efficient 10m displacement powercat (build thread)

Discussion in 'Boatbuilding' started by groper, Apr 15, 2012.

  1. groper
    Joined: Jun 2011
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    groper Senior Member

    Love the workshop, wish i had a space like that to work in, although the trade off not having it where i live is something to consider. Im working towards buying acreage where i can have a shed like that in my back yard :)

    Its Interesting tho... i often wonder whether its quicker to make a mold and not have to fair and finish a part as opposed to just "getting on with it" and put up with the fairing and painting. Flat panels gets around that and its a no brainer, but the limitation on non compound curvature is very inconvenient sometimes... Next boat i build, i think ill use a vinylester and so opens up the whole gelcoat and making more molds possibility. I dont see why boat designs need to be any heavier using VE and gelcoat either... The mechanical properties of some vinyls are pretty darn good, well good enough to use with e-glass at any rate.
     
  2. waikikin
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    waikikin Senior Member

    Maybe somewhere in between production style tooling & the one off foam methods & panel boats there lies a workable compromise in finish, shape & cost, similar to the Kelsall system, molded full length hull topside panels & rounded to purpose hull shoes in one off foam, so much of the "faired" section is sub waterline & curvy stuff is much easier to fair than flattish surfaces too. Jeff.
     
  3. Frosty

    Frosty Previous Member

    I cant hold back any longer -- yeah its great fantastic work really nice job---but.


    Its too light-- I mean how can you even come along side without stoving in the sides.

    If you drop your car keys on it you will damage the hull.

    I would not feel safe in such a boat..

    On the other hand it will be light and fast.

    No im not jealous in any way I got one. I see the walls of the galley bulge as we pull along side.

    Fortunately the galley top is right where it should be but on the other side is back of the on suite bathroom 44 foot.

    The inner skin is about 4 mm with 1 inch balsa and the outer is about 3mm.

    You would think thick enough woul'dnt you
     
  4. groper
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    groper Senior Member

    Frosty, what does your boat weigh? Do you have any links to pics or otherwise where i can see your boat?

    Sandwich panels are very stiff, but yes foam cores are quite fragile with thin glass skins especially weak in impact resistance, but this is a trade off im willing to make for much improved fuel efficiency. However If i drop my car keys, i will not damage the deck or hull. Ive already dropped tools and what not on my bridgdeck, they just bounce, no damage at all.

    If you keep the overall weight of the boat light, there is less inertia when you pull alongside and press against the dock thus the loads are lower. Its a sprial, if its light then you can afford to build it lighter as all of the loads are lower etc... Despite this, all of my laminates are actually heavier in terms of fibre content than all of the circa 40ft DUFLEX boats being built in australia at the moment. I put heavier skins on to help deal with the impact problem of foam as opposed to balsa - which is double the weight - so in the end i probably come out about even weight compared with duflex panels...
     
  5. waikikin
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    waikikin Senior Member

  6. groper
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    groper Senior Member

    10 tonnes... say no more...

    why do you think your boat sides flex when you come along side frosty? Assuming your boat weighed 2 tonnes and otherwise identical construction, Do you think the sides would still flex when coming alongside?
     
  7. hambamble
    Joined: Jul 2012
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    Location: Gold Coast, Australia

    hambamble Junior Member

    Racing yachts are built on the light side of sandwich construction. They have huge slamming loads in offshore conditions, combine that with the keel and rudder forces, and the rig loads they take huge strain. Over time the hulls tend to get a bit flexible, but they are built for performance, not longevity.

    If you build something light, it doesn't mean weak. HOWEVER, if you build on the light side, it is likely to be weaker as its often poorly done. You need to be smart about it, and not waste weight anywhere to keep it light, and you need to reinforce high load areas to keep it strong.

    Infusion is a great start as it gets near perfect resin content for optimal strength and minimal weight. Gropers laminate schedule does sound a bit light, but I haven't run the numbers on Groper's design. By the looks of how much effort he is going to, I bet he has and he knows what hes doing. Production boats are built for profit margins, and tend to be on the safe side when it comes to scantlings. Its only when you build your own boat that you can push the limits.
     
  8. groper
    Joined: Jun 2011
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    groper Senior Member

    Havnt done a great deal lately, just boxing in the rear beam and mucking around with the fuel tanks... laminating the fuel tanks with novolac vinylester, i dont like working with it at all, its goes very tacky on your gloves and tools when laminating, eats the polyethethylene plastic drop sheet i use, and also the vinyl gloves i have. The styrene smell stinks and its generally just not as pleasant to work with compared to epoxy... ill be glad when these tanks are finished...

    [​IMG]
     
  9. groper
    Joined: Jun 2011
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    groper Senior Member

    Again, not alot to show... work has got the better of me and so the boat building has taken a back seat lately...

    [​IMG]

    The rear beam is all taped and glassed on the inside, just need to do a bit more fillet and tape on the outside, then drop the top peice on - which will be a complicated piece including rebates for hinged lids so i can use the inside of the beam for various compartments and a heavy uni schedule for the top beam flange etc... ill get around to that much later as i still dont know exactly what i want to use this space for...

    Been taping the inside of the tunnel, panels were set ages ago but never got around to taping the bottom sides... This one was 3 layers of 750gsm weft triax, the beefiest tape schedule in the boat as its a highly stressed area at the base of the cantilevered beam model which shows highest stress here which tapers off to lower stress in the center of the tunnel/beam.

    [​IMG]

    The port fuel tank is just about finished, 320L capacity, just gotta glue the top on...

    [​IMG]

    After cutting the inspection hole, a peice of aluminium plate will have all the through tank connections welded to it, and it will be bolted down into a tapped out solid bog edge as shown here; will laminate the top skin whenever i get around to it :p

    [​IMG]
     
  10. waikikin
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    waikikin Senior Member

    Hi Groper,
    Still making forward progress, pity earning a living gets in the way;) The Alu plates with the tube/fittings are a cool detail, I was scrolling through the pics thinking that myself, do they have an alu backing plate as well? Those are the tanks with the vinylester lining, with the baffles are those raw foam edges? to be filled or glassed over? The angle bonding flanges look like neat detail to splodge the lid onto!

    All the best from Jeff.
     
  11. groper
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    groper Senior Member

    Cheers jeff, yeah work sux but hows yours going?

    Nope, im not going to add a backing plate, im just going to tap bolts into the high density bog you can see in the pic... i think ill put bead of sikaflex (if its fuel safe) and do up the bolts loose with baking paper on the ally plate, then once its cured, remove the paper and bolt it down tighter so its like a poor mans o-ring seal...

    yep, i re-laminated over the original epoxy hull skin, with more glass and a novolac vinylester resin, gave it several coats and taped in the foam core baffles - some 10mm klegecell i had laying around, thats why its brown...(and makes 5 different types of foam in this boat :D) yep, on the top edges you can see raw foam edges, but this will all be covered in glue bog (vinyl ester again) as i put the top onto the bonding angles...
     
  12. masalai
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    masalai masalai

    Sweet work groper, I should have had you do my build...
     
  13. groper
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    groper Senior Member

    Ok ive been racking my brains trying to figure the best method of doing the curved sheer and deck - things like frame and batten molds with transverse foam strip plank, or longitudinal foam strip plank directly onto the boat frames etc - it all seems a bit too bloody expensive and time consuming... :p

    So i went back to the drawing board and figured i could change the boat by trimming and planing some of the bulkheads down so that the deck has only single curvature instead of compound, and same for the sheer line. So i came up with this and decided that it looked quite acceptable to my eye, whats everyone else think about this new look?

    [​IMG]

    [​IMG]

    [​IMG]
     
  14. masalai
    Joined: Oct 2007
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    masalai masalai

    Hi groper,
    Looking good, My deck is one single piece, (joined on the shed floor), of 19mm end-grain-balsa Duflex, and the curves from centreline out happened naturally and the edges, hull to deck), were shaped with the router and taped...

    My car is being 'worked upon', so will be ready when it is ready - I will let you know when I know...
     

  15. groper
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    groper Senior Member

    Starboard fuel tank is almost finished, baffles are in and just needs its lid on to finish.

    The back deck just got a bit bigger today too;

    [​IMG]

    [​IMG]
     
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