This thread really got me thinking about building an ocean surf kayak. Does anyone in seattle have one I can come look at for some inspiration?

I do!

awright: much to my dissappointment, despite the infinite proliferation of info on the wacky worldwide web, despite much searching for info on this subject far and wide, (some of) the best info yet I've turned up happens to be from Sweet Composites...
This link below talks about making plugs and molds.

http://www.sweetcomposites.com/Mold.html

I'm so turned off by the idea of having chunks of pink foam left behind inside the boat, that I think I'd be willing to go ahead and make a mold from the plug and then layup a boat inside that. Sure it would take longer, but the end result is what matters most.

Of course, the whole boatbuilding thing is still a pipedream at the moment, but it keeps nagging at me.

Making a plug and then making a mold is a good way to go because if you change your plug afterward and make v2, v3 or v4 you can always go back quickly especially if you break the first prototype. The molds can pile up but its an accurate record of what you have all ready done. On another note pouring acetone inside is a very dirty process and takes more acetone than you think to get it all out. Also, what doesn't come out is now hard as a rock. So, unless you have lots of acetone and unlimited access to hazardous waste dumping I don't think its a good choice.
Cheers-

I'm still very interested in doing this, so, I'm dumping all my ideas and questions on the group.

I've got a design mostly worked out in Kayak Foundry, but would like to know what other tools people are using for design. Because of the limitations of KF (it is really intended just for sea kayaks), I'll end up having to use pencil and paper, or just an image editor to make some refinements.

I have read in various places that:
a. the

I still need to paddle a bunch of different boats to make some design decisions, so I'll hit everyone up for loaners soon.

One thing I have only now started considering is seat height. A higher seat would give me more reach and mobility above the boat, but would cause a higher center of gravity. I'd love to hear all your thoughts on seat height.

Summing up some other ideas, I agree with Shape-changer and jP that a two piece casting from a reusable mold is the way for me to go.

I think the standard is to use two-pound rigid polyurethane for the plug. Any suggestions on where to get a big block of it, or at least pieces to glue into a big block. In that case, what type of glue should I use?

Should the plug be glassed, or is just having it puttied and sanded smooth enough? It seems that puttying and sanding would be less work than glassing it, but I really don't know.

The mold will need to be at least a couple plies thick to prevent distortion from shrinkage during curing.

Would someone please tell me how many plies they think the mold should be? And for that matter, how many plies should the boat have? It sees to me that the deck shouldn't need to be as thick as the hull, but maybe that isn't true.

Since I want to have a copy of my final version last me a good long while, I'll eventually need to make repairs. Additionally, I may need to "fix" some elements even while it is brand new. It occurs to me that by tinting the epoxy one color for the first few plies and then another color for the last few plys, it would be easy to see how far into the boat I have sanded for repairs. Any comments on that?

The finished plug needs to be a tad bigger than the actual boat will be because of shrinkage when I glass the plug, and additional shrinkage in the mold when it cures.

I shouldn't make any edge too radical because of the stiffness of the fiberglass.

Fiberglass comes in S-glass (strong-glass) and e-glass (electrical glass). Using S-glass seems like the obvious choice.

Carbon is said to be rather weak compared to fiberglass, though kevlar, or a fiberglass-kevlar blend may be an option for me.

I have never laid up any kind of composite. I know an accelerant can be used so that the cure time is shorter, and that adding too much accelerant can cause "spontaneous combustion." Still, I have no idea how long a cure might take with no accelerant, or with a modest amount.

Also, can two or more plies be wetted out at the same time? This seems like a bad idea, but I really don't know.

I think that orienting each ply 45 degrees offset from the previous ply makes the most structural sense. Is there any reason not to do this?

Do I need to sand each ply down after it has cured? Does this make more sense for the boat than for the mold or for the plug?

I'm still pretty tempted put a hatch in, but I don't know yet.

Alright, I know a lot of you are smarter than me, and all of you are at least as experienced as I, so let's hear your thoughts, criticisms, and suggestions (and encouragements).

Well, here are my thoughts. This is what I have found out while making a bunch of slalom boats and home made play boats.



I would certainly make a seat where you could change the height. On one boat that I made, I made a foam seat that sat on the hull, and I could change the amount of foam that was under it to change the height. This was for a surf boat also, so I wasn't afraid of having a rigid spot on the hull because I wouldn't be running it over rocks.



There won't be shrinkage because it will cure to the exact size of the plug. Then the boat halves will be the exact size of the mold. There is in plastic boats, but not fiberglass boats. You do want a stiff mold to make sure the final boat isn't twisted or anything.

How I have always done molds, is to make the first layer glass to get a great smooth first layer, and then use inexpensive mat to complete the plug. There is no reason to use anything expensive for a mold other than the first (maybe second) layer. You want the mold to be stiff, so the more the merrier with the mat. I would do 5 layers at least over the S-glass first layer. Almost all molds are black so that you can see any imperfections in the mold.

For the final boat, it depends on how light you want it and what materials you want to use. For a midweight boat, I would do: glass, kevlar, carbon, carbon for the hull, and glass, kevlar, carbon for the deck. The carbon can be replaced with glass for a large $ savings, and a small weight gain, and a small loss in stiffness.



You should be able to tell how far you have sanded into the boat by the change in stiffness of the area, and often times, you can see the layers as you sand through them. Don't use Kevlar if you want to sand the boat other for repairs, though. When you sand Kevlar, it fuzzes something fierce. Also, if the boat fractures, you want to grind out the entire fracture, not just a layer or two, so it won't be very important to know how far you are sanding through the boat anyways.
   I have had sharp edges on fiberglass boats without issue before. The worst part about it is getting the glass to lay in there while laying up the boat, but that is where bias cut glass saves the day.


S glass is what you want.

Carbon is stronger than fiberglass for the same weight. If someone told you differently, you might want to check what they tell you in the future. Carbon is more brittle than glass, but is stronger and stiffer. One layer of 6 oz carbon will be stiffer, stronger, and lighter than one layer of 6oz s glass.

Kevlar is also very strong, but flexes well. This is why it is good in whitewater boats, it can handle hitting rocks better than glass and carbon (it will flex instead of break). However, it doesn't help making the boat very stiff. Also, Kevlar is a bastard to work with. It is near impossible to cut without the $75 kevlar shears, and it fuzzes when you sand it.


Accelerants are more common in polyester resins, and I recommend using a good epoxy resin without accelerants. I use 3M epoxy and like it much better than any polyester. The resin gets jello like in around maybe 30 minutes or so depending on temperature, so I mix in smaller batches to avoid waste.

You can, but it can turn into a disaster sometimes. The first layer should be done alone to make sure you have a good layup without air bubbles. If you are using light weight materials, you can do more than one at a time, but I wouldn't. If you are going to vacuum bag, then you do them all at the same time, but I wouldn't try it your first time.



The amount of a pain that it would be to offset the weave of the glass 45 degrees will be about 100x more of a pain than it would be worth.

Don't sand between layers on a layup. Don't even bother letting it cure unless you need to. You want to avoid getting contamination between the layers, because they have a chemical bond. What I do is the first layer with great detail to make sure the final product is going to be perfect. The first layer can be layed down with a little extra resin. Once you are happy, drop the next layer on it. It will soak up much of the spare resin from the first layer, you will still have to add extra to get it completely saturated. The last layer, you want to try to work out as much of the resin from the lower levels as you can to avoid extra resin (weight), but make sure it is completely saturated.

Thanks Shaun, and everyone, for your excellent input.

I reread my other message on carbon, and that person was just saying carbon is more brittle than the other materials.

Shaun, you suggested glass, kevlar, carbon, carbon for the hull, and glass, kevlar, carbon for the deck for a mid-weight boat. I understand this to mean the glass would be the first ply to go on to the mold for each, and the carbon would be the last ply to go over the mold. Is that correct?

Since I have all options available at this point, what would be the optimal hull, prioritizing strength/durability over weight? Would glass, kevlar, glass, kevlar be structurally different in any way than glass, glass, kevlar, kevlar? Would either of these provide enough stiffness? From Shaun's post, I gather that glass, kevlar, glass, glass is probably best, but I want to be sure. Also, does that assume 450 glass?

As Shaun pointed out, the bulk of the weight comes from the resin. I see now that I had previously made too much of an issue of the materials' weights. I'd really rather have a strong stiff boat, even if it weighed as much as my plastic boat, though I'd be very happy to have a lighter boat.

Thx,

D

UKC is hosting a workshop on repairing composite boats at the Seattle REI on 1/22/10.

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