power cat foil

container · May 20, 2022

I'm building a foil for an 8.5 metre power cat, from memory the boat weighs about 2.5t and the foil is designed to carry ~1 ton @ 20kts or there abouts.

It will be female moulded, wet epoxy/carbon layup and not vacuum bagged.

The foil as moulded is 1200mm x 240mm x 19mm, with the actual span being ~1050mm. It lands on the hulls just beneath the chine flats and is supported by a vertical strut mid span.

The layup i'm considering is:
(all cloth 300gm)
2x DB +/-45*
5x UNIS 0*
1x DB
5x UNIS
1x DB
Once the halves are bonded together the leading edge will get 3x 300gm DB tapes

Does that layup seem sufficient?

Since it wont be bagged it will have to be done in 2 or 3 seperate lams. With that laminate there should only be a few mm between the 2 halves of the foil, I'm undecided whether to use a 80kg pvc foam core here or just fill it up with unis ($$$).

If using a foam core, should there be some kind of sheer web or stack on unis down the middle as per the picture?

any help is much appreciated
cheers

fallguy · May 20, 2022

Really very cool project. So, the foil is just to help a semi-displacement form up on plane? Or a planing hull on less?

I don't have enough credential or raw wisdom to help you on the layup. Take me words as a grain of salt. I do not understand how this part could have a core, except if the core is merely there as a former. And the uni stack seems unneeded then. That is, the glasswork should not consider the presence of the core. But that is just a very uneducated amateur builder opinion.

I would love to hear more about how this will perform as I have a 10M powercat nearing completion. A foil is almost a fantasy!

fallguy · May 20, 2022

@Richard Woods

Have you seen this foil business? Thought it may be interesting. Not sure if it is at all relevant, but so curious.

Alan Cattelliot · May 24, 2022

Hi,
Estimating that the maximum stress would occur in way of hulls, and assuming its fixed mounting,
1t of pressure is shared in two half. The equivalent force is applied between supports.

The maximum bending moment is 0.5t x 1.050m / 2 /2 = 131.25 kg.m. For commercial application, the safety coefficient of your skin is ok, but you should use balsa instead of PVC ($$$

for your core.

I estimate your laminate according to ISO 12215 standard, a ply-by-ply analysis would be give roughly these security factors,
providing that you are able to produce a laminate with sufficient mechanical properties (t99 is thickness in the table below, for you to check your fiber content rates)

Two scenarii. One with GURIT PVC80HT core, which do not seem sufficient to have enough shear strengh to your application, The other with balsa core, which gives an acceptable safety coefficient.
As to read the safety coefficient, the negative sign stands for compression. so it's ok for a value to be negative. Every values of factor comprise between minus one and plus one do not pass a safety criteria of 2 before rupture.
For instance, a factor -8.9 means that the safety factor for that ply is 17.8 before rupture in compression.

Please, consider this is only rough calculations based on ideal fixity connections, not taking account into the exact shape of your foil, not verifying the hydrodynamics capabilites of your profile, arbitrary majoring +4 the safety coefficient due to the unknown quality of your composite. ( but I would use these results indeed to give a quick answer to a boatyard ...). Without any form of agreement, I shall assume no responsability in the calculations given here, nor on any application of them, in any case.

Code:

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  <tr>
    <th class="tg-vjr2">TypePliMateriau96</th>
    <th class="tg-vjr2">Zna97</th>
    <th class="tg-vjr2">Reference98</th>
    <th class="tg-vjr2">t99</th>
    <th class="tg-vjr2">Factor_contrainte104</th>
    <th class="tg-vjr2">Factor_cisaillement105</th>
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  <tr>
    <td class="tg-girr">Ame</td>
    <td class="tg-girr">12,2178751</td>
    <td class="tg-girr">End grain balsa</td>
    <td class="tg-girr">5,38</td>
    <td class="tg-girr">520,6</td>
    <td class="tg-girr">2,0</td>
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    <td class="tg-771h">Ame</td>
    <td class="tg-771h">12,2178751</td>
    <td class="tg-771h">End grain balsa</td>
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    <td class="tg-771h">-564,6</td>
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    <td class="tg-girr">Carbone HR</td>
    <td class="tg-girr">12,2178751</td>
    <td class="tg-girr">BX45 300 g/m²</td>
    <td class="tg-girr">0,52</td>
    <td class="tg-girr">-23,2</td>
    <td class="tg-girr">10,3</td>
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    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178751</td>
    <td class="tg-771h">BX45 300 g/m²</td>
    <td class="tg-771h">0,52</td>
    <td class="tg-771h">-21,3</td>
    <td class="tg-771h">10,4</td>
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    <td class="tg-girr">Carbone HR</td>
    <td class="tg-girr">12,2178751</td>
    <td class="tg-girr">UD90 300 g/m²</td>
    <td class="tg-girr">0,45</td>
    <td class="tg-girr">-15,0</td>
    <td class="tg-girr">10,5</td>
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    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178751</td>
    <td class="tg-771h">UD90 300 g/m²</td>
    <td class="tg-771h">0,45</td>
    <td class="tg-771h">-14,1</td>
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    <td class="tg-girr">Carbone HR</td>
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    <td class="tg-girr">-13,2</td>
    <td class="tg-girr">12,7</td>
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    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178751</td>
    <td class="tg-771h">UD90 300 g/m²</td>
    <td class="tg-771h">0,45</td>
    <td class="tg-771h">-12,5</td>
    <td class="tg-771h">14,3</td>
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  <tr>
    <td class="tg-girr">Carbone HR</td>
    <td class="tg-girr">12,2178751</td>
    <td class="tg-girr">UD90 300 g/m²</td>
    <td class="tg-girr">0,45</td>
    <td class="tg-girr">-11,8</td>
    <td class="tg-girr">16,5</td>
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  <tr>
    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178751</td>
    <td class="tg-771h">BX45 300 g/m²</td>
    <td class="tg-771h">0,52</td>
    <td class="tg-771h">-14,7</td>
    <td class="tg-771h">17,9</td>
  </tr>
  <tr>
    <td class="tg-girr">Carbone HR</td>
    <td class="tg-girr">12,2178751</td>
    <td class="tg-girr">UD90 300 g/m²</td>
    <td class="tg-girr">0,45</td>
    <td class="tg-girr">-10,6</td>
    <td class="tg-girr">20,5</td>
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  <tr>
    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178751</td>
    <td class="tg-771h">UD90 300 g/m²</td>
    <td class="tg-771h">0,45</td>
    <td class="tg-771h">-10,1</td>
    <td class="tg-771h">26,5</td>
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  <tr>
    <td class="tg-girr">Carbone HR</td>
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    <td class="tg-girr">UD90 300 g/m²</td>
    <td class="tg-girr">0,45</td>
    <td class="tg-girr">-9,7</td>
    <td class="tg-girr">38,1</td>
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  <tr>
    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178751</td>
    <td class="tg-771h">UD90 300 g/m²</td>
    <td class="tg-771h">0,45</td>
    <td class="tg-771h">-9,3</td>
    <td class="tg-771h">70,2</td>
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  <tr>
    <td class="tg-girr">Carbone HR</td>
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    <td class="tg-girr">0,45</td>
    <td class="tg-girr">-8,9</td>
    <td class="tg-girr">579,7</td>
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    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178751</td>
    <td class="tg-771h">BX45 300 g/m²</td>
    <td class="tg-771h">0,52</td>
    <td class="tg-771h">-11,2</td>
    <td class="tg-771h">0,0</td>
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    <td class="tg-771h">BX45 300 g/m²</td>
    <td class="tg-771h">0,52</td>
    <td class="tg-771h">-21,3</td>
    <td class="tg-771h">10,4</td>
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    <td class="tg-girr">12,2178741</td>
    <td class="tg-girr">UD90 300 g/m²</td>
    <td class="tg-girr">0,45</td>
    <td class="tg-girr">-15,0</td>
    <td class="tg-girr">10,5</td>
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  <tr>
    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178741</td>
    <td class="tg-771h">UD90 300 g/m²</td>
    <td class="tg-771h">0,45</td>
    <td class="tg-771h">-14,1</td>
    <td class="tg-771h">11,5</td>
  </tr>
  <tr>
    <td class="tg-girr">Carbone HR</td>
    <td class="tg-girr">12,2178741</td>
    <td class="tg-girr">UD90 300 g/m²</td>
    <td class="tg-girr">0,45</td>
    <td class="tg-girr">-13,2</td>
    <td class="tg-girr">12,7</td>
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    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178741</td>
    <td class="tg-771h">UD90 300 g/m²</td>
    <td class="tg-771h">0,45</td>
    <td class="tg-771h">-12,5</td>
    <td class="tg-771h">14,3</td>
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    <td class="tg-girr">Carbone HR</td>
    <td class="tg-girr">12,2178741</td>
    <td class="tg-girr">UD90 300 g/m²</td>
    <td class="tg-girr">0,45</td>
    <td class="tg-girr">-11,8</td>
    <td class="tg-girr">16,5</td>
  </tr>
  <tr>
    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178741</td>
    <td class="tg-771h">BX45 300 g/m²</td>
    <td class="tg-771h">0,52</td>
    <td class="tg-771h">-14,7</td>
    <td class="tg-771h">17,9</td>
  </tr>
  <tr>
    <td class="tg-girr">Carbone HR</td>
    <td class="tg-girr">12,2178741</td>
    <td class="tg-girr">UD90 300 g/m²</td>
    <td class="tg-girr">0,45</td>
    <td class="tg-girr">-10,6</td>
    <td class="tg-girr">20,5</td>
  </tr>
  <tr>
    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178741</td>
    <td class="tg-771h">UD90 300 g/m²</td>
    <td class="tg-771h">0,45</td>
    <td class="tg-771h">-10,1</td>
    <td class="tg-771h">26,5</td>
  </tr>
  <tr>
    <td class="tg-girr">Carbone HR</td>
    <td class="tg-girr">12,2178741</td>
    <td class="tg-girr">UD90 300 g/m²</td>
    <td class="tg-girr">0,45</td>
    <td class="tg-girr">-9,7</td>
    <td class="tg-girr">38,1</td>
  </tr>
  <tr>
    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178741</td>
    <td class="tg-771h">UD90 300 g/m²</td>
    <td class="tg-771h">0,45</td>
    <td class="tg-771h">-9,3</td>
    <td class="tg-771h">70,2</td>
  </tr>
  <tr>
    <td class="tg-girr">Carbone HR</td>
    <td class="tg-girr">12,2178741</td>
    <td class="tg-girr">UD90 300 g/m²</td>
    <td class="tg-girr">0,45</td>
    <td class="tg-girr">-8,9</td>
    <td class="tg-girr">579,7</td>
  </tr>
  <tr>
    <td class="tg-771h">Carbone HR</td>
    <td class="tg-771h">12,2178741</td>
    <td class="tg-771h">BX45 300 g/m²</td>
    <td class="tg-771h">0,52</td>
    <td class="tg-771h">-11,2</td>
    <td class="tg-771h">0,0</td>
  </tr>
</tbody>
</table>

Alan Cattelliot · May 24, 2022

Sorry for the poor presentation of the results.... I do not know how to post html table in the forum, so I post the code.

Alan Cattelliot · May 24, 2022

Here is a capture of what you may see if you use html viewer to display the code. One DB is not in place in the laminate sequence, but that should not change the overall conclusion. I will change that and re do the calculations if you can just confirm the laminate stacking sequence.

Cheers,

Gasdok · Aug 16, 2022

I'm building an assymetrical cat and the foil will use boron or galvanized rebar.

power cat foil

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