Desperate to sail 2015

Hi all,

I'm back from holiday. I promise to reply to other threads as soon as possible, but right now, I'm on a deadline.

In two days, I'll depart to the lake where I spent last summer, trying to rig a fishing boat . However, the boat was stolen, but the rig and sails still remain. This year the owner of that boat got a new boat. He said I can rig it, as long as I don't leave a mark on it - that means no screws or drilling.
I know nothing about that boat. I hope it is similar in design like the previous one, but I can't be sure. So I've been working on a design that will work if the boat has a center seat. Here is screenshot from CAD design on which I've been working this whole day:

http://static.dyp.im/SqPSedZREz/3749e51b252221eec986d524fd082394.JPG

The idea is that the cross beam transfers forces from mast to the leeboards directly, without straining the hull. Diagonal beams should add structural strength, and the "arm" that is wrapped around the seat will handle longitudal forces on the downwind.

The design is folding, and should fit into the boat if wind dies and I'll have to row.
There are 4 parts: 2 leeboards and 2 structures. The big one includes mast step, the "arm" which rotates on 2 joints (long screws) and the diagonal beams, which rotate on door hinges.
The other part is the cross beam.

All 4 parts are connected by following system: a hole in a part is drilled, and a brass plug with threads is hammered and glued in. Another part, featuring same diameter hole, just without threads, is then pressed against the former,
and a screw with a loop is inserted via both holes, and then screwed by hand into the brass plug until both parts are tight and secure.
See this used as a clamp in rudder hinge design. The left screw is screwed into brass plug (gold-looking one), while the right screw is removed for better view.

Specifications

All beams are 40x40mm, dried pine wood. Planks are 20x91mm, same. All screws with loops are 8mm diameter, and ones used to clamp leeboards to the hull are 10mm. All other screws are also 10mm. Door hinges are 40x60mm.
Total weight (without the mast) is estimated at around 7.5kg.

The sails

I have heard many virtues of balanced lug rig, foremost being ease to make and control. However, I don't have one.
I have two sails right now, both made of Tyvek. They were once used in my ill-fated cat. I used the jib as mainsail last year on the now-stolen fishing boat, but with area of 3m^2, it was obviously too small.
However, the other one is a monster, boasting 8.34m^2, and due to curved luff, will be unusable as a lug. However, if I were to cut it, and make a new sail out of it, more like 5-6m^2, it'd be perfect.
The only problem is that I have my doubts about the mast. Last year I cut down a fine Lithuanian pine, de-barked it, and used as a mast straight away. Never varnished it. It damn heavy. After that, I left it under that house by the lake to dry.

However, due to such amateur handling of timber, I expect it to be a bit weaker than it should be. From here start my questions:

Questions

1. For a boat of ~4m LOA, ~1.6m beam, 200kg displacement, 4.5m mast height and a 5-6m^2 lug rig, what is approximate diameter of a mast? Please consider that it wasn't fallen down properly, as described above.
2. What taper could be added? If, for example diameter at pentersen should be 6cm, is 4cm at the top a good estimate?
3. Do these leeboards look big enough for you, considering such sail area?

4. Does this whole design idea seam reasonable? Are there any mistakes or faults I should know about?

Conclusion

I forgot to mention - I decided to invest into some proper tools. I'll buy a jigsaw a day after tomorrow, as well as a hand plane, some wood rasps, and a set of drill heads.

I hate to ask it like this, but I have very limited time to make this wild guessed design. Tomorrow is still available, but the day after I have to buy tools and materials, and the next day I'll depart... So any rapid advice would be more than welcome. I promise lots and lots of pictures

Thank you again once more...

 

I'm sorry to be asking like this, but I have around 12 hours left until I have to buy the materials for this project. After that, options will be much more limited.

If anyone has any insight, now is the time...

 

I'm glad to see that you are back with us Laukejas. May you have the best of luck with your project.

 

Thank you, messabout. Could you be so kind to look through the project, and offer your opinion, if you have some time?

 

OK here are some comments. The structure that you have drawn is simple enough and it will have sufficient strength sideways, that is across the boat. I cannot see any part of it that will keep the mast from collapsing forward. If you can secure the mast base plate to the boat then you might get away with this arrangement. However you have said that you cannot drill holes or use screws in the the other mans boat.

Consider the mast to be a long lever. The lever will pivot at the top support, or cross member that you have drawn. Suppose that the distance from the cross member down to the bottom of the boat is.......40 centimeters. (These are just numbers to explain the situation, not necessarily the ones on the boat)....The center of force on the sail might be 1.6 meters above the cross member. The lever ratio will be 4 to 1. (160/40) If the sail develops a forward thrust of............say 20 kg then the force on the base plate will be 4 times 20 kg. or 80 kg pushing the base plate aft.

What to do???? You will need a duplicate cross member and framework that is strongly attached to the one you have drawn. The second framework to be placed at least a half meter forward or aft of the first one. The second frame need not have the mast socket , though I would put a base plate on that one too.

It is easy to feel the force of the sail in the sideways direction. That is what causes the boat to heel. It is not so obvious that the sail is also pushing forward. If it did not have forward thrust then the boat would not go forward.

The second observation is the location of the lee boards. You have it drawn as if the boards are at the same fore/aft location as the mast. If done that way, the boat will have very bad weather helm. That is to say that it will always try to turn the nose of the boat into the wind. The lee boards need to be farther aft, somewhere in the neighborhood of one third of the length of the foot of the sail. You will need another, separate, cross member to fasten the lee board to. If you make its position adjustable fore or aft, you can find the right place for it by experimenting.

I am sorry that I could not explain this with fewer words. I hope that this helps a little bit.

Laukejas, I admire you greatly for your determination. You are going to build things that will make a boat sail come hell or high water. If it were not such a long distance to Lithuania, I would come there and help you. I suspect that there are quite a few other forum members who would do the same.

 

Thank you for your advice, messabout. Also for your kind words and support.

What I failed to mention is that in this design, the lateral forces from the mast step are to be handled by the "arm" (the triangle) that goes around the seat, and transfer forces to it. The cross beam will be tightly clamped by leeboards so it doesn't slide forwards of the boat. I know friction alone might not be enough for that, so I hope that if boat has anything to secure ropes on it's sides, I will lash the cross beam right by the leeboards.
I cannot secure mast base to the floor, but I made it wide, and I'm considering adding this kind of mat to add a little friction. I know, it won't do a lot, but combined with other things, it may do something. If mast is compressed down to the floor enough, the friction and the size of the base plate might prevent it from moving.

I know this isn't perfect, but I can't think of anything better. Adding another cross beam will be very complicated, and since I know nothing about the boat... I hope that the wide base plate, pressed against the floor with the help of non-slip mat and the "arm", lashed to the seat, will be enough...

Your argument about weather helm is very sound. The leeboards can be pivoted back somewhat, but the this inevitable disbalance is the reason why I want to make a lug sail - it can lie both fore and aft of the mast, so I can adjust it's position until weather helm is acceptable. If it will be too far in front, I'm afraid the bad tack will be really bad. In that case, I will consider re-making it into dipping lug. But that is too far ahead of me right now.


Considering this, do you still feel it might be not enough to keep mast from falling forwards?

P.S. This is a screenshot of a proposed lug sail that can actually be made from the old gaff sail of my cat. It looks like it still has some weather helm, but it being a lug sail, I can always shift it forwards... Mast height allows for that.

 

The trip to the hardware store was a success. I got all that I needed. Also picked up a few doubts on the way (like... maybe I should have made leeboards out of plywood?)

I also consulted with a good friend of mine who is an experienced boat builder, and he also expressed doubts about mast support from falling forward. He suggested NOT to utilize the seat (because it is not known at this time if it can handle the forces from the mast before breaking down), and offered a different approach: make another triangle-like support which lies on the floor.
I modeled it in CAD, since materials I have are compatible with this design.

Here is the screenshot.

The idea is that when mast wants to pivot forward, the beam which runs along the keel will press down on the floor, preventing mast from falling, while mast step won't be able to lift due to cross beam holding it in place (it being clamped to sides by leeboards). I don't expect the mast step to raise, but if it does, I can tie the cross-beam to the seat with rope. Surely forces lifting the mast step will be much less than what average fishing boat seat can handle (unless it's removable).

Please, take a look at the screenshot. At the moment this is my preferred design. In 14 hours, I'll depart to the lake to see the actual boat.

If anyone can offer a quick insight into these modifications, I'd be most grateful

 

laukejas,
Not sure if I comprehend everything but I want to give some answer.

The first thought I have is that the easiest way to quickly rig a boat you don't even have dimensions for is with stays. You appear to be trying to do a free standing mast which would take lots of your vacation time building.

Just because you are doing a lug sail doesn't mean you can't run stays if your mast is tall enough and your yard is peaked at a steep angle. The drawing of your sail shows a very tall mast with enough room to run a stay from the top to the bow. If you run stays from the top to the rail on each side a foot or so behind the mast you should have it fully secured. The other benefit of stays is they greatly reduce the strength requirements of the mast compared to unstayed. The only additional location needed would be at the base or your leeboard mount. If you can clamp the leeboard mount to the rails that would do it.

 

One more quickie sail setup is to use a long oar or paddle with an extension and make a clamp on it's shaft so that it can be hung on the rail so the blade acts as as a leeboard and the shaft can act as a mast. With a stay to the bow and transom you can hang a genoa on the forestay. This rig has some pointing issues and you have to tack the oar from rail to rail but it is about the least work you can do to make the wind power an unseen boat.

 

Skyak, thanks for reply. I have been waiting for you

Problem here is that I cannot make a simple mast step that is needed for stayed mast. There is nothing on the floor to attach to. I cannot drill the boat. Last year, I made a mast step by lashing ┌ shape structure to the seat (http://www.boatdesign.net/forums/attachments/sailboats/83248d1375619121-desperate-sail-2013-08-04-12.52.53.jpg). It was the closest I could have to a mast step. And I have to tell, rigging the boat every time, every day took like 20 minutes of hard work, really hard, sweaty work.

But the stays were possible because that boat had rails to which I could tie stays to. This new boat probably doesn't have any attachment points for stays. That's the main reason why I can't have them. I doubt that friction of the clamps alone could hold the stays... Should they fail, consequences would be disastrous.

So that's why I'm adding such complex structure - to make sure that capsizing would happen before dismasting.

Skyak, do you know how much can I slender the mast? I want to save some weight aloft. I'm thinking of 6cm at the base, and 4cm at the top. If mast were to be unstayed, is that enough for 5-6m^2 sail?

 

Is there a photo of this? I have a hard time imagining it...

 

I looked but didn't find it on the web so this is my sketch. I tried to detail a clamp which is actually behind the sail.

 

Those outside dimensions are about what my laser mast is. The lower section is fairly thick wall at 3mm but the laser has a very flat hull which raises the stress. If you are holding your mast at points more than half a meter apart you should be ok with 2mm wall thickness lower. The upper migh only need to be 1mm thick wall.

Boats almost always have handles or holes at the bow and the stern to attach to and gunnels that can be clamped to.

 

Wow, this is really imaginative. I have never thought that something like this is possible. But this is really, really desperate, way more than my project!
I will keep this in mind, but right now, I cannot risk breaking the oars of a rented boat, should they be too weak for the job...

So, do you have any idea about mast diameter?

 

Sorry, didn't see the post above.

I assume you meant hollow aluminum mast? Mine is not. It's a tree that has been cut down, debarked, and dried for a year.
My idea is to slender it until base is 6cm in diameter, and top is 4cm. Are these numbers okay for 6m^2 lug sail?