Knitted fabrics. 45/45 vs 0/90 vs 45/45/0

My experience with a larger number of boats with strakes is indeed to make the strakes fairly lightweight and basicly sacrificial, until they are level with the hull, then apply the (plenty strong) hull laminate.
Other solutions usually form cracks or other mayhem.

On the forgotten link: Here it is:

http://www.brandscomposiet.nl/products/documentation/n/B20 Glasvezels.pdf

 

The other reason for filling starkes is it makes the hull bottom a little stiffer . Glass strands laid flat and straigh make better panels so going down into strakes makes the panels more able to flex and work in the strakes and over time create weak spots and later damage so need more and better internal framing and has to be better glassed in and onto the hull bottom !!
Filling the strakes helps enormously and in the case of hitting things will deflect better without causing damage .
Me i like hull bottoms that move and take up shock from hitting waves etc They are smoother riding and more comfortable on a long ride . The differance is noticeable !!! one day manufactures will cotten onto this . Stiff hard riding boats are not user friendly and uncomfortable specially for long trips all day and hours later onshore you have sore legs and your back starts to play up . Its a well known fact the human body can only take those kinds of conditons for limited periods of time before perminant damage takes it toll!!. Knees , backs and knecks suffer the most !!!

 

Tunnels is right. I have raced enough carbon racing boats to know these are uncomfortable, noisy and bumpy machines. Lightweight, yes. (or sometimes not even that)

Even the 4 meter (13 ft) carbon racing dinghies were "harder" than their wooden equivalents.

 

Question: Wouldn't a less stiff boat have a shorter service life due to constant flexing of the laminate?

 

Turn that round the other way !!a stiff boat is less forgiving and much more prone to damage and breakage and shows signs if stress because things have no natural give !! the more it moves the longer it will last provided its built that way !!

With any boat its what glass is used and how its used and what resin is used
A boat with flex has to be built that way ,if you use just everyday off the shelf glass then it might have a shorter life depending on how its made and how good the workmanship was when it was first made .

My own boat was made 1975 sure has stress marks in the bottom where its had a hard life some where but its as sound as the day it was made and its just chopped strand and woven roving .

How do you determin the life exspectancy of a hull ?? what would make one boat last longer than another ?? in most every case its the people making the boats that determin how long its going to last along with that is the types of glass and resin used . and lastly the internal construction and the way its been put together , The more wood used in the boats framing and construction the shorter its life exspectancy , i learned that way back in 1984 when i was workshop foreman for the best powerboat manufacture in NZ at the time , there second hand boats even today fetch a really high price and are a investment because of the way they were built , everyone in the company was proud of there work and it shows even more that 20 years later .
I got rid of my wood and glassed over transom as it was wet and the only wood left ,100% of the boat now is glass. and will never have to worry ever again !!

 

A good way to get to know glass is to go to the shipyard and observe repairs to boats that have had " fender benders" or Humpty Dumpty boats

De lamination , resin strength, secondary bond failure, " peel" strength ,type of structural glass used.

It easy to see the engineering and you will be amazed with how poorly many production boats are built.

 

On flexi boats, problem areas are "hard spots". Avoid these, and you are good to go.

See the amount of flex a wind turbine blade takes. And in a lot higher frequency than any pleasure boat.

 

Thanks everyone. I have been away from computer for a day or so.

Much appreciated.

Ian.

 

Boat repairs is a place everyone involved with glass should spend a year doing ! have been there done quite a bit . its 90% poor workmanship where you can point your finger and 10% poor choice of materials where the faults are ! its not ony production boats , its boats in general !! well built you never see. after storms and boats washed up and hit into things thats the place to go !!
Good ahh!!!

 

Some of these production boats with cored construction have no fibers in the outside hull skin !!

Incredible.

The picture is a piece of outskin hull laminate from a XYZ production boat.

Last week A roller scaffold ran away in the yacht and its steel pipe poked in a production balsa core hull.

Id mention the name but I might get sued.

There is no fiber in this skin...only core mat ? chopped mat, gelcoat.

I can easily snap a section of hull skin in half between my fingers.

 

So made in China is not so bad after all !!
Like i said its the miss use of materials not the materials them selves ! the company wants a good swift kick where it really hurts in there bank account and the persons invloved inn making such products need to go play on the railway tracks . trouble is who was the person that suggested it and who were the people that did the job . some where some one was saying this is not right and should not be done . the forman of said company should have his name in lights and big posters of his face on every bill board . inonimously the company should be exsposed and it should be made known publicly . find a tv crew and show them , how many people watch tv ?? everyone every where !!cell phones and video and exspose it . you could save some ones life !! just buy a sim card and send the message then remove it from your phone . i always carry a spare simcard for just such occassions . can buy them at the local corner shop no names get recorded .you see phone video all the time .:idea::?:

 

I guess this brings us back to the original question .... what should the skins of a boat be. Its laminate schedule, minus local reinforcment.


For me its a dark science.

Some boats seem to be all unidirectional fibers ,some boats a mish mash of mat and roving...... some boats only coremat

 

Ok the last statement you need to discribe in more detail !!!

The only place for Core mat in a hull is topsides and its a core material to help stiffen the top sides not for any other purpose !! so it will be in the middle of the schedualled lay up for that part of the hull .
When you say all unidirectionall fibres its what most materials are made from !!! layers of uni running in differant directions !!double bias !, triaxle !, quad !! are just layers of unis !!

Mish mash of rovings ?? !discribe what you mean ??:?:
Its not a dark science at all :idea:it just plane common sense and understanding thats it .
keep it simple and straight forward and you wont get it wrong !!
You can build any size of boat from a 10 foot dinghy to 100 foot boat its not that hard to understand !!
theres just basic rules to follow , things you can do and you should do and things you should not do and if you do you get into strife !!!

Step one you have the laminate of the hull , then step two you have additions like framing and stringers and bedding for stringers etc etc .

The moment you start changing and stepping away from the basics you will get into trouble for sure !!
First is the mixing of types of materials Glass , carbon and kevlar
And when you using the more exspensive materials then resin systems need to change to match the strengths of the stronger fibres .any of this make any sense ??

 

Yah.

2 layers of Uni directionals at 45, 45 to centerline with a layer of uni running for and aft. I see it on a small foam core racer cruiser in the yard. Boats about 15 years old. Those UNI fibers really print thru the skin after a few year of hard use.

And yes...that chunk pictured, of coremat and csm peeled directly off the balsa core of the boat in the yard hit by the roller scaffold.

Honest,,,I picked it apart and cant find a fiber longer than say 5mm. I can snap it in two with my fingers.

By dark science I mean that I dont understand it and I cant see it with my eyes. Two nice boat A and B. Which has the better, more robust laminate schedule ?

How do you know ?

With wood or metal material scantlings and construction details are obvious.

 

So bak to original question... If you were going to spec the lamination schedule for a 25 foot boat (Surfhunter type hull performance requirements) where do you start?

Hull sides -
Gel coat
1.5 CSM .75 oz at a time allowing to harden between layers.
2 layers of 90/+-45 (90 running gunnel to chine)

Hull bottom
Gel coat
Same CSM
1 layer of 0/+-45
strakes treatment from above
2 layers of 0/+-45

How much is too much?
How much is too little?

I started thinking about this when reading the Fairy Hunt 18 mold restoration and build thinking that the layup was very light in that boat. I know that hull and it can take some pretty big water for its' size and I would have thought there should have been more glass in there.

(beautiful work... Just questioning layup schedule.)

Cheers!

Ian.