what material better wood metal etc

Discussion in 'Boat Design' started by Garth, Jul 25, 2006.

?

what material to use

Poll closed Aug 18, 2006.
  1. wood

    42.3%
  2. glass

    3.8%
  3. metal

    42.3%
  4. other

    11.5%
Multiple votes are allowed.
  1. jonsailor
    Joined: Sep 2005
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    jonsailor Boat designer/builder

    The best workmanship makes the best boat

    Pick what you like, hey, I have done them all.
    I have gone from ferro to cold moulded to strip planked to aluminium to steel and the most exotic sandwhich available.
    They all have thier good and bad points and the best answer is that you use the best building practices for the material chosen. Any one of the mentioned materials not done properly, will give you trouble.

    Probably my favourite for cost effective strength and weight with insulation....would be Western Red Cedar strip planked with epoxy "E" glass inside and out:p :p

    www.sayerdesign.com
     
  2. CORMERAN
    Joined: May 2006
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    CORMERAN Junior Member

    Red Cedar

    Hi jonsailor,

    I agree with you - re: red cedar.

    I've also designed and built in various. From Ferro Cement to Carbon Fiber.
    However - my personal inclination leans towards stuff that once had
    leaves on it.

    -This is another one of those endless bar room discussions.
    - For every instance of dry rot, there's a story about rust.
    - Or sad tales about concrete boats being only half built. Stong and
    long lasting - of little use. If you can't finish the thing !
    A lot of enthusiastic people discovered the hard way - that it takes
    real SKILL to do a good job with cement.
    - That's the operative word. SKILL.
    ..........doesn't matter if it's chewing gum and popsical sticks.
    Good workmanship is the first criteria - when it comes to building boats.
    - Also, I'm often frustrated by clients, spending so much energy on
    talking about the hull material.
    - Which is, maybe, only 20% of the value of their dream boat.
    - Then, with little discussion, go out and buy $ 50,000 to $ 100,000
    worth of electonic toys for said boat.
    Half of which are redundant and seldom used.

    Cheers.
     
  3. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member

    No of course not ............

    There are very good reasons why steel dominates the workboat world.

    The design strength for materials is the yield point . This yield point for brittle materials is also the point of Ultimate tensile strength (UTS) this is where rupture occurs for a brittle material. In a monocoque construction (eg wood epoxy , GRP ) this rupture (hole) in turn leads to high localised stress concentrations and continued collision results in the massive catastrophic failure we see so often when a brittle material boat is washed onto rocks or hits a floating object. With Planked each plank that the UTS exceeding force is applied to successively stoves in .

    For any given hull steel will always be approx twice as strong as far as UTS is concerned and the amount of energy required to reach failure is considerably higher again since steel yields then deforms for a considerable distance absorbing impact energy (doing work).

    So if you really want a really strong boat then steel is the by far the best choice. This adds up to a lot of free insurance of both life and property.
     
  4. longliner45
    Joined: Dec 2005
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    longliner45 Senior Member

    Ok man Im partial to wood ,love it its natural , and been around for millinia.,,,but it is getting hard to come by ,,,old growth stuff, maybe you can look at JC boats from NewHampsire. made of airrex? (check the spelling) it is stronger and lighter than fiberglass ,,and it floats.and dont be discouraged by the naysayers and the never do"s,,,,,,,,,good luck,,,,,longliner
     
  5. FastLearner?
    Joined: Jul 2006
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    FastLearner? Junior Member

    Perhaps some numbers, rather than subjectivity, would help clarify things.

    To preface, let’s note that what is important in boat building is the relationship between strength and weight. Without considering weight you could make a case for most any material…all you need to do is make the hull shell thick enough (not being concerned with weight) and it will meet your strength requirements. So, using Douglas Fir as an example, let’s look at the ratio of strength, in the two most important measures, to weight:

    1. Ratio of Tensile Strength to Weight (PSI/Lb./Cu.Ft.):
    Doug Fir: 388
    Steel: 121

    No comparison here.

    2. Stiffness (modulus) vs. Weight (PSI/Lb./Cu.Ft.):

    Douglas Fir: 60,938
    Steel: 60,606

    Much closer this time, but wood still wins.

    We could slice and dice it further, but practically speaking, in every case wood wins the competition. Wood has greater tensile strength (e.g., better resistance to puncture) AND is stiffer, pound for pound. The above are facts, and cannot be disputed. Bottom line: unless one has a strong and irrational bias for steel, wood is clearly the better choice for boat building.

    Regarding foam/composite construction, in the size range the original poster is considering, foam probably makes more sense than wood. Shorter than 25’ – 30’, the additional FRP thickness required on the outside surface of the hull to offer the appropriate puncture resistance generally results in a heavier and more expensive hull than wood composite. In the 40’ – 50’ range, however, puncture resistance should not be an issue and the foam composite hull would generally be lighter.

    If one likes welding and is okay with a much heavier hull, steel is fine. Otherwise, between steel and wood/composite, steel is the loser every time, and that’s a fact.
     
  6. Redsky
    Joined: Jul 2006
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    Redsky Senior Member

    as somone else pointed out to me recently even ships of VLCC mostly use only 1/2" plate on the hull...its the frameing that matters most...
    lots of wood boats and builders out there in wood/composite wood..however renewable resourse wood is it still only grows so fast.
    steel is recyclable however to a point also.
    i even considerd a thermal engineering plastic as a replacement of the kind they use for plastic drums however that material at tropical temps starts to sag/form over time
    my current bet overall for what im planning myself is steel hull w angle iron frameing structural angles and T's out of same steel as hull and rivits. and since i want to kep the hull w out a huge hanging keel off it and for structural reasons concrete reinforcment/ ballast shell to just above waterline
     
  7. MikeJohns
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    MikeJohns Senior Member

    This is not entirely correct
    It is a combination of strength and mass and the position of that mass wrt COG.
    Also consider the displacement factor. For example a medium or a medium-heavy displacement yacht ( a crusing boat) over 40 feet will have little benefit from the weight saving of lighter hull materials . If you consider the proportion of the hull material mass with the overall displacement the hull material density has little effect on the COG in your weights and moments calcs.
    You design to a desired displacement and the desired RM . Hull material density is often not that significant. ( Some vessels are simply too light for comfort, but that is another topic ).

    Again if the design paradigm is for fast light weight racer then it’s a different story.



    As a train of logic it is what we call the prejudiced leap from the small reasoned errors to the grand fallacy :)

    Unfortunately though you or the person you are quoting falls into the trap of partially understanding the issues.

    The wood fibres are strong but the fibre matrix is weak and the material is anisotropic.
    There are different modes of failure to consider;
    Tensile
    Compressive and
    Shear.
    If you only consider tensile then the numbers look very appealing but now re-do your calculations for compression and shear .

    Note that when you punch a hole the material it fails in shear not tension.

    There are more issues, nothing is ever as black and white as you would like to believe, for example I could go on for a while about structural rigidity comparisons, section modulus equivalents, buckling characteristics abrasion resistance but It would turn into an engineering materials lecture.

    I like well made wooden boats, they are one of the few areas of real quality craftsmanship in our modern world, but as an engineer I think steel has numerous advantages for the amatuer builder who wants to explore the coast of New Zealand.
     
  8. Poida
    Joined: Apr 2006
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    Poida Senior Member

    Of course Mike, one of the things I think to be taken into consideration is what do you feel comfortable in building with. I am in the metal trades so I feel that if I built in steel it would be a far better vessel than one I built in wood as my carpentry is not up to scratch.

    Probably a person who normally builds in wood, would not do a very good construction in steel.

    So apart from all the geek calculations, one should also look at the soundness of construction in relation to their skill.
     
  9. chandler
    Joined: Mar 2004
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    chandler Senior Member

    This is kind of an aside from the subject, and goes back to the subject of the education thread. But is Dave Gerr a structural engineer? Or any other type of engineer? Mcnaughton, is he an engineer? They have very differing views on scantlings.
    So the only publications of scantlings on general construction of a wide range of materials come from 2 men that are at best designers. Unless I am mistaken neither is an engineer or a N.A.
     
  10. MikeJohns
    Joined: Aug 2004
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    MikeJohns Senior Member


    I've been avoiding calculations to keep things simple.

    It can take a while to become fast building with wood-epoxy even a fast experienced builder is slow compared to an amateurs metal boats rate of construction.

    With steel a strong tight good performing yacht can be built with little time spent learning the trade. Any woodworker of merit would be considerably more able to build in steel because of their familiarity with tech skills. There is always woodwork internally regardless of hull material that takes skill and time.

    I observe that most amateur built metal boats I have advised on are launched within 2 years and a high proportion of them are used for extensive cruising by their owners. The opposite is true of the finely built craftsman type of wooden boat in that they take years to complete the hull alone.
    One of the reasons wooden boats take so long is the tedious nature of their assembly and the fact that the keen builder gets a bit cheesed off with the project.

    The majority of home built boats are being built in steel for good reason.

    It is the fastest method by a long shot
    It is very forgiving of poor building techniques and easily repaired
    Then the result is far stronger than any other form of construction.


    There are many scantling rules published, all of which are very similar. I think you will find that Gerr simply meta analysed the various rules and produced an easy to follow guide for laymen.

    Authorities for commercial vessels require either strict rule adherence to Lloyds, ABS, USL, NBS or ISO or they require specific engineering calculations . You cant have different views on material strength either its strong enough or it is not.

    If we defined best from the completion and successful use of home built yachts Bruce Roberts would win by 3 fields ahead of all the others.
     
  11. Poida
    Joined: Apr 2006
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    Poida Senior Member

    Yes Mike you bring up a good point with speed, I'm sure that building the hull with steel would be much faster. I can't however agree completely with the time it would take to teach someone to weld. Maybe to do a simple weld wouldn't take long but I would assume that welding a hull would take a lot of experience in overhead, vertical as well as overhead welding. It is something to weld two pieces of metal together but another to produce a sound weld with no slag intrusions.

    As you said timber is used inside the boat but the quality of the cabinet making does not add to the strength of the boat.

    It is common for people to think that everybody should be able to do something because they themselves find it easy. You are probably more talented than you think you are.
     
  12. MarkC
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    MarkC Senior Member

    Poida said:

    Instead of this debate about 'what material is better' how about concentrating on what boat do you need for your local area?

    Go to a reputable designer in your local area and ask them what sort of craft is really going to really suit your local conditions. It has really got to suit your local conditions. Then make a decision with guidance about a design.

    For example - my home waters used to be Sydney Habour, Australia. Mostly deep water - not many shallows. Outside the harbour we had often 20kns and over 2m waves in a usually SouthEast pattern. I did not need a centerboard yacht, nor did I want a flat bottom or an open-boat. My home waters in Adelaide, Australia were shallow sloping beaches, big tides, with an often short-sharp chop with 20kns in the afternoon. Centerboard yachts are very popular there - openboats everywhere - and a flat bottom (but with a sharp bow!) could have been ideal.

    And just to stir the flames a bit - in my mind - if your skills are in metal-work then build a metal boat. That makes sense. You know where to buy the deals with metal, you are knowledgeable with the tools. There are books and whole web-blog-sites that deal with metal boats...

    In addition, there are designs for steel boats - alu boats of many different sizes - many smaller sizes, not just 40, 50 or 'over 100ft' . Have a look at some of the dutch designs.

    Plus a designer takes into consideration the relative merits of all materials when he/she designs a structure and hopefully uses the material to its advantage.

    Lecture over.
     
  13. MarkC
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    MarkC Senior Member

    Sorry to have highjacked your thread Garth.

    I see that you would be returning to England. Have you seen what the Dutch offer second hand? Amazing range. I dont know what cutoms would do if you bought a yacht from holland - but the choices and prices are good.

    Check out www.botenbank.nl.

    Here's a nice example (a Laurent Giles in steel):

    http://www.botenbank.nl/yachtselect/boten/2156750/view
     

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  14. Grant Nelson
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    Grant Nelson Senior Member

    Chandler:
    Dave Gerr founded Gerr Marine, Inc., in 1983. Based in New York City, it designs both yachts and commercial vessels, and probably works on a wider assortment of boat types than any other design office-sail and power, yacht and commercial, monohull and multihull.

    In 1979, Gerr started as a naval architect at MacLear & Harris, Inc., where work concentrated on megayachts, power and sail, and where much pioneering design in large and small multihulls was done. Gerr also has built, repaired, and lofted a wide variety of boats, and has supervised FRP production on the shop floor.
    In addition, Gerr performs specialized surveys for insurance companies and law offices. He has been an expert witness on a wide variety of cases, from marine-related homicides to routine insurance and damage suits.
    Gerr is the author of Propeller Handbook, The Elements of Boat Strength, and The Nature of Boats, all published by International Marine/McGraw-Hill. He has written over 340 articles on boats and boat design that have appeared in almost every major boating magazine, and he has been a contributing editor for Yachting, Offshore, and Boatbuilder magazines.
    A graduate of the Westlawn Institute of Marine Technology, Gerr studied physics at New York University and industrial design at Pratt Institute.
     

  15. Garth
    Joined: Jul 2006
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    Garth New Member

    i like the look of te voyager 450 or the robers 434 as i siad one of these days i would like to find my self globely coast hopping so where planing on having to live on it for some time and at 19 stone and 6'3 room on bord is needed
    there's a differents between wood and steel and that what im trying to find out. as we no there are container flooting around the ocean and a steel hull is more likely to absorbe the impacked at lest that what i think not that im planing on finding them with my yacht. and i have read that epoxey dose not like the sun uv ray and gose brittal after time is this a fact or what. I am a chippy in london so working on a new boat in stead of a old house that need load of epoxy to hold it together rather than fixing it properly would be a dream [nice clean job from start to finish] wether it wood epoxy or steel. at the same time i now people wouldn't build a boat in wood epoxy unless it was up to the job. and the the fact that reseached it the cheapist part of any project. in the end its up to us anyway but i only have one point of veiw and its limited. and i think it wouldn't be impossible to work on steel a lot more foregiving than wood you cant just weld add a bit on if you cut it to short
     
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