Drilling aluminum I-beam.... weakening it?

I think I know the answer is "its fine," but I thought I'd ask y'all.

My boat trailer is made from aluminum I-beam; about 3x5". The side clearance marker lights are toast and I have some little LEDs to replace them. They're the kind where you drill a 3/4" hole and the lights pop into a rubber grommet.

The current lights are mounted to a steel bracket that is held on with an existing structural bolt (3/8" I think).

Instead of drilling the ugly/rusted/shin-slicing steel brackets for the 3/4 grommets, can I just drill the aluminum instead? How much will I weaken it? Will it make places for stress cracks to start? Boat is about 2200 dry, so at least 2600 until I put a full tank of gas and all the normal things in it like skis, anchor, etc. I'm guessing overall towing weight is in the 3400 range.

In my non-professional opinion, I would think that it would depend on where you drill the hole. Which part of the I beam, what is the load like (force vectors and E36 M3), near the end or near the middle, etc. Remember that aluminum is 1/3 the strength of steel.

You are probably better off duplicating what's there, rather than drilling holes in structural aluminum.

I agree with the Dr. Location will be critical. If it's at the very rear of the trailer, as far from the axle and suspension components as possible I'd think it wouldn't be a big deal.

Location critical, you are adding a stress riser, also you must keep in mind that aluminium is rather vulnerable to cyclical stresses. You may be inducing something that will result in a fatigue failure some time down the road.

One .750" hole in a 3"x5" aluminum beam is not a problem. It's a trailer.

Apexcarver wrote: Location critical, you are adding a stress riser, also you must keep in mind that aluminium is rather vulnerable to cyclical stresses. You may be inducing something that will result in a fatigue failure some time down the road.

^^^^^^This. A picture would help

In the center of vertical web, no problem. I would avoid the horizontal web.

You might also consider crevasse corrosion. I would seat the grommets with silicone.

Toyman01 wrote: In the center of vertical web, no problem. I would avoid the horizontal web. You might also consider crevasse corrosion. I would seat the grommets with silicone.

This - the vertical web, the "I" of the beam, is generally safe to drill, provided we're talking drill bit and not hole saw (and sometimes even then). The two webs at the end are less so.

I'd drill closer to the less-loaded side.

Actually, I'd use the cheapest possible LED marker lights I could attach with 3M double-stick foam tape.

Another thing to consider. A large portion of the structure in a boat trailer is actually in the hull of the boat. All of my boat trailers are pretty floppy until the boat is strapped to it.

I'd go along with the Doctor, aluminum is a flexi flyer anyway, why risk it? Replicate the steel sheet metal with aluminum. I've got some stainless sheet if you can send me dimensions.

Dan

Picture coming. I have pathetic internet up here at the lake. Things like images are stoopid slow for me to access. I tried streaming music yesterday and I got about 10 seconds of music and then 5 minutes of buffering

The lights in question are at the front of the I-beams where they meet the tongue. They don't have to be in that exact spot, they could be back a foot or so. So far I have sliced my shin on one and whacked my knee on the other.

There are two more amber sidelights, but they are on the steel support for the fenders, so they are a no-brainer.

My question is are those front marker lights even required? Maybe it depends on the state you live in but I don't think I've ever seen them mounted there on a boat trailer in Minnesota.

why not a clamp on bracket for the lights w/ no drilling?

the arm for the trailer winch looks to be galvanized. Can you move the lights up there just above the trailer "deck"? I also spy a hole in the top of the tongue (which also appears to be galvanized) why not make a little bracket that bolts into that hole? this puts the lights out of harms way and keeps them from harming you as they are now protected by the winch arm and the top of the trailer.

for what it is worth, I am against having permanent lights on any trailer that gets submerged. I would rather have them hook on, strap on, or clip onto the trailer or even the boat so you can easily and quickly remove them before launching. Should be easy enough to find a way to make them hook onto the trailer when the boat is not on it.

If you are dead set on drilling the aluminum to place the lights, do it between the ends of the aluminum I beams where they bolt to the tongue and the first crossmember where the tongue ends. This is probably the strongest and stiffest part of the trailer and where the aluminum us under the least amount of stress due to how close the I beams are to each other and the connections to the galvanized tongue

1. Unbolt galvanized winch arm.

2. Make bracket that can use the same mounting holes as the winch arm, and straddles each frame rail. This could be simple flat stock with appropriate bends.

3. Reinstall the winch arm so that your new bracket is sandwiched between the tongue and winch arm.

stuart in mn wrote: My question is are those front marker lights even required? Maybe it depends on the state you live in but I don't think I've ever seen them mounted there on a boat trailer in Minnesota.

knowing that people do not seem to notice trailers (or boats on trailers) I would want as many lights and reflectors as I could stand on the trailer. When I brought my 23 foot WHITE sailboat down from Lake Champlain a few years ago, I had somebody try to merge right in behind the bumper of my Disco before realizing there was a huge boat taking up the spot and looming over them. I almost lost said boat trying to maneuver out of their way and they almost lost control trying to steer the other way to get away.

mad_machine wrote: the arm for the trailer winch looks to be galvanized. Can you move the lights up there just above the trailer "deck"? I also spy a hole in the top of the tongue (which also appears to be galvanized) why not make a little bracket that bolts into that hole? this puts the lights out of harms way and keeps them from harming you as they are now protected by the winch arm and the top of the trailer.

The winch tower would be great, except for two things. 1) drilling the galvanized steel makes a big non-galvanized place. Not a big deal, but I'm not keen on taking away corrosion resistance. 2) that square tubing is sealed on the bottom with the mounting plate. I could drill it, but again, see #1

for what it is worth, I am against having permanent lights on any trailer that gets submerged.

That's the exact reason I'm switching lights: These LEDs I'm putting on are sealed units. I already put on the main taillights, also sealed LEDs. I get tired of replacing light bulbs and cleaning rusty sockets to try and get trailer lights to work... or replacing fuses in the truck if I forget to unplug the connector before I back in the boat.

These front lights won't ever be submerged anyway.

stuart in mn wrote: My question is are those front marker lights even required? Maybe it depends on the state you live in but I don't think I've ever seen them mounted there on a boat trailer in Minnesota.

Federal DOT requires them on any trailer that is wider than X or longer than Y (I forget the actual numbers, but its something like 66" wide or 16' long.

No one will notice if they aren't there, but with my luck I'd get that one butthead officer.

Good suggestions, all. I'm still smelling a lot of "fabricate a bracket" which may have to happen. I just don't like it. But I'll get over it.

Why not just "glue" them on? I would go to Lowe's, grab a tube of Marine GOOP, apply a liberal amount to the back side and then clamp or tape them in place overnight.

I use the stuff all the time and keep a tube in every toolbox.

Just another thought......

lotusseven7 wrote: Why not just "glue" them on? I would go to Lowe's, grab a tube of Marine GOOP, apply a liberal amount to the back side and then clamp or tape them in place overnight. I use the stuff all the time and keep a tube in every toolbox. Just another thought......

Not a bad plan, except the wires exit directly out the back and they're pretty stiff. Molded into the plastic and have a beefy shrink tube on them.

Can you fab a bracket that attached to the spare tire mount? Possibly a flat strip of steel under the spare tire with the ends bent up to mount the lights?

That would avoid drilling the frame, the lights would be tucked in, and the spare would hide the bracket.

Make a pair of L brackets out of aluminum with the appropriate hole drilled on one leg, glue them to the bottom of the beams with 5200, or PL premium if you're feeling cheap.

Jeebers this group would overthink taking a dump and E36 M3 their pants.

Stick them on there with glue or make a bracket or drill the hole. This isn't going to make a difference. And approximately 74% of trailers don't have lights that work anyways, so you could probably put bike reflectors on there and the officer wouldn't know the difference.