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63' Bertram Possibly stuffed off SC???

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Old 01-18-2010, 04:13 PM
  #161
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Did you see the video Dave . What do you think?

Hey Dave could you send that schematic to me also ? Always curious to see stuff like that my address [email protected]. Thanks.
yea, just watched it. That thing is a mess. I think it stuffed and dove slightly and carried a fair amount of momentum, the water pressure just blew blew right through the boat. With the path of destruction i saw it was enough water to do significant and catastrophic damage but at the same time may not have been enough to slow the boat much for the first few seconds after impact. So basically it cut its own head off, the mass of water blew a hole straight through the boat. As far as to why the hull(bow) failed, thats a tough one. Build quality? Light lay up? Hit something? whos to say, I can tell you it does not take to much of a breach to have catastrophic results. A small hole can be blown out HUGE by water pressure. I think i read somewhere the captain said the transom was still attached after initial impact while going down. I am certainly not going to say its a lie but i think it may have been some kind of mistake like it was still visible in that location but the damage had already been done (separated at the perimeter). Is there a detailed report from the captain anywhere? These are some long threads and i have not read all of them.
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Old 01-18-2010, 04:32 PM
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yea, just watched it. That thing is a mess. I think it stuffed and dove slightly and carried a fair amount of momentum, the water pressure just blew blew right through the boat. With the path of destruction i saw it was enough water to do significant and catastrophic damage but at the same time may not have been enough to slow the boat much for the first few seconds after impact. So basically it cut its own head off, the mass of water blew a hole straight through the boat. As far as to why the hull(bow) failed, thats a tough one. Build quality? Light lay up? Hit something? whos to say, I can tell you it does not take to much of a breach to have catastrophic results. A small hole can be blown out HUGE by water pressure. I think i read somewhere the captain said the transom was still attached after initial impact while going down. I am certainly not going to say its a lie but i think it may have been some kind of mistake like it was still visible in that location but the damage had already been done (separated at the perimeter). Is there a detailed report from the captain anywhere? These are some long threads and i have not read all of them.
Thank God No one was hurt or worse, Boats can be replaced ,I will be interested in the findings here.
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Old 01-18-2010, 04:43 PM
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Uncle Dave ĖEvery couple of months when I need a diversion from work, I browse this site for amusement. You seem to be getting a tough time here which isnít really fair as you havenít had a technical answer to your inquiry. Therefore let me have a go. You canít look at the raw data of the core material in isolation when you are dealing with the dynamic loading of a panel for which the coreís is only a component part. Peter at Skater ďgetís awayĒ with balsa in his boats due to his proper bonding technique and epoxy resins which together permit the construction of very light and strong boats. Therefore it will be a very rare instance where the forces exceed the ultimate strength of his balsa panel. However if they do the result is an instant catastrophic failure. With Linear or (to a slightly lesser extent) san foam core, whilst the panel will have a greater deflection than a balsa panel for a given impact, such defection absorbs the energy of this force. As the linear/san foam will maintain its structural properties throughout this deflection (subject of course to the panelís elastic limit), the total amount of energy absorbed from an impact prior to de-lamination (subject to the resin) will exceed that of the stiffer balsa panel. In high impact dynamic loading structures you need to look at the area under the stress strain curve. Whilst the balsa panel will have a very step curve with very high stress capability, the area under this curve will not match that of the lower stress linear/san foam core panel and thus is not capable of surviving the same magnitude of impact. Again in force calculations mass is a key component so Peterís light and extremely well built boats will generally never exceed the energy absorption limit under his panelís stress/strain curve-even though this area is less than that of the equivalent linear/san foam panel.

Hope this helps
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Old 01-18-2010, 04:53 PM
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Thank God No one was hurt or worse, Boats can be replaced ,I will be interested in the findings here.
I hear ya, seeing the damage at the helm with it pushed back like it was tells me a huge column of water rushed through there blowing the transom on its way out the back. But this is all speculation, it will be interesting on what their findings are. Even more interesting is who will be liable and have to pony up for the loss. Glad they got off the boat ok.



nautdesign1- welcome aboard and thanks for the response. Very well put, looking forward to more of your thoughts.
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Old 01-18-2010, 04:58 PM
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Uncle Dave –Every couple of months when I need a diversion from work, I browse this site for amusement. You seem to be getting a tough time here which isn’t really fair as you haven’t had a technical answer to your inquiry. Therefore let me have a go. You can’t look at the raw data of the core material in isolation when you are dealing with the dynamic loading of a panel for which the core’s is only a component part. Peter at Skater “get’s away” with balsa in his boats due to his proper bonding technique and epoxy resins which together permit the construction of very light and strong boats. Therefore it will be a very rare instance where the forces exceed the ultimate strength of his balsa panel. However if they do the result is an instant catastrophic failure. With Linear or (to a slightly lesser extent) san foam core, whilst the panel will have a greater deflection than a balsa panel for a given impact, such defection absorbs the energy of this force. As the linear/san foam will maintain its structural properties throughout this deflection (subject of course to the panel’s elastic limit), the total amount of energy absorbed from an impact prior to de-lamination (subject to the resin) will exceed that of the stiffer balsa panel. In high impact dynamic loading structures you need to look at the area under the stress strain curve. Whilst the balsa panel will have a very step curve with very high stress capability, the area under this curve will not match that of the lower stress linear/san foam core panel and thus is not capable of surviving the same magnitude of impact. Again in force calculations mass is a key component so Peter’s light and extremely well built boats will generally never exceed the energy absorption limit under his panel’s stress/strain curve-even though this area is less than that of the equivalent linear/san foam panel.

Hope this helps


BTW Thanks for the recognition of the tough time.

I've never had an easy run in any site yet- never expected this one to be different.

Superb explanation.

Interesting how according to what you say technique affects the overall materials worthiness and applicability to this application.

Implication being unless you can really do it right, just use foam.

Are there any other material issues to consider in the choice of Balsa over Foam?


UD

Last edited by Uncle Dave; 01-18-2010 at 05:05 PM. Reason: word omission- tough
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Old 01-18-2010, 05:11 PM
  #166
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BTW Thanks for the recognition of the tough time.

I've never had an easy run in any site yet- never expected this one to be different.

Superb explanation.

Interesting how according to what you say technique affects the overall materials worthiness and applicability to this application.

Implication being unless you can really do it right, just use foam.

Are there any other material issues to consider in the choice of Balsa over Foam?


UD
"Implication being unless you can really do it right, just use foam."

No with the linear's more care is needed In respect to Both Shop Practices and Material selection.

Last edited by Steve 1; 01-18-2010 at 05:14 PM.
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Old 01-18-2010, 05:13 PM
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Any thoughts on T2's comment about how greater flexibility can lead to core shrinkage?



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Old 01-18-2010, 05:15 PM
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Any thoughts on T2's comment about how greater flexibility can lead to core shrinkage?



UD
The Better cores cause Wallet shrinkage.
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Old 01-18-2010, 05:19 PM
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The helm damage you see Dave is simply the hinged instrument console floating freely above the helm. That is a lightly connected area and most likely just broke free as the boat was sinking.
The only way that transom has that damage is because somebody was trying to tow it stern 1st. Boat ripped cleanly at the hawsepipes passing thru the coaming.

Your theory of water blowing out the transom does not work because the water would have to shoot up the companionway and thru the salon. and than back down the cockpit steps to the transom . As the Capture of the Princess Bride would say.
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Old 01-18-2010, 05:24 PM
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The Better cores cause Wallet shrinkage.
Funny! and often a motivation......

I actually misquoted all due respect - "constrict" the core was the actual term.

This another downside I hear quoted in regards to foam, but I have never been able to verify..

Since we do have the a boatload of guys that are here - Id love to hear the thoughts on this.

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