[PSUBS-MAILIST] R300 FRP work

Fri May 22 12:19:33 EDT 2015

Sean, good to hear from you.  I am waiting to get on a plane to Barcelona so this will be brief.
>From what I understand of the photos, you design the hydrodynamic
fairing and then create virtual slices of the completed design, which
you fabricate out of expanded polystyrene.  I presume the slice
thickness just depends on the available thickness of polystyrene board
Yes, I used 4'x8' x4" sheets.
and/or how much work you want to do in shaping?  I notice that you have
these sections joined with wire ties in the photos... am I correct in
assuming that this was a temporary measure, and that you moved to
adhesives etc. prior to the body filler?
Yes, used a special spray on adhesive that joined the sections.  I used a CNC flat bed cutter that a local furniture fabrication company had to cut the section profiles based on a Autodcad drawing of the sections.  Bailing wire was used to temporary hold the sections until the adhesive set.

Once you've carved the EPS down to shape, you cover in a layer of body
filler which you can further refine and sand to a smooth finish, which
you then painted.  Is the paint necessary?  Or can you just apply a mold
release at that point?
Paint is probably not necessary but I wanted to make sure the mold release worked correctly.

After that, it would appear that you added flanges to define the mold
split lines.  Were these centered on the split line, or did you move
them slightly before laying up each half?  
Slightly off-center so that face was on centerline plane,
Furthermore, was it necessary
to split left and right, or do you think you could have done the mold as
only two parts?
Not sure I could have removed the female mold from the plug mold without splitting down the middle.  Also it made it easier to do FRP layup on the haves.

Do you just use a mold release on the plug and then start fiberglassing,
or do you apply a gelcoat first?
I used a mold release on the plug first.

Did you lay up the whole mold at once and then cut at the flange, or did
you do a section at a time?
Section at a time.

Once the female mold was finished, I presume you did some further
finishing / smoothing to the inside surface?
Yes, even though I sprayed a gel coat the surface was not clean enough so used normal auto paint procedure to paint the FRP shell.

Then a mold release / gel coat / glass to create the shell?
Yes

Once the shell was done and trimmed, how did you join the pieces
together and smooth the seam before casting your syntactic in?
Assembled on the pressure hull and used normal FRP layup techniques to join sections.  This normally included grinding down the joints and doing a layup.  

Om my next boat I am looking at generating a polystyrene plug mold 
cut on a 3-d CNC machine.  I would then apply tin foil to plug and lay the final FRP shell on this.  This will give better dimensional shape and should be quicker.
Got to run.

Cliff Redus
Redus Engineering
USA mobile:  830-931-1280
cliffordredus at sbcglobal.com 
      From: Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Friday, May 22, 2015 10:28 AM
 Subject: [PSUBS-MAILIST] R300 FRP work

Cliff - I have once again been studying your photos of the R300 build,
and I was hoping you might be able to elaborate a bit on the process you
used to construct the FRP fairing.  There are a couple of details that I
am still fuzzy on...

>From what I understand of the photos, you design the hydrodynamic
fairing and then create virtual slices of the completed design, which
you fabricate out of expanded polystyrene.  I presume the slice
thickness just depends on the available thickness of polystyrene board
and/or how much work you want to do in shaping?  I notice that you have
these sections joined with wire ties in the photos... am I correct in
assuming that this was a temporary measure, and that you moved to
adhesives etc. prior to the body filler?

Once you've carved the EPS down to shape, you cover in a layer of body
filler which you can further refine and sand to a smooth finish, which
you then painted.  Is the paint necessary?  Or can you just apply a mold
release at that point?

After that, it would appear that you added flanges to define the mold
split lines.  Were these centered on the split line, or did you move
them slightly before laying up each half?  Furthermore, was it necessary
to split left and right, or do you think you could have done the mold as
only two parts?

Do you just use a mold release on the plug and then start fiberglassing,
or do you apply a gelcoat first?

Did you lay up the whole mold at once and then cut at the flange, or did
you do a section at a time?

Once the female mold was finished, I presume you did some further
finishing / smoothing to the inside surface?

Then a mold release / gel coat / glass to create the shell?

Once the shell was done and trimmed, how did you join the pieces
together and smooth the seam before casting your syntactic in?

Thanks in advance.

Sean
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