How much mast can be unsupported by rigging?

[Rivers & creeks]

I have a 16' GRP dayboat that's a shell project. The mast is 15' long and is hollow wooden, very substantial at a guess 4.5" diameter. It's meant to be Gunter rigged but for our purposes as a river pottering boat and sailing trainer for my young children I want to have the mast with a sleeve main like a laser and an unstayed mast. The easiest solution would be to fit an aluminium tube glasses in and supported. But what length of tube would I need and would it support a wooden mast like that? Would I be better buying an aluminium tube mast - easy to get hold of I guess but I'd prefer to use the nice wooden one.

 

[William_H]

I can only suggest that you look at the very successful laser mast system. Which obviously you are familiar with.
I would suggest that the tube be as long as convenient perhaps up to the goose neck as providing support for the wood as much as possible. From there it might be any one's guess as to how strong the wooden mast is although at 4.5 inch diameter it must be pretty stiff/strong. I imagine also quite heavy. Which may send you to look for a laser mast or similar.
olewill (so no help at all sorry)

 

[Lon nan Gruagach]

Strength to weight ratio wood vs ally only figures I can find put oak between 2 different alloys.That said the page didnt mention how the wood grain was managed.
One thing is size, ally will be smaller.
If you have a well made hollow wood mast I would stick with it.
As for stepping it, I am building :http://rosslillistonewoodenboat.blogspot.co.uk/2011/07/flint-capable-boat.html but with the mast further back (might be balanced gaff or junk rig). The plans suggest a cup on the top of the keel and a yoke at fore deck level (a few inches higher than the gunwale). The mast is strapped into the yoke.

 

[bbg]

If it is a sleeve mast like a laser, why would you want it to be wood? You won't see it while sailing and the weight saving for having ally or even carbon fibre would be enormous.

 

[Rivers & creeks]

If it is a sleeve mast like a laser, why would you want it to be wood? You won't see it while sailing and the weight saving for having ally or even carbon fibre would be enormous.

True but it's one less thing to buy. In time we'll refit the gaff and mainsail once the children know how to sail.

 

[Rivers & creeks]

Strength to weight ratio wood vs ally only figures I can find put oak between 2 different alloys.That said the page didnt mention how the wood grain was managed.
One thing is size, ally will be smaller.
If you have a well made hollow wood mast I would stick with it.
As for stepping it, I am building :http://rosslillistonewoodenboat.blogspot.co.uk/2011/07/flint-capable-boat.html but with the mast further back (might be balanced gaff or junk rig). The plans suggest a cup on the top of the keel and a yoke at fore deck level (a few inches higher than the gunwale). The mast is strapped into the yoke.

Thanks - if I fit a yoke at deck level does it provide as much support as a tube running up to deck level? Dumb question maybe but I'm not any good at theoretical engineering! A yoke would make stepping and unstepping much easier than a tube.

 

[lw395]

1) For teaching kids to sail, it's much better to have a boat that sails well. You can get e.g. a Topper for modest money, then sell it for 10p less when you're done with it.
2) Lots of Finns and OKs have substantial wooden masts, you might find dimension info from some of the classic Finn enthusiasts?
3) The loads on the boat are not trivial, if the mast is stepped through a thwart, there is substantial leverage on the thwart. both sidewise and backwards.

 

[Lon nan Gruagach]

Thanks - if I fit a yoke at deck level does it provide as much support as a tube running up to deck level? Dumb question maybe but I'm not any good at theoretical engineering! A yoke would make stepping and unstepping much easier than a tube.

The only issue is with the thickness of the yoke (plans are in the car right now, I'll look it up later) A tube needs to be really snug for the load to be distributed further than the rim.

 

[Rivers & creeks]

The only issue is with the thickness of the yoke (plans are in the car right now, I'll look it up later) A tube needs to be really snug for the load to be distributed further than the rim.

Hmm, that makes me think - the Freedom cat ketches have about 80% of the mast above the deck and the mast is only braced at deck level and doesn't sit in a tube. I think this is doable

 

[dunedin]

Out of interest, why do you want a laser style free standing mast and sleeved sail on a boat of this size?

To move at all if it will need a fair sized sail. This plus a heavy wooden mast will be very tricky to lift in fully rigged with a sleeved sail - and unable to be easily dropped via a halyard if the wind gets up, or to come ashore. I would think this is not suitable for purpose for a learn to sail requirement.
The Laser style rig is intended for cheapness & simplicity, not for ease of use. It works because the boat and rig are small and light. I would have thought a stayed mast with a simple triangular sail on a halyard, with no boom, would be a better trainer sail. This would also be easier to set up on the boat, and could quickly be swapped with the full Gunter sail when desired.

PS owner of Laser and also had two Toppers, West Eleven and Mirror for kids in past

 

[Owl]

You need about 10% bury of the mast in the boat - so at least 1 1/2 foot. Preferably more. I don't think it matters how you fit it as long as fittings are strong enough.

At 4.5" diameter the mast is probably sufficient in diameter as-is so I'd try it and see. Don't go out in F6 first time - see how it fairs in lower wind speeds first

I've just built a junk rig with an unstayed mast for an 11' boat and it is remarkable how much lower stress everything is under is compared to a stayed bermuda rig. You can get away with less than you think as long as you take it easy to start with and see how it goes.

 

[Daydream believer]

I would obtain a 4.8 metre sailboard mast - there must be loads about unused in peoples garages these days-I have at least 2- Then insert a length of timber inside it to prevent it distorting the circular shape where it exits the deck & extend that about 200mm above that point. Epoxy it inside the mast & you have a nice light mast. If you are into sewing you could use a sailboard sail & boom & cut part of the triangular bit of sail off the bottom where the mast goes in the deck so the boom sits nearer along the bottom of the sail more like a normal boom. Might need a bit of bodging but you might even get a set given to you if you ask around as many people have given up sailboarding & there is no market for the old gear
4.8 masts are extra long ( 4.2 is standard) but they are about & can even be obtained as 2 part carbon ones although a GRP one would be best as less susceptible to damage

 

[NUTMEG]

While you are researching it might be worth looking at this pic https://thelunepilot.wordpress.com/gallery/salcombe-2009/

This is a Lune Pilot, 14' and very heavy. The mast is unstayed and supports a standing lug rig. Simplicity itself to raise and lower and, being unstayed, the rig weathercocks on a run if required, de powering instantly.

The mast steps on the keelson and is held by a wooden wedge at the forward seat. Really simple and, I would think, easy to DIY.

I have one of these and it is a joy to sail, really. No centreboard and a ballasted keel to boot.

Worth thinking about a simple lugsail?

 

[bignick]

I've just built a junk rig with an unstayed mast for an 11' boat and it is remarkable how much lower stress everything is under is compared to a stayed bermuda rig. You can get away with less than you think as long as you take it easy to start with and see how it goes.

Go on, I'll bite.
How do you work that one out?
Work out the compressive stress in the leeward side of the mast for a cantilever unstayed mast and then try again...

 

[Rivers & creeks]

While you are researching it might be worth looking at this pic https://thelunepilot.wordpress.com/gallery/salcombe-2009/

This is a Lune Pilot, 14' and very heavy. The mast is unstayed and supports a standing lug rig. Simplicity itself to raise and lower and, being unstayed, the rig weathercocks on a run if required, de powering instantly.

The mast steps on the keelson and is held by a wooden wedge at the forward seat. Really simple and, I would think, easy to DIY.

I have one of these and it is a joy to sail, really. No centreboard and a ballasted keel to boot.

Worth thinking about a simple lugsail?

That's more like it, I've got a red sail for it that I could make a spar for and convert to a standing lug. What ballet does the keel have?

 

[Rivers & creeks]

You need about 10% bury of the mast in the boat - so at least 1 1/2 foot. Preferably more. I don't think it matters how you fit it as long as fittings are strong enough.

At 4.5" diameter the mast is probably sufficient in diameter as-is so I'd try it and see. Don't go out in F6 first time - see how it fairs in lower wind speeds first

I've just built a junk rig with an unstayed mast for an 11' boat and it is remarkable how much lower stress everything is under is compared to a stayed bermuda rig. You can get away with less than you think as long as you take it easy to start with and see how it goes.

Thanks, junk was another option but making the sail myself would be more complicated. Does it make any difference to the integrity of the mast if it is in a collar at deck level or in a sleeve?

 

[NUTMEG]

That's more like it, I've got a red sail for it that I could make a spar for and convert to a standing lug. What ballet does the keel have?

75kgms, sand in bags under the floor, although I have recently acquired 100kgms of lead, so am thinking about casting some suitable blocks.

 

[DownWest]

Couple of thoughts about the idea. 16ft is a biggish boat for kids to learn on and they would need help lugging it around.
I started pretty early, but the 12ft racing dinghy was considered a bit too much, so father bought a Cadet for us kids and I used to sail it on the Lea after primary school, so aged around 8/9. I could launch it by myself, but needed help to drag her out. Had a lot of fun.
So, might a Mirror or some other small boat be found? Having a sail made up might exceed the cost of a cheepy dinghy to learn on.

Unstayed masts are easier to step in a keel socket and 'gate' at deck level. Technically better than a tube as well due to the way it bends.
The unstayed lug rig alternative for my current boat has around 10% bury. Boat 15ft mast the same and about 3." section at deck level.
The unstayed mast of the new boat is 23ft long and has 2'-10' bury, so a bit more than 10%, but that just happens to be the depth of the hull, so convenient. Section at the partners is octagnol and 3.5" Sail 120squ ft.

As said above, the stresses are relatively low on the hull, compared with stayed masts, esp if the chainplates are not far from the mast.
DW

BTW, Bending resistance goes up as a cube of the section, so your 4.5" section is way stiffer than my 3". BigNicks concerns about compression stress on the lee side also depend on what type of wood.

 

[Rivers & creeks]

Unstayed masts are easier to step in a keel socket and 'gate' at deck level. Technically better than a tube as well due to the way it bends.
The unstayed lug rig alternative for my current boat has around 10% bury. Boat 15ft mast the same and about 3." section at deck level.
The unstayed mast of the new boat is 23ft long and has 2'-10' bury, so a bit more than 10%, but that just happens to be the depth of the hull, so convenient. Section at the partners is octagnol and 3.5" Sail 120squ ft.

As said above, the stresses are relatively low on the hull, compared with stayed masts, esp if the chainplates are not far from the mast.
DW

BTW, Bending resistance goes up as a cube of the section, so your 4.5" section is way stiffer than my 3". BigNicks concerns about compression stress on the lee side also depend on what type of wood.

Thanks - this is very helpful stuff. If I later added a Gunter that would increase the height but does it mean that the unstated mast needs more "bury"? The estimate at the moment is a 15' mast with 2'6" bury so a good percentage.

 

[DownWest]

Thanks - this is very helpful stuff. If I later added a Gunter that would increase the height but does it mean that the unstated mast needs more "bury"? The estimate at the moment is a 15' mast with 2'6" bury so a good percentage.

Just looked at the plans for mine and the gunter mast is actually 14'3" while the lug is 15'3" The sail areas for each are around 90sq ft, and as the lug is high peaked, the centre of efforts are similar, so leverage on the hull too. The section is actually 2-3/4" on the plans and the same for both masts. One thing, the jib on the gunter needs a tightish forstay and shouds are the usual way to get that. So when you switch to gunter, stays might be an idea, though not probably needed to keep the mast up. Worth looking in to spectra or similar synthetic ropes for that. I used wire as I have the swaging kit.
If I did it again, I would probably use the lug rig, as far less string and fittings. At the time, '07, I had not sailed a lug and was familiar with the gunter. Incidently 'The Sailmaker's Apprentice' Is a good read and I got nice results at first go.

New boat is an unstayed cat yawl, so a bit more sailmaking coming up

If you are worried about bury, put the thwart at sheer height, rather than seat level like the Lune. If you have 2'6", then I would think there is no point in trying to increase it