Dynel

Back in the day, this stuff was the ultimate for wear resistance. What is current thinking?

 

Some opinions and answers here - albeit from 16 years ago, but I doubt that much has changed re popular opinion during this time.
Dynel vs. Fiberglass - as wood strip sheathing https://www.boatdesign.net/threads/dynel-vs-fiberglass-as-wood-strip-sheathing.3430/

And from 2009 -
Can the Dynel fabric used instead of fiberglass? http://forum.woodenboat.com/showthread.php?92931-Can-the-Dynel-fabric-used-instead-of-fiberglass

 

It would never occur to me to substitute dynel for glass in this instance, although Lindsey Lord certainly would have. I'm just thinking of a final surface on the glass, because I expect to land on rocky beaches regularly.

One of the threads you provided, Bajansailor, mentioned better materials than dynel for abrasion resistance. What would those be.

 

Xynole, apparently.

 

Actually testing shows them both to be pretty equivalent.

Well, the Xynole salesman was pretty adamant that xynole was better. But then the Chevrolet salesman did say that Chevy is better than Ford.

 

Would you consider sacrificial rub strakes along the two hull bottoms in place of any exotic material and simply stick with epoxyfiber?

 

At canoe speeds, yes. Maybe at sea sled speeds. I'm not a good enough NA... Actually, yes. There's not going to be any spanwise flow across the forward chine, that's for sure. So yes, I think that's a great idea.

 

One of the comments in my links suggested that you could put a layer of dynel over the glass for better resistance?

I am thinking that the areas of your hull that will be 'taking the most licks' (as we would say here) will be in way of the keels (I think you will effectively have two in the forebody?) - so would it be feasible to put some extra layers of sacrificial glass in the areas where they will come into contact with the shoreline?

 

I would suggest below canoe speeds for beaching.

Bajansailor makes a good point, beefing up the keel bottoms in the bow instead of sacrificial rub rails.

 

Yes to the first. Very precise testing at the west system lab showed that Dynel had 4 times the abrasion resistance of glass and epoxy.

If I'm putting sacrificial material forward, I may just use long strips o f high density polyethylene

 

Extra glass forward would grind off very quickly.

 

Not if they're Xynole.

 

Is there a 'flat' already on the base of your keels up forward? Or is it a 'vee' shape?
If a flat, then strips of polythene sound good - in the past I have used this stuff (we would call it Umpey for short) - they say it has very good abrasion resistance.
Ultra-high-molecular-weight polyethylene - Wikipedia https://en.wikipedia.org/wiki/Ultra-high-molecular-weight_polyethylene

You would have to bolt them on though, as I doubt that anything will bond to Umpey. And have the bolt heads recessed to allow for wear.

One advantage of having a flat on the bottom is that the stress (force / area) is much less compared to a vee shaped bottom as there is so much more surface area to take the impacts.
The cat in my avatar has 10 mm thick (and 100 mm wide) aluminium keel plates for beaching - she was built almost 20 years ago, and they still have a LONG way to go before these keel plates will be worn down.
In contrast, another aluminium cat here with vee shaped keels (a pontoon boat) has been needing to have new sacrificial strips welded on every 4 or 5 months. Next time they haul her out they are going to slice off all the previous repairs and weld in flat bars instead which should last much longer.

 

I was just thinking exactly that. That I should cut off the sharp apex of the chines with a recip saw, and leave a flat. Then bolt on hdp blocks, and form them.

 

An interesting post by PAR from another forum in 2009:

"Kevlar has several things that make it not the best choice for abrasion resistance.

Epoxy coatings alone don't offer much protection from abrasion. It doesn't take much before you're through the epoxy and into the wood.

'Glass cloth increases abrasion protection substantially. If you want to have a natural wood finish visible, then 4 ounce or light fabric. 6 ounce fabric is just barely visible, if the light catches it right. The heavier the fabric, the better the protection and the less transparent.

Dynel Is a polyester fabric that is 3 times more abrasion resistant then regular 'glass cloth. It's not going to permit you to have a natural wood finish, as it dries with a cloudy look. It requires a lot more resin to wetout and can be a pain in the butt to apply if you've used too much resin (it floats). Dynel is about 15 to 20% more costly, but a far better product for the bottom of boats.

Xynole, is a modified acrylic fabric and about 6 times more abrasion resistant then regular 'glass. It isn't cheap, also needs lots of resin but out performs most other fabrics. It too will not permit clear finishes and can be difficult for the novice to apply, but performance of this stuff is well accepted.

Kevlar is a difficult fabric to recommend on home built craft. It has some wonderful qualities, but also has some butt kicking draw backs, cost not considered. It is self abating on flexible structures and frankly I wouldn't recommend it for any home built boat."