[Billy1119]

A friend of mine is taking an engineering economics class where he is writing a report and doing a cost/beneift and risk analysis of different materials used for ship building. He asked me for some help, and not being the most well versed person on the subject, thought I'd ask those more qualified for some assistance.

He decided to focus on motor yachts for the project. I suggested he focus on boats in the 125' range, because they're likely to use either of the three materials for the hull (steel, aluminum, and fiberglass). I'm looking for any information you can contribute, sources you think may help him out, or whatever you think may be relevant.

What we want to do is take a similar boat for a fair comparison and analyze the pros and cons of each material when applied to this given boat, from the design process, building, maintenance, cost, electrolysis, return on investment, longevity, and everything in between. I know I'm leaving out some information, but I'll clarify further as I find necessary or idea come to me.

Any help is welcome. I already have found the following threads that apply somewhat to the topic, but would like to try and get one going that is all inclusive with the three materials.

http://www.yachtforums.com/forums/al...=titanium+hull

http://www.yachtforums.com/forums/te...=titanium+hull

http://www.yachtforums.com/forums/te...-blisters.html

Thanks for any help!

[AMG]

I think emotions is another factor, some builders or owners favor some materials for reasons beyond rational.

When thinking of the different materials, it wouldn´t surprise me if all three will turn out to have cost the same after ten years of use...?

[KCook]

Then there are numerous designs that mix the materials. Anybody know of examples with fiberglass superstructure on a steel hull?

Kelly Cook

[Billy1119]

The recent launch of the 240' Delta is a steel hull with an fiberglass superstructure. Laurel is the name.

[AMG]

Originally Posted by KCook

Then there are numerous designs that mix the materials. Anybody know of examples with fiberglass superstructure on a steel hull?

Kelly Cook

I think the Royal Denship Princess Mariana is such a combination...

[Billy1119]

We're primarily worried about the hull though, or we'll make the assumption the superstructure will be made of the same material as the hull to avoid too many options.

Lars, perhaps that is the case, I really don't know. I guess the idea is to prove that this (they will end up costing the same) may be the case (or not). We'll end up needing specifics regarding the different materials to prove why we believe one over the other (or think it'll end up being similar). Does that make sense?

[Loren Schweizer]

As Lars says, the materials for a hull can become a Chevy vs. Ford kind of thing, i.e., pick a side and argue for it.

Being currently engrossed in Expedition steel hull/aluminum superstructure-type boats, here are some arguments for that side, keeping in mind that we are discussing displacement hulls here:

Sudden impact-- fiberglass can crack, aluminum can tear, and steel, with it's higher modulus of elasticity and greater yield strength, can undergo quite a bit of deformation prior to failure.

Fire--though rare, it always is a nasty possibility. FRP burns at 500F, aluminum melts at 1220F, steel @ 2800F. I could be wrong, but steel and aluminum, unlike FRP, more easily meet IMO ( SOLAS ) fire containment standards.

Mechanical-- welded hull/deck joints ought to be at least a tad stronger and more leakproof than a screwed/bonded FRP joint. Chocks, cleats, and towing bits are welded on, not just bolted on. FRP composites have the possibility of core delamination, unlike a single metal skin.

Over the years-- a hull surveyor can utilize audiogage + X-ray to precisely determine structural integrity.

Rust-- steel still gets an unfair rap here. No longer called 'paint jobs', the Coating Systems have pretty much done away with that. Steel that is pre-primed from the mill and is coated with more layers of inorganic zinc primers, fairing, then epoxies, then the final LP coats tend to look like FRP finishes and last as long.

Tankage-- fuel/water/waste are typically integral resulting in more capacity for a given size boat, plus a side benefit of having a double bottom over a good portion of the submerged surface.

Interior volume--metal boats just seem to have a greater useable interior compared to a FRP boat.

Stability at rest-- by keeping the weight aloft with an aluminum house atop a steel hull, it's relatively easy to achieve a proper metacentric height, i.e., a GM number resulting in a short roll period and good stability.

Like Burger King, have it your way-- metal boats, unlike FRP which requires tooling costs/constraints, are easily custom built to suit an owner's needs.

Again, I have my biases, and Lars makes an example of Royal Denship who will build in any of the three materials as well as in various combinations.

[KCook]

Thanks guys

[Billy1119]

Thank you, Loren. This is the type of content I am hoping to discuss and expand upon. I can see it becoming a Ford vs. Chevy debate (I drive a Tahoe, by the way ), but I hope to avoid the bias. I'm hoping for facts, but am more than willing to accept opinion based on experience. Cost structure is also important. Not just the initial costs, but all future costs as well (we'll leave the time value of money out of it, I suppose ).

I guess I should add, let's assume that whatever boat is built with these materials, it is a custom build (avoiding the benefits of having molds for the glass, creating a bias of sorts).

Thanks for the contribution. Keep 'em coming.

[lurker]

You mentioned that the paper will focus on "cost/beneift and risk analysis". What do you mean exactly by risk analysis? Are you talking the material science aspect (clearly each have their pros and cons) or the financial aspect of things (how likely will the hull crap out on you e.g. rust, crack, and the repair cost if repair is possible)?

I think the purpose of the boat and the type of hull will dramatically affect the cost/benefit. If we are talking about full displacement hull, then I will also strongly favor steel. But if we are talking about a semi-displacement yacht, then I have good arguments for the lighter aluminum and fiber glass.

If money is not an issue, then I would go with carbon fiber. If the hull is cracked and somehow I am still alive, then I will build another boat.

[wdrzal]

What about climate? If a yacht is not a world traveler and say spends most of its time in the warm latitudes compared to those that stay or venture to the colder ones,what impact would that have? Heat transfer through a steel & aluminum hull would be much different than composite hull.I sure climate affects Them in other ways Also.

How would the total environment a yacht is in affect your hull choice,say from the cold waters of Alaska down to B.C . to a yacht that will spend most its life in south Florida and the Caribbean? As to how water temperature ,sunlight, what lives in the water ,to the water itself(wave frequency, average wave conditions,etc. ) would affect a yachts hull choice.

Every answer brings another question for me. In the End, how much consideration does a buyer give to these parameters? Or does it just usually come down to a given "look" a buyer wants when it comes to hull choice?

[Billy1119]

All good points to raise, I think, wdrzal. Seems to me, as you implied, it would be much more difficult and maybe take up costly space to properly insulate a steel or aluminum hull for use in cold waters (and air) versus composite materials. Then again, maybe not?

Lurker, well, that's a pretty good questions. I guess I worded it different than I should have. This is what is under the risk analysis heading for the project, which includes cost/benefit. I'm not asking people of necessarily concern themselves with all of these, though.

Risk Analysis
- Risk Identification
- Risk Assessment
- Contingency Plan
- Benefit-Cost Analysis
- Engineering Economic Analysis

I guess the risk part would just be kinda a cons type thing - the potential problems with using a given material. EDIT: I meant to add, I guess I mean to discuss all those options you mentioned, both financials and material science type of information. I'll get further clarification.

Thanks for the input!

[KCook]

Interesting ... hard to see where the steel ends and the fiberglass begins ...

http://www.yachtforums.com/forums/14564-post5.html

Kelly

[JWY]

Fiberglass expense: last week a professional captain was hired to bring a high quality, well known fiberglass trawler from East Coast to Lauderdale. After passing under the 17th St. bridge in Ft. Lauderdale on its way upriver for a dock, the mate ran aground. After several hours, tide enabled capt. to finish the trip. Owner hired a diver who took pictures and reported damage. Boat was hauled out yesterday. Since it is my listing, I went to check on behalf of absenteee owner. This was nothing more than a grounding mishap that happens to every boater and captain. However, there is still expense for the diver, for captain and mate delivery to and from the yard, haulout, fiberglass repair, and bottom paint. All from a minor Lauderdale grounding.

From my extensive experience in attending sea trials and surveys on steel trawlers, I have no doubt that even the diver expense would have not been needed if this had been a steel hull.

I have many "survival" stories from owners of steel trawlers who had little or no damage during hurricanes and when they were the only undamaged boat in the marina. Even have an email from a steel trawler that self righted in the Phukett tsunami with the owner aboard and no damage.

If I were building, no question I would choose steel hull.

Judy

[casper]

I agree with Loren about the rust factor on steel hulls, if the right coatings are applied rust is not a big issue, my hull is of corten steel and was galvinized inside and out and two part primer and paint applied and have no rust problems, the downside of the galvinizing is when welding has to be done the area has to be well cleaned (grind) to obtain a good weld.
C