Mounting a pedestal seat on aluminum floor

[ajrunke]

I have a 14' inflatable that I want to replace the bench seats with pedestal seats. Has anyone done this? I assume the way to do it would be to drill holes for the mounting hardware, countersink the bottom of the floor boards a bit to let the head rest inside and push the bolts upward rather than having them sticking down underneath the floorboards.

The aluminum floor boards are about .5" thick. If anyone's done this, please share your process and pics if possible!

Thanks!

[nobrainsd]

The specifics depend on your particular aluminum floor. But the issues remain the same for installing something like a seat pedestal that is going to exert a lot of force on the floor. Most AL floor sections are hollow. The sheets that comprise the floor top and bottom are thin. Countersinking into thin sheets is going to leave little support under the cap screw head. Also, bolting a seat base to the middle of the floor section is going to flex that section under side loads. It is possible to have cap screws and washers under the floor that are covered so they don't wear the underlying material, but I tried something a little different.

On my Zodiac I removed the side caps from the flooring and accessed the hollow floor sections. On some boats these are much smaller sections, but it is still possible to install backing plates. The backing plates only go a few inches in. As you can see in my examples I used a top plate to span the floor for attaching my ski pole. The top plate bolts to the backing plates, which extend all of the way out to the edge of the floor under the cap rails. This effectively extends the assembly so it is captured by the side rails, transferring the stress to the strongest part of the floor.

For my seat bench I skipped the cross top plate and just bolted right into the backing plates in the floor. How crazy you have to get depends on how much you blast around. My rail mounted zodiac bench seats rocked and wore the track. The backing plate installs have been abused for years and haven't moved or deformed the AL floor. The pole mount is very secure and I now have my custom gas tank and battery installed on a top plate installed under my front console bench. Rock solid. Just one way of doing it.

Don't underestimate the leverage a pedestal seat exerts! Good luck.





crossplate.jpgbackingplates.jpgbenchmount.jpg

[ajrunke]

Thanks for the reply, it was insightful. Unfortunately for me, the end caps of the floor boards are riveted on, disallowing easy access the the internal structure...which will also make it incredibly difficult to line up holes for drilling without interfering with the internal structure support.

[nobrainsd]

Since I don't know the specifics of your floor board construction it is hard to say, but I would probably remove the rivets and gain access to the hollow floor sections. My zodiac came with a large bait tank that was just screwed down to the top aluminum sheet. The top sheet was deformed around the holes and had begun to crack. A pedestal seat would really torque on the floor without through bolting! If you do just drill through the floor section it isn't going to be a big deal if you hit one of the inner ribs. You would only be drilling through a small portion of the rib and that shouldn't be a structural issue. If I really couldn't see a way to fasten the pedestal through the floor I would consider adding a base plate of al and bonding it to the floor with something like DEVCON B (like JB Weld but better). Maybe add a couple of screws into the top sheet just for a little mechanical fastening strength too? Good luck with this application and be sure to post up some pics when you decide how you are going to do the install.

[likalar]

Nobrainsd, good post, and great-looking solution.

You stated: "Don't underestimate the leverage a pedestal seat exerts! " Good advise. Taller pedestal=extra leverage. I hate to imagine the mess created when a big guy on tall seat on a bouncy ride rips apart a less-than sturdy installation while underway. Would there be any benefit of also installing AL stiffeners fore/aft, the full length of the floor?
Larry

[nobrainsd]

I haven't had a need to reinforce along the length of the floor. The installs I did effectively key into the locking side rails. I must admit that I was concerned while traveling fast over whitecaps fully loaded, but the side rails held up. I guess at some point if you bolt too much stuff down and have a ton of load it would be better to have a rib?

I could see putting a backing plate on the bottom of the floor, with the through bolts counter sunk into the thicker aluminum and the edges of the plate beveled off so they wouldn't wear the floor material. My hollow floor is pretty sturdy when sandwiched. I don't think you would crush it with a pedestal if the stress was spread out like that.

[jamnn]

I used a piece of 5\8 thick aluminum plate 12'' by the width of the boat. It was expensive but holds my pedestal firm with no stress. Will post pic if you like?

I have added a pic:

pedestal stand on aluminum plate.jpg

[jondavies]

Looks good.

If I were you I'd cut off the excess thread from the bolts and maybe find some rubber caps for the nuts. Stepping on one of those with bare feet could be nasty.

[Peter_C]

Nobrainsd, how did you knock the side of the floor piece off? Was there any set screws or did a hammer and block of wood remove it? I need to mount my electronics tower and am probably going to do something like you did. I just haven't looked yet how to remove the side.

Thanks!

[jamnn]

Looks good.

If I were you I'd cut off the excess thread from the bolts and maybe find some rubber caps for the nuts. Stepping on one of those with bare feet could be nasty.

I have been meaning to do that. It is a big OUCH waiting to happen.

[Peter_C]

Nobrainsd, how did you knock the side of the floor piece off? Was there any set screws or did a hammer and block of wood remove it? I need to mount my electronics tower and am probably going to do something like you did. I just haven't looked yet how to remove the side.

Thanks!

A block of wood and hammer did the trick! Got the base mounted for my electronics tower. Still a ton of work to do...

[ajrunke]

Still haven't gone with this project, yet. I'm figuring out the best way to go here. I don't know that I'd want an aluminum plate across the beam. I was tempted to just try bolting the pedestal stand to the floor with through carriage bolts up from the bottom so the smooth, rounded head is against the material. I understand leverage and all that, but the large base for the pedestal seat seems wide enough and with the structural ribs in the floor, I think is would be enough. However, I don't want to just "attempt" this without more insight.

http://forums.iboats.com/inflatables-ribs/my-new-12-5-ft-sib-w-pictures-424216.html

This is the install I'd like, except he didn't explain how he did it and how it's held up. I'm curious to know, but he hasn't been active for a long time.

Still thinking this one through....

[Drowned Rat]

Better off going with a frame. More pricey but lots better. >

[Pack Rat]

Drowned Rat I've seen those frames from NRS and wondered about them. Price is $570.00

Are they more of a river thing when your primarily using oars?

[Drowned Rat]

I guess you could say that's their primary purpose, but they really work great on SIB's too. All the weight of the passengers and, in this case, the cooler is supported on the tubes and off the floor. It makes for a very smooth ride regardless of the water conditions. They are pricey, but very sturdy and will last forever. I also mount the oarlocks on them and rod holders.

[Pack Rat]

I never thought about the weight on the floor causing stress....hmmmmm.

I'm kind of looking at the frame too for use with the oars in situations I don't want or need a motor running all the time. Do the blue straps go under the boat to the other side?

[ajrunke]

I can't see myself getting a motor anytime soon. All I do is row so maybe the frame would be a better idea...though I'm wondering how is it anymore beneficial that the aluminum bench seats that already hook to the tubes? I could just mount a seat to that.

[Drowned Rat]

I never thought about the weight on the floor causing stress....hmmmmm.

I'm kind of looking at the frame too for use with the oars in situations I don't want or need a motor running all the time. Do the blue straps go under the boat to the other side?

The straps just go to D rings that I glued to the tubes. Also got them from NRS.

[Drowned Rat]

I can't see myself getting a motor anytime soon. All I do is row so maybe the frame would be a better idea...though I'm wondering how is it anymore beneficial that the aluminum bench seats that already hook to the tubes? I could just mount a seat to that.

Yeah, you could sure do that, I've seen it done before with the cheapie seats from Wal Mart and it worked just fine. As long as you have the oar locks already on your boat, you should be good.

[jamnn]

I guess you could say that's their primary purpose, but they really work great on SIB's too. All the weight of the passengers and, in this case, the cooler is supported on the tubes and off the floor. It makes for a very smooth ride regardless of the water conditions. They are pricey, but very sturdy and will last forever. I also mount the oarlocks on them and rod holders.

That is a really cool looking setup. You say it provides for a smooth ride? I find sitting on the tubes much rougher that a pedestal mounted chair.

[Drowned Rat]

Yes, if you're just sitting by yourself on the tubes without a frame, you can get bounced around quite a bit. But my set up you have several hundred pounds of weight spread over a dozen linear feet of tube. Even in rough water, you barely move. Often times I'll notice the floor heaving in moderate chop or wakes and seated on the chair, you're rock solid.