Need Lamination Advice

Forum Members,

I am about ready to purchase glass for the construction of the deck, cabin, and other misc. structures on my unfinished 46' motorsailer hull. The existing hull is prepreg glass and kevlar over 1" Core-Cell. (purchased from a defunct manufacturer). I have settled upon Core-Cell for the remaining structure, and will be using stiched fabric with epoxy resin. Can you please provide some input on the following questions?

1. If, for the sake of this discussion, we consider the entire deck/cabin structure as a simple flush deck enclosing the entire boat, and I use only unidirectional fabric, what percentage of the lamination would you want to see running at 0 deg, fore and aft, and what percentage would you want to be running in the +45deg and -45deg directions? (or 90 deg?).

2. Is there and benefit in constructing the main stringers (and engine bearers), entirely from unidirectional material (fore and aft) or should the lamination contain material running in the 90 deg. direction, and if so, approximately what percent?

Any thoughts you can share would be most appreciated.

Regards,

Doug

 

In partial answer:
2. I think here the unidirectional material will satisfy your needs extremely well for the stringers, though I won't comment on the engine bearers as I have no experience putting motors in my sailboats, or (besides outboards) on ANY of my boats/designs for that matter.

1. I, personally, would just go with weave for the deck...saves me from having to decide how much uni to run in each direction. Then again, I'm not into international championship racing so, if you are, then uni would likely pay off for you...but I would be a bad person to take advice from.

 

Thanks Rob,

and one more question to the group...

What is the heaviest fabric you would recomment that an amateur try to install in a single hand lamination? When using a vacuum bag?

Doug

 

there is nothing wrong with using uni directional glass for the whole structure just you need to think about what you are doing . Engine beds the same just you need to understand what uni is all about. Its strength is in one direction something to remember always at 90 degress to its self it has vertually no strength at all , dont forget what i have just written . Uni used with and in combination to other fabrics can be and is benificial to the stiffness and flexual strength of a laminant . Flexual strength can and does act as a shock absorber if used the right way and is very hard to break . it will bend a mile before fracturing .So to use solely uni you have to think real hard anbout what you are trying to achieve .

 

Thanks Tunnel. I understand what you are saying about the properties of uindirectional fabric. In an stringer it would seem to me that there should be at least some percentage of the fiber orientated at 90 deg to the long axis. However, I'm not sure what this percentage should be. Dave Gerr makes a comment about this in his book, implying that a 0/90 deg fabric is better that a +45/-45 fabic for stringers because it has at least 50% of the fiber running in the longitudinal direction as opposed to the +45/-45 fabic with 0%. If 50% is good, is 75% better? is 100% too much? These are my questions.

 

As a basic stringer configuration
double bias 45/45 from on the hull , up the stringer over the top and 50mm down the other side , then do the other side of the stringer the same along , up and over down 50mm . Along the top of the stringer run uni's from one end to the other in a unbroken layer going out onto what ever is at each end at least 150 to 200 mm and spreading the ends like a fan tail on all layers .Its important to start the layers on top the same width as the stringer and gradually bet bigger as you put on more layers The number of layers depends on the size of the stringer . 4 layers of a 450 gram is the minimum Glass need t be laid with no kinks or bends so as straight as possible . Tieing the ends is very important so spreading in a fantail gives excelant bonding to whatever there is at the ends. To finish the stringer the same as the first layers , a double bias along up and over and down 100mm . Is important to hide ends of glass strands under a finish layer and peel ply to give a smooth and nice finish .
ON the top of a semi bulk heads it possible to take the uni's through a elongated hole to the outside skin of the hull and then fantail the glass . dont with race boats sometimes .
You will have the idea of what its all about i would say .

 

Thanks again Tunnel, that was just what I was looking for.

 

Tunnel,

Another quick question. I understand that ideally you would like the top of the stringers to be perfectly flat. However, if I set the top of the stringers at the proper level in the engine room (amidships), I need to lower them forward. Likewise, I as they move aft, I want them to rise slightly and follow the rocker of the stern. My plan was to make a very gentle transition where the stringers change elevation, or is there a better way to handle these changes?

Regards,

d.

 

The top shape is not a issue it can be flat ,it can be a part of a curve, any shape at all ,just use the same principal .The thinner the stringer the harder it is to apply this principal ,But there again a bulb shape along the top edge applies and cover it with the double bias. When strain goes on a narrow stinger its the fear of the stringer collapsing to one side or the other so more glass will need to be applied to the sides to keep it standing vertical so it does its job properly .
Changing shapes longtudinally causes weaknesses where the change of a straight line is , a sharp angle up or down is a weakest point so a gental curve is better but more glass can be appied to the side and up and over just in these areas to counteract this ,any extra glass is better done under the top covering layer
Its is better to use glassfibres as it will streach and absorb shock rather than someting like carbon that does not streach and with throw enormous loads on the rest of the stringer and cause alsorts of problems .
Uni glass is a fantastic medium to play with and has endless possablities .
I have made whole hulls and decks using just uni and chopped strand matt along with a good quality polyester resin .
This was done for surf life saving where the punishment on the boats is far more than a human can take . Even after 8 years of continuous use showed no signs of fatigue or stress and always passed its 4 times a year total survey with flying colors.