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Hurricane Safe Harbor


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#1 Mel Miller

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Posted 28 August 2006 - 09:35 AM

As each hurricane season begins, we are reminded of the need for a safe harbor for approximately 1000 boats, all of which are normally floating on Miami city controlled waters.

Although there is disagreement as to a series of legal and usage issues relating to actions available in the immediate future, it ought to be possible to agree on the engineering issues that define a safe harbor and to conduct a basic cost-benefit analysis of candidate areas and engineering approaches to achieve an appropriate hurricane safe harbor.

I invite anyone who is interested to join in a virtual Ad Hoc Dinner Key Hurricane Safe Harbor Technical Working Group. To avoid the premature inclusion of issues that are best left to the political process, I believe that the study should first quantify the forces that act on a vessel during a hurricane, the resulting motion of the vessel, and the forces on the vessel when this motion is resisted, and the structures (pilings, bulkheads, anchors, moorings) needed to withstand these forces. The study should then consider candidate methods for reducing the storm forces.

The preliminary work will be of interest primarily to those who are comfortable with engineering concepts, but this should not discourage all interested parties from contributing ideas, suggestions or comments as to the analytical process or candidate solutions for a safe harbor.

Although I believe that some of the analytical work has been done for the general hurricane case and for the specific cases of other marine centers, it would seem to be needed for the special case of Dinner Key. In my opinion:

The hurricane induced loads should include:
1- Flotation loads water rise (surge) and rate of rise.
2- Wave loads cyclic and impact
3- Aerodynamic loads (sustained, gust and twisting)

The resulting vessel motion studies should include
1- All three rectilinear and all three rotational degrees of freedom for a rigid body
2- Quasi static, cyclic and first order impact induced motions

The motion resisting forces should include
1- Single point loads from anchors or moorings
2- Multiple loads from fenders and lines
3- Impact and abrasion loads at non-fendered contact points

Vessel failure (safety limits) should be determined by
1- manufacturers working limit for lines and attachments
2- Elementary elastic or failure deformation at vessel designed attachment or fendering points
3- Safety limits should be determined for a number of vessel types

Once the maximum survivable values are determined for the hurricane induced loads, force reduction should be calculated for
1- breakwaters
2- wind breaks
3- surge or shock reduction techniques


I believe that a number of these studies are appropriate for both undergraduate and graduate engineering research projects, especially at those institutions that still believe that the best published research actually saves lives or property.

#2 dinnerkeyadmin

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Posted 03 September 2006 - 06:59 AM

Mel, I think this is great.

My suggestion is that this could also develop some educational guidelines about best practices for securing a vessel in a legitimate safe harbor. Often, one poorly secured veessel can turn an otherwise safe harbor into a pinball machine. I've watched people tie lines directly to anchors without using any chains, thimbles or shackles, and I've helped a lot of people who had broken loose six figures for a boat but had neither the ground tackle nor the awareness of what they might do with it.

Let me know how I might facilitate your idea.

Dave

#3 Andrew Marshall

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Posted 07 September 2006 - 05:53 AM

That is a good idea Mel.

Perhaps it should be tied in with the trees being cut down en masse on the western most Dinner Key spoil island. The adjacent island is also stripped of trees, thanks to Hurricane Wilma. As things stand a good portion of the Dinner Key Marina is now exposed from the South and West, and similar cutting of non-native species appears to be designated for the other spoil islands as well.

Increasing accessibility to the spoil islands is wonderful - but its "folly" not to take a balanced approach or to sacrifice the spoil islands' historical purpose of protecting vessels (/seaplanes) at Dinner Key. My intention here is to be practical - not negative. Over the last 15 years I've stayed aboard my vessel in every hurricane that hit S. Florida, and based on my experiences there is no engineering standard that can be practically implemented to protect vessels at the DKM if the facility is exposed to a major weather event from all seaward directions. As Wilma demonstrated, the berths are too narrow and the pilings are too short to handle the surge and chop.

#4 Mel Miller

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Posted 15 September 2006 - 09:12 AM

QUOTE(Andrew Marshall @ Sep 7 2006, 10:53 AM) <{POST_SNAPBACK}>
That is a good idea Mel.
Thank you Andrew. Unfortunaely I have not yet been able to obain more than preliminary interest from the local engineering schools, so the working group is off to a slow start.

Perhaps it should be tied in with the trees being cut down en masse on the western most Dinner Key spoil island. The adjacent island is also stripped of trees, thanks to Hurricane Wilma. As things stand a good portion of the Dinner Key Marina is now exposed from the South and West, and similar cutting of non-native species appears to be designated for the other spoil islands as well.
I agree that any reduction in protection will increase the probability of storm damage, but I belieev that the study should first quantify the expected damage as a function of wind, waves and surge height before considering methods of reducing those forces.

Increasing accessibility to the spoil islands is wonderful - but its "folly" not to take a balanced approach or to sacrifice the spoil islands' historical purpose of protecting vessels (/seaplanes) at Dinner Key. My intention here is to be practical - not negative. Over the last 15 years I've stayed aboard my vessel in every hurricane that hit S. Florida, and based on my experiences there is no engineering standard that can be practically implemented to protect vessels at the DKM if the facility is exposed to a major weather event from all seaward directions. As Wilma demonstrated, the berths are too narrow and the pilings are too short to handle the surge and chop.
Fortunately, I can remove my vessel each May and not return until November. More than fifty years of boating, and almost the same as an engineer who secialized in material and structural failure, has covinced me that Dinner Key is dangerous in a strong storm. However, I believe that the real probabiity of damage to boats, docks and moorings can be reduced in a cost effective manner, and I believe that the first step is to generate a mathematical model, acceptable to all interested and affected parties, that relates storm conditions to asset damage.


#5 Andrew Marshall

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Posted 05 October 2006 - 02:04 AM

QUOTE
More than fifty years of boating, and almost the same as an engineer who secialized in material and structural failure, has covinced me that Dinner Key is dangerous in a strong storm.


I didn't realize that you were an engineer specializing in material failure (although it's would seem that you work in Kevlar - which is fascinating stuff).

Not that I'm an engineer or proficient in formulas and calculations. But as you've indicated without relying on calcilations, it doesn't take an engineering degree to know that DKM is dangerous in a major weather event. This conclusion derived from experience. It is, after all, difficult to determine the strength to stretch ratios of various lines in differing wave/surge conditions with regards to the weight and windage of a vessel, nor is it easy to define cleat/bolt/backing plate/and deck thickness/material strength variables in all possible cogigurations. The same it the case with regards to the effect of age, weather, and cyclical loads and stresses on the materials involved, or decreases in strenght due to exposure to a marine environment and tropical sunshine. Additionally, the study includes the beam of a particular vessel to the slip width, various wind and surge conditions, the height and duplicity of lines tied to pilings (and the slack, diameter, age, and effect of sunlight and other weather on the line itself), the composition of deck core materials, the integrity of deck core materials (i.e. water intrusion, rot, and so forth) where the cleat ajoins the deck, the effects of salt water intrusion on bolts securing cleats to deck (i.e galvanic reaction given various bolt/cleat alloys), the size and material of backing plates with regards to various deck composites, and so forth. The variables are inexaustable.

Some of these calculations are available from ocean/mechanical engineers, marine equipment manufacturers, and the insurance industry - but not in each and every variation. Nor would such definitive information be useful to the average boater.

I'm not discouraging quantification, but in like manner common sense shouldn't be disregarded either. In this regard, over the years DKM has attracted wealthier boaters, which means power boaters with vessels that have more beam than the sailing vessels DKM previously attracted. Given that storm surges and winds remain the same, or increase with global warming, comparatively narrow slips and increased beam will inevitably result in damage in a significant weather event. The fact is that most vessels are designed to be secured with nylon rode - which is designed to stretch in order to absorb load. The problem is that there simply isn't ample room in the slips given the increase in vessel beam.

We witnessed this during Wilma. Powerboats with wider beams were damaged or destroyed against polings, while nattower sailboats rarely suffered this sort of damage.

The bottom line is that cutting trees off the spoil islands inevitably increases DKM's exposure to wind and sea conditions. Moreover, vessels from the outer Anchorage (/"Managed Mooring Field" ), upon breaking loose whould seem more likely to skirting over the islands into DKM. Trees formerly acted as a safeguard. It also ould appear that trees cut from the spoil islandsare going to be replaced with aesthetically pleasing sand beaches.

Real estate developers are not (or are at best only seldom mariners, and don't have the experience, orientation, or willingness to receive public input or otherwise comprehend the matter. Arial photographs of the Spoil Islands' sandy beaches will attract tourists, money, and increase real estate prices.

#6 Mel Miller

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Posted 08 December 2006 - 07:55 AM

QUOTE(Andrew Marshall @ Oct 5 2006, 07:04 AM) <{POST_SNAPBACK}>
QUOTE
More than fifty years of boating, and almost the same as an engineer who secialized in material and structural failure, has covinced me that Dinner Key is dangerous in a strong storm.


I didn't realize that you were an engineer specializing in material failure (although it's would seem that you work in Kevlar - which is fascinating stuff).

Not that I'm an engineer or proficient in formulas and calculations. But as you've indicated without relying on calcilations, it doesn't take an engineering degree to know that DKM is dangerous in a major weather event. This conclusion derived from experience. It is, after all, difficult to determine the strength to stretch ratios of various lines in differing wave/surge conditions with regards to the weight and windage of a vessel, nor is it easy to define cleat/bolt/backing plate/and deck thickness/material strength variables in all possible cogigurations. The same it the case with regards to the effect of age, weather, and cyclical loads and stresses on the materials involved, or decreases in strenght due to exposure to a marine environment and tropical sunshine. Additionally, the study includes the beam of a particular vessel to the slip width, various wind and surge conditions, the height and duplicity of lines tied to pilings (and the slack, diameter, age, and effect of sunlight and other weather on the line itself), the composition of deck core materials, the integrity of deck core materials (i.e. water intrusion, rot, and so forth) where the cleat ajoins the deck, the effects of salt water intrusion on bolts securing cleats to deck (i.e galvanic reaction given various bolt/cleat alloys), the size and material of backing plates with regards to various deck composites, and so forth. The variables are inexaustable.

Some of these calculations are available from ocean/mechanical engineers, marine equipment manufacturers, and the insurance industry - but not in each and every variation. Nor would such definitive information be useful to the average boater.

I'm not discouraging quantification, but in like manner common sense shouldn't be disregarded either. In this regard, over the years DKM has attracted wealthier boaters, which means power boaters with vessels that have more beam than the sailing vessels DKM previously attracted. Given that storm surges and winds remain the same, or increase with global warming, comparatively narrow slips and increased beam will inevitably result in damage in a significant weather event. The fact is that most vessels are designed to be secured with nylon rode - which is designed to stretch in order to absorb load. The problem is that there simply isn't ample room in the slips given the increase in vessel beam.

We witnessed this during Wilma. Powerboats with wider beams were damaged or destroyed against polings, while nattower sailboats rarely suffered this sort of damage.

The bottom line is that cutting trees off the spoil islands inevitably increases DKM's exposure to wind and sea conditions. Moreover, vessels from the outer Anchorage (/"Managed Mooring Field" ), upon breaking loose whould seem more likely to skirting over the islands into DKM. Trees formerly acted as a safeguard. It also ould appear that trees cut from the spoil islandsare going to be replaced with aesthetically pleasing sand beaches.

Real estate developers are not (or are at best only seldom mariners, and don't have the experience, orientation, or willingness to receive public input or otherwise comprehend the matter. Arial photographs of the Spoil Islands' sandy beaches will attract tourists, money, and increase real estate prices.



Andrew
Your points are well taken. There are many variables that influence the storm damage that a specific boat will suffer from a particular storm, and it is intuitively obvious that some boats cannot be reasonably protected in their current slip. If we can get this study to move forward sufficiently, I have no doubt that minimum vessel requirements will be established for permission to remain in the marina or the adjacent waters but that determination should not be made until there is general agreemnt as to the quantitiative relationship between storm parameters and the probability of vessel and marina damage
The tradeoff between storm protection and beautiful vistas is, indeed, influenced by developers, but also reflects the interests of various activists. Hurricane gates are somewhat ugly and the associated rules are not loved by owners who love the freedom of boating. That is why I want to concentrate on the non-subjective techncal issues.