Trying to learn about composite construction, a hypothetical build

Discussion in 'Fiberglass and Composite Boat Building' started by Smokeyr67, Sep 7, 2020.

  1. Smokeyr67
    Joined: Sep 2020
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    Smokeyr67 Junior Member

    Hi everyone,
    First of all I'd like to reinforce that I'm not going to go out and build a 50 ft go fast boat on the strength of this thread, I'm just trying to learn about composites and specifically how they can be used in boat building.

    My experience with boat building is limited, I've made a few wooden boats, helped building a concrete yacht, but other than that - nothing.

    I've build car parts and RC aircraft using glass and carbon, I've vac bagged it but never done any infusing.
    I'm not an Engineer, nor a Naval Architect and I won't pretend to be knowledgeable on the subject, I'm here to learn so feel free to tell me that I'm wrong:)

    O.K. on to the hypothetical money no object dream boat...

    Lets say I'd like to build a 20ft mono hull power boat, and I'd like it to be as light and strong as possible. I've got some plans, I've built the buck and then the mould, here's what I think would be a good layup;
    1. Gel coat
    2. Fiberglass woven cloth (full hull)
    3. Aramid tape along the keel for impact resistance
    4. Bidirectional carbon cloth for strength and rigidity (laid north to south)
    5. Unidirectional carbon tape along keel and as laterally as ribs (to support bulkheads)
    6. Core material (foam)
    7. Bi directional carbon cloth (laid east to west)
    8. Fiberglass woven cloth.
    Reinforcement in high stress areas (maybe aramid?)

    After that had cured I'd add the bulkheads;

    foam core, carbon bi directional cloth, fiberglass cloth over the top.


    From what I've just typed I'm sure that you can see that I have no idea, so please educate me, tell me where I'm wrong and why, I won't take offence:)

    Shane
     
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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Isn't it wonderful how a mountain of work can be covered by just one sentence ! :) As in, "I've got some plans, I've built the buck and then the mould " It reminds me of the instructions in workshop manuals for an engine. "Step 1. Remove the Disconbobulator assembly " ( I made that name up). Six hours later, thanks to seized fasteners and impossible-to-detach-without-specialist tools, you wonder why you started ! You don't want to get that feeling x 100 with a boat ! It is well recognized that GRP, especially female moulded GRP, is a terribly long-winded and expensive way to build a one-off boat such as you allude to. It is really only applicable to series production, on a commercial basis, where the high cost in terms of $ and hours spent, is defrayed over a large number of boats. I guess the creative impulse can lead us into these somewhat impractical exercises, my suggestion would be to first design the boat, if it is really the design aspect that intrigues you, and show it to a few people, to get some feedback on any possible flaws, before proceeding. If you aren't really interested in design, you are better to rejuvenate an old, proven design GRP boat and get into the dust and sticky goo of working with GRP that way. There are many dreamers in the boating world, and I like dreamers, but tempered by a modicum of practicality. Really, if looking to make a novel boat, you should make an actual boat as the plug, and test it out as a functional thing, not just as the dummy for a mould. That would probably be made of wood/veneer/plywood.
     
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  3. Smokeyr67
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    Smokeyr67 Junior Member

    Mr Efficiency,

    As I thought that I'd made clear in my OP, I have no intention of constructing bathtub let alone a boat, I just want to learn about the use of composites (glass, carbon, aramid etc) in boat hull construction.

    I'm just a curious person, I haven't even owned a fibreglass hull in decades, I prefer my boats made from metal, but when I browse websites such as Grady White, Viking and Boston Whaler they all call their hulls composite, not glass, so that piqued my interest.

    I'm sorry if you got the wrong idea, but this is a purely hypothetical discussion, just for my education, to satisfy my thirst for knowledge. I've read a lot on the net, watched a hell of a lot of youtube video's on the subject (watching a craftsman construct a mould or lay down some pre preg is hypnotic :) ) but I thought that a forum such as this would be a great place to ask knowledgeable people to help me understand the uses and limitations of composite materials with regard to hull construction. I tend to learn best (apart from hands on) in a discussion forum where I throw out my ideas and have them shot down and explained to me why I'm wrong.

    To reiterate, I'm seeking knowledge for knowledges sake, I may take away some ideas for my next RC plane build but I'll be buggered if I want to spend months getting glass rash and epoxy snot while I build a boat that will probably break in half the first time it's launched!

    Shane
     
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  4. Mr Efficiency
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    Mr Efficiency Senior Member

    You certainly fooled me, I could have sworn you wanted to build a boat, by what I read. Simply put, plain old GRP is a composite, of glass, and resin, not a homogenous material like metal. That is basically what is conveyed by "composite". Whilst people like to think they have the latest "hi-tech" materials and methods going into their boat, at the practical level it may not even be desirable to have the boat, as you put it, " be as light and strong as possible". With planing boats, light=low inertia=high accelerations=this isn't much fun. Sufficiently strong is good enough, and being light can be a handicap in terms of both comfort underway, and at rest, it obliges the designer to limit the deadrise angle, so the boat does not flop around too much at rest, and a combination of light weight, and low deadrise, can create a punishing ride in choppy water. Going the expensive exotics route in reinforced plastic is more a specialty thing. You mention "cloth", which has little place in lamination schedules, being an inefficient way to build laminate thickness, and also lacking inter-laminar cohesion in some cases. It might also create "print-though", if directly against that gel coat.
     
  5. Smokeyr67
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    Smokeyr67 Junior Member

    "Hi everyone,
    First of all I'd like to reinforce that I'm not going to go out and build a 50 ft go fast boat on the strength of this thread, I'm just trying to learn about composites and specifically how they can be used in boat building."

    "O.K. on to the hypothetical money no object dream boat..."

    Sorry, I though that the thread title and the sentences I've quoted would have made it clear that I'm not planning on building just learning. I may have been able to make it clearer, I'm just not sure how.
     
  6. Rumars
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    Rumars Senior Member

    Just in hypothetical manner then (in reality the plans specify the layup):
    Gelcoat, print blocker, diverse layers of reinforcement arranged to take the loads, core, reinforcement layers.
    The print blocker can be a skim coat (CSM) or barrier coat (sprayed). If you want to use carbon then vinylester resin is recommended. There are some gelcoats formulated for epoxy so that could also be an option, but epoxy boats are more often painted.
    Bottom core selection would be critical for a planing powerboat. The core must work with the reinforcement to resist delamination from slamming loads.
     
  7. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Shane,

    Welcome to the Forum and all it's quirkiness.

    I believe I get what you're after.
    I think you worded it fine.

    Build a boat from a proven design and you'll learn more than we could ever teach you here.
    You've got a good start and, what appears, a good attitude.
    You should have no problem.
    But don't go too large on your first build.
    I tiny speedboat may be fun and not too expensive.
     
  8. Smokeyr67
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    Smokeyr67 Junior Member

    Thanks Rumars, whilst I don't necessarily understand all the terms you've used, it gives me something to google :)

    I've not really thought about the interaction between the reinforcing material and the core before, I've only ever built foam cored wings for model aircraft, and to be honest you can do that with a lot of TLAR style engineering.
     
  9. gonzo
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    gonzo Senior Member

    If you want as light as possible, delete the fiberglass and stay with carbon fiber and aramid. Further, the resin should be some type of epoxy. As far a layup schedule, you don't have close to enough information to design it. You need to calculate the stresses on the skins and structural members to get that.
     
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  10. jehardiman
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    jehardiman Senior Member

    Yep, you need to start with the loads to determine the layup...unless you just want to make it bullet-proof, but of course that does not guarantee it will be suitable for a boat.

    Edit to add...really see Tsai's book on Composites Design
     
  11. Rumars
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    Rumars Senior Member

    Unidirectional fabrics, especially the heavier grades, do not make a good surface finish, so unless you want the surface to look ribbed like corduroy, you need something between the gelcoat and the fabric. This is traditionally one or several layers of chopped strand mat (CSM) hand laminated into the mold on top of the gelcoat. This is called a skim coat, and you can then continue to hand laminate or infuse over it. To speed up production there are now barrier coats, wich look like a sprayable filler, you spray them on top of the gelcoat, then laminate or infuse.
    At the reinforcement-foam interface you have a somewhat similar problem, maximising the contact area between the uni fibers and rough foam, so to improve adhesion again CSM is used. Another technique is to use a structural putty to glue the foam to the laminate.
    Core selection is important, the skin needs to stay attached to the core under load. Not all foams will work with any thickness of carbon skins. Glass/foam is typically a good match, as is wood/carbon. High end boats use a patchwork of cores with different properties (weight, elongation, etc.) to get the best result. It is as important as tayloring the reinforcement (weight and orientation) to properly take and distribute the loads.
     
  12. Smokeyr67
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    Smokeyr67 Junior Member

    Hi BlueBell,

    I just want to learn about stuff, I'm old, retired and curious.

    If I where to build anything boaty, it would be an RC boat, but that would be a totally different construction (just a big roll of fiberglass, some kevlar to make it pretty, no carbon because that can annoy the reciever)

    I understand that I'm never going to learn all the intricacies of composite hull construction, but every little bit helps to keep my mind ticking over.

    One question that comes to mind regarding carbon fibre is electrical conductivity.

    Is static electricity an issue when laying up carbon cloth? How do you insulate any electrical fittings ? Is a boat made with a high carbon content more susceptible to lightning strike? These are the issues that keep me awake at night :)

    I'd just like to begin with a rough idea of where various materials would be used in a "cutting edge" hull, what are their real world strengths and weaknesses and how they interact with each other. I understand a bit about CF, it's strengths and weaknesses, kevlar is a bit of a mystery (its strong, tough but degrades in the sun) and fibreglass - its easy, it's strongish, flexibleish, it makes your arms itchy.

    Shane
     
  13. Smokeyr67
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    Smokeyr67 Junior Member


    Bullet proof would be great, but yeah it might not be the best thing in a short sharp chop. As for loads, perhaps I need to refine my hypo boat...

    I've found the book you referred to, thanks very much for that!
     
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  14. jehardiman
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    jehardiman Senior Member

    Yeah, "bullet proof" is not what you want. Ballistic composites are designed to fracture between layers to absorb the energy of the projectile. A "bullet proof" hull would become limp very quickly...but it is an easy layup to specify...
     

  15. BlueBell
    Joined: May 2017
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    BlueBell Ahhhhh...

    Hi Shane,

    You can Google exotic, expensive boat building materials.
    Carbon Fiber, titanium, etc will likely pop up.

    Epoxy with fiber is one of the best compromise materials I know of.
    Even makes great R/C boats when applied over shaped foam.
    The foam can then be chemically dissolved for weight saving.

    By "bullet proof" did you mean tough or literally bullet proof?
    "Bomb proof" may be another term for describing toughness.

    Boat building is more about engineering and matching and balancing
    budgets, material and design around stress points, loads, and more.

    Build the R/C boat and have fun!
     
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