7/8 months? So for us normal boatbuilding people, maybe 15 months. Not bad for such cool design. Once again, Dominico, I am super impressed not only by the quality of your work but also your speed. And that Duo900 looks like it will be fast.

I am curious about the mast head. Do you have any other shots with more detail of the mast head? I will be shortening the mast from a Hobie 16 for my ECO 6 and building a new mast head for it. I am thinking of using wood (both plywood and some solid wood) reinforced with carbon fibre. Any advice?

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Doesn’t that make the wall thickness 5mm……?

Okay thank you all, I wouldn’t have even considered 5mm to be the answer but that makes sense to me now.?

Of course it is 5 mm

Bernd

As the outer diameter includes not only one wall but also the second wall in the opposit position, I would think 5 mm thickness.

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You are right. The first number is the outside diameter? (100/90) second number is the inside diameter
Resulting in a wall thickness of 10 mm.

Cheers

Bernd

Hi Domenico

Thank you for the photos.
Looks very good, as usual.
Do you have any idea how long it took to build the boat?
Any idea will be helpful.
I know it was only stop work in between building the KD 122.

So next week sailing?

Ciao

Hello Bernd the Duo 900 the construction has come to an end, I'm waiting for the sailmaker who brings me the mainsail and the jib to assemble it before launching into the sea.
Ciao
link?/g/K-designs-Multihull-Sailboats/album?p=Taken%2C%2C%2C20%2C1%2C200%2C0&jump=1&id=256248

Hey forum, I have a couple of questions for you. When a plan describes an aluminum tube as 100/90 or 90/80 does that mean the thickness of the tube wall is 10mm??

Second question is how do you attach the inner part of the trampoline? Would you attach a stringer with holes in it to tie the trampoline to the inner hulls and cabin??

Thanks!
Geoff

Thanks Domenico! The steps look good. My steps are not as many and you can’t remove them. Good job.
Cheers
Patrick

?

Hi Ron

Watch it. Drawing 17 is to scale, meaning 1 :1. The sort of sketch is a JPG file and not to scale.
The wooden "eye" is only an example. You can also use a bull's eye on each side.
The angle is automatic determined by the position of the plastic tupe and the distance of the rudder
to the lower corner of the rudder housing. It is a triangulation ;-))

Cheers

Bernd



?

Thank you, Bernd. That helps. Now I understand where the bungee cord goes. ?Figure 17 ? says "The drawing is to scale. Print it out" What size paper is it being printed to in order to get "full size" and "to scale"? Also, I see the rudder is at an angle to vertical. What is that angle? How is that angle determined?

I apologize for all these questions. Perhaps all of this is clear to others but it is not clear to me and I don't want to do a bunch of work and then learn I have done it wrong.

Hi Rod

The rudder automatic is very simple. You can fasten the bungee cord in many ways.?
Example sketch attached.
The elasticity of the bungee cords differs from type to type.
You have to test it. If the rudder jumps off at too low a speed, tighten the cord.
The rudder jumps up but settles down to a given extent. Mostly this is enough
to have rudder in the boat.?
Have fun

Bernd?

I will provide a proper update in a few days. I decided to go with Dominic's approach. Thank you, Dominic, your photos were very helpful. ?This second attempt has been successful, enabling me to use the Meranti plywood. I will attach one photo today with others to follow after I have shaped and then fibreglassed both rudders. This was earlier today after gluing up the second one.

Now I have another question. I have puzzled over the drawings for the rudder housing off and on all winter. I sort of understand them but I don't. It is not clear to me where the bungee cord goes and how it is routed. Also, with this set up, is it possible to sail with the rudders partially down, as might be the case if a boat was in a shallow waters? Or is it all down or nothing? Have other builders adopted other approaches??