Opinions on alternate keel material

[grousehunter]

Eighteen foot open daysailer, centerboard, bent oak frames (.75in x .75in), carvel planked (.625 in thick) hull, knockabout rig of approx 200 square feet. Diaplacement will be close to 1,200 lbs. (A very close copy of an Alden O-Boat but of a different architect's design). I would like to use longleaf pine in place of the white oak keel. The plank's finished cross-section is 1.625 in by 5.50 inches. It has a fair amount of camber and needs to be sixteen feet long. It widens naturally to accept the slot for the centerboard and tapers to about two inches at both ends.
I am proposing the swap in YP but intend to duplicate the strength in pine by bumping up the moment of inertia of the existing cross section so that bending stress, once calculated, ends up being about equal to that with oak. I am assuming that using bending stresses to find the new cross section in yellow pine, is better than using either sheer or torsional.
Comments are very much appreciated.

[Thorne]

Re: Opinions on alternate keel material

I am proposing the swap in YP but intend to duplicate the strength in pine by bumping up the moment of inertia of the existing cross section so that bending stress, once calculated, ends up being about equal to that with oak.

Main question is, "Why"?

[Paul Pless]

Re: Opinions on alternate keel material

Main question is, "Why"?

Why not?

Perhaps its a locally available substitute. Surely Long Leaf Pine, Pinus Palustris, would make an equivalently strong and rot resistant keel as white oak, wood it knot?

[ishmael]

Re: Opinions on alternate keel material

Yellow pine would work fine assuming you can find something resistant to rot. Nothing much to do with the stability curves. The stability of those little Alden and Alden-esque centerboard boats didn't come from the wood in the keel. It came from a few hundred pounds of lead pigs in the bilge. Yellow pine or WO, minuscule differences as to stability. Not to mention Ipe, or other SA hardwood, which have been more available, perhaps until recently.

[grousehunter]

Re: Opinions on alternate keel material

Good point Ishmael.
I should have also asked if there are any construction considerations in making this swap. The only one that I know of and plan to heed is the lower compressive strength normal to the grain, of YP. Because of this I will build the mast step to distribute the load over a couple more frames to take care of this.