Steel hull closed cell foam insulation question...

Discussion in 'Materials' started by parkland, Apr 9, 2013.

  1. parkland
    Joined: Jul 2012
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    parkland Senior Member

    Yes I suppose the grease is a bad idea.
    It seemed like a good idea at 1st though, honestly, haha.

    I looked at the pontoon option a while ago.
    First problem, you can't use an old deck boat, they don't have much weight capacity.
    OK, so go buy brand new bigger pontoons... /a pair of 40 ft 36" diameter pontoons is only around 10,000$.
    Oh oh, take 24" for trailer tires, 36" of pontoons, and you're not pulling that anywhere, plus it will be crazy top heavy...
    3x24" pontoons? way too much drag at low speeds.


    A steel hull seems like my best option, just keep reading, make sure it's got lots of the proper coatings and paints. I'll just have to find a way to insulate without putting anything against the steel skin.

    I also wanted to use a diesel inboard engine, and a full displacement hull.
     
  2. pdwiley
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    pdwiley Senior Member

    I haven't looked but it can't be hard to find a design that meets your requirements, surely. If it is impossible, given the range of designs out there, I'd start wondering if your requirements made sense....

    Anyway if you want to trailer it, I'd go aluminium despite the welding issues, and pay someone to weld up the bare hull. In a former life I had 2 different 9m aluminium powered work boats, they worked very well and took a lot of abuse.

    I can buy the right to build and a flat pack of CNC routed aluminium for a work barge 15m x 4.5m with a draft of ~600mm for $54K locally. Welding it together is like assembling a big jigsaw according to the local boat builder who made one. I've seen it and it's on my short list as a floating liveaboard barge when I get tired of dealing with local govt.....

    PDW
     
  3. parkland
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    parkland Senior Member


    I have several things working against me...

    Living in the prairies, anything boat related is scarce, except for little lund boats and fiberglass cruisers with v8 gas engines. Aluminum, aluminum supplies, and aluminum experts, are scarce. I had ads up last year, to hire an aluminum welder for a project, and out of 3 responses, all 3 were at least an hour away, 2 were kids just looking for easy money with no experience, and 1 was a guy who had experience welding metal car parts etc, but nothing marine oriented at all.

    I contacted a few aluminum shops about building the entire hull at they're place, and the prices were not something I was ready to pay. 10,000$ design fee, even if I brought designs and blue prints. Basically they charge they workers out at 200-300$/ hour, and pay the guys about 14-20$ and hour. I could understand if a design need a lot of custom parts and design help, but for a rather simple boat it doesn't make much sense to me.

    Compare that to steel, I can weld steel, a local guy welds for 20$/ hour, another guys welds for 35$/ hour, tools are cheap and plentiful for working with steel. If I could weld aluminum myself, I would. I'm sure I could learn to weld aluminum, but I don't think newbie aluminum welds are a great idea for a boat, when failure could lead to death.

    I think my requirements make sense, all I want is the biggest possible boat that I can tow with my truck.
    8.5 feet wide or less, 40 feet long or less, and 13 feet tall or less, sitting on the trailer.
    Other requirements are a small diesel engine, large cabin, stable, strong.

    My truck is rated to tow about 14,000 lbs.
    By my calculations so far, the hull would weigh almost 8000 lbs, with 1/8" steel skin, and 1/8" x 4" ribs every 18" and stringers every 18". And thats with 48" high sides. Not a light boat by any means, but not a deal breaker.

    The engine and transmission and prop shaft assembly would tag about another 1000 lbs, and the cabin and everything else would weigh another 3000 lbs, bringing the total to about 12,000 lbs. Simple trailers are only a couple thousand pounds, so finished weight down the highway should be very close to rated for the truck.
    People tow a lot more than that with these trucks, just illegally, but nobody really cares for a personal vehicle what the weight is.
    Although it would be nice to know that empty dry weight could be under the rated trailer towing weight, just in case.

    I wish I could reliably build an aluminum boat, but I lack the skill.
    I wish I could reliably build a fiberglass boat, but I lack the knowledge.
    I also wish I was a millionaire, so I could just pay to get one built.

    I only make a hundred and some thousand a year, don't get the wrong idea guys, I hope to make it as nice and good as I can, but she ain't gonna be a yacht.
     
  4. jonr
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    jonr Senior Member

    For me, TIG welding aluminum took more practice and instruction, but the difference from steel isn't that great. I expect that MIG is even more so.
     
  5. parkland
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    parkland Senior Member

    How much practice did it take till you could do reliable welds, and are you confident in you're ability?
    I don't ask in a doubting way, but I'm scared of trusting welds that I do if I'm not sure. Would you put yourself and friends and family in a boat you welded, or do you consider it more of a passing hobby skill rather than a full out ability?
     
  6. pdwiley
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    pdwiley Senior Member

    Ummm.

    You want to get a big trailerable boat.

    Just *why* do you need to get the hull done locally, if there's nobody experienced in boat building to do it?

    Go where boats are built from aluminium and tow the damn thing home when the hull is done. But FIRST you need to have a design.

    FWIW my 9m aluminium work boats displaced ~6 tonnes with twin Steyr 225HP turbo diesels. No fitout to speak of, they were workboats.

    FWIW(2) 3mm steel for the hull is going to distort like crazy unless you're very careful and your technique is good. 3mm thick frames and stringers is way, way too thin. Think 5mm minimum for framing. I have never seen a boat from any designer using 3mm framing.

    And don't even think of using angle iron. You will never be able to maintain behind the leg.

    Personally I'd take option 1 above - go to where boats are built - or I'd take myself off to a college of some sort and learn to MIG weld aluminium then practice on scrap in all positions until I was happy with my technique. It's not all that hard but you do need to do it correctly. I used to just get one of my staff to do aluminium, that was simpler :) Now I've got a 250 amp MIG I'm thinking of having a go myself.

    I would take people to sea on the boat I'm building, incidentally. I'm pretty sure it's going to float......

    PDW
     
  7. jonr
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    jonr Senior Member

    For me, say 15 more hours to learn aluminum welds that I trust as much as my steel welds. How safe is a non professionally welded boat (steel or aluminum)? - that's not something that I've looked into.
     
  8. Titirangi

    Titirangi Previous Member

    Parkland
    Would you consider building your hull(s) with 12mm treated marine grade plywood.
    Its easy to build with, doesn't require a huge amount of boat building skill and no hi tech equipment, no big power bills, big hammers and upset neighbours.
    Depending on the hull shape you can use sheet or strip, single, double or triple layer (diagonal strip plank).
    Sheath the hull with a layer of Corecell and you have a hull that will outlast steel, is as robust as steel or aluminium, requires no insulation and build time is relatively quick.

    Again depending on design you can either build outside in using jig formers to form the hull or set up plywood or router cut aluminium frames then sheet over.

    In NZ there are still launches, fishing boat and the navy's Commodores barge in use after 50yrs and these were built with the early epoxy resins and only a few of these were even sheathed - woven glass. US & UK WW11 PT boats & mine sweepers are a good example of the method using fairly primitive materials by todays standards.
     
  9. pdwiley
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    pdwiley Senior Member

    We've had this claim over and over again and it was crap the first time and it's still utter crap.

    Unless you have a really perverse and self-serving definition of 'robust', sheathed marine grade ply is not even close to being as robust as steel and if you seriously think it is, I've 2 simple tests for you.

    1. Tie both boats up to a nice rough piling with a fair sort of a lop running and see which one gets a hole rubbed in it first.

    2. Try a beam-on crash derby. I'll bet on which boat is still going to be floating.

    Lots of advantages of sheathed ply over steel, for sure, but 'robust' is NOT one of them.

    Let me see, ultimate test of robustness in a boat, what do they build ice breakers from...... ?

    PDW
     
  10. Titirangi

    Titirangi Previous Member

    I disagree with your assessment, based on the first work boats I owned & used in commercial operations and others that after 50yrs are still in use around NZ doing exactly the same work that a steel or alu hull does.

    While not as resistant to damage as steel epoxy carvel planked or plywood hull sheathed with Corecell is no more prone to damage than an aluminium or GRP yacht or ferry hull if tied up in the wrong spot. The sheathed plywood can take a hit a lot better than a GRP hull struck on the beam by another vessel and repairs are not as complicated, that qualifies as robust in my book.

    So where is the disadvantages of building a recreational hull with a proven material that doesn't require professional skills, expensive or complex moulds or hi tech equipment.
     
  11. pdwiley
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    pdwiley Senior Member

    Your statement was "is as robust as steel or aluminium" which you now agree is incorrect. A ply/Corecell hull is nowhere near as robust as a steel hull.

    That was my point.

    I am not saying or implying that such a hull isn't fit for purpose or a good choice. I just strongly dislike people making claims that are known, and very well known at that, to be false.

    PDW
     
  12. Titirangi

    Titirangi Previous Member

    I stand by my original statement on the reference - robust and do not agree that it is incorrect.
    The term robust is a relative term, and takes into consideration the scope of the comparative requirements.
    In this case it relates to the plywood hull being of robust quality equal to doing the job a hull capable of handling the same sea states as a recreational steel or aluminium hull of the same design & purpose, with inboard engines and passenger carrying ability.

    If the vessel in question was a 300000ton bulk carrier, container ship, aircraft carrier, cable layer, ice breaker, offshore platform supply vessel, ballistic proof etc the plywood hull would not be as robust.

    Using your analogy as a measure we should be building our tenders in 5mm steel plate
     
  13. pdwiley
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    pdwiley Senior Member

    Your statement was "is as robust as steel or aluminium" which you now agree is incorrect. A ply/Corecell hull is nowhere near as robust as a steel hull - even in the small pleasure craft sizes that Parkland is talking about so your attempt to drag in bigger vessels is irrelevant.

    You are just arguing and goal-shifting now to try and save face. The fact is, what you said was incorrect, you know it and everyone else knows it as well. Give it up. Do it gracefully. You get more respect for being able to admit error than trying to be right when you're not.

    I am not going to respond to you on this topic further as you're rapidly shaping up as the type who insists on being right come hell or high water and will keep arguing forever just to have the last word. Well, feel free to do so but that doesn't make you right.

    PDW
     
  14. Titirangi

    Titirangi Previous Member

    Parkland; I can put your in touch with several very experienced ANZ boat builders if you want expert advice about using Corecell sheathed marine plywood for your hull as a viable alternative to steel.

    FYI: greased packing between layers of steel has a high risk of explosion if heated to a red heat through welding or oxy/gas cutting. Two men were killed in a shipyard incident when a turrent they were cutting free of the deck exploded, the cause was a build up of grease inside the turntable housing.
     

  15. parkland
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    parkland Senior Member

    You are right, with enough heat, grease could become very flammable.

    I think I'm not going to use wood, just because really I can't get marine plywood here for a reasonable cost, and also I don't think it would be even close to as forgiving as steel when it comes to accidentally hitting a rock or something.

    I think that wood is "structurally" strong, but really the material itself is almost a foam (really low density compared to steel, and less flexible), you could easily destroy a wood boat with a sledge hammer and an axe, meanwhile a steel boat could probably have some dents, from the same infliction.
    There are lots of strong wood boats, but I don't think they're as strong as steel, not even close.

    IMHO wood is good for houses where they provide cheap structural support, and don't need to really take impacts.
     
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