How to design aluminum dinghy

Hi
I'm looking for advices to build an aluminum dinghy. I'm looking way more about the dinghy part and not much on aluminum part.
So I designed a 3D model largely inspired by GoDu and Odysea dinghy (picture below).
I actually use a old and tired Caribe C10 and I'm looking for similar size and usability.
What make a good and useful dinghy? Here some question I have to start:

-Angle and position of the transom?
-Seat in the middle? Removable? With compartment under the seat?
-Handles, how to fix them? Thread holes in the tubes/floating compartment is it acceptable? Weld?
-Floor surface. How to have grip?
-Seating surfaces. How to keep them cold under the sun. What material can be use and how to fix it on aluminum.
-Front compartment for battery or gas tank and other stuff. Good or bad idea?
-How to protect the external sidewall? How to fix protector over the aluminum?
-Paint or not.

Let start with that.

 

Answers in bold.

 

Inflatable boats have the great ability to be easily transported, but the increase in engine power has resulted in ribs . For me rib its not very logical design despite huge popularity both among people and in various services . And old inflatables folding and ribs copied some design failures in milions.

Make normal light vee bottom without those round sides for good hydrodynamics .Normal transom without those tails ,in second picture transom is ok. . If you need high buoyancy its side thickness vs space inside .
transom angle : Transom Angle? https://www.boatdesign.net/threads/transom-angle.34448/
Aluminium is cold . Tandem center seats will be the best on choppy sea however not confortable for tiller .

 

Cool! Lot of good info here. I take notes.
I would like to have a look at few nicely design dinghy in order to be inspire and take the best feature from different boat and put them in my design based on my needs.
What are the few nicely design dinghy in the 10-11 feets range?
Inflatable, carbon fiber, aluminum or anything else doesn't matter, I try to learn here.

 

Up boats makes a carbon dingy that made a splash a while back, saw one at a show but didn't get a chance to get up close.

Did see an aspen carbon cat in person it was nice.... and spendy.

 

Wow, nice! A thing a really like on those two boat is the seat surface who is entirely flat
It look like the shape of the hull is responsible to lift the nose of the boat when moving.

I kind of really like that, as flat surface is nice when the boat is not moving and the seat surface will be a bit easier to build.
Down side is the hull will be more complex to build in aluminum, but also the floor will have a strange shape.
And what about draining water if gravity feed them in the front

 

Proper Course: Outboard on Table https://propercourse.blogspot.com/2010/10/outboard-on-table.html
Don't worry about lift .

 

I am attaching 5 photos. The 4 with the tiller control has the floatation profile taken up to the bow. This boat was 12 feet long. Deadrise 0 degrees.
The single picture with the steering forward has the floatation profile taken up about 65% forward from the transom. This boat was 14 feet. Deadrise 5 degrees.

I am making the assumption that you would build with aluminum.

The deadrise was very shallow as both of these were outboard jet powered and built to run skinny water. Both boats had a tunnel that went forward about 30 inches. plus or minus.

1)Put the transom right to the back. You wanted a 10 foot boat prox. Inflatable boat manufacturers run their tubes past the motor as they have to stabilize a transom with fabric.
Your boat is extremely short so you need every inch of usable length that you can get. I am the second person to suggest this.

2) In order to gain usable space in the boat, get rid of the square tube profile. Use a taller C section. This will get you a higher freeboard and perhaps give you another 12 inches of inside
width. You can see the enclosed C profile in the picture with the fish. I broke/ bent, the angles in the C to provide rigidity to the sheet that made the profile.

3) Weld any handles eyes

You do not need to continue the profile around to the bow. Reasonably difficult to build as compared to the 12 foot shown where I just continued a single skin to the bow.

Note the boat will be heavy. Without knowing all the dimensions, I would expect this boat if it has a 72 chine width would weight of close to 250 + pounds if you use .125 inch material. This does not include any seating, stiffeners, which you will need etc.
Make the boat wider than your C10 to maximize lift at lower speeds. I would not make the deadrise more than 12. A bit harder riding but better for lift.

You will want to put in some sealed baffles to have multiple floation chambers
ABYC and Transport Canada require that if you are using air chambers for floation you must be able to puncture the largest one and still provide floation. Interesting as the requirement
is for level floatation when flooded. ??

If you fill the tubes with foam, (I hate foam as a pinhole will allow water in to saturate the foam and reduce bouyancy) you add more weight

So I have built two almost as your drawing.
If I had to do another, I would build a normal profile hull, wider than the riveted boats, 12 degrees of V, and install floation to meet requirements and personal safety in
an inclosed bow well, perhaps the rear cross seat, and 2 dedicated compartments in the back.

Install the fuel at the transom. Both of thes boat had a 35 gallon built in tank against the transom. Note that I probably had a 7 foot chine width or close to

 

Oh! Good advices. I had to search for 2-3 words I don't understand and that lead me to more questions about my design.

I would like to see this in detail as I'm not sure to correctly understand the C section.

The deadrise is actually 20° on my design because I read GoDu is 24° as you can see in picture. Why 12°?
I realize this design imply important reverse chine (blue circle). So, it's an advantage for stability, but what is the down side? Is it better is I finish the hull flush where the flat chine start?

 

20 degree is a bit steep for a beaching dingy, and the reverse chine is gonna slap in a chop.

 

Yes using the term C section was misleading. We formed a C in the brake and then filled the back of the C.

Really the section would look like a D. But instead of a nice round curve, two "kinks" in the round part. (because we had a brake not a roll) The picture of the 14 shows this

Click on this picture, hold Control CTRL on your keyboard then scroll your mouse to make the image larger

 

Then I have hard time to understand why GODu design with 24° and consider this as an advantage. They also have an important reverse chine.
Below is the design at 12° deadrise with no reverse chine, so hull finish flush with flat chine (if I can say this).

 

Ok. It simply like in picture below.
One big advantage is the access to the weld inside (blue arrow). Way easier to weld. Also wider inside space as you said.
12° deadrise below.

 

I think I found a nice design.
So the D shape give me more space inside and easier access to weld, but the long thin inside walls stress me a bit for the rigidity.
Then I can add a shape on this inside wall (blue circle) to add a lot of rigidity and that can also allow me to add welded anchors point inside (small weld flat bar).
Also, I can ask the shop who will bend to use large die to have a large top inside radius for better comfort (blue arrow).
Those shapes are way harder to bend..., but I do the design and the welding only and know a good shop who bend

 

That is the profile that I used, BUT with the transom to the back of the tubes. No use giving up easily available space.
It will depend on the height of the tube as to whether you need to form a stiffener in the vertical part of the D.
I used 1/8th material and did not find any issue with flex. Certainly the slight bending that you did will increase stiffness. I would still run the tubes up from the transom maybe 70 pecent
and single skin the rest. Advantage? More interior width in the bow area and a bit more interior longitudinal space, transom to bow.

Also, I would form the C part of the D with a 1 inch extra bend at the end of the C, so that this tab extends down from the top 1 inch and 1 inch up from the bottom of the C.
Then form the vertical section of the D, insert it behind the two 1 inch tabs and make up the weld. This then provides a fillet weld as compared to a butt weld.

I would not bother trying to go to a larger radius on the inside of the tube. The flat part of the tube will not be that wide and a rounded corner will provide an easy place to slip.
We used a 2 inch bottom die which gives you a tight corner but it will not be an issue to sit on.

If you have to use any butt welds assembling the tube to tube, insert a backing plate at the joint and have the two profiles fit overtop. Again, this can, when welded correctly, provide an easy method to make up a joint with full penetration. ( as compared to a butt well only)

I am not sure why they installed some tabs on the inside vertical. ???

I would also build it to 12 feet if you can deal with the extra length and weight

You mentioned that you are going to weld it yourself. What is your experience with welding aluminum, tig mig. etc