The Melatelia: light wind dinghy

I am perplexed that there is no fabric available. Nothing better than bed sheets? Then bed sheets it is!

Do a little experiment with a cotton pillow case. Paint it with some exterior latex. Fill it with air and roll the end several wraps around a stick and clamp to prevent it from unrolling. Take it to water and float on it for 30 minutes. Did it hold? Did any water get in? Urethane is much better. You can layer for increased strength. High thread count cotton will hold air when wet, even without a coating.

 

Could you please elaborate on that? I did not understood where this piece would be, and what it would do.

I see. I must have confused what you said and what sharpii2 said (he offered very similar advice, and he said to make thwart flush with decks). Sorry about that, it's getting hard for me to keep track of who said what.

Here, I adjusted it:



Is this what you meant? Looks a little over-engineered to me, but if you say so. Weight 24.2kg.

You mean the bow bulkhead piece that runs from partner to step? I thought that's what you suggested in this picture:



I mean those black lines. Or again, have I misunderstood you?

Well, muscle power will only be required in total no-wind conditions, so I don't mind moving slowly with sculling. After all, it's not like I'll have to fight wind or current while doing it.

I'll research more into sculling oar shapes. I don't want to make a any complicated system, just a decently shaped oar in a notch. I heard it can be done with any oar, but specifically designed ones work much better.

So, if sculling is a viable option, then I'd rather not have thwart.

So, with my latest update, what else is lacking? What's that piece on top of DB case you mentioned, are the knees good, and can you clarify on that bow bulkhead vertical piece?

As for fabric, thanks for the advice. Problem is that I couldn't even find heavy duty fabric. I specifically went to a manufacturer who claims to make heavier-than-usual fabrics, and as they gave my a sample, it was light enough to tear with my bare hands.
I guess I could make do with a simple bedsheet, but right now, I'm still under weight limit (in this latest update), so I don't think it's worth it. But thanks anyway!

 

While waiting reply on the hull matters, I updated other things:

Rudder - removed rudder box entirely. I don't see much point of having all that complicated system when I'll sail in deep waters with very little chance of grounding. Haven't modeled it yet, but the rudder will be held down by bungee chord. That, coupled with sloped, more traditional rudder shape will absorb some of the impact energy in a very unlikely event of grounding (rudder should jump out of it's hinges). Rudder blade will be made from timber (no ply available anymore for this), and will be 2cm thick.

Tiller - changed the shape into something more fancy, yet still easily buildable. I also copied tiller-rudder attachment idea from Nutshell Pram - tiller can be removed if tilted all the way up. No un-screwing required. This will allow it to be removed and stored onboard along with the blade itself when sculling.




Daggerboard - also changed shape to something more boat-looking. Because of the slope, it should also have a small chance of jumping up in case I hit the bottom. It will also be made from timber, and will be 2.8cm thick.

Sail - had to reduce area to 6.4m^2. Still quite a lot for boat of this size. Boom is 80cm above deck at it's lowest point, should clear the heads easily. CE and CLR coincident vertically.




Hull issues are still a priority, but if someone has an opinion on these updates, please tell me.

 

without centreboard

http://www.hopwood.uk.net/Adriatic 2009/Boats - theirs and ours/slides/DSC00325.html

 

Everybody got silent here... I'll take that as a good sign. With all issues (that I could think of) solved, I'm updating plans once more. That might take me about a week.

In the meantime, I wish to ask. Since my boat now has a considerable number of plywood panels that will be bent to shape (bottom, lower and upper chines, side deck surfaces and sections), as well as other complex-geometry parts (bow deck, cross-section, transom, transom reinforcement), I'm not sure how should I proceed to plot them on plywood sheets. The way I see it, I have such options:

1) Plot all these parts on a 914mm roll, and print it at 1:1 scale at our local office. They charge 2$ per meter.

Option A: To fit those parts on a roll as short as possible, these parts overlap That means I won't be able to cut-out them and glue on plywood. I'll have to lay this roll over desired place on those sheets, and transfer lines with pins or trace paper. This would cost 12$ to print.

Example of what I would print (please take note, a big image):

https://static.dyp.im/fr4vxbAtBb/00e9d39abe0122a33a59ceb8fbb64410.JPG

​

Option B: Plot those templates so that they don't intersect (I can cut them out and glue on plywood, then cut with jigsaw along the lines). That would cost 20$, but would be easiest in terms of time and least error prone.

Example of template:

https://static.dyp.im/qKdF1JBWYD/30b899f8827bc929a12906fe51d79df8.JPG
​

2) Plot manually with pencil, ruler, square and battens. It would be a good learning experience, costs nothing. But mistakes can happen (misjudged dimensions and so on), and since parts on my plywood sheets have clearances down to 0.5cm, there isn't much room for error.



If I go with printing templates, there is a question of paper stability. I'm not sure if that is a consideration.

Can anybody please advice, which method would be the best in my circumstances?

 

Do it the old fashioned way, pencil batten, square, etc.

You quoted a tolerance of 0.5 cm. Did you mean 0.5 mm? Half a millimeter is taking accuracy to an extreme. A half centimeter tolerance is easily kept using battens and pencil. In fact I'd want to keep the tolerance to 0.2 cm which is also easy enough with a pencil if you keep it fairly sharp. If you can get within 2mm on your main panels you will have an entirely buildable boat. It is easier to plane to an exact line when the lines are marked directly on the ply. I'm pretty sure that you know to saw outside the lines and plane to the line later.

Full sized patterns on paper are subject to some deviations on account of humidity and whatever kind of paper it might be. When using paper patterns you will need to adhere the paper to the ply so that it can not move around. That means that you will use some sort of adhesive like 3M 77. that'll hold the paper in place but when the paper is peeled off the ply you will have to deal with the adhesive residue.

You could use paper and trace the lines into the ply with a perforated wheel like a wall paper cutter. You will need a batten to guide the wheel. Might as well lay out the lines on the ply, the tried and true way, in the first place.

 

Where did you got the idea that I meant 0.5mm? I meant 0.5cm for sure! If I really tried, I could maybe push it up to 0.7mm, but probably not more (unless I buy larger plywood sheets).

Speaking of clearances, I hope that those sheets are of exact dimensions as seller announces. If they are bit larger, no problem, but if they are smaller by even a centimeter, I'm in trouble. I left myself a note to check those sheets when buying.

I'll do it the old fashioned way, thank you. I was quite puzzled how can I nest all those parts on plywood sheets and be sure they're in the right places so that they don't intersect. After a considerable thought, I've thought of this method: each part has a "centerline" which runs from the farthest points of that part. Location of each end of this centerline is defined by distance to the corners of plywood sheets, and, of course, the length of this centerline is also defined.

I'll plot those centerlines on plywood sheets, and then plot offsets and curves with battens. This is the best way I could think of to make sure each part is in it's right place.

I'm attaching part of building plan that is now updated. Please take a look to see what I mean.

http://www.boatdesign.net/forums/attachment.php?attachmentid=99151&stc=1&d=1428179412

Messabout, a while ago, you expressed an intention to give some cold shower regarding the sail I'd be more than happy to hear what criticism you might have about it until it is too late (time is ticking fast on my end).

 

Any criticism that I might try to heap on a lug rig is mostly just a matter of old man's bias. I can find several things that are negative about the lug but that is true of other layouts too.

The yard is a wild beast when raising or lowering in brisk weather. The long part droops down and threatens to wreak havoc on sailors heads and bodies. Once up and in place the sail is manageable. In really bad conditions I might try to get the boat to the beach and careen it before unrigging.

For a positive example: Michael Storers Goat Island Skiff uses the lug rig to very good advantage. The GIS is a good little boat and apparently so is its rig.

 

I will mention a couple of thoughts from my own dinghy sailing experience.

First, if winds are normally "light", you will not be able to have 2 people on the side. In my bigger (16 foot, 112 sq. foot sail area, 100+ pound Windsprint), normal seating is nearly on centerline, with one or two people.
I think you should figure a second person will be sitting just aft of the mast. So will they be comfortable? The wind has to start blowing before, sailing alone, I start moving forward and off centerline.

Second, I added a 45 degree angle to the tiller, which slides fore and aft, and can rotate 360 degrees for flipping side to side. If you are sitting near centerline, it is way more comfortable to have the tiller offset.

Just a couple of things I have faced sailing in light wind.

 

Well, I see. Thanks for bringing these considerations up, I'll keep this in mind.

Every several pages or so on this thread people remind me of this I am well aware of that. There won't be a problem with such setup. In light winds, one crew member will sit on windward deck, while another will be seated on leeward one. They will be able to switch if boom gets in the way. But generally it shouldn't, because it's really high up.

Are you speaking about tiller extension here? Because if so, then I'm planning on it too. It won't slide fore and aft, but it will have free rotation, so it will be comfortable enough to switch when tacking.


The work is going well. Right now, I'm writing down procedures for installing these side decks. Due to my complete lack of experience in such thing, I'm not sure how should I proceed. Right now, I'm thinking this workflow:
1. Position side deck sections (sides of tanks) at correct position and angle (with some pre-beveled timber pieces to ensure that angle), bend them along the lower chine and hold in place with sticky tape;

Drawing:



2. Add thickened epoxy fillet on the inside;
3. Add thickened epoxy filet on the outside;
4. After it cures, add deck surface on top of this side piece;

Drawing:



5. Screw this deck surface to these timber pieces and glue with epoxy.

Now, I see a problem with this approach - I won't be able to add epoxy fillet to the inside of this tank once I add surface piece. However, I can't think of any way to put that fillet, because in whatever order I add those pieces, the last piece will close access to the inside, so I won't be able to decently glue it.

If someone has experience with this, could you please tell me of the best way to install those side tanks/decks? How do I add enough epoxy on the inside so I can be sure it will hold strong?



*Sigh* I have another question... Right now, the bottom edge of side panel of this tank is coincident with lower chine. So, three edges - that of hull bottom panel, hull lower side panel and tank side panel - meet at the same spot. However, since hull panels are stitched and glued together first, and with a decent epoxy filet, I'm worried that later this side deck panel won't fit there anymore because of that epoxy filet. Maybe it would make sense to move deck side panel away from chine and towards the centerline of the boat? Meaning that it would join only with bottom panel.
What I wrote is probably confusing, so if it's not clear, please tell me and I'll draw sketches to show what I mean. This is a very serious issue, and I'd be very grateful if anyone could share an opinion.

 

I knew this double chine construction would cause trouble. I knew. But I didn't know why.

Other than moving the tank sides inboard, so they don't land on the chines, you could make the sides, the bilge panels, and the tank sides first, joining them together, so the boat looks kind of like a catamaran. Then, after the epoxy has set, you can sand and grind the excess, then add the bottom panel, almost as an afterthought. This would insure the integrity of the tanks, plus the integrity of the bottom panel joint. The edge of the bottom panel joint may project a little, but that should not effect performance noticeably. And it will be stronger than than the alternative.

As for the side decks, I'd use timber clamps for them, as there is no effective way to fillet them. Such clamps need not be continuous. Small blocks spaced apart, even, could work, if you plan on taping the top seams.

I am presently designing a boat myself. It is also going to be about 3 m long.

I find myself spending a lot of time thinking about how I'm going to build it.

 

Okay. That seems terribly difficult. Maybe I'll just offset these sections more towards the centerline.

As for these "timber clamps", if I understood you correctly, that's what I shown in my previous post - those three timber pieces.

I've offset those tank sections 2.5cm away from chine. Any more and parts become too big to fit on ply sheets. Here's how it looks:



As messabout suggested, I also added a keelson to the bottom panel to add more support for the bottom panel. It is a 3.4x1.5cm timber piece:



I also decided to make bow deck from one plywood piece, bent into oval shape for more strength. I also re-made mast partner (5cm deep, 20cm wide at bulkhead) and mast step (3cm deep, 18cm wide at bulkhead). I wanted to make it deeper, but it becomes very awkward. Anyway, I can't imagine mast jumping out of that.

Bow bulkhead now has a smaller cut-out so it is stronger. Please also note two holes for water to flow through on each side of mast step.




The problematic place now is the keelson and cross-beam intersection. It would be ideal if each could run for it's length without interruptions, but I can't join 3 pieces in the same place. Two can be joined with obligue cross-halving joint, but not three. I must either terminate the keelson OR cross-beams at this junction. Here's how it looks:



My woodworking skills are very novice. I have never worked with chisels before. I'll have to learn as I go. What would be the easiest-to-make solution for this junction?

P.S. Oh, and I also added 4x1cm reinforcing pieces to the edge of daggerboard box. All in all, the total dry weight is 25kg exactly.

 

Check out the today's article in duckworksmagazine.com. It clearly illustrates what I mean by "clamps" for the side deck.

The designer of this boat uses them to seal off the tops of his seat boxes.

I don't know whats going on with your 'X' shaped bottom re-enforcement.

You would probably better off to have your bottom stiffeners run parallel to the keelson, placed half way between it and the seat tank.

With my boat design, I intend to have the bottom panels turned 90 deg. so the visible grain runs from side to side rather than lengthwise. This will force me to add one more butt joint. Such is useful because it stiffens the bottom at that location by doubling the plywood thickness there.

There are two advantages to doing it this way. That is

1.) the plywood will be much easier to bend along the rocker profile and
2.) the plywood will be stiffer between its actual support points.

 

You mean this? I could do the same in my boat, but I would need to bevel such timber piece long it's length. And it wouldn't help me establish the correct angle of this side deck section. How would you propose I do that?

I just showed it now as it is to explain the problem I'm having - I don't know how to join those pieces there.

Well, I already have bilge runners from the underside of the boat, they run parallel and pretty much halfway between centerline and chine.

I don't remember who (maybe you?) suggested that X shape cross beam would give best reinforcement against hull twist. I thought it is a good idea, so I did it, instead of having those beams run parallel.
Now I'm a bit confused about this.


P.S. An idea. What if those beams ran not paralell, but perpendicular to the keelson, in front and aft of daggerboard box? Then we'd have keelson and bilge runners running parallel to the centerline, and those cross beams running perpendicular. Seems like a sound design to me.

 

Your drawings are looking better all the time, at least to my inexpert eye, but here are a few thoughts:

1) I am a bit sceptical about the diagonal members on the floor - assuming they are drawn at least roughly to scale I don't think they will do much to stiffen the floor and the way they intersect at the aft end of the daggerboard case looks a bit strange.

2) The new keelson will do at least something to stiffen the floor, will it do enough though? I think you said that there are external rubbing strips, those will certainly help. It seems normal practice to make the keelson wider in way of the daggerboard case so that the case can be slotted through it, this can be done by placing 'doublers' each side of the case, these overlapping with the keelson.

3) I wonder how well a sculling notch works on a boat with a low transom, especially if the transom is vertical. My own boat has a fairly low transom and a few years ago I fancied entering into a fun race for one oar sculling. I made a little bracket that mounted on the rudder pintles in place of the rudder and which located a sculling notch about a foot above the top of the transom and angled so that the oar would not jump out. This seemed to work well, perhaps too well because a couple of the other competitors blocked my boat from getting up to the start line!

4) Are the knees that support the daggerboard case 'solid' wood (I dont know what to call wood that is not plywood when discussing plywood boats - maybe 'normal wood' or even 'UniDirectional Wood'). If it is UDW then I would think it is taking up more of your weight budget than it would if it were just a thin plywood bracket with strips of UDW to make the edges of the ply robust. Also I am not sure it is right for these knees to stop just short of the bouyancy tanks rather than being joined into the sides of the bouyancy tanks.

5) Re your assembly drawing showing the bouyancy tanks, I would have thought that you might need strips of UDW along the inner plywood edge as well as along the gunnel - so that you can just screw the deck down onto wet epoxy.

6) In an earlier post you ask about 'nesting' the plywood parts and getting the parts cut out. It looks as though you have done a good job of the nesting already - did you do that by eye or automatically with software? There certainly is software that will do this kind of thing automatically. I attach a five page .pdf file for the plywood cutting for a rowing boat that I have just started making (I have done some of the metal fittings, but not yet started on the woodwork). This was done using a program (app) called 'mynesting' which is not free but you only pay for the output files that you actually export for cutting and if you dont make any mistakes you only need to do that once for each boat you build at a cost of about £7-00 per boat, so not all that expensive. Mynesting does seem to work OK, but I am not in a position to recommend it since I have not tried any of the alternatives, some of which may be even better and/or completely free of charge for all I know.

As for getting the wood cut I am not sure that I have the patience to mark out and cut all the shapes by hand. I have not investigated this in detail, but from one phone call to a company with computer controlled cutting equipment it seems that waterjet cutting might be the way for me to go. This would increase cost a bit but could also save a lot of time and ensure that the work gets off to a good start with all the parts accurately cut out. I realise that there are some strange shapes in my .pdf file, I would be interested in comments from those here who have knowledge of cutting by watejet/router/laser. The shapes could perhaps be simplified a bit if necessary.