The Melatelia: light wind dinghy

...sail

 

Okay, maybe I'll go with 85cm or something. It seems that after these hull changes and boom height adjustments, my sail downgraded to 6m^2. Not much I can do about it.

Thanks, but why are you even showing such a thing? This sail looks like that of a windsurfer. I bet it is laminate-made. With all the battens and shaped mast. Non reef-able, impossible to lower. My boat aims at the exact opposite.

 

yes it is a windsurfer sail;
are easy to find also used, of different sizes, and are very efficient

 

Thank you, but it has nothing to do with my needs. Apart from what I told, it is expensive. I've seen them for sale (second-hand).

I need a cheap, manageable and safe sail. With reefing, ease of taking up and down.

 

My answer to why there are sailboats with seats below the shear is that it is easier to sell pleasant lies than unpleasant truths. Both boats are claimed "unsinkable" and anyone can tell you that there is no place for "capsize" in the sales pitch. Side decks are on the vast majority of production sailboats under 4M here. JP gave a fine comparison.

I am not ruling out the open boat/sit-inside idea but I am saying that it is a very different direction that likely should abandon the buoyancy tank in the bench down each side. Sitting low and inside can make a wonderful boat, but it will very limited in space and righting (sail carrying). My view of the best examples are classic sailing canoes. My personal solution to your SOR is a sailing canoe -nesting to meet the length limit. The reason is that light wind often includes periods of no wind so efficient paddling will take you further faster more reliably.

If you go with the sit-on-the-side-deck layout you can have far more sail area and a variety of sitting positions. if the sides are buoyancy tanks you really are not restricted on topsides height -it is not an 'open boat' anymore. If you are swamped you capsize which dumps all the water out and you continue on sailing. You have this design pretty much drawn but I suggest two things -you need a thwart for structure and as a seat for the crew. I would cut away the main bulkhead 10cm below the deck (so the forward crew has room for their legs under it) and extend it 5cm above the deck to act as a cowling (deflecting water). The positions might need to be tweeked for ergonomics but that is why I suggested that the daggerboard size and position is not as immobile as most suggest.

There is one other reinforcement I have been thinking about -a cross brace forming the front of the daggerboard box with about a 60 degree included angle (see picture). It would be the height of the DB box at it's intersection where it needs strength but it could be 6 to 10cm tall over it's run. Torsional stiffness is what the hull shell lacks and that is exactly what this brace provides. It directly connects to all the major forces -crew weight, CB, mast and DB. And most of it is hidden under the thwart. This makes so much sense I am surprised I have never seen it done.

One last suggestion -print your patterns cut them out of cardboard and glue them together into a little model. with paint slopped on you should have a toy good for a half hour of play in water. This will show you how your boat flexes, floats and sheds water.

 

Driving away would just be rude. The friendly thing to do is cut right in to the front and loads up a plate. It would be even friendlier to invite the whole parking lot over for lunch and suggest they help themselves to a beer in the bus refrigerator!

Like my elementary school teacher always said 'I hope you brought enough for everyone!"

 

Interesting. I suppose there is sense in such a claim. Again, I know too little of boat market to argue for or against.

I've paddles canoes for many years during childhood. My parents would take me with them to an expeditions beyond Polar Circle - usually in Russia (back in days when our countries were friendlier). We would go to no-mans lands and travel through the mazes of rivers and lakes with our canoes, often with no people to be found for hundreds of kilometers away (so, no camping infrastructure, no cell phone coverage, no calling for help in emergency). These areas were so isolated that we would arrive with cargo planes that fly once in month or several times a year. These trips were extreme, as we had to carry everything - food, tents, tools, maps, medicine in our backpacks when on foot, and in our canoes when afloat. That was a lot - we stocked up for month of traveling with no expectation of finding anything on the way to help us survive, except for the fish.
I had more than 10 of these expeditions, and they always involved traveling with canoes through rivers and lakes. I often had to paddle for 12 hours a day, sometimes for 6 hour stretches with no rest, no climbing out to straighten sore back. And it was like that every day, for weeks.

In other words, I had my share of sitting in canoe I also know from firsthand experience how unstable they are. Hydrodynamically, it's a very good hull shape, requiring very little power to move through the water. However, hydrostatically, I don't see why people would want to use it as a sailing vessel. Narrow beam, no option to hike out - how do you create righting moment, then? If you add outriggers and turn it into a trimaran, then it is a very effective sailor, but without? Maybe with a small sail, in low winds. But any gust may spell capsize in a moment. And I've capsized a lot. It is not a pleasant feeling to be trapped in a upside-down canoe...

Even that aside, canoe has only a few options for crew to sit. And it gets uncomfortable pretty soon. An open boat with wide cockpit is more suitable for long passages, I think. You can change your posture in a number of ways. You can even stand up and stretch your bones without capsizing the vessel.

Well, anyway, these are my two cents of opinion.

Okay, I'll lower topsides to 20cm above waterline, then. As for sail area, it is still quite limited because of boom height. I calculated that with two people onboard with slight hiking out creates a righting moment of over 1000Nm (unless I miscalculated). Considering out usual low winds, I could have a much larger sail, but the mast limits it. Adding jib adds complications, I'm sure this time I can do without it.

As for thwart: well, since I had to make boat shorter (3m LOA now), there is not a lot of space for both crewmembers if they want to keep boat at proper trim. The problem is with bow crew member. If I add thwart, crew will have very limited space to sit and move around, especially when tacking. Thwart will get in the way. This is current arrangement, with crew at perfect trim position, please take a look (rigging removed for a better view):



Now, if I add thwart, aft crewmember will have to move aft to clear it. Forward cremember will have to go further towards to bow to compensate, and as you can see, there isn't a lot of space for him to move. Now, from a practical standpoint, I will be sailing with my girlfriend, who weights 55kg, and I weight 80kg. I will be aft crewmember (so I can steer and manage mainsheet while girlfriend sunbathes), so in fact I'll have to sit even more forward than in this picture.

Having thwart will seriously complicate that, because it's likely that the perfect trim position will happen to be right over the thwart, and there will be no place to put legs to, except for "riding" the thwart like it were a horse. Not looking forward to that, really.

I plan to make a removable thwart for rowing - a simple board with only enough fixation so it doesn't slide around, but it won't be placed here during sailing because of reasons stated above, so it won't add anything to structural integrity.

I can't imagine how I could solve this problem. This thwart would be in the worst possible place. I viewed your drawing, and I can't imagine how crew could properly trim the boat with thwart there.

What do you think? Maybe structure integrity can be solved without thwart?

Your suggested cross brace would provide excellent torsional stiffness. However, it will cause the same problems as the thwart, as I wrote above. In fact, it will be even worse. Crew will have to watch out for it constantly so they don't trip over. I fear that someone will get a twisted foot and severe bruises on the very first day.

EDIT: unless you meant that those support beams are laid on bottom panel. Then one shouldn't trip over them. Could you clarify please? What you wrote and what you drew seems conflicting. But probably that's my misunderstanding.

From a constructional standpoint, cross brace makes a lot of sense, but I see it as far from practical as it can be. We need cockpit spacy and clear of any obstacles. To trip over a brace during involuntarily gybe is one of worst things I can imagine.

I'm halting updates until we can sort this out. Please let me know what you think of my worries about these issues, Skyak. I hope I misunderstood you somewhere, or that there is another solution.

 

Curiosity got better of me, so I went ahead anyway and made following changes:

Lowered sheer to 20cm above waterline at full load;
Made a big cut-out in bow bulkhead;
Added cross-beams on the bottom panel. 3x1cm. Here's how it looks:



Skyak, is this what you had in mind? The only thing I didn't add from your suggestions is spray deflector (maybe a bit later) and thwart, due to reasons stated before.

I'm not sure how I'll make those joints between cross beams themselves and between daggerboard case knees. Probably I'll have to put those chisels to some good use.

Another question. With this bow section cut-out, do I need to add some more support for mast partner? There is no structure behind what you see in the picture. I'm not sure if 4mm ply with epoxy fillets will be able to handle forces from 4m long mast and 6.5m^2 sail, halyard and two downhauls (vertical and angled).

Total dry weight of the hull is 23.5kg. Safely within limit. Please let me know if I got it right!


EDIT: I've decided to try and model it with thwart anyway. Thwart is 2x20cm plank. I've positioned it so it could support daggerboard case.



The problems as I see are:

1) Crew will have a hard time moving around this thwart, there is very little space for bow crewmember (he/she will have to duck downhaul when tacking too), and it will be hard to quickly trim the boat with this thwart in the way;
2) The daggerboard case is way too high, I don't see much justification for it - it was already high enough to clear waterline with a decent reserve in previous screenshot;
3) The boat is 1kg overweight with this layout, and I don't see where can I compensate.

Skyak, as well as anybody else - any opinions?

 

I envy you your adventurous childhood. Wilderness like you have seen will not survive one more generation without protection. We will talk more later but you should be writing arias for profit and worrying less about making your boat small enough to afford.

You can support the DB case along the floor -I drew a minimal bulkhead in red (see drawing).

I still prefer a thwart seat that your girlfriend could sit on with her feet behind or in front of the mast. The wind does not always blow hard enough to support 2 on the rail. Your revised drawing shows the DB case too high and the thwart too far forward -thwart goes to the side of the case, not ahead of it. Your manikins look quite large but it still looks like your GF could sit on the thwart legs forward, on the floor legs on the thwart, or on the rail ahead of the thwart. That is the flexibility I am after.

About the cross brace -that is kind of what I had in mind but a little taller. The way the boat is now with the big side tanks all we need now is to support the DB case with a mini bulkhead or thwart. The X brace would be a good start for a wide open hull.

I also question your trimed crew placement. To my eye I see 2 bodies in a boat closer to the pointy end than to the wide end -if those bodies are anywhere near the same weight there is something quite wrong and we haven't even considered the drive of the sail. IMHO with your GF sitting on the thwart legs strait forward, you could be completely behind the DB case. Maybe we should review the displaced volume with the experts.

 

The thwart does not have to be solid wood. You can almost halve the weight by making it as a series of stringers with spacers (similar to an open gunwale). Like a very tightly spaced ladder.

I think we might have considered this already but moving the mast further forward would give more room to the front crew, especially if you have a vang. Something like a catboat or optimist.

 

To save weight I would replace the plywood on the forward deck and the inner flotation tanks with waterproof fabric over stick frame. The fabric weighs less than the paint you would put on the wood. It doesn't need to be perfectly leak free either. It just need to hold water to a slow leak for a few minutes. You can also do simple closures so the space can be used for (reasonably dry) storage.

 

Thank you. Anyway, musicians in our country live poorly, even the most successful ones. I've never heard of anyone who owned a boat - any kind of boat.

Well, if I make thwart intersect with daggerboard case on top of it, not in front (like in current state), then the thwart needs to have cut-out slot. For that, it either needs to be much wider (and heavier), or, it must be cut in two parts, with each part attached to the daggerboard case. That would reduce its strength a lot.

And there's the weight issue. I don't know how to solve it. The daggerboard case is just too heavy being this tall. Also, it will get in the way for sure.

I kind of like the general thwart idea, but I can't see how to make it work. It takes too much of space and weight. Skyak, do you have any ideas how to fix that? If I could then I'd stick with thwart.

By taller, you mean that instead of 3x1cm I should go for like 3x2cm? Please clarify on this! I can adjust this but I need to be sure. I'd rather make them wider than taller, though (less chance to trip over).

Crew is placed with total center of weight exactly amidships (1.5m from each end of the boat). Lateral center of buoyancy is also at the same spot. I know that while underway, forces from the sail will require moving center of weight aft, but I do not know how to calculate how much. In any even, it won't be a problem for aft crew member to move further aft. And since I expect most of the sailing to happen in light winds, wind pressure will not have a heavy effect on trim, even on downwind.


Skyak, I'll try modeling the boat with extended DB case knees like you drew. In the meantime, could you offer your insight to the problems with thwart I mentioned? (Weight, daggerboard case size and taking up cockpit space, problem with thwart intersecting case at it's middle)

True, I can make thwart lighter like you suggested. But it won't be enough on it's own to make current arrangement (with thwart) light enough.

Yes, I've considered it, but moving bulkhead forward results in heavier boat, and the boat is getting very narrow from there anyway, so I don't think that space is worth a lot for crew. Also, moving bulkhead extends side tanks, and if they are any longer, they don't nest on plywood sheets.

Your proposal makes sense, but I'm afraid mast is as forward as possible without causing complications.

 

Thanks, but as I've mentioned somewhere in this topic, waterproof fabric isn't something available to buy in my country, at least at prices I can afford. I searched for some heavy duty fabric (anything heavier than bedsheets) with hopes to waterproof it myself, but that isn't available too.

What you say makes sense, but this road is a no-go. I checked and re-checked dozens of times on this when I wanted to make SOF boat.

 

Here, I made those knees longer, extending almost to the side tanks... Weight 23.9kg



Anyway, I had a thought. Rowing arrangement isn't very handy - it requires thwart, and it will also require back seat at transom for another person, since he/she won't want to sit on floor (which is wet most of the time), and siting on either side seat will heel the boat, which ain't good when rowing.

So, I'm thinking, why not scull instead? As you can see, I made sculling notch some time ago (just in case), but now I'm wondering if it can be primary propulsion when wind dies. Sculler will sit on one side seat, passenger - on another. No thwarts needed.

What do you think?

 

First we must finish the DB box.

The TOP edge of the box needs horizontal support. If you are going to run a mini bulkhead it must reach the top edge of the DB box and it should also reach to the float chamber side. The top edge of the DB case will also have a small piece of lumber. Because this support goes farther, it weighs more than a thwart that goes direct. I still don't understand why you raise the DB box height when you add the thwart. My plan for it as a seat needs it to be low. The bit of the main bulkhead that runs across the floor does not do much if anything. If you minimize this bit and maybe put a little higher peak on the foredeck a person has plenty of legroom in this forepeak area. Your mast is unstayed so there should be no significant compression to the floor.

A proper thwart seat would weigh less than the brace you need to replace it and you could remove it for camping.

The real problem with rowing is you have no place to put the big oars when you are sailing -much bigger problem than thwart. A sculling oar is smaller and will move you slowly. Two would move you a bit faster but still less than one good paddle.

There are some powerful sculling setups that are like weird extended rudders. I have been meaning to design a convertable setup where you use the DB and rudder foils. This could more efficient than rowing.

This is a crude version https://www.youtube.com/watch?v=dtv-5t8F29U