.

I was thinking angle iron because it is cheap and stronger than aluminum of a similar size. The plan for this boat was to do it quick and cheap, use it for a couple of years, and then trade up.

Jokes on me though. I’m not one to do something that I know is going to cause problems for someone else down the road. As a result, nothing about this project is going to be especially cheap or all that easy lol

Bantou · Sep 10, 2024

DaleH said:
Simple isloation for anything SS to tin can be accomplished by layers of duct tape, heatshrink on bolt/fasteners bodies, or nylon washers, just for example.

I don't know why I didn't think of a separation layer. I work in commercial roofing and we put one down all the time when overlaying an existing roof.

DaleH said:
For bolts, the US Navy even developed a 'goop' made expressly for use when adding SS

I wonder if Penetrox or a Dielectric grease would do the same thing, or at least close enough for this purpose. A quick google search says "it should" but that's a hell of a lesson to learn the hard way.

LDUBS · Sep 11, 2024

Bantou said:
I was thinking angle iron because it is cheap and stronger than aluminum of a similar size. The plan for this boat was to do it quick and cheap, use it for a couple of years, and then trade up.

Jokes on me though. I’m not one to do something that I know is going to cause problems for someone else down the road. As a result, nothing about this project is going to be especially cheap or all that easy lol

Is the boat used in fresh water? Reason I ask is if so, the exposure to galvanic corrosion would be significantly reduced. Still, use aluminum instead of iron angle.

Bantou · Sep 11, 2024

Yes, exclusively in fresh water. Mostly on Aquilla Lake in Texas

1973 Monark transom/stress crack repair

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