Thread: Carbon kevlar

Howdy Lone Duck,

The question is ... this is a very complex situation ... and you are choosing one reason out of many for the screws loosening ... so how do you know it is the expansion and compression of the teflon that is making the screws come loose?

Getting rid of them will resolve that part of the problem.

I doubt anyone can give you an accurate answer whether carbon/kevlar will work or not. Basically you can hit any structure hard enough to break it. But I can make some general comments about the materials.

Kevlar is very good at dealing with impact. Carbon is not so good.

There are a couple of possibilities for how the teflon is protecting the boat. One possibility is that it is not doing anything that the wood itself cannot do and has little real effect ... right through to the idea that it is quite thick and soft compared to any other covering so provides some cushioning.

Kevlar is the devil to cut, wet out or smooth out (it blunts any tools and furrs up when abraded) - this is the other side of "impact resistance". So often the method is to do the lamination with the epoxy kevlar with everything cut neatly to size then fair over the top using a lightweight bog or a fibreglass "tissue" as a surfacer or a mix of both those methods to provide a smooth shape basically to reduce the amount of direct shaping that has to be done in the kevlar.

Best wishes
Michael

Just a thought ... do you have the teflon sheet over the whole bottom of the boat or just on the keel and any bottom skids or strakes?

MIK

I would second Michael's comments on Kevlar. Trust me, you don't want to use the stuff. It costs more then the whole of your last marriage, including divorce, is very difficult to work with and your boat just doesn't need it.

I'd recommend you remove the Teflon and bond a sheathing of Dynel or better yet Xynole on the underwater portions of your boat.

I'm not sure what the brand names for these poly fabrics are down there, but I'm reasonably sure you can get it.

The major thing you can address is abrasion resistance. Dynel is about 3 times better then conventional 'glass fabrics. Xynole is about 6 times better.

Impact protection is better resisted with a heavier sheathing on the inside of the hull (amazingly enough). If impact and breach concerns are a worry, then a layer or two of biax fabric will serve you well.

Kevlar would be helpful in protection in this role (impact an penetration), placed on the inside of the hull. Carbon fiber you just don't need. I can get Kevlar for about $50 (USD) per yard. I'm not sure what it'll be in your neck of the woods, but the prices are going up rapidly. I can get Dynel for around $5 a yard, so it's a pretty simple business decision for me.

Another old school method is to use sacrificial rub strips on the bottom of the boat. These are typically hardwood strips, bedded and screwed to the hull. When you tear them up, you remove the remains and replace them. This will likely be the easiest and fastest way to get you some protection.

Originally Posted by PAR

I would second Michael's comments on Kevlar. Trust me, you don't want to use the stuff. It costs more then the whole of your last marriage, including divorce, is very difficult to work with and your boat just doesn't need it.

I'd recommend you remove the Teflon and bond a sheathing of Dynel or better yet Xynole on the underwater portions of your boat.

I'm not sure what the brand names for these poly fabrics are down there, but I'm reasonably sure you can get it.

The major thing you can address is abrasion resistance. Dynel is about 3 times better then conventional 'glass fabrics. Xynole is about 6 times better.

Impact protection is better resisted with a heavier sheathing on the inside of the hull (amazingly enough). If impact and breach concerns are a worry, then a layer or two of biax fabric will serve you well.

Kevlar would be helpful in protection in this role (impact an penetration), placed on the inside of the hull. Carbon fiber you just don't need. I can get Kevlar for about $50 (USD) per yard. I'm not sure what it'll be in your neck of the woods, but the prices are going up rapidly. I can get Dynel for around $5 a yard, so it's a pretty simple business decision for me.

Another old school method is to use sacrificial rub strips on the bottom of the boat. These are typically hardwood strips, bedded and screwed to the hull. When you tear them up, you remove the remains and replace them. This will likely be the easiest and fastest way to get you some protection.

Thank you for your comments. Looks like I will stick to the teflon. When the SS screws work the wood to much, I will remove teflon , drill out the holes, fill with epoxy fillet, redrill pilot hole and put the teflon back on. On this river it is an absolute must to protect the bottom. On the aluminum jet boats here they drill right through the hull and bolt teflon on. Over time , the bolts work the aluminum skin an they leak. then they have to repair big time. Thank you again.

Yes. If the screws are properly glued in they might not come out.

you can release them later by heating them with a soldering iron. But this might be unfeasable because of the number!

Michael

Rather then using a soldering iron to remove epoxied in fasteners I use a propane torch. I heat the shaft of a screw driver until it's glowing, then press it into the goo that has filled the slots in the head. After burning off the goo in the slot, the heat quickly transfers to the fastener and I start breaking it free by hand. Once I get it to break loose, I can then use a drill to remove it the rest of the way. As a rule I usually remove fasteners by hand until I'm very sure I will not twist off the head or break a shank. It's slower by hand, but I don't have to dig out a broken fastener, because I tried to go too fast or almost as bad, strip out the slot on the fastener head with a with a power drill.

Originally Posted by PAR

Rather then using a soldering iron to remove epoxied in fasteners I use a propane torch. I heat the shaft of a screw driver until it's glowing, then press it into the goo that has filled the slots in the head. After burning off the goo in the slot, the heat quickly transfers to the fastener and I start breaking it free by hand. Once I get it to break loose, I can then use a drill to remove it the rest of the way. As a rule I usually remove fasteners by hand until I'm very sure I will not twist off the head or break a shank. It's slower by hand, but I don't have to dig out a broken fastener, because I tried to go too fast or almost as bad, strip out the slot on the fastener head with a with a power drill.

Perhaps I did not make it clear . I am not going to glue the screws in. I am going to drill a pilot hole in the hardend fillet and insert the screw normally. There are 250 screws holding 4 sheets of 1/4" teflon on. The biggest error I made was the thickness of the teflon. I should of used a 3/8 or a 1/2 " Then I could of drilled an over size hole in the teflon and used a imbedded washer on the screw to give the teflon some movement. That is how they do it on the aluminum craft with bolts. But I was trying to save weight and $. Oh well it gives me something to do in the off season. The reason for all this is because sometimes you have to slide over 8 or 10 ft. of gravel bar under power or you won't get home. And ohh what a rush. when you do it.

Originally Posted by PAR

It's slower by hand, but I don't have to dig out a broken fastener, because I tried to go too fast or almost as bad, strip out the slot on the fastener head with a with a power drill.

Good method with the torch! The soldering iron is convenient for one or two or five fastenings - and there is usually little problem. But if there are a larger number of fastenings or they are heavier gauge ... then the torch sounds great.

MIK

A thread will not "grip" the fillet, but rather it will break it up into dust and fibers. If you're going to place any type of fastener there's only a few ways to do it in thermo plastics (epoxy, poly's, etc.). The best way is to bond the fastener which is to literally glue in it location. The next method is to "key" it, which requires the fastener to be inserted in still curing goo, then the goo cures around the inserted fastener, keying it's threads to the substrate. If using this method and you want to remove the fasteners at some point, like you do Lone Duck, then coat each fastener with a release agent or you can use regular old automotive wax. This still permits the goo to key around the threads, but it can be easily backed out when the time comes.

Both of these methods are clearly described on Michael's web site ( http://www.storerboatplans.com/ ).

I developed the torch method for screw removal when I started doing a lot of lapstrake repairs. Many of these boats are clenched, some with screws or machine bolts at the frames and still others with screws along the laps and frames. We're talking about thousands of fasteners on an average 25' boat. Each will have it's head coated with who knows what type of putty or other goo to hide or seal them. Picking them clean enough, with some sort of bastardized dentist tool, to get a good tool purchase in the slots is ridiculous. Often I don't try very hard on these fasteners. If they don't break free, instead of trying to force them, I just drill out the head and insert a bolt extractor. This is especially true on small fasteners, say #10 and under. On larger fasteners, I'll use the torch. It literally burns right through the nastiest of filled up slot, paint, epoxy, polyester, it doesn't matter, it blows right through in a second. Now the driver has a good grip and your chances of removal are much higher. Of course the heat also weakens the goo bond in the fastener hole and also any tannins, resin or other sticky stuff that's attempting to mess up you day.

A hard earned tip: be sure not to touch the shank of the screw driver as you back out the fastener. I apparently like to rest my index finger on the shank as I twist. Trust me, after you get the shank red hot, you really don't want to touch it. I've learned this the hard way, even though I was fully aware of how hot it was. I found that gloves limited my "feel" and hid the heat until I was really cooking, so I'm just more careful and gloveless now.

Originally Posted by PAR

A thread will not "grip" the fillet, but rather it will break it up into dust and fibers. If you're going to place any type of fastener there's only a few ways to do it in thermo plastics (epoxy, poly's, etc.). The best way is to bond the fastener which is to literally glue in it location. The next method is to "key" it, which requires the fastener to be inserted in still curing goo, then the goo cures around the inserted fastener, keying it's threads to the substrate. If using this method and you want to remove the fasteners at some point, like you do Lone Duck, then coat each fastener with a release agent or you can use regular old automotive wax. This still permits the goo to key around the threads, but it can be easily backed out when the time comes.

Both of these methods are clearly described on Michael's web site ( http://www.storerboatplans.com/ ).

I developed the torch method for screw removal when I started doing a lot of lapstrake repairs. Many of these boats are clenched, some with screws or machine bolts at the frames and still others with screws along the laps and frames. We're talking about thousands of fasteners on an average 25' boat. Each will have it's head coated with who knows what type of putty or other goo to hide or seal them. Picking them clean enough, with some sort of bastardized dentist tool, to get a good tool purchase in the slots is ridiculous. Often I don't try very hard on these fasteners. If they don't break free, instead of trying to force them, I just drill out the head and insert a bolt extractor. This is especially true on small fasteners, say #10 and under. On larger fasteners, I'll use the torch. It literally burns right through the nastiest of filled up slot, paint, epoxy, polyester, it doesn't matter, it blows right through in a second. Now the driver has a good grip and your chances of removal are much higher. Of course the heat also weakens the goo bond in the fastener hole and also any tannins, resin or other sticky stuff that's attempting to mess up you day.

A hard earned tip: be sure not to touch the shank of the screw driver as you back out the fastener. I apparently like to rest my index finger on the shank as I twist. Trust me, after you get the shank red hot, you really don't want to touch it. I've learned this the hard way, even though I was fully aware of how hot it was. I found that gloves limited my "feel" and hid the heat until I was really cooking, so I'm just more careful and gloveless now.

Right on! Thanks Par. And all the rest of you. You have probably saved me some grief when the time comes to replace the screws.