Catastrophic delamination on a new Bertram

[tunnels]

Originally Posted by Alik

Wrong statement. Core is part of structure and it works for SHEAR, while skins work for TENSION and COMPRESSION.

And as far as floatation is concerned forget it on any sized boat .
dont for get when in compression buckling and possibly skin shear as well in rare situations

Originally Posted by tunnels

I would like to see the video you are refering to ! can you put up the video address again please .
Tell me how glass boats should be built ! what would you use and how would you use it for the hull construction of a 36 ft power boat that should do 25 to 35 knots and what kind of hp would you recommend to get the boat to that speed ! Single motor or twins ?

The link still is where it was posted yesterday. (of course reading a bit would help to get familiar with the topic, BEFORE one contradicts)

No, I will not tell you what I WOULD use or how I WOULD calculate propulsion demands for your entertainment.

And I do´nt produce GRP boats in the range you asked.

My production line goes from 17 to 30 meter in wood epoxy and from 32 to 46 meter in GRP.

For the latter I use solid laminate for the entire hull, the only proven and honest way to do it.

The Bertram boat in question was completely destroyed (I mean completely, even the transom fell off), by hitting something (maybe just diving in a wave, but most likely a buoy), with the bow at 1,5 meter ABOVE waterline!!!
She HAD a solid laminated bottom.

Originally Posted by tunnels

dont for get when in compression buckling and possibly skin shear as well in rare situations

Could you please use another formulation for this? I did not understand. Thanks.

Regards
Richard

ahh, did I mention: foam cored hulls are crap?

[Fanie]

You need to really think about what you have written here !! so if you have a strong skin inside and out it dosent matter what the core is !! are you really sure about that ???

In your case I would like to see it is lead Where did I say it doesn't matter what the core is ? We're discussing foam cores in hulls so obviously I refer to them.

so if the glass on each side of the core comes loose and the core crumbles it dosent matter ! is that what you are saying ? its what i am reading !!

Correct. in the sense that even if the core evaporates then the hull structure must not be compromised - is why this thead was started in the first place. Go back and look at those pictures and you will see why the hull perished.

As for the 'sheer' component, I have two foam sheets here that is used for marine foam core hulls. I can rip it apart easily by hand, shearing, bending, any way you prefer. It will not contribute to any kind of strength, and I will not use it in any of my boats. I use PE foam and for good reason, but not structure or shear or whatever else you want to add.

One question = do you build boats for a living ??

So by implication you say that if one does not make a living out of boat building you don't know **** ? If your argument is correct then Richard is right because he has built the most boats around here

[Fanie]

Originally Posted by tunnels

And as far as floatation is concerned forget it on any sized boat .
dont for get when in compression buckling and possibly skin shear as well in rare situations

Floatation is one of the main concerns for using core materials, especially foam cores,
which is why many boats can be rated 'unsinkable'.

What do you use it for ? Structure ?

[Fanie]

For the latter I use solid laminate for the entire hull, the only proven and honest way to do it.

CORRECT, I 100% agree !

After that is in place you can add whatever you like for booyancy etc, because then it won't compromise the structure strength.

Originally Posted by Fanie

What do you use it for ? Structure ?

That is the crux Fanie, yes they do.

It is absolutely correct that a cored panel is much stiffer than the two platings together, but unfortunately stiffness is only one part of the game.

And ALL, absolutely ALL foams fail in core composites, there is no excemption. Balsa is a better core material, but has other issues as we all know.

So, leave it where it belongs, short living race machines.

Alfred Neubauer the racing director of Mercedes Benz said once:

"The best racecar is the one that falls in pieces right behind the chequered flag"

But of course customers want "high tech" "performance" "state of the art" as Alik mentioned so well.

Give them what they want! But only to a certain degree, the life and safety of those premature critters are still in our hands, and we have to take care of them!

Regards
Richard

Unbelievable video. Or, no unbelievable that this is a 20M boat, falls in pieces like gingerbredhouse.

Good we build in wood!

Sasha

Just a update (at least for this auditorium).

Too often the core foam cr@p pops up on different threads.

Look at these pictures, read the text carefully, understand what you see,

http://www.yachtforums.com/forums/be...ram-630-a.html

and forget about that **** in boatbuilding! forever!

Regards
Richard

Core, no core. Lay up your own panels and beat 'em with a sledge hammer!
You'll learn a lot very quickly and have a lot o' fun too.
This particular builder has had some very serious difficulties meeting payroll since the italians took over. When you don't pay a guy Friday he may not be there Monday. And when you have a limited lamination "window" with no workers on the floor to stay within that window......well.....secondary bond.
Not too reliable when working with "esters".
This was not the only delamination failure for these guys.

[tunnels]

Its the age old story !! 90 % of failures are bad workmanship and poor quaility control the other 10% is bad choice of materials and not understanding them !!

[Ilan Voyager]

Originally Posted by tunnels

Its the age old story !! 90 % of failures are bad workmanship and poor quaility control the other 10% is bad choice of materials and not understanding them !!

I agree totally with the statements you made in your posts of this thread. I have worked on glass fiber-cored boats since more than 30 years with none problem of delamination.

It's a well known technic today and the engineering has no special difficulties; the shipyard Tecimar mastered it already in 1972.

I've worked on boats from 18 feet to several mine hunters made in sandwich and honeycomb, all strong (mine hunters need to be very strong...thus the use of a fiberglass sandwich) and sound.

Lot of cored composite boats are mass produced in Europe with no particular problems. Several fishing boats until 50-60m long have been made sucessfully in cored foberglass.
And I almost forget all the race multihulls of the 80's which are always navigating.

These failures come of a very poor craftmanship and engineering, not from the cored system principle by itself. I would say rather it seems that some shipyards are unable to master sandwich boat building.

[tunnels]

Once a company gets in this deep its better to shut the door and walk away and dont look back . its been posted on the net and thousands of people will have seen and read all the posts . the company name will always be remembered for what has happened and all there boat will be frowned upon for ever more . The second hand value of these boat will have slumped drasticly after all this write up i would say . No news like bad news , no one is interested in good stories but they sure as hell like bad stories .