using aluminum instead of wood

[bulldogdaddy]

thinking of using aluminum braces from the stringers ,through bolted with stainless bolts,to the transom. this would be 3/8 90degree with a transom plate,all welded. would this idea work instead of using wood and glass?pros and cons please!would the throgh bolts cause stringer stress and crack,any response is greatly appreciated

[Alan Power]

I would tend not to use through bolted brackets on the transom, you would have to put large backing plates outside the transom and if you didn't the force may pull the bolts out. I dont know if I would like it just bolted to my stringers, I would def. glass it, much stronger. Also its just another thing to leak.
If you glass in knees you would spread load better, it would probably be easier and would not be any heavier, on the basis of strenhgt to weight.

If you do go with the through bolt system, Techno has a good way of sealing bolts, see - Fiberglass and Composites Discussion > fiberglass layup - (on the second page of this thread).

I have done something similar to this, but bolted to rear seat boxes not a very good job. Maybe someone that has done this before could guide you better with the aluminium brace???

Alan...

[ryan_L6]

its up to you but , by putting stainless bolts thru aluminum, you run the risk of dissimilar metal corrosion where the stainless touches the aluminum down the road. just because a bolt is stainless steel does not mean that there is no chance it will corrode. anything that is metal can and probably will corrode given enough time or the right circumstances.

i would suggest making the 90 degree parts out of stainless steel if possible.

then again a little corrosion on a boat is not a big deal .

[Alan Power]

I was going to mention galvanic reaction between dissimilar metals, but yachts have aloy masts and are held up with s/s rigging. To do this is in your situation is against text book, but the real world is a different game.

[bulldogdaddy]

for gods sake !i didn't even think of the corrosion issue and i'm a sheet metal roofer,hope my boss dosen't see this,lol,thanks for the reply guys!

[Reese]

I’ve seen many designs using alum, steel, plywood, fiberglass and composite materials including Kevlar and carbon fiber…all probably work equally well. The bottom line is...what are you comfortable with…and how much design knowledge you have.

The only real negative I see with a through bolt arrangement is that over time the wood will shrink and the bolt may end up loosening. Also, many boat use lumbar not plywood for the stringers that tend to crack much compared to plywood stringers.

If you want to see a good example of a well designed through bolted knee brace, check out Cougar Boats. I believe Cougar uses metal channels for their stringers instead of wood.

I have to admit that even with the advent of space age materials, plywood is still very hard to beat in many areas including price. Here is the back end (work in progress) of my latest project incorporating a built-in set back with a knee brace.

Good luck with your project...

[Scott]

I wouldnt use Aluminum, stainless etc. When we started the Baja transom, like you, I spent some time checking into all the options. We used wood. If you plan to keep the boat forever and ever amen, there are products you can apply to the wood that make it permanently water proof and solid as rock.
We glassed in knees, from the transom to the floor and braces from those knees to the sides (at the floor level). Lots of glass cloth and mat. As long as water can not get to the wood, it's light and plenty strong.
I removed some glass on the inside to insure that the glass from the knees actually mated to the transom wood. Just in case there was any separation between the innger glass and the transom wood.
Said it before, got to say it again, H2ONut really kicked butt when it comes to this repair. You would do well to get his pics and pick his brain I was really impressed with his approach.
Ours is not as neet but functional....we hope!

[sho305]

I am am sure it can be done, but may not be worth the hassle. I still do not like end-butt connections. I might use some simple L brackets so I can put screws in there and glass over it. Screws hold tight. Like in the knee to transom area, then the wood is connected too. I see little flex happening here. Then again, they don't come apart without screws either.

Talked to an old guy who ran plywood hydros, he said he just used eye screws from stringer to the motor clamps, and it worked great. I think if you make an aluminum frame that spread out the stress to the stringers, you could use a light transom then. May be good to glass a mount/cross-pieces to the stringers to mount it to so you do not compromise the stringers. Depending on what you have. Or a plate on the stringers, then mount to that. Then use the tubes-through-transom method mentioned above for the bolts through the transom.

If I had the whole transom out, I would figure out how to mat a plate of aluminum in/on the inner transom skin, and no wood in the center at least. Then put an aluminum frame in there connecting to the stringers to hold the motor. What else does the transom have to do when not holding the motor? Just hold the sides together is all. Then you have no problems with wood in the transom, or crushing it. My Bayliner only has wood in the center, and a narrow piece out each side for the transom tie rings. It is kneed into the stringers, sort of, a couple inches beyond the board. It is only 90hp though. A couple of stiffeners across the transom ought to work with a frame.

I am no pro boat maker, but I think this is not done as it would be more work, more work for the manufacturer as well as me repairing it. I'll have the glass out anyway, so wood is easy. Few people have access to a welder for aluminum. And nobody tells how somebody like Allison is doing their transom with metal. Also, lots of people point at the old proven way of making boats, and say that is the way 'cause we know it works. Fine, but this is almost 2003!!! I'd use aluminum stringers if I could, and I might. Problem is I can toss wood in there cheap and easy, and it will work until I get rid of the boat. It wouldn't be as cool though...:cool:

I did not mention of course, you would have a problem with stringers as the aluminum is so stiff. It could cause cracking to the flexable fiberglass if layed directly on it without proper support. I think you would need more stringers like an airplane has, so you did not have unsupported glass ramming the aluminum. Where the wood would flex some too, with the glass. I find it hard to believe the transom flexes that much though, or 260hp would trash it.:cool:

Looking at some more, I think you need to get the braces on or close to the motor bolts. On the motor bolts, and you should not have the motor or brace pulling the bolts through the transom.