How much of a strength increase is realized with tape over a fillet?

Planning to start a modified 12 foot Glider by Mark Gumprecht as a practice run for the 16-18 foot sled. I'll be increasing the beam by 1.6 feet and fitting a full width sole instead of having a center seat over the tunnel with your feet down in the hulls.

My question is should I tape the outside joins between sole and hulls which make up the top of the tunnel sides and the outside of the sole/cross beam which make up the front and rear edge of the tunnel or would fillets be strong enough?

I'll be starting with an electric trolling motor but may put a 10 hp or so outboard on her in the future. Changes I've made to his design are beam increase to 5 feet instead of 3.4 feet, 11/32" full width sole instead of 1/4" seat, keeping the frames at station 2 instead of them being temporary (since the sole will sit on top of them) and increased the front and rear cross beam thickness from 1/4" to 11/32".

 

"oversize" fillets inside would be strong enough....BUT.....tape outside of the joint does a far better job of protecting ply end grain than just plain epoxy. I would not hesitate to use tape, the cost is little, resin use is hardly any more, and possibly less AND lighter dependant on your fillet medium .

 

Lightweight 4hp at the most. Look for an old Johnson/Evinrude CR3 block 2 cylinder 3 or 4 hp. The 3hp one cylinders (they are all Tohatsu powered as far as I know) have plenty of power for it, but are a bit tinny and vibrate quite a bit. I did some silly strength testing using an old 2 stroke six hp and got my cat dink up to about 30 knots and went wake jumping with it. WAY overpowered for my 85 pound boat.

I'm guessing the glider pictured is 4mm meranti throughout. To increase the beam, and to accommodate motor power, you will need 6mm stuff. Fir or Okoume with a 4 oz skin and taped seams, or 6 oz skins overlapped 2 inches at all joinery should work.

I'd also recommend extending the foredeck forward if motor powered.

 

This one will be lucky to stay under 150 just bare hull. Then it will be loaded up with me (165 lbs), the doggo (120 lbs), an occasional passenger (230 lbs), lights, wire, fuel, battery, engine, anchors, rode, chain and fishing gear. I plan to stow everything as out of the way as possible so she'll get four hatches in the sole and might get a couple in the rear decks.

The designer calls for 3mm luan on sides and deck, 6mm luan on frames, seat, cross beams and bottoms. Spruce for stringers and mahogany for rails and beams. With 4 oz glass on bottoms and 1-1/2" up the sides. No tape anywhere. The plans say suitable for small outboard but no max hp is stated. I agree on moving the foredeck forward to minimize spray.

I was planning to use 1/4" (6mm - species undecided at this point. Will be exterior grade WBP, boil tested first and probably not marine grade) everywhere except sole and cross beams (11/32). I intend to heat infuse every piece with one coat of epoxy and then wet on wet a couple more coats, tape the outside seams, cross beam and frame/hull joins and run the bottom glass up about 6-7" higher to get below the waterline sheathed. I don't have access to any spruce I really want to use. I don't like the look or the price of mahogany. I do have access to real southern yellow pine for a dollar a board foot if you can believe that and sassafras for about half again that. Both are incredibly tough and rot/insect resistant. They are both stacked and sticked and have been sitting outside under a shed for a year or so at the sawmill.

She will be trailer launched and recovered with every use and stored inside.

 

Here's how I did my dink floor when I rebuilt it. It is practical and very strong. And having a gutter around the edges keeps things dry(er).

 

The way I would regard it is that a fillet will probably hold the face veneers together inside the boat,but doesn't guarantee that the glue within the ply will be enough to hold everything in place.Adding tape to the outside will seal the edge grain and tie the outer veneers together.Using tape would be my choice.