Saturday, December 26, 2015

Made the spars for SEI today.

The spars for SEI are simple rectangular sections with rounded corners, sure they're tapered but only in one plane. Easy stuff.

I’ve already got the mast done fiberglassed with a glass sleeve material from Duckworksmagazine and painted, it just needs a leather piece around it where it goes through the partners and the fittings for lazyjacks and halyard bolted thereon.

Heres the glass sleeve link, I did a comparison between a mast of the same size and SEI's mast with the glass sleeve and its markedly stiffer.  Good stuff.

So now its time to make the yard and boom.
Yes I know, “Boom” is a noise used for starting yacht races, English is a wonderful language isnt it.

I’d a piece of Fijian Kauri, nice wood, this one seasoned for several years in my stack of interesting and useful pieces of wood, so it can be relied upon to be stable and not warp. Agathis Vitensis is an easy wood to work , not quite as strong as New Zealand Kauri but slightly lighter in weight, both are stable, both strong for their weight.

First job, the piece I had was 50 x 250, ( two by ten) by 4m, (just over 13 ft) which is plenty long enough for that job.  The “Long Steps” build is not far off getting serious and I’ll be needing stringers, so while sawing the lengths for the SEI spars I cut the rest into 25 x 32 stringers for that project. When scarfed up that will give me four stringers long enough for the lower ones on LS.

The two pieces on the right are the boom on the right, the yard on its left. The pieces cut from the ends will come in handy somewhere in the next build, you'd be suprised at how much wood you can soak up in small pieces when making up cleat stock and grounds for frames and seating.  
The rest will be stringers for Long Steps, I'll need about three times whats there but its a start.

Having cut the blanks for SEIs spars, I then used the lovely Leuco sawblade I have in the sawbench as a planer to take the roughsawn grain off, it leaves a near planed finish, beautiful and much easier than dragging the thickness planer out and making a heap of shavings ( note to self,  fix up the old single phase dust extractor system and bring it up to this shed, it’s a pain in the low back region having to manually clear the sawdust from within the saw cabinet).

That done, the spar blanks down to dimension, I marked out the tapers on both, and cut those on the saw.  You don’t get quite the same finish when cutting freehand in comparison to running along the fence so I clamped the blanks to the bench and hand planed them smooth.  Note the Record number 5 plane, the longer the plane the straighter it will make the work.
Note, I cut the taper from the near end toward the middle of the spar blank, dont  try it the other way.
The sawbench by the way is an MBS 250. These are sold under various brand names but always have the serial number plate marked MBS 250 or 300.  I get to work on sawbenches among other woodworking machinery, and these are the BEST I've come across and that includes the European and USA built ones, I'll do a review on it soon.
Out comes the elbow grease powered planer, in this case a Record number 5 of about 1930s vintage, very good tool.

Having done that, out came the old Ryobi Router I inherited from my elderly joiner uncle, it’s a beauty, heavy, simple, robust and way better than anything that Ryobi make today.
With a 12mm radius bit I ran along all the corners of both, then got the sander out.
 Rounding the corners off, the router makes the job very easy but I am always seriously careful with them, they bite.
Measure, mark length and trim. It pays to leave the pieces a little over length until you are in the last stages of finishing. The saw is a Japanese Razor saw from Duckworks, I'd be lost without it.

With 120 grit paper and a soft pad on the old Bosch PEX 125 random orbital sander set on slow, I went along and sanded the ends rounded then took out any defects along the full length of the spars. A couple of places had faint sawmarks still showing and my hand planing had left a couple of visible marks which the sander coped with in short order.

With that done I hand sanded the two with 240 grit, laid them out on stickers and after a wipe with a tack rag gave them their first coat of varnish.

Varnished, they will get another two coats tomorrow. I'm using an exterior grade spirit based satin finish varnish, I'll be able to tell you how it lasts in a year or two.

Two more coats of varnish then I can put the leathering on, and the fittings, lace the sail on and we’re getting close to sailing.


  1. Have there been studies of the relative drag comparing a square section, rounded-corner mast and a round mast?

  2. Yes there have. In Frank Bethwaites book High Speed Sailing you'll find the results of some comparitive testing. Otherwise there are several papers in the Royal Institute of Naval Architects library which have some very interesting wind tunnel testing. The results are not what you'd expect.
    In my case, the boom being rectangular is not an issue, and the yard, being fairly small in section with well rounded corners may have a theoretically higher drag than the optimum shape which is a short "D" shape but its so small that its not worth the effort to produce that.

  3. Excellent! Looking forward to the first sail.

  4. I've got four coats of varnish on, one to go. That light golden kauri wood looks as though its been dipped in honey. Lovely.

  5. Great post! I found it very useful. Love the final result. Thanks for the inspiration and the tips.

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