Sunday, January 5, 2014

Tulip Poplar for Oars?

Our new Core Sound 20, Summer Breeze, needs a set of oars.   After researching various oar designs on the web and comparing the mechanical and subjective qualities of various woods, I've decided to make them out of Tulip Poplar which is cheap and plentiful here in south eastern Pennsylvania.  People are surprised when I tell them of my choice so I'm posting my analysis here.

Table 1 shows a few select woods that I wanted to compare.  Most of the mechanical properties are taken directly from the Wood Database, a fantastic resource for investigating boat building woods.

Table 1. Properties of woods for making oars

The table provides Density (how heavy the oars will be), Modulus of Rupture which denotes strength against bending force, Modulus of Elasticity which denotes bendyness, and price per board-foot.  FAS is code for furniture grade wood.

I want a wood that is light, strong and bendy.  It should look good but not cost too much.  Typical woods for oars and other spars include Sitka Spruce, Ash, Pine and Fir.  I am lucky to be 30 minutes drive from one of the best hardwood suppliers in the country, Hearne Hardwoods. The large yard is piled high with flitch cut logs air drying or waiting to be milled.

Flitch log at Hearne Hardwoods
They have great prices on Ash, Cherry, Pine, Tulip Poplar and lots of other exotics.  Most of the prices in Table 1 come from Hearne.  I've ranked my selection based on weight (density), elasticity, strength (modulus of rupture), quality (FAS, common, select, clear) and price:
  • Sitka Spruce is very expensive ($15/BF Chesapeake Light Craft).  It has a good strength to weight ratio and is very elastic.  Too expensive around here.
  • Eastern White Pine is the lightest in my list but also the weakest and most brittle (least elastic).  Hearne has some very clear white pine, but it is expensive.  
  • Spanish Cedar is great to work with and beautiful to look at but it is brittle, a bit heavy and on the expensive side.
  • White Ash is the strongest (modulus of rupture) and most elastic but also the heaviest.  Many great paddles and oars are made from White Ash and it is inexpensive but too heavy for my taste.
  • I included Black Cherry just out of curiosity.  I think it might make fine oars.  It is more rot resistant than Ash but also less strong and elastic and costs more.  It is prettier, easier to work but not as tough.  There is a lot of locally grown cherry in PA so it is relatively cheap here.
  • Western Hemlock (Hem-Fir) 2x stock from Lowes is cheap and has great mechanical properties.  Because it is only available around here as construction lumber (common grade), even the best planks will have some small knots.  
  • Tulip Poplar has great mechanical properties, is fun to work with and looks good.  Hearne has great pricing on FAS grade (furniture grade) stock in many dimensions.
Grahame Byrnes of B&B Yacht Designs told me that Hem-fir is a great alternative to sitka spruce.  The wood database confirms this (Table 2).  Tulip Poplar appears to be another great alternative.  Robb White, a well known boat builder and writer used Tulip Poplar for many of his beautiful custom boats. Compared to hem-fir it is much prettier, easier to work with, just as light, about as strong and elastic and not much more expensive.

Table 2.  Hem-Fir and Tulip Poplar vs Sitka Spruce

Tulip Poplar is the wood for me.

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