Dinghy infusion challenges

I've been infusing small 8' dinghy sailboats (sabots/prams) for about 18 months and have a consistent problem with voids / spots where the glass is not wetting out next to the gel coat. I've now had to trash two boats as about 1/3 of the glass is dry and the other few boats have needed the gel coat chipped out of many spots, then wetted out, faired, re-gelcoated and polished - a ton of work... I've been using VE infusion resin for all boats.

To reduce on voids I thought I'd go from the 28 Hg vacuum to about 18 to reduce pulling gas from the resin. I've also made a few changes to the lay-up, they've been:

1. My best one
Gel coat (thin and clear to see how well I did with core templates)
stitched 20oz triax 0/90 - 45/45 cloth
1/2" scored & perforated foam core
same 20oz stitched cloth
peel ply
bag

2. some dry spots on hull
Same lay-up but 1/4" foam

3. some voids to be filled
Gel coat
Biax 20oz 0/90 - CMS
4mm Soric core
20oz stitched triax
peel ply
bag

4. More dry spots on hull requiring fairing of the hull
Gel coat
Biax 20oz 0/90 - CMS
1/4" scrimmed/scored foam
20oz stitched triax
peel ply
bag

5. I thought the CMS might be compressed to keep the resin to move over the gel coat. But this boat was so bad I had to toss the 1st try. The 2nd try had dry spots on hull requiring significant fairing of the hull:
Gel coat
20oz stitched triax
1/4" scrimmed/scored foam
20oz stitched triax
peel ply
bag

6. Just made this boat and checked it this morning. May dry spots (see attached photos) and will have to toss.
Gel coat
this surface veil to reduce print-though (maybe better wetting out?)
20oz stitched triax
1/4" scrimmed/scored foam
20oz stitched triax
peel ply
bag

Yeah, running out of ideas. Was going thinking of trying a Continuous Strand Mat next to the gel coat but that might add too much weight to the boat. Any ideas would be surely appreciated. You an see a time-lapse of boat #6 at http://bedfordboats.com/2014/12/sabot-hull-6/ - thanks!

See attached thumb nails of 1) voids on the rails and 2) dry spots under gel coat

 

The voids under the rail is called alligatoring, caused by the laminating resin attacking the gelcoat. There are various causes, usually too thin of gelcoat or the gelcoat not cured enough before laminating.

 

Yeah, good call. It could have been pretty thin at the rail as my mold is the same color as the gelcoat for this boat... Thanks!

 

Also, I'm now inclined to hand lay-up the glass to the gel coat then load the boat with the rest of the material and then infuse it. Any thoughts if this is crazy or not? Thanks...

 

You might have 2 different problems, improper gelcoat application/cure being one and the resin distribution system for the infusing being another.

As far as hand laying a skin coat, there's nothing unusual about that but if the laminate is ending up dry, it wouldn't seem to remedy that problem unless there are air leaks in the mold which the skin coat might seal up.

Try 'searching' in the fiberglass boat building section using various search words. Gelcoat problems are numerous and mysterious and have been discussed extensively. 'Infusion' should bring up a number of threads about the process and it's problems.

Also, when you pull up a thread, scroll down to the bottom of the page for a list of 'similar threads'.

 

You might have 2 different problems, improper gelcoat application/cure being one and the resin distribution system for the infusing being another.

As far as hand laying a skin coat, there's nothing unusual about that but if the laminate is ending up dry, it wouldn't seem to remedy that problem unless there are air leaks in the mold which the skin coat might seal up.

In the fiberglass boat building section, try the 'search this forum' function using various search words. Gelcoat problems are numerous and mysterious and have been discussed extensively. 'Infusion' should bring up a number of threads about the process and it's problems.

Also, when you pull up a thread, scroll down to the bottom of the page for a list of 'similar threads'.

 

Thanks SamSam, I'll give search a try...