Werzko 4.5 - 15' ply stitch-n-glue sail dinghy

I am studying the plans for this 15' sail dinghy before I begin cutting the parts.
This will be the first boat I build, and both I and my son want to learn the fine art of sailing. I have some questions that I hope to see answered here.

I have already found a supplier of marine-grade okume plywood here, but he currently only stocks 12 and 15mm thick plates, while the project asks for 10mm, which will add unnecessary weight.
I do not know which kind of wood I should use for the keelson, for the edges of the keel case, the deck bearers, gunwale and structural rods in general. Most are mainly rods measuring 18x35mm. Since I would like a relatively light alternative to partly compensate for the heavier plywood, which wood would you recommend?
I guess cedar would be better and last longer than (knot free) pine, although it would certainly be more expensive (my little beloved country has few resources but brain power, so most everything here is imported).

Buoyancy: Another question is about the aft and rear flotation chambers: should I use car tyre tubes? polyethylene bags filled with canned styrofoam? PET bottles?
As a 56 y.o. beginner, I beg your mercy if my ignorance shows too much! For instance: perhaps some lightening holes in the bottom of the boat would help?

 

Welcome aboard, Aharon!

I was too cheap to buy inflatable buoyancy bags for my kayak so I got ahold of a 10 gallon Ziploc and stuffed it full of Styrofoam packing peanuts and taped it shut. It's been close to a year and it's working fine. I wouldn't use this anywhere I couldn't get at for inspection and replacement though.

 

Thanks for the welcoming, cthippo!
And thanks for "naming that thing"! I googled "inflatable buoyancy bags" and I see what you mean. They look good and "professional". Hopefully they will not cost me one arm and one leg - lol!
Yes, the 4.5 plans provide inspection hatches for both the aft and rear buoyancy tanks.
From all the alternatives I have listed, the PET bottles seems the least elegant of them all - although "environmentally friendly".

Hope other friends will give me some hint on the woods to use.

 

Pingpong balls have been suggested, and the Mythbusters have proven they work.

Welcome aboard.
Lurvio

 

Hehe, Lurvio - So Buster was put to the test again? OK!!! If they say so~ Ping-pong balls are also very light, an added advantage.
Thank you!

 

Actually they sunk a boat, then floated it back to the surface by pumping the balls into the hull via a waterhose.

Youtube video search results

Lurvio

 

empty plastic milk bottles are coastguard approved provided they have plastic caps...even cheaper ..tie handles together with strong cord ( if they have handles )

 

I was going to use 2L soda bottles which are plenty strong, but they're also fairly heavy.

 

Transom size x behavior

I have been reading the thread "Ready for Design Review", and questions began logically to pop up in my mind.
Different from the designer Radoslaw, who sails in calm lakes, my only option is the Mediterranean Sea (Israel is not known for any plentiful of water-bodies...).
Please have a look at the boat's transom in the pictures and tell me what you guys think about the behavior expected in salted water (I intend to learn to sail on this boat).
The bottom is flat with a slight curve, overal weight shall be something between 130 and 150 kg (don't ask me what is that in pounds!).
Thanks a lot for your input.
Aharon

 

Using 12mm would add around 10-15 kg to this hull. It's up to you whether you're worried about that or not. The thicker ply would be harder to bend, which may mean a bit of swearing getting the bilge plank on, but it should be do-able. Note that marine ply is not necessarily better timber or glue than some grades of exterior ply. It depends on the brands available locally (I've seen some very good exterior and some fairly crappy marine).

ETA: In Australia, durable racing dinghies of this size were commonly built out of 4mm ply, and you can get a very strong boat out of 6mm. Of course, this is assuming the structure is designed to suit these thicknesses.

Use whatever you have locally that isn't ridiculously hard or heavy. Cedar would be fine. Douglas Fir is always good for this sort of thing. Any similar timbers would work.

Why put anything in them? Filling them up with stuff is just more weight and trouble and makes it harder to find leaks and rot. If the boat is built reasonably well the tanks shouldn't leak anyway, assuming you are putting hatches on them. It's common for dinghies to not have anything except air and a little condensation inside bouyancy tanks.

If you and your son are beginners you should be reading the forecasts and staying ashore in dodgey conditions. The transom will be fine in any weather you should be out in. It could get a bit hairy when running down steep waves in a lot of wind, but if you get caught in that situation just drop the mainsail, run under jib, and stack the crew aft. By the way, this boat would sail best if not heeled much in normal winds. Try to keep it pretty flat, except in drifting conditions when you can heel it some to help fill the sails and to reduce wetted surface. The flat bottom wiil pound a bit upwind in a chop but it shouldn't be too bad.

Oh and there are 2.204 pounds to the kg, although sensible people don't worry about the 0.004 bit. 130-150 kg is 286-330 lbs.

ETA: Just thought of something important. After you build the thing, pick a nice day and find some water just deep enough that you can't stand up in it. Then tip the boat over. Then figure out how you are going to get back on it and get the water out. It's very useful to figure this out well before you need to.

 

Planck thickness

NED, perhaps I misrepresented the situation: the thick plywood is just for the bottom and 2 formers. Side panels, etc. are all 6mm ply;

Do you mean even the bottom plank is 6mm? I would love to see one such plant. If you remember a model name, pls let me know, so I can consult the oracle (google) and get the plans.
The monocoques you get from stitch-and-glue are impressively strong. If one such project also allows the "whole shebang" (I love this word, it's funny!) to be light at the same time, it will be still better. I do not intend to be restricted to building this or that dingly just because the plans are for free, if you know what I mean.
Thank you for the hint on conversion. Does Australia use Imperial or Metric standard?

Thank you, sir! I have a slight idea on how to right it, but I keep thinking about the water that will remain inside... I guess I should take some cans along?

 

Oh, ok. In that case don't worry about it. Just use the 12mm. It'll be fine.

Yes, the whole lot. Even the plywood web frames inside the boat were often 4mm. This was standard construction for a lot of classes 30 or so years ago. These days they're all carbon, etc.

Mind you, these boats were durable in terms on sailing loads, not in terms of bouncing up and down on rocky beaches. It depends what you're after. They also required more internal structure than boats with heavier skins, and the designs tended to be the sorts of boats that beginners wouldn't want to poddle around in. Examples are boats like the NS14, Farr 3.7, Gwen 12 and umpteen others.

That boat looks like a nice boat you could have a lot of fun it. If that's what you want then I wouldn't be too worried about building it. The construction sounds sensible. 10mm bottom with 6mm sides and decks is both strong and light at that size.

Officially we're metric but people often use either, especially if they're old enough to have been raised with Imperial. We changed over around 1970 I think (can't remember offhand). Of course, all the local factories just changed the names of things like timber sizes and bolts, but the tooling and actual sizes were still the same.

Buckets are good.

 

Aharon, you might want to check out Vulkyn's threads. He's in Egypt building a boat and has dealt with a lot of the same materials sourcing issues you are facing.

Start here:

http://www.boatdesign.net/forums/open-discussion/dummies-guide-boating-stuff-33407.html

 

Aharon will be glad to pass the links and info i gathered, PM me should you need anything ....

 

Thanks, Vulkyn! I have just spent hours in the link cthippo suggested, and I am delighted with the wealth of knowledge and camaraderie I am enjoying here.
Just as your wife, mine is also complaining about the time I spend in front of the screen.
You do a great job, neighbor, both as a seaman and as a "mensch" (in either the German and the Yidish meaning of the word, if you know what I mean).
I wil PM you for sure. "Dummy" is a temporary status!
G-d bless!