Quick question - increasing the shear

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?

 

Do you have any photos that you can post of the boat that you want to modify?

If not, what is the current hull depth and width, if the hull length is 18'?
And what type of hull form - displacement, planing, semi-planing......?
How did you determine that it "needs" less than a foot of additional height of the sheerline?

Edit - I posted the above before I saw that you had posted the same question your 'Need a naval architect' thread here -
I need a naval architect please https://www.boatdesign.net/threads/i-need-a-naval-architect-please.68154/page-5

And then I realised that the boat in question is the TX-18 sea sled - that boat which you have just bought in the other thread looks like a good bargain!

 

The thing about adding sheer is the strength, as I said on the other forum. You'll want to create a bonding flange; then add the sheer, but a whole foot is going to need frame extension and/or gunwhale put up; otherwise you hit a dock and she'll crack on you, not to mention, overtime; it'll sag sans frames.

The guys on the other forum are all ply people. The bonding flange can be made using 1708 tabbing; something like 3 layers, 6,5,4" or staggers of say all 5" pieces starting at 3" on the old boat, 2" on new, 2" old, 3" new, 1" old 4" new, or close. The ply former is nice because it'll hold the old hull shape; so the glass way is harder to get right.

 

If the boat is unfinished; you can also bolt the former to the outside and wax it like 4-5 times and add your extension and glass tab it on the inside, add the frames to the inside and the gunwhale, then remove the former and glass the outside.. the glass needs a minimum 2" overlap. I might go something like 3",2",1"

 

Thank you so much banjansailor and fallguy. Frames are not in at this time and the plans call for an 8" gunnel of 3/8" okume and are included in the kit. The frames will be cut longer to match the additional shear with knees at the gunnel.

How wide do you think the former should be for this application?

It's a TX 18 hull and cnc kit I got as a partially completed project. Hull panels are tabbed and glassed inside and out, stringers are stuck in but not filleted yet. No fairing compound or paint.

Current depth is 17" and was wanting to increase to 28". Hull width is 7.9'. Planing hull, inverted V. It's designed as a low sided center console flats type hull and I would like to make it into a dual console seating arrangement - the higher shear will add peace of mind to myself and Mrs. Geno when we're offshore.

The designer (Jacques Mertens) said he doesn't care what seating arrangement I do as long as I respect the hull/frame/stringer requirements.

First owner build thread is here: TX 18 Build - Boat Builder Central - Builder Forums https://www.community.boatbuildercentral.com/forum/viewtopic.php?f=12&t=25638

 

Another approach would be to use transverse frames and the gunwhale as the molds for the sheer.

 

We really need a picture of the inside of the hull to help you best.

 

The full size mdf frame templates are included and are stacked up at the back left corner of the shop.

 

So, this boat is intended to be monocoque construction. If you apply permanent frames; you won't be able to glass well.

I'd hotglue temporary frames to the outside of the hull to support the sheer changes you desire.

Then spot hotglue the sheer extension and glass it with a 2" overlap onto existing hull/sheer. Not knowing the glass schedule, if it is 1 layer of db1200; then you will need more tabbing at the seam. So, tab it with say a 6" db1200 patch all the way around over the 2" overlap one inch and 3" onto new sheer.

Then apply structural framing and the gunwhale; bonding to the existing hull and new shear; you may need to use xtra putty to deal with the tabbing.

Then once the structural work is all complete; remove the hotglued formers and glass the outside to spec with staggered overlaps.

how I'd do it

 

You will have to find a way to deal with the existing sheer clamp/gunwhale because it must go. Probably cut it off unless wholly impractical..

on further, I see it is same height as transom

so, you'll want to keep the thing back at the transom and maybe cut it off or grind it off the hullsides in the other plane....

 

I was planning on cutting/grinding that sheer clamp right off there. Formers are just temporary frames on the outside. Makes a ton more sense now, I wasn't understanding what you were saying to begin with. I think that is a very good plan.

 

Want to be clear about grinding this off. It will take a day and some safety gear and maybe flap discs. But should be ground off in the vertical plane and not cut off in the horizontal plane because you will affect hull integrity..

 

Actually, a router would work best with a fence set for the top edge of the hull..

 

Flap discs on a grinder are the best invention since sliced bread. If you have fine motor skills, anyway.

I do not have a router but was planning to purchase one along with an electric planer for the build.

 

You can add an extension to the inside and leave the rubrail in place. The new sheer will have a second rubrail. Make it an aesthetic feature.