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Old 12-04-2009, 17:51   #1
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Full speed grounding......

I have read that any blue water, cross an ocean, higher latitude boat ought to be able to withstand a full speed grounding.

Other than alloy boats are there any fiberglass production boats that are able to withstand such a blow?

You can't cross the sea merely by standing and staring at the water
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Old 12-04-2009, 18:18   #2
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Depends on the bottom. I've had a couple of slammers on my Pan Oceanic 46 in the mud of the Chesapeake with no damage other than to my ego and my faith in charts. They have Full keels as thick as my arm is long with encapsulated ballast and a sloping forefoot that allows them to ride up on a mud bank and get stuck really well.

Wouldn't want to try it on sand or rocks though.

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Old 12-04-2009, 18:58   #3
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Grounding is one thing but it is the pounding up and down in the swells afterwards that beats the boat to death. We had an encapsulated keel cruiser towed into the marina I worked at and she was done for. The keel was broken open and her hull was breached in several places. It was a sad sight to see a lovely boat beaten to death by the rocks.
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Old 12-04-2009, 20:31   #4
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Car Crash Example

The force exerted has a lot to do with the deceleration. If you come upon a gradual shoal, then things happen differently than on a ledge.

The other issues have to do with the contact area to the hull. A sharp ledge agaisnt a hull will concentrate loads differntly than a differently shaped bank. (Coming upon a sheet of very hard ice can cause titantic problems of localized damage.)

Aside from the hull, the rig may not stay in one piece in severe "stops".

I believe that the general discussion (at a qualitative level) would lead one to conclude that a smaller boat would fair better than a larger boat coming to an abrupt halt a hull speed. The forces square and the hull speed of (say) a Westsail 32 compared to a Swan 47 would be the difference between 5^2 vs. 9^2 or say 3 times the force -- assuming (the imaginary) all things equal...
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Old 12-04-2009, 21:02   #5
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In Suva Harbor in Fiji, I turned left when I should have turned right, and I grounded out on a shallow sandy shelf. I bounced along for about fifty feet before I came to a halt. I put the engines in reverse to try to get off, but no luck. Fortunately, I was not on a falling tide, and my two teen age kids jumped off the bows and gave a series of huge pushes as well as bouncing the bows up and down. The shoving coupled with engines in full reverse got Exit Only off the sandbank. There wasn't any coral present, and so no harm was done, except that everyone in the anchorage saw us run aground because my wife was talking to people in the anchorage on VHF when it happened. She announced to the world over the VHF that we had just gone aground.

When we were in the Bahamas, we travelled with a 44 foot catamaran who wasn't as lucky. He grounded out on a hard sea bed on a rapidly falling tide. He was instantly stuck. There was about five knots of current flowing pinning him there. We tried a kedge anchor, two dingys, and people in the water pushing. No luck. We had to wait for a high tide to float him off. He only got a few scratches on the bottom of his keel. No real harm done there as well.
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Old 12-04-2009, 21:07   #6
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When I was in Dania, Florida, I saw a Prout 45?? that had both sacrificial keels ripped off from a grounding. There is another bottom to the hulls internal to the sacrificial keels, so no water entered the yacht's interior. The Prout was in a boat yard, and this was the second time it had been there for repair of damaged sacrificial keels. The keel damage had happened more than several hundred miles away, and the catamaran simply motored back to Dania where the second repair was performed. I can see a real benefit to sacrificial keels that are fiberglassed to the bottom of the hull.
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Old 12-04-2009, 22:52   #7
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I have never done it at full speed, but we did hit a rock at 5 knots and go dry with a 47' Skookum with only minimal damage to the gel coat on the keel, other than that no real damage. Skookums built in the '70s had a tremendous thick layup and very strong hulls.
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Old 13-04-2009, 01:26   #8
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The P.O of “Southbound” hit a rock, with the very lowest part of the keel, at about 5 kts speed (under engine power), in the St. Mary’s river (The Soo). The boat was brand new, having just been factory-launched the previous week.

The impact hinged the keel, such that it separated downwards towards the bow, and was driven up into the interior aft.

He called C&C describing the etiology and damage, and George Cuthbertson said it sounded as tho' the boat was ok to sail, as long as he could keep the water out.

He applied an underwater epoxy patch and sailed her 350 miles (hand-pumping about 10 min per hour) home to Thunder Bay.

Norm < Norm's Boating Centre Inc - Fibreglass Services > did an invisible repair, which never leaked at drop over the next 15 years, until I sold (& lost contact /w) her.
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Old 13-04-2009, 05:18   #9
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Hit the bottom, reef, in my last cat at 14 knots on a reach with the boards down.

Jammed the board, lifted the hull almost clear of the water pivoting on the board, but did minimal damage to the hull, about a 12 mm crease in the skin at the back edge, nothing visible on the inside.

I had heavily reinforced the daggerboard hull exit area, but the hull and case were 10mm WRC and 440gsm db in and out

Didn't do much to the board either, but did crack the ribs of one of the crewmembers that was standing up and continued forward and got the cabin top edge in the chest when the boat rapidly stopped.

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Old 13-04-2009, 05:48   #10
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Depends on many factors such as did you run into something soft like a mud or sand bottom or something hard like a rock ledge or coral head. Did you hit it or ride up on the rock and bounce around and get stuck up there or bounce off and continue on? Did it hit the keel, top or middle or the hull?

The term grounding implies that the boat rain out of water and was stopped as opposed to hitting something submerged which could stop the boat, but it may not be aground.

Collisions with the forward and especially the lower end of the keel will do one or more things. If can cause the keel bolts to shear or bend as the keel is stopped and the hull momentum stresses the bolts as it move forward.
It can cause the aft end of keel to push up into the huil and the pull the forward end down. If the keel hil lay up is very stiff this will cause the entire boat to pitch forward. If the lay up is weak enough the hull may flex and even crack aft or forward at the keel. This depends on the amount of force involved in the collision.

If you sail into think water a full speed heeled over with soft bottoms you tend to get stuck more than damaged. If there are larger waves this could become a serious problem.

GRP hulls do flex and can absord stresses. Bulkhead joints etc then to be the weaker points in that they can't flex (and aren't meant to).

Go slowly in thin water and try to avoid charted submerged objects!
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Old 13-04-2009, 07:21   #11
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Originally Posted by slowasigo View Post
Other than alloy boats are there any fiberglass production boats that are able to withstand such a blow?
Yes, but as always, it depends. First, what are you grounding on? Obviously, a rock will impart more shock than mud or sand.

Boat design and construction go hand in hand here. A deep keel with a short root chord (meaning a short fore and aft attachment to the hull) will exert a lot of leverage in a hard grounding, trying to push the back end of the keel up through the hull. Even the best built hulls may not survive without significant damage. Modern racing boats do not like hard groundings.

A full or long keeled boat should have no problems. Think Island Packet.

Also, for boats with externally attached keels, a lead keel will deform a little on a rock, where cast iron will transmit more shock to the keel bolts and hull structure.

Assuming equal construction standards, the longer and shallower the keel, the less likely a hard grounding is to cause significant structural damage. Consider a Bermuda 40 with the CB up.

Assuming identical designs, obviously a boat with more robust scantlings will hold up better.
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Old 13-04-2009, 10:36   #12
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