On going steel boat maintenace

Discussion in 'Metal Boat Building' started by kens2114, Dec 8, 2008.

  1. kens2114
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    kens2114 New Member

    I am looking at purchasing a 36-38 yacht & am considering steel.
    I have read a lot over the years but keep getting told stay away from steel.
    How do you tell the paint system used if the vendor doesn't know, what does it entail to keep a steel hull in good condition, does it need to be blasted & repainted every few years.
    I find steel appealing & has the perception of strength, down hear in Aus most seem to take the safe way & select standard production designs in glass, which is OK but I want to canvas steel before I make a final decision.
    I would appreciate any comments.

    Cheers, Ken
     
  2. Ilan Voyager
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    Ilan Voyager Senior Member

    Steel can be the worst and the best.

    For 36-38 feet boat it's too heavy and not the best material for a yacht of this size, and definitely fiberglass or epoxy wood is better in these sizes. Metal in small boats has also the inconvenience to need an insulation which is expensive and adds further weight.

    Steel needs good preparation with sandblasting and primaries to have a lasting paint after building. It needs a constant maintenance tracking all rust spots, repainting immediately any scratch, or the boat will look like rusted junk within months. Yes it has to be blasted and repainted regularly (the frequency depends on a lot of factors) and that costs a thick pack of green Franklin portraits.

    If you are not a lover of painting maybe you'll think that a steel boat makes life miserable.

    To conclude, against common belief, steel is not a strong nor rigid material for its weight and on small boats has to be worked in thin plates which bumps at the smaller accident.

    If you do not believe me make the following trials:

    -take 2 inches wide 2 feet long samples: a 1/8 inch thick steel strap, a fiberglass strap 6/10 inch thick, and a 2 inches thick piece of fir. They have about the same weight, and try to bend them with your hands on the angle of a table. The fir will win as you won't bend it by hand, fiberglass second and it'll come back like a spring, while the steel will bend definitely. 1/8" is the common thickness of a steel deck plate, often it's a 1/10" on a small yacht.

    -take a good hammer, try to bump the straps by hitting hard. Fiberglass winner, fir second and steel bumped.

    -throw the 3 samples in a bucket of sea water and leave them a week. Have a look; the steel is a piece of rust.
     
  3. bober
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    bober New Member

    i like tests :).
    let's take the same materials and place them on a good sturdy and solid surface.
    now hit them with a shape edged tool such as a double bladed axe.
    which materials will be cut in two pieces(sheared)?
     
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  4. Frosty

    Frosty Previous Member

    Oooh I know a good test. 4 boats run aground on rocks, the boats are wood, fibreglass , cement and steel. A 1 foot hole is ripped in the side of each one.

    Which boat will be repaired and off the rocks the quickest
     
  5. Wynand N
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    Wynand N Retired Steelboatbuilder

    Come on Iceman, why be so generous - if all four run aground on rocks with some nice waves pounding them, one will be splinter wood, one will be bit and pieces, another cracked and holed and lastly one will have its paint job spoiled, saved for a few bends and scratches.....make your pick.

    A nice example of this scenario was when Bernard Moitessior boat Joshua was blown on the beach somewhere on Mexico coast if I remembered correctly in the 80's.
    Fibreglass boats looked like driftwood all over the beach and I remembered the photos in Cruising magazine where some GRP boats laid broken over Joshua. The junk was removed from his boat, a front end loader used to dug a trench and pushed Joshua into the water where she floated. Mr Moitessior gave the boat away just there and then. The point is, that was the only boat that survived the storm and she lived to sail another ocean or two.
     
  6. Wynand N
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    Wynand N Retired Steelboatbuilder

    A well build steel boat shotblasted and epoxy painted with a compatible system - that means, primer, tie coats, top coats with a coaltar epoxy on the inside and outside the waterline below the tie coats will have less maintenance than a GRP boat, period. If done properly, it will last a lifetime and only preventative maintenance needed as is the case with any other material. If chipped for instance, repair soonest, same with tupperware boats.
    Modern epoxies are unbeatable and hard to beat and GRP / gelcoat is like comparing cheese and chalck.

    Steel got its bad reputation from amateur built boats - guys that used strange brews to remove rust, no surface preparation for the paint to bind to, cheap paints (seen some enamel painted hulls), expired overcoat times and I can go on, on on....then again they try to save some bucks and that is the very reason they built it themselves in the first place.
     
  7. Ilan Voyager
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    Ilan Voyager Senior Member

    I was sure to get some posts ;)

    There also some other test non very representative of yacht strength: the 20mm cannon, a water jet cutter, 1 kg of C4 and detonator, 52 m of free fall like the Norwegian life boats for the oil drilling platforms on North Sea, or a hit by a 320mm marine shell. And all we know that yachts are tested by the US Coast Guards with a good axe lent by the fire station.

    For the grounding on a reef with a 1 foot hole, and not staying grounded battered by the sea: my experience of fixing a few dozens of grounded boats says the plywood or cold molded hull will be punctured with a few broken ribs and repaired easily, the fiberglass will need a further surveying of the bulkheads and a good fixing, the steel hull if punctured really with a 1 foot hole will be badly deformed on a extensive zone with major work as steel is ductile so not easily punctured, and ferrocement will need a good survey for the cracks or crevices plus the big fixing.

    As weathered naval engineer I maintain than steel is nor strong or rigid for its weight that's the detail like said Cantinflas. Fiberglass and Kevlar are used for armor plates, and wood composites have a ratio weight/modulus just beaten by carbon. And for making light and stiff hulls, nothing is better than a low density thick material with a correct modulus. Pure maths in engineering illustrated by a myriad of sandwich hulls.

    While waiting the eventual ultimate storm, you'll have to move all the time the "dead" weight of the steel and its insulation, the bigger ballast, plus the bigger rigging, the bigger tank of fuel for the bigger engine, the bigger winches and hardware for the bigger sails, and from time to time an expensive sandblasting and paint job, and a everyday maintenance. And these expenses are for sure, not an eventuality. It's so true that a lot a pro fishing boats owners do not want steel boats under 45 feet. Maybe a better insurance with the saved money will be more interesting.

    The former statement is for small yachts like a 36-38 feet. On bigger yachts is not the same, although aluminium is a strong contender... and for ships is the lone economical material, so no competition.

    Whatever the size of a steel boat, constant maintenance is mandatory and tiring for an ordinary yachtman. As we say in the Navy to the young recruits: etiquette is simple, salute all that moves, paint the remaining. I'm sorry to say that white metal blasting, best epoxy tars, the cream of primaries, and the top of paints on the best marine steel -all that of a high price- does not guaranties a long life protection, just some years and the smallest scratch will rust, with reparations which need to make locally all the process again.

    About the Moitessier boat, all my friends in post at Papeete who saw the boat told me that it was badly corroded and looking like a piece of junk. It's true that Moitessier was getting old with poor health. When the Joshua was grounded, it was so beaten and deformed that Moitessier renounced to repair it, it was not a money problem (a lot of people in France offered help), and at the end gave the boat to some young people. How nice was the boat after reparations by these young fellows, I don't know.

    Steel can be the worst and the best.
     
  8. Ilan Voyager
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    Ilan Voyager Senior Member

  9. MikeJohns
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    MikeJohns Senior Member

    Ken

    Steel is an excellent material and a very sensible material for a cruising yacht.

    I have a problem with Ilan's very simple illustration. To properly compare the materials with your simple experiment you would need to make the sections equal moments of inertia. By making the section deeper because it is lighter you make it stiffer not due to its material properties but because you have given it a higher BD^3 so you would need to adjust your observations by this factor. That’s why steel plating has an associated framing structure. Or why the beams in your house are rectangular wood or I beam steel.

    To get more specific:

    Comparing GRP CSM 30% and common 300Mpa yield boat building steel
    Steel is 4.3 times heavier by volume than GRP

    GRP is 1/32 the stiffness of mild steel, adjusting for weight that’s still less than one seventh as stiff.

    In collision brittle hull materials fail in shear not tension.
    The inter-laminar shear strength is the limiting strength with GRP and it fails at around 1/12 that of steel for size and 1/3 by weight. However this is really meaningless as GRP construction often weighs as much as steel (without the ballast) because of the poor stiffness issue. So for 2 inches of solid bottom laminate you could have 12mm steel bottom plate for equal weight. Even in a heavy displacement 60 footer we only use 8mm steel and the vessel can be lighter that its equivalent GRP counterpart.

    Douglas fir is around 1/25 as strong as mild steel and is similar in stiffness to GRP and much worse in cross grain shear.

    Then consider abrasion resistance, creep, matrix aging, water absorption, hydrolysis, flammability, repair-ability and lay-up and manufacture related hidden faults.

    One glance at trends of material properties with age should quickly convince anyone that metal is a superior material if you are concerned with raw material longevity.

    Steel is a very good material providing the boat has been designed and built by someone who understands the pitfalls and the requirements for reliability. It is this factor alone that gives steel its undeserved reputation for corrosion as Wynand already pointed out.

    Modern coatings have made regular repaints a thing of the past, providing they were done properly initially. I am seeing 25 year old epoxy coatings that are in good repair with minimal touch-ups. Epoxies have come a long way, we now have high build epoxies developed for the oil industry that can be applied up to 3mm thick in one pass and it is very tough.

    There any many 36 to 38 foot boats that work well in steel in the medium to heavy displacement range. There are 100 year old steel sailboats in common use and no reason that they shouldn’t see several more life spans since the material is so quickly and easily repaired to full original strength.

    Steel is also unique in having a practical long term fatigue immunity there is what is termed a fatigue limit in the SN curves that don't exist for other common boat building materials. GRP has a finite life that makes older used boats a minefield for the buyer and surveyor. Many 'bottom jobs' to cure osmosotic delamination have a life of less than 6 years, long enough to shift the problem onto another poor owner .

    We had a chat about GRP here:
    http://www.boatdesign.net/forums/materials/how-long-lasts-fiberglass-11455.html

    feel free to email me

    cheers
     
  10. Wynand N
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    Wynand N Retired Steelboatbuilder

    The point is that Joshua survived that terrible storm, floated albeit a bit dented and crooked. The pictures I saw she was buried under some big GRP boats that laid broken over her. At the end of the day she was restored to her former glory, but not one of those fibreglass boats from that terrible storm was put together again.
    What I try to illustrate; It is night, hell of a gale going and to top it all, it is spring tide. You missed your navigation or perhaps felt asleep and a big wave lift you band onto a razor sharp reef where you are stuck, and waves start pounding that boat with vengeance. In what boat would you rather be?
    I can tell this much, within a few hours nothing will be left of the GRP boat, and perhaps you as well......

    Ilan, thanks for the links:cool:
     
  11. Frosty

    Frosty Previous Member

    If you are happy with a mallet and chisel then wood is good, If you are handy with an oxy cutter and a welder then steel is better. If you love bieng itchy and like to mix 2 pack chemicals with a shelf life of 6 months fibre glass is your choice and if you like to own a boat worth less that your T shirt get a cement boat.

    As you can see I sort of sway towards steel Ive had glass and steel and both have there problems.

    Dont forget most glass boats today have balsa core or some other water absorbing middle bit which gets you worried and you cant sleep at nights.
     
  12. kens2114
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    kens2114 New Member

    Thanks Fellahs

    Thanks for your comments, I suppose its like all things, houses cars & boats if they are well built & prepared maintenance is commensurate with quality of build.
    I suppose I'm trying to get a real feel for the the day to day, year to year regime of up keep & that really depends on the quality & paint systems used.
    I haven't made a detailed enquiry of the boat of interest as yet as I thought I would like to get an opinion of the material first.
    The boat is 37', 12' beam 6' draught, pilot house with a mostly flush deck she is a well equipped,big volume boat. I have a 28' fiberglass yacht for sale & as it turns out in the same bay as this boat.
    The design appeals & while not as glossy down below(which the other half likes) has a real character of its own as well as a lot of practical attributes.
    Cheers,
    Ken
     
  13. Ilan Voyager
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    Ilan Voyager Senior Member

    You're welcome Dynan, Joshua is a piece of history and I was worried by the idea of this boat rusting abandoned.

    Like almost all materials (let us forget the ferrocement), steel can be the worst or the best. While designing a boat, each material has its advantages and drawbacks. As Frosty explained, there also are the personal tastes, a mix of rational and irrational.

    None is the ideal, and applies within a range of uses, or sizes or other concerns.

    Let's illustrate; For spending good time in French Polynesia, I would use a light schooner catamaran of 45 feet, very minimal, in plywood/strip plank/epoxy able to run effortless 300 miles day, and to beach between 2 cocos. I helped to design a such boat, so I know it well. I wouldn't go to the Cap Horn with this boat.

    To see the whales in the Behring I would take a strong monohull in steel, insulated with heater and well ballasted. You accept the maintenance as price to pay for the security. But, a such boat is a pain in light breeze and a nightmare in a lagoon.

    In the other side, a common sailor, using as many his boat in weekends and holidays, will be more happy with a polyester boat -apparently maintenance free- that with a steel boat, which requires whatever the quality of the paint more maintenance and soon he will be bothered by the small spot of rust that Wynand would fix while drinking his morning coffee without thinking about.

    That explains why polyester is generally better for the "common" sailor, the kind of guy who does not know by what end a screwdriver must be hold and who calls the mechanics, the electricist, bref anybody to fix everything on his boat. I'm not despising the common sailor, he is the guy who make us live, and I understand him. He works hard the week to get fun sailing, not fixing rust spots.
    ******************
    Initial subject of the thread.

    Ken asks about purchasing a 36-38 feet boat, used, and he is asking about steel, he has been told to stay away. If he was buying a new boat he would be informed by the shipyard, so not asking here, or the shipyard owner does not do his job. Very probable that a 38 feet steel boat is in sale in the marina, and surely cheap.

    Analysis;

    1-he doesn't talk for circumnavigation or special tasks. Let's assume the ordinary use weekends holidays. If he asks about steel, it's because he has no special knowledge about boatbuilding, and probably someone is trying to sell him a steel boat, and other telling him to stay away. Good thing he tries to get information at the good place.
    2-The boat is 36-38 feet, the very low size for steel which is not competitive in such small boat (see further).
    3-The boat is probably used, so nobody knows how it has been painted and it's an essential point in steel.
    Conclusion: Stay away. A 36-38 yacht in steel badly painted would be a pain in the ... and an economic disaster. It's already not good being too heavy for a week end sailor who need fun, not struggling with a slow boat. Do not take risks. Buy a good polyester boat made by a shipyard of quality.

    **********************

    About Mike post;

    All the thing in engineering is that the inertia sections ARE NOT EQUAL because of the density of the materials. It has no sense to compare so different materials in the basis of equal inertia. The struggle in naval engineering is to get THE MAXIMAL INERTIA OF THE SKINS AT THE LEAST WEIGHT.

    The main criterion is the stiffness, general and local, so the deformations are kept within acceptable limits with maximal stresses no going beyond the maximal safe stress of the material, including a coefficient of security, which reflects the fact we do not know all the possible stresses. Included also the fatigue coefficient as any material submitted to alternate stresses or cycles will lose strength. For example aluminium is very sensible to fatigue and calculations are made with big coefficients of this factor, while wood has little fatigue but shows warping if kept permanently under a stress close to 60 % of its maximal capacity.

    We can consider a hull as a hollow beam with very thin skins. The analysis becomes easier; general flexing/compression/twisting and as the skins are thin, local flexing/compression/twisting plus internal shear, local impact etc. So you identify the stresses and put just enough material to counteract it. A bulkhead under the mast is an example.

    To get stiffness you use inertia. A deep hull with an integrated roof has more inertia than a shallow one flush deck. So it will be more rigid, needing less material (=less weight) at equal stress of the material.

    Same thing for the skins of the hull a thick skin will be more rigid at equal stress of the material, or will stress less the material at equal stiffness. There resides the trick.

    The densities of the usual materials are in kg per cubic meter:
    7800 for steel, 1540 for fiberglass, 2700 for aluminium, 650 for a composite wood/epoxy.

    A 3 mm steel weights 23.4kg/m2.
    At this same weight; thickness of fiberglass 23.4/1.54= 15.2 mm, aluminium 23.4/2.7= 8.6 mm, wood composite 23.4/0.65=36 mm. As inertia varies at the cube of the thickness the inertia in mm3 (which will become mm4 with the width) are the following:
    steel: 3^3=27mm3, aluminium 8.9^3= 705 mm3, fiberglass=15.2^3= 3512 mm3, wood/epoxy= 46656 mm3 so at 23.4kg m2 the inertia of a wood/epoxy skin is 46656/27= 1728 times the inertia of the steel skin.

    I won't enter in the ultimate fiber (=the surfaces of the skin) stresses considerations varying at the square of the thickness. With more thickness you'll get the same strength with less stress, that means that you can employ a less strong material than steel to obtain the same strength with a superior rigidity= less deflection for less weight.

    As the principal criteria is the stiffness, general and local, the low density materials with enough resistance and modulus giving thick skins are clear winners. Illustrated by all the race boats in sandwich.

    So I maintain my provocative post you'll bend by hand the 3mm steel while the 36 mm wood/epoxy (or 50mm clear pine) wouldn´t. That's on flexing, on compression the situation for the steel would be worst as the Euler Formula relies heavily on the inertia.

    And if local strength is enough to harbor without making a bump or hole in the hull I'm happy.

    Practically a typical panel on a 36 sailboat is 18mm (very comfortable) thick plywood or molded wood with 40*20 stringers espaced of 305 mm. Shitty strong. Weight about 13-15 kg square meter, that means roughly in steel a 2.2mm plating and 38*2.5 stringers every 150mm because of the thickness. Sorry it's impossible to use a 2.2mm steel hull on a 36 feet, it's not enough strong, it will be around 3 to 4 mm, so from 28 to 35 kg m2. Very rough calculations, made by head while writing the post.

    For information in prepeg carbon fiber/nomex the weight will be around 7 to 9 kg m2, and strip plank/carbon 9 to 11. Very rough estimations made smelling the wind.

    That explains how a 60 foot trimaran, with all its hulls surfaces, long beams, in spite of all the stresses induced by speeds attaining 35 knots, weights only with a good margin of safety (it's an ocean going boat) about 6000 kg. Made for only regatting with a 25 knots max wind it could be done at 3500-4000 kg.

    Boats are not built to withstand grounding by a hurricane as cars are not made to hit a wall at 100 mph, nor planes crash at 500 mph.

    A lot of books about naval architecture and engineering give more detailed explanations. The present post is a overly grossly simplified demonstration, that Ive tried to make without maths. I hope that everybody understood, English is my third language and I'm not so fluent.
     
  14. Ilan Voyager
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    Ilan Voyager Senior Member

    Cheers Ken
     

  15. MikeJohns
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    MikeJohns Senior Member

    You are testing unequal sections and will consequently get unequal results which when considered sans structural arrangement are misleading .
    If you wanted to properly compare the materials you would test equal sections then you can compare and evaluate the results scaled by mass if you want. This is simple materials science and is the response of the material to an equivalent extreme fiber stress.

    We design to the intrinsic nature and strength of the chosen material arranged in ways to enhance it’s properties.

    Precisely and we do this with a structural arrangement of the material which works in unison to provide rigidity and strength. It is this arrangement of material that is all important and is not well indicated by your simple strip illustration.
    For example a strip of writing paper in your ‘test’ would simply collapse under its own weight and yet a sheet of writing paper standing on its edge can easily support a brick.

    The stiffness of GRP is very poor and is one of the biggest problems designing with this material within a weight budget, and yes that is why cores are used but then they have their problems too and we have not talked about fabrication and repair costs here either.


    There are many small steel boats that are good strong stiff boats. I think you just are in the wrong geographical area to meet them.

    One example which illustrates the size where steel starts to make sense;

    A very popular steel 34 footer commonly owner built here called a temptress deigned by Bill Bollard in the 70's. It displaces 4 1/2 tonnes with 1 tonne of ballast has a 4mm hull plate. They are a stiff reasonably fast but seaworthy cruiser and a joy to sail. If built well including good access to the hull interior they can be an excellent buy when 25 years old.
    If they have been maintained they will be in much better hull condition than an equivalent GRP vessel, because of issues with GRP due to aging, fatigue and water ingress.
     
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