Thread: Is that a 12' GIS I see hull down on your horizon

Originally Posted by tommyboy

Optimaster 310: A Sail-Training Dinghy for Adults - Professional BoatBuilder Magazine

70kg! Is that possible for such a small boat? This little weighty tub is no car-topper that's for sure!

See this link:

Optimaster 310: A Sail-Training Dinghy for Adults - Professional BoatBuilder Magazine

If I understand correctly, the boat was designed by an architect and designer, but not someone who has experience and/or studied boat design/construction in great detail before taking on this project.

Looking at some construction photos (there is also one included in the above link), there is quite extensive framing + sheeting of the outside of the boat with glass that adds greatly to the weight.

But the boat has a modern sail of sufficient area with a large dagger board which promises some performance (I am sure that a more proficient hull would be possible though).

Main thought seems to be a solo training boat, like the Opti, for adults (the fun is lost a bit when they put 4 adults with a trainer in a larger keelboat). I also think that one learns better to sail in a smaller boat than in a larger one (more direct response of what one does to boat speed and such).

I think that the additional idea is good in the sense of purpose and execution of the design (rig, dagger board, rudder, profile of the boat) but that a lot can be improved (weight, refining of construction method, hull shape) to improve performance whilst still making it suitable as a training boat.

Joost

Any progress made with the 12 ft build?

New pictures?

And has a name for the boat been decided yet (I never know how to refer to it)?

Too many questions, I know, but I like this design a lot...

Joost

Howdy Joost ... all the bits should be close to arriving at Rick's.

I still have to track down the high tech rope for the standing rigging. But not tooooo far away.

Rick has been busy with various family things .. and won the 2013 PDRacer Championships this weekend.

MIK

Rick has the box of fittings from duckworks ... which coincidentally has just started stocking Ronstan fittings from Oz.

He thinks it comes in at about a kilogram .. which is great. The only things missing are fastenings for the fittings (he's buying them locally) and some tubing and rod items.

I was a bit worried about the weight. Now I need to do pages of sketches so he can see how they go together.

MIK

Looking great!

Why the worry about weight, since they seem to constitute the regular things to be fitted?

Any new pictures of the hull coming together?

Joost

Hi Joost ...

Normally boats are weighed with permanent fittings in place. And I definitely want the boat to weight in light

That will be one of the selling points ... lighter than a Laser ... hopefully significantly

MIK

for the blocks and fittings. The Ronstan Orbit ratchet is the best you can get.

Are those the stays as well Mik?

Originally Posted by woodeneye

for the blocks and fittings. The Ronstan Orbit ratchet is the best you can get.

Are those the stays as well Mik?

Stays are coming from elsewhere ... 4mm Amsteel Blue

The Orbit block is following your suggestion

MIK

So the benchmark weight will be 59 kilograms with all permanent fittings attached and the boat fully painted/varnished.

Okoume/gaboon weighs appr. 400 - 500 kg/m3. 244 cm x 122 cm x 2.8 cm (2 sheets of 6mm and 4 sheets of 4mm) = 83.35 liters. 83.35 x 500 kilograms = 41.7 kilograms maximum for the plywood. I estimate perhaps 1 sheet of 4 mm plywood as scrap and I used the higher weight, so most likely the ply will weigh less (anywhere between 30 - 35 kilograms for the plywood?).

A total boat weight of less than 59 kg should be feasible, I think, being careful on the glue and glass tape, epoxy for coating and using light timber where specified.

I am anxious to see what the final weight of Rick's boat will be.

Joost

I'm really hoping it is in that range too. I'm inclined to be pessimistic with estimates but usually find builders can do better.

Which a better way around than the opposite!

MIK

No problem I think. We've been building 15'6" Goats in that range. Sensible building should achieve under 55kg. A good target using Paulownia and good quality Gaboon would be 50kg or less.

A bright finish is much lighter too. Primers, undercoats and paints contain lots of solids.


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You would be amazed what difference decks make to a boat.Even under the standard Oz or NZ scheme for dinghy building in ply ... the hull weights come out at 8 to 10 lbs per foot of length when boats are of 4mm ply.So the goat would be about right at somewhere between 128 and 155lbs.Shes of thicker ply but still hits the bottom of that range because of the lack of deck. That would be close to a sheet and a half of ply or a 25 percent increase in weight.I'm hopeful the 12 footer with deck will be under 120 with permanent fittings and I'll be happy with every pound under that.Now what's that all in KG ???MIK

Originally Posted by Boatmik

Now what's that all in KG ???MIK

For sure below 59 KG!!!

So, have the first test sails taken place yet?

Joost