Man made material

I have a fiberglass work skiff whose hull is in very good condition however the deck and ribs are rotted beyond a bandaid and require replacement. The deck will be 3/4 ply covered with polyester resin and fiberglass. I would like to use something other than wood for the ribs. The current ribs (10) are 3/4 ply. What would be a good substitute that would handle heavy loads? I have read recently of entire work skiffs made from PVC sheet. Any suggestions?

 

Would this be what you're looking for?

http://youtu.be/UcBdvChtQkU

 

take a look at these folks; available in densities greater than oak.http://precisionboard.com

 

Why use polyester if you are going to go to all that trouble and money?

Use Epoxy.

 

Welcome to the Forum.

Ply is a poor rib material and tbh should not have been used in the original build if just supporting the deck loads. Better would be to replace the ribs with q/sawn Doug Fir or similar epoxy coated and maybe glass sheathed. The deck could again be poor quality ply or badly sheathed/sealed. There are a number of solutions, but I must emphasise that ply should be completely sealed prior to glassing, not laid up with dry glass on top and then roll the resin on. Near all failures of this type of build are down to poor/cheap ply and poor build practice. Epoxy is better for long term sealing and waterproofing but more expensive, and cure cycles are generally a bit longer. Fortunately there are no real issues mixing polyester and epoxy systems.

There are foam cored alternatives for the deck but it may depend on who is doing the work? and/or the facilities available. I'm sure PAR will be along soon, to fill you in further, and he will give you good advice.

 

If you are going to use wood in one area you might as well use wood in the rest of it too.

Wood is both good and bad in a boat like this, it's low in cost, locally available, easy to work with, strong, and can last a very long time when used and installed correctly. The down side is that it will eventually rot if any water happens to find it's way to the wood, it doesn't make a difference which type of resin is used, if water finds the wood, it will rot.

How long do you plan to use the skiff? Wood will typically last 10+ years even when installed poorly.

There are several options other than wood, the problem is the cost and availability of these products tends to prevent the DIY owner of a small low cost boat from using them, a sheet or two can easily exceed the value of the boat.

Hollow stringers work well, or just over build the stringer with glass so when the wood rots away it is still strong enough to carry the load.

 

Go to the www.seahorsemarine.co.uk site to see good strong boats built from HDPE they have built these boats since 1996 many fisherman use them and have boats over 20 years old and still in use no maintenance needed.

 

Trying to incorporate PVC sheets in this build would be difficult, and probably not that productive, PVC foam yes, solid sheets, not so much. There are PVC bonding resins, and it won't rot, but.....

 

As to the ribs & beams, as long as you're working with epoxy, it'd be easier by far, to simply get/make some half-round or hat sections & glass several layers of tape reinforcement overtop of them, than to laboriously fit new ribs (which will be getting glassed anyway).
Kind of akin to carbon capping stringers, only in this case, whatever you use for a "stringer" wouldn't be a structural material, nor necessarily load bearing. All of that would fall to the reinforcing layers which you glass overtop.

There are a whole variety of materials from which to choose from to use underneath of the glass, in lieu of ribs, which are easy to work with.
Anything from; foam, to balsa, or even half rounds of hose. If memory serves, there's a broad selection listed in the book "On Boat Construction". Which is available for free download at the WEST System site, in addition to all of their user guides.
All of which have loads of info which may prove helpful in your restoration project.

 

Try using HDPE... Go to the www.seahorsemarine.co.uk site to see good strong boats built from HDPE they have built these boats since 1996 many fisherman use them and have boats over 20 years old and still in use no maintenance needed.

 

Thanks Ian. I would like to be clear in my mind about bonding HDPE to an existing GRP structure. Are you saying it can be bonded successfully to wood/FRP/GRP/Al/steel, as opposed to welded integrallly as would appear to be the case with the Seahorse Marine boats?. Nice work on the designs and craft btw.

 

If weight or dimensions are an issue, the strength/weight and strength/volume of hard woods are better than thermoplastics or hard foams. As suggested, sandwich construction is one way to equal or exceed original wood physical properties.

Dino