How to fix gap in side of fiberglass hull

Sounds suspect to me, and perhaps misleading, intensional or not.
Anywhere a crack appears should be ground down extensively and glassed accordingly.
This is significant damage and requires an extensive repair.
Not sure a boat design forum is your best source of advice in this case.
Is there a qualified repair facility or surveyor who can give you sound advice in person?
Pictures are a far cry from an in person evaluation.

 

As mentioned, it doesn't really look like wave damage, at least not from just a couple of pics.

 

I completely agree.

 

The boat has white bore bonding putty in it, I can tell mostly at the chine joint of the horizontal and vertical balsa coring...By color - it is white - what type of core bonding "putty" do you think it is? Or should I use regular thickened resin for this repair

 

He did show me pictures of the boat partially sinking in the water while hes was driving it...I will be checking the stringers under the floor also, but from what I've already looked at not much other damage is showing

He might of hit some debris or maybe even a rock in the water...

I have the inside fiberglassed and will cut back more coring before it is replaced

More pics to come

 

Check the stringers before you spend any more time on it. If there is a structural deficit in the stringer; fixing this part is lipstick on a pig.

put ship tape on the plywood, overlapping it, releases well

I figured it got run into. In order for a wave to break the boat up there; you’d need a deficit in the cap or stringers I’d say.

 

It may well be that there is a need to look at the stringers,but it probably won't be as a result of any collision.A topside impact is unlikely to have caused such,however if the boat has sat around with water in the bilge,it could be that water penetration has occurred and should the stringers have a wooden core,there may be some deterioration.A stringer repair is an order of magnitude easier to carry out as the cosmetic aspect can be disregarded.I tend to agree that the damage didn't look to have a connection with wave action.From a safety point of view the biggest challenge will be achieving a solid bond between the new outer skin and the core that will need to be added.I hope our OP has given the matter some thought

 

Here's the damage before I started tearing into it...

 

Got a good release and flush enough alignment outside - obviously large area to repair /round the edges/color match on the exterior - I liked your idea of the parting board secured with self tapping screws and packaging tape, very easy to install but now I have to address all the screw holes before I put coreing on the inside !! The inside is somewhat flush as well so I don't expect much issue installing the balsa core. I will use putty and even have large transom clamps for the vertical piece and can weight down the floor section with blocks

 

The pre-repair photos are interesting.
No impact marks indicating water induced damage, but how?
Did the boat go completely airborne at speed, rotate (roll) and hit stern first from the top-side?
But then the outboard would have been ripped off leaving tearout in the mounting holes.
If only there was video of the event.

No offence @aaronhl, but this is a job for a professional. ($$$ I get it)
Your patch corners should be radiused, the patch areas should be larger
allowing for 20:1 transition taper to better distribute loading.

Is there no one in your area that can give you hands on guidance?

 

I'm semi professional so why pay someone else to do it if the point of the project is to learn things myself? This and that is what I SHOULD be doing but nothing is going to be perfect...I don't feel I have hacked it up too badly so far

As far as the 20:1 I used 12:1, maybe even a little larger than that

The edges/corners will be radious a little from the outside before I laay down fiberglass from the exterior

What would you recommend for core putty if I dont thicken regular resin?

I've noticed in the small floor area where I removed the core, that the fiberglass (gelcoat and layers) is only about 1/16" thick with 5/8 thick balsa core. The vertical fiberglass sides are 1/8" thick with 1/2" balsa core.

Yes he was hitting large waves - this is an smaller offshore powerboat - I think the crest of one of the waves knocked through the bottom of the boat and took a vertical brace with it, cracking the side and pushing the top up at the same time

 

Because the learning curve is too steep.
The repair will be finished, all that work and money spent and time invested
and then it fails and you've learned it wasn't done properly.
Is that cost effective learning? No.
Again, I'm not interested in insulting you, my motivation is to help you.

Why not 20:1? That's not "perfect" it's what's accepted as standard in a repair.

Those aren't the corners I was referring to. Your actual patch corners.
Too late now.

I wouldn't use balsa, I'd use low density microballoons. Are you using WestSystem?

Ah, okay, I hadn't considered that mechanism of damage. That's a pretty serious impact. Why didn't he repair it?

 

I don't mean to discourage you Aaron but I'm concerned this is not repairable.
There's just too much visible damage and who knows how much invisible damage...

 

This is a polyester project and will be matching existing balsa

 

Okay, I'm starting to catch on now.
And I now see you're using mat and presumably polyester not epoxy.
I don't think my advice is going to help you.
Sorry to have rattled your cage.
Carry on.

EDIT: Sorry, didn't see your last post before I posted this.