The Melatelia: light wind dinghy

use the double thickness for the dagger board (stronger would be better here), but single thickness for the rudder. Actually a thinner foil will hold a higher angle of attack before it stalls, the flow stays attached better. It is just the stall is not as gentle as it would be with a larger leading edge radios. On your boat it will not make any difference, there is not real danger if you over control the rudder. But the higher stall resistance in the rudder would be a good thing, the dagger board will stall before the rudder, which is always desirable for a recreational boat.

 

Optimist has daggeboard and rudder of the same thickness: 15 mm

 

http://www.land-ocean.net/english/sail.htm Here's some wooden board dimensions, 420 boards are close to your dimensions so I think you should be fine with 18mm. Our classic snipe has a 10mm thick alu board and it sails nicely despite the profile thickness.

 

Hi Laukejas,

I only recently came across your thread. Nice design and hope the build is going well. I have done something similar, it does not sail badly. Did not do as much thinking about it as you have obviously done.

Please excuse me if this is mentioned somewhere, but what are your thoughts regarding sails and the options for making sails? Which materials would you use?

Again, good luck.

 

Okay, so 18mm for rudder. Petros, you suggested to double daggerboard thickness, while others said that 18mm should be sufficient because of similar designs. Could you please elaborate a little on whenever the added strength of doubled daggerboard is worth additional expenses, weight and work? I lack the necessary knowledge on the subject to make an educated decision.

Thank you for joining in, Driers, and for your kind words. The build hasn't yet started, it is in a final design and material gathering stage, both of which are going extremely well. The set date for starting the build is 6th of May, although first few days are reserved for preparing the workshop (making sawhorses, workbench, sharpening tools and so on). I will post regular updates once it starts. Stay tuned

It isn't easy to find a specific mention of something in so many pages. I'm very pleased for your interest, though. I'm planning to use a standing lug sail, around 6.5m^2 in area. It will surely be made from Tyvek, taped with double-sided sticky tape. I haven't yet decided on the building method, though. First, simpler option is to forgo sewing, make sail flat and add darts at corners, and thus have quick and dirty sail which can be made in 2-3 days. However, if I feel up to it, I have already prepared a plan to cut Tyvek into 40cm strips, and in addition to the sticky tape, sew the sail traditionally, utilizing broadseaming, and all the reinforcements a proper sail should have. In other words - follow the path a real sailmaker would take, only with inferior material.
If I take the second path and the sail turns out to be more or less usable, maybe someday I'll order real sailcloth from overseas (I'm living in Lithuania, Europe, and they don't make sailcloth here that is affordable for students), and make a bold attempt to make true sail. But that's a very long shot from where I'm now.

So, to answer your question - Tyvek, double-sided sticky tape, standard aluminum grommets, synthetic thread. If you're not sewing, be sure to use reinforced sticky tape, or specialized tape for Tyvek (very expensive, though). Non-reinforced sticky tape, in my experience, does not chemically bond to Tyvek. I'm not sure why. But whatever tape you use, be sure to test it - stick two pieces of Tyvek, and if it survives you trying to pull it apart, leave it in one place for a few days, then check again. I can't stress this out enough. In my experience, I once used non-reinforced tape, which, at first glance, bonded perfectly with Tyvek - survived tearing, stretching, cutting, submerging, heat. However, on the third day it came apart by itself - I just found my sail in pieces. Needless to say, repairs were very difficult. Be sure to test whatever tape you use before you make your sail. However, if you're also sewing through the tape, then it isn't as important - tape only has to hold long enough until you sew, and, held in place by threads, it will probably still add some strength to the seams.

Also, during my research this year on proper sailmaking techniques, I have red many books on the subject, consulted a considerable number of sailmakers, including the famous Todd Bradshaw. I have collected an impressive amount of information on the subject, but I'll confess I haven't yet had the opportunity to put it to the test. If you need to know anything, I'll be glad to share whatever information I can. Just let me know.

 

I'm just guessing, but I think you don't need a thicker section for strength. There's not a lot of righting moment needed when the boat is at 90 deg, climbing on the board is more about taking a nose dive into the cocpit as the boat rights so no need to swim around to stern. A thicker laminar flow profile could help a bit when recovering speed after tacking, but I'm thinking you would need more boatspeed to see any real gain.
Your designwork is very detailed and the boat looks good. You'll get those design hours back on the build, I know as I'm doing things on an opposite order

 

Thank you. Indeed, the boat is looking better all the time, but there's still something missing from an aesthetic point. I just can't point my finger at it, but something is not yet right. Maybe it's the proportions or something, but I really don't know. Take a look, for example, at the Tideway. I know this boat is larger than mine, and also has a round hull and bow, but apart from that, the hull lines (especially the sheer line) have some kind of aesthetically pleasing shape that my boat doesn't have. This is one of the most beautiful dinghies I have ever stumbled across. I wish I could have a top-down view or something of this boat, then maybe I could figure out what my boat lacks.

Maybe I've already pretty much done what I could in the constrains of my requirements, but I still hope to make that tiny change that would make my boat look more... Like a boat.

Or maybe I'm just overly critical.

 

Basic lines look proportionate, it could be the rendering looking too clean. You could try dividing that deserted bow deck in centerline with a wooden molding, or adding a V-shaped spray rail like this: I stuffed said snipe's (not the one in this pic) bow in a big powerboat's wakes heeling a bit windward. New crew immediately checked moisture level of his pants and said "damn, that thing actually works!"

 

Yeah, I know, but the bow is actually okay to me. If viewed from above, side or front/back the proportions look okay. But the stern that's looking strange if viewed from a certain angle. Like this:




Ah, maybe I'm just being picky. But I'd really like to understand why, for example, Tideway's lines look so boaty and perfect. Maybe my internal arrangements (side tanks) screw up the looks. I don't have an artisans eye to determine exact cause.

Anyway, never mind this. This is really not an issue.

 

I have made dagger boards for a 14' boat about 3/4" thick (19 mm), out of strong dense straight grain doug fir. the board is plenty strong, where you need the strength is when you have to climb up on it when it is out of the water to right the boat. The thinner section will have less drag and weigh less, but I do not know the strength nor quality of your lumber. If I was using western red cedar I would make it a min of 1.25" (32 mm) thick, so if your 18 mm is strong enough, it will work just fine.

The most severe loading is not when sailing it, but when using the dagger board to right the boat when it is on its side. If you are aware of that limitation, than using 18 mm would likely work out fine, save the cost, weight and effort. If you fail the dagger board you will be done sailing for that day, but it would not be too much work to make a stronger one later if need be.

Thinner sections are actually more stall resistant and have less drag, the only reason to make them thicker is to get the strength necessary out of them. This is always true in aircraft, propeller blades, and in foils and dagger boards. The thickness is determined by strength requirements, not for fluid mechanics.

On something very weight sensitive like an aircraft, thicker wing sections means much lighter structure, so all of the effort has gone into designing thick sections with low drag and high lift (best L/D). So it is not surprising there is much confusion over this issue. If you can make it light and strong enough, the thinner the section the better, in all circumstances. You have to trade off weight vs. drag on a light aircraft, for low speed they tend to have thick sections and try and get the lowest drag possible out of a given section thickness.

 

Thank you for clearing this up. I just thought that foils with thicker camber produce more lift, and keep flow attached in higher angles of attack. I thought I red this in a book about aircraft. But I guess this isn't the same.

The wood used to make these boards is Birch. Same as my plywood. Although heavier than most other species, it has a reputation of being exceptionally strong. I red that Birch is often number 1 choice wood for aircraft frames, despite it's weight.

So I guess it should be okay, and as you've said, if I break it, it won't be very difficult or costly to replace.

 

You were right. To produce a needed amount of lift on a typical fixed speed and angle of attack, a overly thin profile board needs to be bigger and therefore have more wetted surface area and more drag.

 

Got it. So it's 18mm daggerboard, then.

 

It's a nice looking boat. I would build a model next and flush out the concerns that others have raised.
You could build it with stiff paper and tape, just big enough for accuracy.
Then maybe go to a bigger model to refine the construction details.

 

Tideway was designed to be a yacht. Your boat is designed to be a pleasure boat. The difference between the two is that appearance is high on the scale of priorities with a yacht and not so high or even non-existent with a pleasure boat.

IMHO, a yacht's main purpose is to impress. I can have a 60 ft pleasure boat and a 6 ft yacht. The pleasure boat would be made of unpainted aluminum and be quite plain. The six foot dinghy can made of several beautiful species of wood, covered in glowing varnish, with all kinds of custom bronze fittings.

Although it is customary to refer to any large sailing pleasure boat as a yacht, I think doing so does a at least a slight disservice to the truth.