# Offset Seat Post - More Stress?



## aalbanese102089 (Jun 5, 2017)

So I made my front casting deck this weekend. I put in my seatpost and realized I don't have as much space up front as I thought I would. So I am considering an offset seat post. I was wondering if this would cause anymore stress on the bracket when I sit/lean back? The base secured with machine screws and nuts (6 of them) to 3/4" plywood. Let me know your guys thoughts.

Sorry it's sideways, I don't know what's up with that. I am about 6' 2" and 250lbs


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## Shaugh (Jun 5, 2017)

An offset post will increase the leverage applied to the deck simply because your weight will no longer be directly over the post. Normal sitting and bouncing will always be in a leveraged position. This will cause stress in the joint all the time. The maximum leverage applied by leaning will not increase but the average will significantly. At your weight I'd consider beefing up the floor in that area. maybe a 14" x 1/8" steel plate bolted to the decking between the seat and deck or similar.

Why not just add a strong rectangular plate that allows you to mount the seat overhanging the edge a bit ? Probably be a lot cheaper than one of those posts...


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## richg99 (Jun 5, 2017)

I'm the same size and have the same problem on my 1652 G3. I think Shaugh's suggestion is an excellent one.

Yes, more stress is generated as you cantilever your butt out to one side. Really large flange washers should be added, at the least, IMHO. 

richg99


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## Stumpalump (Jun 5, 2017)

Give it a little time before you decide. You may just get used to it.


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## richg99 (Jun 5, 2017)

fixed

( I am just experimenting with some photos)


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## wmk0002 (Jun 5, 2017)

The applied torque from an offset is called a moment. A moment is defined as force times distance. So in your case M = 250 lbs x 3 in = 750 in lbs or 62.5 ft lbs. 

If you are familiar with torquing fasteners, those torques are fairly significant. Adding something under the wood like suggested would go a long ways towards beefing it up. While I am only 170 lbs, I use a 3 " offset post on my 1648 and it is very solid. Similarly it has 3/4" plywood for decking but it also has a thin sheet of aluminum on top and a slightly thicker one underneath that came factory from Alumacraft. Those not only thicken the area up where the torque is applied which lowers the stress but the aluminum also has stronger material properties which means it can handle higher stress too.


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## hipster dufus (Jun 6, 2017)

i have a curved offset post on the front of my jon. i had to drill and use a clevis pin to keep the seat aligned straight on the post. if i didnt the seat would move in 2 different planes and u were always moving the wrong way when u sat. the only way it moves know is when u move the post.it did free up some room on the front. i had my base rewelded to the deck recently.i dont worry too much ,im a little less then 200#.im in the process of learning to run the tm standing.


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## Shaugh (Jun 6, 2017)

I'd try something like this from 1/4" steel. you'd have the whole floor to stand on if you wanted. most of those offset posts I've seen are only 3"... this would give you 8" or more.


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## aalbanese102089 (Jun 6, 2017)

Shaugh said:


> I'd try something like this from 1/4" steel. you'd have the whole floor to stand on if you wanted. most of those offset posts I've seen are only 3"... this would give you 8" or more.



Thanks for all the replies. Lot of good info.

I actually like this.. but wouldn't it still put a lot of stress on the bracket and the wood underneath?


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## richg99 (Jun 6, 2017)

If one wanted to add some vertical support to that neat extension/addition..I'd think about a simple piece of 4-inch or maybe even 6-inch PVC. Some sort of block, or even a flat PVC cap, might have to be fit under the PVC so as to not dent the deck.

A column such as that should add great strength and take up almost no room.

I am NOT any sort of engineer or have any qualifications to make this recommendation. You are on your own. Ha Ha

richg99


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## Shaugh (Jun 6, 2017)

aalbanese102089 said:


> Shaugh said:
> 
> 
> > I'd try something like this from 1/4" steel. you'd have the whole floor to stand on if you wanted. most of those offset posts I've seen are only 3"... this would give you 8" or more.
> ...


Stress would be minimal because you're only overhanging a few inches. The key is using a very strong plate like 1/4" steel. I would have no doubt about it being adequate. I should have photoshopped it a little wider so the existing square plate would fit inside the round.


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