Cross Indian ocean in 4 meters dinghy sailboat

My experiences are just coastal cruising: Cal-25, O'day-25, Columbia 27, Jenau-42 Cat, Southern-California, and Gulf of Mexico.

 

I suggested earlier that you could use a single outrigger rather than two, enabling your boat to have a self-righting ability with it's ballasted keel that multihulls normally lack. (That means it would have to be a proa, as capable of sailing backwards as forwards.) If that's a direction you want to follow, there's a trick you could use to keep the outrigger small to reduce drag dramatically, so I'll just point you towards an example of this and let you think about it.

Frog http://forums.sailinganarchy.com/index.php?/topic/197322-frog/

 

Thank you all guys, still thinking many things. I haven't the time to check for the self-steering yet, and i find very interested the suggestion @David Cooper and thanks for the info @Angélique and @exp30002

The good news, this week i will build a small 3m long boat to test building process such epoxing parts and so on. this small boat will not be for the design but will be to test how i made it building it and testing few things such sliding keel with bulb, sails, outriggers etc.

I really want your recommendations for the hull on the bigger boat. Materials: plywood, wooden frames, epoxy, fiber glass.
Thinking of frames with 1/4 plywood and layers of epoxy and fiber glass. The other option is instead of 1 layer of 1/4 plywood to be 2 or 3 layers of 1/4 plywood on the bottom and sides (which will make the boat heavy).

 

1/4 frame is way thin. Weak and difficult to attach anything to it. Also very wobly at bigger panels.

I think these scantlings questions are very difficult to answer in isolation.
Size of boat, general structure, amount of glass all impact the choices.

 

Start by making a suggestion based on the information on this topic.

Everybody understand that you are just making a suggestion, not a guideline and no warranty.

 

I am suggesting you clarify your suggested structure and detailes and people can make educated guesses.

25’ minimalist cruiser.
I’d say solid quality wood ”frame” with 15mm (5/8”) plywood for frames. Language fails here a bit.
10-12mm skin from single layer of plywood. Some longitudal strong beams (keel + soneting on sides too)
All from quality marine ply.

It’s a crapshoot and you would be better of reading a book than asking vague enough questions that the busy pros will not bother answering and all you get is the hobbyist like me giving you numbers.

I would go for single skin vs two thinner for sure. Much easier to build and cheaper. Good design makes the bends possible.

 

Finally found all the materials i need, especially different types of fiberglass. While building the small boat, tomorrow i ll make some tests with fiber glass. The results of these tests plus the result of the small boat even building it entirely in 1/4 marine ply will determine the design of my larger boat. I have few plans and things im looking into.

@kerosene im thinking 1/2 marine ply and solid wooden frames (non-plywood).

Another im planning to use aluminum screws between plywood and wooden frames which i will epoxy too indeed. Any thoughts on that? i will screw from outside to of the ply hull to (inside) the wooden frames. Then after epoxy the joints, i will epoxy the entire hull. On top of that i will fiberglass. Do you think it could be any problem between the aluminum screws and the fiberglass? (there will be a layer or two of epoxy) Or other suggestions how to do it?

@Angélique yet didn't see in extend the self steering which im very excited to look into it.

What do you suggest for a small portable if possible water desalination?

 

Here i would like to add some summary information about the boat.

The boat will be 6 meters (19.6 feet) and 1.20 m wide (beam), height around the same, hopefully it would weight 950 kg (2100 pounds) full loaded. Sail area will be about 15 sqm (160 sqf) but i would prefer 20 sqm (215 sqf).

The design. The sides for the first 1.5 meters will be a curve starting from the front and open to 1.20 (60cm each side) then upright and straight line until the back, at the back will be a small curve. The bottom will be round like shape for only 20-30 cm height. In the sides will be 2 small hulls (outriggers as i am calling it) for stability purposes. The mast will be aluminium 3 mm thick round, 6 meters long (is that good or not?). There will be a sliding keel with a bulb on the bottom (which can go up and down), looking to put about more than 100kg on the keel bulb (is that good or not? what do you think? 950 fully loaded but, including 150 for the keel bulb..)

Solar panels and some self steering gear yet to think of it. Electric trolling motor (i doubt if that's useful yet to search it too). GPS, satellite phone and i guess radio. Water desalination (please suggest, small and portable as possible). In total 2 cubic meters ballast (spaces sealed with air).

This boat probably will give draft at 15cm (waterline height on the boat). and the waterline LWL will be 6 meters, the boat will be straight upright in all sides.

Structure/ solid wooden frames screwed to each other with aluminum screws and epoxied. Plywood 1/2 for the hull screwed on the frames with aluminum screws and then epoxied. Then fiber glass 2 layers of 45 axial fiberglass and epoxied. Thinking if the screws will be a problem even epoxied, for the fiber glass that will be put on. Please make suggestions.

Do you think i forgot something? Do you think im thinking something wrong, please make your corrections or suggestions.

 

Myself would use stainless steel screws rather than aluminum which is too weak. Trolling motors and batteries add more weight, and are too weak in power and range for propulsion, unless you just want it for maneuvering.

 

A picture would be worth 1000 words.

15cm draft sounds ridiculously low for a boat with blue water in mind.

I still you don’t get what is wrong with your approach (and as a result you don’t get any informative replies).
Questions in isolation are like asking how long is a string. Pick a book like elements of yacht design, take 3 months to study it.

6m mast sounds very short.

 

Also the way you describe the hull it is not easy to understand the shape.

 

It sounds like a canal boat with outriggers, a deep keel and a mast stuck on it. I'm not sure that would be the most comfortable or robust kind of craft to take into big waves. When you look at most boats, you see them start narrow, gradually get wider towards the middle (and with increased draught to match), then they narrow again towards the back. The result of this is that the middle contributes more to their buoyancy than the ends. If you have too much buoyancy at the ends and you encounter the wrong shape of waves, the bow and stern can at times be doing most of the lifting work while the middle is relatively unsupported, putting a lot more stress on the hull - those forces will try to snap it in half.

 

@portacruise thank you very much, im making a small boat (3.4m) with aluminum screws, this is a test boat to practice with materials, epoxying and fiberglass. I will revise to stainless steel screws for the bigger boat. How about bronze ones? I want the trolling motor for secondary choice, to sailing when there is no wind, the boat will wait 950 kg fully loaded (estimate).

@kerosene i do not want to show plans until it is done and tested as i mentioned in an earlier post but i will provide images with the section lines in the following days. About the draft i was wrong, i was talking for my small boat, but anyways the draft in the bigger boat i think will be 20-30cm max. however it will be a sliding keel with a bulb or about 100-150 kg. The keel can extend even 2m long. Im sorry for my description, i will provide images with section(s) lines.

@David Cooper lol but absolutely right, it will look like a canal boat with outriggers, a long sliding bulb keel and a mast on it. now i realize thats how canal boats looks like. So like a canal boat without the structure on top. Indeed it wont be comfortable and the purpose will be the passage and the adventure. I have seen a lot of designs and i notice all these specifications and other rations as you mentioned and thank you. Making it long with outriggers will be the same thing with less drag (which in rough water it will more likely hit on the waves). I was thinking to concentrate about 300kg of supplies in the middles and below that it will be the bulb keel of about 100 to 150kg. The mast mast will be next by at front of the keel and a little big more back the outriggers. I will concentrate the most of the weight at the center, i was planning to have ballast at the ends on top (sealed air), but now im thinking what you said. What do you suggest?!

 

I'd recommend that you have a much higher displacement of the boat in the middle third rather than having nearly equal amounts at the bow and stern, especially if you're planning to put most of the weight in the middle (as that will try to snap the hull in half even more strongly). You can achieve most of this just by varying the width of the hull gradually, starting narrow at the bow and only reaching maximum width towards the middle, then narrowing again towards the stern, though not as much as at the bow. There's also a slamming issue to consider when you come off the top of a wave and crash down into a trough: you don't want a wide, flat underside near the bow, so you should consider having a V-shaped stretch of hull there instead to absorb the impacts more gently. You can let other people do most of the design work for you just by looking at the shapes of tried-and-tested boats that are popular and successful, and if your construction method doesn't make it easy to produce the same shape, it's okay to compromise by replacing the curves with a series of flat sections that work together to approximate the same curves. The draught of the boat may be the same at the front as it is in the middle, but at the front there's a lot less volume because it's narrow there and the sides are steeply sloped. At the stern the draught will likely need to reduce so that you have the same displacement there as at the bow to keep the boat balanced correctly.

You should try making experimental hulls out of cardboard and sticky tape and then float them to see how well they work - they don't need to last very long to tell you what you need to know about them, and this is a quick, inexpensive way to get good answers. Make sure they're strong enough to carry a bit of ballast so that you can test them properly. Once you've found some promising designs, build better versions of them and varnish them, then test them in choppy water.

Don't let flat plywood sheets dictate the shape of the boat, because thinking that way will likely lead to you producing coffins rather than hulls. Create the shape in your mind first, then work out how to build something close to that using flat sheets. Experiment with the plywood to find out how much you can bend them to produce curves. You will later build a strong frame to attach appropriately shaped pieces of plywood to, and they will then add to the strength of the frame. It's better to use one big piece of plywood than lots of small ones, so bending a panel gradually over a distance is better than using two or more panels at slightly different angles - where you switch to a different panel it should either be because you have to make a sharp change in angle or because you have no choice as you've already used the full length of one sheet and need to continue from there with another piece. Studying existing plywood boat designs will give you a better idea of how to go about this, and of how much you can safely bend and twist the wood.

 

@David Cooper thank you very much for the info, actually very very helpful

here some images of the sections

Imgur https://imgur.com/h28vqdp
Imgur https://imgur.com/0Hxm2st
Imgur https://imgur.com/Q9qwjao
Imgur https://imgur.com/A06mTsr

These are draft yet on the design. Every square represents 10cm

The cockpit might extend until the keel and the outriggers i would prefer it longer and attached to 2 tube supports.