RN Superjet reinforcing hull with 1708Biax, where and how thick (couple noob questions)

[g.b.]

Hello people!

I'm getting ready to reinforce the inside of my superjet hull. I bought some 1708 Biax (with stitched backing mat) and epoxy resin kit from Uscomposites.

Right now, my tray is removed and foam completly out. I was wondering if I should reinforce the tray area also before closing the area and reforming. (bottom and sides) ?

I am planning to reinforce the floor area, the underneath of the pole area (from inside), and the sides, but for the sides, I was wondering if I should do both halves (top and bottom) or people usually do only the bottom part?

I've seen a video of a guy filling the bond line with thickened epoxy (cabosil), then laying a single piece of glass that does the top and bottom halves, but I wanted to make sure this was the usual procedure.

Also, with 1708 biax (with 3/4 oz mat stitched), how much layers should I lay? Maybe more on the floor area and less on the sides? I really don't know

thanks a lot for the help!

 

[mikidymac]

I would say 2 layers on the side all one piece you want to join the top and bottom.

I used 2 layers of 1708 without mat.

Filling the gap with cabosil makes a nice smooth transition.

 

[McDog]

Use 1208 instead if you havent already bought 1708. Plenty strong still and will weigh less. One layer is all you need if its prepped correctly.

 

[Req]

17oz non backed biax is my new favorite. About the build thickness of 1208 without extra resin to wet out the matt backer (matt absorbs resin to fabric 1.5:1 vs 1:1)

The backer materials are just harder to work with and weigh a bit more, they have there place for sure, where you need thickness and want a quick build up they shine.

As far as how thick you should go, it depends on what you are planning to do with the ski. If its a lake only ski and will never get beat on too hard, very little reinforcement is really needed.

I did too much on mine but I wanted it bullet proof, for my next SN project I will be going much lighter on my layups as it will be a lake only ski.

I think good reinforcement without going overboard is probably 17oz biax without mat or 1208 with matt from the floor of the engine bay to the hood seal, firewall to nose, filling the bond line in with 3m glass bubbles and resin. You can leave the floor of the engine bay alone, its super thick. If you are cracking the tray you could also do one layer of the same from the top of the gunwales (if they are exposed) to the bottom, if you are wanting a bit extra and dont mind the weight you can extend that reinforcement to the pump tunnel area.

Much more than that is unneeded weight for lake riding, surf is another story I understand, also if you want adjustable holds that would need a lot more glass on the gunwales.

What are your plans for the ski?

 

[g.b.]

Hey thanks for the replies guys!

The ski is built to be lake ridden, but I don't think I'll build a lot of skis in my life and I want to do this one right. I may go crazy and end up jumping boat wakes, going to rivers, etc. I'd like it to be a all-round ski, or at least have the possibility to.

I don't know what happened with the previous owner, but the floor of the engine bay, under the waterbox area had already been patched with polyester glass. I wanted to know why so I dug deeper and realised that this was just a surface patch and that the actual structure was cracked and delaminated. I removed the delaminating glass to end up with a 3-4 inch diameter hole. I will be repairing this too soon. This is what made me think that I probably should be reinforcing the floor area too to avoid similar misfortune in the future. They probably hit a rock in shallow water or something similar.

About the bondline, i've mostly seen people filling is with epoxy resin+cabosil, did you mean that or you really meant glass bubbles? I got both but I was planning to use the cabosil for bondline and glass bubbles to create an easy to sand finishing putty for the exterior of the hull.

I already bought 1708 WITH backing. I asked the guy as Uscomposites the purpose of the backing because I couldn't decide what to buy. He advised to me that the backing purpose was to add grip to the surface so I told myself: Hey, this is exactly what I need: extra grip to my actual hull so it won't delaminate. So i went with 1708 W/backing.

After playing around with the 1708 W/backing, I admit that it seems a bit on the tick side. It looks a bit hard to work with in tight areas and will probably be hard to make it conform to different curves. However, I already bought a lot of it and brought it back to Canada (where I live) so I'd like to be able to use it. I will see if it's possible to unstitch the backing from it, otherwise, I'll probably just use it as-is.

I also have to install some footholds and I'm a little worried that the 1708 will be too thick. will have to play around with it some more to decide what I will end up doing.

Also, I won't go with adjustable holds. It's not in any future plans I have... for now.!

thanks for the help!

g.b

 

[Req]

I used a lot of 1708 in my build for the same reason, I had it so I used it. You can use either filler, I think I mixed 50/50 on mine, cabosil is pretty heavy and glass beads are good for faring and plenty strong enough to fill the bond line imo.

 

[g.b.]

You ended up using 1708 with or without mat? Just out of curiosity?

If I end up using what I have (1708 w/backing), then what would you advise? A single layer everywhere? I'll also reinforce the tray area while it's opened!

 

[mikidymac]

For a lake ski one layer of 1708 is all you need. Mine will be 75% lake and 25% surf so I did 2 layers just on the side none on the bottom.

 

[Req]

You ended up using 1708 with or without mat? Just out of curiosity?

If I end up using what I have (1708 w/backing), then what would you advise? A single layer everywhere? I'll also reinforce the tray area while it's opened!

I went through my 5 yards of my initial purchase and when I re ordered i got it without matt. I used it to build thickness on the tray sides, reinforce the lower tray, build my dash, build my tray floor, and reinforce the upper engine bay section. I am following that up with 17biax with no mat on the engine bay lower. My ski is a combination of 1708 and 17biax with no mat.

If I were to do it again I would use much less 1708 with backer however hindsight is 2020. Places like where I beefed up the pole bracket and tray sides I would likely use 1708 again since nothing builds thickness as fast but the lower tray section, dash, and foothold, would have been much simpler to do with 17biax no matt.

Single layer everywhere sounds pretty good for what you are doing, maybe a few more layers in the area of the repair with each layer tabbing a little further than the next.

Also, since you are working with 1708 watch this. This will give you an idea of the technique.

 

[g.b.]

Thanks a lot! I have seen this video yesterday, seems like that I will be doing! I will most probably be doing 1 layer everywhere and fill the bondline and be done with it!
I had ordered 3 yards of 1708 but since, the project got bigger, didn't plan on reinforcing the area under the tray at first and I will need to use a lot more in the tray area than expected: while removing the tray, it broke under the area where the is a lot of glue on the top of the pump tunnel, need to fix that. I might end up needing/ordering more of it.

Would you think 1708 without backing offer an as good structural strenght as 1708 alone, while lighter? And having an as good adhesion despite what the Uscomposites guy told?

I consider this a critical part of the build and I don't want to mess those steps, that's why I'm beeing very carefull because I won't be able to fix this later after the tray is closed, underhood painted and all mechanical installed.

Thanks again for helping out!

g.b.

 

[Req]

The way it has been described to me is that the backer adds very little in the way of strength, just thickness. Additionally it soaks more resin than straight cloth or biax and while good for waterproofing I suppose just adds weight without strength for our application. Regarding 1708 with backer adhering better, I heard that same speech from the same guy and did the same initial order as you, I then used non backer biax on my pump tunnel and it adhered just fine to the SMC hull bottom, just prep it well. Oddly enough the reinforcements that have wanted to delaminate for me were 1708 with backer because its so hard to keep down sometimes.

*Tin foil hat on.

I have a theory that US composites pitches 1708 with backer to sell more resin, I suspect that is the cash cow for them.

*Tin foil hat off.

 

[mikidymac]

In my experience it’s the prep of the substrate and the epoxy that determines good adhesion not mat backing but then again what do I know?

 

[McDog]

Just use microballoon thickened epoxy over every "open" area you create on the tray before laying the glass over it and you will be fine.

 

[g.b.]

Thanks Req, thanks everyone!

I will try to unstitch the actual 1708 with backing I have, to be able to use it. I am in Canada and would like to avoid another USA order with the fees implied. Not sure if they will separate well or not.
However, I'm not sure I'll be ok with the 3 yards for a complete layer everythere + installing footholds + repairing tray + repairing hole in hull.

Will probaby end up ordering more anyway -_-

McDog, do you mean microbaloon or cabosil, I'm wondering now what I will use, I was told prettymuch everywhere to use cabosil for this, it probably don't really matters in the end anyways

Thanks!!
g.b.

 

[Req]

I wouldn't un stitch, I suspect it will come apart. I would just roll with it, at most we are talking a few lbs. Next build try the non backer stuff

 

[Baja 252]

Does the backing side go towards the ski or facing out when you use it?

 

[g.b.]

Should be toward the ski according the UScomposites guy.

 

[g.b.]

I'll make a couple test and act accordingly!
I love this project, but in a way, I also wish there will not be any other similar build... it's a bit much for me and takes SOOOO much time!

 

[Carrera911]

Definitely lots of time. I didn't keep an exact log, but I'd say I easily spent 400 hours on mine.

Before I did my build I couldn't find much on 1708 mat vs no mat. I saw it was cheaper with the mat and that's what I went with.

That being said, the mat just makes it a bitch to stay stuck down IMO. Not sure why, but I guess the gaps between all the strands don't give as much surface area for the surface tension of the glue to stick to. Laying down just regular cloth is way easier to keep in place and work out the bubbles.

 

[g.b.]

It will probably be about 400hours too, but I'm not counting; it's just a rough estimate and I honnestly prefer not knowing.

On my side, 1708 was a little more expensive with backing, about 0.40$/yard. Have I known, I would have bought without, now I'm stuck with it and I need to make another order for 1708 without -_-