wood planking on aluminium frame

[yachtsmanbill]

I tend to agree that wood on wood is the best bet, BUT how about joining ANY new construction to 30 year old FG?? Engineered expansion joints come to mind to prevent expansion differences/cracking and it seems to me that alum is strong and easily fabbed into neccesary compound curves etc.
I just figured that bolting alum to FG and bedding with 5200 seemed logical and much easier and sanitary than trying to " glass in " new bulkheads and deck bracing etc. I just dread the thought of mixing 55 gallon barrels of resin and glassing sheets of 3/4 inch plywood. I guess I am just an old man trying to cheat the young hang-man.
As far as I know Hatteras used cored 'glass on their decks, but most superstructure stuff is solid/molded with an unknown ( at this point ) framing system. Any guesses???
Thanks for the input, and I WILL keep you apprised. Bill

[CORMERAN]

To yachtsmanbill:

When I hear 30 yr old anything - I tend to take a deep breath......

The due date for Jet plane in commercial service is only 25 yrs.

Commercial steel ships might exceed a working life of 30 yrs.
However - the carefull shipping co. will be wise to take a long
look - when a vessel passes her teens.

Hatteras are boats with a good rep.
So let's for the moment - consider that when the vessel was
constucted - that the FG was done right.

However.............

Over the last 30 yrs Hatteras had no control over said vessel.
- Simple sunshine kills FG.
- The warmer the climate the more this is a factor.
- As stated in other threads: the catalyst never stops working.
- So the FG will get more brittle as time passes.
- Every solid impact - like pounding through head seas - ages
the hull.
- The dreaded osmosis - created by water mixing with the various
chemicals in the FG ( which, dispite the salesmen's hype
- IS NOT waterproof.) is INEVITABLE.
With better made boats this will take longer - but it will happen
eventualy.

- In short: the worst thing you can do to a boat - is to immerse
it in corrosive salt water - and go offshore on a sunny day !

So before you spend a lot of time debating how to add stucture
to your boat.......

A simple core sample test ( From your FG hull ) - by a good lab is
what I would do.
No matter how much this costs (within reason) it's way....way
cheaper than spending hundreds of man hours and thousands
of dollars on new constuction.........
If before the end of the day your 30 yr old hull starts to crumble
under your shipwright's feet.

I'm sorry - but; I've seen this happen many times.

There are no forever materials....... or forever boats.

[yachtsmanbill]

It used to be a standing joke in the nuclear electrical generation game, that as a ground zero facility, the only thing not vaporized by a nuclear blast will be the 6 inch stainless steel rulers in our pockets. As a young Corvette enthusiast I was told by a chemical engineer that fiberglass will continue to cure until its dust.
The old Hatt is no exception in that she has been continually top coated with AWLGRIP ( another catylized process ) and moored in fresh water 75% of her life. There are surprisingly few stress cracks on the boat and really only one small soft spot in the coring.
I have always liked boatbuilding and figured this one will see me well into my grave. If its ever really done, the fuel costs will see most of her cruising at dockside. The 12-71s run well enough for another 1000 hours--thats 100 hours for 10 years.
So now, what would the panel recomend as a building system?

[CORMERAN]

To yachtsmanbill:

OK....OK !!
You are satisfied with the condition of your hull.

Also you indicate a level of sophistication, that our
suggestions will be given due consideration.
Not always the case - in this forum.......

So I will outline how I would proceed.
- First, I have found epoxies preferable to other stick - ums.
- The co - efficients of FG and wood are closer than alum.
is to FG.
So I would lean to plywood as a base. As epoxy bonds well
to both FG and wood.

- I would STRONGLY advise against using FG resin over ply !!!

However............

You are comfortable with alum. So go for it !

Cheers !!

[bertho]

gents,
i'm interesting by the comment from tanton, regarding artica II built on th 50' and still OK or by minesweeper boarbuilding, it's no discussion forum about about fiberglass, i work for 20 year with composite material and for me the biggest problem i how to return this material to dust...a clean one of course..)
all this exotic product do some incredible progress last 15 year, and will continue, ..
let's focuss on your point of view, suggestion, about this wood compsite assembly with aluminium, both are excelent material when used alone, both have also some weak point, i fully agree about the composite wood/epoxy, with carbon or fiber, it's probably on the top ten for composite, but why aluminium wood is not conventional, it's the topic of this thread to understand why?
problem of mixing different know how, it's sure, corrosion problem, fastening, dilatation, don't look as unsolvable issue, let's be creative, or lessoning from past experience...
thanks to all
bertho

[Poida]

An interesting thread as I have long thought of making a boat with a steel structure and a plywood shell.

I live in a part of the world where boat building wood is not easy to get. Our timber (lumber) is brittle and not structural so building a boat with a wood structure is something worth looking at.

Coefficient of expansion - Would a steel structure inside a ply hull heat up enough to make a difference. Metal fixings are used to hold a wooden structure together, surely if the coefficient of expansion was a problem they would come loose.

Timber trusses are common with steel plates holding the components together, these are used in roofs that will get much hotter than the inside of the hull of a boat, in fact steel brackets and bolts have been used for ages in the sun with no problem. Maybe the timber has a cooling effect on the steel.

Fairing - Good point, make the steel frame smaller and screw timber battens to it allowing enough meat for fairing.

I have seen wood boats where the timber inside has cracked and steel strips have been bolted either side of the cracks (I was told they are called sister strips) to strengthen it. Why not have a steel frame in the first place?

[Syed]

Linear Temperature Expansion Coefficient
- α- (m/m.K x 10-6)

Aluminum 22.2
Brass 18.7
Epoxy 18 - 20
Iron, cast 10.4
Steel 13.0
Steel Stainless Ferritic (410) 9.9
Wood, oak parallel to grain 4.9
Wood, oak across to grain 5.4

In countries where minimum and maximum temperature during the year does not vary more than 20 Celsius this may not be an issue (for practical purposes). In areas like ours, the variation is about 50 Celsius, so I shall go for the combination of steel / wood or ss410 / wood, if I have to.
As far as the fastening screws are concerned this factor of contraction / expansion is critical and significant only longitudinally. There are no chances of loose joints, but hair-line cracks can cause sealing problems over passage of time.

Regards,
Syed

[CORMERAN]

Thankyou Syed !!

Some hard numbers to refer to.

So please note - bertho:

The expansion coefficient of the the ferros metals
are ONLY around twice that of oak.

Whereas: the expansion of alum. is FIVE times
that of oak !!

Twice - is a lot in engineering; but five times - is WAY out there.

````````````````````
Minesweepers only confuse the issue.

People take very divergent directions in designing such vessels.......

If memory serves:
- A very large 'sweeper, was built, post WW 11 - in the US
- all in WOOD.
- In Australia the choice was: FG.
- In Germany: STAINLESS STEEL !
- Perhaps, the most bizaar choice of materials was recently,
by the Can. Navy: -Plaine Jane STEEL !

Instead of looking for abberrent examples of the use of alum.
- I suggest reflecting on WHY; mixing it with certain materials
IS NOT common practice.
i.e.
- Since the Falklands war - both the British and Canadian Navies
avoid using STEEL combined with ALUMINIUM.

- Not so well known - the US navy lost an ALL ALUMINUM
"go - fast" vessel to fire - when the gas turbines overheated !
- The vessel did not have diesel backup engines - to move
at slow speeds.
- Turbines don't idle well...... they can get VERY hot.
So - no suprise, once the flash point of was alum. reached...!

Obiously - I'm not a big fan of aluminum.
It does have practical uses. However, other people than myself
- have found out the hard way, it's by no means - an
ALL PURPOSE material.

`````````````````````````````

" Progress in engineering - all to often - occurs after a good
number of people have died, due to erroneous assumptions."

[bertho]

Ok, Ok,
i built sometime also minesweeper in composite for french navy..even large sandwich topside for fregate..( after malouine war who show the weakness of aluminum,,) i know a little bit the problem.. , but we agree, navy are not rationnal as we need to be for our pleasure...!
just a comment..epoxy and wood have not so far the same dilatation ration than the wood and aluminium?? and they look happy when married together.. i don't thing the dilatation ration can be the only caracteristic to be compare..i will be interested to have designer point of view.. wood and brass frame bolted have been use successfully since many year, even if it's expensive ! but if you look on the bilge of some boat from great designer, W.fife or N. Herreschoff...it's look not so bad.. since year !

[cabinboy]

Great topic, I've been thinking about wood/metal composite hulls for a while now. (I can't afford to build one, I'm just thinking). Have you taken a look at the new Spirits? They beat me to my own idea. CNC cut stainless planked in wood. I assume the stringers would be wood as well but the webs are all stainless and boy does it look good. Is it just me or is wood making a bit of a come back?

[D'ARTOIS]

The issue of wood planking over metal frames is far away from new, for example the Classic "Thendara" was made this way. It was for some time very popular in the Uk to build sailingboats in this way.

But:

They were built over steel frames.

Aluminium and wood are not the best of compatibles; aluminium provokes in direct contact with wood excessive corrosion. Wood over steel, yes.
The very old Thendara, completely rotted away, could be restored to her former glory although she was (re)built from scratch. Thanks to her steel frames.

If you insist of having a wooden hull and your design caters for a very large yacht, than this is a sensible method. Exactly the reason that steel frames were used because of the scarcity of wood for the frames.
But even with steel, you have to cater for a proper insulation between the frame and plank.

And CORMERAN: there is an ideal material in which you can build a boat almost forever. (Actually 2).

[waikikin]

In the 80s I worked on a replanking job(more like brick laying at the scale of vessel) on an alu framed mine sweeper at Garden Is Dockyard, the repairs where to open up the job so the very corroded(heaps of soap like powdery stuff- many times original thickness) aluminium could be replaced. She was double planked longtitudinally originally with mahogany, but we put back Douglass fir because of availability/cost.Jeff.