Using Different Woods

I have read that cedar is the most common wood to construct wooden hulls. Is this true?
When laying 50 foot strips of wood together
does one have to allow for expansion or contraction of wood as I found to my cost when laying a wood floor at home?
I would like to add an extra layer of thin wood strips at an angle to increase the strength, which wood would you recommend and how wide?

I would then fibreglass the hull.
Is it really necessary to have an extra layer of angled wood strips when I am to epoxy and fibreglass the hull?

An important question, can I use all sorts of different woods mixed together of differing lengths etc as this would be so much cheaper for me?

I would be most grateful for any help or advice you may offer.

 

Cedar is indeed a very popular wood although certainly not the only choice. Framing and internal structure would usually be of a harder\stronger material. Supplies of clear cedar are falling and can be quite expensive. For a 50' boat the genral recomendation would be for something a little harder, like douglas fir or yellow pine.
A boat will expand and contract as a whole so dimentional changes due to moisture content will balance for the most part. Epoxy encapulation will stabilize the moisture content. The wood must be uniformly dry at time of construction or stresses will build after construction. If you are going to sheath the boat with fabric you really should fully encapusalate the wood, FULLY, or your hull will trap water within and rot will be a problem. Epoxy really changes everything about wood boats. For the better! Except the goo factor. Polyester resin is a poor adhesive and is not water proof. Even the best are a poor second to Epoxy and are really of little use in wood boats.
For structural guidence I use:
"The Elements of boat strength" by David Gerr, Pub. McGraw Hill/International Marine ISBN# 0-07-023159-1 He adresses diagional plies and when you need them vs. thickness of laminates over your hull. The widths are unimportant,it's thickness that counts. He covers almost any material of method you might consider using. Excellent book!

Different woods have dirrerent rates of expansion with moisture content. I would think you could get into trouble if they were to different. Some woods will absorb MUCH more water than others.
The Forest Products Labortory www.fpl.fs.fed.us/ has a publication "Wood as an engineering Material". More than you ever want to know about wood. Avalible in PDF. format on line. See the documents area of their Web site.
If you mix woods they should be of similar densities as well as similar expansion properties. Your boat might wind up stiffer on one side as well as heavier. Random lengths and widths are OK, varying widths make layout harder but there is no structural reason not. Bend and edge set will limit the widths you can use. Using Epoxy really lets us use wood of lesser quality than required for traditional construction. You can't use junk but you don't need the near perfect wood that was necessary for planking/framing in the past.
The Book "Gougeon Brothers on boat construction" is quite good, if a pitch for their products (West System). Good stuff if rather expensive.
www.gougeon.com/
Reuel Parker's "The new cold moulded boatbuilding" is pretty good too. His methods are for flat floor boats with very thick hulls and very little internal structure.
www.parker-marine.com/

Hope this helps more than it hinders.

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