Wednesday, 26 August 2020

Making the most of the dyneema - splicing rings for boom attachment points.

The 12 strand dyneema SK75 is really nice to work with. Much easier to splice than double-braid, and incredibly strong. I've been using it for all sorts of things on Elena; shrouds, outhaul, and also to fashion attachment points for blocks.

On my boom, I'm attaching the three blocks (two for mainsheet, one for vang) using simple loops. I simply make these by cutting a length of dyneema, then passing the two ends into the rope, while it's attached to the boom. it's extremely simple. With long tapered ends it's very secure under tension, and some lock-stitching (using waxed dyneema thread) holds it neatly while it's not under tension.

Here's a view while working:

And the finished result:

Tuesday, 26 May 2020


Welsford’s plan for the Navigator shows a rudder with an up-haul and a down-haul. I’m not too keen on the idea of down-hauls, as if I hit things and the down-haul doesn’t release, then bad things happen.

So I figured I’d omit the down-haul, and instead weight the rudder with lead, similarly to the centerboard. Hey, every little bit of tighting moment has to help some, right.

This time with the lead, I just went and bought a pile of lead flashing. I melted it in an old cast iron pan outside, and poured it into a mold made from steel and aluminium.

I cut that into the rudder core, made from four 12mm thick jarrah planks.

And then glued on cheeks made from Tassie Oak, roughing it to shape with the bandsaw, power plane, and jack plane, then 40 grit in the sander.

I’ve added a pivot point (16mm hole with 12.7mm bronze bushes), and an eye for the up-haul, which I think will have to be 2:1 on account of the weight.

Tuesday, 5 May 2020

I can stop any time

A picture of my frypan collection.

They’re all Le Creuset, mostly vintage. Two of them have had the enamel stripped and replaced with seasoning.

And the omelette process. We start with my favourite pan, a 23cm Le Creuset with the enamel stripped, seasoned with lard. When the seasoning is just so it’s a little glossy.

Ingredients for a basic omelette are a bit of butter, two eggs, some finely cut spring onion and a little grated cheddar cheese, with salt and pepper.

Chuck the butter in the pan and heat it until it’s foaming. While that happens go at the eggs lightly with a fork, and add salt and pepper.

Add the eggs to the pan when the butter quietens down. Then chuck the spring onion on top. Move it around a little with a fork to get the folds, and allow the runny egg to run onto the bare pan.

I like to add a teensy bit of grated cheese, which I melt with a torch. I used to pop it under the grill for a few seconds, but the torch is much more controllable.

Finally fold it in half with a fork, and slide it onto a plate.

Et voila. Bon apetite!

Sometimes I just chuck in whatever’s in the fridge. Pepperoni, chorizo, cherry tomatoes, mushroom, etc. But that usually ends in a thicker omelette that won’t fold.

Sunday, 3 May 2020

Doodles towards a new boat

So these are the constraints I'm working to:

  • Beam of around 2300mm, to allow the boat to be stored behind my house (the gap between the fence and my garage is 2400mm). This will also allow for trailering without wide load placards, being under 2400mm.
  • Length of around 6000-6500mm. This is a bit more vague, as there's no specific constraint here, but the 6m length tends towards a 2300mm beam, so this is it.
  • Maximum draft of around 800mm. More than this makes trailer launching at boat ramps really hard. Indeed even launching a boat with an 800mm draft will be hard. Stability and cabin room is however directly related to draft, so there is a strong push to maximise draft at the expense of trailerability.
  • Maximum weight of around 1800kg unladen. The tow vehicle I am considering has a maximum towing weight of 2500kg. If we subtract 700kg for trailer, we end up with 1800kg for the boat. Stability constraints again push us upwards here, and trailerability constraints push us down. I think something around 1400-1500kg is probably reasonable. This implies a displacement of around 2000kg.
  • As much sailing ability as I can get given those other constraints. Ideally I want something I can sail across the Great Australian Bight in, so some measure of blue water capability.
Some of these constraints are directly contradictory. Trailerability comes at the direct expense of blue water ability. I think I can find a happy compromise that ends up in a boat that's enough different to Elena to make the exercise worthwhile.

I'm working on the premise of a 6m LOD, 2.3m beam, 0.6-0.8m draft boat with centerboard mounted in a trunk below the cabin floor. Katie comes pretty close, but the draft is perhaps a little on the shallow side, at around 0.48m board up. Pretty-much everything that's designed without a board has a draft of over 0.9m, which I think is just a little deep.

To find a better compromise, I thought I might try developing my own hull shape. I started with the table of offsets for Buzzard's Bay by Herreshoff, as published in Sensible Cruising Designs. I found the table of offsets to be surprisingly lumpy, so abandoned any attempt to stick to the table of offsets and instead just started drafting lines in Sketchup. The process was first to draw a profile (face), and overall plan view, to constrain LOD, beam and draft. The shape is similar to Buzzard's bay but I brought the bow up more vertically above the waterline, and increased the radius of the turn of the bilge, giving the rabbet a hard inflection rather than a smooth curve.

Then I drew waterlines and stations, got them to line up, drew buttocks, found they were miles off fair, edited the waterlines, edited the stations, edited the buttocks, and went around the loop half a dozen times, until the waterlines, buttocks and stations all intersect with errors of <1mm or so. I think the shape is reasonably pleasing.

Here's the profile:

Draft ended up 760mm, which is just shy of my maximum of 800mm. LOD is 6380mm. Beam is 2300mm. There is 750mm freeboard at the bow, dropping to 470mm amidships and raising again to 600mm at the transom.

The plan view is below:

After the issues I had with Elena getting the garboard plank around to the bow with a strong concave section, I kept the bow mostly convex, even down at the garboard. There is s reasonably strong turn to the bilge at the stern. This gives a nice shape to the transom and I think will also provide additional stability.

The rear view is also shown:

I haven't put any tumblehome in to the stations. I'm wondering if perhaps bringing the gunwales in a tad might make for more strength to the form, but also want a decent amount of room on deck to be able to get past the cabin, when I design one in. I may change things around a bit as I keep going.

Finally the quarter-view. I haven't sheeted the hull in sketchup, so it's just a bunch of lines.

Friday, 24 April 2020

More rigging

Much of the rigging for the mast is done now. I have a vang, mainsheet and outhaul. The virus has made a real mess of things. I’m waiting on rudder fittings, boom end fittings and more cleats. From the sound of it I might not be getting those for months.

So today I assembled everything I have for a test-fit. It took us about half an hour in the driveway to put it all together. First views from the side, aft, and forward:

A closer view of the bowsprit arrangement, with cleats added for tensioning the bobstay and forestay:

Here’s the vang. I did it as a 4:1 using a 40mm fiddle block with becket and cleat at the mast end, and a 40mm fiddle block at the boom. I wrapped a dyneema line around the mast to secure the bottom. At the top it’s got a loop of 6mm double-braid through a hole in the boom.

You can also see the missing bronze fitting that’s supposed to go on my boom, plus a bunch of cleats. At the bottom is my 3:1 centerboard lifting line, using a 29mm double block and a sheave with becket in the board.

Here’s a pic showing a dinky little 22mm block that runs inside the boom to give me a 2;1 outhaul:

Here’s my mainsheet. I’m using 8mm double-braid, in a 3.5:1 system, using a 40mm block with becket on the bridle, running to a double 40mm block at the end of the mast, then a 40mm block mid-way along the mast runs the line down to a 55mm high-zoot factor ratchet block at the back of the centerboard case, which I hold down with a dyneema soft shackle.

I’m holding off until I get the sails before I install the jib sheet blocks, so I can locate them just so.

Sunday, 19 April 2020

Meet Katie

So I made a decision in record time and have ordered plans for Katie, by Harry Bryan.

There's a lovely video tour of Katie available at Off Center Harbour.

Katie is a good compromise between draft and stability. She makes use of a lead keel plus a centerboard. My only reservations with Katie is that the cabin is a tad small (Harry designed her to have a big cockpit instead) and I can tolerate a bit more draft than she has in order to improve stability. So some quick doodling on the picture of the plans that I have to illustrate my changed:

Firstly I scaled her vertically by 105%. This small change adds about 25mm of draft (from 480mm to 505mm) and 25mm of freeboard. It also gives me an extra 50mm of headroom in the cabin.

Then I add ballast to bring her waterline up by 25mm. That resets the freeboard to 480mm, and now my draft is 530mm.

My keel extension will add about 50mm on the bottom of the boat, giving me a total draft of around 580mm. I reckon this is still trailerable. It's certainly a lot less than the 900-1200mm draft of other designs I've been looking at.

Harry mentions that Katie originally suffered from mild weather helm. He cured that in the original by adding keel at the rudder end. I propose extending the centerboard back by around 250mm to deal with this. Additionally because of the taller keel we're able to drop the centerboard down a tad so most of the centerboard case inside the cabin is at floor height.

Finally we simply extend the cabin by moving it's bulkhead back around 500mm.

The results of my doodles is shown below:

Friday, 17 April 2020

The dawning realisation of life without a boat to build.

One of the truly shocking realisatons of late is that shortly Elena will be built, and then I won't have a boat to build any more.

That's utterly unacceptable.

I'm thinking now of starting on a small "pocket cruiser". Something that I can pull out of the water and keep in the back yard under the pergola when I'm not cruising in it, but still with enough size, weight, and cabin to really go places.

Also I'm fed up with plywood, so I want to make a boat from cut timber. Clinker is the romantic ideal, but strip built is probably going to be a lot more amenable to keeping out of the water for extended periods, so I don't completely get away from epoxy.

I asked for ideas on the woodenboat forum, and have been inundated with suggestions. Seems a lot of people have been thinking along these very same lines.

Here's a spreadsheet tabulating most of them.

Monday, 13 April 2020

Shroud attachment details

Being stuck in the house, and being almost out of epoxy, I’m working on odds and sods. One of these is the shroud attachment. My copy of “Sensible Cruising Designs” by Herreshoff, shows a short cut for attaching shrouds using two plates and a clevis pin, rather than a shackle. Ditching the shackle eliminates a potential rattle, so it sounds good to me.

So this is what that looks like for Elena:

I’m not super happy with the forestay attachment. I had a lot if difficulty bending the bronze strap neatly, and it shows. It’s not a particularly good fit, either.

I’m wondering if perhaps a cooler way to do this might be a loop of Dyneema rather than bronze.

Edit: I made a 20cm bridle from 5mm dyneema. This is the shortest I could do maintaining 20:1 bury in the brummel lock splices. The eyes go over some 12mm dia bronze tubes, which sit under the shroud attachments. I reckon this is much nicer.

It’s certainly miles simpler, not to mention lighter. If I want to easily detach the forestay, I could even use a small gaff saddle shackle.

Saturday, 11 April 2020

Apocalypse craft

Here in Australia, the public health advice has gradually been changing regarding the wearing of masks by the general populace.

We started with "Masks don't work, and they'll probably increase your risks of getting the virus", accompanied by pictures of health workers wearing (you guessed it) masks, and newspaper stories about the incredible shortage of masks and other PPE for health workers.

Any idiot can tell the reasoning for the message is that while masks do work for reducing spread of the virus, if everyone tries to buy them then those who need them the most (health workers) can't get them. So it makes good sense that the health authorities would lie to us here.

Now the conversation is getting a bit more honest. There's a grudging admission that masks do work, especially when worn by people who have the virus and aren't showing symptoms yet. So the advice is to make something, using multiple layers of t-shirt cotton or teatowels.

It's straightforward arithmetic. A certain percentage of people have the virus but are not showing symptoms. The public health response around people who are showing symptoms is quite good, limiting transmission. It's the asymptomatic carriers that are responsible for an increasing amount of spread. Social isolation works in general here, and widespread wearing of masks in public also helps.

In general, act in public like you have the virus. If you have the virus, the first thing you'd want to do is stick something over your face so you can't breathe droplets of it over everyone.

Being an engineer, I'm not convinced of the efficacy of a piece of woven cloth. The weaving pattern makes uniform sized holes in the weave, through which stuff is easily able to move. I've previously used non-woven poly cloth (specifically engineering wipes) as efficient filters, so a bit of google-fu revealed that this material is the secret-sauce in real facemasks.

So let's make some facemasks. They aren't going to be N95 or P2 certified, but they're going to be a whole lot more effective than something made from t-shirt fabric.

We start with the ingredients. My fabric is electrolube ECW engineering wipes, which are widely available, from for example Farnell. Each wipe makes two masks. I also use some 6mm elastic for holding it to your head, and some 1mm magnet wire for forming the nose bit.

Cut the wipe into an axe-head shape and sew two pieces together along the rounded bit of the axe head, leaving a small seam allowance.

Unfold it, seam side up, and sew the top and bottom with a more generous fold, to allow the nose wire to be inserted.

The engineering wipes make really good fabric. They don't fray, they're strong and don't tear, and are just super-amenable to sewing.

Make the nose wire from a piece of magnet wire, or really anything that you can stick in that will bend easily and retain it's shape. I whack a little loop in the end before insertion so that it doesn't poke into your face.

After pushing the magnet wire down one of the seams to the middle, the last seam goes at the ends of the mask, again leaving a generous pocket for the elastic to go through.

And tada. A non-certified, comfortable, durable, and hopefully effective mask.