The Melatelia: light wind dinghy

Wen used about 3l epoxy to build/coat our Duo. And yes, allow 10sqm /L for paint. I would use oil based paint if you can get it

RW

 

I've scanned through the six pages of this thread.

I've seen a boat that was originally designed to sail in very light winds and be quite light itself, morph into what looks more and more like a racing dinghy. It now has very weak support for the dagger board case and a weak looking mast partner.

Frankly, I find this a bit disheartening.

Moving to a double chine flat bottom will save a little bit of Whetted Surface Area, but the unsupported flat bottom, with minimum rocker seems vulnerable to me.

It has one advantage that so far has not been exploited.

The dagger board case can be moved to one side.

This can be done with the "V" bottom too, of course, but the flat bottom makes this much more obvious.

I see that the stern seat/air box has been eliminated in favor of two long side seat/air boxes, which have been progressively raised until they reached the top of the shear.

This would be good for a boat sailed in windy conditions, that was expected to go fast.

For a boat sailing in chronic light conditions, I see two problems with this:

1.) The crew could end up too far to windward or too far to leeward, during typical sailing conditions.
2.) If the crew were to sit in the bottom of the boat, they would be too constrained by the seat risers.

I liked the original "final" design better.

IMHO, it had just one flaw. The bench, which supported the dagger board case was set too low. I'd set it at shear height, and forget about using it as a rowing bench.

The reason for this is to allow the bow passenger to put her/his feet and legs under it.

This bow person would then sit in the bow, facing the stern. He/she would sit on a boat cushion there, and could slid his/her butt to windward, if needed.

As an added bonus, cup holder holes could be cut into this bench for beverages. The bench could also have a halyard cleat, so when the boat is being single handed, the sailor does not have to go all the way up to the mast, to set or strike the sail. This would require a turning block at the base of the mast, as well as a cleat there, for when the boat is being sailed double handed.

The other sailor would also sit in the bottom of the boat, but face the bow. He/she would also sit on a boat cushion.

This would allow better seating for the expected conditions and would also allow a lower boom height.

Both the bow and stern tank could then have their tops at the shear line.

This would save on some construction complexity as the tops of each could follow the natural curve of the shear.

Torsion rigidity could come from three sources:

1.) the bow and stern bulkheads,
2.) strong knees for the dagger board bench, which may extend all the way down to the chines, and
3.) timber in-whales and out-wales, separated by short blocks.

Since the stern tank will not be used as a seat, it does not have to be that long.

The separated in-whales and out-whales would also provide handy lifting handles and tie down locations.

An added bonus of this design would be that, when righted from a capsize, the boat would float level and reasonably high, but would still have a considerable amount of water in it.

This, off course, is not desirable for a racing dinghy, as quick recovery is a major goal, so the boat can still be in the race after the capsize.

Racing sailors know how to quickly re-board such a boat, even if it doesn't have a drop of water aboard and is lighter than they are. I saw the technique demonstrated on "You Tube" and was quite amazed.

But for a casual day sailor, which might not have athletes for its crew, having to bail out half a boat of water might be worth it, in the interest of lower seating and easier re-boarding.

In the interest of keeping the weight down, sitting on boat cushions, on a slight "V" bottom, might be worth the trouble.

 

Hopefully I can forget about the bottom and move on...

-------

reinforcements can put them inside;
You can also compare the structure of your boat with the Optimist, here:


http://digilander.libero.it/cvastura/Piani Optimist/Optimist.html

 

So, oil-based is enamel, right? Any problems with bond with epoxy? Did you use primer? (I red that it is not needed if you paint over epoxy)

Also, did you fiberglass Duo? How many coats of epoxy did you put on?

Any advantages of having them inside? It seems that bilge runners help protecting the bottom of the boat when dragging on the ground.

I'm not sure what you mean by racing dinghy. Short waterline, wide beam, seats instead of side decks? I'd say it's anything but a racing dinghy...

As for daggerboard case support, I can extend the knees further on the bottom panel, maybe even up to the chine.

As for mast partner, you say it's too weak? Original design had mast partner much weaker. This has a solid wood block (which can be screwed decently to the bulkhead, unlike sandwitched plywood), and a bow deck extended over this partner. That, coupled with generous epoxy fillet. If it's still too weak, how can I make it even stronger?

Richard Woods seems to think that flat bottom will be okay, if coupled with bilge runners. How vulnerable are we talking about? I don't plan on hitting rocks or dragging this boat on a rocky beach.
Anyway, I can add two more bilge runners if you think that would help bottom vulnerability. It should be possible within weight limit.

As for side daggerboard case, I remember when you suggested this in the very first steps of this project! Yes, it can be done. But frankly, I'm not a fan of this solution. It looks weird, has somewhat unpredictable hydrodynamics, can make it difficult to recover from capsize from one side of the boat. I don't know about this. I've seen only a few boats employ this design solution. Surely there must be a reason for that?

Correction - in my latest design update, side seats are not flush with top of shear. They are below. Raising them to shear makes crew sit very high, takes a lot of cockpit space, and most importantly, makes boat go overweight by a margin that I can't compensate for. Also, it makes plywood parts too big to nest on 3 plywood sheets, so I'd need at least one more, which adds to expenses. I don't think it's worth it.

Well, for light conditions, I thought one crew member would sit on windward side, while another sits on leeward. That should balance the boat. Leaning forward or backwards would give a fine-tuning for the balance.

Oh, come on. I'm not going back to that. The original design was criticized heavily, and for a good reason. Buoyancy tanks were too low (raising aft tank to sheer is a no-go because of weight), there was too little space for forward crew member, boat had too little torsion rigidity, and it was very, very complicated to build with the V bottom. And then there's the question of cushions, which give just another "needed" complication to this project.

Please don't take my wrong, sharpii2. I respect and regard your opinion. But I can't just jump forward and back with this design, or I'll never finish it. I have to stick with something. In my eyes, the current design has least flaws, and is easiest to build. Sure, it ain't perfect. Bottom isn't exactly meant to break rocks in half. Seat height doesn't allow a lot of hiking out. Boom had to be set higher. The daggerboard case is a bit in the way of the crew. But I see those flaws a lot less important than the shortcomings of original design.

I understand, you just state your opinion of it. It ain't easy for me to decide between so many opinions, some of which are in completely disagreement with others.

I'll consider moving daggerboard case to the side seat. I could also reduce beam from 1.4m to 1.3m to make bottom panel narrower (from 77cm to 71cm), increasing rocker to compensate. Anyone else thinks this is a good idea?

EDIT: I made daggerboard knees much larger (12x12x2 now), and made mast partner 5cm deep. I could make it deeper, but I doubt I'll find a solid wood block that thick to buy.

 

I have a couple of considerations for you while I work on a structure/sailplan.
Spoiler alert -I don't believe there is a fixed ratio of dagger/rudder on small boats.

What is the point of topsides higher than the seat? When the boat heels, which takes on water first? Consider lower topsides with deck at the top. Sharpii I stand by my statement that it is important to minimize water inside on recovery. Small boats lose stability with surprisingly small amounts of water sloshing. There is no value to getting into a boat full of water because it will not stay upright. Inside is the wrong place to be in capsizing boat full of lines and sails. Higher topsides are not what you want to see from the water.

About crew positions at various wind levels -the helm should not have to move much -stationary on the rail -the crew should have a nice seat anywhere from the center to hiked out -so a nice thwart seat would be appreciated.

I also object to abandoning human propulsion in this low wind design. My own solution to the SOR is the opposite -a paddled canoe that can make great use of wind to sail. 2 sheets 19' by 30" -but that's my design, I will try to respect yours.

 

True. But I thought it's good to have rudder area 50% of daggerboard area. I remember having red about it somewhere. Is that a good guideline?

Well, it's just that I can't raise seats up to the sheer line (topside) because of the reasons I stated before. I can lower topsides somewhat, but that will also mean that the boat will take on water at lesser heel angle. I was told on this same forum that 25cm is the minimum safe distance between waterline and lowest point of topsides. Now it's 27cm. Are you suggesting I should go below 25cm?

Anyways, I don't understand what's so bad with having seats below topsides. Most of the sailboats I've seen of this size have such seats. Sure, it isn't as good as decks when capsizing and recovering from it, but that's about it. What about height of crew weight, added materials weight, having to raise boom higher to clear heads? I thought seats as decks are more usual in racing boats where you have to hike out a lot, and this is definitely not a racing sailboat.
Also, I see a current design as a middle ground between sitting on the floor and sitting on the deck.

So, I can lower topsides, but down to the seats? That is like only 10-15cm above waterline.

Well, I'm thinking of having a removable plank which can be placed at the middle of the boat when rowing. I could make some simple reinforcements on the side seats to keep it from sliding around. However, having a non-removable thwart would get in the way when trimming the boat.

 

My 'rules' for keel and rudder
-all the force the sail can exert on the boat must be resisted by the combined keel and rudder
-the hull has lousy lift/drag so you don't want it going sideways
-the rudder must have sufficient extra lift potential for control purposes. The AOA at the beginning of stall is about 12 deg so the max it should need when not turning is say 6.
-the last rule is that the force on the tiller cannot overwhelm the skipper -on such a small boat this is no restriction.

About seat tanks and topsides -you are wrong. When heeled the inner edge of the seat is higher than the outer edge. On your boat the height of wave the boat can keep out is the height of the rail. The water that comes in to the seat will dump in the bottom when the boat comes upright -if it does so, you just took on a large weight. I have not done the calculations but the topside height above the seat in your present design might (likely) be a detriment.

This may sound like I am just prejudiced to my design but I just know you have done so much studying but missed a critical point. Calling it names like 'race boat' does not change the facts.

Answer this -what is your angle of vanishing stability? The heel angle from which you boat takes on water. And what is it for my proposal?

Topside height is subjective. On open boats it is terribly critical. On self draining sailboats it is meaningless.

 

Understood, thank you. I kind of knew it, but useful anyway. Some people say it's better not to include rudder in this calculation so that you can have neutral helm - and them move CLR or CE forward or aft to get desired amount of weather helm. It's probably just a different way of solving same problem.

That makes sense. But please tell me then, why so many popular sailboats have no side decks, but just seats like in my design? Many don't have side buoyancy tanks at all. As a matter of fact, after viewing hundreds of designs, I got a feeling that boats with side buoyancy tanks/decks make up a small percentage of all sailboats.

So how come they don't have this problem you're describing? I'm really puzzled about this.

With my current design, this angle is 25°. With your proposal, it's around 65°. Okay, I can see your point... You busted me there. Your argument is superior (no sarcasm indented). Thank you.

So, even though I don't like it, I'll modify my design to raise seats to the sheer line. I'll definitely have to lower the sheer line itself somewhat so I can fit this boat in 3 sheets of plywood, and, of course, have it under weight limit.

Question is, how low do I go? My boat is open, so you're saying this height is critical. What height would you recommend?

 

An update (hopefully no one is replying yet while I'm posting this).

It occurred to me that I can have side decks that take up less of cockpit space, while being level with sheer line if I tilt side panels of these decks. For now, I chose 15° tilt, which gives around 20cm wide decks. I measured my ***, forgive the expression, and determined that it should be enough for comfortable seating.

I also lowered sheer line from 27cm to 25cm. I could go lower, but I'm not sure if I should.

Dry weight is 25.1kg. Boat would start taking on water at around 48° heel.



I'll have to raise boom and stuff, but this design seems within requirements. Haven't checked nesting on plywood sheets, but it should fit. Skyak, Sharpii2, please tell me if this is what you had in mind. If so, what's the next move?

 

I think whether to go with side decks or seats sunk below the gunwhale is one of the trickier decisions to be made when building a small general purpose sailing boat such as you have in mind. There are advantages both ways, which is why we see dinghies with both solutions - eg. Mirror dinghy has seats below the gunnel, Cadet dinghy, an otherwise similar boat and also very popular in its day, has side decks.

A big advantage of side decks is that, as Skyak says, the boat can heel a lot further before the boat swamps and then usually also capsizes.

A big advantage of seats at a lower level is that there is a lot more usable space in the boat for purposes other than just sailing - e.g. for making picnics, carrying luggage, even camping on board overnight. Side decks are not usable space for such activities since any object left there will probably disappear overboard.

If you intend to regularly press the boat hard under sail then you will find side decks more comfortable for sitting out (some say hiking out). However, people sailing the kind of boat you are proposing often prefer to reef or stay on shore rather than sit out.

Sitting on seats at a lower level does give a feeling of being better protected from the weather and less likely to slip overboard than sitting up on side decks. This may be partly an illusion, a fence a few inches high around the seating position does not give all that much protection, although because of the wind gradient I suppose that wind chill is slightly reduced.

With older style wood plank construction side decks tend to leave parts of the hull interior difficult to access for regular maintenance which is probably one reason that traditional work boats tend to have no side decks and just a few transverse thwarts which are probably removable for a serious overhaul.

In a really small boat seats below the sheerline can be too low to be comfortable. You might find it worth checking this by making a 'mock up' of your boat seating to test the ergonomics - you just need some planks and breeze blocks or such like to simulate the arrangement of the seating and check that the seat width and height is suitable and that there is enough leg room. You do have some computer drawings with human figures included and I have to say that those figures look rather big for the size of the boat!

Although its not something you are considering, if you want a self draining cockpit in a small dinghy you will probably need side decks since seats much below the sheerline would be too close to the floor to be comfortable. On a larger dinghy you may be able to combine side decks with lower level seating further inboard. On even larger boats the side decks become too high above the floor for comfortable seating, so these inboard seats start to become footrests for crew sitting on the side decks.

Side decks give structural support to the gunwhale, valuable if the boat takes some knocks coming alongside a quay or going through locks. Without side decks you will need more reinforcement along the sheerline.

These are just some of the points you might consider, there are plenty of things to weigh up!

 

Richard - Actually, when we saw our boat being used in that way we were just too stunned to think of anything like that, but the thought certainly occurred to us afterwards! We are probably far too nice, we let them finish serving their lunch but we did ask them to be a bit more thoughtful in future.

Even if our car had a flat enough roof to use as a serving table I dont think it would have been used for that purpose by strangers, but a boat, well what does that matter.

 

Didn't mean to be such a PITA.

Build the boat you want to build.

Your present drawing shows much better support for the dagger board case. And your much narrower side decks make sense, even thought they top the shear line. This will simplify building.

Having the air box sides sloped may not be necessary, as even plumb vertical, they will have plenty of enclosed volume.

There was a considerable amount of discussion on the pdracer forum on just how wide the side air boxes had to be. Four inches (10.2 cm) was pretty much settled on as being an acceptable minimum. But having them sloped may make the boat more comfortable with the crew sitting in the bottom (probably while sailing single handed).

Due to the low free-board of the boat, which won't allow much heeling anyways, I'd consider moving the dagger board case to one side. This would make it less likely to be tripped over. But leaving it in the center, with its support knees, does stiffen the bottom there somewhat, and it looks more boat like too, so I don't blame you for keeping it that way.

As for the rudder. Keeping its area equal to one half of that of the dagger board makes a lot of sense on a boat which often might have fore and aft trim issues (like any really small boat). IMHO, it is always better to have more than enough rudder than not quite enough.

In closing I'd like to say three things:

1.) There are differing design philosophies. Just because one may totally contradict the other does not make either one invalid.
2.) This is your design. You have final say over it. You make the decisions, because you will have to live with the consequences. Just don't let me, or anyone else with strong opinions, bully you into changing it to please me or them. And
3.) I hope to see construction pictures later this year.

BEST OF LUCK.

 

Thank you for this thorough summary, John. Compelling arguments for either choice. It's even harder to choose now that I know what's the best of either world! Something to consider for a time being.

It's okay. I appreciate your input, and I'm sorry if I've shown any frustration. Sure, it's my design, but it's not easy to stay on track when some regarded people say "your design is okay, don't worry" and some say "you'll have a hole in your boat". Well, maybe I'm exaggerating a bit, but you probably understand that feeling.
It's not easy to avoid getting sidetracked when I'm such a novice. If only I had enough experience to know I'm not heading in a disaster, it would be easier to choose and dismiss between so many opinions.

Yes, but as I've tried to make them vertical I saw that it makes boat overweight (a lot), and leaves very little space in cockpit. And it looks horrible. So I guess sloping them won't hurt anything. I'm still not sure how exactly I'm going to build these decks. I'll probably have to bevel some timber pieces for joining those panels together and keeping them at proper angle while epoxy is curing. It would be great to add epoxy filet from the inside of those seats/tanks.

Both options have their advantages, I suppose. Maybe I'll keep it on centerline this time. Stiffening the bottom is needed, and I must agree it would look better.

Okay, no problem there. That's what I intended anyway.

I'm not sure if by that you meant that you're leaving this discussion for now, but in any case, thank you for your advise and support. And patience with my difficult temper. I am very grateful for it. And there will be pictures!

 

A side question, as I'm now modifying the sail: how high should the boom be compared to the crew as they are sitting on the deck? Clearing the heads completely isn't good for sail area, but having boom too low will make tacking a headache.

Is there some general guideline for boom height? Like, shoulder level, or eye level?

 

I'd say 30 inches (76 cm) would be about minimum. Most people can comfortably duck below that height.

With my sit-in-the-bottom-of-the-boat-designs, I usually go with 36 inches (91 cm).