Fiberglass type

Exactly that's the one

 

I have had similar failures on plywood boats with taped chines as @fallguy with the standard 0/90 fiberglass tape.
I now use a 45/-45 tape.

 

Thanks for the info.
I will use pvc foam . I will reinforced the chines.

 

The glass choice is important. Glass oriented 0/90 laid along the hullside is poor because half the fibers contribute so little; if any. It isn’t about reinforcement, but fiber direction.

 

I understand. Thank you. I'll us the 45/45

 

As mentioned, something is not right in post #37. Based on published data, the displacement is not correct using the standard L*B*T*Cb formula. Since you confirmed that this is the Arrow 40, I decided to play around it in my Excel. This is my way of doodling things as I can scale any lines plan to any coefficient I want and at the same time carry calculations. Based on your specifications you designed it at 1,000 kg displacement, 7 meter length waterline, 0.23 m. draught, and using 0.40 Cb (0.40 to 0.45 typical), The drawing turns out to be like this. You can get only 5.8 m length waterline with the transom high out of the water. Using Simpson’s rule for greater accuracy, calc seems to be on point but typical sailboat this size is 2,500 to 3,500 kg. displacement. You need to check your design.

My “doodle” allows me to find the reasonable frame spacing and panel size. The designed displacement, hull dimensions, and estimated speed of 8 knots will allow me to calculate the hull pressures. I assumed you are going to use this in inshore use with 2 meter wave height. Thus, ISO calculates about 8 kN/m2 bottom pressure, 45.5 kN/m2 peak. LR calcs it at 20 kN/m2.

You have chosen PVC 20 mm core bottom, 390 gr/m2 twill fabric, and using Diolen fabric over Carbon Fiber “for protecting carbon fiber. It doesn't crack and more uv resistance. I am thinking to do vacuum bagging or maybe hand laying.”

My next post will contain my analysis and comments on your chosen materials as there are many ways of doing it.

Spoiler alert. You can laminate the bottom with 600 gr/m2 (50% Gc) each side with 10 mm PVC core of 48 kg/m3 with a 840 mm x 420 panel size. It passes the ISO core shear requirement but not the min. inner and outer skin thickness. Failed at both ISO and LR criteria.

 

Thank you for the informations. I use delfship to design and calculat the displasment and I'm working on the design.
I appreciate

 

Beyond the desired hull shape and the plan for a foam core,how do you propose to undertake the build process?One does not simply throw a quantity of the chosen materials into the workshop and move a complete boat out at the conclusion of the process and the assorted compound curves near the bow may be challenging.

 

I have built 2 wooden dinghy when I was 16 years old for fishing. I repaired boat as well in the past. I build many furnitures. I understand tat boat building is not that simple, need patient. I have a modest garage and storage and helpe from friends and neighbours. I am confident that I can build this boat. For the compound curves St the bow I use s guide line from the smalltrimarandesign Website explaining how to do it more simply.
I try to keep things simple.

 

That is not how you calculate the displacement. You add all the weights of every part of the boat, its equipment, and the crew. Then you calculate the Center of Gravity, and it has to coincide vertically with you planned Center of buoyancy. Delfship will not do that for you automatically. This is one the most important and tedious part of boat design.

 

I understand. Thank you.

 

I am uploading the updated version of the spreadsheet. Page 1 shows the 5 meter version with the corresponding downloaded dimensions and hull lines. Based on the data, it appears that the displacement is not correct. Page 2 is your 7 meter version. The displacement is about right at 1,000 kg that you gave. With the given draft, it shows the Lwl is only 5.8 m., not 7.

Though that seems incorrect, that is your dimensions and I fed the data to my spreadsheet.

Sorry but my spreadsheet is not working. I have to disable it as it is interlinked to a wider database which is cumbersome to upload. The core sizing shows that with a 800 mm x 400 mm panel size and 10 kN/m2 of pressure and a WR for facing (skin), a 10 mm 48 kg/m3 core will suffice.

The Lloyd’s stress analysis results are self explanatory. It shows that even wth the 10 mm core and a single layer 0.374 mm. Glass Fiber skin will suffice. The core shear stress meets ISO standard and the stress on the skin is minimal. However, the minimum skin thickness is not met as it subject to “puncture”.

A biax was added to increase the skin thickness. With 2 layers, the min skin thickness was met, stress was reduced. It is overbuilt for the condition but the criteria was met.

In one of your post you intend to use Epoxy and Carbon Fiber so we investigate.

To increase impact resistance, either you make the boat “limber” by decreasing modulus so that the boat twist and gives at every impact without exceeding the safety limit. Fiberglass has low modulus. On the other hand, you can increase the modulus so that the impact is resisted and is spread quickly into a wider area, dissipating the impact. This gives you a “stiff” uncomfortable boat. High modulus = Carbon fiber.

One layer of carbon fiber shows it has sufficient strength but lacks the thickness criteria. Two layers show it meets the criteria. The numbers speak for itself. Carbon fiber laminate is just too much waste of money and overdesign. An overkill. Too stiff the software could not even calculate the deflection.

Next I will investigate your plan of using Diolen fabric.

 

Thank you so much. Ghat is so helpful. I appreciate .
Yesterday I contacted the company to tell me the prices of shipping and taxes and availability of the materials. They have only 5 sheets of 60 kg/ 15 mm. After reading your post I am going to ask them if they have 10mm pvc foam 60kg.They don't have 48kg pvc panels in their website.
Thank you for your help.

 

60 kg/m3 15mm will do. We can go higher bottom pressure at 20 kN/m2 and up to 1,200 kg disp.

Fine tune your displacement calculation as Gonzo has suggested.

 

The weight of my crew and cargo about 400 kg ÷-.
But I don't know how much the boat will weight at the moment.