Aluminum Crack Repair

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he lives
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Aluminum Crack Repair

Post by he lives »

Hi All,

A couple years back a buddy and I went in together on an 18.5' Aluminum Jon Boat that came with a Mercury 115hp 2-stroke and a bow mounted trolling motor. We've been using it for duck hunting and fishing, but want to take it on some bigger rivers for salmon fishing. We have picked up a 9.9 4-stroke kicker motor to use for trolling and to have as a backup engine to get us off the water in a pinch.

When we bought the boat it had a couple cracks in the "cap" of the rear transom. The cracks haven't grown in the 3 years that we've owned the boat, but we want to get it repaired before mounting the kicker motor. I'm hoping to get some advice on the best way to repair a couple cracks like this. My first thought would be to drill a hole near the tip of the crack to prevent them from running, and then have a fab shop weld it close?

I'm also not quite sure how cracks like this formed in the first place and want to avoid them returning once the repairs are done. Do you think it could be from previous owners not using a transom brace when trailering?

PS the photos make the cracks look worse than they are because the boats paint is peeling a bit as well.

Any advice is much appreciated.
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Skiffing
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Aluminum Crack Repair

Post by Skiffing »

You can see the previous repair at these cracks where the cap is welded. What's the boat rated for? Do you have too many ponies?

Stain in 3rd pictures shows water is getting inside. Engine probably kicks up spray that get inside the outside edge of the cap.

Is there a wood core? If so, check DaleH current thread - 'cause that's what you'll be doing :(

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BigTerp
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Aluminum Crack Repair

Post by BigTerp »

Looks like those are caused by the stress the motor puts on the transom. My transom cap welds are both cracking on the fore portion of the caps where they are welded to the gunnel. My buddy welded them up last year, but they are just coming back. I'm going to take some 1x1 aluminum square tube and run it from the top corners of my transom riser to right in front of my transom caps. Weld the tube in place creating some reinforcement and keep my transom from flexing as much with the stress of the motor. Should do the trick.
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DaleH
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Aluminum Crack Repair

Post by DaleH »

BigTerp wrote:Looks like those are caused by the stress the motor puts on the transom.
Ditto ... you don't need a REPAIR ... you need a REPLACEMENT!

And fix the transom core, as the crack on that piece is a symptom that the transom is flexing.
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he lives
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Aluminum Crack Repair

Post by he lives »

Thanks for the responses so far. Seems unanimous that the transom wood should be replaced. I'm very new to boats, so what would the risks be of getting those cracks welded up and running it to the end of the season before replacing the transom wood?

lckstckn2smknbrls
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Aluminum Crack Repair

Post by lckstckn2smknbrls »

I would also make bigger corner caps, have them come closer to the motor.
1971 14' Ward's Sea King Jon Boat / 1983 Mariner 25HP

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Captain Ahab
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Aluminum Crack Repair

Post by Captain Ahab »

he lives wrote:Thanks for the responses so far. Seems unanimous that the transom wood should be replaced. I'm very new to boats, so what would the risks be of getting those cracks welded up and running it to the end of the season before replacing the transom wood?
Quick fix:


Get some fairly thick aluminum L or Channel - Reinforce the entire top of the transom and either bolt or weld on


I would also reinforce inside with some flat plate Aluminum especially around where the motor bolts through - does require you remove the motor(s)
Trying to Fish as often as Jim works :LOL2:

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Captain Ahab
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Aluminum Crack Repair

Post by Captain Ahab »

Skiffing wrote:You can see the previous repair at these cracks where the cap is welded. What's the boat rated for? Do you have too many ponies?

115 hp Merc is gonna be some weight and torque (on the transom) on a boat that small
Trying to Fish as often as Jim works :LOL2:

he lives
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Aluminum Crack Repair

Post by he lives »

All,

Just getting home from work and I am reading back through the responses you sent and the consensus is that the cracks are caused from the engine overloading the strength of the transom. Sounds like the likely possibility is that the wood core of the transom has rotted, leaving a void and weakening the transom. Unfortunately, the boat is sitting across the state right now, so I can't inspect it until I pick it up this weekend.

I'm also understanding that welding the cracks would be a waste of time and money, as they will just reform. I'm probably just trying to convince myself the transom wood doesn't need to be replaced [-o< , but does anyone think its possible that the cracks may have formed from towing the boat without a transom brace?

I need to look at the boat to further assess the cracks, but if replacing the transom wood isn't going to be feasible (this is a welded, not riveted jon boat), I may try to do as Capt Ahab suggested and "recap" the length of the transom with some channel or angle. Distributing the normal force that the engine applies to the transom with a plate seems like good advice as well.

lckstckn2smknbrls
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Aluminum Crack Repair

Post by lckstckn2smknbrls »

Remove the wood transom and replace it with a all aluminum transom.
1971 14' Ward's Sea King Jon Boat / 1983 Mariner 25HP

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richg99
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Aluminum Crack Repair

Post by richg99 »

There are lots of things that I'll do, but "going to sea" in a boat with a very large engine, hung on a suspect transom, isn't one of them.

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BigTerp
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Aluminum Crack Repair

Post by BigTerp »

I just reinforced my transom riser yesterday. The welds on the fore portion of my corner caps were starting to crack. We fixed the cracks last fall, but they are coming back. My transom flexes noticeably when underway. Nothing crazy by any means, but enough that you can see it. I have a Johnson 50/35 which is right at the max motor size my Coast Guard plate says I can put on my boat. I'm sure my homemade transom riser sort of "centers" the forces/stress my motor puts on my transom. We used 1x1 aluminum square tube. Raised the motor a bit with a floor jack to take the static stress off the transom and then welded the tube on. It REALLY stiffened up my transom.

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he lives
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Aluminum Crack Repair

Post by he lives »

That looks great BigTerp...I'm sure those aluminum struts help to give some bending resistance to the center of the transom.

My boat has a deck that runs right up to the transom, so I'd have to get a little creative on running struts similar to yours. I'd also be slightly leery of tying into the side rails of my boat. I've never seen anything getting into the specifics of boat design, but I imagine they're designed as a membrane type system. In that case, the rails on my boat would not be meant to absorb the type of forces put out by my engine.

A little off topic, but has anyone ever run across the calcs involved in developing the HP ratings for transoms?

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