Kevlar .12 Rigger Project

[MikeP]

Mike,

What is Kevlar like to work with? I have heard it is very difficult to cut cleanly after it is moulded. But it is cheaper than carbon fibre, and tougher. I think the toughness is probably more important for boats than the high stiffness of carbon.

Ian.

What little I have done with kevlar has been difficult. Kevlars best feature is it resists abrasion. It is hard to cut the fabric, when you cut and drill the finished product you get hairy edges that are hard to remove.

I didn't buy the special ceramic sissors. I use regular sissors and keep a sharp edge on them, resharpen about every yard or so. The rotory cutter doesn't work.

For the hairy edges after cutting the finished product I like to add more glue to the hairs and sand with 3M gold sand paper. There is a recomended type of sand paper for sanding Kevlar but I didn't write it down and can't remember the site I saw it at.

-MikeP

 

[MikeP]

I finally got the mold release aplication figured out, I was putting it on too thick and it left a bumpy finish. Thin smooth even coats are needed.

Now I got to figure out how to make a good solid mold that wont flex in the vacume bag.

 

[Ian Inverarity]

Mike,

Well, keep us up to date on how it goes! I would like to try Kevlar one day, but am dreading it from what I have heard! :

Ian.

 

[MikeP]

moving right along

 

[MikeP]

pic

 

[wswatzell]

Ok mike, I am very ignorant about vac-bagging, :-[what is the black stuff? Did you color your resin, or is that a kind of mold release?

 

[Dennis Whitt]

Hey Ian weir can I see more of that siver hull ?please ?

 

[Ian Inverarity]

Dennis,

I found the pics on a European website which had pics from the last world champs, I dont remmember the site anymore. There was no details and the site was not in English anyway, but I think this is a pic of the same boat. 8)

Ian.

 

[TimD]

Ok mike, I am very ignorant about vac-bagging, :-[what is the black stuff? Did you color your resin, or is that a kind of mold release?

Correct me if I'm wrong but is it powdered graphite mixed with the resin? Gives a good surface to the mold, right?

 

[TomMoorehouse]

i think the black will help to show if you have holes/bubbles when you do the parts layup?

that is one cool rigger..... beautiful craftsman ship! wish i had that skill!

 

[MikeP]

Howdy,

The black stuff is powdered graphite. It is mixed in the epoxy along with silica to make putty. The putty is brushed on the plug to fill the sharp angles that cloth doesn't get into and makes sure I have nice crisp clean corners. The powdered graphite makes whats called the tooling surface, very hard and will hold up to the making of many parts.

I removed the plug by pouring a little gas on the foam, the mold turned out nice. 1 down 1 to go.

Ian,

What do you think the running surface of those sponsons look like? I would think they have to have square edges , not like the top of them are.

-MikeP

 

[TimD]

Mike,

Have you put any thought into how you are going to join the 2 halves together? especially in the tight spot at the end.

We used to put a lip on one side of the mold and an opposing lip on the other side for them to lock together nicely.

Tim.

 

[TomMoorehouse]

on the first page of the thread you can just bearly see it mike.....

 

[Ian Inverarity]

Mike,

I have no more info than those pics which I have posted. As Tom said, on the one on the first page you can just see a step on the side that would be the end of the riding surface. Behind that is just an aerodynamic fairing. Also I cant see any curvature at the lower edge.

I think they would have to have pretty conventional type riding surfaces. Something like the top would not plane very well at all, the water would come right up the sides instead of breaking off at the edge of the riding surface. But also it looks like the sponsons dont have any anti-trip to them either, which means the turn fin would have to be really good!

The second photo seems to show a single ski type rear sponson, but there is not much detail so I have no idea what it really looks like.

I just like the pics because they seemed to be the only interesting riggers at the World's that weren't SG's! Have a look at the boats in the background..... I like something different! 8)

I am not sure how much the aerodynamic approach is worth persuing tho. Aero drag is important, but i think aero stability is more important, and water drag is far more significant. Probably from a weight point of view the aero stuff may not be worth doing. I dont know. But the 21 looks like it was really small and light, those little wings at the back and the rudder are carbon fibre! Very nice stuff! Great workmanship.

Did any of the internationals who read this see those boats? How did they go?

Ian.

 

[MikeP]

Mike,

Have you put any thought into how you are going to join the 2 halves together? especially in the tight spot at the end.

We used to put a lip on one side of the mold and an opposing lip on the other side for them to lock together nicely.

Tim.

I was going to use what I think they call a joggle plate. It is 1/4" plastic and is removable. It is pinned on top of the mold. The center is cut out to match the mold except it overhangs the thickness of the layup. The end result is you have a 1/4" lip that fits inside the other half flush. However after reading your post about the opposing lip lock I think I will make opposing joggle plates. I should be able to keep good pressure on the joint until it sets up. Thanks alot!

-MikeP

 

[TimD]

Mike,

The lip serves a purpose in that it gives a larger bonding surface and also improves torsional rigidity. The added bonus is it makes joining halves in tight corners a lot easier. Can you imagine trying to get glass into that tight point at the back ( I don't know if Transom is a fair term for a pointed tail???)

Sorry I didn't mention it before you finished the plug - you could have incorporated it into the mold.

 

[MikeP]

This should keep things straight in the vacume bag.

 

[TomMoorehouse]

dam mike..... you sure can build!

 

[MikeP]

Laid up the Kevlar today, 3 layers of 1.7 oz. Thats what they use for gliders, seems a little thin to me. Tune in tomorrow to see what comes out.

 

[Jr Branham]

Mike,

Can you give us a few details on your vacuum bag set-up. How many inches does your pump pull down to? Do you adjust the vacuum in any way? How long do you leave the pump on for? Any info is appreciated.

J. Branham