Tape striping/Stich and glue hybrid

First of all let me thankyou for such a great site. I have been surfing many post and have gained a wealth of knowledge.

I really wanted to do a S&G boat but the shapes lack in curves
I have since acquired a 13ft FG skiff that is completely rotten. It has a beautiful shape and i have begun screwing 6mm ply in a striping style fashion to retain the shape.
I plan on glassing 6oz cloth (?) inside and out and adding front and rear casting platforms and filleting them in.

What i cant find out is if i need to tape the joins in the ply striping. As as far as i can tell you dont tape a striped boat, but you tape a S&G.

Do i need to tape them or will filling with carbosil/glue and 6 oz cloth be enough.

I plan on mounting a 15hp engine.

 

It seems like a fiberglass hull, so it can't possibly be rotten. Where are you screwing plywood to?

 

Welcome to the forum.

Your asking about the engineering of a hybrid construction method. There are about a dozen distinctly different "strip plank" methods. Some are traditional, requiring fasteners and edge set, but no sheathings, while the other end of this spectrum, are really wood cored composites, where the sheathings play such a huge role, they can't work without them and of course several are between these two extremes.

The boat pictured does appear to be a 'glass production, full plane mode thing. Your "scantlings appear to be quite light, for this type of build. If using plywood as your strips, you'll have to bond them with a sheathing, both inside and out, as well as edge bond the strips. Epoxy would be the only adhesive choice in this type of build. 6 ounce cloth is a finishing product and over stripped plywood, will offer next to no strength, just some abrasion resistance and water proofing, assuming full encapsulation of the plywood.

When working on the scantlings for a boat like this, bottom loading is a prime consideration, plus the weight of the major elements (engine, tanks, etc.). Simply put, the hull volume can only hold up so much and top speed potential has to have scantlings adjusted to suit the loading, the bottom will need to endure. This assumes you have the CG in an appropriate place for the performance envelop and hull form balance (plus a crap load of other considerations).

 

Thanks mate.
Please excuse my ignorance, but as I understand it your advising I add extra cross structure (bulk heads) to help spread the stress?

Sort of like adding the strong backs used to build a stich and glue?

Yes I only plan on using epoxy.

The hull had 3 steel bars running through it that had rusted out. Also 2 pieces of timber that were completely rotten.
I was able to snap off the back metre of the boat simply by jumping on the back

 

I'm screwing the ply directly to the outside of the hull, using it as a mould. Unconventional but works well

 

If you are screwing strips of plywood to the hull that is the mold, you will have to fiberglass over the strips. That will prevent you from taking the screws off. The screw would have to go from the inside out. If you do a wood or plywood diagonal lamination over it, you can take only a few screws off at a time.

 

I plan on taping the joints then removing the screws

 

It sounds like you'd have been better off just repairing the old hull.

No, I'm not talking about bulkheads, but the structure's scantlings. This would include the hull shell thickness, increases in thickness in highly loaded areas, which are typically based on target speed and masses, not to mention load paths. Scantlings would also incorporate sheathing schedules, on powerboats longitudinal stringers, engine beds, rail reinforcements, possibly some bulkheads or ring frames, splash well if outboard equipped, etc.

As a rule, plywood isn't the best choice for a core, as it's 2/3's as stiff longitudinally as solid veneers or conventional strip planking with solid stock. This requires a stiffer sheathing schedule and usually a thicker core too.

How much effort have you put into this project, because there are lots of ways to do what you're doing without inventing new build methods, developing appropriate scantlings and engineering on the fly, about stuff you clearly haven't a strong grip on. No offense intended, but if you just take a guess at it, the end result will likely not float where you'd like it to, perform nearly as well as you hope and possibly could be dangerous and/or illegal too.

 

Thanks PAR
Can you recomend any decent plans for a small bass/bay boat ?

Its hard to find plans using new age composite construction.

 

Here ya go. Designed by one of your fellow countrymen.
http://www.bandbyachtdesigns.com/ec018.htm

As PAR said, no offense, but I have never ever seen a project like you are contemplating come off well. The devil is in the details which you may not even be aware of. Best to get some plans from someone who knows what these details are and has routed the devils out before you get to them.

 

I can whole heartily recommend the Marissa as Tom has. It's a great little boat, well designed and thought out and available as a kit too (I think), which can save some bother, cutting time, precise joints and insures good materials.

 

Had a bit of progress.

Since the pic of the inside i have added 2 longitudinal stringers in bettween the keel and the chine.

Still have to add 3 beams that will support the floor and casting platform.

What do you think the capabilities of it would be ?

I know this bowdidge 12ft S&G 6mm is rated to 15hp and does 24knots.
http://www.bowdidgemarinedesigns.com/Bowdidge_Marine_Designs_1/Tropic_12_Study_Plans.html