Aluminum boat..Help!

With structure looking like that on an 8.m boat, what are you doing, racing across the atlantic at 60knots??

2200kg is a lot for a small boat like that, for structure weight!

 

aluminum help

I would like to see some 3/16s angle used in the side walls for strength

 

I'll decrease the thickness of the deck to 4mm to minimize the structure weight. some one mentioed that the weight should be around 1700 kg, what is the appropriate weight of this size !!!

Do you think the scantlings/shpes of (stringers, frames) are fine , do you advice to remove the girders?

 

I exchanged the topside FB stringers (70x5mm 2.75"x0.190") with angles of 65x50x5mm (2.55"x2"x.19"), do you think this is suitable?

Is it the section modulus the reason for recommending the angles? what would be the difference if I used Flat bars with the same section modulus of the angles?

 

ringoo
if you send me a message with your email addy, if you want to send the midship/scatinling section, i'll have a quick look at it for you, and give you some pointers..

 

I sent you a msessage including my e-mail, couldn't attach the midship, this option is not available when sending private msg. please send me your e-mail.

Thanks

 

Drill a lot of big holes... Seriously structure is way overbuilt. Lightness is main reason for aluminum boat. What alloy are you using/

 

I already made holes, I don't have any spacess for more holes, unless if you want me to drill the shell plates

Any other suggestions

 

looks like one of our river boats!!!

is it too late to change some stuff???

On the bottom, rather then run the tall straight longtitudinal beams, take the aluminum and make it into U's - and make a bunch of longtitudinal boxes.
On the sides of the boat, put some bends into to to stiffen it up.

The gunwales could be bent into something that gives some structure.

There is no way that thing is going to be less then 10k pounds, unless you build it all out of some really thin sheets.

These guys build a nice boat, and if you look at the 28 footers you can get some ideas.
http://www.hellscanyonmarine.com/hcm/builds.html

 

Thanks for your input, I can easily replace any of the structural members, it's not big deal...do you have any other suggestions, I didn't like the idea of using U or box longitudinals, flat bars and angles can be easily bended, I'll flip up the angles.

The weight of this structure + the shell is exactly 4500 pounds, still have to add the cabin roof, soft hatch stiffeners, brackets, welds. The total weight then would not exceed 5000 pounds. The full load displacement was estimated 7000 pounds.

I didn't understand "The gunwales could be bent into something that gives some structure."

Good website but all the structre built of Us and Boxes.

 

U's can be easily bent also, then you weld the ends to the bottom, and you have a box!
and the boxes are more then twice as strong then straight metal, and have twice the surface area and support on the bottom, and get rid of a bunch of twist issues.
Maybe your bulkheads will deal with the twist of the boat, I don't know.
Old school boats used I beam longtitudinal down the boat. Worked Ok, but heavier for the same weight, and weren't as strong torsionally.

Your gunwales when viewed from the top are "narrow." If you bent them over, gave them some "width", they will be a lot stronger.

Or, weld a larger diameter rectangular tubing instead of your small tubing you have now.

What are you going to power this with?

 

2 x 150 DF Suzuki

 

Huh.
I'll be curious how you tie the transom into the floor to take the loads.

 

I stiffened the transom with 2x2x.190" T's in addtion to 2 side girders and 3 brackets, I believe it will take the loads...don't you think so?

 

so the lateral braces support it in bending. not as strong as compression.

if it were mine, I would run huge gusset triangles from the transom forward and down to the bottom.
like the thing in the middle here.
http://www.ozsite.com.au/boatbuilding/pics/transom17.jpg