Thread: The Search for the Perfect Lug Rig Boom for A goat Island Skiff

and I just did it yesterday, not enough time to get to the wiki.

Okay... okay... I knew I could edit the wiki but I figured Christophe could too and I was just giving him a bad time. I just added FrankenBoom's data to wiki but without any 'standardization' adjustment. Reviewing the data, I realized there is little standardization - including my own measurements.

I plan to rig Karen Ann today to make sure she's ready for Friday's Pirate Festival in Grand Haven. I'll measure the Mk 2.a box boom today and add the data to wiki later. If I remember to take the camera out of its bag there could be photos of Karen Ann in trailer-sailor mode.

Thanks BobWes!

Hey ... its not to do with International Talk Like a Pirate day is it?

MIK

Don't think so as International Talk Like a Pirate Day is September 19.

The Official site for International Talk Like A Pirate Day - September 19

Link to the Michigan Pirate Festival:

Michigan Pirate Festival

I crewed for my niece last year and decided to take Karen Ann this year... My costume isn't nearly as elaborate as some...

I was thinking more like this!
[ame="http://www.youtube.com/watch?v=l84VdVOjqfY"]guy taps out to triangle choke - YouTube[/ame]

Dang, I love Monty Python humor. Benny Hill would come in second place, so I found this nice clip:

[ame="http://www.youtube.com/watch?v=P-gch_wlPBI"]Benny Hill - Birds and the Bees Poem - YouTube[/ame]

Box Boom Mk 2.a

Good thing I decided to check Karen Ann over before Friday's outing… Discovered several rigging details needing attention. Better to get those taken care of before my next sail. The sheeting arrangement in the following photos is NOT my normal set-up (one of the details to be tended to before Friday's outing). I do use mid-boom sheeting without a traveller but the block shown is not my standard set-up. I do use mid-boom sheeting without a traveller but the block shown is not my standard set-up. Normally there are 2 blocks, including a ratchet block, on the boom for the mainsheet. The correct blocks are sitting on the work bench at home.

I took the opportunity to measure the Mk 2.a box-boom - my latest effort in the Search for the Perfect Lug Rig Boom… The Mk 2.a was created by planing 1mm from each side of the Mk 2 box-boom.

On the positive side the Mk 2.a boom weighed 2.26kg (5.0 lbs) including epoxy coatings, varnish and hardware (pad-eye, cheek block, cleat and 1 block for the mainsheet). The earlier version weighed 2.2kg (4.85 lbs) without epoxy, varnish or hardware.

Today's disappointment is that, apparently, white cedar may not be the best material for smaller cross-sectioned box-booms built with lap joins. The white cedar appears to be sensitive to wall thickness.

Mk 2 Box-Boom (60x45mm, 12mm thick walls):
Vertical deflection ('down bendy') with 12kg at mid-point: 7mm
Horizontal deflection ('side bendy') with 12kg at mid-point: 12mm

Mk 2.a Box-Boom (58x43mm, 11mm thick walls):
Vertical deflection ('down bendy') with 12kg at mid-point: 28mm
Horizontal deflection was not measured.

Despite my earlier barb about standardization of weights used, I reported the results using 12kg as that was what I used to measure the Mk 2 version last fall. Other data points from today's measuring:

Weight Deflection
4kg 11mm
6kg 13mm
8kg 18mm
10kg 21mm
12kg 28mm

Photo showing boom with hard down-haul, tight(er) sheeting and no wind pressure:




Today's data makes me wonder if I erred when measuring the Mk 2 boom last fall. On the other hand, I've learned what doesn't work so well. White cedar is relatively light and may be suitable for creating adequately stiff booms with larger cross-sections and thicker wall thicknesses. I am working on a box-yard design which may lead to an improved box-boom design.

In the meantime, I'm going sailing!

Would aspen be terrible for spars? It is pretty light, but is it too light/weak?

Woah Bob put his hatch right where mine is! Or I put mine right where Bob put his!

We have to sail these every unique Goats together now.

I think I found the answer to my question for if aspen is good for spars: http://www.coste53.net/downloads/War...ation-Sall.pdf

Aspen (at least here in the Nordic countries) is apparently having a little bit better bending strength than spruce. I think it would be easier to find boards with good quality of aspen rather than spruce (spruce is having so much knots). I wonder if I would dare to even make the mast out of aspen.

Let's make that happen, Christophe!

The yard is much more critical in terms of engineering than the mast.

The mast really is overdesigned for the real loads most of us are putting on our goats. (me when borrowing someone elses!!!)

So if the Aspen will work for the boom it will certainly work for the mast.

For the yard I would divide the density of fir by the density of aspen - then take the square root. It should be a number greater than 1. This is the amount you can increase the diameters of the yard (multiply by this factor) without increasing the weight over the fir.

The yard will be stiffer, which is the way most people are going. You could add a little more beyond this factor too if you wanted.

Michael

Aspen is about the same weight as Spruce (423 kg/m3 compared to 416 kg/m3). This means I will not be able to add anything to the diameter if I want the same weight. With aspen I get a little bit more stiffness, and I get less knots. The Finnish spruce is full of knots. The biggest drawback for aspen is a really soft vulnerable surface. Hopefully epoxy will make it hard enough.

I will probably make both boom and yard hollow and add to the diameter in that way.

Spruce is lighter than fir - so you can increase diameter a bit.

Might be a good timber for the mast ... but double up the glass tape at the partner to alleviate the risk from softness.

MIK

I can also imagine some damage from boom and yard hitting the mast... What is the best way to put glass on a whole mast/boom/yard?