Proof of Concept

A Windsurfer mast can be bought in two pieces.. like a fishing rod... easy to store.

The advantge of a windsufrer rig is that they are areodynamically pure and fast. Since the windsurfer mast is free standing with its own boom it could have several different mast step positions to improve upwind or reaching performance.

Also Well worth investigating oars as a mast.

I would avoid the complexity of foresails..jibs. and only use mainsail or mainsailis.

 

kvsgkvng,
check out this post: http://www.boatdesign.net/forums/hy...-underwater-hull-form-41874-9.html#post540750 . Since you are looking for simple solutions, it might be something that could interest you. Could eliminate the need for a daggerboard, if you're not looking for tight upwind beating angle, but requires a full-length keel or a flat-bottomed hard-chine hull.
Cheers

 

Flat bottom hard chine would be a winner. Easier to keep the shape of the boat after you chop it into sections.

pin lock chines ,sheer clamp and keel

 

Thank you all who took their precious time, read my rumblings.

As I slowly would like to think that, I am going forward, it is not certain. I am trying to do my best in “designing” this small boat. Compared to other posts and pictures on this site, especially in the galleries, this little thing appears to be insignificant. However, for me it is a design lesson where I am studying very basics of naval architectural design. I tried to think of many factors influencing the design of this dinghy and the attached picture is the result of it. I hope to succeed.

What I lack is the some sort of feedback from members who know this simple stuff in and out. I wonder, would you please be so kind as to give this, perhaps insignificant for you, model evaluation? Perhaps, I am missing something so obvious for experienced sailors and architects, that it would be just ridiculous not to mention it.

I consider this a learning curve and hope that you would understand my efforts. Thank you very much.

Kind regards, kvsgkvng.

 

The center of effort of the sail rig seems well aft of the point shown. For calculating the sail CoE the portion of the staysail that overlaps the foresail should not be counted, or you end up counting this area twice. As shown the boat may have a strong tendency to head up into the wind and could be unsailable.

When you first sail an untried design, it is probably wise to have an oversized rudder to handle imbalances; it can be cut down after the rig has been adjusted. It is considered good for a sailboat to have a tendency to head upwind when the tiller is released, but it should not require a lot of effort to bring back on course again. If the boat heads into the wind too strongly it can prove impossible to work up enough speed for the rudder to bite before you find yourself stalled again.

 

what kind of software doyou use for these drawings?

 

I use off the shelf Paint.NET It is free, small and very able little program.
http://www.getpaint.net/download.html#download

 

Thank you for your reply, AC. It seems like you understand my commotions. I checked the numbers and the math for static moments is correct. I attached a spreadsheet which computes Longitudinal Center for each sail and for combinations.

Only aft small main sail: LCG=2.37 ft
Only small mid-stay: LCG=5.10 ft
Only large fore-stay: LCG=6.90 ft

Aft main + forestay: LCG=4.18 ft
midstay + forestay: LCG=6.30 ft
all 3 sails combined: LCG=5.56 ft

So, the Longitudinal Center for sail combinations will move (counting from aft!) from 2.37ft in case of a single small main in the aft to 6.9 ft if only large main stay sail is used. The keel center is placed approximately at 6.1 ft from aft. The calculated Lateral Resistance Center is at approximately at 5.9 ft (all measured from aft). So, perhaps I don’t understand something and my numbers are grossly off.

I would not plan using just aft small main sail. It would be very useful during stormy weather to keep the boat pointing toward the wind while the boat is under outboard power.

Please correct me if I am making a mistake somewhere.
Thank you very much!

 

The hull looks like you have a winner, I like the concept very much and the hull design.

But the sailing rig has issues; Why are you installing an aft mast? That is a very difficult rig to solo operate, way too much sail, and if you have to reef it will throw the balance way off. In my opinion that sailing rig will bring you lots of grief, I would never build it that way (and would never recommend it for a first time boat). I have built 14 or 16 small boats (most of my own design), have owned or sailed lots of others, including racing in both mono hulls and catamarans. Whatever the theoretical merits of an aft mast, in practice it is almost NEVER done. Fastests and most efficient sailboats ever built have conventional sloop rigs, stay with that please.

There is a reason most sailboats have the mast in the forward third of the length. What you have will be uncontrollable in many situations, and no fun to sail in any conditions even in very light wind.

For a first time boat, stick with what has been time proven. Move the mast to the area of the forward bulkhead/separation point. Reduce the size of the jib greatly, and increase the size of the main. this will make you have to move the dagger board forward, which is a good thing, the further the distance between the dagger board and rudder, the smaller the rudder can be, and it will have more effective control, reduce tiller forces, keep things simple.

I would keep it simple and just go cat rig, one large sail. Easy to control, less parts, less work to trim, etc. You also have way more sail on that thing than you need, there is no class racing you can do with, even if you wanted, so all the extra sail does is make it more work to sail it and add much more cost to building it.

Sorry to be so harsh, but if I understand your motivations correctly, this rig would be a mistake. You will build it, and than either abandon the project all together, or end up building another more conventional rig anyway just to make it sailable. If you want something different, build a modified junk rig, they have much to be said for them as I posted before.

 

I agree with Petros. I would like to see you get some more informed input* on the rig. BTW I think there is an error in the LCG calculation for the “no small stay” combo - I get(314.64 + 37.33) / (45.6 + 15.75) = 5.74

Relatively small errors in balancing lateral areas can have a big effect. My small sailboat has three mast step positions (for sail rig experiments) and once I mistakenly stepped the mast in the wrong one. That put the mast a foot aft of the correct position - all I could do was sail downwind until I hit something and then row back.

Picture how you will sail the boat in practice. In a light wind you will want to set a lot of sail. It would be smart to make the larger staysail from light material so it will set itself. You won’t want to have to go forward on every change of tack to push a heavy, balky sail to the other side.

In a stiffer breeze you will want to reduce sail and it would make sense to take down the large light-airs staysail and set the smaller staysail, which might be a heavier fabric. You may then find you cannot balance the boat as the LCG has shifted aft almost 2 feet, until the has been reefed to 50%. That’s a 50% loss of total sail area; you need to reduce sail in smaller increments than that.

Your rig should have more flexibility. With the arrangement you have, you can only get that if the large staysail has a roller reefing arrangement. That sort of complexity is totally at odds with the entire concept of a cutter rig.

* I recommend you start a thread in the sailboats forum.

 

Thank you, Petros and Ancient Kayaker! I really appreciate your advice and listen to your suggestions. All of your points are well balanced and taken with appreciation. The reason of me asking many questions is that this may be most valuable information in learning something new.

I am posting my last picture for a some time because I think I am going to spend some time on building a scaled model of the hull.

Hopefully I will be able to complete this task withing few weeks. It will be very helpful to hold the hull in my hands and evaluate it not on the screen, but in real life. Most likely I will use scale 1/8"=1" Then the model would be around 19" long and 8" wide. It should be enough for now.

Again thank you for the help and advise.
Regards, kvsgkvng.

 

much better sail plan. Nice looking boat too.

Personally I would consider making the boom length about 2 ft shorter so it will swing clear of the helm position with each tack. or raise it several feet (both results in smaller main, which is not a bad thing here). Otherwise the tacks will be tedious and there will be many times you forget to duck, especially on unexpected jibes. Trust me, you will hate it when that happens.

Post pictures of your model! Use some 1/16" plywood, or even plastic sheet or fiberboard and tape to build the model. make sure you simulate a scaled sailor (use a clay man), and cargo if any is planned. On a boat this small it will help you see how balanced the hull is in the water.

 

Looking good! When I make a serious scale model I look around for the thinnest ply I can get and base my scale on that, using slightly thicker than scale ply. For example, I am buying 0.8 mm ply tomorrow for a model of a boat I plan to build in 4 mm ply; I will likely use 6:1 or even 8:1 scale instead of the 5:1 you might expect to provide a little more area and error tolerance on the joints.

 

For your consideration, here is a picture of a similar sized boat with a junk rig, looking good!

 

An important question is what is the mission of this boat ?

What is most important ? Sailing ability ? Utility ? rowing ability ? Cruisabilty ?

It matters greatly . All boats are a compromise. Your proposed sail plan will move the boat, but is poor. If you must sail upwind to enter a river or bay you will never get there. Its possible that upwind sailing abilty matters little because you are optimising your design for speed under oars.

Simple details make the boat.

For instance if you plan to sleep in the boat you will need either floorboards along with their weight and hassle to keep you dry or you mold a keel recess into the bottom to collect water drips.

What do you estimate the finished weight of boat and gear will be ?