Kevlar

I am going to build a stich and glue 14' drifter. I want to build a boat that does not wiegh a ton but is very strong and has a reinforced hull. I have read a lot about racing boats using carbon fiber and kevlar. Has anyone on this site used kevlar or carbon fiber to build thier boats? If so what weight did they use? And how many layers was applied to the bottom of the boats. Someone told me to put a spray on truck bed liner on my to be constructed boat, but I am concerned about its wieght charateristics and plastics can react to each other over time with very bad results. I beleive that lineX stuff is PVC based plastic and out gases of a long period of time, pvc also is very reactive with other plastic types. So that considered I like the idea of kevlar, its a little more expensive than glass but it very tough stuff. Anyway what is the groups opinion on kevlar and carbon fiber?

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Permalink Reply by Randy Dersham on June 14, 2009 at 10:20am
I have not used Kevlar. I do order my fiberglass from Fiberglass Supply in WA. They do a lot of surfboards and might be a resource. They have Kevlar, Carbon, and hybrid woven cloth that is very interesting.

How do you want to use your boat. What water will you be floating most often. That will determine where you want to put the weight in your boat and where you need to have the most strength. There are a number of ways to lighten a boat. Keeping it light and strong is always a challenge. For some white water conditions lighter is not always better.

Most fiberglass reinforced bottoms have either one 20oz layer of tri-axel fiberglass cloth or two 10oz layers of fiberglass cloth. I'm certain you can use Kevlar or Carbon in the same way. The only real savings in weight is the difference between the cloth and the Kevlar or cloth and the woven carbon. Most of the weight will come from the epoxy. If you punch a hole through an epoxy bottom of a drift boat that has 20oz fiberglass cloth you are in a life threatening situation. It will take a car wreck sized collision to do that much damage.

I you are after an extremely lightweight boat you might consider a very light weight Kevlar on both sides of a 4mm Okume side panel. That would be tougher than canvas on frame but would very light. It would also be a pretty flexible side panel that would need to be reinforced. The reinforcement might make up for any savings in weight from the Kevlar and thin plywood combo.
Permalink Reply by Joseph Podesta on June 14, 2009 at 5:15pm
I honestly dont think I would be looking to take this boat through white water. Mostly I will be fishing the lower Sac, Yuba, Feather, Ell, Smith, Fall, and Klammath Rivers. White waters scares me a bit as I almost died in a rafting accident when I was in my teens. No more river rafting after that, and my college dean just passed away last year up in Oregon in a rafting accident. I love rivers but like to stay off the white water these days. I just would like a strong bottom to stand up to the rocky river bottoms on some of the rivers I mentioned above. I decided to go with www.butlerprojects.com clark fork drifter. That design reminded me a lot of montana boat builders design. I dont want to build from a kit, seems like cheating to me. Plus per one of the posting on here that I read, you shell out a couple grand and still have to build a boat. My dad was an architect and I grew up on job sites.
Permalink Reply by lhedrick on June 17, 2009 at 5:23pm
My current white water boat uses kevlar.

Place a piece of glass cloth on top of a plastic sheet. Then wet it out with epoxy. After it is cured peel it off the plastic. You will now be able to tear it like a piece of paper. You can't do that with kevlar but, it's 5 times the price.

Carbon is out of the question. It is strong and very light but, it is brittle and does not stand up well to impact and is 2 times the cost of kevlar and 10 times the cost of glass.

Your choice is glass or kevlar cloth. For white water I would recommend the extra cost of the kevlar. If you are building a fishing boat which will be used on Class II and an occasional class III run I would save the money and use 2 layers of 10 Oz fiber glass cloth over a plascore honey comb bottom on the outside and 1 layer on the inside. Just patch it as time goes by. I understand this is a wood boat forum but I no longer use plywood for boat bottoms. If money is not object then go with 2 layers of 6 Oz Kevlar on the outside and 1 6 or 10 Oz layer of Glass inside. Kevlar is harder to work with in that you can't cut it with a razor, you can't sand it and it is a more difficult to wet out then glass cloth.

Good luck and let us know what you decide.
Permalink Reply by Joseph Podesta on June 17, 2009 at 8:00pm
thanks for the info, I am a bit new to the whole composite conversation. I glassed my parents pool when I was in highschool and thats about it. So why are you now in favor of plascore vs plywood these days? Montana boat builders only use that these days. It seems a lot more expensive than ply. What is the advantage, wieght savings?
Permalink Reply by lhedrick on June 17, 2009 at 8:41pm
First, you can get it in 5 X 10 foot sheets. This means you are not stuck with a 48 inch bottom.

After shipping 5 X 10 foot 3/4 inch is about 100 per sheet. I did tests with 3/4 in plascore and 3/8 plywood by dropping a 30 pound rock from 4 feet. All the plywood samples broke. The rock bounced off the plascore. It is lighter then plywood, it can be cut with a knife and it is much stronger. On impact the honeycomb has the ability to deform and dissipate much of the energy of impact. It is bonded and fiber glassed just like wood. If you do put a hole in it you patch it just like plywood with epoxy and glass cloth. Since it is polyethylene it can't rot.

I am not knocking plywood in any way, my current white water boat has a 3/8 kevlar covered plywood bottom but, I have switch to honeycomb composite bottoms on anything I build from now on. On light water you will do fine with a wood bottom for years if you check it and patch it properly if you hit a rock which cuts through the glass/epoxy. I believe a 16 whitewater boat (decks, sealed compartments, bulkheads, hatches) built from all honeycomb would be 100 pounds lighter than and all wood version. It's in the planning stages for me.

If you plan on modest class II water I doubt you would ever do more then put a scratch on the glass surface with honeycomb and I think that wood will also give you the same result at a bit or weight.
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Permalink Reply by Jason Knight on June 18, 2009 at 7:55am
I am by no means a whitewater boat aficionado... but wouldn't you want the heavier part of your boat to be the bottom? Is there something lost for stability in lightening the bottom of a boat built to stay upright in heavy water? I am just thinking about sailboats and the like... School me if this is flawed logic.
Permalink Reply by lhedrick on June 18, 2009 at 1:53pm
In my view weight is never an issue. If I could build a boat which was zero pounds I would do it. A trip through the Grand canyon can last over 20 days. Food (25 dozen eggs plus enough other food for 16 people), propane, ice, tables, chairs, tents, cots, clothing, steel horse shoes (no horse), SAT phone, 10 gallons of water, dutch ovens, charcoal, spare oars, fire pans, safety gear (ropes, pulleys etc), rocket boxes for trash and other waist we won't go into, repair kit with tools, SLA battery with inverter for some power tools even kayaks and paddles get lashed on. This is just for starters. My first trip down the Colorado river I could not believe the mountain of stuff we had get packed on the boats.

Want to talk about beer for 20 days. 4 beers a day * 20 days= (not up for math right now), some wine or fine scotch. I think you get the idea. 3 week ago one of our boat people was a home brewer, we had 2 kegs of beer and CO2 on his boat (so we had that going for us).

Any weight we cant' get off the boat is a plus in my view. The stronger and lighter the better. A loaded raft with people and all the gear can easily go 1500 pounds and we will be rowing it for 3 weeks. A 16 - 17 foot dory won't go 1500 pounds but it's not like an afternoon of fishing over on the Green.

I have never understood why some people think the boats needs to be heavy to be stable.
Permalink Reply by Jason Knight on June 18, 2009 at 2:26pm
Yea I suppose if they are loaded that heavily it's not a factor... it will never be an issue for me anyways bc we don't have big water out here... I would imagine the width of the bottom and the flair of the sides would speak more to stability than weight. But again - I am speculating...
Permalink Reply by Joseph Podesta on June 18, 2009 at 4:10pm
where did you buy your plastcore?
Permalink Reply by Jesse Ronnow on June 20, 2009 at 7:26am
Larry,

That doesn't sound like your run of the mill weekend float, its sounds more like a western river's version of Marti Gras with out the women.... or maybe with the women you did mention that list was just for starters.... ;)

Jesse
Permalink Reply by Randy Dersham on June 20, 2009 at 9:17am
A boat does not need to be heavy to be stable, but it does need to have a proper distribution of weight. The lighter the boat the more critical this weight distribution is. A low center of gravity is the key.

I think the question that Jason is asking is about static weight distribution of the bare hull. The question was "wouldn't you want the heavier part of the boat to be the bottom" Your answer is yes and that you distribute that static weight with payload when you load the boat for a trip. I agree with your answer.

Many of us run white water on rivers that allow us to fish for a day with nothing more than one cooler and a few aluminum chairs as our static payload. In this case the built-in center of gravity of the boat hull is not significantly changed by the payload as it is in your description of a multi-day expedition. I believe it is possible to have the bottom of a white water boat be too lite if you are not obligated to load it down with gear. I am interested in looking into Plascore. I'm a big believer in the honeycomb core for strength and interested because it won't rot. I'm working out how to use Plascore but still maintain the low center of gravity for the static weight of the hull with built in seats/decks. I am a firm believer that a lower center of gravity will lead to better performance and the low center of gravity is critical when the boat has no static payload. If you are depending on the cargo to generate that low center of gravity then it means you need to run with cargo. Many of us don't so we are careful to maintain a low center of gravity in the build of the empty hull.

Some rowers have experienced this similar issue in the horizontal direction in a boat with a fixed rowers seat. With a fixed rowers seat that is back of the boat's center line (as the traditional McKenzie Drift Boat is designed) it is difficult to trim the boat level if you are rowing by yourself. You have to either put a couple hundred pounds of payload in the front of the boat or talk the neighbors kid into going fishing with you. We affectionately call them bow-puppies;)
Permalink Reply by lhedrick on June 20, 2009 at 5:50pm
I agree that weight down low is better then up at the gunwale, but just like the issue of a hard chine creating certain performance advantages I don't think they are enough of the total equation to make a difference. It's the rower and passengers who determine most of how the boat will behave on the river. A passenger who hight sides at the right time will have a much larger effect on secondary stability then boat design.

I think most of us already know this and I can only recommend that people who have limited experience with bigger water give themselves the chance to gain expertise before they take on bigger challenges. I am a much better boater than I was 10 years ago but, last month I made 2 mistakes on the Colorado River I should not have made since I had been there twice before and they were on the smaller rapids. The 2 mistakes had nothing to do with the boat. Last year I almost went over at Warm Springs Rapid on the Yampa because I got pushed to where I should not have been. I over reacted and tried to ferry out and almost got my ass kicked. No item in the design of the hull or it's weight distribution could have overcome my mistake of taking a hit sideways. If my passenger had not moved to the right gunwale as I did that one would have been my first flip. What can I say other than each time I learn more and like to think I become a little bet better as a boater.

While I value everyones design suggestion here on this forum let us not forget the most important parts of the system are the people running the show. I think it's important to note that developing rowing skills are a better investment in time then boat design and there is place for both.

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