Beams from ally or douglas fir

Discussion in 'Boat Design' started by Vantage475T, Jan 17, 2018.

  1. Vantage475T
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    Vantage475T Vantage475T

    Hi,

    I am starting the next stage of my ISOmaran project shortly (finally) having had a nightmare 12 months with work and health.
    The basic outline is a kind of a stretched Weta I guess:
    4.75m long with 3.8m beam.
    Main hull about 1 metre at its widest.
    Floats will be 4.25m with bouyancy in the order of 400kg - quite sizeable - and very different from the Weta in that respect.
    ISO dinghy sailplan so 14.5m2 main and jib with 18m2 assy.

    I'm aiming for single handed use mainly and the ability to fold using a sort of farrier type system.

    I weigh about 80kg but there will be the occasional extra person ranging from 60kg to 105kg (fat brother) hence wanting something a bit bigger than the Weta but still easy to handle on shore by one person.

    On my test rig I used 70mm round ally x 16swg which weighs around 1.09kg per metre. I snapped those beams off at the deck joint when we took off over a wave at high speed. It was badly fitted (rattling in the socket) and not unexpected (the hole drilled through for the holding bolt was obviously weakening it and too near the deck edge) and it was quite amusing when it broke with a pistol shot sound effect.....

    Anyway, looking at what I am now planning and learning from that project, I am comparing beams and trying to get an idea of what to use.

    If I use 70mm as a guideline - making it from the original ally the tramp frames will come in at around 16.5kg total or using douglas fir laminated 75mm x 75mm hollow centre 25mm wall comes in at twice that.

    I will have to go up a thickness for the ally I think to 10swg so the weight would be comparable. I can go bigger radius and keep thinner wall no problem 100mm 16swg for example or 100mm 10swg but the weight is really going to mount up

    A couple of questions if I could:
    How can I estimate and compare the stiffness of the different beams? Any figures around for laminated douglas fir? How it is made from laminations etc will ahve a big effect and I would also glass wrap it as much as needed. Would laminating thinner strips just add weight and no more strength? ie I could use multiple 6mm or much more simply 25mm thick. I sued 8 layers of 6mm when I made the beams for my Sport Tandem outrigger but the floats on that give about 50kg of bouyancy. The beams are incredibly strong - not tested to destruction but can take some punishment for sure.

    Would it be worth using douglas fir for the top and bottom (edge to edge ie 75mmx25mm) for example then something lighter like cedar for the sides ie 25mmx25mm. I could upgrade this size if needed no problem. Would that reduce teh strength too much for a trivial saving?

    If I stick with the ally I could look at a dolphon striker support underneath to keep the weight down BUT it will get in the way of the folding I think.

    Can anyone give me an idea of beams they have used / made on anything remotely similar? I can make and break them it's not a big deal but seeing if I am in the right ball park will be very helpful.

    I'm hoping to get an all up weight in the region of 150kg if possible.

    Main thing now is to try and get the diameter sorted at least so I can get the mountings planned in the main hull.

    I don't think I have the skills for carbon etc and this is also still a tester so no point throwing money at it.

    I will make them from wood initially anyway jsut to get dimensions sorted as doing the ally and welding it up does cost - get it wrong and you can't really change it...

    Any thoughts/advice gratefully received.
     
    Last edited: Jan 17, 2018
  2. JosephT
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    JosephT Senior Member

    A lot of scattered information here. It would help if you could provide the following:

    1. Plan view or sketch of your proposed boat with noted dimensions (top view, profile, sail plan if using a sail).
    2. Be sure to note the materials.

    You mention the use of Douglas Fir for a ferrier (collapsible outrigger for trailering). The Douglas Fir is is a heavier wood and is typically used on larger boats/yachts. Western Red Cedar is a better choice for a lighter boat. From the craft you describe you may be better off ordering a kit boat. The Trika 540 might be something you want to look at. You can row it or sail it. Order the plans or the complete pre-cut kit...will save you a lot of time.

    Trimaran Kit with Folding Akas http://www.clcboats.com/shop/boats/other-designs/trika-540/Trika-540-Trimaran-Kit.html

    The W17 is a nice boat too...sailing with higher freeboard for taking on bigger wind & waves (fun!).

    W17 Trimaran Sailboat Kit by SmallTrimaranDesign.com http://www.clcboats.com/shop/boats/other-designs/w17-trimaran/W17-Trimaran-Kit.html

    The CLC boats are very popular internationally and there are other plans out there too.
     
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  3. Vantage475T
    Joined: Aug 2016
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    Vantage475T Vantage475T

    Hi,

    Thanks for the reply. Yes all a bit scattered.

    I've previously built a CLC Sport Tandem outrigger which I heavily modified with trampolines (crappy picture attached) and a furling jib and can't really see a plan boat that covers what I want. it also ahsa various mast and sail options depending on conditions - twin sailboard masts and sails is quite amusing.

    Stitch and glue worked well on this and it is very easy so planning on the same again. The test float for the ISO took two weekends to make and has taken a beating so sturdy things can be built quickly and cheaply it seems.

    The farrier type folding mechanism will be stainless steel.

    Weta way too expensive I think and very few about it seems

    W17 is just a bit too large - I have very tight access at home and can just get my ISO in and out but with an inch to spare and getting the W17 in and out at 2.2m wide will never happen and up the ramp where I sail might be painful as it weighs about 190kg? I do like this though.

    Trika 540 effectively quite similar to my Tandem Sport outrigger I think with roughly the same sail area so no real upgrade and I like the extra speed - although doing 10+ knots with your backside below water level feels quite fast.

    I was interested in the CLC Outrigger Junior but there are still no plans available - it is something different that I think would be fun.

    I've attached the outline of the proposed hull shapes which will change and be refined some but basically this sort of thing.

    The test bed ISOmaran can be found here
    Small Trimaran https://www.youtube.com/channel/UC3evMZcrGGGCWwonCBHOuHQ
    and is part of the Sport Tandem image as well.

    There are a couple of videos of the ISOMaran, the kaymaran and my electric boat mover which would help move a W17 but nowhere to keep it....

    The ISO is quite heavy and this had the simplest (way too) flat bottomed outrigger hull and a load of botched on aluminium framework. It is a great laugh, single trapeze old skiff which is very tippy normally, but the outrigger (which had the vertical struts a little bit too long as well) kept it very vertical and it generated stupid power and would just scud along.

    I'll be using this rig again as part of this learning process as it cost almost nothing and I have plenty of spares.

    I quite often have movement and hand/neck/back issues so something with plenty of stability in case things go **** up while out is very handy as I can get "stuck".

    However I do want something that goes a bit - the ISO had registered just over 20 knots peak speed when it went bang which was great fun.

    In the interim I have a Spitfire catamaran that I sail with my wife that is fab and really moves, but I also want something I can sail single handed and do some more longer trips on - the Spitfire is fab but not really a cruiser and single handed would be a nightmare I think both on land and sailing.

    So a slightly bigger Weta for thrashing (but a bit smaller than the ISO), that I don't mind breaking (but hopefully won't), some storage/space/stability and a learning tool.

    I just like dicking about in the garage essentially.
     

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  4. Vantage475T
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    Vantage475T Vantage475T

    If anyone has Weta hull dimensions and can slightly stretch it would be great!
     
  5. JosephT
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    JosephT Senior Member

  6. fallguy
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    fallguy Senior Member

    I have never heard a designer spec WRC for beams. The post got sort of overwhelming. Don’t you first need to know the loading; then design the beam. Seems the carts leading the horse here.
     
  7. fallguy
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    fallguy Senior Member

    Richard is rather busy, but perhaps he might coin in. I will let him know he was mentioned here if the op desires.
     
  8. JosephT
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    JosephT Senior Member

    Looks to be a problem during the construction phase to me. Vantage475 stated:

    "It was badly fitted (rattling in the socket) and not unexpected (the hole drilled through for the holding bolt was obviously weakening it and too near the deck edge) and it was quite amusing when it broke...."

    Most beams are fitted into a very solid, well reinforced pocket that distributes the load. Older wooden Polynesian style sailing craft use rope lashings to fasten the beam (aka) to the hull & ama (float). Today's modern big OC6 canoes with outriggers/amas still use lashings. The lashings are very strong and absorb & transmit the load nicely. It's pretty rare for them to snap unless the ropes are rotted out or have weakened fibers from UV damage.

    It goes without saying these joints are among the most important so they should be built from a good specification. No shortcuts allowed.
     
  9. Vantage475T
    Joined: Aug 2016
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    Vantage475T Vantage475T

    Thanks for the responses so far.

    Essentially I am trying to get an approximation of what is likely to be "about right" or in the "right ballpark" eg what is the beam specs on a Weta, or an Astus 16.5 or a Pulse 600? Very different boats and a big range I am aware. I can fabricate it from wood or weld up aluminium so I am open to anything.

    Sorry this will be another long post trying to give some background and vague thought processes here.

    The point of the test rig was getting an idea of where things would go, approximate dimensions and how it would roughly fit together. It was never intended to be a fully working rig but as it happened we had lots of really great sailing with it and had a huge amount of fun. All from the base of a boat with two trailers, spare new mast and multiple sets of sails some of which are unused so I can tool around to my hearts content with little cost.

    Anyway, I was trying for example to see a lot of basic things in no particular order:
    • how much space we wanted/needed on the trampolines
    • sorting out location and fitting of the hiking straps
    • making and sewing up my first trampolines - they worked really well but I have learned what I would change with how to make it and attach it
    • how the outboard mounting would work and where to place it exactly on something that was never intended to have an outboard
    • how that interacted with the rudder position and did it catch the boom/main sheet when raised - yes until I moved it around
    • how to store the outboard when not in use and how easy to deploy it - want an option to get back if I have a physical problem while out and can't sail
    • trying out an electric trolling motor - pro#s and cons. it moved the boat ok but power doesn't last long enough
    • what beam overall was likely wanted/needed for comfort and storage and practicality - see below ref our narrow launching ramp
    • some rough feel for the buoyancy provided by the float in relation to the power generated by the much more powerful rig than I had on the Sport Tandem
    • approximate ride height as I wanted the beams and tramps angled to lift them up out of the water so when heeled over the beams remain above the water - this was an issue with the Sport Tandem - when powered and flying along the curved beams would drag in the water. That obviously has a very low freeboard obviously but I am going to redo the shape of the curved beams to flare up away from the water as I have taken that deign way beyond what it was designed for
    • testing tiller extensions lengths and finding having 2 far better - passing a very long extension when tacking is annoying
    • I like the adjustability and the power of the ISO rig for a few hundred pounds but the alloy spaceframe supporting the mast although good makes taking the mast up and down on the go very difficult so an open mast gate will be needed and I will be putting in a pivoting pin in the base. the mast is so light and can just grab it, lift it vertical and drop it in on land but lots to go wrong and get caught. I want to be able to to places where taking the mast down will be needed like doing the Hayling Island race
    • getting routing and layout of ropes sorted out for a completely different layout to understand what goes where and why and is best for us and how we sail
    • understanding if I could get around easily enough when not feeling good
    • trying out anchor options - a mantus dinghy anchor has turned out to be fantastic weighs nothing and sets like rock
    • what are the issues with storing and deploying the anchor - testing out options, where to store the rope/chain and how
    • trying out furling jib and spinnaker options - one annoyance on the Spitfire is the non furling jib which and spinny which I will convert this spring as my wife has a hard time with them. I'm not bothered about one design racing and if we sell it we can convert it back
    • looking at options for beams eg slot in like a weta, folding like a farrier, folding like a W17. The Sport Tandem collapses down and is lashed on but that is not scalable. We have a narrow ramp where we sail from and using the test bed as a proa took up most of the ramp and getting in and out when busy was a nightmare. if we had both sides we would fill the entire ramp hence realising that a farrier type system is needed so i can deploy the floats when launched and bring them back in before taking out of the water
    • trying out using my mobility scooter for moving the boat around on land - we've come back in when one of my hands has stopped working and it is quite difficult moving it around. hitching up the scooter means I can move it around with one hand. I need to upgrade the power as it struggles a bit but when I am struggling to walk I can still move 150kg around by myself
    • understanding the foils on the ISO - they weigh a ton and my wife struggles to get the daggerboard up and down and the rudder tilting mechanism is a good idea but clumsy - I have reduced the tiller length as well as it overwhelmed the cockpit specially going down wind
    • would the basic premise of a planing hull trimaran work well as most people just took the piss - "why isn't it super narrow like normal" being asked all the time? I wanted something with more load capacity and fast cruising capability. turns out it works very well - it flies along with almost no effort or skill (luckily for me) being needed
    • the list goes on and on
    and it was all driven by slapping it together in a couple of weekends to understand those basics and get on the water so I was definitely putting the horse before the cart. The first few tests were literally bits of scrap that I riveted together to get ride height etc and when it stayed together we thrashed safely in Mudeford harbour until it was falling apart so I then welded up the frame with new dimensions learned from that test.

    For example I moved the front vertical 18 inches forward which really helped with balance.

    The sockets for the beams were wholly temporary and just riveted square section for ease and I added plastic spacers to the beams to reduce slop and make easy sliding, but it worked way better than expected but I was limited by what was possible with that boat and layout. I bolted through the beams to help make it last longer as on compression the tube starting to buckle due to slap and this kept it going much longer. I knew it would fail but when we were testing and it went like stink and stayed together far longer than expected so we decided to use it until it broke as I had no time for further work on it last year due to massive work issues.

    Off the back of that my wife was convinced it was viable and she absolutely loved it. She is always concerned by me doing bizarre things and ******* myself up once and for all but understands that I need to push myself and feel alive. The adrenaline rush of doing something that you know could leave you back in a chair is quite exhilarating and takes your mind off the pain better than any drugs can. I can't ride motorbikes any more after I had to ride back from Turin to London one handed (had to tape my hand to the throttle and work it by dropping my shoulder) and I don't snowboard any more as on my last 2 efforts I broke my foot very badly on the first day but due to not feeling pain properly I carried on for a week and utterly mashed it which the doctor wasn't too impressed with and then final time got helicoptered off the hill when everything stopped working and I can't get any insurance any more.

    That is just some background - I just get on and do things while being told all the time I can't which is how I can walk again.

    Although I can do/make most things, I don't have an engineering background. I've rebuilt many classic cars and motorbikes, designed and built my oak frame garage (I did get an engineer to do the calcs), recently designed and built my SIP summerhouse this year and I make lots of our furniture etc. I just like making things, it is a way to relax for me to take my mind on unending physical pain so I go down the garage and make things when I can't sleep which is most nights.

    This project is driven by the enjoyment gained from the Sport Tandem project which showed me how much I loved the sailing side and then wanting something with some go - I've sailed some small dinghy's on holiday and enjoy the sailing but we much prefer the available cats (darts and topaz) due to the speed and I love making things.

    I'm not bothered about it being the best, I could just go and buy something but I get far more value out of trying to understand something and if I can do something myself I will.

    Interestingly I have just found this thread:
    Need help with trimaran beams https://www.boatdesign.net/threads/need-help-with-trimaran-beams.48555/page-2
    which is rather useful. When trying to sue the search function I came up with very little.

    For the folding system I have sketched up the beams at the main hull end will fit into snugly fitting round moulded sockets and locked in place with rounded bolt down clamps so loads will be well spread there.

    The biggest weakness in the test bed was having to drill locating/holding holes and I have found some weight / strength tables for ally tube which suggest going from 70mm 1.62m to 100mm 1.62mm increases the weight by about 35% but decreases deflection for a given load by about 60% which sees like a good trade off. Before anyone dives in to point out I don't know what I'm talking about, this is just a basic indication for me that a small weight gain helps a lot with the deflection nothing more.

    At this moment I think will be looking at mocking up 100mm beams in wood again to get rough dimensions and test the folding mechanism then can rebuild it in ally once it can tested and proven to work. I can always use a thicker wall then, make changes etc.

    I am quite happy to make and test and rebuild, in reality the cost of remaking is not an issue as it a a few hundred pounds, it is imply giving me something to **** about with.

    If anyone has reached the end of this well done....
     
    fallguy likes this.
  10. Vantage475T
    Joined: Aug 2016
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    Vantage475T Vantage475T

    fall guy,
    I have the zeta and strike 15 plans from richard - we swapped some thoughts a year ago before everything went **** up for me at work.
    Super helpful and nice guy - if I remember correctly, he didn't think the ISO sailplan was suitable for the Zeta and I wanted more float bouyancy for it and the Strike 15 just doesn't really do it for me how it looks. the 16 and 18 just won;t work size and looks wise so didn't really look at them.
    I would love to see some video of the Zeta being given some stick though as the only video I can find is very low wind. That is surely the closest to a Weta alternative?
     
  11. Doug Halsey
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    Doug Halsey Senior Member

    _MG_0036.jpg If you can possibly tolerate the inconvenience of having waterstays, they can give you a much stiffer & stronger structure with significantly less weight.

    The forward crossbeam on my 15' foiler Broomstick is a 4" diameter aluminum tube with 0.049" wall thickness. It weighs about 12 lb. & can carry >350lbs, while deflecting <1".
     
  12. Vantage475T
    Joined: Aug 2016
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    Vantage475T Vantage475T

    Doug,

    I've seen your broomstick videos on the web and love it. That is amazing.

    With the proposed folding system there will effectively be waterstays as 2 cantilever arms will be bolted through the hull in under each beam and when folding will bring the floats in on their side so that should spread the load quite significantly.

    I've been mocking up the placement points in the garage and I can tool around with it once I have the the main hull basically prepared as I can use the old test float and just botch on some cardboard to replicate the new dimensions to see how it all folds together. That's really useful knowing dimensions you used there - a larger diameter but thinner wall. I've got enough ally around to use up the old 70mm tubing with spacers just to get my dimensions done if I want to then move to the more permanent solution.
     
  13. Vantage475T
    Joined: Aug 2016
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    Vantage475T Vantage475T

    Just had half an hour to test a jury rigged folding mechanism on the bench with heavy 45*120 lumber as the beam.

    I've approximated the hull mounted bracket location and the beam used is the intended 1.9m and I've taped on an approximation of the largest section of the float.


    upload_2018-1-21_11-28-45.gif
    That is the arse end of the Sport Tandem trimaran main hull above my head.

    In the real iteration of the new project, the beams will be canted up around 5 degrees so I can raise the beams above the water a little but it at least gives an idea that it will work ok.

    I am planning on making the brackets and folding cantilever beams from stainless steel and then having two quick release clamps over each beam to spread the load when under pressure.

    Using this sort of scheme does anyone think I need to go as big as 100mm on the beams or reverting back to my 70mm beams would likely be sufficient?
     

  14. JosephT
    Joined: Jun 2009
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    JosephT Senior Member

    Sorry for chiming in late. That's a nice retraction mechanism you have Vantage475T. On the beams & brackets, bear in mind the more you change the materials (e.g. stainless brackets, wooden beams, type of wood, laminated with fiberglass, etc etc) this changes the calculations on what is required. When you change materials you're also affecting the weight, center of gravity & stability of the vessel. Yet another variable is the sea state while sailing. Anything above moderate seas or a storm will put heavier and potentially unforseen loads on the structure so you'll be smart to avoid taking the boat out in rough conditions. Granted it may be more fun at first in fast winds & bigger waves, but you could snap something or get hurt if you're not careful.

    With all the questions you have (and there are a lot) I would recommend two routes:

    Option 1. Work on a comprehensive plan with a nautical architect. Many small boat designs can be scaled up a bit larger rather predictably...many designers do that. However, some can not if their designs are already highly optimized (light weight, use minimal materials). Many of the fastest boats are built this way so if your urge is to modify a fast boat, you had better get full approval from the designer. Customizing a boat this way won't likely be free and you'll have to abide by the specification vs. changing the plans to suit your experiments. In short: Build it per the blueprint. Saile it per intended sailing conditions.

    or

    Option 2. Continue searching for an existing set of plans (or a used boat). It shouldn't be too hard to find plans for a tandem trimaran. I ran across another site you may or may not be familiar with. Search on "plans" and it appears some are available...excellent web site.

    Report on Nine Small Folding Trimarans http://smalltridesign.com/Trimaran-Articles/review2.html

    Above all else you want to have a safe + fun boat. Aside from that, I presume you're a good sailor. If not, I have quite a few friends in the UK who can point you in the right direction on your training needs. Cheers & good luck!
     
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