DNV rules

[willfox]

Does anyone know if you are able to use the CSM tie layer in the minimum skin weight requirement for DDNV high speed craft?

[Ad Hoc]

As far as I am aware, you are able to do whatever you like, so long as you satisfy the minimum amount of reinforcement (g/m^2) in tables A1 of section 5 & 6.

[willfox]

Thanks Ad Hoc

[mizkuzi]

Hello dear friends,

Is it okay if I use ABS Rules in my scantlings calculation for FRP boats when in fact the boat will be classed to DNV after construction? I hope so since I find ABS more easier & understandable for me to use than DNV Rules, and I didn't find any downloadable pdf for DNV rules for building and classing FRP vessels (perhaps somebody can give me a copy please???). THANK YOU

[Ad Hoc]

Mizkuzi

You can do whatever you like. But the pressures and derived scantlings from ABS wont be the same as those from DNV. They be either higher or lower. But as the graphs below suggest as a comparison between DNV & ABS, they will be lower. In which case your vessel wont pass DNV plan approval.

[rxcomposite]

Originally Posted by mizkuzi

...I didn't find any downloadable pdf for DNV rules for building and classing FRP vessels (perhaps somebody can give me a copy please???). THANK YOU

DNV rules link was posted by AH in this forum. You can download it. DNV composite formula refers to ISO standards and there are two spreadsheet available for free. One was created by TANSL. The thread is active. Search DNV rules as I get lost navigating and cannot paste multiple links.

Be careful using local resins. DNV uses the strain formula and local ortho resins microcracks earlier than expected and will fail before the limiting strain required by DNV. Use high quality ISO resin.

[rxcomposite]

Originally Posted by willfox

Does anyone know if you are able to use the CSM tie layer in the minimum skin weight requirement for DDNV high speed craft?

There are two rules that I remember in DNV. The tie coat next to gel coat and the csm for the last ply (in high speed craft) which can be dispensed with only if it can be proven. The interlaminar ply tie coat of light CSM, I am not sure of but I remember it is LR rules.

1. The tie coat next to gel coat is also a reinforcing layer, a permeability barrier, and a means to prevent print through. It is not wise to dispense with. My experience is Veil + 300 grs. CSM + 450 gr. CSM works best to cure all.
2. The tie coat in between layers is necessary if the last lamination has been permitted to cure at an advanced stage that it is considered a secondary bond. It can be dispensed with if an adequate surface preparation has been made such as an application of peel ply which can be impractical. Technically, hand lamination is supposed to be a continous process and the composite designer should be in tune with the production. If the production is continous 24/7, no problem. For overnight curing LR recommends sanding and prepping. DNV recommends peel ply.
3. The last CSM ply is to promote good bonding between the skin and the frames/stiffeners. It also acts as a permeability barrier as the bilge is not always dry. The premise of DNV is you need a good secondary bond. Most of the time, the last piece of the frame/stiffeners will be laid days after the skin coat has cured to an advanced stage so cannot be dispensed with.

From a technical stand point, WR over WR laminated all at once or continously is accepted but too strong for the thickness. Designers add CSM in the least stressed layers to add bulk, a cheap way of increasing thickness and stiffness.