Need help from fiberglass structural expert

Am in the process of converting an older 28' Pearson Cabin Cruiser into a pure fishing boat with a large open cockpit and small cabin with the helm station on top. I have removed the fiberglass top that covered about half of the existing cockpit. Have removed the fiberglass that came down diagonally from the cabin rear bulkhead/hatchway. Have removed the helm station. I want to do away with about 2/3 of the cabin.
Now my question, how will this affect the structural strength of the overall boat. A person told me that fiberglass boats are sort of like unibody cars, they don't have the framework that wood boats have and rely on the entire unit to hold it's self together.
Would like some input from some folks with experience building or rebuilding 'glass boats. If I am losing structural integrity what can I do to overcome the loss (any type of framing, etc?)
'preciate any advice y'all can give. Pel

 

An old-timer once explained it to me this way: Imagine a shoe box without its lid on - you can twist it every which way, but if you glue or tape the lid on it becomes surprisingly stiff. A boat, wood or glass, behaves in much the same way as that shoe box. If you start removing parts of the deck, cockpit or superstructure (the lid) you'll lose stiffness unless that stucture is replaced somehow.

It's also not correct to say that glass boats don't have framing. Unless it's a canoe or other small boat, glass boats have frames, stringers, and bulkheads.

This isn't to say that you can't do what you're planning to do. Removing part of the cabin and extending the cockpit shouldn't be a problem as long as you don't start taking out bulkheads. Raising the steering station (through the cabin roof I assume) also shouldn't be a problem since the new structure will replace the removed material. What it does to the centre of gravity is another story though.

From your description it's hard to visualize precisely what you've done and plan to do. Post some pictures and/or drawings and I'll try to give you some tips on how to proceed.

 

Re Fiberglass mods

Hi there
I have worked in the fiberglass industry for over 20 yrs in most forms of building Renovation and Mold making. Eleven of those yrs was with my own shop. What you are proposeing to do is not that difficult if you are a fairly handy person. One who doesnt mind getting dirty and itchy for a while. Modifying a GRP boat is a fairly simple afair with very little need for rocket science. If you take out or remove a bulkheadyou must replace it somewhere reletivly close to where it was. You can taper your bulkheads in very quikly after aprox 8-10" above the waterline.Best advice is look at simular boats to what you want. Talk to the owners look on net and draw somw pictures what works on a hull simular to yours will work on yours is just a slightly different taste in desighn and styles of the yrs.Fiberglass is a great material to work with if you take the time to talk to supliers read and watch how its done it will save a lot of time and mess

jpampu@shaw.ca