Thread: Double Aluminium Sheet vs Plate

Hey guys looking to do some work on the old Noah's Ark raising my transom from 15" to 20" to suit a bigger horse power motor and also more weight i have seen it done, just wondering if 2 sheets of 4mm aluminium 6061 bolted together would be the same as 8mm plate?

Theoretically the 2 x 4mm are the same as 1 x 8mm if they are securely bolted together with closely spaced fasteners. Its probably less hassle to use a piece of 8mm plate and also a better job in that you don't have the two mating surfaces and the potential for corrosion in that crevice.

If the 2 x 4mm aren't securely connected to each other the piece of 8mm is 4 times stiffer.

Awesome thanks Bob exactly what i needed to know, since the 8mm is 4 times stronger i don't think i want to compromise the strength so i will hunt around for the plate tomorrow

Does anyone know of any cheap interstate aluminium companies that sell part sheets i need either 400x400mm x 2 or 400x800mm

3M for one make adhesives designed to glue sheets of metal together for situations like yours. Which would give you the stiffness of 8 mm plate.
Sorry, I don't know the cost, so you may need to be sitting down when you find out.

The other thought is can the boat handle the extra weight hanging off the stern?

Try Action Aluminium, Smithfield, NSW

Originally Posted by ian

3M for one make adhesives designed to glue sheets of metal together for situations like yours. Which would give you the stiffness of 8 mm plate.
Sorry, I don't know the cost, so you may need to be sitting down when you find out.

The other thought is can the boat handle the extra weight hanging off the stern?

Thanks Ian, Do u perhaps know the name of the glue? the motor is only 15kg heavier than the alternative motor, there is one other boat like mine for sale on the internet with a similar style motor as i have

Originally Posted by jchappo

Try Action Aluminium, Smithfield, NSW

Thanks i was going to call them

Originally Posted by gazza2009au

Thanks Ian, Do u perhaps know the name of the glue?

two possibles
https://www.masterbond.com/applicati...num-substrates

https://www.3m.com/3M/en_US/company-...1834075&rt=rud


have no experience of either.

Thanks Ian, I looked up these products after you mentioned it as i have never heard of this kind of product before, i found Loctite but a bottle of the glue was $400 that stuff is really pricey i than called Action Aluminium and was quoted for 800x400x8mm $77 plus GST i was expecting the plate to cost over $300

Yeah, I wasn't expecting the glue to be inexpensive. After all they're a specially product for use where welding or bolting is not really an option, or the cost of making the work area safe for welding is prohibitive.

Guys i am looking to buy the aluminium probably tomorrow so i had another idea, instead of using 8mm plate on the outside and 8mm plate on the inside do u think one very thick plate on the outside would be sufficient the plate on the outside would be as pictured and measures 40mm thick do u think a 45 horse power motor weighing 92kg would fall off?

the plate would measure 47cm high, 32cm wide 4cm thick

i have no idea if i can get a plate this size and thickness so i am throwing that idea out there for now untill i confirm tomorrow with the shop

My thinking is a sandwich with plate inside and out would be better than a thicker plate on outside only. Maybe thickness of metal on the boat will also need to be considered and larger pieces used to spread the load.

This is the inside

Originally Posted by gazza2009au

This is the inside

Well then my idea sucks. LOL.

I would suggest having a chat with an experienced boat builder before nyou go too far. A mate of mine did something similar and ended up having to replace the entire transom because of the extra weight AND the extra power is transmitted through the transom to both sides of the boat which wasnt designed for it
Cost him a bomb.

Roger.

Here is the tricky bit my boat is around 1977-1982 model it was compliance for 35 horse power motor but back in those days we only had light weight 2 stroke outboard motors and there were never any transom weight carrying load ratings

These days transom's have a loaded rating and a horse power rating, all though i can restrict my motor from 45hp to 35hp and get certification from the mechanic for legal reasons and registration however the 70's and 80's 35hp motors were 2 stroke this motor i have is a 4 stroke

2 stroke 70/80's era 35hp weigh 52kg

4 stroke 90/00 era 45hp derated 35hp weigh 92kg

i really want to run the later model 4 stroke motor it would add value, it would get double to fuel economy, there will be no choking on fumes but i guess its just a porker, i do have two other motors i may have to use one of them

it was a dream but i guess it was never going to work, there is a guy on Gumtree selling the same boat with a porker motor 50hp yamaha 4 stroke i asked how his went and he replied a bigger motor can go on it...