Huricanes Don"t Destroy Boats Marinas Do

[captddis]

Sooo why did you not keep the 45 there? The comments were about keeping BOATS tied up to exposed docks. Leave your boat there and see if you still claim bullcrap.

[Genesis]

The water depth did not permit Gigabite to come in there.

At any time - hurricane or no.

That video was taken more than six hours after the peak of the storm - Ivan's landfall was at approximately 2:00 AM.

The windage of that total structure (including the top deck) exceeds that of any boat that would have fit there. Point being, there was ZERO movement. Why? Because of how the dock is built.

All pilings are upsized and pylocked. The entire dock structure is unitized so that forces taken at any given point are transmitted and buffered through the ENTIRE structure, instead of being able to wrack the point of impact loose, causing a progressive failure of the structure.

If I had the depth to keep Gigabite there, I would have, and would have upsized the structure even more (I had it designed, engineered and built to my specifications.) Since dock structures (residential anyway) cannot be insured, and knowing that I live in an area that, on average, takes a Cat 3 hit every 10 years, I built my dock to survive such an impact.

Again - that was the only dock on this part of the bay which was standing and intact. The rest of them were destroyed, with many being reduced to bare, twisted poles.

We didn't even lose the DECKING nor was any of it loose due to wracking forces. In short the dock simply did not move. The video afterwards was LITERALLY the first full day after the storm - ZERO repairs made. We still use that dock daily.

Interestingly enough, if you look at that video again, you'll find that the boathouses are all still there. Why? Because there's a code for those, you see, as the county gets pissed off about whole roofs flying around at 140mph, so they actually have a code for those and inspect.

There is no code for the actual dock strength, however.

By the way, the MARINA where Gigabite was moored (and which we moved her from previous to the storm), was far better protected than my home's dock is; it has spoil islands on all sides but the inlet which faces another land mass less than 1/2 mile away to the northwest (not a high-risk direction for storms.) It is less than 2 miles away by water. They evicted many boats prior to the storm's arrival.

Nonetheless, huge parts of those docks were utterly destroyed - just as were the other residential docks in this vicinity.

Why? My opinion, given what I observed there over the years I was present, was that the structure was weak and severely deteriorated by the passage of time, lack of maintenance and inadequate design up front.

Point being, properly built docks do not automatically fail when storms come, it is entirely possible to build them that won't, and the difference is simply a matter of whether you wish to spend the money on proper design, engineering and maintenance.

It is not an unsolveable problem nor an "Act of God" when they DO fail.

You cannot sell a car in this country that kills you in a 5mph frontal collision or one that has seat belts made out of toilet paper. Why marinas are allowed to operate with dock structures that are so badly wasted that they move noticably under HUMAN traffic, or which have pilings that are WAY short of the expected tidal surge in a storm that is otherwise surviveable, thus GUARANTEEING that your boat will be destroyed if it is there when the storm comes, is beyond me.

[thoward]

We are talking about marinas with boats attached! What you fail to take in to mind is that if you have slack lines your boat is going wrack that dock and I am pretty sure 100,000 pounds of repeated pounding is going to tear any dock apart. Also lets not forget the surge where your boat is going to lift those loose pilings up and go for a ride. My boat went through Katrina in Mississppi and that is exactly what happened. She pulled the entire dock and went for a ride. You guys are expecting way too much for a structure that has a million pounds of shifting weight pulling it apart. If a 3000lb car can snap a telephone pole at 20 mph then it does not take much of a step to understand the damage a 100,000 lb boat can do.

[Brian Degulis]

I don't think anyone would suggest that all huricane damage can be prevented but I bet 80% could be.

A common sight at todays marinas is to see a slip for a 60 footer consisting of a floating dock and 2 pilings about 70' out and that's it. Do you think thats OK? I think any structural engineer would tell you that with a typical 60' boat in that space the safe working load on that structure would be exceeded in winds of about 40 MPH.

The Tampa area saw 2 marinas completly destroyed and one almost destroyed from winds that never exceeded 80 MPH. Would you consider that exceptable.

I stayed at one of those marinas over the weekend it's been rebuilt with nice heavy concrete piers but the pilings where so short that the rub rails on my 61 MY where above the tops at high tide.

My point is this every time a huricane strikes there's a lot of damage that could easily be prevented if marinas where designed and maintained corectly.
Crapy designs and poor maintenance destroy more boats than the storms themselves.

Brian

[Genesis]

In a word, nonsense.

If you're improperly secured then your boat goes under!

I've seen it happen - the pilings do just fine - you're literally held down and sink.

People think this is rocket science. It is not. If I can stick a boat on the end of a rode in a hurricane and have it hold, I can also stick it in a slip at a marina and have it hold, provided that the pilings and structure are built properly for the loads contemplated.

"Loads contemplated" include storms. You guys never get severe weather? Where do you live? You think it requires a HURRICANE to get 100mph winds? Ha!

How come my little bitty house stays together in 130mph winds with flat sides that act like sails and catch the wind? Its because the structure of the house is unitized. This is also why if you lose a window you're hosed - the structure is not designed to take pressure loads from the INSIDE so once the wind gets in the roof comes off.

This is an engineering problem guys and it CAN be solved. Yes, the boats have to be properly secured, but these are not snatch loads - there is tremendous stretch both in the lines and the pilings.

How many of you have actually been through a hurricane with a boat? After Ivan Gigabite (which was moored AT A DOCK guys!) had the chafing gear showing BURN damage in a few places. The dock it was secured to held and so did the deck hardware. But the evidence of extreme stress was present in the lines used (they were all discarded after the event, natch.)

This is NOT an impossible problem to solve. I know a lot of people think it IS impossible, but its not, any more than its impossible to build a dock that will survive breaking seas far above the deck height.

Now look - if your deck hardware is inadequate, if your lines are inadequate, if you get holed by someone who gets loose, if you're improperly tied, ok. There ARE marinas and slips that cannot be made safe for YOUR boat, mostly because the slip is too narrow to permit proper line setting (you can't set up for the surge without banging the pilings and/or simply have insufficient clearance) or the pilings are too short which is how you get speared and sunk from the bottom.

But having gone through this both as a dock and boat owner, more than once, I will say this - if your marina is sited in a place where it has several MILES of unbroken fetch it shouldn't be there! That permit should NOT have been granted - period! Some sort of break should have been mandatory to cut the breaking seas down to size, or if that couldn't be done, the permit should have been denied. Absent a HORRIBLE location the rest of the problem is one of inadequate design, engineering and most of all maintenance.

After Ivan I can't tell you how many pilings I saw that were snapped off at the bottom. Upon inspecting the broken pieces what was seen was clear evidence of wastage. Those pilings did not fail due to storm loads, they failed due to deterioration - they should have been replaced BEFORE they failed! I also saw stringers that were NAILED, which are GUARANTEED to come loose under load, instead of being through-bolted. I saw "bolts" that were so wasted you could have snapped them with a 1/4" drive socket IN YOUR HAND.

Never mind floating docks on pilings that are 3-4' above the water - gee, what do you think happens when a 6' surge shows up? They all float off and......

I have ALSO seen properly-designed docks RIGHT NEXT TO structures that were NOT properly designed, such as my NEXT DOOR NEIGHBORS dock and mine. HIS came apart because of the sins of original construction. Mine held. There was ONE HUNDRED AND FIFTY FEET separating them. Same conditions guys.

[Pascal]

we had about 100kts here during wilma in 2005 and most boats, even the most exposed, held just fine on two pairs of pilings. I have no doubt that with one or two extra pairs, they woudl have held up much higher winds.

it's all about preparation and spreading the loads. floating docks and insuficient pilings are not going to cut it.

same with homes... When my house was built on St Barth in the late 80s, it was built like it shoudl be on a hurricane prone island. Blocks with reinforced concrete pilars at every corner, door and window, with reinforced concrete at the top of every wall, and a roof structure that was all thru bolted.. no nails. Roofs are anchored into the concrete with threaded bars bent around the steel

after strong and slow (36hrs) near cat 5 Luis is 95, there was no damage. Even teh 8' galleries in front of the house stayed on.

compare that to local florida building codes where roofs are nailed and "luxury" homes built out of nail matchsticks....

it's all about anticipating the loads...

[thoward]

Nonsense? So what works up there will work down here? Sorry boys but geology has a lot to do with how the dock is going to hold up. Pilings in mud/silt are not going to hold like those in sand. My marina for instance has 6 pilings for the smaller boats and 8 for my class set in a sandy bottom. The dock is screwed together and crossbraced but twice(once it was only 1 year old) was broke off at the ground. We are directly in the inlet so I am sure it had a great deal to do with it. You may be able to have one hold up great in some areas but there are some areas that there is no way it is going to hold up. You are also going to have a darn hard time setting your lines when the surge is 8-10' or more in some areas. I will lay dollars to doughnuts those 8 pilings will not hold our boat in a Cat 2 + hurricane and I will not take that chance.

[Genesis]

If you have enough width surge is not a problem; take lines to FURTHER DISTANT pilings so as to both give you a smaller angle AND more stretch (less snatch loading.) This was the strategy we used for Ivan with excellent success.

If you don't have enough width and are forced due to piling configuration to run short scope on the lines then you're unsafe in that location.

The biggest problem with a properly-configured dock structure is providing fairlead and chafe protection on your lines in a severe storm; you can't use long chafe guards that have no permeability because of the tremendous HEAT generated internally in the lines - nylon will literally melt under hurricane loads! The water (from the rain in the storm and windblown water) is actually an essential part of maintaining line integrity. While old fire hose makes excellent chafe protection its lack of permeability can be a problem for this reason, especially if you try to get cute and use a longer length of it than you really need.

Ideally you want the chocks/fairleads CLOSE to the cleat where the line terminates so that the stretch and thus motion to that point is small; this allows you to use smaller chafe guards and allow cooling water to get to the line under the guard.

[Jaxfishgyd]

Here's a portion about properly built marinas.... The entire story is at http://www.yachtsurvey.com/huricane.htm


The Coco Plum Experience This private marina at the south end of Coral Gables gave us an excellent lesson in hurricane protection in the aftermath of Andrew. Most of the boats in all the marinas to the north and south of Coco Plum were destroyed, even though all these marinas directly front Biscayne Bay. And yet, incredibly, not one boat at Coco Plum was lost, and only a few had significant damage.

So what distinguished this marina from all others? First, the entrance channel to the marina has a sharp dog leg that greatly reduced wave action. Next, the marina was protected by a buffer zone of dense mangroves. But just as important, the concrete docks at the marina have very wide slips with heavy, tall pilings. This allowed boat owners to tie their boats well off the docks. Even with a 10' storm surge, not one boat came down on the pilings, and hence none were lost. Whereas at Diner Key, Matheson Hammock and Black Point, nearly all the boats were lost because all had narrow slips and inadequate pilings. The lesson for boat owners with boats in narrow slips is that your chance for survival is very slim indeed.

[Pascal]

many boats suffered rub rail damage at DKM during wilma because the slips are too narrrow. I had to adjust my lines a couple of times during the storm to stay off the pilings as winds shifted.

pilings are too low too, even though surge was only 5' or so i got a few scratches as the rub rail reached 2' above the piling tops.