How would you make this repair?

TL;DR - how would you fix the leaky cracks?

Long version:
So, a couple months ago, I picked up a Santa Cruz Raptor from a member here.  It was free, but needs some repair - it developed cracks in the seat area, was repaired before, and has cracked again.

I took it for a quick shakedown ride, and everything else seems good. On a calm lake, no water in the hull, which tells me that below the waterline all is well. I did notice that the seat lip deformed under my weight. I'm about 210lbs, and it was warm out.

Got home, sprayed with the garden hose to clean up, and sent a little camera into the hull and it is definitely dripping through the cracks in the seat area.

So, I'm thinking I have to address two things:
1: the leaky cracks
2: the soft plastic that doesn't support my weight.

I am worried that if I just plastic weld the cracks again, my weight will say the seat area again, and just re-crack the new work.

I've got two idea right now to address this:
1: cut out a large area around the seat, add rigid foam to the hull to help support my weight, reinforce the piece I cut out with new plastic, and then plastic weld the piece back in place, or
2: scrape off old repairs, make new repairs to get it water tight again, and try to stuff rigid foam pieces through the hatch and align them under the seat area.

I'm leaning towards option 1, because I think it will be easier and faster, but I would be introducing a lot of new plastic welds to what is already a pretty old boat, so I might end up with more leaks. Option 2 would be tricky to get all the pieces in place, but I'd probably end up with a better overall repair.

So, what do y'all think? I really like this hull - it is super stable and paddles nicely, and I think if I get it water tight, it will make an excellent boat for my saltwater pursuits.

I'd go option 2.

I've been dealing with leaky Malibu X-Factors for lots of years - same spot, same type of issue.  One X - my original Malibu - finally went to the dump it got so bad.  The other 3 all have various repairs/liabilities.  You'll never fully escape the trouble from cracks like this, IMO, and cutting it more to do a major surgery and 'joint replacement' in a place like the seat well, that flexes more than anywhere on the boat, is pushing your luck, as I see it. 

Scraping all of that old repair off, and then really dedicating some time and ingenuity to getting some kind of bracing under the cracked areas before welding it back together sounds like a plan.  I think you should also consider putting a big, ugly piece of Flex Tape (~$20 for a 5' x 8" roll at Ace) over the repairs to cap it off.  The shit's gonna move again, crack again, leak again and possibly kill the boat, but...  you can prolong its life and possibly enjoy a full life with it!  You'll find out, when monitoring how much leaks in on various levels of rough/choppy days and when various levels of weight are carried on the boat. 

I have also used stainless steel mending braces in the past, but the additional screw holes near the already compromised plastic cracks may have led to the death of the first X...  The stainless braces over welded cracks, coated with 3M 5200, all with foam bracing underneath, eventually failed, but that boat had been through a lot!

Best of luck.   

Thanks for the advice, Eric, and thanks for validating my concern with cutting out the whole seat - I think option 2 is the best path. For the repair itself, I think I'm gonna do basically what the previous repair did, melt some hdpe into the damaged area. I might try to also add a whole fresh later on top of that too, and kinda laminate them together, just to stiffen everything.  The flex tape is a great idea too - will pick some of that up.

I'm also gonna try to wedge some rigid foam under the seat, just to get some more support and keep it from sagging too much.

This will definitely be a "stuff as many pool noodles in as I can" kinda boat when I'm finished, but I'm hopeful that she has a few years left in her.

Here is how far I made it today. Gotta go to work now, will continue a bit tomorrow!

https://www.manualslib.com/manual/1930116/Malibu-Kayaks-X-Factor.html

I'd contact Baitman, who is the dude who made that boat, and see what he suggests. You might even be able to hire him to plastic weld it for you. I got a G2 from him, and it had a few minor leaks that he welded, and they were never a problem after that.

As for reinforcing the seat, my Hobies have pieces of rigid foam wedged into that area (and a few other high-stress areas). That seems to work well.

As for cutting a giant hole in the boat as a way to repair much smaller holes... That seems like a bad idea to me...

I'd contact Baitman, who is the dude who made that boat, and see what he suggests. You might even be able to hire him to plastic weld it for you. I got a G2 from him, and it had a few minor leaks that he welded, and they were never a problem after that.

Thanks for this - I will reach out to him.

As for reinforcing the seat, my Hobies have pieces of rigid foam wedged into that area (and a few other high-stress areas). That seems to work well.

Yes, I think a lot of kayaks have foam built in as double duty - support for weight bearing surfaces and additional flotation should the boat become swamped.

As for cutting a giant hole in the boat as a way to repair much smaller holes... That seems like a bad idea to me...

Yeah, it was a thought I had to give me some space to work with to introduce more support, but I'm gonna try to re-do the patches and see where we get.  Once that is done, I have some foam to shape into blocks that will get crammed under the seat for extra support.  Fortunately there is a big hatch in the front that I should be able to stuff some foam blocks through, and hatches in the back that I can use to help maneuver the blocks into place.  I think if I can keep the new patch as rigid as possible, it will hopefully not crack again.   

Bucket patch in place. I left the mesh that was previously in place. It was embedded in the hull plastic, so I figured it would do more damage to remove it than to just leave it.

For material, I used a harbor freight bucket. They are also made of HDPE, the material is pretty thick, and I actually wanted a different color so I could easily see how much base material was mixing with the patch material.

I found heat gun on low along with the plastic welder was the winning technique. I got the base surface nice and hot whole waiting for the plastic welder to heat up. Then, using strips of the bucket, I just worked my way from the center to the edges of the patch area. I put a layer over the center first, then another full layer over the whole patch area.  I feel good about the patch.

At Eric's suggestion, I'm gonna put a layer of flex tape over the patches areas. I got the gorilla brand tape, but it's the same stuff. Super sticky glue layer under a very tough tape layer. This stuff would probably make a pretty good hull protection tape, haha.

Now, to figure out how to place some reinforcement foam under the seat area. I got some 1" foam board, and cut it into 6"x8" pieces, then glued them flat sides together into 2" thick pieces. That's as tall as I can squeeze under the center pocket, so I gotta figure out how to get them on top of each other, under the seat, and secure them in place.

It looks sturdy!

Kevin, How about adding another layer of mesh and plastic over the entire seat area. That way, its supported around the rim of the seat and tied into good solid material. It may not be very pretty but it will spread the weight stress out over a larger area.
Kevin

Kevin, How about adding another layer of mesh and plastic over the entire seat area. That way, its supported around the rim of the seat and tied into good solid material. It may not be very pretty but it will spread the weight stress out over a larger area.
Kevin

Hey Kevin, I thought about that. I still have about 2/3 of a bucket, haha. I feel good about the patch I did yesterday, and I'm working on placing some structural foam under the seat to reinforce it from below. If my repairs still crack, then I will definitely do a large patch to the whole area, with heavy duty mesh embedded under it. 

Maybe heat the whole bucket in an oven and cut a large sheet and from in to,the seat area.   Then weld the sides.

I think I'm done until I test it. I wedged big foam blocks under the seat, between the seat and the bottom of the hull. They are in there pretty tight, and I am confident they will support my weight, which will in turn help prevent cracks in the new material.

Was a bit of an adventure getting them in there though. They had to go in the front hatch, but there wasn't enough space to fully assemble them outside the kayak first, so I had to slide 3 pieces in through the front hatch, all the way to the rear hatches, where I glued them together before wedging them in place.

I also replaced the front hatch gasket - it was kinda leaky also.

All in all, I think it's gonna work out! Will do the garden hose test soon, and I hope to get it on the start again soon!