Crowther Spindrift

Discussion in 'Multihulls' started by waikikin, Oct 18, 2014.

  1. rberrey
    Joined: Oct 2010
    Posts: 593
    Likes: 65, Points: 28, Legacy Rep: 112
    Location: AL gulf coast

    rberrey Senior Member

    Tensile Strength of E glass is 500.000 , S Glass 665,00 , Carbon fiber 470,000 , Compressive Strength , E glass 250,000 , S glass 332,500 , Carbon fiber 338400 , I will skip to cost at the time Ed Horstman wrote this book , E glass 1x , S glass 2x , Carbon 6 to 8x . You still have to have a core , it is not like converting a ply build into a fore core with glass as you would need a NA to convert E glass to S2 glass to get proper scantlings or you would just be wasting your money on S2 glass . Then there is puncture resistance needed in that type boat . The price difference between ply or foam for build material is nothing compared to fit out . If you are going to do away with mat and weave in a build replacing it with tri X or bia X glass then I would say put a layer of S2 glass as a finish layer to serve as some puncture resistance at least on the bottom . Baltic birch form ply might be another option for you where your at , form ply like Finnform , not standard Baltic birch , it has to be made with water proof glue , all edges would have to be sealed .
     
  2. Andrew Rowe
    Joined: May 2024
    Posts: 39
    Likes: 2, Points: 8
    Location: Sunderland UK

    Andrew Rowe Junior Member

    RBerry

    Thank you for your useful information.
    If you were considering a self build 40ft Cat original construction in 12mm ply for hulls & underwing & 9mm ply decks with only 1 layer of 600 woven rovings externally & internally each & the architect has passed away.

    Q; what materials would you use for hulls & deck building to a budget

    Q. If building in marine ply would you use 9mm throughout the boat but with a much more technical & stinger triax lamination schedule

    Q . What lamination schedule for ply for a strong boat ?
    Q would you keep 12mm ply

    some builders have done an 18mm basic foam core build in 1990s but with an old weak lamination method.

    Q: what foam core & lamination schedule would you use for a bit better stronger & lighter boat than ply.

    thanks for time considering

    Andrew
     
  3. rberrey
    Joined: Oct 2010
    Posts: 593
    Likes: 65, Points: 28, Legacy Rep: 112
    Location: AL gulf coast

    rberrey Senior Member

    The designer should have scantlings for either foam or ply . From one of Ed Horstman,s book,s . to convert Cold mold plywood to foam fiberglass construction .
    Cold Mold = cm
    Single fiberglass skin = sfgs
    sfgs , single skins refers to to hulls that are built up of fiberglass lamination,s only , no foam
    A. Ratio 1 cm to .66 sfgs , B. fsgs x 2 = core thickness , C. .7 of sfgs = total fiberglass laminate
    Example . using 2 1/4" plywood skins equaling 1/2" plus the glue and fiberglass hull cover of say 1/16" which gives .25 + .25 + .062 = .0562" of cm .
    1. (A) ratio 1 to .66 or .562 x .66 = .371" sfgs
    2. (B) .371 x 2 = .742 " or 5/8 or 3/4 core thickness
    3 (C) .7 x .371 = .259" total lamination,s thickness
    4 .259 divided into 2 surfaces = .129" thickness of fg laminate per side
    for 4 you might add 105 to outside laminate to compensate for the extra abuse it receives .
    This give,s you a rule of thumb to convert ply to foam , or reverse to convert foam to ply .
    Keep in mind you in general you will need either Biax 45/45 + Biax 0/90 or Trix if you use foam , or a Woven and mat . Even using an extra layer of 45/45 on the bottom with a 6oz S glass finish cloth you should still have a weight savings on a 37' boat if you keep to a 50% epoxy wet out . In the long run a foam build is the way to go for resale , no termites or rot , ect . Price out your materials both ways , foam and ply but don't sub ( downsize ) any material the designer speced , you have to have apples to apples , you cant just say will 9mm be alright , you have to know .
     
  4. rob denney
    Joined: Feb 2005
    Posts: 968
    Likes: 364, Points: 63, Legacy Rep: 436
    Location: Australia

    rob denney Senior Member

    All boats are built with a 'specific strong lamination'. There is no 'smart' way to reduce this using ply. There is with foam: vac bagging or infusion.

    Could be wrong, but I'm pretty sure no one in Aus is building 60' race boats, and if they are, 4mm ply would be a peculiar choice.
    Most boat applications are about stiffness, not strength.
    Stiffness improves with the cube of the thickness, so twice as thick, 8 times as stiff.
    4mmm ply with 1mm of glass each side is 6mm thick, would need a lot of stringers and frames to stop the hulls deflecting.
    For comparison, a 20mm core with 1mm of glass each side (near enough the same strength) would be 22 cubed/8 cubed = 10,648/216 so about 50 times stiffer. 2omm foam with 1 mm of glass each side is roughly what a 60' race cat/40' cruising cat would be built from.
    4mm hardwood (birch) ply is about 2.7 kgs per sq m, 20mm H80 foam, 1.6 kgs per sq m, so it would be less stiff, heavier and (in Aus) more expensive.

    Even with import costs, the foam option is much cheaper (in Aus). It would be interesting to see your comparisons when they are complete.

    Be careful with the plastic honeycomb. If there are any pinholes in the faces, you fill it with epoxy when you infuse or bag it. If you don't infuse or bag it, the scrim soaks up a lot of resin.
    Nomex is 'interesting', do some panel tests first.

    Bitumen coating is good stuff, until you want to stick something to it. I regretted using it when I needed to repair damage.

    Sure, as long as you are not concerned with the weight and the bigger rig, gear and motor required to push it. The ply shell will weigh at least double the foam shell, take longer and require more, and harder work than infused foam. See the weight numbers on Post 40 of the "Which one out of these small multi-hull designs will be the best for my needs?" thread. Add a bit to the foam weights if you infuse with slots instead of mesh.

    Premade panels limit your laminate options and need extra glass on the joins, which then need fairing. Slower (and more expensive) than infusing your own panels.


    Carbon is way stiffer, and uses less resin. The 'goodness' of the epoxy and the 'carefulness' of the construction will be the same.

    The relevant number is specific properties (SG). ie, properties for a given weight. Carbon SG is 1.8, glass 2.5. So increase the carbon strength by 1.4 to get equivalence. Strength is what you need for chainplates, stays, etc. For hulls, it is more about stiffness, see above.

    Kevlar is superior to S glass in terms of puncture resistance, although bouncing a 40' hull on a rocky beach would puncture both. If you are concerned about punctures from floating objects, you would get a better bang for your buck having kick up rudders and boards, protected props and sacrificial bows with strong bulkheads.

    Horstman was (is?) a smart guy, but when he wrote, infusion had not been invented.

    9 and 12mm quality ply don't need 600 glass on each side. Generally speaking, they are plenty strong and stiff enough to have 3 coats of epoxy on the inside and a layer of 200 on the outside, mostly to stop the ply from checking. Whether you use 9 or 12 depends on what support is under it.
     
  5. redreuben
    Joined: Jan 2009
    Posts: 2,073
    Likes: 267, Points: 83, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    If your considering S glass then maybe look at Basalt.
     
  6. oldmulti
    Joined: May 2019
    Posts: 2,929
    Likes: 2,000, Points: 113
    Location: australia

    oldmulti Senior Member

    Andrew. The largest boat I know with a 4 mm skin is a very light 36 footer in NZ but the maximium size of cat running around with 4 mm skins are 28 foot. A 42 foot cat in Canada with 4.8 mm skins fell apart. In the Philippines there are some 60 foot fishing 'tris" (bamboo floats) that have 4 or 6 mm skins but are backed by a 300 x 300 mm frame and stringer matrix, These are boats I would not go to sea in, but are built that way because ply is relatively expensive. Please understand, Rob and others are saying when you design boats above about 25 foot put some science or a lot of experience behind it.

    To give an extreme example. There is a fast catamaran company that builds cats with solid glass bottoms, foam e-glass hull and deck shells, carbon fibre in cross beams and prodders, Aluminium or carbon fibre masts, carbon fibre boards etc. Each component is engineered to suit the size of cat which ranges from 44 to 55 foot. There is no general rule. Old designs were some calculations and experience, now its more calculations. Rob has mentioned panel stiffness which can be obtained by frame support or a degree of curvature with less frame support. The specifics of this is in the calculations and what conditions the boat is going to sail in. A 6000 lbs cat will have a different structure to a 16,000 lbs cat. If you are unsure speak to a designer. They appear expensive up front but are a cheap investment in the long run.
     
  7. Andrew Rowe
    Joined: May 2024
    Posts: 39
    Likes: 2, Points: 8
    Location: Sunderland UK

    Andrew Rowe Junior Member

    Hello Folks you’re all so knowledgeable thanks for all the advice . As some folks have suggested I’ve been doing further research looking at some designs from Kurt Hughes , Tony Grainger , Mike Walker ,Dudley Dix & Wharram . I think foam core fibreglass sandwich is the way to go as glass & resin are more available worldwide and can be kept onboard this allows for a temporary repair if needed at sea until you can make it safely to port. Dix has some fast strong & stiff designs with fully protected internal helm like Gunboat he won’t do a foam core version , & it has to be Okoum ply .I’ve found that there are some new plywoods now eg prem core white birch ply which is also lighter than marine ply which is interesting if it’s fully protected with epoxy. I’m looking again at Hughes & Walker but I’m still undecided . I’m looking for build ability stiff hills shorter build time good deck protection 3 double berths average build cost.

    Andrew
     
  8. C. Dog
    Joined: May 2022
    Posts: 307
    Likes: 105, Points: 43
    Location: Coffs Harbour NSW Australia

    C. Dog Senior Member

    Good luck Andrew, every second spent scratching your head will save many hours and considerable expense down the track. It is also an opportunity to collect peripherals like stoves, pumps and safety gear at good prices before the final panic when you'll pay top quid just to disembark.
     
  9. redreuben
    Joined: Jan 2009
    Posts: 2,073
    Likes: 267, Points: 83, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    Look at Richard Woods, by Walker do you mean Waller ?
     
  10. redreuben
    Joined: Jan 2009
    Posts: 2,073
    Likes: 267, Points: 83, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    All this talk about ply v foam seems to have missed a few things.
    Tooling and skills.
    Now I grant you a foam carbon boat is a better boat, skip the carbon and maybe even same price or cheaper. But can you build it under a lean too with a jigsaw and a squeegee ? No vacuum pumps bleeder cloth tubes and bags and a skip to put it all in. For many people that has zero appeal.
     
  11. rob denney
    Joined: Feb 2005
    Posts: 968
    Likes: 364, Points: 63, Legacy Rep: 436
    Location: Australia

    rob denney Senior Member

    Certainly can. I taught a class last year of Fijian rural youths who barely knew what a sail boat was, much less fibreglass or epoxy. They built an 8m f'glass/40% bio epoxy/recycled PET foam mini cargo proa in 6 weeks, in a covered 7m x 3m space which was totally exposed on 2 sides. It has carbon beams, mast, booms and leeboard. A light laminate doesn't make much sense for infusion unless you have allergy problems or are building a race boat.

    A few years ago, I did the same exercise with some highly (not in epoxy) skilled Marshallese boat builders in a mostly enclosed shed. This boat was ply, stringers and wooden beams. Took 5 weeks, but we didn't have to build the rig.

    The former required scissors, utility knife and a hot melt glue gun, ended up a bit more than half the weight. The latter had every hand power tool known to man, and we used most of them.
    We used the same foam/scissors/utility knife technique to build a 6m solar/electric water taxi (in an extended shed), ended up having to do a little sanding where the peel ply died in the sun.

    These are simple boats (no strongbacks, temporary frames, the levelling and fairing is automatic), but the more complex they get, the more work ply requires. Fairing and planing keels and stringers is hard work, as is scarfing. Butt blocks have their own problems, we used both.

    The simplicity is probably a better takeaway than the method. You don't need to build complex boats for cruising.

    The foam boat has only been sailed a couple of times (waiting for safety authorities permission and a launching ramp), but has been used as a tool bench while they concreted the ramp, bed for 3 big Fijians, seat for 20 big Fijians and been dragged around on the concrete. No damage, but if there was, there is no rush to fix it. The ply boat was inspected after 12 months and no problems (careful epoxying and no damage). The second one they built had a rotten section in a sealed section (small leak), would not have been obvious until the hole appeared.

    Rightly so, although once they try it on a big boat with flat panels, they are usually smitten.
    It is a different feeling to putting a wooden boat together. Although getting a cnc machine to cut the panels while you get suited up to epoxy and fair it seems a bit arse about face to me.
    Arguably, a boat that uses twice as much epoxy as one that uses several metres of plastic sheet is arguably doing more potential environmental damage. Plus, the phenolic resin holding ply together is far more toxic than epoxy and much more likely to end up in the environment than land fill plastic.
    I'm not happy about either. We are waiting for the equipment to arrive that will allow us to recycle all the plastic, glass offcuts, floor sweepings, epoxy pots, etc into useful products. Exciting times.

    The yellow boat in the video and at Waan Aelõñ in Majel (Canoes of the Marshall Islands) | Majuro https://www.facebook.com/wam.rmi (see Majol Games pics for an amusing bunch of pics) is the ply one in the Marshalls. The white one is the foam boat, the wreck is one of the ply boats built in Fiji for the Amazon Challenge, one year after it was completely refurbished and re epoxied.
     

    Attached Files:

    guzzis3 likes this.
  12. redreuben
    Joined: Jan 2009
    Posts: 2,073
    Likes: 267, Points: 83, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    Yeah Rob, but you’ve been a professional builder for how long ?
    Not first time builder working alone and starting from scratch staring at a set of plans.
    Get real.
     
  13. rob denney
    Joined: Feb 2005
    Posts: 968
    Likes: 364, Points: 63, Legacy Rep: 436
    Location: Australia

    rob denney Senior Member

    Building for 55 years, but 'professional' implies standards which I am nowhere near.
    Simple boat shapes are easier to build than non simple shapes and make far more difference than the materials used. Simple foam/glass without vac bag or infusion is within the scope of anyone who can read, use scissors and a ultility knife. By the time the first time ply builder has figured out scarphing, the foam builder has his hulls built.

    Infusion for a beginner is the same as anything new. Start small, do tests, ask questions. Enhanced for Harryproa plans with an exceptional set of drawings (not by me) and very detailed instructions, including the learning and test processes. It's easier to learn than your average handyman setting up frames on a strongback and shaping stringers with a power or hand plane. Safer, too. The vast majority of Harryproa builders are 'first timers, working alone and starting from scratch'.

    Non simple non infused foam boats are different. You need a similar high tolerance for tricky, sticky and physical work as you do for a non simple ply boat.

    'Real' is a bunch of Fijian village women building their own boat in 4 days under my supervision, then one of them (a subsistence farmer) building her own, then running a workshop for 9 other women, then getting sufficient teacher training to be employed to teach a Certificate 3 boat building course. All while being Mum to 6 kids and having a 2 hour walk and bus ride each way to get here. https://static1.squarespace.com/sta...a64c351e6e5e85/1708440491669/CPPBB Aug 23.pdf

    The ply mini cargo proa in the Marshalls doing some load testing.
    image1-2.jpeg
     
    oldmulti likes this.
  14. redreuben
    Joined: Jan 2009
    Posts: 2,073
    Likes: 267, Points: 83, Legacy Rep: 349
    Location: South Lake Western Australia

    redreuben redreuben

    And again your the supervisor. look at Richard Woods clients most but not all choose the simplest hull, dory or chine and the simplest method for them, ply.
    you don’t have to convince me foam or a vacuum is better
    I know it is.
    But many home builders want simple and something they have confidence taking on, like it or lump it that is usually plywood.
     

  15. rob denney
    Joined: Feb 2005
    Posts: 968
    Likes: 364, Points: 63, Legacy Rep: 436
    Location: Australia

    rob denney Senior Member

    The reason I post on forums is to change perceptions. It's why I appreciate people like you pointing stuff like this out. Thanks.
    4 days of supervision is less than they would have required to build a ply boat.
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.