Wooden Spinnaker Pole

Update: Well the Ronstan spinnaker pole ends I order just don't look up to the task (they looked much stouter online) so they are going back and now I have to source something else. Hard to find external pole ends these days. I am planning a trip to one of the local marine consignment shops. Hopefully I can find a nice set of bronze pole ends.

Okay, this is pure folly. I admit it. I have no time to add a new project to my list but I am going to try to anyway. For some reason I have decided that I would like a wood spinnaker pole for Bolero. I have no good reason for this, I just want one. Oh, I could argue that the one that came with Bolero is beat up and shot (it is). Or I could say that the aluminum cast pole ends are pitted and ugly (which they are). But mostly I just like the idea of a varnish wood spinnaker on the foredeck or mounted to the mast.

This idea started out simply enough, I was going to buy a solid piece of Sitka Spruce and create a solid tapered pole. Then I stumble across hollow bird's mouth construction and I started down that path. But in the end I decided to make a bit simpler first attempt and follow the approach described in "Skene's Elements of Yacht Design" by Norman L. Skene and revised by Francis S Kinney.

Here is the spinnaker pole sizing table from Skene's.



I find it interesting the way they define the "Area of Spinnaker in SQ FT" as the base of the fore triangel times its height. For Bolero that equates to:
Area of Spinnaker = (9.4) (30) = 282 sq ft
From Skene's table the width of a tapered wooden spinnaker pole can be expressed by the equation:
Width = (Area of Spinnaker + 650) / 450
Plugging the base time height area from Bolero the pole width dimension becomes:
Width = (282 + 650) / 450 = 2.07 in
This seems a bit small to me but then I don't have any experience in wooden spinnaker pole design.

Skene also specifies that the tapered ends be 65% of the maximum section. This is often dictated by the available pole end fittings. In my case I have ordered Forespar RF601 1.5 in external Pole Ends.



Using the end fitting as the design parameter the middle of the pole becomes:
Width = (1.5) / 0.65 = 2.31 or approx 2 5/16 in
Using Skene's 20% wall thickness relationship t becomes:
Thickness = (2.31) (0.20) = 0.46 or approx 1/2 in
I sketched up these section as shown below.



So the plan is to wait for the pole ends to arrive and then make a test out of inexpensive wood and go from there.