STEEL HULLS with Composite Superstructure / Topsides

[Wynand N]

The quote form a steel boat builder in post #22 was made by me.

A few issues I want to amplify on.

The only time saved by using CAD cutting files is not to have mark/develop the plates themselves. Nut much time saved in cutting plates and I always preferred to do it by hand.
To assemble the parts take much the same time as non cad cut parts and I seen a case where it actually was disastrous for the builder with an accumulative error that made all further parts to be fitted obsolete and had to took everything down again....
Whereas, doing it the old fashioned way and one does have a slight misfit that can be "hidden", its a simple matter of making next plate to fit and problem solved simply put.
I never liked cutting files, never will and it is totally over rated but most of all, it takes the purpose of boatbuilding out of building a boat, namely lofting. A boat that is not lofted is a boat not built.

Unfortunately, regardless of CAD files or old fashion way, steel boats are custom build units and labour intensive which = expensive.
Because of this reason I spoke to my old friend Dudley Dix at my place in 1990 about the feasibility of a fiberglass deck fitted to fast build frameless hull - easier to mold deck with perfect detail and steel decks takes up a lot more time than the hull area for area.
Dudley did his thing and we decided to go that way and I commissioned the DIX38 in that year (then called the Force38, hence the "F" detail still visible on the hull side stripes on design) and the boat was a frameless "RADIUS CHINE" hull with cored GRP deck bonded to a flatbar flange on the hull. First frameless radius chine hull was produced and dare I say probably the only frameless radius chine ever to be built anywhere, and the deck plug was made by an associate of me in GRP boatbuilding.
Before the deck could be molded, I closed shop and abandoned the project with all other work - the hull was later fitted with steel deck drawn by Dudley Dix and he retreated back to steel decks for the Dix38.
This would probably been the fasted and most cost effective steel boats produced if I carried through the project. That said, the SikaFlex joint of the GRP deck to steel hull would have been suspect for long term integrity and I always wondered if it would lasted....

Fast steel hulls for production boats are the frameless v/d Stadt chine hulls of which I had built 2x34ft and 2x40ft designs from Stadt. These are the fasted build method in steel I had built, period.

Tad is correct, the best part of a steel boat is the very fact that it is a solid welded unit that is strong and waterproof, and usually deck joints are the leaky parts on boats.

 

[michaeljc]

Sensible post thanks.

One of my builders has help build scores of CAD:CNC cut alloy boats. We have recently built 7 in our own workshop. All of these craft were drafted by one particular draftsman who is now an expert. He had the opportunity to check his work on the floor over many years. His boats just fall together. Fold lines are marked and I recall a horizontal pipe orifice within an angled plate that was cut perfectly. If one had to cut the plates by hand construction time would be trebled, in my view.

CNC does work but as is the case with GRP it requires experience and skill.

M

 

[brian eiland]

I was going to eventually bring up Dudley Dix's kit boats. He has done a LOT of such designs for plywood construction.
http://www.dixdesign.com/kits_plywoodUSA.htm

Buying a pre-cut kit for one of our plywood designs will speed up your boatbuilding project, saving you much time spent in measuring, drawing and cutting parts to build into the boat. Time saved depends on the project and your skills but expect it to be between 10% and 20% of the total build time. That time saving comes at a relatively low price because the kit suppliers have access to better pricing for materials than you will as an individual builder. The cost of your kit may not be much more than the stack of plywood that you would buy to cut the same parts yourself.

He has done both plywood and metal boats in this fashion.
http://www.dixdesign.com/matlist.htm

I particularly liked this catamaran design of his.
http://www.dixdesign.com/55cat.htm

So my question, is plywood panel boatbuilding that much different than steel panel boatbuilding or Polycore panel boatbuilding...in terms of computer cut panel kits?? I hope you understand I'm being just a little sarcastic here. CAD, CNC panel boatbuilding certainly has to have a lot of similarities reguardless of the panel material. And certainly it gets better with the improvements, refinements of these computer cut pieces.

Wynand, thanks for joining the conversation. I was going to contact Dudley about this project I'm investigating to determine any interest he might have in participating.

 

[brian eiland]

I can't see any really compelling reason to add the expense and complication of a composite deck to a steel hull.

To me one of the very greatest features of a steel boat (hull, deck, and house) is the welded watertight integrity of the thing. It's truly great to be able to attach all deck fittings and hardware with a weld, no bolts and leaky holes.

Using prefab composite panels will mean very little or no shape like curved house sides or deck camber. It will require endless hours in cutting away core and re-building solid edges to accept backing plates for leaky hardware joints, hatches, windows, doors....all problems with short life span gaskets.

These old motorsailers are not particularly weight sensitive designs, and they don't have huge deckhouses AFAIK. The main reason for a composite deck and house would be to reduce VCG, but that seems to not be an issue here.

And market for motorsailers? Roughly half the Nordhavn motorsailers produced so far (9?) are for sale or unsold (and price reduced).......

Dear Tad,
I will shortly post a design under consideration that might make more sense to you why I am looking at this method of construction.

I don't understand this quote from you,

Using prefab composite panels will mean very little or no shape like curved house sides or deck camber

If you can build curved cabin sides and cambered decks with plate steel or plywood, why not with polycore panels??

As far as that Nordhaven motorsailer is concerned I never really considered it a viable mortorsailer,...and its over priced on top of that. Not surprised its not a good seller.

 

[brian eiland]

One of my builders has help build scores of CAD:CNC cut alloy boats. We have recently built 7 in our own workshop. All of these craft were drafted by one particular draftsman who is now an expert. He had the opportunity to check his work on the floor over many years. His boats just fall together. Fold lines are marked and I recall a horizontal pipe orifice within an angled plate that was cut perfectly. If one had to cut the plates by hand construction time would be trebled, in my view.
M

Are you fimilar with this fellow David deVillers ??
http://www.devilliersyachtdesign.co.nz/cms/
He has done a fair amount of this work, including some with Steve Dashews' projects.

 

[michaeljc]

I see no reason why composite panels cannot be used just like other sheet materials. In most respects it is similar to plywood. It can be CNC routed I expect, with the right cutting tools.

Metals have one big advantage: They can be swaged or folded to enhance stiffness without adding stiffeners. Look at the walls of a ISO shipping container. This is 1.5mm corten. It also can be welded, which brings out the major challenge, distortion - particularly when building in alloy. Only tradesmen on the floor can deal best with distortion. The designer can help by ensuring all sections have a degree of curvature. A very experienced tradesman can impose compound curves into plate just through the sequence of tacking and welding. But, when it goes wrong.......... . All this is not so bad when a hull is to be painted. Filler can be used. But, many smaller craft go out uncoated. Designing hulls for these with no welding between the chine and the gunwale does require some thought. Great care has to be taken not to scratch the sections as they are assembled. Exterior welds are ground and banded or tig welded which can be attractive when done correctly.

Just some prattle

M

 

[Wynand N]

Plywood, especially molded plywood is in my view the best material for building a boat. Light, extremely strong and very durable if used with modern epoxies.

If I have to do it all over again, this would be my preferred material to work with

 

[michaeljc]

Yes, but what is commonly unknown is that few marine plywoods are made from naturally durable timber. By durable I mean will last for 50 years in any environment. 'Marine grade' refers to the bonding and the quality of both interior and exterior lamina ie no hidden knots. Many brands of marine plywood will decay within 10 years when exposed to the wet:dry zone. I don't know of any marine plywood that is chemically treated against decay. Liberal dressings of epoxy, inside and out may solve the problem but one would have to fastidious about the internals and joins.

If we look at timbers from any region less than 2% are ground durable. Furthermore, most ground durable timbers are very dense - not suitable for plywood as they do not peel well and take on seasoning shake.

I have been told about some internationally available marine ply that is durable but cannot remember the brand or species. It will be expensive.

There is also the threat of marine borer. A few species are resistant including the very dense durables which are normally used only as keels stems etc. We have an interesting timber in NZ called Totora. It is very light, stable, very durable, beautiful to work and resistant to marine borer. It can still be bought but at around US$ 2200 / cube. The sailing schooners used Totora planking sheathed with copper. but there is always a downside: Totora is not a strong timber. However due to its density it can be used in thicker sections. Nevertheless very durable timbers that are of low density are very rare.

Recently I had an opportunity to study boatbuilding timbers in the Philippines and Fiji. There still some good timber available but not for much longer I feel.

I would like to build a wooden boat one day. It would probably have an alloy frame. I remain of the view that wood is still the ultimate boat building material especially if it is clad in glass epoxy. But - expensive to build.

m

 

[brian eiland]

Plywood, especially molded plywood is in my view the best material for building a boat. Light, extremely strong and very durable if used with modern epoxies.

If I have to do it all over again, this would be my preferred material to work with

Plywood is still very much in consideration in my plans, but I really want to fully explore this PP honeycomb sandwich panel option first.

I've seen/heard of my share of rot in plywood decks, and water migration into the end grains of same. And it does not offer the 'insulation' qualities that the PP core could in decks and cabinsides.

This might be a good place to bring up another application of PP core I ran into.....posting to come.

 

[Wynand N]

There is also the threat of marine borer...

Plywood is quite immune to the wood borer worm because of the glue between layers of ply. When you do strip plywood molding with resin bonding between layers, it is totally impervious against the Teredo worm.
As a boat building material it is without peer weight wise and is about 4.5 times lighter than Aluminum on average per cubic meter and the skin thickness used not much more than ally for comparable hull. And when molded it is extremely strong.
Modern epoxies took care of previous problems that plagued plywood in general. But as with steel, these molded plywood hulls take time and skill but nothing beats it for a fast, lightweight and strong boat hulls.

Best plywood to use is marine grade which comply to British BS1088 standard or similar rating depending on geographic regions - my country marine grade ply is graded BS1049 for instance that complies to Lloyds requirements.

Many old plywood weekender sailboats from the 60's are still going strong on some local dams here bear in mind they were built before the vent of epoxies and modern glues. In the end, as with any other boat building medium, it boils down to preventative maintenance.

 

[brian eiland]

Zinc Protective Coatings for Steel

Dear Wynand,
I've not had time yet to fully go thru the numerous ideas, postings, etc presented for 'protecting' the inner skin and supporting framework of a steel hulled vessel. But if I recall correctly many of these are based on Zinc.

I believe I have also seen where there are some more modern thoughts on not using zinc at all, but rather some more modern and recently developed coatings. Can you enlighten us on any of these?

 

[brian eiland]

Strip Plywood Molding vs 'Panel' Plywood Construction

Plywood is quite immune to the wood borer worm because of the glue between layers of ply. When you do strip plywood molding with resin bonding between layers, ....

I believe there is a distinction to be made here? Strip plywood molding would be a little different than large panels of plywood construction? Strip molding is more time consuming, labor detailed, and expensive than the type of panel construction that D Dix promotes on much of his website,...is that correct?

 

[Tad]

If you can build curved cabin sides and cambered decks with plate steel or plywood, why not with polycore panels??

Well I guess we are speaking in generalities......To me a cored self-supporting panel will be stiff, not floppy like 1/8" steel. And once plywood gets more than .5" thick, it gets really difficult to bend very much, so you need to use multiple layers. Usually deck core is 1" to 1.5", it does not bend once the skins are applied, so cored, cambered decks are built over a temporary mold.

 

[michaeljc]

I believe Wynand is referring to cold moulding? Frameless hulls can be built using this technique. One would struggle to do this with plywood or composite panels as it requires compound curves and what would we do at joins?. Several thin layers may do it but by the time one builds all the moulds, and glue e.t.c it would be cheaper to go traditional composite. A topsides built of thick composite panels is at risk of looking slabby. Cabin tops would need extra beams.

There is a trick one can use to put compound curves into plywood panels - if you are brave enough. Soak it, then leave it lay flat (grass is good) outdoors in the sun. clamp it on immediately it takes on the curvature required. Let it dry, then glue and attach.

This can be done with planking also. Wide thin planks milled with the right grain orientation will even curve along the short axis. The trick is to lay out plenty as they all behave differently. Select what suits the profile being clad. Some eucalyptus will warp and twist directly off the mill. Very handy. Some species are good boat building timbers.

I recall some pics some where of a yacht being build entirely by cold moulding lamina. If a beautiful fair hull is required this is the ultimate. But there is still an awful lot of glue and sanding required. I would still go with solid lamina, not plywood but thats just me. Whatever, cold moulded wood is my ultimate.

There are cold moulded craft in NZ that date back to the 1800's. They are referred to as 'triple skin Kauri' The lamina (not plywood) were layed at diagonals. NZ kauri is superior to Fijian or Australian.

 

[Titirangi]

Zinc coating steel - hot dip galv, zinc sprayed or cold zinc paint as a ferrous metal surface protection isn't equal to blasted then 2pk epoxy paint finish for long term protection.
Zinc in any form is used as a sacrificial protective coating to deteriorate until recoating.

For aluminium superstructures with compound curves we use English wheels that work up to 10mm thick plate combined with a brakepress to form any shape required and fast.

I'm a big fan of plywood moulded hulls and I have seen worm damage, but as Wynand posted although the glue was a barrier the damage to the outer layer was beyond repair as the worm continued to tunnel the length of the hull, in this case 70% of the hull skin replaced.