moisture content

[CK 17]

I'm about to start my 1st boat--the riverside dinghy. I'm using"building small boats" as a guide.

My question is: what is the maximum moisture content I can get away with? What is the normal moisture level found in lumber yard stock?

The book suggests anything less than 25% will inhibt rot. There seems to be a great deal of traffic on this subject. Should I build a kiln before I build the boat?

Thanks

Joe Schena

[reddog]

joe;
I see no one has bitten on your question so I'll put my 2 cents worth in.Congrats on your first project.
There are a number of variables which would govern the best moisture content.Type of construction,woods used,etc.In my area for carvel or clinker,(lapstrake),construction using dimensional lumber air dried is the preferred.Here in Nova Scotia if you air dry for one year per inch of thickness,properly piled and stickered,you can expect around 12 to 18% MC.This will dry somewhat further during construction.
For cold moulding or strip planking you would go with a lower MC,possibly kiln dried.Kiln drying can make the wood brittle and difficult to take a bend.
Construction grade lumber can range from sopping wet to 19% MC to kiln dried.If it is grade stamped it should have the MC also.That being said construction grade lumber usually does not yield high grade boat timber.If you're on the west coast,have a good mill and are willing to pick through the piles you may find some decent stuff.Further drying at home will probably be necessary.
Clear as mud,eh?
Good luck and all the best:Earl

[CK 17]

Earl,

Thanks for the info.

joe

[reddog]

No problem Joe.Kep us appraised of your progress.
Earl

[CK 17]

Earl,

Actually, I'm relatively close to you in New Hampshire. I'm planning to use cedar(white,northern, eastern, whatever I can find)and White oak for the frames. This is what the plans call for. Hopefully I can find it relatively dry. I would hate to delay the project 6 months or more waiting for the stuff to dry out. I'll keep ya'll posted.

Joe

[A. Mason]

Joe, my father always warned against using the same type of lumber used for building a house for building a boat. Locate a source for "marine" lumber, tell them what types of wood were originally specified for the design, and ask them what the available alternatives are today.

Many of the woods my father specified in his designs are no longer readily available today. Moisture content is one consideration and the weight of the wood is the other consideration.

If you substitute the wood specified, you need to pay attention to its weight. Also be sure you make all the parts exactly the thicknessses specified.

My father used to warn that even fractions of a inch increases or decreases in thickness can make a tremendous difference in the final weight of the boat. This will have a direct influence on whether the boat will perform as it was designed to perform.

Hope this helps,
Anita

[Bruce Hooke]

As far as the building process goes, and moisture content, rot isn't really the concern. It's very unlikely that wood would start to rot during the building process unless you let rainwater get at it or set the wood right on the ground.

As background, some of the important issues relative to moisture content are:

- If you will be steambending the wood then wood that is somewhat on the green side is better. There is lots of controversy, well covered in the forum archives, about how green is best for steambending. My opinion is the sharper the bend the greener the wood should be.

- If you will be using epoxy then it is essential that the wood be relatively dry (below 18% or so).

- Wood with a high moisture content will likely dry out and therefore shrink during the building process, which could cause problems (joints opening up, checking), but then, if the boat will 'live' in the water it will re-expand when the boat goes in the water. If you are building the boat in an unheated space with a dirt floor then the wood may stablize at 18% or so, if you are building in a heated shop then it will likely get down to 10%, or even less in the winter. Wood with a very low moisture content may expand too much when the boat goes in the water.

So, as you can see, you may need to choose woods with different moisture contents for different parts of the boat.

With that as background, to get to your original question, your average construction lumberyard will have nothing much of use to you for this project expect for construction lumber for building any jigs, bracing, and similar temporary stuff. For reference, however, most stuff at such a lumberyard will be dried to around 12-15% or less, except for the douglas fir and some of the large dimension stock, which may be a good bit wetter. So, the next place to look for wood is a hardwood lumberyard. There everything will most likely be dried to under 10-12% because the assumption is that it is destined for indoor furniture and trim. That is fine for parts like thwart risers and rubrails (they are small enough that shrinkage & expansion is rarely an issue), but not so good for steaming, where wetter stock is better. To get greener wood for steaming you will probably need to hunt down either a sawmill or a place that specializes in boat lumber (or both together). For the planking stock (which is what I assume the cedar would be) I would probably ideally look for some stock that has been dried to outdoor levels (say 15% or so) as a compromise between stuff that won't shrink too much as you work and won't expand too much once the boat is launched. Cedar is something you will probably have to go to someplace that specializes in boat lumber to find anyway, so once you find it the moisture content will probably be reasonably on target. If anything it may be greener than you need but if you buy it now and stack and sticker it for a month or two in high summer it will probably dry out enough unless you are starting with completely green, just cut, stuff. And unless you have a lot of time to put into this project it will probably take you that long to get to the planking stage anyway. If you are going to be building very quickly and then launching in late summer then slightly greener stuff might be better anyway because the wood won't have as much time to dry out between when it goes into place on the boat and when the boat goes in the water and the wood starts soaking up water again.

I've thrown a lot at you here so in closing I'll add two points:

1. Don't get too wrapped up in the whole moisture content issue. You can be off by a good bit without it causing too much trouble. I would basically break things into 4 groups and figure that as long as you're close to the right target area you should be OK: 1)Green, 2)Less than green but still wet (18% +), 3)Dried to outdoor levels (12-18%), 4)Indoor dried (mostly likely by kiln - <12%).

2. If any of the above left you lost speak up. I am just 'rambling' this off so I'm sure I jumped over some things.

Hopefully others will jump in and add other perspectives & corrections.

Congratulations on starting your first boat!

- Bruce

[CK 17]

Bruce,

Thanks for your post. Yours and the others are very helpful. I'll keep you posted.

Joe

[Ed Harrow]

Joe, you should hook up with Andy (Abe). I know he's busier than a one-armed paperhanger at the moment (didn't even make it to the show for crying out loud). Do a search and you should be able to find a post, which will likely have his email address. Heck you probably even know him given that your home digs isn't exactly Manhattan, LOL.

Look in the back of WoodenBoat, you'll likely find a relatively local source of wood right there. Finding a mill the specializes in supplying boat builders should be high on your list.

Good luck!