Hull thickness of a 24 ft center console ply

Discussion in 'Boat Design' started by yellowfinii, Oct 4, 2009.

  1. yellowfinii
    Joined: Sep 2009
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    yellowfinii Naval Architect

    Ahoy all,

    i am a first time poster here, but have been reading this site, and have seen this site around often.

    i am building a 24 ft center console, 22 deg dead rise, 60-70 deg bow entry.

    i am in the design process of this hull, (guess it can be compared to a contender,regulator, yellow fin, shape of hull) i have the frames designed at 16 inch increments, a 6 inch center keel, for the gunnel, i plan on using 3/8 in marine ply, and am thinking about using this for below the waterline. i am a little nervous with the 3/8 inch ply being the skin of the boat, since it has the possibility of taking a beating. All the ply will be fiberglassed inside and out.

    if i use 3/8 in ply do you think it will be sufficient, or should i use 1/2 or two layers of 1/4 ply.

    All input would be greatly appreciated.
     
  2. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    What is you experience at designing structures, in particular boats? Your questions shows a lack of understanding and this makes me wonder if you really should be attempting this. The deadrise angle suggests a high speed, deep water machine which will require lots of power. You really need to engineer you load paths, various centers and etc. on craft like this or you can get embarrassed pretty easily on launch day, hopefully without anyone getting hurt or swimming back to shore.
     
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  3. yellowfinii
    Joined: Sep 2009
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    yellowfinii Naval Architect

    I am a naval architect student in my final year,

    I am plenty capable of designing a hull and while I may not have the experience of say the naval architects at contender or regulator I do have enough experience in this feild to attempt and successfully complete this project.
    I am using the Maxsurf Suite, I have my hull designed on maxsurf, did various extreme dynamic loadings using Hydromax, a program which does all the hard hand calculations of finding the center of buoyancy,gravity, flotation. The hull i have floats the way i want it to, within a limit less than an inch of the DWL.

    This forum I believe is to help others and discuss possibilities to problems or questions one ask's, so how bout we get to the point of this post, and not question one's ability
     
  4. apex1

    apex1 Guest

    And what meant this?
    just conversation?
     
  5. Yellowjacket
    Joined: May 2009
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    Yellowjacket Senior Member

    You didn't indicate what you were using for stringers (shape and thickeness if they are an inverted T section) and spacing between them, and how much glass you were thinking of using.

    The width of each stringer makes a difference in that the spacing basically defines the unsupported width of plywood that we are talking about here, which defines the necessary plywood thickness.

    The amount of glass can add effectively no reinforcement or can relagate the plywood to be basically a core, so there is a wide range of results that can be obtained based on how much glass you want to use on the inside and outside of the hull....
     
  6. BWD
    Joined: Aug 2006
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    BWD Senior Member

    Well I am just a total amateur, but have comments and questions:

    I think you asked some questions without giving all the information to make them answerable, for example beam or displacement and how big an outboard you are gonna hang on it (or is that what you had in mind?). That might have bothered someone....

    Sounds like you are planning a more traditional style build, but with a fairly modern shape of hull.
    Without doing any calculations, this amateur guesstimates the skin thickness 3/8 may be adequate given the close frames, assuming:

    -the glass is structural
    -intended speed is not too high
    -you are planning additional longitudinal framing of some sort that you did not mention.

    For durability and higher speed I would surely think of 1/2 inch skin and likely layers to make curves up front.

    I would also think of how to glass the inside. 17 frames and a keel would give a minimum of 34 compartments, a lot even if they are shallow. Throw in some stringers, chine logs, and you could have many more.....
    Stitch and glue may be worth thinking about as an alternative, if you want to work on your composite figuring chops, since it sort of encourages you to make a strong grid and makes glassing inside easier. There are other solutions too. Maybe you have one already. Good luck, hope you get a great result!
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    We get quite a few who "think" they can design a boat here, each week. No offense was intended, though your post left considerable to be desired, if interested in real answers. If you think you've offered enough information about the design, then I'll leave it for others to play with. A lines drawing and some design goals would be nice as a start, don't you think?
     
  8. srimes
    Joined: Sep 2008
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    srimes Senior Member

    I'm building a 2400 sq ft house, mostly with a 10-12 pitch roof but 1 gable will haft 12-12 pitch. Will 8 inch rafters be OK?

    I drew it up in autocad, and it came out as tall as I wanted it to, less that 1/64" off, so you know it'll be a great house. Anyone want to hire me?

    :p
    :D
     
  9. srimes
    Joined: Sep 2008
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    srimes Senior Member

    ok, maybe I was too much of an *** in that last post. Here's what I got from your post: you're arrogant. You sound like you don't know what it is that you don't know, and you got defensive when asked basic questions. Humility is a fundamental trait of a good engineer.
     
  10. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    I was looking on the Glen-L site to see if they had plans for a 24' deep v and what they used for the bottom planking and I see they have for sale a 1 hour interview with Ken Hankinson on dvd. I have a better understanding of why he might have dropped out of the boatbuilding scene like he did, and what he might be doing with his life now. He looks happy.

    [​IMG]
     
  11. yellowfinii
    Joined: Sep 2009
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    yellowfinii Naval Architect

    [​IMG]

    Here is the lines plan.


    There will be frames (floors) every 16 inches, depending on the location of the frames, 2x4 / 2x6 in such areas of the pounding region.
    a center keel will be a 2x8 micro-lam
    between the floors, against the keel will be 2x8 bridging making the keel 6 in.
    off approx 2.5 ft from the keel will be a longitudinal keelson 2x8 notched for the frames.

    I plan to have 2 base coats of glass on the out side, reinforcing edges with meshing, after those to coats.
    Glassing the inner hull will also occur, at least 2 base coats, and heavy meshing at edges.

    The glass will be structural poly ester or vinyl ester resin.

    At 8ft, 12ft, 16ft there will be transverse ply 3/4in at these approx locations. these will provide stiffness and be watertight bulkheads.

    The deck will have transverse beams approx. 10in off the DWL

    As for the transom design, i have that designed to be integrated as to be once with the hull. A 250 HP outboard will sit off the transom.

    Lightship i made a heavy estimate of 3100 lb

    Hydrostatics:

    Displacement 6355 lb
    Volume (displaced) 99.32 ft^3
    Draft Amidships 1ft 9.85in ft
    Immersed depth 1ft 10.06in ft
    WL Length 21ft 3.75in ft
    Beam max extents on WL 7ft 4.62in ft
    Wetted Area 144.98 ft^2
    Max sect. area 5.74 ft^2
    Waterpl. Area 125.19 ft^2
    Prismatic coeff. (Cp) 0.812
    Block coeff. (Cb) 0.343
    Max Sect. area coeff. (Cm) 0.487
    Waterpl. area coeff. (Cwp) 0.795
    LCB length 9ft 2.58in from zero pt. (+ve fwd) ft
    LCF length 8ft 10.99in from zero pt. (+ve fwd) ft
    LCB % 43.240 from zero pt. (+ve fwd) % Lwl
    LCF % 41.836 from zero pt. (+ve fwd) % Lwl
    KB 1ft 3.37in ft
    KG fluid 1ft 9.85in ft
    BMt 4ft 7.55in ft
    BML 36ft 10.6in ft
    GMt corrected 4ft 1.06in ft
    GML 36ft 4.11in ft
    KMt 5ft 10.91in ft
    KML 38ft 1.96in ft
    Immersion (TPi) 0.298 Long Ton/in
    MTi 0.403 Long Ton.ft
    RM at 1deg = GMt.Disp.sin(1) 453.47 lb.ft


    Design Goals:

    Be able to take moderately rough seas smoothly.
    Be somewhat efficient. not particularly necessary
    Be able to take an occasional pound.
    I plan on having this replace the 17' I have.
    Will be able to dependably go 150 nm offshore in decent weather, but in case of rough weather be able to maintain its structure and dependability.


    As to that house comment, srimes, lol, houses don't have to worry about where the trim of the vessel, weight of the structure

    PAR, i apologize for coming in 'arrogant'.
     
  12. SamSam
    Joined: Feb 2005
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    SamSam Senior Member

    A 24' deep v center console boat on the Glen-l site had 2 layers of 1/4" ply on the bottom and 3/8" on the sides. They don't say anything about frame spacing or structure.
     
  13. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Is there a reason you've elected to use polyester or vinylester, where the peel strength and effectiveness at moisture vapor penetration are limited at best? Epoxy is far superior in every regard and for one offs, really the only choice. Lets not talk about efficiency with that deadrise (which you clearly acknowledge). I estimate around 38 knots as a guess by her lines, Cp, HP, etc., possibly higher. You don't indicate fabric weights, but I'll assume just some mat to waterproof and fair. My initial thoughts are the weight estimate seems light, particularly with all the 2 by structure in it.

    Your initial questions of planking thickness now seem quite light, even with the framing structure. I'd use 1/2" minimum (BS 1088) on the bottom, probably better at 5/8" if much offshore work is planned, Reduce topside thickness to 3/8" to save weight and any decking should be this as well.

    I'd be inclined to go the monocoque route with this type of boat. You'd save on materials (except epoxy costs of course), eliminate considerably on the internal framing necessary (labor) and you end up with a homogenous structure that's less inclined to leak, squeak, tweak, point load, etc.

    The lines themselves are a not especially sensational or ground breaking, though I suspect you were not looking to do this so much. I would like to see more flare in the forward sections, considering this craft's intended employment. You could dramatically improve her initial stability (for fishing, diving, etc.) with much wider chine flats aft. These would also her "get up" out of the hole.

    And yes, you wouldn't believe how many people want to build a boat out of PVC pipes and duct tape (no kidding).
     
  14. pamarine
    Joined: Sep 2009
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    pamarine Marine Electrician

    I am by no means an expert, but for your intended use I would definitely suggest more flare forward and a wider chine aft.

    We are using a 1" thick laminate of 1/2" core-cell with bi-axial/mat on the inside and 3 layers of plank-stripped mahogany on the outside to give a light-weight monocoque hull (it's a 26' runabout).

    You may also want a bit sharper entry at the bow for rougher seas. But again, I am marine mechanic who dables in boat-building.
     

  15. yellowfinii
    Joined: Sep 2009
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    yellowfinii Naval Architect

    Thanks for your input, i have looked at the design a bit and now have a bit more flare on the bow, i'll post the new lines later for you to see its sort of a drastic change, but after some thinking, its more of what i want.

    as for the resin, i have never used epoxy besides the 6 inch dual tube thing used for minor gluing, i have much more experience working with glass, but may do some research and may use epoxy instead/ on some parts, have any thoughts about use of epoxy, as you seem to have good experiences with it.

    I am going to use 3 layers of 1/4 ply

    i also decided to change the frame spacing, 24" towards the stern, and as it gets closer towards the bow have 16" framing occur to make the shell plating easier.
     
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