Anonymous wrote:

Andrew wrote 

The two main questions would be how to work out the position of the mast and how to size the mast and sail area.

I guess the real starting point is to read the books!

Certainly read the books and notes as recommended by Jan. But at some point you will need to take the first step and start making some decisions. My expereience with a boat about that size, with a fractional rig a bit like yours, is that even with an ultra high balance sail such as a SJR with 33% mast balance, you will probably still want to move the mast forward a little. Even more with a low balance rig.

So, the starting point for me would be to make a drawing of the current sail plan. I can't find one on the internet to copy, but there is a Hunter 20 Facebook page so you might be able to find someone who has a sail plan drawing. If not, you will have to  make your own.

It is not difficult. Don't waste time with photographs. You don't need to draw the hull, just a straight line will do, representing the hull length, and the current mast position, to a suitable scale. Then you will need to get your sails out and measure their dimensions, and add the sails to your drawing. Then you need to calculate the geometric centre of area of each of the two sails and from them, a resultant single geometric centre. (The geometric centre of area is often referred to as the "centre of effort" or CoE.) It is not a difficult exercise in geometry to find this position and mark it on your sail plan. Lots of books and designer notes explain how to do this, with a sloop rig such as yours.

Now you have the centre of effort, or geometric centre on your drawing You can rub out your original sail plan and mast now, or leave it there and ignore it.

If you are not confident at that point, you can post your scale drawing (including the scale ruler with the drawing) and someone will be able to help you along from there.

There are now two ways to go.

1. If you have junk sail plan in mind, you need a scale drawing of it to fit onto your sail plan. The geometric centre of your new junk sail will be somewhere along a vertical line (it doesn't matter where) which goes through the midpoint of the boom. That will be near enough to start with. Position the sail on your plan so that the geometric centre is on the same vertical line as the original geometric centre of the original rig. Your sail plan will have a mast position on  it which matches the plan form you have chosen, (because there will be an optimal mast balance which suits that sail) - it might be anywhere between about 10% to 30% depending on the shape of the sail, yard angle etc. (If not, post the drawing of your sail on the forum and get help deciding where the mast goes, relative to the sail). That way you will find out where the mast has to go.

2. The other way to go is to pick a position a little forward of the mast where you have pre-determined where you want the mast to go. Internal accomodation, deck structure etc might lead you to choose the mast position you want. Put the mast onto your drawing, and then place your chosen junk sail drawing so that the geometric centre aligns with that of your original sail as before - and that way you will find out what your mast balance will have to be. You have a fair amount of wriggle room because it could be anywhere between about 10% and 30%. You may have to change the shape of the sail (but not its position) so that the sail shape harmonises with the mast balance you have arrived at. Again, submit some drawings and ask for help if you can't do this.

So, you either start with a pre-determined mast balance and find the resulting mast position, or you start with a predetermined mast position and find the resulting amount of mast balance the sail will have. Either way, the geometric centre of the sail will be in the right position - aligned with the designed geometric centre of the original sail.

(There is an exception to this above procedure if you want to look at some unusual and specialised features such as the sail on the front cover of last July's JRA magazine - that's a kind of special case, but the above procedure holds for what we might call a "conventional" junk sail, of which there are many different shapes and types.)

Clear as mud? If not, then make a drawing and give some dimensions, post on the website forum here. There are some good sail design experts who watch this forum who might do it for you.

You are safe enough by choosing a sail area about the same as the original bermudan rig. A little more if you like, because your sail will be easily reefed. But no need to get carried away with sail area. A modern cambered junk sail is every bit as powerful as a bermudan rig.

Finally, the scantlings of the mast itself - I would rather leave that to someone else to advise. I have made my own masts and had no problems but when it comes to advising someone else, I am not qualified. Your free standing junk mast will be stouter than your original stayed mast, that's about all I can tell you. You also need to consider any structural issues on the hull and deck, which now needs to support a free-standing mast. You can copy the details from any other boat of approximately similar size, and the same applies to mast design, scantlings etc.

Graeme, thank you so much. That is brilliant! I'm especially excited by the idea that the mast may not need to be moved forward by much. The main sleeping arrangement is the forepeak, ahead of the lifting keel box and it would be nice to keep that as a double berth for those romantic nights anchored up in a secluded bay!
I'll get cracking on a drawing ASAP. Thanks again.

Andrew wrote 

The two main questions would be how to work out the position of the mast and how to size the mast and sail area.

I guess the real starting point is to read the books!

Certainly read the books and notes as recommended by Jan. But at some point you will need to take the first step and start making some decisions. My expereience with a boat about that size, with a fractional rig a bit like yours, is that even with an ultra high balance sail such as a SJR with 33% mast balance, you will probably still want to move the mast forward a little. Even more with a low balance rig.

So, the starting point for me would be to make a drawing of the current sail plan. I can't find one on the internet to copy, but there is a Hunter 20 Facebook page so you might be able to find someone who has a sail plan drawing. If not, you will have to  make your own.

It is not difficult. Don't waste time with photographs. You don't need to draw the hull, just a straight line will do, representing the hull length, and the current mast position, to a suitable scale. Then you will need to get your sails out and measure their dimensions, and add the sails to your drawing. Then you need to calculate the geometric centre of area of each of the two sails and from them, a resultant single geometric centre. (The geometric centre of area is often referred to as the "centre of effort" or CoE.) It is not a difficult exercise in geometry to find this position and mark it on your sail plan. Lots of books and designer notes explain how to do this, with a sloop rig such as yours.

Now you have the centre of effort, or geometric centre on your drawing You can rub out your original sail plan and mast now, or leave it there and ignore it.

If you are not confident at that point, you can post your scale drawing (including the scale ruler with the drawing) and someone will be able to help you along from there.

There are now two ways to go.

1. If you have junk sail plan in mind, you need a scale drawing of it to fit onto your sail plan. The geometric centre of your new junk sail will be somewhere along a vertical line (it doesn't matter where) which goes through the midpoint of the boom. That will be near enough to start with. Position the sail on your plan so that the geometric centre is on the same vertical line as the original geometric centre of the original rig. Your sail plan will have a mast position on  it which matches the plan form you have chosen, (because there will be an optimal mast balance which suits that sail) - it might be anywhere between about 10% to 30% depending on the shape of the sail, yard angle etc. (If not, post the drawing of your sail on the forum and get help deciding where the mast goes, relative to the sail). That way you will find out where the mast has to go.

2. The other way to go is to pick a position a little forward of the mast where you have pre-determined where you want the mast to go. Internal accomodation, deck structure etc might lead you to choose the mast position you want. Put the mast onto your drawing, and then place your chosen junk sail drawing so that the geometric centre aligns with that of your original sail as before - and that way you will find out what your mast balance will have to be. You have a fair amount of wriggle room because it could be anywhere between about 10% and 30%. You may have to change the shape of the sail (but not its position) so that the sail shape harmonises with the mast balance you have arrived at. Again, submit some drawings and ask for help if you can't do this.

So, you either start with a pre-determined mast balance and find the resulting mast position, or you start with a predetermined mast position and find the resulting amount of mast balance the sail will have. Either way, the geometric centre of the sail will be in the right position - aligned with the designed geometric centre of the original sail.

(There is an exception to this above procedure if you want to look at some unusual and specialised features such as the sail on the front cover of last July's JRA magazine - that's a kind of special case, but the above procedure holds for what we might call a "conventional" junk sail, of which there are many different shapes and types.)

Clear as mud? If not, then make a drawing and give some dimensions, post on the website forum here. There are some good sail design experts who watch this forum who might do it for you.

You are safe enough by choosing a sail area about the same as the original bermudan rig. A little more if you like, because your sail will be easily reefed. But no need to get carried away with sail area. A modern cambered junk sail is every bit as powerful as a bermudan rig.

Finally, the scantlings of the mast itself - I would rather leave that to someone else to advise. I have made my own masts and had no problems but when it comes to advising someone else, I am not qualified. Your free standing junk mast will be stouter than your original stayed mast, that's about all I can tell you. You also need to consider any structural issues on the hull and deck, which now needs to support a free-standing mast. You can copy the details from any other boat of approximately similar size, and the same applies to mast design, scantlings etc.

I hope not Jan. I have been a JRA Member since 1988 and my regret is that since then until now, no mainstream boat builder has produced a Junk Rigged boat. My Swallow Baycruiser 21 has roller-reefing and is easy to pull up the mainsail but extraordinarily difficult to get it down afterwards. You have to grab handfulls of luff and pull instead of just letting go the halyard. The Junk Rig is easier in every way and nowadays just as efficient. I think yacht builders have just not experienced a modern Junk with cambered sails. 

Paul

Thank you Paul. I'm sorry, I missed your post at the time, I have lost the whole sailing summer due to a back injury in July.

I did manage to sell the 5 tonner without losing too much money and have the Hunter on a mooring in the Fowey river. Haven't managed to hoist the sails yet but with 3 weeks to go before lift out, I'm determined to get one sailing trip in.

Then, I'm fairly sure that I can convert her over the winter, or certainly do most of the donkey work. She's a bit small for my liking but being able to keep her in the garden over winter will save enough money to pay for a lot of the kit.

I have not managed to find any examples of a junk Hunter Medina so if anyone could advise how to start the process, I would be very grateful. The two main questions would be how to work out the position of the mast and how to size the mast and sail area.

I guess the real starting point is to read the books!

I recently got tons of great advice here on converting my Yachting World 5 Tonner, especially with Arne's fantastic drawings. The time has come for me to make a difficult decision, keep the 5 tonner or keep "my other boat" which is a lovely little Hunter Medina 20 footer, currently on a trailer in our garden.

There are many good reasons to come down on the side of the Hunter. We can keep her at home over the winter, saving a thousand pounds storage fee. She's easier to sail for an old timer like me. She can be left with the mast up, on the trailer at a boat park 7 minutes drive away and dropped in in half an hour. We can creek crawl up the river with the keel up and beach her.

The main downside of the Hunter is that she's small, an oversized dinghy really and a bit tender for coastal cruising. Converting her would presumably be much cheaper, smaller mast, smaller sail, everything much more lightweight. I sailed on David Tyler's Hunter Duette and was extremely impressed but that was 2 or 3 feet bigger. Would junking a 20 foot boat make her more seaworthy or is that really down to just the hull. Would it still be like sailing a dinghy?

Thank you for any advice / opinions. Or should I sell them both and get a Hunter Sonata? I've chickened out a bit with maintaining a 77 year old wooden boat.