Triaxial versus woven.......

[Roly]

Can anyone clarify my thinking here......
My estimation is that 90deg +/- 45deg triaxial is nearly double the strength of
woven glass of the same weight in the 90deg dirrection? Is this borne out in reality?
David Gerr's book (Elements of boat strength) for strip planked glass/wood/glass gives a glass exterior weight of 1500gm for scantling number of 1.6 using woven glass. If one substituted triaxial instead, could one reduce the glass weight? The strip scantling wood thickness exceeds spec. by both dimension and density.

[nero]

MacNaughton's Sheathed Strip Construction Scantlings Rule calculates for the amount of glass running 90 degrees from the planking. It also calculates for carbon fibers for the same.

Perhaps Gerr's book does the same.

MacNaughton claims that triaxel used to counter torsional loads is not neccessary. I used unidirectional glass on my cat hulls.

[Raggi_Thor]

I think Mac Naughton is right. It's like plywood, you don't have any 45 degrees veneers. The wood in the core is strong enough longitudinally and at 45 deegrees angle, but not at 90 degrees of the fibres. That's where you need the glass or carbon (or another layer of wood).

[Roly]

I have new timber & glue lines between the planks to within 500mm of the sheer but I am concerned about the integrity of the glue lines from sheer to WL. The old strips are nailed with 65x2.8mm edge nails but I thought the two 45's would compensate for this unknown adhesion factor in these. Any open lines we will clean out and force epoxy in. I am also removing the transverse framing from inside the boat and glassing inside. To reduce the athwartship framing MacNaughton states that this can only be done if the vessel is cold moulded with 45deg & fore & aft veneers. Sheathed scantling rules -3rd edition
(or, in my interpretation, has layers of glass at 45deg.)
MacNaughton's Sheathed Strip Construction Scantlings Rule calculates for the amount of glass running 90 degrees from the planking. It also calculates for carbon fibers for the same.

Nero, my booklet (Sheathed Strip Construction Scantling Rules.- MacNaughton & assoc.) is not specific.
"Cloth and epoxy skin"
"The glass cloth weight of the total thickness of each skin, in oz/sqyd, equals 3.67 x ^3. If carbon fibres are used you should use .037 x ^3. (at .01" nominal thichness)"
Does "glass cloth" mean uni-directional? Where does it say that?
Thanks for your help---I need to get this right!!

BTW--I may leave a few trans. frames in , in the chain plate area on the old planking & glass over. (they are only 50 x 40mm)

[Windvang]

It all depends on how big the boat is, 1500g/m2 triax is more or less bulletproof on boats up to 50'. I always use triax in woodcore with some extra 0 deg. ud in the foreward slamming area.

[Roly]

LOA 34'
LWL 29'
Beam 10.25'
Displ 3.5tons
Draft 5.5'
ballast 3360lbs

"with some extra 0 deg. ud in the foreward slamming area."
How much? Station 2 to 6, or just forward of the mast?
Thanks for your comments!

I think that is the area where the old glue lines let go.

[Windvang]

Without calculations I would say around 900g/m2 will be save with a 350g/m2
UD running form 1' behind mast bulkhead to bow up to 1' above w.l. Rebate the planks a bit for a smooth transition.

My GT 33 design, with nearly the same spec., is even lighter than that without any problems.

Regards,
Arthur

[nero]

I called MacNaughton and asked a few questions about what type of glass would be appropriate for my project. From what I remember, he stated that it was only the fibers across the planking that were counted in the cloth weight. He likes unidirectional cloth, but said it could be difficult for some to get the cloth to lay correctly.

I had no problem laying dry cloth across the planks on my lightbulb hull. I work alone. Sometimes it is neccessary to trap and pull some of the uni strands straight.

Send Tom MacNaughton an email to verify.

[Roly]

Many thanks for the responses! I might put it to Tom on his definition of "glass cloth" but I have pestered him enough. Advice given me (obviously without eyeballing) was light glass or no glass, and beefed up frames)
(Consensus from Tom Mac. & others)

I have gone with restripping with new timber to waterline and any > 19%mc above wl.
Now,my gut feel is to brace hull with glass so I can remove frames (contaminated with diesel/moisture), glass interior and insert lesser weight grid & glassed in floors. Total encapsulation.
Arthurs numbers/glass type, correlate with Hi-modulus fabric Ltd
engineers advice (810gm), and the extra band in the slam load zone rings bells for me. Worth the effort? Probably, not but it is the only boat we will have so, hell, we can't turn back now.
This problem has occurred in this boat before and various attempts at a fix
were made,unsuccessfully! I prefer a more complete approach.

Thanks again,
Roly
----"pukka sahib"------1969 Stewart 34

[nero]

You could go ahead and re-strip the rest of the boat. That way you would have a new boat with no hidden hardware.

Currious as to how much damage to planking there will be when you demo the inside framing? Could the holes act as a perforated line similiar to paper sheets on a tablet? probably not.

If not maybe adding new planking to the waterline plus 10 cm would be a good idea.

Another idea: Perhaps you can epoxy coat one joint before you remove the planks. Then you could destruction test the pannel joint to see what type of bond and depth of epoxy penetration you can expect.

Continued good luck and courage! Obviously, you're doing quality work.

[Roly]

If not maybe adding new planking to the waterline plus 10 cm would be a good idea.

Nearly complete.



Screws will be removed after glue sets & bottom glassed and faired. Flip & remove frames & fill any holes with micro fibres. Cut off any fastners
to old strips rather than removing. Glass interior to shear clamp. Glass in new floors /ring frames/bulkheads to accepted centres.(Sounds a stupid way to (re)build a boat huh!) It was either this or burn it.

Is your cat in the water? Any pic's..please! A cat is on the wish list.
Roly

[nero]

My cat is far from the water. It will be another 4 years at my present pace.

There are several picts of what I have built posted in the multihull gallery.

The design has changed. I am shortening up the back of the deck and adding another trampoline. Also going to dual helms.

[zerogara]

If nothing else, a very good looking design. Good job nero!
I hate the rig though!

[Roly]

To reduce the athwartship framing MacNaughton states that this can only be done if the vessel is cold moulded with 45deg & fore & aft veneers. Sheathed scantling rules -3rd edition

Remove "only".
His first paragraph states,"Sheathed strip planking differs from other construction methods in having no athwartships or longitudinal framing."

As edge glued strip plank is torsionally very stiff ,a cold moulded veneer, or biaxial glass at +/- 45deg is not needed. (In the frameless, sheathed, context.)

I think I would be more comfortable with the correct wt of glass to rule transversely and an extra component +/- 45 and take the weight penalty.
As a house builder, diagonal bracing makes me feel secure. All those uni fibres across the grain just seem like an invitation for parallel stress cracks.
No reflection on Tom's rules, just my own insecurity.

My apologies for the mis-quote.

And,Tip of the hat to Nero.... re the uni. ( English is my first an only language???) Duh!

Roly