Fiberglass vs Steel Hull they both claim the best

Well, a question I long had about aluminium, now that we're talking it, from what I know it looks like the price (of both build and maintenance) is the foremost limitation for alu hulls, yet even high-end boats where costs are almost a non-issue are often built in steel hull/alu superstructure configuration which sounds like inherently electrolytic... Is it just the case that "on big displacement hull, the small weigth savings of alu just not worth the hassle of assembling and maintaining it"?

Arcanis,

Price and maintenance are not so much the limiting factor for aluminium. The thing is, if you go into bigger boats, the slamming loads dictate the use of very thick aluminium plating, which is costly and more difficult to weld.
E.g. Damen Shipyards build their small Axe-bow crew suppliers in aluminium, but sizes over 50 m have a steel hull because of the slamming loads.

Also the heavier steel hull increases the stability which is always a problem in these high and empty boats. Heavy steel below and lighter aluminium above = good. Often you'll see even a composite mast (or entire upper deck) to continue this trend. Which incidentally is also good for radar shadows and the sat receivers (as long as you avoid carbon).

The connection between steel hull and aluminium structure is done by using a special material (called tri-plate) which is basically steel and aluminium welded together by explosion bonding (I believe with a third layer in between but can't recall which material). You can never weld aluminium directly onto steel.

Bruno

Detacouple is the most commonly used transition stock and it is a mild steel base with a thin layer of 1100 series AL topped with a layer of 5000 series AL. The 1100 alloy improves the bonding characteristics.

Yes. The Spaniards, having witnessed the devastating effects from the use of fireships at the earlier Siege of Antwerp, fled in all directions at the sight of English fireships, at midnight July 28, 1588, drifting down upon them, i.e., they were no fools--they understood, every last one of them, that wooden ships on fire soon became sunken ships.

That was the intended historical reference.

Whiskey Tango Foxtrot = Why The Folly

...Unless you have a Potty Mind

Loren - T.G.I.F.!

Has anyone heard of titanium steel or a titanium-aluminum alloy being used in yacht construction? That would seem to resolve strenght/corrosion issues, wouldn't it? How much more expensive would it be?

FRP seems to hold its resale price and time-to-sell better than steel hulled vessels less than say Westport size. I have a friend with a 56' steel hulled sail boat, he has had a difficult time selling it solely because it is steel vs FRP. The best discussion by a boat builder I have read is Dashew who favors Al, his website is very detailed on this issue.

I am well aware of an older steel Feadship in the 60' range that had surveyor found metal issues on the 35 year old vessel particulalry in the prop shaft areas. The fixes were easy, not cheap though, and definitely put the time-to-sell way beyond the sellers most pessimistic hopes.

The market tends to dictate what sells and what doesn't. Fire issues vs build material is generally way down the list for "smaller" yachts going through the sales process. Bad wiring and hot turbos are way up the list for my fire concerns when vessel shopping. Surprisingly, my insurer says Marina fires consume innocent boats about 3 to 1 with covered storage the worst in this regard.

They both have their merit's based on the type of boat. Steel is heavy, but very strong and easily fixed comparitively speaking. On a long range yacht or full displacement, I like steel. However, I don't think it would make a good material for a sportfish or fast motoryacht.

Not always true

My "steelie" Roamer Offshore 38 weighs 21,500. The new Back Cove 37 weighs 22,000 with similar length and beam. Both are 38 feet overall.

Safety At Sea

A couple comments from experience:
Having been on a steel hulled aluminum superstructure ship in frightful sea conditions... first aluminum cracks... and if in the hull will leak... and once a crack starts it is very hard to stop it progression and repair is challenging both technically and in practice... particularly underway. Not too critical in the superstructure... but still can be dangerous. It is "notch sensitive" and easy to tear. Once in the test lab testing for tear resistance... I proved the point to skeptical junior engineer... grabbing the tear test sample while in the machine while under test after the tear started with my fingers I basically tore the 1/16" thick sheet with hardly any effort.
Second, steel seldom cracks but usually in highly stressed components subject to abnormal outside forces... like high pressure steam pipes... but hulls seldom crack and fail in modern shipbuilding practice... though cold induced brittle fracture can be a problem in thicker sections. It is not notch sensitive. In the days before design, metallurgy, manufacturing process and fabrication processes were well understood... it was common to see riveted crack stop seams used but is unnecessary today.
Fiberglass / composite is better than both as to crack propagation and harder to start cracks. But has other well known failure modes usually associated with poor construction/design and or matrix (the resin) deterioration in the laminate if exposed for long periods to solvents like water. If the layup is not perfect void free with fibers fully wet out the material is basically ****... to simply put it and repair is a putain de merde. Kevlar is very hard to achieve proper void free and full "wetting out". Carbon is very very sensitive to inter-laminate shear failures when impacted at low velocity... and very very resistive to the same at high velocity. Drop a hammer on the laminate WILL damage it and cause inter-laminate defects... where shooting a bullet through it will not... other than the localized production of a hole. There are proven test methods to check integrity of the laminate, voids and problems but they are not easily reliably applied to boat hulls. The rates at which most impacts boats undergo are classed as "low rate". So go ahead and build your boat out of it but I have NEVER seen proper process in any boat hull... some come close. Proper process likely costs in the range of $350-400 per pound of material... but it better be something like a day sailor or race boat with rescue nearby. Simply it is a waste of the material in most boat hull situations.

Also, having been at sea long way from rescue in a major fire... it is the scariest thing imaginable. I assure you seeing a bulkhead glowing red... SMARTENS You Right Up... INSTANTLY. That is why serious commercial and naval vessels are predominately steel.

Couple comments on titanium... the USSR built some submarines from it but is is not practical for yacht boat building... and neither are monel or copper alloys.

Re your observations about copper alloys for yacht building, were you talking specifically about cupra-nickel alloys for (supposedly) marine growth-free steel hulls?

As to Copper and Nickel Alloys

My comments are as to completely copper nickel (90% copper / 10% nickel or 95% copper / 5% nickel) and monel metal (alloy 400 predominately nickel) constructed hulls. Not as coatings for a steel boat... though that is possible via plasma or flame spray finishing... as a practical solution for marine growth.

Some copper alloy and nickel alloy boats have been built they are not practical as the modulus of elasticity is low in comparison with steel. Meaning they bend and dent easier. But that can be made up for with increase in thickness... the formula for comparison is Young's Modulus X (thickness x thickness x thickness) = stiffness. Copper alloys and monel are around 15,000,000 young modulus and steel is around 30,000,000 you see the thickness being a cube function can easily overcome the limitation. But Copper and Nickel alloys are approximately .33 lbs/cubic inch and steel is around .3 lbs/cubic inch making them heavy in comparison. In practical forms for ship building they cost around $8.00 lbs and steel is around $0.90 lbs. Numbers for aluminum are 10,000,000 YM, 0.1 lbs per cubic inch and around $4.00 per pound. Numbers for Titanium are around 16,000,000 YM, .15-.17 lbs / cubic inch and around $80.00 lbs. Note, as fabricated the material cost are much much higher... those are raw material numbers. You see no one but governments will afford such extra expense as a copper alloy or nickel alloy hull... billionaires did not get to be billionaires wasting money cold hearted as they are. Its really a cost issue.

It used to be common to use copper nickel alloys for seawater piping but in yachts that is being replaced more and more with plastic PVC. Naval ships are still copper nickel seawater piping. This is safety at sea deal too... the submarine Thresher was lost do to faulty soft solder joints in the seawater system... along with other things. I don't know if I would feel real comfortable crossing the Atlantic in winter with plastic piping.

I have not heard of any yacht builder metal spraying hulls with copper alloy or nickel alloy... however, before coating and paints got to be so reliable it was common to see zink metal sprayed hulls which does nothing to prevent marine growth but is very good with corrosion. Modern coating have rather this process redundant. Some time ago a company offered copper nickel adhesive tape for coating hulls after painting fro marine growth... but this is not available now.

Fiberglass number actually achieved in hull building are pitiful compared to steel. Yes, some high performance sail boats and a few builders do a good job. I am not prejudiced against it my daily driver car is a nearly all fiberglass Lotus car, and I was intimately involved with the introduction of advanced composites to car racing. But really its is hard to do right. Right is less than 1% void ratio, under 40% matrix to glass ratio and a whole lot of other stuff... and it is process critical... remember in composite construction you are making the material as you build the boat. It is possible to achieve satisfactory results with the OOA (out of autoclave) techniques now being developed and beginning to more common... but they are labor intensive. A comment is boats are big and usually the hulls are attempted as one part for the whole bottom... very hard to achieve what is necessary without missing something here or there. Composites strengths are also based on critical flaw and probability theories of the material... remember you are fabricating the 'material' and the hull at the same time.

Titanium's total ownership cost....

Check out U.S. Navy: The Business Case for a Titanium

Granted, its a paper study, but for someone who can afford the upfront cost, they make the case that in the long run its an option worth considering.

For boats less than 120' or so, owners tend to favor FRP due to resale and shear numbers of FRP vessels in this size range. The herd buys and sells FRP about 30 to 1 in this size range, paying little heed to steel and Al debates.

Titanium

Though this is a thread on steel and composite some comments on titanium.
It is the perfect shipbuilding material and the article does point out may advantages and possibilities... if the fabrication and economic problems could be solved. But it is a DoD study and has the buzz word "leap frog". When you read that understand it is written based on bureaucratic systems of perpetuation of the bureaucracy which means it is a funding sales pitch basically.

Aircraft have used titanium for many many years... structure and components. NO structural or highly mechanically stressed Ti part is ever welded. Certainly the old Navy A6 Intruder had wing slat guides of Ti for corrosion, weight and strength reasons and these were commonly repair TIG welded for wear. But those were small surface build up welds not structure critical... and all were done in the APD shops of Lockheed California (nowhere else). Noting that is where aircraft Ti fabrication in aerospace was first developed... Y12 / SR71 was primarily Ti... so they knew all this is to know.

All aircraft structural Ti construction and fabrication is riveted or bolted or bonded together... sometimes in combination. Same for aluminum. A structural frame is constructed... riveted and bolted together from solid pieces... the aero interface panels are riveted or bolted in place.
THIS IS EXACTLY HOW ADVANCED COMPOSITE AIRCRAFT CONSTRUCTION IS DONE. Certainly bonding is now used but that is highly controlled and very technically challenging... talk to Northrop Grumman guys on the Titanium/Carbon vertical stabilizers on the F18... not easy and expensive and risky. Note... I know of no welded aluminum structure on aircraft though that is common in boat fabrication... but different alloys are used.

Titanium was used to fabricate by welding some USSR era Submarines which all had horrific problems. They were direct research to fabrication with little engineering development between the two. Very dangerous. But some sense in this as submarines when submerged are basically pressed together by the water pressure. EVERY submarine ever made of metal has cracks in the pressure hull... and operate with them. Every once in awhile they get welded up... but more appear... whatever material is used steel or Titanium. I suppose a submarine could be built with perfectly fitted butted seams and if somehow you could hold it together and submerge... pump the water out it might actually work without and any seam welding, riveting or bonding... but at some shallow depth or on the surface it would fall apart! This was the problem with the Soviet subs... poor fusion welds cracked for all the known reasons (poor process and usually formation of Ti carbides in and around the weld).... at depth... and then on surfacing the thing basically would come apart at the seams.

You could build a boat in titanium by riveting, bolting and bonding... right now! Welding... not in reality... unless it were small and you had lots of time and money.

The bigger problem is Titanium itself. It is not easy to make into wrought products. It is made very much like steel was before the bessemer process... by pounding the lumpy crumbly void ridden mass into a solid wrought product by heating and forging. And, most of the supply is in titanium bearing sands in China and Russia... some in Canada. During the cold war the Y12/SR71 aircraft was primarily made from "sourced titanium" from those countries. In military aircraft construction the big problem is the recent ITAR laws... and the mandate for USA sourced Titanium... as that really does not exist. If you were to build your boat from Ti you would have to be registered with the Dept. of State and heavily regulated as to material and your fabrication technology. Your yacht may end up be limited to US waters only... and you might not be allowed certain nationals on board... and you would have a mountain of red tape at every turn during construction... and operation. Your interviews with yachting magazines would have to be pre-approved... to the word and exactly what you could show. Your discussions at the yacht club the same... ! The shipyard would have to be an ITAR approved facility etc. Oh... you say I am just building a row boat... read the regs... in the next year or two you could rack up enough fines to pay the national debt.

karo


Your comments on Al vessels are not accurate according to some Al yacht builders, it comes down to the alloy used and build techniques. Al's low yacht use is more due to cost, potential corrsion due to dis-similar metals and finish issues. Coastal Craft is building great Al vessels as is Dashew. Never heard of a Dashew "ripping apart" - they have been at it now for many years. Maybe some Browards have "ripped apart" that I am not aware of. What yachts with Al super structures are referring to?

The world is awash in Ti bearing sands and sedimentary rocks. Australia, if the producers there so chose, could produce most of the world's Ti demand. The overwhelming markets are paints and pigments. One of the world's largest new reserve is in Paraguay. Ti metal production is a bit more sophisticated than you portray with very close QC by the world's end metal users.

The comments about aluminum are based on my naval experiences in severe North Atlantic conditions in winter and are my personal opinion. We had ability to repair underway the issues with highly skilled hull and welding techs. Certainly conditions where no pleasure vessel would tread. The sea is fickle and unforgiving and though no yacht will intensionally go into those conditions... it may find itself in that situation. Aluminum techniques have improved in the last 40 plus years... but the basic boat building techniques and alloys have not much. Personally I would be very careful having been a survivability engineer for many years and having worked with the US Navy on survivability issues. I would have no problem with an aluminum yacht that would never see those situations setting mainly at the pier at Ft. Lauderdale or on the French or Italian Riviera... and used for quick sprints for fun and games... or a racing sailboat. But in general I would be nervous crossing oceans in bad conditions in just any aluminum vessel.

No producer is immune to problems... about 30 years ago now... the Navy had two nuclear submarines (steel admittedly) built at Electric Boat Works which basically every single joint and every weld was bad... despite all the quality, care and specifications in the world. They were completed before this was discovered but then the problems had been covered up by the yard and those supervising the construction and it cost the taxpayer over a billion dollars to correct. I trust no yard no company without proof... and proper supervision. Some materials take more care than others.

Obviously you must work with ATI or Timet someone in the Ti industry. I was describing in a simple way the consolidation of the metal into a usable wrought form once it becomes metal. As describing the "mechanized panning" of it (much like panning gold) from the sand and the reduction into titanium hexaflouride and then to titanium metal is very technically sophisticated and complex... likely too much for a yacht forum. However, it it could be very good for boat and ship construction. I think if you approached building a Ti boat or yacht from an aircraft fabrication approach you would likely be successful... but if you tried to approach from a boat building technology base you might run into huge engineering developmental issues.

But if you did successfully build a boat with Titanium, I think now-a-days you might find yourself up against Dept. of State and ITAR regulations along with Arms Export Control Act and Executive Orders... in the last year this picture has really changed. You might find your pleasure boat classified as potential military technology and the use of a strategic material you might not be able to buy several tons for your "hobby project" without issues. Why is the techniques you used would have military importance whether you think so or not... and you might be in competition with someone or something militarily important for the material... whether you could pay for it or not. And, innocently sailing beyond US territorial waters you my find yourself in hot water... go better consider a Russian yard for the project... but then you would have to disclose such intent to uncle Sam.

Good feedback on titanium

Karo,

Thanks for the comprehensive response... the article I posted had interesting points, but not having much depth in that material I was curious what others thought. You more than answered that call!

Yes, it is DOD article, which makes the analysis a bit of a self licking ice cream cone. I figured the only private application of titanium would be for an owner with a bottomless checkbook, but you rightly point out that the endless bureaucracy (at least within the US) would kill any fun that might be had for an owner.

The construction methods are another facet I hadn't considered. Some of the bleeding edge laser welding technologies might get the penetration with enough precise energy to make future construction a possibility, but thats a topic for another time.

Anyways, thanks for the great response!

Musing on Advanced Boat Construction

Thanks Chuck B... some musing on "advanced boat construction"

In thinking of the construction of boats and what is "best possible".
Like I alluded to in the comment of like aircraft or properly as this is a boat... submarine construction... basically:

"Produce a structural frame then placing an inner skin to the frame which is watertight and designed for the normal loads the boat would encounter, like the pressure hull of a sub. Tankage/storage is made outside the inner skin and then an outer skin is attached by riveting or bolting to the frame as removable preformed panels (could be permanently attached too) wherein the outer shell forms the hydrodynamic surface... but not necessarily a watertight skin. The outer skin has to take the impact loads and possibly seal the void between where necessary. "

The framework could be fabricated out of steel, aluminum, titanium or even cold molded wood... or composite using appropriate process. Titanium this would be likely formed sheet and machined shapes riveted or bolted together as appropriate with adhesive between the joints, note proper surface finishing for bonding. Aluminum could be done as the titanium or welded; if riveted bolted one could use a high strength alloy like 7050 which is very corrosion resistant, if welded it could be something like 6013 with post welding heat treatment of the components, these are very much stronger... i.e. lighter than needed with conventional boat building alloys of the 5000 series. Steel... welded of course. Wood laminated with glass between the layers. Composite laid up from prepreg, consolidated and cured; noting ideally a mostly glass carbon hybrid with a UV cure resin... and the layup vacuum bagged during cure using edge lit curing (note the glass acts exactly like fiber optic and transmits the curing light into the core of the laminate). This does not entail the costly problem of using identical expansion rate mold material for a heated cure cycle at elevated temperature but only works with glass and glass hybrids... carbon graphite and kevlar no as you have to get the light to the resin matrix in all areas.

The inner skin needs to be structurally and water-tightly attach to the framework once it is erected. It is like the structural "pressure" hull but does not need to take submerged compressive loads like a sub pressure hull if a surface vessel. This could be best applied to the inside of the framing. It does not need to be thick or really designed for any impact or pressure loads due to water velocity and impacts. Only to take the normal structural loads and provide a watertight seal. If welding attachment is not appropriate it can be a different material from the framing but is best the same material to prevent engineering design complications. For a titanium boat this would be riveted and bonded into place. In composite construction bonding it could be molded separately with the frames placed over it or laid up on molding between the frames. If steel welded. Aluminum welded or riveted and bonded as appropriate.

Tankage, plumbing and some mechanical systems can be installed in the space outside the inner skin and within the framework.

Then an outer skin is attached to the framing which can be attached by the means appropriate. in some places or over the either structure is can be removable if riveted or bolted. This skin, in my opinion, would best be fiberglass panels. It can be sealed or left unsealed to framework in appropriate places. This make it easily removable for service or replacement.

Why this design scheme is that it has proven itself in submarine construction and likely it results in the best use of space and structure and it is very safe. Safe as the watertight portion of the hull is protected by basically a double bottom or outer structure. Importantly, it makes the structure easily repaired and serviced without disrupting the internal installations of the boat. It is not the cheapest means nor common outside of aircraft and submarines. It is not the lightest but comes close but is likely the safest. Personally I like a steel inner "hull" if you will and framing with a fiberglass outer hull shape surface...
and then have the best of both worlds and just happens to be the very subject of this forum thread!