Seat wore a hole through kayak hull

-- Last Updated: Jul-31-11 7:15 PM EST --

I need to reinstall the seat in my Azul, fiberglass, kayak. When I removed the seat, I discovered the seat had been in contact with the bottom of the boat and it wore a hole through the fiberglass and actually had made some pinholes all the way through the gel coat. So, my question is, how can I make sure that doesn't happen again?

Lacking any better idea, I should probably ensure there is foam under the seat to support it, and that the foam is securely attached.


seat gasket

– Last Updated: Jul-31-11 7:47 PM EST –

Most hard seats are suspended off the bottom. Since you have to repair the bottom of the hull, I would add another layer of glass too. Then you would use a rubber gasket material like an auto floor matt or something like that. Foam is too weak.

Talking with a kayak rental company
they told me that’s the place that always wears out first. His #1 suggestion was to always rinse away all the sand and debris from underneath the seat.

wear and cracks
wearing of the hull from the seat rubbing against it is not uncommon. Most suspended seats come from factory with a weak layer of compressible foam that after a short time wears through.

I had the same problem with several kayaks of mine.

To aggravate the situation most suspended seats swing when the kayak is used in textured water or when rolling. My seats usually cracked where suspended against the coaming/cheekplates.

The really best solution is to anchor the seat to the bottom of the kayak.

Some manufacturers provide a fastener to secure the seat to the hull (Tahe for example:

I anchor my seats with a thick layer of polyurethane goop. I remove the seat, clean the area, apply polyurethane from a caulking gun (nice an thick), slump the seat into the goop and secure it with fasteners.

If one day I have to remove the seat I use a thin blade to cut through the goop under the seat.

What is polyurethane goop?
I see it sold as caulk, such as Dap 18810 Poly Adhesive Sealant. Do you just go to the hardware mega stores and look for a tube that says poly? Also, is the expanding foam stuff polyurethane?

The expansive power of that foam stuff scares me. Get too much of it in the spot you are trying to seal and it is going to bend whatever it is you are working on.

I like the idea of something permanent that fixes the seat in place and prevents sand from getting in there to form a grinding machine. The poly products claim to be highly adhesive, so I guess that will do it.


Gooping the seat to the bottom is
OK for sea kayaks, but if it were done with a composite ww kayak (not many around anymore, but I have one) then the hull would wear faster from the outside, because the hull would not be able to flex away from rocks and ledges. Another issue is that if damage to the hull, under the seat, does occur, a repair would best be made from inside, but the seat and goop would be in the way.

OK, to be specific I use Sikaflex polyurethane.

It comes in tubes with a nozzle that insert into a caulking gun. It looks similar to silicon but it will not contaminate the laminate the way silicon does. Clean up is done with methilated spirits (alcohol) and the stuff is paintable.

I have used before the two component expanding foam (also polyurethane) but with limited success.

The seat eventually became wobbly again.

Sikaflex polyurethane sets much harder, kind of like soft rubber, sticks like the proverbial sh*t to a blanket (keep that roll of kitchen absorbent paper handy) and is salt water resistant (very).

Relative motion + sand = wear
You want something that fully contacts both seat and hull, and is attached to both.

Copious amounts of goo might do. But it seems messy.

A few pucks of foam, a little time spent making them fit nicely against the surfaces and some contact cement will be cheaper, lighter and easier to remove and re-do should the need ever arise.

Chip why wouldn’t you just put on …
… a sacrificel layer of some hard materiel .

How about a piece of laminate (countertop lam) , or anything that’s hard and smooth . And shouldn’t you ought to put one on each side . Looks like the other side has some wear indication also , just not as advanced .

What Worked for Me… So Far
I found a little pointy piece of plastic on the bottom of my seat that wore the hole. I filed it down. I went a little ‘overkill’ on the fiberglass repair, then I put some foam barrier in place.

Sacrificial Layer
I don’t know of any material that will stand up over time to grinding with sand. Stainless steel might last for a long while, but eventually, it will grind away, too.

Two approaches make sense to me:

  1. ensure there is some separation between the hull and the seat. Leaving a gap will prevent the surface-to-surface grinding.
  2. fix the seat to the bottom, eliminating motion between the seat and the hull, and preventing sand from getting in the junction between the seat and the hull. If the seat is fixed to the hull, there is no motion to drive the grinder, and if there is no space between the seat and the hull (because it is filled with polyurethane), then sand can’t get in the joint.


They didn’t have Sika in the local HW store. I bought a tube of Locktite Polyurethane. I hope it works more or less the same.

I believe I read you also use polyurethane to glue the wire runs to the hull. Same stuff? Do you tape the wires down while the polyurethane sets up?

Lexel sealant seems similar, but nowhere on the Lexel label doe it say it is polyurethane. Are the products interchangeable?


oh I don’t know about that Chip …
… countertop laminate is pretty hard stuff and it’s thin . Should be able to be epoxied right over the wear spots after your patch work is complete .

Somewhere around here I have various scrapes of white laminate , you can have some if you want it . You could try sanding through a piece to see if it’s tuff enough for you .

Also have some sausage tubes of Sikaflex that will never get used , med. beige color , you can have one of those too if you want . A sausage tube is way more than you need but you can throw away what’s left over , or not .

Let me know and I’ll see they get droped off if you want them .

PolyU pillars
After reinstalling the seat on top of the block of foam that had been floating around, loose, under the seat, I was surprised at how much space there was between the seat and the rub spots on the hull. The foam piece is now fastened down with contact cement. The distended bolt hole in the seat hanger was filled with epoxy and redrilled. The butt cheek pans are a half inch off the hull.

I formed loops of 0.75" foam rope that were about four inches diameter and positioned them under the seat and over the wear spots. I drilled a pair of holes in each cheek pan above the wear spots. I injected polyurethane caulk into one hole until it started coming out the second hole. The foam rope loops were intended to keep the caulk from running all over the place. So, I should have a pillar of caulk under each cheek pan.

My hope is that the caulk will support the seat pan and prevent the accumulation of sand on the wear spots. It is also my hope that I don’t have to take the seat pan out again.

When the boat was new there was a seat cushion of half-inch foam poorly glued to the seat. I astounded myself by finding this piece of foam where it had been tossed in a corner of the garage about five years ago. This was handy, because I contact-cemented it onto the seat pan, covering up the four holes I drilled in the seat pan. So, cosmetically, the seat reinstall looks good. Now, I will just hope it all holds together per plan and I avoid rubbing another hole in the hull!

Time to paddle the boat and find out what happens.

Thanks for the thoughts and suggestions.


Lexel is not
Lexel is not that popular here Downunder (I don’t know where I could get it) but I don’t think it’s the same stuff; poly being more rubber like.

I use poly for adhering wires to the inside of the deck, among other things. I suspend the kayak upside down from the ceiling when working inside on the underdeck. I temporarily secure the wires with masking tape til the poly cures.

that repair
that repair you did seems really sound and solid.

If you have to take the seat out one day just grab a hacksaw blade, wrap one end with a rag so you don’t cut your hand and slide it under the seat to cut the poly. A minute later the seat will be free.

Securing the seat to the hull will prevent the seat from wearing larger holes where fastened to the sides and might also prevent possible cracks in the corners of the seat. No swinging, no damage.