Building cold-molding "monocoque"

[jusembo]

Hello,

I start the construction of a 6.5m sailboat in Epoxy-Yellow Cedar

The construction will be "monocoque" hull and roof in one piece (with continue planking)


Does anybody has experience in such construction or has already heared about that?

the web-site is: www.solalelouna.com (the site is in French)

Thanks for answers (in simple English please)

David

[Eric Sponberg]

You should get a copy of the book "The Gougeon Brothers on Boat Construction." It will teach you everything you need to know about building monocoque boats, and boats of other types of construction.

Eric

[jusembo]

Hello Eric

Ok i will mail order it but it will take at least 1 month to receive it, here, in China

Did you heared about anybody who build cold-molding with continue planks from hull to roof

What's you opinion about such technique??

Thanks for answer David

[Eric Sponberg]

Cold molding is certainly a very viable method of building boats. To make the veneers continuous from hull to roof poses complications. You would have to have a generous radius at the hull to deck joint to carry the veneers over the corner. Also, you might have to build the boat on its side so that you can run the veneers over the corner and down the hull and deck to achieve a continuous layup over the corner. You would also have to have a rolling mechanism for the hull so that you can do first one side, then roll the boat over to the other side for the next veneer. You should not build first one side, then the other, because a lot depends on keeping the hull straight during layup, and for making the joints of the veneers on the hull centerline that should be done as you go along building both sides of the boat at once.

Eric

[jusembo]

Hello Eric,

Thanks for your professionnal advices

- The rolling mechanism was in my plan, it's why i build the (temporary) carrying structure inside the boat and not outside (see attached pictures). Still need to strenghten the carrying structure to give a stable geometry when the boat will rolling
I'll post some picture of that mechanism when it's builded.

- The 2 mm veneer will be wet bended and dried one by one in electric hot press before epoxy glueing (to avoid any damp)

So it's time to start, it's the best way to see if it's work or not

David

PS: Here is the copy of the message i received from Interlude on "boatdesign" thread

*More questions than answers. How thick strip planking? What geometry planking? No fastenings I presume?
I built a 37 ft cedar strip plank boat with 26mm square planking glued and nailed to ribs and together and then epoxy glassed inside and outside.
I had no trouble bending and joining the slightly opened joints as they round the hull. Your tighter radii might be a problem around the deck "joint".

*Hello Interlude,

Thanks very much for your message
I have given up hope that somebody will made the effort to answer
The planks will be first coat longitudinal +- 5mm to give a strong base and three diagonales of 2mm or 2 diagonal of 3mm
Final thikness should be about 11m
Fastened with stainless staples
For fitting the diagonal planks around the deck joint i will probably bending every plank with hot press before to glue them
I would like to avoid to use fiber glass outside as i'm afraid of "delaminage" (i don't know if it's the right translation from French) after a long period, due to UV radiation and expansion, for example after 20 years...what's your opinion?
It seems nobody has experience with such thing..?

Thanks for answer

*Hi Jusembo. Your boat looks good. I used Japanese cedar which is very light and the "fibreglass skins" were to strengthen the "composite". Your diagonal planking would be stronger but could still benefit from skins. A fibreglass skin would also ensure a proper barrier to keep worms out and give a stronger surface on deck. Epoxy glassing adheres pretty well to wood as compared to polyester resins, but epoxies must be protected from UV and therefore painted (with a light colour to avoid getting too hot from the sun). Maybe something like 2 diagonal layers of 150 gram twirl instead of the 3rd diagonal wood layer could be considered. Your laminated ribs inside with a glass skin outside would be very strong. Some old epoxy decks I've seen seem to have lasted OK

[jusembo]

Hello Interlude,

So the question is: (sorry if it'a a stupide on)
In case if i want to keep transparent finish to the hull; Is it save or not to use epoxy glassing and just protect it from UV with clear or lightly stained varnish?

Following my philosophy the hull has to withstand at least 20 years before will have to be re-cover with new epoxy glassing what mean a deep renovating of the boat...

NB: My target is high quality small serial building

David

[Eric Sponberg]

Again, the Gougeon Brothers book will be helpful here. It has certainly been done before to have a bright-finished hull (i.e. wood grain shows). After epoxy, the hull should be varnished with many coats of good quality varnish which has lots of UV protectant in it. I won't say it will last 20 years, I don't think any paint or varnish can do that, but with careful and consistent maintenance, it will last a long time and make a pretty boat.

Eric

[jusembo]

I agree but the difference with any painting or varnish is that if the epoxy glassing is damaged you need to strip it off what mean a very serious job and then epoxyglass again what request a very professionnal skill nothing similair to repaint or revarnish after sanding old coat of varnish or painting.
But from another side i agree that 2 coats of fiberglass will be more convenient for daily use by giving better protection against scratchs and knocks

It should be great to know, approximately, the live of epoxyglass with good quality (clear) varnish protection

David

[Eric Sponberg]

Epoxy and fiberglass by themselves will last nearly forever, as long as they are properly maintained and covered with enough good layers of varnish. I know of one particular boat that has a brightwork hull that is about 30 years old, and I don't believe it has ever been refiberglassed. The varnish has always been properly maintained. You are right that the fiberglass will give protection against scratches and knocks. If they are touched up and repaired quickly, the finish and the surface will last a long, long time.

Eric

[interlude]

I agree with Eric
In fact I have built 2 cedar strip plank tenders - the first with simply varnished outer hull which took a beating getting bashed on other dinghies and jetties - the second had a layer of glass before varnishing which has lasted much better. The scratches and scrapes don't penetrate through the glass which prevents water ingress - unlike the first varnished only dinghy.

[jusembo]

Pictures of the revolving mechanism

David Jushpe

www.solalelouna.com