single skin vs. sandwich fiberglass

(laughing) yeeeeaaaahhhh...that doesn't sound good

...in concept though the hull should be smooth and fair but not "stiff" in a seaway--no way- no how.

kinda like building a ferro hull and plastering it with a single skin of frp.

i wouldnt wanna be out in a half gale in one...but thats me--maybe i'm totally wrong about it...im no expert. kudo's to the guy for experimenting!!
hope he got to enjoy his own boats..i think he built 3?? last post by him was 2011...about a year ago.

 

Firts lets have a look at what you building !! pictures drawings and size !!

 

So a core is of no use at all is what you saying ?? <insult towards another member removed>

 

An interesting point to throw in here about now!!. Built a 147 foot super yacht with 6000 hp the solid glass bottom was 15 mm thick !!! topsides 40mm thick foam core
The 90 foot boat we are making now will go in the water soon also solid glass hull bottom with 25 mm balsa core in topsides 15 mm thick bottom !!!
All the other power boats we make (28 to 48 feet) are all solid glass from the chine down and have a cored topsides!!
Why would any one want 3/4 inch thick solid glass ?? you obviously dont know glass very well and you need you bumps feeling !!!!

Realisticly 3/4 thick would actually break easyer than a thinner glass hull !!Confusing ah !!!!
Its all to do with the choice of materials and how you use them is the key !!

I have said many time here on boat design "know and understand the material you use!!"
90% of frp failures are from bad workmanship with lack of understanding and 10% from bad choice of materials !!

 

the Core used does have structural properties
the term "composite" means the sum of the parts are stronger than the whole -so it does by definition have structural properties. what determines just how much is a big question...
at the extremes:
core cell @ 12 lb density and 3/4 inch thick would need maybe one skin per side and would probably not be holed with a sledgehammer blow...probably just bounce off it. 5 lb density will just deflect and return to its original shape.


OTOH pet foam might as well be paper mache. I personally like core below the waterline--just not certain types-like balsa- or ply.
others to me are acceptable but im no expert. ive never seen airex but i salivate at the thought of doing a destrucive test on some..

I also think that honeycomb has real potential for below the waterline use since water cannot rot it- or migrate through -it will only stay in local areas and even then it cannot absorb much water period. honeycomb is mega stiff- and 1/4 the price of corecell.

 

No you have some strange thoughts about glass and they are totally confussing and mixed up .
Honey comb has no place in boats full stop so never even consider it any where for anything . oops Sorry let me back up a little Nida core is something i really dont think of as honey comb even though is . but never in a hull . yes people have used and has worked ,BUT!!panels and floor boards ,furnature and all those kinds of things yes but not hulls .
Glasses there new weaves and fabrics coming out all the time all differant all have there uses and all need to be understood how they are made and where thay could be best used . also what resins you use with what materials and the list goes on and on .
You can not compair honey comb with core-cell its 1/4 the price because theres 1/50 of the material there !! it came from the aircraft industry and thats where it should have stayed !! .

 

Maybe you could act more maturely for someone who signs themselves "Old One". The forum is not a place for insults and hot headed remarks.

No I didn't say a core is of no use at all. That would be a stupid statement from anyone.

 

old one says Sorry for the insult but reading this put words on my screen But foam is core and core is foam !!how ever you use it !

 

Could even use cheese. 2 threads running very close.

Truth being then that you could use nothing at all if you could fibre glass over nothing.

 

Surely the answer to the original question in the thread title has to be "it depends", doesn't it? As someone who recently built a small boat using foam sandwich, I can say with absolute certainty that it was the lightest way to make a hull of this size, yet still retain adequate stiffness. It doesn't have the best impact resistance, but that wasn't a major requirement, what it does have is a high stiffness to weight ratio.

Would I use the same technique for a fast planing hull? Probably not, as the weight saving would probably be marginal, using conventional, rather than more exotic reinforcement for the outer skin.

I'd certainly consider using foam sandwich for any structure than needed to be stiff and wasn't likely to be subjected to impact though, as the weight saving could be worthwhile.

There are some serious misunderstandings in this thread about the structural importance of the core in sandwich construction. It most certainly does play a critical structural role in determining the overall strength and stiffness, as anyone who's used it will know and understand. The core takes significant loads in fulfilling its role as a means of separating the two primary load bearing members, in the same way that the cross braces in a box girder bridge do. Failure to understand those loads, and select a core material with the right properties, has, I believe, contributed to the bad reputation that foam cored composites have acquired in some applications.

 

Jeremy, I believe this is a case of the blind, leading the blind, in regard to the engineering aspects of cored construction principles, with mostly a lot of yelling about engineering they haven't a strong grasp of. It's the same bunch that don't understand why you'd mix carbon and Kevlar in the same laminate. This isn't intended to be an insult, but merely identification of a cat fight over fodder, of which they can't grasp. I've long left this thread for this reason, though it's a sin Mike didn't figure this out, before the bilge water got over his waders.

 

with the tme there are various changes in the designing techniques and this is supportive too make better balance of boat.

 

Tunnels- if its been used successfully- what r your gripes on it? not saying your incorrect--it just seems to me that more people are using it below the waterline..

the aricraft industry and modern high tech hulls are very close in relation to each other are they not?

just to qualify--i took some samples of plascore honeycomb earlier this year and subjected those panels to extreme tests--no-not completely scientific or structured...

but let me be the first to say--i could not destroy the 1 inch thick panels--save for lighting it on fire.

they were glassed with 7 oz reg. cloth. about 8-10 layers on one side and 4 on the other--i could not break this--or hole it, i dropped a 20 lb rock 20 ft in the air and it bounced off-with no evidence of cracks fractures, or structural failure in any way that i could see--i threw this rock at it,- nothing. not even a hint of stress cracks or marks on it.


i then dropped a 40 lb concrete block from the same height on an angle to get a sharp pioint and across the panel, in order to make sure that the blow did NOT fall directly on the strongest orientation of the honey comb-which would be perpendicular to the glass face

this did nothing but punch a 1/32nd inch thich mark into the glass....
it did not delaminate no matter what i did to it. it was light, and i could not deflect or bend the panel either despite running over it with a car using it as a ramp.
from my humble tests- the stuff was indestructable and i think this is why areospace uses this--because its cheap stiff-tough and lightweight...


I dont object to your opinion--i just wondered if you can offer me some concrete evidence as to why it shouldnt work as well or better than core-cell below the waterline>??...there is always thick single skin laminates which i also like- but I think i would build a cruiser from heavily laminated core like honeycomb. maybe vacuum infused...

 

Ok i hear what you saying !! Its been on the market for a long long time why isnt everone using it ??? why isnt it the most popular materialon the planet !! in boats its hardly ever seen any where including in bulkhead construction . boats are not aeroplanes and aeroplanes are not boats the stresses and strains between the two are not even in any way related . sure wings bend fom end to end and o have dozens of pictures of wing from planes on the ground to flying and all sizes of planes but its a differant type of strain , boat hulls are twisted and stessed and pounded dozens of times a minute and have huge motors pushing and throwing the hullls in the air as they hit big waves and then come crashng back down again and again and again hour after hour .
Why arnt we all using honey combed core ?????tell me why i know of no manufactures of any boat company in any country any where on the face of this panet that used honeycombed core anywhere ,not even in the topsides or decks of internal construction . why ???

 

Wow, a bit dramatic aren't we?

Your answer is simple, it's a boat and what is used is good enough for the average boat. Horses for courses.

The Oracle AC 45 is built with carbon and Nomex honeycomb. You could see it hanging out when he T-boned the starting line boat in San Fransisco.

Honeycomb can not be wet layup, resin infused or chopper gunned. Basically all the usual boat building methods do not work with honeycomb. The normal use is prepreg skins.

A conventional honeycomb part is a multistage process. First the outer skin is layed up and cured, oven or autoclave. After cure it is unbagged and film adhesive and core placed. Sometimes it is bagged and cured again to bond the core in place. This helps if you need to do precise placement of core fill for hard points. Then the film adhesive and inner skin layer is layed up and bagged and cured. Sometimes if the part is not too critical the core bonding and inner skin are all cured at the same time.

Not many boat people can afford such a labor intensive process. But the fact is if you want the lightest strongest part, it is a honeycomb cored part. If you don't agree argue it with every F1, and Aerospace manufacturer.