Lightweight layup design

[NeedOne]

Looking for advice, done some googling and searching on S&F, this has been touched on but have not come across definitive info..

Using regular materials and open mold method: vinyester resin, CSM, 1708, and 1/2" divinycell:

What is the lightest layup schedule for a bass boat style deck hatch? Duty = lake racer design, to support (1) 200lb max person...

Current layup plan follows, I believe this would be solid, but would it be 'lightweight'?

Gelcoat
CSM
1708
CSM
Core
1708

How about a lightweight cowl, how crazy can you go?

2x CSM
1708 strip around sealing surface & reinforcing hoops

Appreciate any replies, hoping to tie up the loose ends on this topic

[David - WI]

Carbon/Kevlar?
https://www.fibreglast.com/product/k...id-yellow-1065

[NeedOne]

I thought about carbon/ kevlar, but figured unless it was vacuum bagged or autoclaved dry carbon, my assumption was that the weight saving from fabric selection may only be a fraction on a small part.
That is all assumption though, maybe more advanced materials/ process is the answer.

The rear hatch of my gambler is very heavy, just a very thick heavy part compared to other hatches on the boat. I do think I can make a lighter hatch with traditional materials, just don't want to go thru the effort and end up only shaving a couple pounds & could have layed up light-er

[David - WI]

I'm not sure how much weight you can save on a relarively small part, but it should be stronger & stiffer. Look at the car hood this guy makes (first minute of the video): https://m.youtube.com/watch?v=UgKvDw1E60E

Otherwise, there is also S–glass: https://jpscm.com/products/e-glass-s-glass/

Vacuum bagging is pretty easy and will give you a stronger, lighter part whether you use fiberglass or carbon/kevlar... but it might not be necessary? The autoclave is only needed for post–curing "prepreg" (or some vacuum infusion resins), I think

[LakeFever]

I think your hatch layup would be fine. I did similar with my seat boxes and they are stout. Best thing to do is layup what you have suggested and test it. Span it over a couple 4x4’s and stand on it see if it’s stiff enough for ya. The cowl 2x 1.5oz can would probably be fine too. Hydrostream seat shells look similar and they hold up over time

[NeedOne]

I'm not sure how much weight you can save on a relarively small part, but it should be stronger & stiffer. Look at the car hood this guy makes (first minute of the video): https://m.youtube.com/watch?v=UgKvDw1E60E

Otherwise, there is also S–glass: https://jpscm.com/products/e-glass-s-glass/

Vacuum bagging is pretty easy and will give you a stronger, lighter part whether you use fiberglass or carbon/kevlar... but it might not be necessary? The autoclave is only needed for post–curing "prepreg" (or some vacuum infusion resins), I think

That video is a solid reference, for popping a mold too which I need to do, appreciate that.

Ultimately the more exotic (to me) methods will knock out weight no doubt, question is how much extra vs. Hand layup on a 2 ft x 5ft part... I will read up on vac bagging, see if there's data available

Pre preg dry carbon would be the ultimate light weight part but the spend and oven size makes it a no go

[NeedOne]

I think your hatch layup would be fine. I did similar with my seat boxes and they are stout. Best thing to do is layup what you have suggested and test it. Span it over a couple 4x4’s and stand on it see if it’s stiff enough for ya. The cowl 2x 1.5oz can would probably be fine too. Hydrostream seat shells look similar and they hold up over time

Ok cool, thanks for confirming. Good call on making test pieces, I am being tight about using up material, but that's what needs to be done, some old fashioned trial and error...

[David - WI]

That video of making the car hood is a 3–part series... they vacuum bagged (and resin–infused it) it in another episode: https://www.easycomposites.co.uk/lea...n-fibre-bonnet

[LakeFever]

Ok cool, thanks for confirming. Good call on making test pieces, I am being tight about using up material, but that's what needs to be done, some old fashioned trial and error...

test being build the piece as you spec and test it. If it feels flimsy throw another lay or two of 1708 on the bottom side.

[Jim Speros]

Coosa makes rigid foam panels. Easy to work with and panels only need to be skinned with glass. I would not suggest 1708 for light weight panels. Its great for tabbing but heavy when laid in sheets. The mat component offers little strength for its weight.

[OnPad]

Some Bullet bass boats have a lid layup schedule somewhat similar to what you would like to do. These lids are lighter than aluminum, but doubt they are half the weight, and are much more prone to damage at the hinge area. A couple of mine are cracked between the core and hinge.

In regards to the cowling question, I would agree with Jim, csm doesn't have much strength. It can also be hard to lay around corners. I would want a couple layers of lightweight cloth.

[Jim Speros]

I like to inlay a piece of marine plywood into the core where fasteners are located.

[NeedOne]

Appreciate the input fellas. For the hatch I'll run some test pieces cloth and some 1708.. I have some cloth material on hand too, just seems like 1708 is always talked about on here, but looking back it is mostly in reference to tabbing like you say Jim. Reinforcing the hinge area is a great point that needs incorporated. Thanks.

[NeedOne]

Some Bullet bass boats have a lid layup schedule somewhat similar to what you would like to do. These lids are lighter than aluminum, but doubt they are half the weight, and are much more prone to damage at the hinge area. A couple of mine are cracked between the core and hinge.

In regards to the cowling question, I would agree with Jim, csm doesn't have much strength. It can also be hard to lay around corners. I would want a couple layers of lightweight cloth.

The cowling I think will be a harder undertaking both in popping a mold and making the part due to the corners. With how much weight I'm cutting on this boat between gutting wet foam and the light hatch, might skip the cowl.. it just bugs me how heavy the efi fishing motor cowl is

[David - WI]

it just bugs me how heavy the efi fishing motor cowl is

But they are remarkably quiet​ (and tough) compared to the lightweight "racing" cowls.