Rudder Failures

[smackdaddy]

Originally Posted by neilpride

I get this...
Results:
Sail area to displacement (SAD): 19
Displacement to length: 237
Length to beam: 3.08
Theoretical hull speed: 7.58 knots
Capsize ratio: 2.01
Waterplane area: 729.6 ft2
Ballast to displacement: 45%
Comfort Ratio: 45

Hunter legend 40.

Cool. Even a better CR than I thought.

How about that comfort ratio and speed, eh?

[neilpride]

Theoretical hull speed: 7.58 knots

[smackdaddy]

Originally Posted by neilpride

Theoretical hull speed: 7.58 knots

Don't worry dude. I'll wait for you in the anchorage. And I'll save you some beer to go with that popcorn.

Heh-heh.

[neilpride]

Keep dreaming...

[Jim Cate]

Smack, I'm not a structural engineer, but I must wonder if the test to failure that you keep showing us has any relevance to how stresses reach the bulkhead/hull joint? I don't see how one could load a bulkhead at 90 degrees to the vertical, with it in a cantilever orientation as in the test. Bulkheads are supported (at least in good construction at all edges: overhead, hull sides and hull bottom. I think that the major stresses to those joins come from torsion of the hull, introduced by the rig pushing against the righting moment which is mostly generated by the keel... a very different sort of load . What your test shows would be like a bulkhead, supported only at the bottom and being pushed at deck level along the longitudinal axis of the boat. This ain't what I think happens!

Another stress source, at least in our boat where the shroud chainplates are attached to half-bulkheads, is plain tension. The shrouds are trying to pull the bulkhead up through the deck, and it is the join between hull and bulkhead that is resisting the force...and that force is parallel to the plane of the joint, not orthogonal to it as in your test pieces.

So, while the tests are interesting, and do show some good applications for Plexus, they don't seem applicable to yacht construction.

I could be wrong, and am interested in other's thoughts on the subject.

Jim

[Emmalina]

Told this guy to remove his rudder.. Didn't listen No more rudder and I have seen a good few like this

[smackdaddy]

Originally Posted by Jim Cate

Smack, I'm not a structural engineer, but I must wonder if the test to failure that you keep showing us has any relevance to how stresses reach the bulkhead/hull joint? I don't see how one could load a bulkhead at 90 degrees to the vertical, with it in a cantilever orientation as in the test. Bulkheads are supported (at least in good construction at all edges: overhead, hull sides and hull bottom. I think that the major stresses to those joins come from torsion of the hull, introduced by the rig pushing against the righting moment which is mostly generated by the keel... a very different sort of load . What your test shows would be like a bulkhead, supported only at the bottom and being pushed at deck level along the longitudinal axis of the boat. This ain't what I think happens!

Another stress source, at least in our boat where the shroud chainplates are attached to half-bulkheads, is plain tension. The shrouds are trying to pull the bulkhead up through the deck, and it is the join between hull and bulkhead that is resisting the force...and that force is parallel to the plane of the joint, not orthogonal to it as in your test pieces.

So, while the tests are interesting, and do show some good applications for Plexus, they don't seem applicable to yacht construction.

I could be wrong, and am interested in other's thoughts on the subject.

Jim

No - I don't think that the destructive testing in that report is directly applicable to what you'd see in a bulkhead (i.e. - rotational loads). BUT, I do think it's very instructive in showing the strength of the bond itself.

If you recall, there were a couple of things that got this whole Plexus thing started:

1. The video of the failed rudder assembly which had apparently been Plexus'd in place (and now these new photos Neil put up of the the Plexus failure at the aft bulkhead of that other Bene.)

2. Minaret's claim that tabbing is ALWAYS better.

So, what that destructive testing shows me is that the Plexus fillet is stronger overall than the tabbing. And, to me, the questions that leaves is why did the Plexus fail in Neil's photos - and is that going to be a common problem people should look out for? If it just happened in normal conditions (not a severe grounding or survival storm, etc.) that's counter to Plexus' claim of the strength of the bond - as we'll as what's shown in that testing. So was it shoddy workmanship? Or something more concerning?

[avb3]

Originally Posted by smackdaddy

Sure it's important. I think mine comes in at around 2.06, which is a little high. Under 2 is better from what I understand.

Why? Are you worried?

(PS - I have no intention of taking my own older Hunter around Cape Horn if that's what you were wondering. But have I told you about that Hunter 49...?)

I knew about that Hunter 49 over a year and a half ago. Remember reading their blog. It was well prepared, if I recall, and not just off the shelf. Oh, and a capsize ratio of 1.84. Comfy too I bet.

[smackdaddy]

Originally Posted by avb3

I knew about that Hunter 49 over a year and a half ago. Remember reading their blog. It was well prepared, if I recall, and not just off the shelf. Oh, and a capsize ratio of 1.84. Comfy too I bet.

Somewhere on SN I think I copied and pasted the upgrades Michael did to the boat (from his old site). You can see some of his write up by previewing his book (Look Inside) at Amazon:

http://www.amazon.com/Sequitur-Cape-...7110853&sr=1-1

Look at Chapter 1. Apart from adding an inner stay, there wasn't much done structurally. It was mostly gear/equipment added.

That chapter is also actually a very good take on the "Bluewater Boat" debate - and how it really makes little sense. And some of you guys won't like his take on the "excellent" interior hand-holds (that he actually used in the Southern Ocean), etc. So be warned.

So, as for the boat itself, it was surprisingly off the shelf from what I recall. But it was also very well prepared (though the stuff installed by the yard was seriously screwed up and really bit them later - yard guys).

Michael is a hell of a sailor.

[Jim Cate]

So, what that destructive testing shows me is that the Plexus fillet is stronger overall than the tabbing

No, what it show is that when loaded in one specific way it is stronger. But, that way is not representative of its usage in yacht construction, as shown in Neil's photos.

Jim

[smackdaddy]

Originally Posted by Jim Cate

No, what it show is that when loaded in one specific way it is stronger. But, that way is not representative of its usage in yacht construction, as shown in Neil's photos.

Jim

Okay. But you might want to look at the focus of the report first.

[neilpride]

Originally Posted by smackdaddy

No - I don't think that the destructive testing in that report is directly applicable to what you'd see in a bulkhead (i.e. - rotational loads). BUT, I do think it's very instructive in showing the strength of the bond itself.

If you recall, there were a couple of things that got this whole Plexus thing started:

1. The video of the failed rudder assembly which had apparently been Plexus'd in place (and now these new photos Neil put up of the the Plexus failure at the aft bulkhead of that other Bene.)

2. Minaret's claim that tabbing is ALWAYS better.

So, what that destructive testing shows me is that the Plexus fillet is stronger overall than the tabbing. And, to me, the questions that leaves is why did the Plexus fail in Neil's photos - and is that going to be a common problem people should look out for? If it just happened in normal conditions (not a severe grounding or survival storm, etc.) that's counter to Plexus' claim of the strength of the bond - as we'll as what's shown in that testing. So was it shoddy workmanship? Or something more concerning?

Smack i dont know if you are just Trolling us with the plexus debate or just having fun ,, its at builder discretion to use in the tabbing the right number of FG layers, in your test dont explain how many layers of Biax or CSM are used , then the test dont mean nothing to me since you can just shoot a bead of plexus,, with FG your options are wider.

Second no one here , not me, say something like plexus its crap in a boat no matter what, lets say Plexus have a really well bonding strenght in the right application, if you know what i mean, right application mean both surfaces clean and with the theorical designed loads v plexus, since bulkheads work in diferents ways, the most important for me is in shear and tensional loads, why is so hard to understand the Blue Pearl video and my picture?? if the stuff is so great Blue Pearl never should have loose the structure? right? and my photo show just a bond fail in a bulkhead..


The 80% of new owners , cruisers, dont know a crapp about bulkheads not even how the boat is holding together, when there is one problem most of the time is to late , or a big repair is in order, look at the Bene , ok, the owner is really lucky that the bulkhead is not holding a masive tie rod chainplate, in other words, just few cabinet doors open when sailing in one tack..

You say it really well, shoddy workmanship ,, not care for details, etc...
Now go ahead and keep going scrachting the internet to move the whole thing to your side, dude !!do the Minaret test, is not so hard, even a kid can do it, waxed surfaces with plexus and FG , try to bend it and come here with the result... just a sugestion he he...


In the picture show a hell of failure in a Bavaria sailing in the heinekken regata in fair weather, just figúrate why the cropp the tie rod chainplate pull the whole structure by the deck, Plexus remind me rod rigging, when it fail it fail!!!!!!

[Dockhead]

Originally Posted by smackdaddy

Definitely NOT bluewater boats. Heh-heh.

I am actually surprised at the lack of better handholds in those boats, but can confirm that some Swans I have been on were inadequate in that department. On one long upwind passage on one Swan, we had to rig a rope across the salon -- otherwise it would have been impossible to get to the heads.

This is the Moody 54:



Rather better, but still not enough, for a long upwind bash, like I did for 3000 miles this summer.

The problem is worse, with larger boats and interiors. My old Pearson 365 did not really need special handholds, because you could hold on to elements of the fitout. Plus you never sailed that boat upwind and so rarely on much of a heel.

[robert sailor]

The older Swans were offshore racers and were built accordingly, this newer batch while drop dead gorgeous are more for marina to marina in the Med. I'm not suggesting the build quality isn't there but they are appealing to a different market.

[Dockhead]

Originally Posted by smackdaddy

Sure it's important. I think mine comes in at around 2.06, which is a little high. Under 2 is better from what I understand.

Why? Are you worried?

(PS - I have no intention of taking my own older Hunter around Cape Horn if that's what you were wondering. But have I told you about that Hunter 49...?)

With respect to AVB3, capsize screening ratio, which considers only displacement and beam, is meaningless when comparing boats of different types. An Open 60 has a much "worse" capsize screening ratio than a Hunter. This metric does not consider CG or draft, so grossly understates the stability of modern boats with bulb keels and overstates the stability of older designs.

To understand something about stability, you need to do some actual work on stability calculations, starting with AVS.

I doubt if the Hunter 49 has less stability than average "blue water boats", particularly older longer keel shallower draft ones, whatver the capsize screening ratio says.

Stability -- a big challenge for mobo designers -- is not so hard for boats with ballasted keels, and is not really a measure of a good boat these days. Deep bulb keels have a huge effect on CG and dramatically increase stability, compared to older designs. The bigger question for boats like Hunters is structural integrity. Not stability.

The capsize screening ratio was introduced after the Fastnet disaster, to try to catch some cases of boats which had such perverted designs, due to RORC classes, that stability was beginning to suffer despite the inherent advantages of boats with ballasted keels. It was never intended as an objective measure of stability -- hence it is only called "screening ratio".