Softwood vs Hardwood for timber

[Andre]

Hello.

My son and I are planning on building a Tiki 21 this summer.

The study plans for the boat call for soft wood lumber.

"Timber: Use a fine grained softwood (white or red pine, spruce, Columbian Pine
etc.),selecting wood for grain and ‘no knots’. A light weight hardwood, such as a light
mahogany (also called gaboon or occume) can be used."

But we have a friend who just sent us this message:

"I have 1000 board feet of white oak logs sitting in my yard here and we are going to saw them up.
If you have a detailed list we can rough saw to suit and finish plane later."

So my question is this:

Would lumber cut from white oak logs be an acceptable substitute for "...fine grained softwood" in building the boat?

Unless we are told otherwise, we are hoping to take advantage of this generous offer.

If someone knows that this would be a mistake, please let us know.

We'll be checking the forums, or you could email us at:

[e-mail]
or
[e-mail]

Thank you!

[Ricardo Aráoz]

I think oak will weight much more than spruce. I would find out the specific weight of both timbers and calculate the weight difference.
Durability shouldn't be considered as wood is encapsulated in a Tiki. Strength, spruce is more than adequate.

So, I would consider the weight difference against whatever money you may save in materials.

[Ian Bamsey]

Weight is a big factor, but also consider how well epoxy takes to different woods. I found that Douglas Fir takes epoxy very well. It is light and strong. I used some hard wood on my Tiki21 for bits of the deck structure. I have had to replace some bits where the epoxy didn't form a strong bond.

[Andre]

Thank you Ricardo and Ian for your help here. I hadn't even considered the extra weight, but I realize that on a boat this light every extra pound could affect performance. And since the entire boat is held together with epoxy, a strong bond is absolutely essential. Did not know that different types of wood took to epoxy in various degrees. We have much to learn. Very grateful for your help.

[Robert Hughes]

Oak doesn't glue well with epoxy, something to do with the tannin content I think.  Some hardwoods are difficult to glue well due to their natural oil content, but as long as the surface is properly degreased it can be done.  As an example, I've had some success with iroko.  Softwoods are much easier, but most are more prone to rot than many hardwoods.  I've not used mahogany very much, but would expect it to work well as it's quite a "dry" hardwood.

[Andre]

Thank you for this information Robert.

As it turns out, we have decided to wait until next summer to proceed, due to the limited supplies and high prices that are in effect now. When we do proceed we will look for the softwood that is called for in the plans. Better safe than sorry.