Pontoon underskin plan

[calvinator]

I'm going to underskin my 30' pontoon w/150HP. I'm fighting water turbulence against my pontoon's crossmembers. Here is my plan.

I am going to buy 48" x 30' roll of HDPE plastic used to cover dock pilings. It is 0.06" thick.
Going to run from bow to stern and attach with stainless self tap screws w/fender washers.
Should be able to underskin for under $200.

I'm going down this path because my pontoon is 1.5 hrs from my house, stored in a parking lot. Not easy to work on. The HDPE should be easy to cut/attache and work with compared to aluminum sheets commonly used for underskin.

I've done some searching and found some threads discussing using HDPE, but I haven't found anyone who actually used it.

Any thoughts out there about my approach? Maybe something I'm not thinking of? THANKS

 

[Bob_VT]

While that sounds "not too bad" to try have you considered saving your pennies and adding a 3rd toon??

 

[Scott Danforth]

I would go with thicker HDPE. 0.060 is quite thin, and the forces from the waves may eventually tear the material. do they offer 0.093"

we underskinned a friends pontoon with multi-wall polycarbonate, and even that after a while started breaking loose around the fasteners. It took a few years, however constant pounding did take its toll

 

[calvinator]

While that sounds "not too bad" to try have you considered saving your pennies and adding a 3rd toon??

3rd toon is nice to have category. I'm up for the challenge, but many hurdles:

a) no toons close by me - mid-Ohio. Everything is a 2 day trip away.
b) my toon is in a storage lot on cinder blocks 1.5 hrs away. Installing the 3rd toon inconvienent.
c) I don't have a trailer --- marina puts me in and out for $100/yr. They only have a scissor trailer and not compatible with 3rd toon.
d) Adding a 3rd toon means I have more $$$ into the pontoon than it is worth. Darnit!

 

[Grandad]

Unless aluminum is not do-able, I think it would be a better choice than plastic. I like plastics in a marine environment, but it has a high coefficient of expansion compared to the existing aluminum and plywood deck. Over large areas, it may buckle badly when warm and shrink dramatically in winter, so maintaining fasteners may be a headache, even if the sheets don't break. I did a quick google and found on this site http://www2.ulprospector.com/pm/HDPE.asp that they consider HDPE to have "High thermal expansion, Poor weathering resistance, Subject to stress cracking". My opinion is not at all expert, but I'd do a lot of investigation before investing a lot of energy in plastic of any type for this purpose. - Grandad

 

[steelespike]

If you look closely at the fender washers one side has a crisp edge that may cut the plastic the other side is more rounded somewhat less likely to cut.
Also perhaps you could use 2 or 3 layers of the plastic to serve as a cushion for the fender washer.

 

[ahicks]

The expansion/contraction thing is a good thought. A 12' section of plastic siding moves almost half an inch in the midwest. To fight it, you might consider installing the plastic in 4' strips running side to side?

 

[cemcrae53]

This plastic should work fine if you install across pontoon with joints on floor members installed back to front to keep water from stressing joints.Also I would recommend using stainless steel pop rivets to allow movement and stop screws from vibrating out in time. Just install with #8 self tapping screws and replace with rivets when done. They will fit right in holes made by screws.

 

[calvinator]

Thanks for the feedback!!! I'm still heading down this path....BTW, some great youtube videos showing the water turbulence under the pontoon boat. My take is under 15mph that water is pretty calm, but beyond that --- lots of turbulence ! ! !

I'm also thinking I'll use some aluminum flatbar as edge protection on the front and maybe middle sides of underskin. In the middle section of the pontoon, I might add some furring strips to reinforce the hdpe. Those youtube videos really show how & where the water hits the underdeck!!!