Meeting Ophelia

Hurricane Ophelia is bringing strong warm winds from the south. If I’m able to get aboard, Tammy will be riding the storm.

Met Office surface pressure chart

Hurricane Ophelia approaching the UK

It’ll probably be down to a F7 by the time it reaches me.

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The Spitfire sail

I’ve spent most of my limited wakeful time in the past few days reading books by Czesław Antony Marchaj:

  • Seaworthiness: the forgotten factor
  • Sail performance: techniques to maximize sail power
  • Aero-hydrodynamics of sailing.

These are all fantastic books. Not only is Marchaj one of the few writers to present actual hard evidence for his assertions, he writes with a dry wit that implies a great deal of criticism for the rumours and fashions that dominate sailing design. (The junk rig community seems somewhat exceptional in this regard.)

He presents evidence that elliptical foils produce more lift than rectangular or triangular, especially at low aspect ratios. (I’m summarizing here.) This is rather interesting given my earlier drawing of an enlarged sail for Tammy Norie. I think this evidence gives some clues to why the top triangle on junk rig sails is important: it approximates a curved top.

With this in mind I drew this sail plan based on the elliptical Spitfire wing.

The “Spitfire Junk” sail plan, based on research by C A Marchaj, which showed that elliptical sails generate more lift, especially at low aspect ratios.

This plan is based on 4.5m battens, but has a 3.2m second batten and a yard of only 1.9m at a steep angle of 65°. The yard forms the leading edge of the approximately elliptical wingtip.

Given Marchaj’s other results showing the critical nature of the leading edge of foils, the yard shape could be quite critical, but fortunately this suggests shaping it in a way similar to that suggested by Hasler and McLeod to provide strength. In this case it would be arched to fill in the ellipse and have a thin top.

If this plan works, the centre of lift will be shifted forward considerably, hopefully correcting the Coromandel’s balance problems.

I also can’t believe it’s a coincidence that Paul McKay’s Aerojunk looks like a Spitfire wing.


Fantail even resembles it.

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My next boat

While I was working on the new mast step I got chatting to a fellow member of the Fareham Sailing and Motor Boat Club who had restored a traditional wooden Folkboat. He took a look at Tammy Norie and said “What’s your next boat?”

It took me a few seconds to think about this question. I’m not planning to move on from Tammy Norie any time soon — there’s still too much to learn. So I said “Oh, I’ll build one.”

I can now reveal the design of my next boat.

Narwhal

If that doesn’t make you smile I’m not sure what to do with you. The thing is, it’s only half a joke.

At the Southampton Boat Show I picked up issue 15 of Classic Sailor magazine, mainly because of the retrospective of the Folkboat. Inside I found a review of a wonderful boat, the Fairey Atalanta. It’s a fascinating design by Uffa Fox, resembling a submarine or aircraft fuselage as much as a boat. It has double cast-iron swing keels and is self-righting. It’s steered by a whipstaff, and can plane downwind. I recommend reading about it.

Another inspiration of mine is John Riding’s Sea Egg. Another fascinating boat design, about which very little is available online.

But what’s really got me thinking recently is David Raison’s Magnum Mini, winner of the 2011 Mini Transat. Take a look at this revolutionary hull shape. This is a shallow draft scow designed to form an efficient shape when heeled, quite different from the sharp-bowed design of the typical racing yacht.

Matt Layden’s Paradox, Elusion, and Enigma are also fascinating designs, especially because of their shoal draft, chine runners, and lugsails. I was lucky enough to have a close look at a Paradox named Faith at Ashlett Creek.

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And finally, there’s my dad’s favourite, the Thames Barge. Dad led the restoration of a Thames Barge at Pin Mill when he was in his 20s, and he’s very fond of them. He strongly believes in the capabilities of the boxy barge shape and its lee boards.

Honorable mentions also go to the Wadder and the Southerly shoal draft cruisers.

I have many many sketches of boats, including this one I made (very rapidly) for Annie Hill’s Sib-Lim challenge (very sensibly ignored too).

http://www.junkrigassociation.org/technical_forum/3144241?mlpg=24#3384275

I think perhaps you can see a theme here.

Edit: It looks like Yrvind has been thinking along the same lines. He seems to have lee boards and metal sheet ballast (like the Southerly), as I intended in my Sib-Lib sketch above. Time to brush up my Swedish!

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The to-do list

If you are really observant you might have noticed a new page on the blog in the “about” menu: To Do.

I’ve collected together all the to-do notes from my log book and other pieces of paper that I could find. I’m sure I have not found everything.

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Feel free to ask questions about anything on the list. Many of the items need writing up! I have little sketches and diagrams for a lot of stuff too.

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Sailing Single Handed to the Azores and Back

My friend James Drinkwater, who sails a lovely junk-rigged boat Barny out of Ipswich, has sent me a link to a fantastic log “Sailing Single Handed to the Azores and Back” by Mike Spring from 1983, the year after Tammy Norie herself was built.

The voyage was sponsored by 3M and the boat named 3M Mariner. He had all sorts of equipment aboard that we’d consider obsolete today, including a very early satellite navigation system that took 40 minutes to “warm up”.

Highly recommended. Many lovely photos.

This sailing position looks familiar.

 

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Sail art

Curved 4.5x1x40 sail

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2017-09-26 · 20:14

A new mast step

Last week I wrote about my plan to rebuild my mast step. The job is mostly done, and Tammy Norie has a sporty new rake to her mast. This article will describe how I did it, including mistakes and remedies.

If you want to know about the design and thought behind it, you should read my post “Raking the Mast”.

Here are the materials I bought for this job:

  • 50mm × 50mm × 6mm × 1m aluminium angle
  • a sheet of 15mm hard rubber block
  • M6 stainless steel studding, 2 washers, 2 nuts
  • 8 × M8 coach screws and spring washers

The total cost is around £40.

The biggest modification to the boat I needed to make was to cut a larger hole in the berth above the mast step so that I could adjust the angle of the mast. I imagined this would simply mean extending the circular hole into a longer slot. I started out by measuring the area so that I could draw the new hole on the gelcoat. That was when I discovered the first problem: the original hole was not in the middle of the boat!

The distance from the left side of the hull to the centre of the mast was 535mm, but from the right side it was only 485mm.

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I checked this several times, and looked at the mast from several angles. I adjusted the contents of the boat to get her perfectly level, and took at look at the mast from the dock using my spirit level. The mast was definitely leaning to port by a small amount. Oh Newbridge! Well, I suppose I could correct that now.

I found and marked the actual centreline from the hull sides, and that allowed me to draw enlarged hole, with enough side-to-side-to-side movement to fix Newbridge’s mistake.

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The next job was to remove the existing mast step bracket. This is a well-known weak point. Mine had been making ominous clonking noises on my crossing of the North Sea in 2015. It’s a known weakness. What’s more, it had been replaced on every other Coromandel I’d seen.

Down with the mast!

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Out with the mast stub!

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This exposed the bracket, held in with the two largest wood screws I’ve ever seen.

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I had been wondering how I would get these out. None of my screwdrivers were big enough, and a sailing friend has said I would need some violence to remove them. Fortunately, I was able to borrow an impact driver from Dad’s workshop; a tool specifically designed to apply violence to screws.

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This tool applies a turning force when you hit it with a hammer, making it ideal for freeing up screws that have been in place for 35 years. It worked very well indeed. Out came the screws and the bracket.

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The observant among you may have noticed that these are not wood screws at all. They’re machine screws, designed to fit into nuts or tapped holes. The threads really don’t hold well in wood. Was this more poor engineering from Newbridge, or was there something I’d missed?

I took a good look down through the holes in the wood and noticed two things. Firstly, the wooden block holding the mast step did not extend all the way down to the bilge as I had expected. There was some sort of void beneath it. Second, there may have been some metal on the other side. Perhaps there was a tapped plate or some captured nuts on the other side. It was very hard to see.

Unfortunately, this is yet another area unmaintainable area of the boat.  There’s no way to get to the other side of the wood without tearing the boat apart. I made a note to inspect the area with an endoscope during the winter.

I also checked the moisture content of the wood. It was off the scale on my moisture meter!

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The plywood the mast is standing on is untreated, as far as I can tell, and has been getting quite wet. I made another note to dry this area thoroughly during the winter and think about how I could treat, seal, and reinforce the wood.

Next, I checked the exact dimensions for the new step by standing the mast step in the aluminium angle. The rubber chocks would be 15mm thick, and I planned to have then compress by about 2mm. The mast appears to be a 4″ tube, so that made the interior width of the step box 13mm.

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There followed about an hour of hacksaw work in the workshop at the Fareham Sailing and Motorboat Club. I like to work on projects aboard as much as possible, but this really did need a good bench vice.

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I’m very glad I chose to build in aluminium rather than stainless steel. I had enough hacksawing of stainless steel to last a lifetime when I built the Hebridean. (These days John Fleming is offering pre-cut kits!) The rubber block was relatively easy to cut with a hacksaw, provided you oiled the blade.

It turns out my beloved tea flask is almost exactly the same size as my mast, so I was able to use it to get a rough idea how things were coming together.

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The next morning I test fitted the step box around the actual mast.

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And I checked that the mast would be clear of any screw heads one it was standing on a rubber chock.

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Next, I drilled holes for the coach screws and the mast pin. I chose positions for the holes about two thirds of the way out, because the mast forces well be attempting to lever up the angles. I also chose too align the holes in the end angles with those in the sides so that the holes are in a rectangle, just in case.

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I’ve only made one pair of holes for the mast pin so far, with the mast base as far aft as possible. This is so that I can test the mast with forward rake. If I decide to alter the rake I will make more holes. There’s plenty of room for four positions or more.

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I checked how the mast step box fitted in the boat, but since the coach screws hasn’t arrived the post, that was all for that day.

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The next morning I had my coach screws from Sea Screw. These are rather special: large screws with threads designed for wood but with hexagonal heads that can be turned with a spanner or socket. The next person to undo them won’t be using an impact driver.

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So far, no permanent changed had been made to Tammy Norie. It was time to make cuts. After carefully re-thinking everything, I enlarged the hole in the berth using a coping saw.

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And then I carefully lined up the mast step box, made pilot holes, and screwed it down.

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I’m eliding a lot of difficulties here. As I suspected, access to the wooden block was very difficult. I wasn’t able to use my battery drill to make pilot holes, and had to fish out my poor-quality hand drill. It was slow going and the pilot holes were not perfectly straight.

You can also see that the box isn’t lying flat on the wood. The wood is partly glassed-over and that makes it uneven.

These difficulties were enough to mean my careful measurements didn’t with out and the mast wouldn’t really fit between the chocks.

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Fortunately, the solution is fairly obvious: make a base for the box separately and then fix the whole thing down.

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Just right! With this change the mast could be pressed firmly down between the chocks, gripped tightly, but with no possibility of abrasion.

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With this done, I disassembled used a punch through the holes I’d made for the mast pin to mark positions for holes in the mast. These were a bit closer to the mast end than I’d like, and for this reason I’d recommend making a taller box of you’re planning to do something similar — 100mm tall I suggest.

I then drilled 6mm holes in the mast for the pin, and tried to put everything back together. For about an hour.

The thing is, it’s very difficult to navigate a piece of threaded stainless steel studding through six not-quite-lined-up holes when two of them are made of rubber and all of them are in an awkward place you can barely see.

After a while I disassembled the whole thing again and enlarged the holes in the rubber using a 10mm drill bit. The holes still ended up much smaller than 10mm, but at least the studding went through them without force. I also enlarged the holes in the mast to 8.5mm so that I had a hope of finding them.

It still to another 30 minutes of fiddling to get the pin through, and I was very relieved when it popped out of the other side of the box. After that I was very reluctant to disassemble the step again!

I think this could be made much easier by fitting a tube through the mast to guide the pin. I may do this later. I certainly recommend it to anyone making a step like mine.

You might notice that there are no chocks fore and aft of the mast. I’ll be making these soon. In order to maximise the forward rake of the mast I did not leave enough clearance for a 15mm chock. I’ve ordered thinner rubber for this job. I believe the step is already significantly stronger than the Newbridge bracket, and I can make tests of the mast position without these chocks. But for the long term I wasn’t to make sure that the pin isn’t taking any load.

Fortunately, I found that I was able to re-arrange my existing mast partner wedges to fit around the mast in its new position. They aren’t a great fit, and I plan to make more, but for testing these are good enough.

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The next snag was that the disc that helps keep the wedges in place no longer fitted over it’s bolts!

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This was a fairly obvious mistake on my part. The new mast angle has shifted this disc back slightly.

The remember this disc puzzling me when I first got Tammy Norie. It’s made of heavy gauge stainless steel and is probably one of the strongest items on the boat, and yet it’s only job is to keep the wedges from falling out. No other Coromandel owner has such a heavy one, so I suspect this is a modification by the original owners.

Fortunately, there was some ideal scrap plywood in the workshop — the seat of some school chairs. This wood had been moulded for sitting on, and so had a nice circular depression in the middle. Turned upside-down that depression will press upwards against the wedges.

Rather than make a complete disc I decided to make two half-discs with an overlap. And instead of bolt holes I would make slots. This would make the new disc capable of being added or removed without removing the mast, and able to cope with mast rake changes.

I marked up the wood.

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Then I put the coping saw to use again.

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Checked the positions of the bolts.

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Cut slots and then smoothed everything in to shape with my surform.

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Not bad!

Finally, I was able to put the interior back together and make Tammy more like home again.

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There are still a few problems to solve, as you can see here.

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Finally, here’s the best picture I have showing the new mast rake. I think it looks rather interesting and attractive.

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So far I have not had a chance to test the new sailing characteristics. Soon, I hope.

There are more pictures with descriptions in this Flickr album, showing the steps in more detail.

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Filed under A New Rig, 2017-2018, mast