Flexible Hull?

beauwrath

Recruit
Joined
Jul 2, 2020
Messages
3
I purchased a project boat with my stepson and nephew so they could learn about, and respect, boats from he bottom up. We purchased an 18' 1965 Lonestar fiberglass boat, and have already replaced a crumbling transom.

The problem is, the hull is flexible--very flexible, as in you could easily push it in with just a bit of hand pressure. Initially, I thought it the stringers must have all but disintegrated. But this spring, we removed the floor to find no stringers at all.

My question is, was this intentional? Has anyone owned a boat that's designed to flex? And if we built a stringer system, would that affect the way it handles under speed?

Thanks in advance.
 

Attachments

  • photo334090.jpg
    photo334090.jpg
    106.8 KB · Views: 1

mr 88

Commander
Joined
Nov 3, 2010
Messages
2,205
Not a engineer , if it was me at this point I would either put/glass 2 stringers in running parallel with the keel , about 18 " off it. Maybe even run a couple 2 x4s that would connect to the stringer ,sort of a box effect. Or I would dump the boat and find something newer. The stringers will add stiffness ,which you want in a boat and if anything improves the handling. Usually a stiffer the bottom will improve your speed along with being able to take some waves without worrying about it breaking up.
 

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,721
Some aluminum 14' give or take open fishing boats have/had no stringers and no keel to speak of. John, aluminum flat bottoms have the bottom ribbed, like metal roofing (only inverted) which provides lateral support, besides the ribs and sides relying on the one piece curved ribs attached to the sides to control the bottom.

I was in Florida on vacation one year and a friend set me up with a guide. The boat seemed to be as old as the gent running it. Only boat I ever got in that I could watch the bottom flexing up and down....about 18', wooden, 90 Johnson. I sincerely don't think it was designed that way. Glad we didn't venture out onto open water. Not a fun trip.
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
18,104
I purchased a project boat with my stepson and nephew so they could learn about, and respect, boats from he bottom up. We purchased an 18' 1965 Lonestar fiberglass boat, and have already replaced a crumbling transom.

The problem is, the hull is flexible--very flexible, as in you could easily push it in with just a bit of hand pressure. Initially, I thought it the stringers must have all but disintegrated. But this spring, we removed the floor to find no stringers at all.

My question is, was this intentional? Has anyone owned a boat that's designed to flex? And if we built a stringer system, would that affect the way it handles under speed?

Thanks in advance.

Cheaply made boat . . . shallow hull, so yes, probably intentional.

All boats flex . . . some more than others, it is a matter of what is absolutely needed, vs. what is advisable. Small boats don't need much in terms of structure, and the floor, once joined to the hull, provides some stiffness.

You could add a few stringers for your rebuild . . . if anything - it may improve the boat's performance by keeping the hull's shape more consistent at speed.
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
Scariest "flexing" I've ever experienced was in a brand new late 70's jet boat. Stringers were long enough to create a place to bolt the motor. No floor even. Carpet was glued right to the inside of the hull.
 

Alumarine

Captain
Joined
Feb 22, 2005
Messages
3,735
I wonder if once you sandwich foam between the hull and deck if it would improve the rigidity?
 

mr 88

Commander
Joined
Nov 3, 2010
Messages
2,205
I wonder if once you sandwich foam between the hull and deck if it would improve the rigidity?

Sure ,if you can do it like Boston Whaler, which is highly unlikely for the DIYer. Or have some sort of injection machine that can bond the hull and deck together with no voids. Best bet is stick with encapsulated wooden stringers.
 

tpenfield

Moderator
Staff member
Joined
Jul 18, 2011
Messages
18,104
If I were me, I'd

1) put a few stringers in the hull so that they can support the cockpit floor in a level fashion,

2) Lay the floor down over it

3) fill the chambers with foam

4) put some rigid foam under the foredeck and cap areas.

Go boating . . .
 

beauwrath

Recruit
Joined
Jul 2, 2020
Messages
3
Thanks for the advice, guys. We'll add a few stringers and glue the floor to the top of them with resin putty. That old fiberglass is thing--only two layers from what I can tell and prone to holes by the patch jobs we've found. We're going to add 2 more layers of 1708 before we lay stringers down. I'd feel better having a more solid hull under my feet--especially with Lake Erie's temperament.

Absolutely convinced the boat was cheaply made. We'll try our damndest to have it in better shape than when it came out of the factory.
 

mr 88

Commander
Joined
Nov 3, 2010
Messages
2,205
May want to screw the deck to the stringers as well as the glue. You are still going to get some flexing and over time that may break the glue bonding job. Screws would slow that process down and help ad rigidity.
 
Top