Adding shear to an existing hull

[Geno-67]

If you had a plywood hull that's already glassed, could you add a couple of identical panels to each side to increase the shear? Let's say it's an 18' with 6mm okume sides and needs less than a foot of additional side height. Is this doable? I was thinking a butt joint with 6" 12 oz strips on each side would do the trick but maybe I'm wrong.

[TomTom]

The best way to do this would be to overlap another panel with the existing panel.

Drop this panel say 4- 6 inches from the sheer line and then extend however much you want to add upwards whilst following the shape of the bow and transom.

Have a look at the C19 or OD 18 or the FS17 extended sheer as examples of this.

This will be much easier than trying to butt joint.

[joe2700]

Yes I built my FS17 with the raised sheer option and I think it's the standard way to build the c17. Very easy and I also used it to modify the sheer line not just height. But yeah don't butt joint just overlap unless you really don't want the line to be visible. I think on the FS17 it was a 12 in panel with a 6" overlap and 6" added height. I did more like 4" added height at the stern and 8" added height at the bow.

[TomW1]

Geno unfortunately a butt joint will not work. You will have to do an overlap as done in the FS, C and OD series of boats are built, in which the panels are over lapped. This means that you will have to sand all the epoxy and fiberglass off the lower panel to the bare wood. Then attach the new upper panel to it.

Tom

[Geno-67]

So not as easy as I would have hoped. I wonder how seaworthy the TX 18 is in the snot without a high bow and sides? Might be easier to put a rail around it. I just bought a project hull and cnc kit.

I've been using a McKee Craft DC 1800 for a decade now after my wife made me buy a "seaworthy" vessel. I fished offshore in a rowboat as a child (US Virgin Islands) and in an inboard ski boat as an adult. I run 20-40 miles out in the GOM. She's getting too heavy for me to launch and recover in my old age and she is a rough/wet ride in anything over 2 feet and under 2 second cycle.

[fallguy1000]

A bit worse than just adding the sheer and making a bonding flange. The new sheer is going to be pretty weak at 12" high, so you need gunwhale or some way ti stiffen it structurally on top.

[Jaysen]

I think you’re over estimating the effort.

If you want to raise the line by 4”, cut a 9-10” wide (match the existing shear line profile) strip. Make it as long as the entire hull side. Then make a parallel line 4” down from the TOP of the new panel on the inside surface the entire length. Make a mark 5” down from TOP of existing hull on outside of hull. These are your alignment lines. Apply glue (thickened epoxy) to prepared surfaces, align, secure, wait.

That’s it.

Fillet the overlap and glass is really really smart inside and out. Keeps things from breaking off particularly when you get into bigger widths. You might stiffen with extending frames and gunwale at 4”, over 4”, you need to even with glass.

Don’t be afraid of this change if you are keeping it short and constant height. It gets messier with higher and variable height.

Good luck.

[joe2700]

Geno unfortunately a butt joint will not work. You will have to do an overlap as done in the FS, C and OD series of boats are built, in which the panels are over lapped. This means that you will have to sand all the epoxy and fiberglass off the lower panel to the bare wood. Then attach the new upper panel to it.

Tom

Why do you feel you would have to sand off the fiberglass from the lower panel? If the fiberglass is bonded well to the lower panel there should be no problem glueing another panel on top of it. If there is paint or fairing compound yeah sand that off, but not fiberglass or epoxy which should have a bond to the wood underneath stronger than the wood itself.

I think Jaysen has this right both for the steps to take and that it is really not that hard. I think the biggest amount of effort here is honestly that you are increasing the surface area you have to finish.

[Geno-67]

There's no paint or fairing compound on it - just glass and epoxy. I would like to make the TX 18 into a dual console seating arrangement with a walk through windshield.

[Jaysen]

Make sure you give any cured epoxy areas a good “scuff” before glueing new things to it. Cured epoxy relies on mechanical adhesion not chemical. I like 60 grit for the scuff.

If you’re looking to go 12” higher you will need to extend frames. Consider a larger overlap too. Take a look at the various hulls that use overlapping panel methods to see how the joining works. Extending the frames isn’t hard. Create the extension segment. Create reinforcing plates for each side (extend minimum 50% up the extension and equal down). Glue and pin it together. Plane or sand it fair to the line of the hull.

I would do that BEFORE assembling the panels.

I’d say you’ve got a good start there. Should be a fun build to watch!