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poiu · 08-11-2015, 05:54

Quote:

Originally Posted by poiu

I think you are wrong in your assumption. A new Jeanneau is the same price as a used Oyster. I did the comparison when I bought mine.

Sorry Abgreenbank. I need to correct my post, I didn't read your post closely. A new Oyster is indeed more expensive than a new Jeanneau.

Abgreenbank · 08-11-2015, 07:33

Not wanting engage in a slanging match, a quick search reveals this, I was however referring to structural failures and my comment about keels was tongue in cheek.
Maybe failures were due to collision/grounding, but these issues should be addressed in design but I am not suggesting totally mitigated.

One area of failure that seems to be rarely discussed is fatigue failure. My earlier career was flying fighter aircraft, lots of G and consequently fatigue, and just about every type I flew had fatigue issues, and had planned midlife updates to strengthen or replace structural components. Fatigue monitoring was carefully followed and each aircraft had a finite fatigue life and if too much G was pulled fairly major inspection could be required, some individual aircraft even had restrictions on max G to preserve life. All this in pre digital FBW day, modern systems can limit G and incidence.

My point being sailing a yacht hard into a big sea is intimately more stressful than a nice broad reach with a gentle breeze, I guess this seasons transatlantic races have proved that.
In Lanzarote I saw many mini transats with rudder or mast damage after a gentle run down the North African Coast

http://www.oysteryachts.com/breaking...-July-24-2015/

Regards
Ab

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barnakiel · 08-11-2015, 08:19

Quote:

Originally Posted by Abgreenbank

My point being sailing a yacht hard into a big sea is intimately more stressful than a nice broad reach with a gentle breeze, I guess this seasons transatlantic races have proved that.

In Lanzarote I saw many mini transats with rudder or mast damage after a gentle run down the North African Coast

Yes. But sailing a huge downwind SA uldb boat in light conditions can create amazing amt of damage. At times the boat will roll with all its weight while the kite gets a sudden grip on whatever faint breeze there is. At this point the boat gets pulled by the top of its (very fine in Minis) mast with thousands of kilo-meters of force.

Imagine tying the top of the mast to a bollard then waiting for a tug to pass. Can you sense the damage coming?

So I think my point is to a racing boat both heavy going and light conditions can be actually similarly destructive.

b.

**Dockhead** · 08-11-2015, 08:25

Quote:

Originally Posted by Sandero

Your statement about cross section of steel (beams) is not entirely accurate not telling the whole story. Beam action is increased by moving the "mass" of steel... for tension and compression away from the neutral axis but a strong web is required to connect the two making them act as a composite. I believe axial strength for non slender columns is driven by cross section area. Buckling is very much related to the end condition of a column.

. . . .

What you write is entirely correct, but I think that what I wrote was quite enough for purposes of this discussion, and an accurate explanation of the fundamental principle for why cored construction is stronger than solid. It's geometry -- you separate the parts of the structure which are working in compression from those which are working in tension and gain leverage to resist the load. It's a matter of the geometrical translation of the load to be resisted to the compression and tension loads on the structure.

Beam theory formulae for the strength of cored structures does of course assume that the bond between the core and the skins is as strong as the material, and that the core has enough shear and compression strength to resist failure from those modes prior to failure of the skins. If the core is so weak as to allow buckling before the skins reach their failure points, then the formulae don't work.

And the bond is extremely important -- if it fails, the whole structure fails. Which is why until recently balsa works better than foam -- it is much easier to strongly bond to the skins. Newer foams are better and epoxy resin makes as stronger bond, so foam cored structures are getting closer to balsa in strength.

Someone in another post mentioned fatigue failure -- here is yet another advantage of cored boat hulls. The improvement in stiffness of cored structures is even greater than the improvement in strength, and this results in reduced flexing. Hence less fatigue. I think this is important. We know boats which have come apart due to fatigue of the hull (for example, that guy who circumnavigated North and South America single handed via the NW Passage and the Horn). You don't want the hull flexing in a seaway; this can lead to fatigue failure, failure of bulkhead tabbing, etc. That's why quality solid hulls are extremely massive (Oyster) compared to inexpensive solid hulls (Beneteaus -- "Bendy Toys"). I'm not slagging Beneteaus, which I admire and like, but many of them are not designed structurally for long passages in rough seaways.

avb3 · 08-11-2015, 08:38

Quote:

Originally Posted by Dockhead

....
Someone in another post mentioned fatigue failure -- here is yet another advantage of cored boat hulls. The improvement in stiffness of cored structures is even greater than the improvement in strength, and this results in reduced flexing. Hence less fatigue. I think this is important. We know boats which have come apart due to fatigue of the hull (for example, that guy who circumnavigated North and South America single handed via the NW Passage and the Horn). You don't want the hull flexing in a seaway; this can lead to fatigue failure, failure of bulkhead tabbing, etc. That's why quality solid hulls are extremely massive (Oyster) compared to inexpensive solid hulls (Beneteaus -- "Bendy Toys"). I'm not slagging Beneteaus, which I admire and like, but many of them are not designed structurally for long passages in rough seaways.

You're referring to Matt Rutherford I believe.

http://www.solotheamericas.org

I followed his journey picking him up when he had entered the Bering Sea, and followed around until he got back home. I don't recall any mention of any fatigue damage to his Albin Vega. In fact, he subsequently sold that boat, and as far as I'm aware, it is still happily sailing along.

In my opinion, his journey ranks right up there with Slocum.

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**Paul Elliott** · 08-11-2015, 08:50

Quote:

Originally Posted by barnakiel

[...] So I think my point is to a racing boat both heavy going and light conditions can be actually similarly destructive.

Yes. The worst carnage in the Pacific Cup races I've participated in has taken place during light airs and sloppy seas (we've not seen extremely heavy conditions, but plenty of brisk ones). But this has been failures of rigging -- shrouds, booms, goosenecks, masts, etc. We've seen more than a few rudder failures in moderate to brisk conditions, or whale-strikes.

(To clarify, most of this damage was to other boats, not mine. On VALIS we've had the occasional lightweight block explode in slatting conditions, or gooseneck bolt start to work loose -- nothing catastrophic.)

But isn't this discussion about hull failures, liners, and (now) cored hulls? In most cases the sailing conditions aren't really an issue here.

**Dockhead** · 08-11-2015, 09:02

Quote:

Originally Posted by avb3

You're referring to Matt Rutherford I believe.

Solo Around the America's Under Sail | An audacious attempt at sailing the Northwest Passage and circumnavigating entirety of both continents, to benefit Chesapeake Region Accessible Boating

I followed his journey picking him up when he had entered the Bering Sea, and followed around until he got back home. I don't recall any mention of any fatigue damage to his Albin Vega. In fact, he subsequently sold that boat, and as far as I'm aware, it is still happily sailing along.

In my opinion, his journey ranks right up there with Slocum.

That's the guy! What an amazing voyage!

As far as I can recall, he had a lot of trouble with the hull -- bulkhead broken loose, mast pushing through the deck, things like that.

avb3 · 08-11-2015, 11:03

Quote:

Originally Posted by Dockhead

That's the guy! What an amazing voyage!

As far as I can recall, he had a lot of trouble with the hull -- bulkhead broken loose, mast pushing through the deck, things like that.

Come to think of it, I now do recall he had an issue with the bulkhead under the mast that kept shifting and groaning. The mast I think he repaired and bolstered before the journey... can't recall now.

Regardless, your right, what a voyage and adventure. And goes to show what a tough little boat a 40 year old Albin Vega is. I'm pretty sure they had no liners.

nortonscove · 08-11-2015, 14:25

Got me a 20 year old Beneteau and love it. Liner or no liner what I hear is that many people want total assurance on the ocean and that doesn't exist. Many boats sink but because the ones that are out there in the greatest numbers are statistically most likely to report more issues...Toyota to Rolls. It doesn't mean the Rolls is more reliable or better. More posh is obvious but looking simply at numbers is a fool's game. I recall a very expensive and relatively new Swan coming apart in a mere 3 or 4 metre seas within the last year.
A friend just ran his production boat with liner aground at 5.5 knots and then steamed it 4 hours to my lift without as much as a drop of water coming in. 32 years old and beautifully tough.

Sandero · 09-11-2015, 05:39

Core hulls will resist "oil canning" which will cause shear stress in the material and ultimate failure perhaps from excessive flexing. A good way to make a hull stiffer without making it heavier is making it thick. To to this the composite should have a light weight core well bonded to the interior and exterior membranes making them composite. Being composite with the membranes is key to stiffness. I suppose it's possible to use even honey comb cores if they can be properly bonded to the two membranes.

There are other possible benefits in "insulation" when the core has a high r factor than the membranes. This acts somewhat as a thermal break.

Muckle Flugga · 09-11-2015, 05:47

Quote:

Originally Posted by avb3

Come to think of it, I now do recall he had an issue with the bulkhead under the mast that kept shifting and groaning. The mast I think he repaired and bolstered before the journey... can't recall now.

Regardless, your right, what a voyage and adventure. And goes to show what a tough little boat a 40 year old Albin Vega is. I'm pretty sure they had no liners.

Having owned and sailed an Albin Vega in higher latitudes for more than a decade (some misty time ago now) and many thousands of miles I can attest that a classic weakness with them was an insufficiently strong deck at the mast step. The original bulkhead did not adequately compensate for the compression loads. My example had a solid triple beam fix for this problem and was no issue at all. It was a necessary addition to any Vega, and likely had not een done in this case. As to being tough? They are fabulous, dry, safe, easy to handle little pocket cruisers and I weathered many a storm and some furious seas in my wee gem.

Muckle Flugga · 09-11-2015, 05:56

Quote:

Originally Posted by Sandero

Core hulls will resist "oil canning" which will cause shear stress in the material and ultimate failure perhaps from excessive flexing. A good way to make a hull stiffer without making it heavier is making it thick. To to this the composite should have a light weight core well bonded to the interior and exterior membranes making them composite. Being composite with the membranes is key to stiffness. I suppose it's possible to use even honey comb cores if they can be properly bonded to the two membranes.

There are other possible benefits in "insulation" when the core has a high r factor than the membranes. This acts somewhat as a thermal break.

Here's a picture of me in the bows of a cored hull vessel I found in Dominica a few years back.