Mold thickness for 6.5m hull infusion

Discussion in 'Fiberglass and Composite Boat Building' started by hambamble, Jul 11, 2012.

  1. hambamble
    Joined: Jul 2012
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    Location: Gold Coast, Australia

    hambamble Junior Member

    Hi, I am considering building a 6.5 m yacht, probably complying to the mini transat rules just for kicks. I have done a bit of work with composites and infusion before, but most of the molds i used were made by someone else, or the ones i made were so small that you could use as much glass as you wanted and it was still cheap.

    I need to make a female mold from a male plug as cheaply as possible, just wondering how thick you can go and get a good finish on the hull.

    I was thinking:

    4 or 5 layers of 600 gram choppy, with timber reinforcement every 500 mm or so glassed on. The mold only needs to last for one hull, but 2 would be better so i can sell it on afterwards, or possibly sell a few hulls to help pay for the project (but this is time i really don't have)

    what thickness do you think i could get away with for the mold?
     
  2. tunnels

    tunnels Previous Member

    quick and easy !!! are you sure ??

    Are you sure you need to make a mould if its a one off throw away sort of ??
    Whats the plug ?? off and exisiting boat ?? why not just make a boat over the outside and let that be your boat . saves all the costs and hassle and materials of making a mould and can have a hull in the time it takes to make a mould !!.:D
    OR
    Boat builders been doing iTHIS for long time !!,if you have more than one to make do just what i said and the boat becomes the mould that at the end becomes a boat and you wasted little !! just what ever you going to use for a frame on the outside steell is best and just tac weld and lightly glass . when you finished and made the last boat if there was a dozen to make !!hehehehehe!remove the steel frame set it up level in all directionas !! sand blast totally the inside of the hull and fit all you stuff like interior and framing etc etc glass it all in and then roll the boat over up side down and fair and bog the outside and paint . no one will even know its the skin thickness bigger than the reall thing !!. :confused:

    Can use the same glass lay up that the boat would have just add a extra layer of resin to sand and shine so you can wax and polish to take the other boats out of it !! :)
     
  3. hambamble
    Joined: Jul 2012
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    Location: Gold Coast, Australia

    hambamble Junior Member

    Hi Tunnels, Thanks for the reply!

    Basically I want this hull to be as light as possible so i get every advantage possible racing. I'll probably use a glass sandwich layup for the final hull, if the design works well, i will probably sell the original and and re make the hull in carbon/kevlar to save a few kg. The other important thing is that the lighter you can make the hull and superstructure, the more weight you can put on the keel bulb, giving your more stability and a greater righting moment. This will make the boat stiffer, and therefore faster upwind.

    i haven't started work on the plug yet, still trying to price my options, basically here's my options so far:

    1. (cheapest) Build a cold molded timber hull. I don't like this because of the weight, although in a boat this small the weight gain is probably only 100 to 150 kg. The main change though is with the weight distribution - you cant get as much weight in the keel bulb. I have been looking at the Didi Mini and it is an excellent example of plywood construction using the plywood radius chine technique (which is a pretty new concept to me) and the lines of the hull look quite nice. If I built this method just to create a mold, i would need to use far more expensive materials (like marine ply, and high quality timbers) and put a lot of effort into finishing the hull. Not a great plan for a mold, but as a boat by itself not a bad option.

    2. (medium cost) As you said, mold the hull straight over a plug or existing hull. As I am designing the hull myself, i would still need to build and fair the mold. Layup the hull on the outside of the mold (i could still infuse the hull with this method), then fair the hull. If you take into account the different thicknesses of laminate (particularly around reinforcement points like the chain plates) i think fairing the hull could add a fair bit of weight, 15 or 20 kg of filler and a lot of hard work.

    3. (most expensive) If i'm going to all the trouble of building a plug (as for above), I may as well just build a female mold from it, so the hull i knock out of the mold is fair and good quality. I am not concerned about the extra work, i think it actually balances out when you consider that i will only need to fair one mold, not a hull and a mold! My only worry, is cost of building the female mold - i don't really want to double the cost of construction just because i built a mold that will be thrown away. Only bonus is if i build 2 or more hulls from the mold, then i think its worth the money, and it saves a lot of time!
     
  4. tunnels

    tunnels Previous Member

    Sorry not me

    Saving weight in all the wrong places is not me ! the hull is not a place to scimp on materials becasue it can be fatal , light yes but ridiculous no!

    I made 36 foot light match racing yachts to the designers specs and the weight was what was predicted and i know you dont have to scrimp where its nessasary .when making 8 boats fully completed sails rigged motor and tanks etc etc there was just 15 kilograms between heavyest and lightest thats close !!:confused:
     
  5. hambamble
    Joined: Jul 2012
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    Location: Gold Coast, Australia

    hambamble Junior Member

    Hi Tunnels,

    As for your 36' match racing yachts, you built them to the designers specs so they they calculated that it was strong enough. I too will build it to to the designers specs, as you said, its no place to compromise strength to save weight. and by the way, 15 kg is pretty close between 8 boats, great work!

    I will save weight by using different materials. In general, for hulls of the same strength, the order from heaviest to lightest will be:

    Timber
    Fiberglass
    fiberglass sandwich construction
    exotic (carbon/kevlar) sandwich construction

    unfortunately, this is close to the same order for cost as well, so I will sort out a realistic budget before I get the scantlings drawn up in whatever material i choose.

    The boat i want to build is for a box rule, which encourages developing technology (a brief summary of the rules is here: http://www.minitransat650.com/html/design.html). People are pretty protective of their designs and specifications, as they don't want to give away their racing secrets, however i am reliably informed that a 200 kg hull is in the ballpark for composite construction. These boats race across the Atlantic, so they are built to take a pounding! Most boats displace 750 to 850 kg (lightship), but when you compare keel weights, the range is between around 300 to 450 kg depending on the design. My goal is to use lighter and stronger materials to construct the hull, so you can get more weight into the keel. This way, for the same displacement, you get a boat that is stiffer and faster upwind.

    Basically, if i cant afford to make a competative boat, ill just go the cheap (timber) route and build something that will be fun

    anyway, to get back on track... my main concern with this post was going light making the mold. As the mold is merely a tool used to create the hull, a strong or weak mold may effect the lines of the finished hull, but should not effect the strength of the finished hull. I was mainly wondering how thin you can make a mold for a 6.5m boat without it distorting?
     
  6. tunnels

    tunnels Previous Member

    carbon and kevlar are opposites can never understand why they are mixed i will never know !! Still when carbon breaks its like a safety net to hold and broken bits so they dont get lost ,Makes a pretty pattern with yellow and black !! so 50% of the material is just there for the ride !! so much for the weight saving theory Jezzz wayne !!! :D
     
  7. chunpei
    Joined: Jul 2012
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    Location: wuhan

    chunpei Junior Member

    Tunnels,你是中国的吗?我是武汉的一名大学生,我是一名专科生,但我学的是全国只有我们学校开设的游艇专业,我知道在中国游艇刚起步,在学校学到的和了解的很有限,所以我来到这,想主动去了解游艇,因为我发现我喜欢上它了,但又不知道怎样从我这个起点去了解它,熟悉它,希望你能给我一点建议帮助,非常感谢!
     
  8. tunnels

    tunnels Previous Member


    尼华岛!不,我来自新西兰的工作在苏州为Seama游艇。已经在中国呆了两年。
     
  9. chunpei
    Joined: Jul 2012
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    Location: wuhan

    chunpei Junior Member

    很高兴你能在百忙中回这封邮件,我看到你Location: china is great and interesting !!我想你对中国有一定的了解,而且你在苏州为Seama游艇工作,能问一下你是怎么看待中国游艇的?或好或坏,我想更加全面认识这个我将从事的行业,再一次的感谢!
     
  10. tunnels

    tunnels Previous Member

    This place the skill level is quite low so the construction methods are behind the times !!
    They work to what they know and have done always so change is almost impossible with older workers
    To compensate for this they over build and use to much materials and the wrong kind of materials . i have been trying in vane to get them to change to use better glass cloths and thicker cores but is not easy to get them to accept .
    China has some reall good and nice materials , and we have been using this in the construction of the 28 metre boat . :D
     
  11. chunpei
    Joined: Jul 2012
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    Location: wuhan

    chunpei Junior Member

    嘻嘻,不好意思,我不会用英文回你,但我能看明白你写的,你说的在中国各行各业都能看到,老一辈的人有些墨守成规,不愿去冒险做一件他以前没做的事,创新的意识以经消退,但他们的经验确实一笔宝贵的财富,所以我来到这个大论坛,去接收更新的思维,我想要的中国人所缺少的创新思维,我不想一味的模仿一味的守旧,谢谢你中肯的评价,我希望我们新一代用好着丰富的资源。呵呵,话有点多了,作为一名大学生,你觉得怎样去自我培养自己的创新思维?
     
  12. idkfa
    Joined: Sep 2005
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    Location: Windward islands, Caribbean

    idkfa Senior Member

    hambamble are you able to buy epoxy cheaply? any cheap epoxy will do, ie. better than the best PE or gel-coat.

    I'm suggesting,

    mat takes loads and loads of resin and shrinks, so you get print-through....and also gel-coat application problems crap!

    But if you build the mould out of epoxy, then you can use a only a couple of layers of 1808 biax, then some thin MDF pieces patch-worked on with bog, and finally a 9oz over top. Will be thicker than 5-6layers of matt - thus stiffer, be lighter, need less framing reinforcement and less sensitive to heat - so you could post-cure your boat (low temp). Also an epoxy mould will release easier - lot less porous than gel-coat/surface reactivity? Finally you could store the mould covered outside!

    no gel-coat, less resin, similar cost? better product!

    idkfa

    ps. mat and PE go hand in hand, and is even less useful than gel-coat!
     
  13. tunnels

    tunnels Previous Member


    (我们每个人都是一个个体的人,我们都有件事我们可以做自然和事物我们苦恼和不擅长做的)(当我还是学生时,我总是很感兴趣的船只和划船和想要一艘船建设者) (所以我做了模型船,很快能看到镶板在塑造和发展成一艘船船体)(我曾经把我的船在我们的鸭子的池塘,看看他们漂浮,逐渐我研究出如何改变事情看起来不错,让我的模型更好)(当我离开学校的时候,我买了我的第一个支付木材和订厚度木作我的第一艘船,只有12英尺长,我设计了一切,让一切都自己,) (我的小船就很好,我很高兴,)(后来我去工作的公司制造的游艇和使用玻璃纤维) (所有我的生活我发现玻璃很容易处理)(我工作已经有许多公司和学了很多的信息和知识)我过去常常被问问题,其他人进行排序,使事情的人被告知是不可能的我发现玻璃fasinating和容易理解,如果你知道了一切生活更加容易。船是我的爱好,船是我喜欢做,就无所谓什么尺码的! !汽艇和帆船不管。
     
  14. SamSam
    Joined: Feb 2005
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    Location: Coastal Georgia

    SamSam Senior Member


  15. hambamble
    Joined: Jul 2012
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    Location: Gold Coast, Australia

    hambamble Junior Member

    Thanks Idkfa, great idea! I have used epoxy in molds before with great results (just much much much smaller ones), just didn't occur to me for something this big. I'll have to price the epoxy, but its a good option. I would really like to be able to store the molds and have the opportunity to use them again so its something to think about. Even if it costs a bit more, it might be worth the extra cost. building a second hull would be a few years down the track (if at all), and storing the mold inside for that long would not go down well with the space available. to be fair though, i think a polyester mold would probably last a few years outside without a problem as well.

    Besides, I will take any excuse to avoid chop strand. I hate working with that stuff!
     
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