Need help with fiberglass layup

Discussion in 'Boatbuilding' started by Aqtek, Nov 3, 2010.

  1. Aqtek
    Joined: Nov 2010
    Posts: 5
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: USA - Colorado

    Aqtek Junior Member

    I just purhased a mold set for an open 23Ft center console bay boat. The specs are:
    LOA 23'-0"
    BOA 8'-6"
    Deadrise 15 degrees
    Boat weight (dry less engine) 2,,650 lbs

    I need to know what layup to use or for a non-cored layup. I'm trying to estimate what a high quality boat would cost. The bottom has to be tough enough to be beached once in awhile on sand.

    Or maybe there is a fiberglass supplier who could provide this information?

    Thanks
     
  2. rwatson
    Joined: Aug 2007
    Posts: 5,754
    Likes: 257, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    Using McNaughtons scantling tables, for 2500 to 2900 lbs, you need 7/6 -

    which means as I understand it 7 layers of 2 oz matt
    6 layers of 24 oz woven roving.

    Application notes :
    "Solid Frameless Hull & Deck Shell
    Material: Alternating layers of 2 oz. (per sq. ft.) mat and 24 oz. (per sq. yd.) woven roving with polyester
    or epoxy resin. First and last layer to always be mat.
    Thickness: From the table
    Remarks: This method gives adequate fatigue resistance and stiffness, and more tensile strength than necessary.

    This is the simplest form of construction; though heavy and with high material costs."

    24 oz per square yard = about 813 gsm according to the thread

    http://www.boatdesign.net/forums/materials/glass-cloth-weight-conversion-table-18555.html


    Hopefully this will give you a good start. I would bet you could go a lot lighter, but expert advice on layups is hard to find.
     
    1 person likes this.
  3. Aqtek
    Joined: Nov 2010
    Posts: 5
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: USA - Colorado

    Aqtek Junior Member

    Thanks for the information, but you say expensive material cost. The number of layers would indicate high labor cost as well. Also sounds very heavy. Suppose I use a frame structure (grid) in the bottom?
     
  4. rwatson
    Joined: Aug 2007
    Posts: 5,754
    Likes: 257, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    according to McNaughtons figures, those layers result in about 20mm ( .7 " ) thick hull, which is a very conservative thickness, designed to handle all sorts of groundings, collisions, etc. as the book actually states.

    Hand layup of the layers could be done in 1 layer of mat + 1 layer of woven in the same "session", so you are looking at seven "steps". So, not too onerous to do.

    My opinion is that you could leave out some layers in less stressed areas, but you might need more where engine beds etc, are to be placed. You may be able to create some strong points by glassing in some high density marine core material (Airex etc)

    The big question you need to consider is where the boat is going to be used, and do you have to insure the hull, possibly sell it one day ? If so, do you have to have the hull certified by someone ?

    If you dont have too many official concerns, if would do say, 5 of the 7 layers - and make an assesment on the rigidity. There would be no reason you couldnt pop the hull at that stage, put on some temporary cross beams in place of the deck, and put a small outboard on the back, and actually launch it, get a feel for the hull flex, weight and thickness. If you spotted some potential problems, you could glass in some stringers, a frame or two etc. "Common sense" might inspire you to add extra re-inforcing during the layup to stress areas like the keel and transom.

    But, if you dont have the time to do the 'trial and error" method, you are going to have to pay an expert to work it all out in fine detail.
     
  5. raw
    Joined: Jul 2006
    Posts: 133
    Likes: 5, Points: 0, Legacy Rep: 59
    Location: Oz

    raw Senior Member

    Here's a ballpark answer for costing only. None of this is engineering advice and is worth exactly what you paid for it. There is also far too little information in the opening post to give a definitive answer. someone like myself who does this kind of work for a living would need detailed plans to sort it out properly.

    As a starting point for costing, bank on a base hull laminate of perhaps 8-12mm thick for the hull bottom and maybe one or two mm thinner for the topsides. This assumes framing is to be fitted throughout. Assume 50% more material for the hull framing. It is assumed that some of the hull framing tabbing laminates will give additional thickness in most/some areas. Assume at least 30-50% db/woven roving in the laminate by glass weight

    Deck thickness will depend on framing layout but if cored will probably be in the order of 15mm foam with maybe 2mm glass either side.
     
  6. rwatson
    Joined: Aug 2007
    Posts: 5,754
    Likes: 257, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    That makes a lot of sense.

    The McNaughtons scantling info refers to 3, 2 if you are using frames.
    (thats 3 layers of the rovings, 2 layers of the 800 gsm woven stuff.) That would work out around the 12 mm thickness.

    Personally, I would reckon 8mm a bit on the light side for a 2 tonne ( with motor, fuel and passengers) in a 23 x 8 ft motor boat.
     
  7. apex1

    apex1 Guest

    First proper reply on that!

    Regards
    Richard

    sorry watson, leave the guessing, you do not help those people
     
  8. rwatson
    Joined: Aug 2007
    Posts: 5,754
    Likes: 257, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    Oh - sorry. I guess providing a detailed layup schedule backed by a well know ( if not popular ) boat builder doesnt provide any useful data.

    He is far better to rely on estimates " None of this is engineering advice and is worth exactly what you paid for it. " - thats a much better idea.
     
  9. raw
    Joined: Jul 2006
    Posts: 133
    Likes: 5, Points: 0, Legacy Rep: 59
    Location: Oz

    raw Senior Member

    watson,

    you cannot give a detailed answer to the question based on the information given. Your "detailed" answer of a 20mm laminate is simply inadequate to build from. A complete layup schedule will include details of laminates for hull sides, hull bottom, chine overlaps, keel overlaps, transom and should be related to the framing etc etc etc.

    As it is nobody here even knows if the boat is of inboard or outboard design.

    What I gave was straight off the top of my head based on what I have specified done in the past for several of these types of vessels. For costing purposes, provided the original poster allows additional for overlaps, wastage etc it will be reasonably close for a polyester construction.


    FYi, to also put your 20mm solid laminate in perspective. I have in the past spec'd a 60' sportfish (3000 hp/~30-35t) with a base bottom laminate of 15mm. Of course, the framing is part of the solution at the end of the day.
     
  10. apex1

    apex1 Guest

    It is just mad to try calculating a unknown structure watson!

    Thats is it. Don´t drivel, you failed.

    Richard
     
  11. rwatson
    Joined: Aug 2007
    Posts: 5,754
    Likes: 257, Points: 83, Legacy Rep: 1749
    Location: Tasmania,Australia

    rwatson Senior Member

    I know English isnt your first language Richard, but I said exactly what you are trying to infer I didnt say.

    he can either use trial and error with some conservative calculations, or he can get an expert to do a layup[ schedule !!

    If this isnt the same advice as you are giving - what is ??
     
  12. Aqtek
    Joined: Nov 2010
    Posts: 5
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: USA - Colorado

    Aqtek Junior Member

    I've been out of the loop for a few weeks - traveling - and am a bit suprised at some of the posts.

    Since a boat is an engineered product right from the start of the outline specification why is there such a scarcity of data on building materials. I'm a degreed engineer so estimates make me very uneasy when it comes time to putting material (and money) to work. Since each pound of material costs a few dollars it doesn't seem wise to put a couple hundred pounds into building the boat realizing that those extra pounds will forever add to the fuel costs.
     

  13. viking north
    Joined: Dec 2010
    Posts: 1,864
    Likes: 87, Points: 48, Legacy Rep: 1146
    Location: Newfoundland & Nova Scotia

    viking north VINLAND

    Aqtek, don't know if this is a prototype for future production or not but when i had to do the same with my Shelbourne Dories i took a step back and decided to visit several fiberglass fabricators and get some idea of price per hull. To my surprise their cost was only about $250 more than materials and labout if had my on call fiberglass man do it. The only catch was they would do it say when they had a slated job completed and had say a half day with two men sort of idle. Fill in work, it's good to keep their staff on and busy.-- just an idea, Geo.

    A yacht is not defined by the vessel but by the care and love of her owner
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.