Help me extend my seat base (make it taller)

Evan B

Evan B

Bobber Downey Jr.
Staff member
Admin
In my ocean boat, I have a captain's seat on a swivel base. It has this pipe here that fits into the bottom of the seat. Problem is, it's too short (actually, it's me that's too short). I want to make it taller without buying an entirely new seat base for hundreds of dollars.

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I have a second seat from the boat I removed with another section of that pipe, so I was going to cut a 6" section off of that. So I need to find a way to securely couple it to the base I'm using.

Was going to maybe try ordering this here. Possibly fit it into the base end and pop a rivet or two into it so it doesn't slide up and down? Use this as a coupler for the two sections of seat base pipe.
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(I'd need the 2.25" one)


While I've done a lot of fiberglass, wood, paint, electrical and HDPE work on my boats, I've not done much of anything with metal. So want to see if anyone smarter than me has better ideas on how to make this extension work and be secure.
 
Seems like a good plan, four rivets on each side of the joint, it should be plenty secure.

I don’t see what the wall thickness is on the piece of tube from Amazon. I would think intercooler pipe would be quite thin. Looks like current pipe is around 1/8”

A taller pedestal will put more torque on the base…. Something to keep an eye on.
 
Walove said:
Seems like a good plan, four rivets on each side of the joint, it should be plenty secure.

I don’t see what the wall thickness is on the piece of tube from Amazon. I would think intercooler pipe would be quite thin. Looks like current pipe is around 1/8”

A taller pedestal will put more torque on the base…. Something to keep an eye on.
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Yeah I had thought about the torque issue as well. I think I'll be reinforcing the floor around it with a piece of HDPE. I also have SOME access to the underside if I go through the cuddy. I may add a layer underneath as well.
 
I think your plan for the splice is good. My only worry would be getting the splice pipe to have a snug fit into your existing pipes. From your photo it looks like the OD is 2.75 + 1/16" or 1/32", with ~1/8" wall thickness. Do you have calipers and can get a solid accurate measurement of the ID of your pipes? Then select a splice pipe with that OD, or just a hair less so it can slide in with minimal slop.

I can't tell if the Amazon tubes are sized by the OD or ID. If the Amazon tubes won't work, you could try onlinemetals.com, I have bought a lot of metal for projects from them, and they have a good variety of shapes and sizes. I'm sure it will cost more than the Amazon pipe though. Update: I just checked and they want a crazy amount for their aluminum tubes.

If you can't find an appropriately sized aluminum tube for a reasonable $$$, you could try Schedule 80 PVC or conduit. The advantage of that is you could hand sand it down if you needed to fine tune the fit. If the fit is snug and has good extension into each side (~6+"), I would think it should be strong enough.

Just my $.02. Good luck and let us know how it goes!
 
Merle said:
I think your plan for the splice is good. My only worry would be getting the splice pipe to have a snug fit into your existing pipes. From your photo it looks like the OD is 2.75 + 1/16" or 1/32", with ~1/8" wall thickness. Do you have calipers and can get a solid accurate measurement of the ID of your pipes? Then select a splice pipe with that OD, or just a hair less so it can slide in with minimal slop.

I can't tell if the Amazon tubes are sized by the OD or ID. If the Amazon tubes won't work, you could try onlinemetals.com, I have bought a lot of metal for projects from them, and they have a good variety of shapes and sizes. I'm sure it will cost more than the Amazon pipe though. Update: I just checked and they want a crazy amount for their aluminum tubes.

If you can't find an appropriately sized aluminum tube for a reasonable $$$, you could try Schedule 80 PVC or conduit. The advantage of that is you could hand sand it down if you needed to fine tune the fit. If the fit is snug and has good extension into each side (~6+"), I would think it should be strong enough.

Just my $.02. Good luck and let us know how it goes!
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The PVC is a really good idea. May go that route if this Amazon tube doesn't fit quite right.
 
Wetswinger said:
You could epoxy the sleeve into the pipes to take up slack. After it dries you could use self tapping screws to secure it.
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I do have epoxy on-hand. I'd like to think enough rivets would secure it, but when jostling around on an ocean commute, any extra security would be welcome
 
I would sleeve it, drill it and run a 3" stainless bolt all the way through it with a stainless lock nut. One on the lower portion and one on the upper. I wouldn't risk PVC, rivets, epoxy or self tapping screws.

You're going to want a thicker wall than that aluminum above, looks like it's only .071" thick. I'd go 1/8" (.125)


If you can find a fab shop nearby that welds aluminum it wouldn't cost much to get it welded up solidly with the piece from the second seat.
 
Modest_Man said:
I would sleeve it, drill it and run a 3" stainless bolt all the way through it with a stainless lock nut. One on the lower portion and one on the upper. I wouldn't risk PVC, rivets, epoxy or self tapping screws.

If you can find a fab shop nearby that welds aluminum it wouldn't cost much to get it welded up solidly with the piece from the second seat.
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I do like this through bolt idea. That's probably what I'll do. If it doesn't feel secure with the inner sleeve only, I'll see if I can fit an outer sleeve as well for reinforcement.
 
Fourbtgait said:
If you’re only raising it 6”, take the base off the deck, build a structural deck riser from marine plywood and epoxy, screw the base to it.
Could extend the front edge to rest your feet on if needed.
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I'd also thought about that. But marine plywood is spendy. I do have a lot of other plywood, but at 3/4" thick, I'd have to cut and laminate a lot of pieces together. It was my "backup" plan if this splice one doesn't work out.

I'd also thought about doing something with plywood on top of 2x4 or other type lumber bolted to the floor as a base.

Edit: The more I think about it, the more I think the 2x4+plywood base should be my first attempt. I have plenty of penetrating epoxy, too.
 
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Why laminate?
So use an exterior/waterproof glue doug fir plywood, encapsulated in epoxy.
I built a seat base for a pram, it was 10” tall.
Think a pyramid cut off flat, top built up to 1 1/2” for bolt strength.
An epoxy fillet on the insides for strength with a 2” wide 6 oz cloth over.
Round exterior corners, install 6 oz cloth.
Fillets inside and out to deck, 2” wide cloth.
Cut a hand hole on front or back to facilitate working inside.
 
Fourbtgait said:
Why laminate?
So use an exterior/waterproof glue doug fir plywood, encapsulated in epoxy.
I built a seat base for a pram, it was 10” tall.
Think a pyramid cut off flat, top built up to 1 1/2” for bolt strength.
An epoxy fillet on the insides for strength with a 2” wide 6 oz cloth over.
Round exterior corners, install 6 oz cloth.
Fillets inside and out to deck, 2” wide cloth.
Cut a hand hole on front or back to facilitate working inside.
Click to expand...
You're vastly overestimating the effort I want to put into this 😂

(edit: but this is likely pretty close to what I'm going to do)
 
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Because I'm simple minded I would first try to find a suitable pipe to insert all the way to the bottom of the existing riser, leaving your 6 inches of additional height sticking out. If that proved to be acceptable, a pair of cross bolts at right angles should secure it in place. Pieces of plastic carpenter shims tightly inserted between the inner shaft and outer sleeve should eliminate rattling. Before final assembly I would place something in the bottom of the existing riser to cushion the bottom of the insert to prevent wear on the deck. Elegant? No. Functional? Probably.
 
Kilchis said:
Because I'm simple minded I would first try to find a suitable pipe to insert all the way to the bottom of the existing riser, leaving your 6 inches of additional height sticking out. If that proved to be acceptable, a pair of cross bolts at right angles should secure it in place. Pieces of plastic carpenter shims tightly inserted between the inner shaft and outer sleeve should eliminate rattling. Before final assembly I would place something in the bottom of the existing riser to cushion the bottom of the insert to prevent wear on the deck. Elegant? No. Functional? Probably.
Click to expand...
That's a good thought as well. I haven't begun my carpentry work yet so may consider it. If I do just end up extending the pipe, I will likely also do something on the floor itself for reinforcement.
 
As much as I'd like to avoid doing actual work due to time constraints, I can't seem to locate a pipe that will fit snug enough for me to want to try it. I can find 2.25" OD pipe, but it really needs to be more like 2 3/8," so may just opt for the new base build up. I'm sure I'll change my mind a half dozen more times.
 
2" schedule 40 CS pipe has a 2.375"/2-3/8" outside diameter.
 
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