Questions re: classic design

[Joe Swetish]

Hello all.

I’ve been reviewing a set of Tehini plans, and I have some building questions.

So here goes:

1. I’ve read in the other forums about galvanized screws, nails, etc and problems with corrosion. There are also reports of some kinds of stainless corroding. I’ve read that some boats are constructed without metallic fittings, at least below the waterline.

What I was considering was using cheap wood screws to hold parts in place until the epoxy cures, then remove the screws. Then drill out the screw hole, and epoxy a wood dowel in place. This would eliminate metal fittings, and would contribute to shear strength in the joint between the stringers and ply sides of the hull. Is this a good idea?



2. The design improvement booklet with the plans provides larger dimensions for the #1 and #4 bulkheads, raising the deck level of the bow and stern by one foot. The beams are at the same level, and the deck above the fore and aft bunks can be raised, creating beam troughs.

If I were to keep the sheer continuous from the bow to the stern, it would raise the beams by one foot. This would also raise the center deck by one foot. I would like to avoid beam troughs as they seem to serve as a potential water trap. Also, this would provide more headroom over the bunks. Would raising the beams by one foot cause any significant structural problems?


3. Regarding beams, could the beams be built in a straight I-configuration, then planked over with plywood? It would seem to be waterproof a rectangular box than the I-shaped beam.



Thanks for any responses!



Joe

[boatsmith]

We build our boats with epoxy and use deck screws as temporary clamps. We then remove the screws and work Thickened epoxy into the hole and move on. Drilling and doweling seems unnecessary and and then has grain running the wrong way which could result in print-thru and/or act as a conduit for water ingress.
Raising the beam height will increase the leverage load and would require some additional reinforcements but is certainly doable.
Building I section beams and then boxing the I is also feasible, it would certainly add vertical stiffness and make for easier glassing. The Tehini is one of my favorites. David www.boatsmithfl.com

[Joe Swetish]

Thank you very much!

I did consider the dowels would create 5000 or so possible leak points. I guess my concern about the strength of epoxy was unfounded.

I did plan to reinforce the areas below the beams, exactly how I am going to try to figure out later.

Joe

[Dave Mellor]

Hi Joe,
Just sent pics .Tanaui 46 raised beams 10 inches,widened same as tiki 46, extra centre bulkhead,strengthened throughout with focus under beam areas. I have no beam troughs and have a spacious interior.Im also very happy with her perfomance .Joe,as everything i have done is not to plan i have to say it works for me but in saying that leave it up to anyones individual judgement and risk to wander off original plan drawings. Best Dave

[Joe Swetish]

I've read about your boat on the multihull forum, and studied all the pictures you had posted.

It was your boat, and Colin Flynn's, that got me to think a Wharram can be modified without resulting in catastrophe.

Thanks!


Joe

[Neville Saunders]

Joe, a couple of thoughts - I have recently spent a fair bit of time carving out screws left in my Narai. Not sure of what metal they were, but they had rusted, causing expansion of the metal, cracking epoxy and paint, allowing more rust...not good. Dug them out, and filled with epoxy bog. Much better. The Tehini design dates back to a time prior to epoxy being in common use, so you really are using a new building technique - including fillets, giving an increased bonding surface area. Maybe I am wrong, but I would use screws and washers as a clamping tool during assembly, remove and fill with bog. Re your thought on raising the beams and avoiding beamtroughs - great idea - troughs are a pain to maintain. If I were building a new Wharram, one thing I would be trying for would be to eliminate as many nooks and crannies as possible, they create traps for water and dirt, and places for opening of joins. Smooth, clean, simple surfaces are good. Some years ago, I saw a Narai called "Blue Moon" advertised for sale, had been built using beams on deck, so something similar has been done. Good luck with the project.