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Old 13-05-2011, 23:38   #166
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Re: Floating Containers In The Ocean

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Originally Posted by niel12 View Post
This is great news for those that do not have Kevlar reinforced boats. What does your boat specs have say on this point Bas? Especially on the point of impact.
I'm no engineer, so I'd have difficulty answering that question. But I saw how the boat was laid up. A sheet of kevlar runs down the center of the boat from bow to stern. It would be significantly more difficult to hole the bow in a collision. If that happened, there is a collision bulkhead one meter behind the bow. It, too, is kevlar reinforced. What this means is that you could crush and/or hole the bow and the collision bulkhead would still keep water from entering the hull.

On a dark, moonless night offshore, when one starts worrying about floating containers, it's reassuring to remind yourself that the bow contains the same material as bullet-proof vests.
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Old 14-05-2011, 01:30   #167
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Re: Floating Containers In The Ocean

Hi Bash, thanks for your contribution i have another question though, is the Kevlar overlay on the inside or the outside of the hull?
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Old 14-05-2011, 05:16   #168
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Re: Floating Containers In The Ocean

Isn't Kevlar's bullet-proof ability due to the fact that it can absorb the bullet's energy? The threads are amazingly strong but supple.

Wouldn't you lose that when you applied resin?
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Old 14-05-2011, 05:42   #169
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Re: Floating Containers In The Ocean

No, the threads are just plain tough, and they don't stretch. Impact will crush the resin, but the fabric will prevent penetration.
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Old 14-05-2011, 06:08   #170
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Re: Floating Containers In The Ocean

Hud, with the resin disintegrating on impact won't the material leak?
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Old 14-05-2011, 07:38   #171
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Re: Floating Containers In The Ocean

With referance to my former post on Kevlar it was interesting to find that the new generation Kevlar KM2 is bullet proof while the older Kevlar must have had certain short comings but certainly and apparantly not as strong as Kevlar KM2. As far as i can establish Kevlar KM2 is freely available. Is there someone who are familiar with actually applying the Kevlar KM2 on glassfibre? Should one remove the gelcote?
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Old 14-05-2011, 08:44   #172
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Re: Floating Containers In The Ocean

G'Day All,

With respect to the forward looking sonars -- I have had one since 1996 (both on Insatiable I and II) and have used them extensively in our cruising. Ours are the Interphase "Probe" model which sweeps a beam from straight ahead at the surface to straight down towards the bottom. The beam width is nominally 12 degrees. We spend lots of time in poorly charted waters, some of which are pretty opaque, and I find the Probe to be useful enough that I bought one for I-2 before we hauled her for survey at the time of purchase!

On the longest range it looks 1200 feet ahead of the boat. We have actually seen a few things out around 800 feet, things like a wall of coral sticking nearly straight up from the floor of a lagoon in ~200 foot depth. In shallower waters the range is typically 3-4 times the depth of the water. So far this sounds pretty good, eh?

But, consider the physics of sonar: The instrument produces a sound pulse in the transducer, focused into a beam around 12 degrees wide. The pulse propagates out at the speed of sound (around 1480 m/s), and if it hits a suitable object, some of the sound energy is reflected back to the transducer. Meanwhile, the transducer has been patiently waiting about to see if it hears anything. It can't produce the next pulse of the sweep pattern until the appropriate time interval for a return at the maximum range has elapsed. On the longest range this delay is on the order of a second or so. Thus even in the "fast sweep" mode, it takes around 15 seconds for it to complete the sequence of straight ahead to straight down when attempting to detect distant floating objects. One can improve this somewhat by limiting the sweep pattern to a smaller arc.

Now, add to this the narrow beam width. If the boat is yawing a bit as it passes through the seas, the beam is directed away from the COG some of the time. This means that there is a chance that when the "straight ahead" pulse from a sweep is generated, the boat may not be aimed at a floating object that is in fact on the course line... and so it isn't seen. This reduces one's confidence considerably!

Further, consider that if there is a sea running, the surface layer includes waves, foam, turbulence etc, and any of these can generate a false signal reflected back to the transducer. This means that in typical sea conditions, there is a lot of "noise" in the return when looking ahead at shallow depths... the depths of interest in avoiding the dreaded container. The operational result of this is that the alarm features of the Probe don't work very well at all. If you reduce the sensitivity enough to eliminate false alarms, it won't see much of anything at all! So, to be of any use in container avoidance, one would have to have an observer watching the display 24/7... not likely on our boat! (Or yours either, I reckon).

To sum it up, the forward looking sonar is a very useful tool for the cruiser who gets away from home waters, but it isn't a realistic means of avoiding small floating objects on a long term basis.

And, to add our little bit of data: we've now covered on the order of 125,000 miles in our cruising (between SF and the South Pacific) and have yet to see a floating container. I agree that there is a statistical possibility of striking one, but my personal evaluation says that there are much better things to worry about in our area of interest.

Oh... our boat (built of strip-plank composite) has not one but two crash bulkheads forward and one aft, features not often found in production boats. The degree of protection provided perhaps does not equal that of a steel hull, but it does help us to relax a bit at sea.

Cheers,
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Old 14-05-2011, 08:58   #173
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Re: Floating Containers In The Ocean

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G'Day All,

Now, add to this the narrow beam width. If the boat is yawing a bit as it passes through the seas, the beam is directed away from the COG some of the time. This means that there is a chance that when the "straight ahead" pulse from a sweep is generated, the boat may not be aimed at a floating object that is in fact on the course line... and so it isn't seen. This reduces one's confidence considerably!

Further, consider that if there is a sea running, the surface layer includes waves, foam, turbulence etc, and any of these can generate a false signal reflected back to the transducer. This means that in typical sea conditions, there is a lot of "noise" in the return when looking ahead at shallow depths... the depths of interest in avoiding the dreaded container. The operational result of this is that the alarm features of the Probe don't work very well at all. If you reduce the sensitivity enough to eliminate false alarms, it won't see much of anything at all! So, to be of any use in container avoidance, one would have to have an observer watching the display 24/7... not likely on our boat! (Or yours either, I reckon).

To sum it up, the forward looking sonar is a very useful tool for the cruiser who gets away from home waters, but it isn't a realistic means of avoiding small floating objects on a long term basis.
Thank you for confirming my unexpressed presumptions. Can't see how these transducers could work reliably with small boats in anything but a smooth sea.
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Old 14-05-2011, 09:14   #174
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Re: Floating Containers In The Ocean

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Originally Posted by niel12 View Post
I was wondering, as i read through the posts, if there is not a way to make sailing a bit safer. I know that we are not on the hard so a garbage truck can come by so we need to look at our vessels. Sure, first and foremost action is avoidance, but this is about that time you wheren't in time!
We owners of plastic boats might have a solution! Kevlar KM2 material that can withstand a bullet on impact. DuPont in the USA manufacture this new generation Kevlar KM2 for the US Army and i am sure the product might serve our reiforcement needs 100%. I will contact DuPont next week and find out if Kevlar KM2 is available commercially unless someone already know the answer to that.
I read in one of the forums that there was a manufacturer including Kerala on the bow in there design. I will have a look see if I can find it.
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Old 14-05-2011, 09:46   #175
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Re: Floating Containers In The Ocean

Quote:
Originally Posted by niel12 View Post
With referance to my former post on Kevlar it was interesting to find that the new generation Kevlar KM2 is bullet proof while the older Kevlar must have had certain short comings but certainly and apparantly not as strong as Kevlar KM2. As far as i can establish Kevlar KM2 is freely available. Is there someone who are familiar with actually applying the Kevlar KM2 on glassfibre? Should one remove the gelcote?
They say don't put glass on top of Kerala if your using it for a repair but I did not delve into it enough to see if it was ok with an undamaged hull but then how do you know it is undamaged unless you have had it from new.
I know you can't grind Kevala it turns into a Brillo pad. A repair Kevlar on Kevlar has to be shot blasted.

So if you have to repair it is it any good for a boat???

Basically you will have to do more research.


Wood vs grp, et al

Kevlar hull repair - Boat Design Forums
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Old 14-05-2011, 13:48   #176
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Re: Floating Containers In the Ocean

I'd say grind the gelcoat off and lay the Kevlar directly on the fiberglass.

I put Kevlar patches on the bow and stern of my whitewater canoe to protect the ABS skin from rock impacts and scraping. ABS plastic is fairly slick, but the patches bonded perfectly.

I sanded the area, cleaned it with MEK and applied the Kevlar with epoxy resin (tougher than vinylester or polyester resins). The epoxy molecules actually entwine themselves around the Kevlar strands and crosslink to form a very durable and impact resistant matrix.

Oh, and cover the epoxy with Saran wrap, gently work out the bubbles and smooth it all out, tape the edges with blue painter's tape and let it cure.
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Old 14-05-2011, 15:04   #177
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Re: Floating Containers In the Ocean

Thanks Hud this info is very welcome and i hope all the plastic yachties spend some time to strengthen their yachts, it might be well worth the effort and at last some form of "combat" for floating containers and debri.
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Old 14-05-2011, 15:51   #178
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Re: Floating Containers In the Ocean

One monohull that has always intrigued me is the ETAP. It is full of pore in place foam between the liner and hull, so is not only unsinkable, but REALLY sound and temperature insulated... (A downside to my single skin multihulls).

In the ETAP, one does loose a lot of storage, and I don't really know about the build quality, but the unsinkable feature would improve "peace of mind".

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Old 15-05-2011, 01:46   #179
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Re: Floating Containers In the Ocean

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One monohull that has always intrigued me is the ETAP. It is full of pore in place foam between the liner and hull, so is not only unsinkable, but REALLY sound and temperature insulated... (A downside to my single skin multihulls).

In the ETAP, one does loose a lot of storage, and I don't really know about the build quality, but the unsinkable feature would improve "peace of mind".

Mark
The Titanic was unsinkable! If you get cut in half then you have a choice. the part that floats and the part that sinks (water tanks fuel engine etc) Just don't hit anything or let anything hit you

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Old 15-05-2011, 02:17   #180
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I have an easy solution. Lets manufacture everything in the states and then we dont have to import these boat sinking steel containers and we might get everyone back to work and the country could run a surplus. Imagine that
Don't believe in export either then
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