What's the best way to attach platform brackets

I just got some swim platform brackets fabricated by a friends dad. I have attached a couple of pics. They are SS. I was planning on using a plate on the inside and sandwich the transom in between. From looking at what the factory did, it looks like I should 'glass in a wooden or aluminum plate. If I did that I would probably install the bolts from the inside and glass them in too so that I can seal the entire area. I was wondering if anyone has a better way to do it. Sorry the pictures are crap, but it was taken with my wife's cellphone.

Thanks,
B

sorry the pics are all turned..I forgot to rotate them.

I might be wrong about this, but those things look like recipe for disaster. Picture the bottom edge of the brackets as your fulcrum/pivot point. The top bolts will be under extreme tension (and the structure they're bolted into), and the lower part of the brackets will be trying to force their way into the transom. Since the pull points and push points are so closely coupled (6"), you're putting an INCREDIBLE amount of strain on the bracket, the bolts and the transom.

My guess is that to stay with your current dimensions, you wouldn't want to go less that 1/4" stock, and the pictures look lighter than that.

For sure (absolutely sure), you'd want to put some aluminum backing plates inside the hull, and don't be skimpy (1/4" stock by like a foot square each side). Make sure you pre-bend the plates to fit the shape of the hull.

Drill the holes through the transom and backing plates make sure the bolts fit, then take it all apart. Dip the bolts and nuts in Vaseline or car wax. Mix a batch of splooge (epoxy resin and milled glass fibers or other filler to where it's thick like frosting) and apply generously to 'glue' the backing plate onto the transom. Slide the brackets on and tighten things down before the splooge cooks off. This step will ensure there is excellent fitment between plate and hull. Don't glass over that. The next day, you'll remove the bolts (hence the motion lotion - don't want bolts gluing together). At that point, you can proceed as normal - 3M 5200 (?) in the bolt holes, the whole backside of the bracket, the threads of the bolts, etc.

The brackets look like they're only tack-welded and will fail in three minutes - get a full bead on there.

Better use some REALLY good bolts - like go spring for hardened stanless aircraft-grade stuff.



(Message edited by toyotafreak on May 24, 2004)

I would not recommend glassing in the backing plate. The last thing that you want to do is to trap water between the backing plate and the hull.

You absolutly do NOT want to glass in the bolts. You will need to get a wrench on these bolts to tighten them, glassing them in will just be a recipe for disaster.

In general, you want the backing plate to be as large and stiff as possible. Ideally, the backing plate will pick up multiple bolts so that it can sandwich the entire area between the bolts.

When you insert the bolts be sure to goop the shaft of the bolt up with a lot of caulking. It is essential that you prevent any water from leaking down the shaft of the bolt. It is very likely that the interior of the transom is made of wood (just covered in fiberglass) and if it gets wet it will rot out in a few years. Not a good thing.

I highly recommend using stainless bolts and nylon locking nuts. I also recommned coating the threads with "anti-sieze" compound as stainless bolts have a very nasty habit of siezing when you put them together. If this happens you end up with a bolt that isn't tight (might not be even close to snug) and you can't loosen it or tighten it, the only thing you can do is cut it off.

Since you're going to be doing a thru-hull application, I would recommend using the 3M 5200 (I think it's 5200) marine sealant. This stuff is incredible. I used it when I put on my wedge. It takes 48 hours to dry, but when it's dry, it's perminent. It still looks like new 3 years after application. I second the stainless sieze up on the bolts.

Derek - The brackets are made of 11 ga. stainless steel. They are more than sufficiently strong for this. I could probably drive a truck up on them and use them as ramps the way they are now. I do agree that they need to be welded longer along the seam. I just wanted to get them fitted up first in case I had to change anything.

I figured that I would have to use a substantial backing plate. I only wish the transom was completely flat so that I could use one huge plate. The only reason I thought about glassing the bolts in was to make it easier to seal, but I see that it would lead to water getting into the hull. I have a pretty good feeling that the transom will be able to hold the platform if I support the brackets well enough on the inside. I hope to start on it sometime next week. The hard part is going to be moving the gas tank a little to gain access.

Thanks

for those that don't know, 11ga is .1196" thick. i've personally never seen swim pform brackets thinner than about 7ga (3/16"), but a lot of the strength comes from the geometry. i've seen several broken 1/4" aluminum brackets, but these were from fatigue, for which aluminum is no bueno. parking a truck on that bracket is a diff loading situation than it will see as a bracket. the gusset would be in tension under a tire, but in compression as a pform bracket.

i'd suggest thru-bolting with 1/4"+ Al backing plates, and using washers on top (outside) of the brackets. you can use Marine-Tex or some other type of epoxy filler under the plates &/or brackets to create hard, flat, parallel surfaces.

I understand that a truck would be putting the bracket in tension while on a platform would be in compression. I still think that the gussets will be strong enough when I weld them longer along the seam. I am also using three brackets, so the load should be distributed better than if I was using only two like alot of new boats do.