Build method for 26 foot foam core fglass yacht

Discussion in 'Fiberglass and Composite Boat Building' started by hambamble, Jun 7, 2015.

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

    hambamble Junior Member

    I want to build a fast racing yacht, and thought building to the GP26 rule would be a good idea. Its about the size my budget allows for and is a class thats taking off. I have a lot of experience with design (work in a design office) and repairs, but have never built a boat from scratch. I came across the Dudley Dix 'radius chine' plans, and also saw this on the net which got me thinking (sorry its in french but the pics do all the talking)

    http://seasailsurf.com/seasailsurf/actu/4701-l-exocet-40-d-elie-canivenc-prend?lang=fr

    I have put a lot of R+D time into this, and have come up with the following plan. Keep in mind that the boat has a hard chine. I will build the hull in three main pieces. Rules state the hull has to be fibreglass/foam so I was hoping to infuse as much of the build as possible.

    Piece 1: centre section between the chines (this is the main part that will come into contact with the water and will be the most important to reduce drag). Has compound curves so needs a mould of some sort for construction

    Build a female mould using CNC cut ribs and plank it. Cut in MDF/cheap ply it should be cheap to construct the mould. I'll probably have to leave out the first few feet from the mould due to the tight curvature and the work it will take to make a female mould this shape from scratch (Its easier to shape a block of foam once the rest of the boat is built)

    Part 2:
    Ribs: CNC cut foam laid up and infused on a the infusion table. They will be cut within a few mm and should slot right in.


    Part 3:
    From the chine to the gunwale, This part is designed as a developable pannel, so it can be made flat.

    use a single , flat panel, laid up on a flat infusion table. It will be bent into shape similar to the pannels in the link I posted above. (Just need to do the maths to make sure it will bend to shape without too much stress). I may have to lay up one side of the sandwich panel, bend to shape and install, then lay up the other side. Just depends on how flexible it is.

    Although the ribs in place should give it a fair amount of strength and structure, I assume minimal additional formwork will be required on top of this to get the shape.

    Deck:
    Hopefully use a similar method, developable panels that can be laid up flat.


    This method does several things:
    reduces mould cost and build time
    speeds up construction (less mould to make and fair, infusing flat, horizontal panels is much quicker than laying up vertical ones)
    Means if I screw up an infusion badly, it won't be an entire hull :D



    Any thoughts on this? I'm sure someone has done similar before so if you know of a build such as this, details would be much appreciated!
     
  2. Jim Caldwell
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    Jim Caldwell Senior Member

  3. groper
    Joined: Jun 2011
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    Location: australia

    groper Senior Member

    My thoughts are to infuse the entire hull in 1 shot... Making flat panels then taping them together and fairing out the joins is a pain in the ***, and takes a lot of time and adds weight.

    Enlist the help of an infusion guru so that you don't blow it, or spend some time learning it and playing with it extensively first - not worth it if can simply get help from a guru in your area, even if you have to pay them good money.

    Any flat panels you need - consider simply buying them already made from ATL composites, the slight increase in cost is worth more than your time - unless you value your time at less than $20 per hour that is...

    Build the mold from CNC routed MDF frames and MDF plank it. Spray on heaps of spray putty and sand it smooth, liberal application of bog where nessesary and then paint it so the mold shines... Infuse the hull in 1 shot, then add the bulkheads and other stiffeners before demolding it.

    Send your CAD drawings to ATL composites and they will CNC rout all your flat panels for bulkheads, stiffeners, and decks etc. tape them in and jobs done more or less...
     
  4. Mr Efficiency
    Joined: Oct 2010
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    Mr Efficiency Senior Member

    Are you talking about building a female mould without a plug first, groper ?
     
  5. groper
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    groper Senior Member

    Yes... There used to be detailed pics of this method on Jon Sayers website - sayer yacht design - when they built the racing yacht " wasabi" but they have taken the pics off the net now... But it is exactly as I described, mdf frames and mdf planks, faired up and painted before infusing the foam core hull on it...
     
  6. hambamble
    Joined: Jul 2012
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    Location: Gold Coast, Australia

    hambamble Junior Member

    I saw the Wasabi build log. It was the first time I saw a female mould built in this fashion and gave me the idea. It was about a 40 footer designed for the melbourne-osaka race if i'm not mistaken. The mold was built in a Left and right half, joined along the keel, with a separate deck section.

    Here are a few points that may clarify why I want to build the topsides as flat sheets:

    1: Less mold to make, less time and less money to spend making it. An infusion table large enough can be made cheaply and quickly, and can be used for a lot more than just infusing the topsides

    2: Weight is restricted anyway, so the few kg I add by joining along the chine will be insignificant, as the maths at the moment is saying I'll need to add some ballast to meet class rules.

    3: as you say, joining along the chine will take time. However, compared to building a complete mold for two separate topsides I think its probably going to save time in the long run. I'll need to fair where the deck joins the hull anyway, so there will be lots of panel work during construction anyway. If i'm clever I can recess the mould a few mm around the join such that it allows for the thickness of the fglass tape along the seam.

    Good points about buying premade infused sheets. I'll have to look into it more closley
     
  7. groper
    Joined: Jun 2011
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    groper Senior Member

    If your already building a mold for the compound curved bottom part, then you might as well add the Chines and topsides as well is my point. Speaking from my point of view and someone who has already done it, the cost savings are not worth talking about, mdf is extremely cheap, maybe $14 per sheet last I bought it.

    You already have to pay a cnc router programming and setup fee, so your only adding a bit of extra time and cheap material to it. The cost increase is bugger all, but it will save you heaps of time. Gettiing those Chines perfect takes considerable time - trust me.

    You don't have to fair out your deck joint. You can include a bonding flange to the deck edge and slip it inside the hull to bond it provided you can build it accurately enough so that you have a neat fit - no glass tapes or fairing.

    It's worth considering building an entire deck mold in the same fashion, perhaps a male mold, or just a frame and batten mold which is also all cnc cut so you have exact figment to the hull. Again, your already paying for the cnc routing setup fees so your just adding a few more sheets and and hour or 2 to the machining fees. Again, if it were me, I would not hesitate to do it this way as I know the time saved pays for itself 10 times over... Ie, make the entire deck as 1 piece and include all your hardware fixing points , hardware locations, any doublers etc and infuse as a single piece. The amount of time you will save later not having to replace core material, joins pieces together, fairing, adding reinforcements for hardware etc you can't appreciate until you've done it and wished you have planned things better :)
     
  8. hambamble
    Joined: Jul 2012
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    hambamble Junior Member

    Thanks Groper, my priority in this build goes in this order:

    1. Quality
    2. Time
    3. Cost

    I am happy to sacrifice some $ to speed up the whole process (but not go insane). I haven't built a boat before, but I have taken on some big projects. Usually, time is the biggest enemy. For the sake of a few hundred dollars I fully intend to get all the molds CNC'd up. I do it lots in steel and it is very cheap compared to the product you get out of it.

    Deck will be done in a mold same as the hull... at least the majority of it. Probably a male mold as its the easiest to make, and the deck will be covered in grip anyway so small discrepancies are less obvious, and they make no difference to performance

    As for the mold construction, my biggest thought was that it would save time doing the topsides separately... the time saved would be in the construction and fairing of the mold. Obviousy, with your experience, you think differently.

    Just out of curiosity, do you think my way will lose time mainly in joining the pieces together, or fairing the whole thing once its together? as a one off, I really feel like fairing a concave mold would be a whole lot harder than a convex hull, but having never built a mould like this, its hard to comment.

    Thanks for your help mate!
     

  9. groper
    Joined: Jun 2011
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    groper Senior Member

    The most efficient means of building I believe to be via making the largest pieces possible- especially if using vacuum infusion processing.

    It is generally easier to fair a convex surface as opposed to a concave one, this is why quite a few people these days are doing male molds for this type of 1 off build and is probably the way I'd be tempted to go for this. You should not have to fair your topsides panels tho as you can plank them with a single plank if the surface is developable. You will need to choose the thickness of the mdf carefully in the topsides area tho so that it will accept the curvature, maybe 6mm? I don't know the curvature, only you can experiment with that but you will need to know it before you get anything cnc cut.

    You should also have no overlaps in the glass in this area either so you won't have anything to fair out if you infuse on a male mold other than the texture of the reinforcement used. The main reason for fairing the mold and painting it, is to make sure it's fully vacuum tight and allows a good release as epoxy really likes to stick in a Mold.

    Time saved comes from an accumulation of many things associated with doing a resin job. Everything from obtaining clean mixing containers , weighing and measuring, application, waiting for cure before starting the next step, aligning panels together, scarphing edges to ensure gap free fitment of adjoining panels, applying fillets and coves, fairing out joins, working out how to clamp odd shape things together, grinding a bonding area before glueing or glassing and again afterwards to clean up the previous work, the list is endless and you have to do it everythime you join something together. Please trust me when I say it's better to make things in big pieces with fewer joins...
     
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