Tufnel or Polypropylene Backing Blocks

[Little Dorrit]

I'm looking at fitting some yacht legs. Instead of marine ply I planed to use Tufnel (after some advice on other threads about the same subject). However, would there be any real benefit of this material over Polypropylene as an internal backing plate to support the hull fittings?

 

[Tranona]

Are you going to glass them in or just use them like a large washer? If glassing them in then ply will be fine and you can taper them to spread the load. Line the hole with epoxy and they effectively become part of the hull.

 

[thinwater]

Why do we waste time and effort rationalizing using materials other than what the boat is made of--fiberglass? Simply get precast fiberglass about 1-bolt diameter thick, grind to match the curve if needed, and bond with thickened epoxy? Taper the edges, no sharp corners (50mm radius), and it will be a part of the boat.

I'm not very familiar with Tufnel, but PE will creep and crack under sustained load. I've seen it and I've tested it. It won't actually be carrying load, it will just look like it is. Same with fender washers.

 

[Kelpie]

I used tufnol when installing my yacht legs. Each block was about 300x150x25mm and I ran it through a table saw to put a bevel on each edge, so it ended being a bit like the shape of a pyramid with almost all of the top chopped off, if that makes sense. I bonded it onto the hull using thickened epoxy, and then epoxied some glass tape over it as well, so it should be pretty solid. I don't believe that polyprop would have allowed adequate adhesion so would be a poorer choice.
If you have good thick topsides you may wish to just treat the backing plate like a big washer, as suggested above. My topsides were pretty thick but for the relatively small cost of the tufnol it seemed the right thing to use.

 

[PetiteFleur]

I like the idea of fibreglassing in a support - this is the best solution but tufnol wilmalso be ok but definitely not polypropilene as it is soft and will probably creep and it is difficult to glue.

 

[Scotty_Tradewind]

Tufnol Whale a great product.
Google it and look for data sheet.

Will not creep or crack and is so dense that tons of weight can be put upon it.

Heavy and expensive for big jobs but a great substitute for small pieces of teak on a boat. imho

S.

 

[doug748]

I don't think it matters too much.

For underwater use Tufnol might have the edge over plywood but it is hard and needs to be more carefully fitted to any curves. For the same reason any knibs of glass need to be faired and, as the surface finish of Tufnol is very smooth, it will have to be distressed for adhesion.

Whatever you choose large purpose made stainless backing plates help spread the load and look much better than washers. I have used marine ply for this job on a couple of boats, it would be my pick.

 

[thinwater]

I don't think it matters too much.

For underwater use Tufnol might have the edge over plywood but it is hard and needs to be more carefully fitted to any curves. For the same reason any knibs of glass need to be faired and, as the surface finish of Tufnol is very smooth, it will have to be distressed for adhesion.

Whatever you choose large purpose made stainless backing plates help spread the load and look much better than washers. I have used marine ply for this job on a couple of boats, it would be my pick.

Regarding irregularities, this is why it is bonded with thickened epoxy; a nice thick bog makes for perfect load distribution, which as Doug points out, matters.

And you still need a backing plate. Although fender washer are a complete waste--what good could something you can bend with pliers do--extra heavy fender washers can be just the ticket. They need to be about 1/3-1/2 bolt diameter thick and at least 5x bolt diameter across.

https://www.boltdepot.com/Product-Details.aspx?product=15891

 

[vyv_cox]

You may have seen the page on fitting Yacht Legs on my website. I used Tufnol for mine, as Scotty says it is a superb engineering material, perfect for the job. A thermoplastic like polypropylene is definitely not as good, strength lower and a tendency to creep under load. Although the loadings on leg supports are far lower than people imagine it is well worth providing enough support in case something goes wrong.

 

[Little Dorrit]

You may have seen the page on fitting Yacht Legs on my website. I used Tufnol for mine, as Scotty says it is a superb engineering material, perfect for the job. A thermoplastic like polypropylene is definitely not as good, strength lower and a tendency to creep under load. Although the loadings on leg supports are far lower than people imagine it is well worth providing enough support in case something goes wrong.

Thanks, I did read the information on your website. My local supplier suggested Polypropylene as an equally good alternative to Tufnol ...but I knew there would be some good advice here! Whale brand seems to be the best (& most expensive) but there are cheaper Tufnol brands some of which are a sandwich made of paper. This is what Scotty_Tradewind used and which you commented on in the Forum thread he started which discusses various other aspects of Yacht Legs. I suppose I was just interested in some general views which I now have. I'm planning on using Sikaflex to 'glue' the Tufnol although I note a few posts have suggested epoxy?

 

[vyv_cox]

Thanks, I did read the information on your website. My local supplier suggested Polypropylene as an equally good alternative to Tufnol ...but I knew there would be some good advice here! Whale brand seems to be the best (& most expensive) but there are cheaper Tufnol brands some of which are a sandwich made of paper. This is what Scotty_Tradewind used and which you commented on in the Forum thread he started which discusses various other aspects of Yacht Legs. I suppose I was just interested in some general views which I now have. I'm planning on using Sikaflex to 'glue' the Tufnol although I note a few posts have suggested epoxy?

I used Sikaflex 291 that I thought would provide a little elasticity if required. Worked well for around 10 years and is still there, although having been based in the Med for 10 years they don't get a lot of use now. Epoxy would probably be OK but I think there might be a risk of cracking in the event of some movement or hull flex.