Remaining Spars Complete - Well Almost!

Over the last two days I have completed the two booms and the two gaffs. This involved adding the jaws to all four spars, rounding the corners of the spars (they are square in section with a radius on the corner) and adding the "B" blocks where needed. There is still a bit of sanding to do -there always is!

Here are a couple of photos of the main gaff and boom. When the boat is sailing the mast will be standing up, the gaff will be raised supporting the top of the main sail and the boom will be about at the level of the folded down mast. There will be plenty of clearance above the heads of people sitting in the boat.

 

 Here are the mizzen mast and the mizzen gaff and boom. I have made the jaws on the boom longer than the plans suggest to allow the boom to fold up parallel to the mast. This is not necessary when sailing but it will allow both spars to fold up along the mast and the sail to be wrapped around them for trailering. It will be an awkward bundle to pick up and stand in place at the transom but should be doable. This will make rigging and derigging the mizzen much quicker than if it has to be assembled each launch.

Main Mast Finished

I have finished shaping the main mast and glued the "ears" that support the standing rigging in place. I guess the next step is to apply some finish to the mast but I will probably leave that until the rest of the spars are done. Here is a photo of the mast in the boat.

 

Yes. that's right, the mast is in two pieces with a hinge so that it can fold down into this position for transport. There is an earlier post about the folding mast with reasons for doing it and photos of the hinge,

 

The next photo shows that the end of the mast sticks out beyond the transom by about 400 mm, I will make a more substantial support for the mast (plus the boom, gaff, sail and rigging) to use when transporting the boat on its trailer.

 

Rudder Hardware

I wanted pintles and gudgeons that were more substantial than the ones that I could find in the chandleries. These are intended for small dinghies and probably work but they don't look very strong to me. I designed my own and had them made up from 316 stainless steel by a small company that specialises in marine stainless steel fabrication. Here they are, 25 x 5 mm flat strip bent to shape with a single long 10 mm diameter pin to ensure alignment of the hinges.

Nicely polished and I will drill the holes for fixing screws when I mount the hardware on the rudder.

Latch for Cockpit Floor Panels

Over the past couple of weeks I have been preoccupied with other things and only working on the boat occasionally. In between the other things I have been working on the spars because they have to be made and it makes a change from working on the hull which I must get back to soon. I had a few photos of the various stages of working on the mizzen mast as it went from square to round but unfortunately the camera (and I) lost them somehow during the transfer to my PC; maybe they are still around but I can't find them. I will try and retake the photos as I shape the mainmast.

In between spars I have been testing out a couple of ideas for parts of the boat. One of these is a latch for the cockpit floor panels. I intend to have a floor at both ends of the cockpit rather than standing on the hull planks. This will provide a flat surface to stand on and a small amount of storage under the floor. The floors will each consist of two plywood panels either side of the centreline supported all round by rails on the bulkheads and seat fronts and another support running along the centre of the keel. Most of the time gravity will keep these panels in place but, if the boat ever capsized, some sort of latches would be a good idea.

While thinking about this I saw the perfect solution on another boat and so decided to test it out and also work out how to make it. Here are a few photos of the test setup.

Two panels with finger holes so they can be lifted. The button in the centre is about 50 mm in diameter and it can rotate freely around the screw in the centre. In this position it is holding the panels down and they can't be lifted. The button is flush with the floor panels so there is nothing sticking up to trip on or hurt bare feet.

 

 Rotating the button a quarter of a turn allows one panel to be lifted.

 

This exposes half the rail that supports the panels along the centreline.

 

Turning the button 180 degrees allows the other panel to be removed

This last photo shows the underside of the panel and the other part of the latch mechanism.

 

 

Making this little test setup took about 30 minutes. The parts are held together with hot melt glue, the button and hole in the panels were cut in one operation with a hole saw in the drill press. This exercise proved that the latch will work and helped me work out the proportions of the button and how to make it.

The Hinge for the Main Mast

I have been making the parts of the hinge for the main mast. These are three 316 grade stainless steel plates, one aluminium packing piece and a couple of pins. Machining stainless steel can be a problem because it easily work hardens. Any rubbing, rather than cutting, quickly raises the temperature causing hardening. I had the stainless supplier cut the plates to shape for me on a CNC plasma cutting machine. This left me with the job of accurately drilling a number of different sized holes through the plates. Fortunately I have a small CNC milling machine to do this job. Here is a photo showing the aluminium packing piece being cut; the white surface is powder coating on the scrap aluminium being reused.

Here are the two identical plates for the upper part of the hinge having the holes cut. Note the clamps and bolts through the first couple of holes to keep the plates together and stop them moving relative to one another. Note the coolant stream to prevent both cutter and material heating up and also to carry away the chips.

Here are the completed parts, upper hinge plates (4mm thick) on the left and right, lower hinge plate (6mm thick) left of the steel rule and the white packing piece (6.35mm thick).

 

This next photo shows the parts assembled. The notch in the corner of the lower hinge plate hits against the pin which passes through the two upper plates to provide a positive stop when the mast is vertical. The packing plate (white) is slightly thicker than the lower hinge plate to ensure that the hinge doesn't bind.

The next two photos shows the hinge clamped to the top of the lower part of the mast its up and down positions. In the up position there is a locking pin (just below the lower bolt in the upper hinge), this will probably only be used when the mast is pushed up until the forestay is tightened and when the forestay is released to lower the mast.

The lower part of the mast is still square at this stage so that the lower hinge plate can be used as a template to drill the five dowel holes. Having the mast square will also help with cutting the slot in the mast for the hinge plate. Doing either of these jobs on a circular mast would be difficult to get right and the position of the hinge plate in the mast is critical.

The plate will be glued into the mast with epoxy after roughening the surface of the steel. Hardwood dowels will reinforce the glue joint. For some reason that I can't explain I have put 5 dowels through the lower plate and four through the upper plate! Maybe I decided that the hinge pin which passes through the upper part of the mast provided some additional support.

It's now a day later and I have fitted the lower hinge plate into the lower part of the mast. Here it is in place in the boat. The mast still needs to be shaped (square to circle) and I am pleased that I drilled the holes and cut the slot while it was still square. I will do the same with the upper part of the mast.

 

 

The Centreboard and its Lifting Tackle

After returning from my break I turned my attention to some of the steel parts for the boat. The biggest item is the centreboard (CB). I drew the CB using a CAD package on my PC and did some phone research to find out how and where I could get it cut. A few calls led me to Midway Metals at Yatala in Brisbane. I emailed a DXF file (standard drawing interchange file) to them on Tuesday evening, received a quote on Wednesday morning, I accepted the quote and picked up the CB on Thursday - pretty good service. The CB is cut from 316 grade stainless steel, 12mm thick and it weighs 48 Kg. The CB cost $380. The cutting was done on a "plasma" cutter and unfortunately plasma cutters can't do small holes. I had to take it to a machine shop to get the 2 holes drilled and this cost $80, expensive holes!

While I was drawing the CB I made a sketch of it in 3 positions with the lifting line. Here it is:

 

It is hard to see the detail so click on the image to get it enlarged. There are 2 dimensions for each position of the CB. One gives the moment arm of the dead weight of the CB, the other gives the moment arm of the lifting force. The moment is the force or dead weight multiplied by the moment arm and the moments about the pivot point must balance. The lifting force needed in each position id shown in the table below.

 

CB position	Lift moment arm	Dead weight arm	Lift force Kg
Down	450	75	8.0
Middle	597	460	37.0
Up	509	575	54.2

 

The CB in my Welsford Navigator is 2/3rds the weight of the Able CB and it is quite difficult to lift. This made me wonder whether lifting the Able one with block and tackle was a practical proposition - maybe the winch called for by the plans is a better way to go. I decided to make a test rig and try the tackle approach.

 

Here is the CB mounted in the test rig. The pivot point and lifting "eye" are located as they would be in the boat.

 

 

I tried the 5:1 tackle that lifts the CB in my Navigator(the boat on the trailer) but it didn't work very well. It did lift the CB but I had to pull very hard to provide the 54 Kg lifting force as the CB approaches the up position. Theoretically the 5:1 tackle should only need about 11 Kg on the tail of the rope to pull 54 Kg. I guess that I had to apply 25 to 30 Kg to lift the CB. Most of the force applied to the tackle is used to overcome friction in the small (20mm) sheaves.

 

I searched through my boxes of old boat bits and found some blocks with larger sheaves and cobbled together another 5:1 tackle and tried this. The result was much better but still getting close to 20 Kg. Here is a photo of the CB in the up position.

 

Last photo shows a close up of the 5:1 tackle, 3 sheaves at the fixed end and 2 at the moving end. A tidy version of this would probably do the job but I will look for 2 triple blocks with ball bearing sheaves to get a 6:1 purchase. Hopefully this will dramatically reduce the friction forces which increase as more sheaves are added and also increase as the gets bigger.

 

I will also look further into the suggested worm drive winch. This is what the small Dutton Lainson winch, suggested on the plans, looks like.

 

 

 

The body of the winch is 140 mm high and the end of the handle is 300 mm above the base. This winch has a 30:1 ratio and a drum 40mm in diameter. To pull in the lifting line 900 mm (CB fully down to fully up) would need over 200 turns of the handle! It would undoubtedly work but it is ugly and, to me, 200 turns of the handle is 10x too many.

 

Thursday, 9 May 2013

Problem Solved

I bought a pair of triple blocks with 30mm diameter ball bearing sheaves. Using these gives me a 6:1 purchase so in theory the force needed on the tail of the tackle is only about 9 Kg (ignoring friction effects). Here is a photo of the new blocks in place in my test rig.

 

 

 I pulled on the tail of the tackle with my spring balance  and raised the CB completely with less than 12 Kg (that's the limit of my balance). Using one hand (gloved) I could raise the CB completely in 6 pulls. So, the ball bearing blocks make a huge difference by reducing the friction in the tackle.

 

I didn't like the winch and now have a solution to the problem of raising the CB.

 

Back to putting epoxy fillets in all the corners inside the hull.

 

Two Weeks Break!

I'm writing this in the middle of a two week break from boatbuilding. Last week I went sailing with a group of guys from the Wooden Boat Association and had a great time. Tomorrow I'm off to Perth for a week visiting relatives and a friend.

The last thing I did on the boat was to make a template for the foredeck. It is made up off strips of scrap ply fixed together with hot melt glue. It is strong enough to withstand the pulling and pushing to get it off and on over the samson post. It remains to be seen whether the 9mm ply deck will be flexible enough to put into place. Here is a photo of the finished template.

As it stands the interior of the boat is almost complete up to the level of the seat tops. There are 3 pieces of timber to glue in place, some cleanup to do and a lot of epoxy fillets to put in/ Once that is done I will start painting the inside of the various compartments before putting the tops on. Here are 3 photos of the interior.