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Old 23-06-2015, 11:41   #751
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Re: The criteria of "blue"

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Originally Posted by noelex 77 View Post
A friend of mine was on the yacht that rescued he crew.

He told me the story, and from memory the life-raft was washed away some time before the sinking. Amazingly in the prevailing conditions, they found the crew floating in the water. An EPIRB was instrumental.

I think yachtsman in general place far too much faith in their liferaft. When they are needed there are many cases where the life-raft is washed away, fails to inflate or is punctured by the yacht. Combine this with difficulty boarding the liferaft and if you need a life-raft your chances of survival are long way below 100%.
I know.. It is an amazing story. The skipper of the search boat did a remarkable job. Sends shivers through you just thinking about it. I bet though that the skipper on the lost vessel if he has replaced his boat has a near temple set aside for his life raft now.

They were so lucky.
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Old 23-06-2015, 16:52   #752
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Re: The criteria of "blue"

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I have always wondered the use of ply in compression. Actually end grain balsa has better strength against compression thou I'd use any reasonably rot resistant end grain hardwood instead...
The reason plywood (or better still - solid laminate or aluminum) is used instead of end-grain is to spread the load imposed by each fitting across a much wider area than just the backing plate - not just to resist those compression loads. End-grain can't spread the load into adjacent structure, thus increasing likelihood of localized crazing around backing plates and fittings, and eventual failure. Are you sure that's a good idea? Not something I've ever heard of before.
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Old 23-06-2015, 17:09   #753
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Re: The criteria of "blue"

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I bet though that the skipper on the lost vessel if he has replaced his boat has a near temple set aside for his life raft now.
Or else he now realizes how useless they are, and buys a multi.
Or a steel tank!
Or maybe one of those French-built unsinkable jobs?
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Old 23-06-2015, 18:26   #754
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Re: The criteria of "blue"

Speaking of unusual and carvel, here is an aluminum carvel planked Colin Archer.

alu sailboat buliding - Page 49
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Old 23-06-2015, 22:58   #755
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Re: The criteria of "blue"

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The reason plywood (or better still - solid laminate or aluminum) is used instead of end-grain is to spread the load imposed by each fitting across a much wider area than just the backing plate - not just to resist those compression loads. End-grain can't spread the load into adjacent structure, thus increasing likelihood of localized crazing around backing plates and fittings, and eventual failure. Are you sure that's a good idea? Not something I've ever heard of before.
That's just stupid engineering to think ply core to spread loads, nor any other core except wood strip core could do that but only on longitudinal direction. Backing plates are for that reason only and they should be generous enough to do that. You can also have additional reinforcement on the skins to do part of that task.
Concur about the solid laminate, aluminum is best to leave for aluminum boats, nothing to do inside the composite layup
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Old 24-06-2015, 02:46   #756
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Re: The criteria of "blue"

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That's just stupid engineering to think ply core to spread loads, nor any other core except wood strip core ...
Ply core gives a more gradual drop-off of the rigidity as load spreads from backing plate to ply to balsa, or to more rigid structure. It does offer engineering advantages over a sudden sharp edge, avoiding localized crazing - think of the large leverage imposed by a self-tailing winch for example. Not sure I understand why ply is stupid but wood strip is not, probably better to avoid both, but balsa (or any end-grain) under a winch seems poor engineering.
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Old 24-06-2015, 03:45   #757
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Re: The criteria of "blue"

The function of the core is to keep the skins apart, prevent buckling and have good adhesion properties, not to carry direct structural loads. Under winches and other deck gear there's additional task to withstand compression of the tensioned bolts. The skins are there to carry the loads, that's anyway how it should be. Ample backing plate (not just washers!) and sound bedding (high density filler epoxy as example) on both sides of the laminate spreads the loads. In highly stressed areas additional laminate thickness too.

Ply only is just cheap cheap..

BR Teddy
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Old 24-06-2015, 04:48   #758
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Re: The criteria of "blue"

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Or else he now realizes how useless they are, and buys a multi.
Or a steel tank!
Or maybe one of those French-built unsinkable jobs?
For f f f f k sake don't go all multi on me Nevisdog
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Old 24-06-2015, 05:04   #759
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Re: The criteria of "blue"

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Speaking of unusual and carvel, here is an aluminum carvel planked Colin Archer.

alu sailboat buliding - Page 49
The build organisation looks interesting as well. Seems to be some kind of nautical commune going on. Quite cool!
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Old 24-06-2015, 05:04   #760
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Re: The criteria of "blue"

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Speaking of unusual and carvel, here is an aluminum carvel planked Colin Archer.

alu sailboat buliding - Page 49
The build organisation looks interesting as well. Seems to be some kind of nautical commune going on. Quite cool!
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Old 24-06-2015, 07:07   #761
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Re: The criteria of "blue"

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The build organisation looks interesting as well. Seems to be some kind of nautical commune going on. Quite cool!
And some quite cute. I'm particularly taken with a certain Irish lass.
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Old 24-06-2015, 07:10   #762
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Re: The criteria of "blue"

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Ply only is just cheap cheap..
Not as cheap as end-grain under a winch.
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Old 24-06-2015, 07:17   #763
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Re: The criteria of "blue"

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For f f f f k sake don't go all multi on me Nevisdog
Nothing wrong with multis, except the price!
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Old 24-06-2015, 10:51   #764
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Re: The criteria of "blue"

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Nothing wrong with multis, except the price!
Not blue unless you have a big one. Mid lats only and highly seasonal if you have a small one. Be careful of the dark side Luke..
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Old 25-06-2015, 01:22   #765
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Re: The criteria of "blue"

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That's just stupid engineering to think ply core to spread loads, ... aluminum is best to leave for aluminum boats, nothing to do inside the composite layup
I'd just like to clear up some obvious misunderstandings here.

Extending a backing plate beyond load area is an inefficient method of supporting and transferring the concentrated loads from heavily loaded fittings. Just as a cored deck fails when the core breaks down and allows outer layers to slide and flex independently, so it is with a large backing plate (except directly in way of bolts): the plate outer edges can move independently of the next layer, so much of the stiffness is lost. A better engineered solution is to build in that backing (whether aluminum or plywood) within the last few bottom layers, so they become an integral part of structure, increasing stiffness without increasing thickness/weight.

Muckle's fear of ply or timber core is sometimes well justified: because the ply is supposedly encapsulated, some builders will use inferior plywoods, they may skimp on sealing the bolt holes against water ingress, and may use the wrong resins (most resins adhere well to end-grain but only epoxy holds permanently to timber or ply). So timber/ply core used anywhere demands quality build. But then so does balsa (think of the number of boats with failed balsa-core decks) and any other core material creates equally serious issues over time, if quality of build/maintenance is lacking.

Let me know if you find someone offering solid glass hulls built entirely with epoxy - except for hi-tec, weight-saving, one-off racing machines (never designed for longevity, and more likely to be cored), they must be rare as hen's teeth. Not sure it offers much advantage in strength either (unless you want to minimize thickness - never a great idea in a non-cored cruising hull). Only the water absorption is prevented, and that can be done with epoxy outer layers alone.

I think that's a fair assessment but feel free to correct anything I missed.
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