Hull survivability in a collision FRP vs Steel

More important than material is quality of construction and the use of a crash bulkhead. Many vessels designed for offshore have a watertight forward zone for the exact purpose you are concerned about.

But the issues as to what can cause a sinking are more than just a container strike. Stabilizers, rudder posts, shaft logs and through hulls are excellent areas to worry about for a hull breach. Or venturing out in bad weather and your vessel is overcome with water through the side windows that are without storm plates. Or the cockpit is too big and a boarding wave swamps the vessel or ------- or-------.

The list is very long as to bump in the night concerns, but I'd place steel vs Al vs FRP well down the list. If you are seriously thinking of venturing offshore become a weather expert and have the correct on board electronics to monitor , send, receive and utilize weather data. This combined with a proven sound vessel seems the chosen path for blue water enjoyment.

I used to think solid FRP could be thick enough to compete with the metals, especially in an expedition/trawler/displacement vessel.

The sinking of the original 70" Delta displacement vessel, "Zopilote" changed my mind as she peeled open her bottom like a tin can on an underwater pinnacle/reef in Alaska and promptly sank, ending a quite illustrious and legendary career.

A Hollywood-scripted trawler tale

As one who has chosen FRP over steel in my personal boats, I'd still say steel is going to withstand most collisions better. However, as pointed out there are many other factors. The container just below the surface isn't a great example to show steel's advantage because with either the object can rip out all the underwater gear and lead to a sunken vessel. The other factor that comes into play too is speed and often when one compares two collisions, one steel and one glass, the glass boat was moving at a much greater speed at the time of impact.

There are many other construction issues to look at and purchasing a boat is also not all about construction. You're looking at one that will best meet your own needs and that differs by everyone. I recognize the strength of steel but other factors don't make it my material of choice.

Hi,

If building from scratch a colission bulkhead, storm shutters, double bottom tanks, closed cofferdams and watertight compartments with good dewatering ability are all good design items to consider as most are very difficult to add after the fact.

I think you need to be a bit more specific.

FRP is excellent at absorbing impacts (better than steel or aluminium for a given strength - see gcol requirements in HSC 2008 for example), but steel is good at staying intact when deformed.

I think you may have misordered priorities. If you intend to cruise the ice fields, steel is of course your material of choice. But I think the question should be which is the lightest material for the cruising you intend to do. You can build an icebreaker, but why if you'll be cruising the southern latitudes? Every extra pound is more fuel burn and slower speed. Why do that if you don't need to. If you're worried about hitting a container get a life raft and a low insurance deductable. I've clocked tens of thousands of hours including 28 + east coast transits. I've seen one container in the water, and a couch that probably came from one. You're more likely to run into a deadhead that'll turn your prop into a baseball.

Ed,

You might want to look st a chart next time you are bored.

Southern Latitudes include places like Antartica and Cape Horn, not the Caribbean Basin.

You will have the most chance of encountering containers near shipping routes used in the winter when most boxes are lost.

Right you are K1W1. Guess I'm guilty of Northern hemisphere bias. Should have said lower. I was actually thinking southern in relation to Calgary (Vancouver to Mexico), as opposed to heading up to the N/W passage where he's likely to encounter ice. If he's going to Antarctica the OP has a lot more to consider than just the risk of running into a container.

I think he has exactly the right priority - survivability/safety 1st for him and his family. Perfect place to start. Pick your worst case scenario, and plan ahead for it. Be as self-sufficient as you can plan and afford.

Out West I know of 4 boats that have hit submerged containers, fast action from seasoned crews prevented two from sinking, the other two had only running gear/shaft/propeller damage. Granted this is over a 30 year period.

That's 4 out of how many million? Remote. I'd be more inclined to get a boat suited for his needs (fuel burn & speed), and invest in a good life raft & survival gear for the remote what ifs. Of all the things that can sink a boat I think that hitting a container is way down the list, and if he's doing 9 kits (which will probably be about his speed with a steel hull) the odds are better that he'll rip his running gear out and the result will be the same no matter which hull material is used. Once again it all depends on the size boat, where he intends to cruise and what he intends to do. There's also what happens to steel in salt water to consider.

Two of the FRP boats that hit submerged containers had major damage to the shaft log, and the crews had very little time to prevent the vessel from sinking. In a steel vessel, it would not have damaged the shaft log in a similar fashion, resulting in less risk for the OP. He is pretty clear about his needs, which may be quite different from your own.

If you are talking about a 9 knot displacement boat, then you would be looking at steel construction with some ballast or FRP construction with a lot more ballast. Your light weight approach really won't come into play for this type of vessel, and the fuel efficiency between the two construction materials will be a wash.

So getting back to the OP's major concerns, it would appear that Steel would have a favorable position.

Now, talking Life Cycle Costs, i.e. maintenance/repairs/consumables, a steel hull will potentially require shorter intervals between paint jobs/cosmetics, especially depending on the boating region, , but it should have a few more options in coatings and would be easier to paint if you take a commercial vessel approach rather than the glossy LP yacht systems that are more costlier.

I noted your reference to seasoned crews and think that once again experience and training come in as keys. If he's concerned about such incidents, then I'd also recommend him taking some courses in Survival Techniques and Sea Survival. If one is going to be spending a lot of time at sea then excellent crew is item one and the second thing I recommend for safety is some education, not just on navigation and handling boats but subjects like Survival, Medical Care at Sea, and Firefighting.

I know how slim the odds of hitting a submerged container and of a boat fire at sea are and somewhat less slim is a medical emergency. But being as prepared to handle such events as possible is often more key than is the boat and surviving is more important than saving the boat. For those with decades of experience in the industry this knowledge may be some they are immersed in. For those relatively new, the fastest track to gaining some of it is formal training.

Actually he wasn't clear about his needs, only about one concern. Also how would a steel hull have helped protect the shaft log?

Most of the Shaft Logs (the Tube where the shaft exits the hull on the aft side and where the shaft seal connects on the forward side) in FRP construction tend to be attached to the hull with a secondary bond. So the quality of the installation is left to the prep/overlaps/thickness and material of this type of construction. Also, with certain shaft angles, the underside has limited access as well for the laminators. This will vary from manufacturer, so it is certainly a construction detail to be inspected.

A shaft tube for steel construction, welded inside/out will be stronger and be most likely better reinforced with easily attached stiffeners/plates and or supports.

Actually he wants some scientific chart with a history of damage in equal collisions. Something like a clinical trial I guess where someone would take two identical boats except for material and run them into something. Seriously, I'm afraid what you're wanting just doesn't exist. You can certainly find information on what steel's strength is but there are so many different types construction with all materials and so it's not a simple strength of material issue. No two FRP builders do it the same and different sections of the hull may be done differently on steel and glass. Also no two identical collisions. I'm afraid you're going to be limited to experience of others and observations over the years.

I'm not saying that's not true. All I said was that the OP said he wanted statistics of boats that were in collisions showing how the boats and the passengers made out.

I indicated the strength of steel in my first post in the thread. I'm an FRP fan but would never argue against steel handling a collision better.

Or perhaps tugboats don't need to be lightweight to perform well, so cheap steel is a better choice than more expensive FRP? Hmm....