Saturday, 22 February 2020

Buoyancy chamber inspection.

I find smol cats are particularly well suited to inspection of the insides of buoyancy chambers. Here’s Sam, our smol cat, ready to go to work:

The inspection procedure commences by entering the chamber at the aft end.

Some time spent inside checking for leaks, and criticising the fillets:

And finally, job complete, we exit via the forward hatch:

Sunday, 16 February 2020

Back to the mast

My mast components have been languishing in the back yard for a year, covered in a length of heavy plastic to protect them from the elements. This has been mostly successful, but on pulling them out there's some evidence of water. I presume being in the bag in the sun there's been some condensation.

In any case, now I'm back to the mast proper. For those who don't remember (I barely do myself) I'm doing a modified birdsmouth construction, with a sail track, in Jarrah and Tasmanian Oak. Neither of these are traditional spar making timbers, on account of their density, but I figure I can get good performance by pushing the boundaries of the traditional birdsmouth technique, and thinning out the walls some. Plus, Jarrah and Tasmanian Oak are pretty-much indestructible.

Here's a photo of my prototype piece, that I did a while ago. It's mainly condtructed from 30mm x 12mm staves.

Luckily, the 6.1m long mast fits neatly across the back of the garage, on the bench I made specifically for this work. I confess this was something that I measured when we were looking at places in Perth, and I rejected a few on the basis that I couldn't do this work in the garage. The garage in the place we're in could be bigger (it'd be nice to fit Elena in lengthways with her bowsprit, but it'll do.

I've opted to fill in the base of the mast with Jarrah up to the boom fitting. If the mast is going to break anywhere, I figure it'll go at the boom, as that's where the main unsupported sideways forces are. There's a slot down the leading edge of the mast for drainage, and I've tapered the staves just above the boom, to minimise stress risers. You can also see here a length of coax that I've put in for a mast-mounted VHF antenna. Also two of the three staves that will fill in the front of the mast are mostly prepared - I just need to taper the tops and route the birdsmouth into the front. However I want to get all the inner details right before sealing up the mast, as I'll kick myself if I forget something.

Moving up the mast to the halyard exits. I'm using 6mm spunport line, which is a modern polyseter double braid, but in traditional colour and finish. I've elected not to use double-sheave exits, and have routed in a long slot for the halyards to come out at a shallow angle. If this proves troublesome, in use, I can always add exit blocks. Note also here that I've started finishing out the interior of the mast with filled epoxy. This is simply to ensure the halyards don't snag on anything.

So now I'm on to some design work. One of the reasons I put this aside previously was that I was unsure what to do with shrouds. The hounds really should be strong. Traditional masts tend to use a band encircling the mast, but that's not going to work well on this mast due to the sail track. I could split a mast band at the sail track, but then I'd be paranoid about the shrouds bending the band apart at the front and splitting the mast.

I think I've come up with a workable solution. Davey do chainplates with the eye at 90 degrees, intended for mounting on the stem at the bottom of the bobstay, or else on the gunnel for bobsprit shrouds, shown below:

Initially I was thinking of simply bolting these to the sides of the mast, with backing plates inside, but there's still the splitting problem as with the cut mast band. So then I thought I could join the chainplates to one another, clamping the mast. I have a pile of bronze rod that I've been turning all sorts of things from. All I need is a couple of lengths of rod with threads tapped in the ends, then stick these in holes in the mast, and flogg the chainplates up to either side. Something like:

The only danger is clogging up the space that's meant for running my halyards, but if I keep the diameter down to 12mm (oodles strong enough) there's heaps of space to run the halyards past.

Editing after some good advice from the woodenboat forum not to put the holes in line on the mast. I've tipped the fitting over a few degrees, and shrunk the holes in the timber to 4.8mm from 12.7mm. The bronze plugs now don't go through the timber section. To ensure that when the bolts (now 10g) are flogged up the mast walls don't get cut into by the plugs, I've added backing plates as well, which essentially act as large washers.

And another edit after a complete rethink. I've decided to fill in the mast in this section, bore a hole for the main halyard through my plug, and go with a more traditional hound. Here is is bolted to my prototype mast section. I used 2.4mm thick x 25mm wide bronze for the jib stay straps, and 3.2,, thick x 25mm bronze for the shroud straps. Bending the jib straps around the mast was a real pain.

The whole assembly bolts through the mast with a single 5/16 bolt (actually I'll use 5/16 bronze threaded rod with acorn nuts on either end.

I'll do a separate cutout for the jib halyard exit box immediately below the stay attachment. I can use the stay attachment for a roller furler, or use the halyard exit box for a normal jib.

My fingers are a mess after beating on those straps.

Wednesday, 12 February 2020

Varnishing the transom

One of the problems with stopping building the boat for a few years is that some bits haven’t aged as well as I’d like. Principally the transom.

Essentially I built this by laminating thick Jarrah planks on to 6mm ply, then hacking at the Jarrah to thin it out to ~6mm. When working on the boat originally I threw a quick coat of unthickened epoxy on to protect it, and went on to other bits.

So that’s how it’s sat for rather a while. Now that the decks are painted out it’s time to varnish it. Unfortunately it’s gone and cracked while sitting. So before varnishing I fed some unthickened epoxy into the cracks to fill them, then sanded the whole lot back to timber before applying another couple of coats of epoxy with the roller.

This is what it looks like after a couple of coats of epoxy. I’m confident the cracks won’t be a problem (after all, they’re only a veneer, so it’s still completely watertight), and it looks okay, cracks and all.

I also bought a gudgeon and pintle for mounting the rudder, but alas the wrong one arrived, so it’ll be a little while before I go drilling holes into the transom to stick more bits on.

And here's what it looks like after sanding back the epoxy and adding two coats of lacquer, thinned out with Penetrol. I'll sand out the gloss before adding another couple of coats.

Sunday, 2 February 2020


I'm trying to figure out how to hold my bowsprit on. The standard bowsprit for navigator is a rectangular block of wood, which is bolted to the kingplank with 9mm (3/8") bolts.

I've made a 60mm dia round bowsprit (more pirate-like), which doesn't really lend itself to just bolting down. Here it is being held on Elena in the approximately correct position by my extremely patient husband:

The observant will also notice I've modified my winch mount a little to get it to work better. I flipped it over and cut down the pieces for the bow roller, making it a little more compact. Then I mounted it a little further up the post. Now I don't have to remove the winch and haul Elena forward on the trailer to fit her in the garage. The last little bit is to undo the front bolt of the hitch and rotate that out of the way, giving me an extra few cm. I've been looking online and have found drawbar pivots, so I could even conceivably cut the drawbar just forward of the winch post and extend it half a meter or more, then simply spin the front section of the drawbar out of the way when needed. Of course then the jockey wheel would need to go behind the winch post, but that's doable.

Back to the topic at hand though, I thought a heel socket and gammon iron were the way to go, something like:

However getting these in just the right size is a bit of an ask. These sort of things are really made for much larger boats. I could fab something from lots of bent and welded plate, but it just wouldn't look that pretty. Truth be told I wasn't entirely hapy with the way my fabricated mainsheet eye turned out.

So I thought perhaps combining some bronze straps over Jarrah bases was perhaps the right go. I could even angle things so the screws through the deck and into the king plank are angled, making them really hard to pull out...

Building that starts with cutting out the strap. I bent it in the vice by simply ruling nine lines across the piece, and bending each ten degrees.

I cut out the heel iron base from jarrah, and cut a flat spot into the deck to mount it. The deck looks reasonably flat, but there's actually quite a pronounced curve:

When mounting, I added a pair of 10g 1.5" screws under the bowsprit. This means the iron is held down wy a total of eight 10g screws into the king plank.

I further reduced the diameter of the heel end of the bowsprit to provide a more positive engagement to the heel iron. In use I expect the forces to be back and down on the bowsprit, due to the tension in the bobstay. Wind loading on the jib will be back and up. So there will be significant backward forces at the heel, meaning the bowsprit could slip back through the heel iron. The step in the sprit ensures this won't happen. The photo shows the sprit partially inserted, highlighting the step.

Finally a picture to show the whole thing.

I had entertained notions of fitting the bowsprit in the parking lot prior to launch, but really it's just not going to work like that. The front of the sprit comes well forward of the trailer, plus the winch gets in the way of the bobstay. So I think really the only way to go will be to insert the bowsprit and the bobstay once Elena is in the water.

Now onto the gammon iron, which can be a little simpler as it really only needs to ensure the sprit can't move from side to side, and doesn't have any upwards forces to contend with.

By leaving the top of the gammon iron open, installing the bowsprit should be fairly easy. Just drop it in the gammon iron and seat the heel into the heel iron, then tension the bobstay.