Hull protection for floating objects

[ShinyHappy]

The cargo ship losing several hundred containers had some discussion about the danger of hitting them and it has been a concern of mine for ocean sailing. I understand the low probability of such a collision, but being that it could be devastating it would seem a builder could provide additional protection for such an event.

A substantial piece of stainless covering the point of the bow below the waterline would take the impact of a hit much more effectively than fiberglass and framing. I'm thinking of 3/8 or 1/2 inch angle just covering the point of the bow.

That would take the brunt of solid impacts and allow the vessel to weather such an event. Glancing blows could still be damaging but it seems the point is lost vulnerable.

It would help even here where we dodge the tree branches floating down river to save scratching the hull.

Is there a reason this isn't done or isn't common?

[Orion Jim]

If there was a perceived market for them the marketing gurus at the major builders would already have offered them as factory options. Individual’s who place themselves at something greater than a casual risk avail themselves of steel or aluminum. The vast majority never give it a second thought. I have given it some thought and since I singlehand offshore. I chose a full keel design to give me a chance of riding up and over or glancing off an object. Since I have no intention of heading to the poles or sailing up rivers during the flood seasons I figure the odds are in my favor. I also have a life raft and an EPIRB....I won’t go down without a fight.

[hpeer]

Our big boat is 3/16” plate for the hull, keel is 1/4” plate. Most of the keel is either ballast or water/fuel tanks essentially creating a double bottom.

I saw a big production boat that hit a big river buoy, knocked a good size hole a few feet back and 18” above water line. Had it not been calm conditions he would have been in trouble. My revenge for laughing at this bloke was to big a big steel buoy at 7 knots on the St Lawrence Seaway. Totally my fault for getting distracted. The bow pulpit got ruined and it put a bit of a dent about waterline a few feet back. This was in our 33’er, 10 gage steel. Thats a hair over 1/8” thick.

Final story, i ran the big boat up over a submerged piling at speed. It was marked but decluttered in Navionics. We must have hit it fair because we went straight up and over, not sure how much it picked us up, somewheres between 6” and a foot. Not a mark on the boat, nothing. Bottom shoe is 1/2” thick.

Just relating the stories to give an idea of the strength and elasticity of steel.

But I still do not want to tangle with a container or hard ice. Everything has its limits. You catch a corner or a bit if sharp hard ice and thats it.

[Chotu]

I’d do the exact opposite (and have).

My boat has sacrificial bows and two watertight bulkheads forward.

This means the first 5ft or so of the boat can be torn right off with only cosmetic and a slight performance hit.

A steel plate will only serve to transfer the energy back to the next piece of fiberglass which will break. You need to absorb an impact.

That’s why cars have airbags.

[Paul L]

Watertight crash bulk head in the bow. This is more common than you might think on cats and monos. Perhaps some Kevlar reinforcing for the forward dozen feet, if you feel the need.
Or just get a heavy, steel boat and deal with the tradeoffs.

[Benz]

My thought is that biaxial kevlar is pretty cheap, and sandwiching a few layers into the hull around the waterline with some extra in the bows would go a long way toward puncture-proofing an otherwise fiberglass hull. It would have to be during construction, since you want it not as the outside layer, but not all the way inside either.
It's a feature of the imaginary next boat I plan to build when I have unlimited funds....
For now, my uncored fiberglass hull has taken some hard blows by floating trees down in Central America--they make quite a thump, but no visible damage yet. I have a collision bulkhead six feet aft of the stem which comforts me in those times.

[Scorpius]

Steel boat. The stem is 5/8" plate 8" wide on edge with the hull plates welded on either side. The bottom of the long keel is 3/4" plate (just part of the ballast). The first time I hit a rock I was down below pulling up the floorboards looking for flooding. Nothing. Next time I hauled it took me ten minutes to file the burrs off the edges of the scratch and slap on a bit of paint to cover it.

At night I've hit a BIG log square on. Very noisy - but it just rolled the length of the boat under the keel and popped up (more like slowly rose - it was pretty waterlogged) behind us. I've also hit a substantial deadhead floating vertically with the end right at the surface. None of these encounters have done any damage.

I have a friend who hit a big nav buoy in the Fraser River at ten knots (he was going downstream with the current) and ended up with a crease in the steel hull of his boat. Most unfortunate but at least he wasn't holed.

There's a guy in the boatyard here who makes his living repairing 'glass boats that have hit things. There's a sports fisherman in the shop that sustained over $100,000 damage during the summer and is STILL under repairs - although the prevalence of Mary Jane [now legal in the entire country] around here may have something to do with the elapsed time.

[Midnight Son]

I know the Caliber LRC sailboats have Kevlar reinforcing in the bow laminates. They have it in their brochures and the website, last I looked.
Best wishes

[ShinyHappy]

Originally Posted by Orion Jim

If there was a perceived market for them the marketing gurus at the major builders would already have offered them as factory options...

Good take. If manufacturers could make money from it, they would. And that would require a perceived need. Interesting that modern boat design has the leading edge much more perpendicular to the water so a collision would be more of a head on rather than a deflection down and under the boat like on your full keeler.

[ShinyHappy]

Originally Posted by hpeer

Our big boat is 3/16” plate for the hull, keel is 1/4” plate. Most of the keel is either ballast or water/fuel tanks essentially creating a double bottom.

I saw a big production boat that hit a big river buoy, knocked a good size hole a few feet back and 18” above water line. Had it not been calm conditions he would have been in trouble. My revenge for laughing at this bloke was to big a big steel buoy at 7 knots on the St Lawrence Seaway. Totally my fault for getting distracted. The bow pulpit got ruined and it put a bit of a dent about waterline a few feet back. This was in our 33’er, 10 gage steel. Thats a hair over 1/8” thick.

Final story, i ran the big boat up over a submerged piling at speed. It was marked but decluttered in Navionics. We must have hit it fair because we went straight up and over, not sure how much it picked us up, somewheres between 6” and a foot. Not a mark on the boat, nothing. Bottom shoe is 1/2” thick.

Just relating the stories to give an idea of the strength and elasticity of steel.

But I still do not want to tangle with a container or hard ice. Everything has its limits. You catch a corner or a bit if sharp hard ice and thats it.

Buoys seem to be a bigger danger than i had imagined!

Agreed that a hard enough knock could hole any boat. But having some pretty good bumps and coming through unscathed sure builds some confidence.

[Clivevon]

You've heard about the Titanic, right? Steel boat, hit iceberg a glancing blow which ripped all along its side? Scaled down, a container is iceberg size to a cruising boat, & your reinforced bow is not going to help at all if you hit the corner of one of those a glancing blow. A collision bulkhead might help or at least buy you time - depends where you hit.
You could buy an "unsinkable" boat like a Sadler 34 which has a thick foam filled gap between the inner & outer hull which is proven to stay afloat even when full of water.
I reckon most of us just trust to luck & "keep our powder dry" (liferaft, epirb, carefully thought out grab bag & water bottles....).

[ShinyHappy]

Originally Posted by Chotu

I’d do the exact opposite (and have).

A steel plate will only serve to transfer the energy back to the next piece of fiberglass which will break. You need to absorb an impact.

My thought was that the plate would spread the impact over a larger section of the bow instead of crushing the spot of impact.

I like your thinking on watertight bulkheads. It's a feature I've seen on a few boats but again, not often. That could could be a function of the price point I'm looking.

[Martkimwat]

Unfortunately most containers float up and down level or just below the surface and often the impact is vertical as the container bobs back up towards the surface. a foot or to of motion may not seem much but bear in mind it is a forty ton item and that equates to a lot of inertia/momentum depending on what it is doing. It's just as likely to be a glancing blow as well rather than an impact straight on so might miss the bow all together. I have considered using a forward looking sonar which can have a 600 foot detection range in deep water,(Interphase) or 300 feet (Echopilot) but at 6~7 knots that's only going to give you 60 seconds (30 seconds with an Echopilot) at best. May be enough if you are quick to respond if the warning is recognised straight away without the hesitation that is likely with a warning alarm that may not be immediately recognised for what it is. After all it's not likely to be going off regularly.

[Scorpius]

Originally Posted by Clivevon

You've heard about the Titanic, right? Steel boat, hit iceberg a glancing blow which ripped all along its side? Scaled down, a container is iceberg size to a cruising boat, & your reinforced bow is not going to help at all if you hit the corner of one of those a glancing blow. A collision bulkhead might help or at least buy you time - depends where you hit.
You could buy an "unsinkable" boat like a Sadler 34 which has a thick foam filled gap between the inner & outer hull which is proven to stay afloat even when full of water.
I reckon most of us just trust to luck & "keep our powder dry" (liferaft, epirb, carefully thought out grab bag & water bottles....).

The Titanic was 48,000 tons moving at over 20 knots. Scorpius is 15 tons and usually moving around 5. Thus the momentum forces of the Titanic were about 3000 times as high when she hit that iceberg as Scorpius's would be in the same situation. Titanic's hull was built of 1" steel plates rivetted together. Scorpius's hull steel is 3/16" and welded. Thus, although the forces on the Titanic (around 15 TONS per square inch!) were 3000 times what could be expected on Scorpius, the hull was only about five times as thick, thus nominally only about five times as strong.

Titantic was further compromised because she was built of faulty steel - faulty even for the time. Titantic's steel (and the rivets holding the plates together) had much too high sulphur and oxygen content. The high oxygen content meant the steel was much more susceptible to becoming brittle at low temperatures than would modern steel. Titantic's steel became seriously brittle (and thus shattered rather than bending) at around 30 degrees F - whereas modern steel would not become so brittle until about -60 degrees F. High sulphur content means there are weak sulphur "tracks" in the steel which act as "tear" lines when the steel is stressed thus seriously weakening it. The rivets were similarly faulty and failed both at the time of impact and later as the weight of the water inside caused high stresses on the ship's structure - opening the ship even more to the ingress of water. Had she been welded that wouldn't have happened. If you are interested here's an engineering paper on the topic:

Causes and Effects of the Rapid Sinking of the Titanic

There's no comparison between the Titanic disaster and a similar impact on a modern steel sailboat with either a container or multi-year ice (which is just about as hard). In 2000 we escorted a 65' aluminum (MUCH softer than steel) power catamaran through the North West Passage without incident - and we encountered LOTS of multi-year ice.

[ShinyHappy]

Originally Posted by Scorpius

Steel boat. The stem is 5/8" plate 8" wide on edge with the hull plates welded on either side. The bottom of the long keel is 3/4" plate (just part of the ballast). The first time I hit a rock I was down below pulling up the floorboards looking for flooding. Nothing. Next time I hauled it took me ten minutes to file the burrs off the edges of the scratch and slap on a bit of paint to cover it.

At night I've hit a BIG log square on. Very noisy - but it just rolled the length of the boat under the keel and popped up (more like slowly rose - it was pretty waterlogged) behind us. I've also hit a substantial deadhead floating vertically with the end right at the surface. None of these encounters have done any damage.

I have a friend who hit a big nav buoy in the Fraser River at ten knots (he was going downstream with the current) and ended up with a crease in the steel hull of his boat. Most unfortunate but at least he wasn't holed.

There's a guy in the boatyard here who makes his living repairing 'glass boats that have hit things. There's a sports fisherman in the shop that sustained over $100,000 damage during the summer and is STILL under repairs - although the prevalence of Mary Jane [now legal in the entire country] around here may have something to do with the elapsed time.

I'm hoping to keep my record of no buoys hit intact.

Everytime I think I've excluded steel and aluminum boats from my wish list, you guys tell stories like this and make me reconsider.