Stringers is the subject !!

[powerabout]

I have a mid 80's Cajun bass boat with an alum honeycomb transom core. Kevlar laid at keel for impact with stumps and logs....I think it was ahead of the curve..

Thats way cool

[W2F a V-King]

That should hold at least 150 cuban refugees and six thousand pounds of coke.

Now that's funny right there.....born/raised in Miami....yup I agree.

Wonder if the customs seized boat yard is still in Key Largo? I always admired all the cool confiscated boats stacked up like crackers in a row.
What a waste of glass and ponies...

[W2F a V-King]

Ever set in the last row on a jet and look up the alley on take off?? Yea, They do flex a bit. And how about those wings?

Here is an article on Hull designs that addresses flexing hulls vs ridged hulls. I copy and pasted a couple snipets from it, however it is not to large to read, but to much to copy and paste here.

http://www.yachtsurvey.com/HullFailPart1.htm

“In the meantime, the conventional stringer, bulkhead and frame system is the method used by about 98% of all boats over 30 feet.”

“ Rigid or Flexible Hulls
Aluminum and steel boats are examples of vessels built to be completely rigid. By the nature of the material, these hulls will not tolerate flexing.
Fiberglass boats, however, are another story. Fiberglass boats can be designed to be either flexible or rigid. For example, if you examine Bertram hulls built over the years one can see a very abrupt change in hull design philosophy. Somewhere in the mid 1980's, Bertram made a transition from very rigid hulls to fairly flexible hulls. And as the Bertram engineers have proved from years of extensive R&D (they were one of the few boat builders that took R&D seriously) you can build light, floppy hulls without danger of them falling apart. Moreover, there is a legitimate need to attempt to reduce costs by reducing the weight of the most costly materials. All you have to do to see how this is possible is to look at the aircraft industry which has invested billions in R&D.”

“ There are limits, of course, to just how far a designer can go with flexibility. In terms of rigidity, we're talking about the difference of the bottom flexing 1/4 to 1/2" or not at all. With the increasing lust for speed and advent of high performance diesels, flexibility causes serious problems. Flexibility is okay for slow or moderate speed vessels, but becomes disastrous to high speed yachts. The reason is not so much inherent in the hull structure itself, but rather in the drive train. Delivering a thousand or more horsepower through a long and large diameter shaft demands higher tolerances of the drive system, and therefore mandates more rigid hulls, not less. Along the length of a 30' drive train, the hull must be absolutely rigid; it cannot deflect or twist lest the whole drive system be thrown out of alignment. “

Bottom line ( no pun intended ) If it goes really fast...no flex. If it is a cruiser some flex is OK, even desirable.

[tunnels]

I really hope lots of people read the yacht survey report number one and two !! very good logical reasoning regardless of what sized boat you working on !! the twist and flex subject is very comprehensive and very important! and the age old subject of stiff hard riding boats built like a tank has its share of inherent problems but with clever design the stability problems could be all but done away with !

[powerabout]

Modern bertrams are flexible because the outside core and inside are not connected
Plenty of failures on new boats and one on the seabed during delivery to prove that

[tunnels]

[QUOTE=powerabout;2928722]Modern bertrams are flexible because the outside core and inside are not connected
Plenty of failures on new boats and one on the seabed during delivery to prove that[/QUOT

So who and what do you blame for the failures ?? and if its something new what are the causes of the failures workmanship , wrong materials , what ?? please we are all interested, explain and elaborate fully !!we would like to know and understand !
Thank you

[W2F a V-King]

Didn't do a lot of searching, but these two came up pretty quick>>

Workmanship not design, and this one was fortunate enough to make it back to port...
http://www.yachtsurvey.com/bad_news_for_Bertram.htm

Another one here that sank being moved from NY to Florida, looks like they hit a buoy and sank??
http://bertram31.com/newbb/viewtopic.php?t=5057

Bottom line ( pun intended ) is even a good design can fall apart if not assembled properly.
The poor designs fail without help.

So what say you tunnels...how do you bed and install stringers on a cored hull?

And if your stringer is 12 ft. long, and your material of choice comes in 8 ft. lengths, how do you make a strong one piece stringer ??

[XstreamVking]

Kinda blows holes (no pun intended) on the idea of the 0/90 uni being the best glass for a hull layup. They had giant filaments going fore and aft with nothing to bond them together and spread the load.

[tunnels]

Kinda blows holes (no pun intended) on the idea of the 0/90 uni being the best glass for a hull layup. They had giant filaments going fore and aft with nothing to bond them together and spread the load.

unidirectional and 0/90 are two completely different animals !! don't get confused, be careful when you dealing with different types of fabrics !! this where confusion creeps in !!
Its deffinitly the wrong place to use any kind of just unidirectional by its self that's for sure !!!!and just goes to show the experiance or lack of by all the non thinking people involved with that whole project from the idiot that thought of or even considered it and then made the decision all the way down through the ranks !!,some one must have had doubts and should have know it was never going to work to the idiots doing the job !!

[tunnels]

Myself I never trust computer predictions specially written by some button pusher that has never had any hands on experiance and doesn't fully understand the products they are supposed to be going to use !!
I always place the plans on the work bench and get all my guys to look and study every detail drawn and written and see if there are any mistakes that are not obviously seen!! There have been such times when some one has picked up a mistake and we all check it so recognie's what the problem is and everyone is familiar as to what to look for next time we are given drawings !!
I love sending drawings back to the office with a note that there's a potential problem but not saying exactly what it is so the person has to find it and then come back to us down on the floor ! Im a sadist at heart when it comes dealing with experts that cant accept they are wrong !!

[powerabout]

High Modulus New Zealand were the pioneers of computer FEA for all glass types, changed the thinking for many an old boat builder

[tunnels]

High Modulus New Zealand were the pioneers of computer FEA for all glass types, changed the thinking for many an old boat builder

Yip sure made me think and want to know more and more and never stop learning ! Mr Richard Honey was the man !! even the last article in the professional boat builder mag he was correcting and making guys think and use the brains !!
Take a simple laminate glass stack of a few different types of glass and with a little knowledge its changes that stack into being much stronger and easier to lay !and if you want to be picky its possible to do away with 1 or 2 layers even
!Remember up to 40 +% of glass used to make mostpower boats is deffinitly not needed !!

[W2F a V-King]

Is there a proper way to add length to a stringer without compromising the integrity of the stringer?

Say your materials come in 8 ft. lengths, and you need a 12 ft. stringer..... ?

[XstreamVking]

Knife edge them (scarf joint) Place glass in between the 2 pcs going along the length of the boards for a few feet each direction. Then just glass normally over them. On 3/4'' thick stringer material I scarf back 12''. jm2cts

[W2F a V-King]

Like this?



I had planned on 1/2' thick stringers, maybe go 3/4" out of a composite material, corelite board 26lb. density.