old fiberglass - how to stiffen

Hello all,

I received an acient fiberglass canoe, much like a clipper, and I am trying to bring it back to life for family/fishing use.

I have replaced the decks, staves, and added wooden seats that brace against the sides of the boat. However, the bottom is still VERY flexy. This boat was made before kevlar or carbon, and is pure glass. How can I stiffen this?

Add ribs? I am a metal sculptor, and have access to stainless to make ribs. I could glass them in.

Add Kevlar or Carbon? I suppose I could run cloth down the middle, with more layers in the center moving out to the sides.

Thoughts? Suggestions? Flames?


Without seeing it…
my quess might be. Forget kevlar it’s too flexible. You might run strips of 2 inch carbon tape down the center and then glass over that… or for less $s a few stringers of wood down the center and glass over them… good luck

In your opinion…
Does the entire needs-to-be-stiffer * AREA * need to be beefed up or do you think a few well spaced ribs ( transverse and logitudinal ) would do the trick ?

In other words, does the entire layup feel soft and sort of broken down or does the layup feel solid but in need of a few ‘studs’ to stiffen it up.

The latter would be way less work to do.

No real need for the SS if you are glassing anyway. Save your money and skip the carbon too… a few plys of unidirectional glass + a 0/90 to consolidate things in a few key spots works wonders.

Call or email if you want to go over it.

What is it? If an old chopper gun or mat
layup there is little you can do. You would be building another canoe inside or outside just to stiffen and make sea worthy the old one.

Find the serial number, ID the hull, and then ask your question again.

Serial number should be on stern of hull under the gunwales either inside or outside the hull. May be plate of metal or something, “Sharpie” written, or imbossed in the hull material.


no id
well, I have looked everywhere for a serial, to no avail. Looked into area around the floatation tanks as well, when I re-did the decks. This thing has been painted at LEAST 3 times, so who knows. No plates anywhere to be found.

Overall, I think that some ribs would work wonders, as it flexes mainly in the center of the hull, but across the whole bottom, not like pockets of weakness.

when the boat bounces on chop or swells it will flex, but not with hand pressure.

I had an old boat with a similar problem and used 2" fiberglass tape and resin to makes the “ribs.”

It worked like a charm.

glass tape as ribs
How many layers of tape did you use? I assume a “bi-axial”? I am pretty new to this work.


Some Hulls Do Flex
Our Oneida 18 tends to flex in the mid-section of the hull - that is, unless there’s gear aboard, the centre of the boat bulges up. While this has never really concerned us from a safety/durability point of view, it has to slow the canoe somewhat. To help with this, I just placed an 18" piece of 1/4" x 4" pine along the hull’s interior centreline, then jammed a snug fitting upright stick atop it under the centre thwart. This keeps the bottom relatively flat. I could glass it in, of course, but we don’t use the Oneida very much any more, and since our makeshift solution works…

First, it’s not "tape’ in the “sticky tape” sense. It’s simply a narrow roll of bias-cut fiberglass cloth…so it needs to be soaked in resin, applied and squeegeed. I like MAS epoxies. They are pretty forgiving to work with. Here’s my source for materials.


I only used a single layer since I needed reinforcment, not “structural integrity.”

I cut the tape long enough to run from gunwale to gunwale…about 50 inches.

I’m sure if you wanted, you could simply cut a large piece of fiberglass and drop it in the center of your canoe like a bathtub.

Good luck! When it comes to crafting anything, I’m more optimism than skill.