Steel Hulls with Composite Superstructure / Topsides

[polyurea]

Looks like I will have to change my Log in name. I just read the commercial rules.

sorry, never seen rules so strict

[RaymondR]

No doubt fully welding down both sides of the frame or, if used, stringers would be the best solution from a corrosion prevention viewpoint. However this would require an awful lot of welding and in addition as the weld pulls the plate as it cools you end up with a fairly buckly hull.

I realize there is a problem with either getting the coatings into the gap between plate and stringers or attempting to seal along the plate/frame edge where the gap is small and consequently imagined that the stand off would need to be about 1/4" (6mm) to allow both some sort of access for coating but as importantly to prevent water being held in the space between plate and frame material edge.

I would use either 1/4" (6mm) round scrap punching or small steel diamonds as the stand offs and fully weld them to both plate and frame.

After 27 years of experience, 12 of them as a full time coastal cruiser, I am firmly of the opinion that properly designed and built steel boats are the safest way to venture out into the ocean and that if reasonably well cared for steel is no more maintenance intensive than those of other materials.

The subject of this thread is composite hulls and whilst, for a number of reasons, it is an attractive concept, in practicable terms the benefits gained are not balanced out by the safety, security and durability properties lost. The key material properties are strength, ductility and flammability.

[beiland]

Originally Posted by RaymondR

No doubt fully welding down both sides of the frame or, if used, stringers would be the best solution from a corrosion prevention viewpoint. However this would require an awful lot of welding and in addition as the weld pulls the plate as it cools you end up with a fairly buckly hull.

I realize there is a problem with either getting the coatings into the gap between plate and stringers or attempting to seal along the plate/frame edge where the gap is small and consequently imagined that the stand off would need to be about 1/4" (6mm) to allow both some sort of access for coating but as importantly to prevent water being held in the space between plate and frame material edge.

Several other steel builders have all identified this 'fully welded' or 'standoff gap' as an important considerations when trying to get the perfectly clean bare steel surface to apply an anti-corrosion primer to.

To this I would also add the problems with trying to get a fully-blasted underside to any 'T' shaped ribs, frames, stringers, etc that might be utilized.

What I want to more fully examine is the possibility of using I-beams constructed of composites (core-sandwich construction)in the place of many of the 'minor' (and possibly major) internal framing of a steel hulled vessel. The I-beams could be cut from a big 'panel' of specially layed-up sandwich core with specific skins to meet a desired strength in the I-beam. These I-beam reinforcements would likely be bonded to the inside of the steel shell with the latest methacrylate's.

This would significantly eliminate a lot of welding of the internal framing, and it would be much easier to prep for a really good anti-rusting of the bilge areas....and other steel areas on the boat.

This might or might not be all oversprayed with a custom blend of polyuria?

The subject of this thread is composite hulls and whilst, for a number of reasons, it is an attractive concept, in practicable terms the benefits gained are not balanced out by the safety, security and durability properties lost. The key material properties are strength, ductility and flammability.

The subject of this thread is NOT composite hulls, it is steel hulls with composite superstructure. Hopefully you can begin to see some of the attractiveness of what I am seeking from the short discussion just above?

[polyurea]

Over-spray is a term that describes a mistake or less-than perfect coating application.
Gaps 1/8 inch or larger need to be caulked before polyurea is sprayed. A correctly applied and correctly spec'ed out polyurea would give many years of complete protection unless very hard impact by other hard objects were to damage the polyurea.
We coated the outside of a 200 ft boat for Silt Filled Ice Protection last year. The customer has never had any coating last even one winter. Our first winter we lost around 10% of our coating and that was mostly on the bow. I believe I can correct some things and will have even more of our coating stand up to the ice.
The customer had even tried $800.00 a gallon ceramics in past.

[beiland]

Originally Posted by RaymondR

No doubt fully welding down both sides of the frame or, if used, stringers would be the best solution from a corrosion prevention viewpoint. However this would require an awful lot of welding and in addition as the weld pulls the plate as it cools you end up with a fairly buckly hull.

I realize there is a problem with either getting the coatings into the gap between plate and stringers or attempting to seal along the plate/frame edge where the gap is small and consequently imagined that the stand off would need to be about 1/4" (6mm) to allow both some sort of access for coating but as importantly to prevent water being held in the space between plate and frame material edge.

I would use either 1/4" (6mm) round scrap punching or small steel diamonds as the stand offs and fully weld them to both plate and frame.

After 27 years of experience, 12 of them as a full time coastal cruiser, I am firmly of the opinion that properly designed and built steel boats are the safest way to venture out into the ocean and that if reasonably well cared for steel is no more maintenance intensive than those of other materials.

Hey RaymondR,
Have a look at this quote from a knowledgeable steel boat designer

Originally Posted by MikeJohns

Hot zinc spraying and then painted over the zinc with epoxy is a great coating system for the interior if you can afford it. Most steel boats I have worked with that were treated this way stay pretty much pristine inside. I have one 65 footer treated this way too.
But a steel craft should also be properly designed and constructed with a view to longevity. Hatch coamings for example should project through the steel decks amply.

If you just epoxy the inside well and keep the water out ( including condensation) you'll find it will outlast you anyway. As for the gaps between frames stringers and the hull, don't fret about them, for starters the paint goes into the gap and secondly these days we often use a bead of sikaflex polyurethane sealant to fill any gap. It works a treat and I can guarantee the sikaflex works we've been doing that for 15 years. We even use sikaflex underwater to seal riveted steel vessel plate boundaries after sandblasting.

[beiland]

What if?,.... Canal Trawler built in Steel & Composite PP Honeycomb
What if one of the vessel designs I was thinking of building with this 'hybrid method' was something like one of these 'canal trawlers':

or....


Both of these are built for 'canal duty' with steel hulls and hardy rub rails. If you look thru the website for the EuroShip vessels (the first referenced above) you will find quite a lot of construction photos for their canal vessels, and many references to their computer-cut plate kits for hull construction.
http://www.euroshipservices.nl/english/

Their cabin sides and decks are also constructed of steel,.....steel skins with support framing. In order to get 'attachment points' for the finishing walls/skins on the interior surfaces, battens (often wood) need to be installed. Provisions for insulation of the living spaces, provisions for limiting condensation on the inner steel surfaces, etc, need to provided for in the cabin sides, the cabin roofs, the main decks, the interior floors, etc..




What I am proposing is to substitute a ready-made, thick, honeycomb panel of PP. It's already well insulated (trapped air space), limited or non-condensing prone, stiff, with flat surfaces on the interior as well as exterior, to which any number of final finishes could be applied. And these 'finishes' could be glued, screwed directly to the PP panels without other battens, etc. It's even possible that the surfaces of these PP panels could be simply painted, with or without a texture. Or some sort of siding could be glued on. Or some sort of wood laminate......

Some posters have expressed a concern about ship's rigidity without a steel deck. I would suggest that a sub-frame of steels beams could be placed across the ship between gunnels, the PP panel(s) placed over these support frames in lieu of a sheet of steel. Concerns about supporting items / equipments that might be added to these PP decks vs steel decks are probably no more of a concern than the extra support that would be required of the steel deck itself. If the loads are a concern for the PP deck, they would likely be a concern for the sheet steel deck. We are not talking 'work boats/construction barges' here where items are often welded onto the decks, but rather yachts,...... many with teak or synthetic teak decks.(BTW, teak onto steel decks would NOT be highly recommended either).

I actually think this type of construction could be a significant time saver.

[beiland]

....just a little addendum to these thoughts that I had penciled in my original notes and forgot to include in the posting above

Quote:
What if one of the vessel designs I was thinking of building with this 'hybrid method' was something like one of these 'canal trawlers':

or....


What I am proposing is to substitute a ready-made, thick, honeycomb panel of PP. It's already well insulated (trapped air space), limited or non-condensing prone, stiff, with flat surfaces on the interior as well as exterior, to which any number of final finishes could be applied. And these 'finishes' could be glued, screwed directly to the PP panels without other battens, etc. It's even possible that the surfaces of these PP panels could be simply painted, with or without a texture. Or some sort of siding could be glued on. Or some sort of wood laminate......

Look at the cabin sides and the superstructure of these two vessels....basically big flat panels. Why build them of steel? Even the cabin roofs are a single curvature camber, not compound,...easily fashioned from PP panels, and self-insulating. One question will be choosing the right core for solar exposure.

For those that are concerned about the main decks being constructed with PP cored panels, I would offer that a sub-frame or a space-frame of steel beams could be placed across the ship, then the PP panels placed over them or betweem them in lieu of a sheet of steel. Remember the gunnels are all steel, an extension upward of the hull sides. These are available to weld items to

[RaymondR]

I am not arguing that any of these ideas are not possible and in a lot of cases not practicable but when you actually get to building a boat, particularly on a limited budget, practicalities tend to intrude. They also tend to intrude when you are stuck with maintaining hull integrity to keep the vessel seaworthy.

I have just completed an expensive hull refit on my steel boat. Every serious problem I was obliged to remedy was caused by frames and stringers installed so that they either created water traps or water was able to enter the gap between frame or stringer bars and the hull plating.

Galvanizing is an excellent protection against corrosion in steel and the US Coast Guard built a number of vessels post WW2 using galvanized plate and repairing welding damage to the zinc coating using metal spray techniques. These vessels remained in service many years and required minimum maintenance. The deck plating of my boat is galvanized plate and if I built another steel boat I would consider emulating the Coastguard.

The theme of my previous postings is twofold, why mix materials if the gains in doing so are outweighed by the detriments assumed, and, you must have long term access to every square inch or millimeter of a steel vessel in order to keep it properly maintained and seaworthy. This is particularly true of the internal hull.

People who have steel hulls do so for a number of reasons: Economy, they have the skills to build their own hull and it is a repetitively cheap material. Or. Security, they want the boat to be best able with being run into or running into things including the sea/land interface in it's numerous forms.

From an economy viewpoint there is nothing easier or more practical than whacking a steel deck onto a steel hull and welding all around the edges. There is no hull joint to leak and since you can weld things on to it you don't have problems with cracking seals on bolted on stanchion bases etc.

From a strength viewpoint a unitary tube is about as good as it gets which is why most aircraft are built that way.

From a durability under stress viewpoint your steel hull will perform much better than any other boat building material. Keels tend to stay on and decks retain water tight integrity when the rig fails and the mast comes down. Put me around 20 odd ton of show off, leaping cetacean and I want to be in a steel hulled vessel, deck and all.

There is absolutely nothing wrong with debating these matters on the forum it can be both fun and profitable.

[polyurea]

All this talk about life time service and design. The biggest aspect that stands out to a coating applicator is shape of substrate to allow cleaning and coating.
This is such an issue in ship construction that it was noted after inspecting with a robot an inspector commented that the places they sent the robot were en-human. I know there is a special small spray gun designed to coat behind beams in ships. I have been told, I am the only applicator in Alaska to own one. I bought it to coat a Sea Water Tank for ConocoPhillips on the North Slope Alaska oil field. 6 inches is the minimum distance we can spray polyurea. That said their are poly's that can be brushed on - at this time I have no experience with them. Hoping to visit a company in Aug. that has these chemicals for Ship Fenders, piling, etc.
So the subject of this post from me is, design frames so they can be cleaned and coated in future years.

[polyurea]

We have coated aluminum river boats for rock protection. Something we did not think about was noise reduction. Every customer has commented how quite their boats are now since the water is in contact with the plastic polyurea coating.
A sprayed polyurea will with stand over 2000 psig of pull pressure before dis-bonding with steel. Talking about life time service - steel with polyurea coating (plastic). How long does plastic last.
There are projects where third party engineer estimated life time service of 50 to 75 years for the polyreau coatings (was not boat projects).
We are coating the outside hull of a 194 ft ship for ice protection. Customer has never had any coating last even one winter, yet our coating did. I lost 10% on the bow and believe I can reduce this percentage of loss. It is a multi year learning experience since each part of ship hull has different amounts of pressure.

[beiland]

Just happened across this trawler construction site. Some interesting discussions here on some of their building philosophies including heavy hard-chine hulls and lt-weight superstructures.

Looks like I'm not the only person sold on this idea for the superstructure of trawlers. Have a look here at what Great Harbor Trawlers has to say:
About Great Harbor Trawlers : Design Discussions : Space Age Core

Originally Posted by excerpt

The non-cross linked foam is more expensive, harder to use, not as stiff but will, when designed as a component of a complete laminate, take one heck of a whack without nearly the catastrophic damage you might see in other cores.

I remember racing a J24 sailboat in the late 70s in Key West for the annual winter regatta and getting hit hard in a port/starboard incident and being shocked to see a basketball sized piece of hull knocked completely out just above the waterline. These were balsa-cored hulls and very well built but when they got hit, it could be a bad deal. On the other hand a good friend of mine hit a piling that was floating offshore. He was in his fully foam cored sportfishing boat running close to 30 miles an hour at night when he hit. There was no major damage and the hull only shows a minor dent today.

Hard hits to hulls made with non-cross linked cores are more like hitting a piece of metal in that the failure tends to be what engineers call “plastic.” We might call it “more forgiving” in that it tends to bend rather then break.