Polyester vs Nylon

[FloatingBear]

Jeff in your U-Tube Tuff Boat vids were those boats covered in nylon or polyester and what weight fabric was it? I undrstand that nylon has more stretch than poly but is the puncture resistance simular with your 8oz poly cloth compared to a similar weight nylon?

[Kudzu]

Nylon will always be more puncture resistant because is stretches. That is what keeps in from puncturing.

Videos were nylon boats, just happened to be what I had needing repairs in the shop. Polyester will take hammer blows the same, but not the sharp claw end. I expect it would puncture polyester.

But keep in mind that you will hit anything anywhere near that hard paddling flat water. Nylon is tougher but polyester is tough enough for normal use. Abrasion is what you should worry about, not punctures.

[FloatingBear]

Thanks! When I get through with my current pirogue project and get my frame built I'll get the pollyester and thread ordered for my next boat.

[Dave Lowry]

Hi Jeff, I am just starting out on my first SOF boat build. I guess the nylon vs poly is a common point of discussion for first time builders. Would you say that poly would be tough enough to go over a sharp submerged branch on a fallen tree? I love the tight look of your poly covered boats but worry about major tears. What about dogs in poly boats?

Also, If I try one covering, I suppose I could always change it if I did not like it. How much does it cost for 16' for the fabric? (I am going to see if you sell it right now)

Thanks,

Dave.

[Kudzu]

Hi Jeff, I am just starting out on my first SOF boat build. I guess the nylon vs poly is a common point of discussion for first time builders. Would you say that poly would be tough enough to go over a sharp submerged branch on a fallen tree?

Very common questions. Everyone is convinced it will rip easily but it is not the case.

I run over trees, rocks, limbs and mystery objects all the time. It takes something very sharp, like metal or extremely sharp rock, like flint to do an damage. I don't paddle salt water but I understand oyster beds are really sharp and can damage a boat. I don't know that for a fact of course. The most common damage is done from abrasion, like beaching a boat without a rub strip. That will run a hole eventually. I have not had a single client tell me to ripping a skin. I have had 2 or 3 that didn't listen and rubbed holes in the bow by beaching the boat on concrete ramps.

The only boat skin I ever damaged was on a flowing shallow creek where I should not have been. Lots of abrasion and with the speed of water pushing the boat I did manage to tear one a something really sharp in the water. But these boats are not intended to be used there.

[Dave Lowry]

Thanks Jeff, I will go with polyester. How much strength does the covering give? I would think a whole lot. Just wondering about the Geo boats using diagonal Kevlar thread to add stiffness to the boat. I guess the idea there is to give a tensioned truss kid of strength.

[Hirilonde]

I wouldn't think the skin gives the boat all that much strength. It probably gives some additional resistance to the hull twisting or otherwise distorting in shape. But as it isn't very tight it would not take up much load until stretched more from the distortion which is unlikely to happen due to the strength of the frame.

I suppose you could place a completed frame and a finished boat of the same design between 2 saw horses and add bricks to the center until both broke and compare But seriously, I think the frame alone does not flex enough to transfer much load to the skin under any facsimile of realistic conditions, even big waves head on.

[Kudzu]

There is a noticeable difference in a frame stiffness with the skin on vs of on most frames. But translating that to strength would be hard. Impact will collapse the frame and the skin provides no strength there that I can see. It probably provides some from forces inside the boat pushing on the frame. But I don't have any way to test that that.

My boats are much difference than Plat's Geodesic designs. Without the Kevlar roving I suspect his frames would collapse. From what I understand they are dependent on Kevlar for structural strength and mine are self supporting. Plat's boats use aircraft Dacron which is rather fragile. I use a much heavier fabric that is much more durable. Not saying his are bad designs, just that they are very different and comparing the two is like comparing apples and oranges.

Everyone worries but the designs works. Don't over think it. I have all ready done that for you.

[FloatingBear]

Plat's boats are what 4oz fabric?

Jeff I lnow you have mentioned it recently or I've seen it in one of your videos but what do you and the bunch like to use as rub strips? I remember someone mentioning those cheap cutting boards and cutting them into strips.

[Kudzu]

The heaviest Aircraft polyester I have seen is 3.2 oz of something like that. I have never seen a 4 oz.

I used wood for a long time for rub strips, they just get beat up and looking bad. Nylon(?) cutting boards are ugly but they are VERY durable. So I use those and gripe about the way they look.

[woodman]

There is a noticeable difference in a frame stiffness with the skin on vs of on most frames.

I notice a big difference...I was going to show a few people a kayak before the skinning.... my last build a 17'X22'' ....With the frame all ready for fabric I straped it to my trailer, which has the supports 7 foot appart......Their was so much flex at both ends of the frame I didn't chance it...

[Dave Lowry]

I notice that people leave the lashings exposed on the outside of the frame. I guess this would be visible through the fabric covering. Have you ever seen anyone come up with a way to hide this?

[P Doug (WA)]

Paint the kayak.

[Ward]

Just returned from three months in Minnesota, the land of 10,000 lakes. Castaway was covered in polyester/dacron in whatever weight Jeff shipped me. I stumbled on some 1/2" screen door plastic trim at the Home Depot which I used as rub rail on the bow. Now that I'm home will add it to the stern. Lakes up there had lots of stiff plants sticks and other things that made me a bit nervous going out in a skin boat. Often launched on rocky bottom and because of Castaway beam can't straddle to get in the kayak so had a number of scrapes on the bottom. Dropped the boat twice putting it back on the car. I truly mistreated this kayak and the worst I could show for it was a bit of seepage of about a cup and a half after 4 hours of paddling. I repainted the bottom, Rustoleum, after 2 months which was purely for piece of mind. The seepage I had was easily cleared with a sponge. I am convinced that these boats can take a real beating and am comfortable with going just about anywhere with the polyester skin. One other little note. The Castaway was washed with a auto wash and wax product. Love this boat!

[Kudzu]

No, I didn't pay Ward to say that.

[woodman]

Good write up Ward I second that.....

I have bought so much fabric from Jeff this year..let's see..I think 6 boats worth so far....I have 2 cedar boats hanging from the garage ceiling which very rarely see the water...

Their is a group of locals around here that race MO.340 etc. their are a lot of surf skies etc......I'de like to get some of these locals into building their own boats...Wonder if anyone has built a sof surf ski?

http://www.rivermiles.com/forum/YaBB.pl

[DURRETTD]

I've been toying with the idea of building a sit-on-top/surfski SOF.

As step one of the process, I built a SOF with a thin plywood skin from the front of the cockpit to aft of a hatch behind the cockpit. The ply made mounting the hatch and cockpit rim simple. It also provides a rigid surface for supporting the boat on roof racks. I stapled the skin in place around the area to be covered by the ply - wrapped around the inside of the gunwales and the frames - then mounted the ply with screws and caulking after painting the skin.

The challenge appears to be getting a self-draining cockpit attached to the frame. It should be doable using 1/4 inch (or thinner) plywood stitched together and glassed. Could you lay up a glass cockpit using a sit-on-top kayak as a female mold? The drains would have to be attached at the low point of the cockpit and run through flex tubing to through-hulls. Could you glue small plywood pads to the skin to accept the through-hulls? Would the weight of the cockpit make the boat unacceptably heavy? Wound the height of the cockpit required to make it self draining and the height required to provide clearance between the drains and the skin make the boat unacceptably tender?

One of Jeff's longer designs should make a good starting point for the hull. Any ideas, suggestions, or experience to support taking this to the next step?

Dan

[Kudzu]

Would love to see photos of you have so far.

A surf ski is possible but I think if you are a serious enough racer to justify a surf ski, you would be better off with a real one. The designers have spend a lot of money wringing out ever bit of performance possible from them. I doubt you could ever get close and I think when you start talking about racing there are some drawbacks with a SOF surf ski. Prices are high but there isn't much weight savings to be had over a composite ski.

Now if you just want one and want to build one, that is another matter. But for me it's like racing. It sucks the fun out of kayaking. Trying to build a Surfski style boat would suck the simplicity out of these boats. You talking fiberglassing plywood and that is something I was getting away from with these boats.

What you have mentioned seems doable, but I don't see any gain using an existing design. Skis are narrow, long and wildly unstable boats.If your going to go to all that effort you should start with a better hull design. An no, I don't know of one.

Another concept would be start with something like Sling Shot. Adapt it to an large open cockpit and stuff the ends with float bags to keep the water out. Draining the cockpit is going to be a problem but that might could be done with small electric bilge pump. A small battery mounted somewhere in the boat. Even with this your going to have a very large volume in the cockpit unless you come up with a way to form a seat and then you get back to be complex.

I have had people mention this but just doesn't seem a like a good idea to me.

[Dave Lowry]

Paint the kayak.

I did not mean visible as in see through, I meant that it leaves bumps. Just wondering if people ever go to the trouble of trying to hide that.

[Hirilonde]

I notch the keel stringer to avoid the bumps, but it is a matter of chafing, not cosmetic. I suppose you could hide them all this way. Just be careful not to notch too deep or the stringers will not bend fair, or even worse crack.