Steel Hulls with Composite Superstructure / Topsides

[beiland]

Let me preface this discussion with this; I come primarily from the Multihull ranks, and steel boats have never really been a contender as a building material for these vessels,.....just too heavy. So my knowledge of steel boat construction is limited, and that might become apparent in some of my postings, particularly some out-of-the-box thinking I might suggest.

Steel boat construction has come to my mind recently as I review 3 older boat designs that I have identified for a 're-design' (modernization) possibility. In all 3 cases these are monohull displacement vessels, and therefore are candidates for steel hull construction.

Why steel? Its an inexpensive material, easily fabricated, and very durable for worldwide cruising. It's a material that inspires confidence in a boat's survivability from mishaps and collisions by both experienced boat owners and newly minted ones.

Why a new steel subject thread? As the thread title indicates I wish to explicitly explore the combination of a steel hull with composite superstructures. Naturally I want to review and cross-reference to those other good discussions on the forums dealing with these two construction materials,....steel & composites

[beiland]

I've been aboard every kind of vessel that there is, made of: Wood, Fiberglass, Cement, Composits, Aluminum, and yes steel. And there is something about steel that just seems to say it all; strength, seaworthiness, a sense of security, and durability (Especially in foul weather.) that the other hulls just don't inspire. Steel, And Fun Everyone is an acronim for Safe, and I think that explains how we all feel on a steel hulled vessel.

True, Aluminum comes close, but I always think of aluminum foil, and how it crinkles, and not that the space shuttle's 2" thick hull is made of aluminum. LOL

And fiberglass, well just having glass in the word is enough to unsettle a real swab.

And didn't they use to put cement goulashes on people like Jimmy Hoffa for a reason?

Now wood is okay for someone like Noah who had no idea of what steel was, as it hadn't been invented yet, and his boat wasn't being built for long term usage anyway, it just needed to float for a while. And too, polished wood is wonderful for a nautical setting inside of a steel boat too, to remind us of our roots.

And finally, composits are fine light weight material when used for building air, and spacecraft, but they cost too much, and are as yet untested by time, and really are no more than a space age form of fiberglass to me. And there's that word glass all over again. Geesh!

Now truthfully, when you measure your boat against another out in the water which one would you want to have under you when they collide in the fog?

Capt John S. Keller
Great Lakes Pilot

...got a chuckle out of that one

[beiland]

…. a recent private note I received from an experienced steel boat builder

The problem with steel boats are the fact that there is not a production boat per se available - all steel boats in reality are custom boats. Its labor intensive, even the cad generated ones with cutting lists are not that easy to build - pictures does not shows the blood, sweat and tears that goes into pulling and docking the plates in shape. Even a little misfit with precut plates are troublesome and therefor its the reason why steel boats are expensive to produce, its very labour intensive and thats the most expensive component of the build if one considers the amount of labor in hours it takes just to produce a 40ft steel hull for instance, let alone the deck that usually takes a bit longer in steel when done right.

I hope this little bit help to decide you if steel hulls are indeed the way you want to go. GRP in all its forms are much cheaper and easier and faster to produce.

Dear Sir,
First off I appreciate any and all input I receive from experienced steel builders

I must take issue with this portion of your reply, “GRP in all its forms are much cheaper and easier and faster to produce.”

This might be true in a large volume production situation, but for a low volume quantities (might be termed semi-production) the cost of plugs and molds for the GRP boat must be factored into each vessel's cost of building for at least the first 10-15 units built. The cost of those plugs and molds can be considerable in both time and materials, and if you seek to hold to a price point on your finished vessel, it could take the builder 2-4 years to recover their 'tooling' investments.

Furthermore if a firm anticipated offering a particular vessel design in a 'kit form' for some private clients, or a remote builder in another part of the world, the traditional 'GRP mold method' does not make sense.

Fiberglass building materials have also increased dramatically in the last several years,...along with oil prices. Couple this with the skill of labor you really need to properly build a composite vessel, particularly a hi-tech sandwich-cored one, and you begin to see a competitive edge for alternatives.

I've chosen to consider this alternative of steel hulls with prefabricated panels of cored composite panels for the decks and superstructure. With the advent of computer-cut steel panels and computer-cut composite panels, the
1) time required to build the basic shell of the vessel might be significantly reduced
2) the skill of the labor to perform this portion of the built might be less
3) a kit form of the basic vessel could be shipped to a private buyer, or another sub-production facility anywhere in the world.

Some have asked, 'why not an all steel vessel rather than mix in composite structures'?? As you pointed out in your note above, the steel decks can be more problematic than the hulls. Neither the steel decks, nor the steel cabin sides/structures are by nature insulated. Also one must add in a substructure (battens, etc) to these metal skin panels to both get a decent attachment for the interior finishing panels, and to get a non-moisture condensing, insulated interior. The cored composite panel decks and superstructure are already self-insulating and non-condensing by their nature. As a bare necessity the inner surfaces of these composite panels could be simply painted a pleasing color, or a decorative wall covering fabric glued on.

So lets summarize at this point. I have 3 different vessel designs in the 40-60 foot range that I feel could have moderate to good success in today's yacht market. But of course in the interest of being cautious the plan is to NOT over-extend ones self with a BIG investment in plugs, molds, tooling for any one of these designs.

A steel hull shell fashioned from computer cut panels that would be assembled in a external jig/frame (reference 'frameless steel construction') appears to be fairly 'quick and dirty'.

This steel shell could then be reinforced with the traditional bulkheads, frames and stringers all welded in,

…....OR, it might well be 'framed up' with composite sandwich members that would be glued in! These 'internals' might well eliminate a considerable amount of welding that is both time consuming, and that distorts the hull plating in many metal boats. Those distortions subsequently result in a lot of 'fairing work' being required for the finished hull.

[S/V Alchemy]

I may be having a memory issue here, but the phrase "coefficient of thermal expansion" is bubbling to the top of my mental soup. I think that the vibration and flexing of a steel hull may be incompatible with that of a fibreglass deck. One could frame in such a deck in steel and could simply adhere or affix a fibreglass deck and cabin house to it, but you are in essence creating a huge seam that would present significant challenges to keeping water out, the enemy of steel.

Steel boats (I own one steel and one FG sailboat) rely in part on monocoque or unitary construction for strength and transmission of imposed forces: they are strong in part because a hit on one point is spread throughout the structure. Mating fibreglass and steel can reduce this advantage, just as a can without its lid is far easier to crush.

Wood decks, on the other hand, with a fibreglass top, might make sense, because it is the wood framing that "takes the hit" of sailing stresses, while the fibreglass remains on the wood, not in contact with the steel. But wood has its own issues, foremost of which is that you would lose the weight savings driving the composite construction in the first place.

It's possible to achieve a halfway solution with a flush steel deck and an aluminum pilothouse/coachhouse that is bolted down, and yet is completely galvanically isolated from the steel hull. I have, for instance, steel sides to my own pilothouse, with an inward turning flange to which an aluminum roof is through-bolted, but with bushings, nylon washers, thin strips of butyl and HDPE plastic and so on to make a watertight, compressive fit, but one in which the aluminum never actually touches the steel.

That took planning. What you are proposing is exponentially more complex in my view. Not crazy, but maybe not worth it from a cost and engineering point of view, like diesel engines for airplanes. They exist, but are pretty rare!

Read Nigel Warren's Metal Corrosion in Boats. It's an essential guide to understanding the pros and cons of these sort of things.

[roverhi]

Composite construction used to be fairly popular in the '50s and '60s. A number of steel hulled boats built mostly with wooden decks and maybe some with Aluminum, the SS United States for one. SS United States - Wikipedia, the free encyclopedia I've looked at a couple of wooden decked steel boats and the problems with the wood steel interface and the deck itself were just insurmountable for me. If you could get a reliable long term seal of the deck material to the steel hull it might be a practical means of construction. Just doubt that a permanent seal and prevention of corrosion at the joint is possible and would be the achilles heel of any composite construction technique.

Steel is a wonderful material for a virtually indestructible, by exterior caused damage, material for a boat but the maintenance is a major headache. There are ways to keep the rustermite at bay but none are permanent. Constant diligence is the lot of the steel boat owner. Have had two steel cruising boats here this year. Both were fine examples of steel construction but both spent most of their several months stay in the harbor dealing with corrosion issues. It's not only the deck and topsides that are the problem though apparently the bulk of the issues. Any small nick or scrape below the water line requires a haulout, grinding to bright metal, sealing with epoxy, and repainting. Not an overwhelming task but just something that can't be ignored or put off for long without dire consequences. Remember talking with Bernard Moitessier and him complaining that he'd had the deck of Joshua rust through in a few places cause he hadn't been diligent enough with maintenance.

Yes, there may be a market for a kit to build a steel boat out of precut pieces packaged and shipped to where ever. Don't think it would be a big enough market to justify the expense of setting up the production cutting and keeping the construction line open.

[goboatingnow]

And fiberglass, well just having glass in the word is enough to unsettle a real swab.

you must be scared rigid of nuclear magnetic resonating imagery techniques so!!!!!!

[Efraim]

There is a boat I know of build ~1961 steel hull plywood deck and house, Al Mason design, still going strong 50 yrs later. Next time I see the owner, I'll ask him about the hull to deck joint.
Just remembered Reuel Parker has an aluminum boat 39' sharpie design that has a plywood deck..seems to work. Of course the material doesn't have to plywood, it could be any of the new composites.

[goboatingnow]

in my opinion the easier way to build a one off, is GRP laid up in a multi chine or radius chine female one use only wooden mould. with a couple of friends a strong ( 1970s) style GRP layup could be accomplished in a week. of layup work.

Cabin/deck tops are more involved of course. but with a simple design ( flush decks etc) again a female mould once, off, could be used.

Dave

[Matt sachs]

I have a plywood deck on my steel hull. The ply is saturated with west epoxy before being bedded into thickened epoxy on sanblasted steel flange then bolted every 8 inches with countersunk bolts then glassed over. (steel deck would have been cheaper, lighter, cheaper and less maintence and cheaper ) Did I mention it would bave been cheaper to go with a steel deck?

[Matt sachs]

ok, just did the math, not lighter......

[Panope]

I too am intrigued by a mix of materials for a hull/deck/house structure. However, my thoughts on the subject are exactly 180 degrees out from the OP.

It seems to me that the worst thing about a fiberglass boat is the cored deck and it's related leaks through penetrations and fasteners. Conversely, it seems the best thing about a fiberglass boat is the hull that can be laid up realy thick and heavy (weight is down low) and very strong (and corrosion free).

It seems to me that the worst thing about a steel boat is the hull corroding from the inside out from trapped moisture (that will eventually be raining through the leaks in the proposed FG deck). Conversely, it seems the best thing about a steel (or especially aluminum) boat is the ability to have a deck that is free of fastener penetrations - weld everything on.

So, I have been thinking that the ultimate boat would have a nice, curvy, heavily laid up (with epoxy for no blisters)(in your favorite mold) fiberglass hull. And an unpainted (except for not skid) aluminum deck and house. No idea if the expansion rates of the two materials would be compatible. I visualize a very heavy flange of FG at the hull deck joint with a gazillion SS bolts (and a box full of 5200) connecting a shoe box type deck "lid" of aluminum. The joint had better not leak or half the rationale of the whole scheme would be for not!

Steve

[beiland]

Let me go back a year or so and reference a forum discussion I entered when I became real interested in this 'prefabricate composite panel' subject.
http://www.cruisersforum.com/forums/...g-22948-7.html

I had known for a number of years about these various kit-boat designers/builder in Australia, and NZ. I had just never really studied about the 'composite panels' they were using. And I was confused about the various 'brand names' being applied to these panels. That's how I came to following this subject thread.
Are Cats from Duflex Panel Kits - Strong?

Then I began to look more throughly at the Propropylene honeycombs rather than the balsa and foam cored products,....ie, NidaCore, Plascore, Polycore. I knew of these as well, but had always rejected them

Originally Posted by beiland

That single factor was always a reservation I had with that product. But note that they thermo fuse a polyester scrim onto the core so that you are now bonding your skins to that polyester sub-skin.

And thus far I have not found a lot of negative problems with bonding to that scrim if done properly. That is one of the reasons I bought up this Nidacore subject again...to have a fresh look at this material that I had ignored with initial prejudice for years.

Then I discovered this kit-boat, The Solitary Island 12M Cat
http://www.multihull.com.au/site/www...fic_40_kit.pdf

Regrettable they had to stop their project due to economic times of the past few years, and a number of the web pages relating to building these kits were taken down. Here are a copule of more sites I find now.
DIY Yachts • View topic - Solitary Island 12
http://polycorecomposites.com/News--and--Events.php

After quite a bit of reading about PP honeycombs, I'm convinced they made VERY good core material for sandwich construction. And in the 'prefabricated sheet form' they are superior to foam panels, or balsa panels, or plywood, etc.

Compatibilty with steel?
Realize that one of the enduring properties of steel is its 'ductility', ...it is forgiving under an impact load. PP honeycomb also is ductile, in fact so much so that it outperforms the plywoods, and the foam cored panels and the balsa cored panels. You can find some proven test about this. This stuff will make GREAT decks.

Now all we need to do is properly bond these sandwich panel decks to the steel hulls. (And I think this is going to be much easier than bonding plywood or aluminium to the steel). Have you looked at the GREAT advances we have in bonding adhesives these days?
Plexus for one.. http://www.itwplexus.com/UserFiles/F...ectorGuide.pdf
They have been bonding deck-to-hull production boats for a number of years now, and often without any other fasteners, etc

3M 5200 could likely do the job.

With a little research I'm sure we can come up with the best bonding agent for this application. And with proper care the correct 'landing' can be built into the steel hull to accept this composite deck.

[gjordan]

The cabin top or sides can be made of almost any boat building materiel, but if you build a steel boat with a steel cockpit(where the compass goes) you will have problems. my own steel boat was tiller steered, so that the compass was mounted to the bridge deck, and could not be compensated for angle of heal. A 20 degree angle of heal might put the compass off by 20 to 40 degrees. It made for really scary navigation. Dont worry about the deck or cabin sides. Weld them up, but be very careful of any thing magnetic near your ships compass. I love steel boats, but my wife said never again. OH WELL,_____Grant.

[Lagoon4us]

I'm a retired Australian Boatbuilders formally acreddited with AMSA as a Ship builder in Steel and Aluminium under the USL Code.

My early days were in Steel and Aluminium round bilge yacht construction ie 'wine glass' shape.

During that early time i built many yachts that are scattered all over the world now ranging in size from 35 to 45 feet.

The recently deceased 'Joe Adams' provided the drawings in the form of offsets, general arrangement, construction and sail plan. In those days detail was in short supply. Now Joe Adams also designed a nice 33 foot centre cockpit that essentially had the same 'lines drawing' as the Adams 35.

Now George Mottle who had this design done for him would gladly sell you a complete deck and cabin moulding in GRP. You then built your steel hull upside down as normal and incorporated a Stainless Steel flat bar margin plate around the deck edge to accomodate the bolting of a fibreglass deck to it after the hull had been blasted/painted/turned over.

It worked very well and was reasonably received as the deck didn't rust from chip points etc.

Forget coefficient of expansion causing a problem i've built many large charter boats 34 metre range that have Aluminium cabins/superstructure welded to steel decks (DuPont) and there are/were/aren't any issues.... These French suppliers seem to have it sorted,
http://www.triclad.com

The question now is 'Why bother' moulded boats beat hand fabricated boats by hundreds of construction hours and that effectively finished those innovative ideas.

I heard back then that a 40 Adams foot deck was also available...Essentially you can do it with any solid edged moulded deck/cabin..

Cheers Frank.

[Lagoon4us]

Originally Posted by gjordan

The cabin top or sides can be made of almost any boat building materiel, but if you build a steel boat with a steel cockpit(where the compass goes) you will have problems. my own steel boat was tiller steered, so that the compass was mounted to the bridge deck, and could not be compensated for angle of heal. A 20 degree angle of heal might put the compass off by 20 to 40 degrees. It made for really scary navigation. Dont worry about the deck or cabin sides. Weld them up, but be very careful of any thing magnetic near your ships compass. I love steel boats, but my wife said never again. OH WELL,_____Grant.

Yachts, boats, barges and ships do not have this issue, you may not have had a compass that had 'corrected irons'???

Electronic compasses also negate any issue.

Cheers Frank