Refit Advice-Stringers/Laminations/Strategy-15Ft 600lb Flats Boat

[Chesfisherman1]

Hi All,
I am in the planning stages of refitting my 2010 15ft Flats Boat and need input (or therapy).
-Boat Background:

Length 15'
Beam 7'
Transom Height 20"
Max Horsepower 70hp (Have Honda BF50 ~210lbs)
Max Persons 4
Draft 6"
Weight 600 pounds (not sure if this is with engine/fuel tank/etc)​

-The hull is from a production mold with Gel Coat then 2 or 3 layers of fiberglass mesh
-The stringers are foam with a white plastic base and were glassed into hull with 2-3 layers of mesh.
-There appears to be no structural bulkheads that perform a hard bond of the hull to the liner.
-The deck is PVC core.
-The hull to deck/liner bonding was performed with a considerable amount of structural putty. (still hard as a rock)
-the last addition was flotation foam (not sure if 2/4/6 lb) through out hull/liner voids. No foam or reinforcement from chine up the rub rail hull/liner join.​

AS-IS: I have a true "Free Floating" flexible boat hull/Egg shell that balloons which fail sooner than later. Last month, I cut front portion of deck out and drilled 4 6" access holes in the rear deck and by the stern/transom for visual inspection. Results-

-no/low putty bond hull/liner
-failed stringers-wet and debonded
-stress cracks inside perpendicular to stringers
-stress cracks inside longitudinal in high flex unsupported areas.
-stress cracks on outside gel coat skin-mostly longitudinal.
-prior owner "fixes" were not small, appeared structural with a cosmetic fix.​

Questions:
Stringers
1-I want to install a stringer system that effective and active. (ie. coosa or arjay).

1.a Is this a dumb move given my hull is an egg shell? (see 2 where bulk up hull is discussed)
1.b If not too dumb...is there a buffer material used between the "hard" stringer material and the "soft" hull that will decrease hard spot issues?​

Hull
2-Bulk up hull for strength.

2.a Is a hand lay up of CSM/1708/Kevlar/1708/CSM on the exterior over kill?
2.b Can interior structural reinforcement be performed with stringers/bulk heads, hull/liner bonds with Plexus MA, and a final 8 lbs floatation foam under deck...without doing hand layup discussed in 2.a.
​

I would appreciate any/all feedback. Trying to schedule a trip down to pop the cap for refit and want to ensure I don't under or over kill this project. I not trying to make my 5k skiff a 35k hell's bay...but i would like it to be safe and structurally sound.

Thanks,
Chesfisherman

 

[Chesfisherman1]

Please see reference pictures of front deck cut out and hole

 

[KD8NPB]

Stiffness and strength are two different animals.

What are you trying to achieve exactly?

If you want to stop the cracks, fix the problems and foam the cavities. That will stop the flexing. Fiberglass is generally heavy and un-needed.