Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors
  #31  
Old 01-05-2017, 04:56 PM
TANSL TANSL is offline
Senior Member
 
Join Date: Sep 2011
Rep: 300 Posts: 3,782
Location: Spain
upchurchmr:
You make me feel like I've said or done something wrong and I think this is not so. Anyway, just in case, I apologize also to everyone, although I do not know why.
Reply With Quote
  #32  
Old 01-05-2017, 09:02 PM
Mr Efficiency Mr Efficiency is online now
Senior Member
 
Join Date: Oct 2010
Rep: 677 Posts: 5,242
Location: Australia
Quote:
Originally Posted by jorgepease View Post
Also, most foam flotation, including in that pic is going to cause the boat to turtle, don't really see how you can prevent it in that style boat. .
Not really. Only if it (foam) gets preferentially placed along the centreline, and water can enter voids away from the centreline, then you certainly are increasing the chances of a capsize. If the whole undersole area is foam packed, the boat has very similar stability characteristics to the same boat, intact and sealed underfoot, with no foam.
Reply With Quote
  #33  
Old 01-05-2017, 09:21 PM
ondarvr ondarvr is online now
Senior Member
 
Join Date: Dec 2005
Rep: 499 Posts: 1,248
Location: Monroe WA
Boats under 20' in the US are required to float upright and level now, back when Whaler started their marketing program that wasn't a requirement. Whatever method of floation is used the boat needs to be able to still float if the chamber is ruptured. Foam has issues, but is a low cost and rapid way to meet the requirement.
Reply With Quote
  #34  
Old 01-05-2017, 09:36 PM
JamesG123 JamesG123 is offline
Junior Member
 
Join Date: Mar 2015
Rep: 10 Posts: 29
Location: Columbus, GA
Quote:
Originally Posted by TANSL View Post
I would never use foam as a structural element. In any case, it would be necessary to study the loads that the foam must withstand and to determine if the mechanical properties of the foam are sufficient for that.
In sandwich skin composite construction, the foam does not actually take any loads, it simply passes them to the skins. The same way that all the stresses on a bolt or shaft are concentrated on its surface. This is why very good aeroplanes (and boats) can be built of foam with thin skins of fiberglass that would be as flimsy as an empty plastic bottle without it.
Reply With Quote
  #35  
Old 01-06-2017, 05:11 PM
TANSL TANSL is offline
Senior Member
 
Join Date: Sep 2011
Rep: 300 Posts: 3,782
Location: Spain
I think we should clarify some concepts. The foam does not transmit any load to the outer layers of the sandwich. What it should do, fundamentally, is to withstand the shear stresses that occur between the various layers. These shear stresses as well as stresses/compressions are due to the loads applied to the structure. The foam must also absorb tensile or compressive stress, but of very low level. That is why it is always placed in the core and not on the outside of the sandwich. It does not have the capacity to absorb great tension/compression loads.
The other issue, that all the efforts on a screw are concentrated on its surface, does not seem right either. In bolted or riveted constructions, the screws or rivets mainly support shear forces. If the subject were as you say, it would not make sense, in some cases, to place these solid elements, they could be hollow.
I hope my poor English has been enough to explain what I think.
Reply With Quote
  #36  
Old 01-06-2017, 05:32 PM
JamesG123 JamesG123 is offline
Junior Member
 
Join Date: Mar 2015
Rep: 10 Posts: 29
Location: Columbus, GA
No offense but your English is better than your understanding of engineering. I suggest you read a few composites books.
Reply With Quote
  #37  
Old 01-06-2017, 06:26 PM
TANSL TANSL is offline
Senior Member
 
Join Date: Sep 2011
Rep: 300 Posts: 3,782
Location: Spain
Thank you, my friend, I will follow your advice. You could also study a little more about resistance of materials and theory of elasticity that is the same even for composite materials.
Reply With Quote
  #38  
Old 01-06-2017, 07:55 PM
upchurchmr upchurchmr is offline
Senior Member
 
Join Date: Feb 2011
Rep: 579 Posts: 2,275
Location: Ft. Worth, Tx, USA
I think the English is the problem.
One little word with a slightly different assumed meaning makes it seem there is a lack of understanding.
Reply With Quote
  #39  
Old 01-06-2017, 11:51 PM
Barry Barry is offline
Senior Member
 
Join Date: Mar 2002
Rep: 153 Posts: 615
Quote:
Originally Posted by JamesG123 View Post
In sandwich skin composite construction, the foam does not actually take any loads, it simply passes them to the skins. The same way that all the stresses on a bolt or shaft are concentrated on its surface. This is why very good aeroplanes (and boats) can be built of foam with thin skins of fiberglass that would be as flimsy as an empty plastic bottle without it.
1) The foam will be under tension and shear stresses and perhaps others. It cannot be under no load as you suggest, and yet transfer loads to the skins.

2) your comments that all the stresses on a bolt or shaft are concentrated on the surfaces are incorrect. Shear only and tensile only stresses are pretty much constant over the cross section unless there is are bending stresses which can create higher tensile stresses at the outer diameter than say toward the neutral axis

Of course stress concentration can be quite high at the roots of the thread and if the bolts design criteria is to resist mainly tension, this stress concentration is often the most significant design parameter
Reply With Quote
  #40  
Old 01-07-2017, 12:08 AM
upchurchmr upchurchmr is offline
Senior Member
 
Join Date: Feb 2011
Rep: 579 Posts: 2,275
Location: Ft. Worth, Tx, USA
+1 I see we have an Engineer
Reply With Quote
  #41  
Old 01-07-2017, 04:31 AM
TANSL TANSL is offline
Senior Member
 
Join Date: Sep 2011
Rep: 300 Posts: 3,782
Location: Spain
Quote:
Originally Posted by upchurchmr View Post
I think the English is the problem.
One little word with a slightly different assumed meaning makes it seem there is a lack of understanding.
You are quite right. I assure you that it is not easy to discuss technical matters when a language is not mastered but, in my opinion, it is preferable to try it, than to remain silent. I believe it will always be possible for a reader with technical and language skills to separate syntactic errors from conceptual errors. At least, I hope so.
Thank you all for your patience with non-English speakers.
Reply With Quote
  #42  
Old 01-07-2017, 02:15 PM
JamesG123 JamesG123 is offline
Junior Member
 
Join Date: Mar 2015
Rep: 10 Posts: 29
Location: Columbus, GA
Quote:
Originally Posted by upchurchmr View Post
+1 I see we have an Engineer
Yes... the only people who can miss the point of a comment in the pursuit of pedantic perfection.
Reply With Quote
  #43  
Old 01-07-2017, 02:30 PM
SamSam's Avatar
SamSam SamSam is offline
Senior Member
 
Join Date: Feb 2005
Rep: 971 Posts: 3,417
Location: Coastal Georgia
Quote:
Originally Posted by JamesG123 View Post
In sandwich skin composite construction, the foam does not actually take any loads, it simply passes them to the skins. The same way that all the stresses on a bolt or shaft are concentrated on its surface. This is why very good aeroplanes (and boats) can be built of foam with thin skins of fiberglass that would be as flimsy as an empty plastic bottle without it.
Attention to detail comes in handy when building boats and airplanes. Correcting these incorrect statements doesn't seem to be pedantic perfection to me.
Reply With Quote
  #44  
Old 01-07-2017, 02:32 PM
TANSL TANSL is offline
Senior Member
 
Join Date: Sep 2011
Rep: 300 Posts: 3,782
Location: Spain
JamesG123 : But my friend, making mistakes is not so serious. We all make mistakes. What is serious is not being able to recognize it.
We all have to keep studying, do not despair.
Reply With Quote


  #45  
Old 01-07-2017, 02:58 PM
upchurchmr upchurchmr is offline
Senior Member
 
Join Date: Feb 2011
Rep: 579 Posts: 2,275
Location: Ft. Worth, Tx, USA
I beg to disagree - most people I know miss the actual point of a discussion, engineers are just really single minded about it.

Quote:
Originally Posted by JamesG123 View Post
Yes... the only people who can miss the point of a comment in the pursuit of pedantic perfection.
Reply With Quote
Reply



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Foam option(s) for prototype hulls? jasonvi Boat Design 5 11-11-2016
07:33 PM 
thoughts on using spray foam inside hulls seadreamer6 Boat Design 6 10-13-2012
11:47 AM 
Foam filled ply for sole blakey1973 Fiberglass and Composite Boat Building 9 07-19-2007
05:04 PM 
Foam filling alluminum hulls Guest Materials 12 12-24-2004
12:03 AM 
Structural Foam for Aluminum Hulls jprev Metal Boat Building 3 08-30-2004
09:51 PM 

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.

All times are GMT -5. The time now is 10:41 PM.


Powered by: vBulletin Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Web Site Design and Content Copyright ©1999 - 2017 Boat Design Net