Question about taping

Hi All

I am thinking about all the work involved with taping, for example the hull to bulkhead etc. Assuming taping is secondary bond anyway...what is the difference if I lay three layers wet in wet vs pre-produce an L-shaped piece of the same three layers and just glue it in place?

I'm aware the problem might be the shape of the bulkhead, but let's just assume for a moment it's a simple Wharram style V-shape with straight edges...wouldn't it be a lot easier to first produce the L-shape, then glue it to the bulkhead and then glue the skin of the hull? What am I missing?


Thank you
Adrian

 

You are making too many assumptions Adrian. The tape layers need to conform absolutely to the shape of the hull.

These hull/bulkhead tapes are a good example; nearly nothing is 90 degrees because of the hullshape. The fillet is made and I prefer immediately taping. This can be done using hot glue to hold the bulkhead or anything.

I actually wetout all the tapes on the table and transfer them into the hull.

Here, the tapes on my side of BH are 90+ and the reverse 90-, and you could never do it prefab as they change in angle up and down the hull. The other thing is the tapes need to be overlapped at 1-2" at the chines, etc.

The side tapes on this cat are about 33' long, and so to do the main side tapes, I wetout 200 feet of tapes one day and laid them on the sides. Use a cardboard tube to roll them on and off the table/boat.

 

An additional important point I missed in the above is hardpoints need to be avoided whenever possible.

So, if you were to prefab; your overlaps would be all in the same places and for 3 tapes meeting at a corner; you'd be raising one of the corners up over 3 tapes or more and all of the ends would be hardpoints versus some staggering. I will mention that none of the tapes in the picture are butt seamed, so some effort is made when measuring to plan the overlaps. And the common add is 25-50mm, although too much overlap is bad; some is needed..as a general rule, I made all my tapes about an inch longer than the intersection and push some up and some down. I found that 2" resulted in some bunching, but I hated measuring short...rounding up about an inch also makes keeping track easier as 18" is easier than 17 1/8", or in metric, something like 10s would work, so tapes are all ending with 0

When applying the bh/hull tapes; in addition to developing stagger on the width; I also tried to stagger the ends; even if just a bit. This problem only manifests itself on the boat. Your prefab tapes would fail here..

How? You take a paper and clipboard and write all the desired dimensions down with a sharpie on the BH and the paper. On the BH, I like black sharpie markers, never red!

Then go cut the tapes and sharpie mark them with dimensions. Then when you get to the boat with 20 tapes sometimes (or more), you can usually get them applied correctly and without going nuts as the tapes show say 17" and so does the boat, etc. I used cardboard for a transfer board...fyi and never stack them neatly as they are harder to find and exo faster! I always wanted to csm side down, so I wrote the dimension on the side I wanted to see which also helped me with the tape direction, if using biax only tapes; it doesn't matter unless you are cutting the overlaps fancier for chines, or darting, etc.

The red markers were literally showing through my first few coats of primer...under tap

 

Curves and bevels make it unlikely that you could choose a "one size fits all" section to manufacture.Even in a simple chine hull,the bevel on one face of a bulkhead can not be the same as the bevel on the other face-unless the boat is a basic square box.While laminating in place means that a good fit is inevitable and you can use lengths that vary as long as the joints in successive layers are staggered.

 

Some manufacturers glue the pre-made stringer grid in place and call it good. Others glue it and then tab it in place, some just tab it.

The glue only crowd have it engineered and tested to ensure it will hold.

 

Thank you for your answers, especially fallguy for all your explanations...It looks like I was seeing things to simple...

I was "inspired" seeing how Leopards are glued together and the manufacturer didn't have problems using 20mm of glue (whatever it was exactly) to make things match.

 

There are boats that don't use tapes, all that holds them together are fillets. The Didi series from Dix for example can be built without any taping, and there were others. When Plexus and similar became widely used I heard of a method of fastening bulkheads into slots (the core was relieved for a single skin transition and the bulkhead was beveled).
There is also the question of engineering, not everything that goes into the boat necessarily needs taping, it depends on how the structure was designed. For example a main bulkhead might need it, but most of the furniture might not.

 

A surveyor pal of mine recently came across (here in the Caribbean) a sailing catamaran with a liveaboard couple from a very popular builder that was having serious problems - all of the bulkheads and frames had been simply 'glued' in with Sikaflex (no additional tabbing was employed), and the bonds were all enthusiastically deteriorating (the vessel is about 20 years old).

My pal knows his onions for sure about sailing cats, and he has been around the world on his 40' Catana over the last 15 years.

Edit adding a note later - they were scratching their heads trying to decide what would be the 'easiest' (or least difficult) way of fixing all these problems - but short of stripping everything out in order to properly tab in all the bulkheads and frames, it will be very difficult.
And here was I thinking that a Sikaflex (or 5200, or similar other material) joint should last indefinitely if done 'properly'.