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Chris Rogers - 7/6/2020 2:36:36 AM

What you have drawn is totally doable but probably more complicated than necessary.  Orientation of the job makes no difference to the infusion part - but overhead is always a pain.  It looks like a solid single skin laminate without core.  What is the material the boat is built from?  E-glass/polyester, e-glass/epoxy, carbon/epoxy?   

If this job came my way I'd go first to vacuum bagged wet-layup with epoxy - or open molded vinylester - but probably epoxy unless a gelcoat repair too.  Its less demanding of perfect vacuum and easier to use - and you could do multiple holes with one resin mix and wet-out.  Structurally, bagged wet layup is very similar to infusion and its easier to control.  If there is no core, you could (in theory) do the whole thing from one side.  A piece of hard-ish (depending on curvature) plastic stuck over the back (inside usually - because access is harder) and secured with tape and covered with a vacuum bag stuck to the hull can be a good former.  Then you can do the whole thing from the outside (drill a few tiny holes near the edge of the repair through the hull to tie the bags together or connect the bag to the pump inside and outside) - then cure and fair.  You can wet out a big sheet of material between plastic sheet and cut staggered stacks to your pattern.  A 15:1-30:1 scarf is common - or whatever your engineer says - for smaller holes, the scarf slope can be less especially if its in a low-load area. 

Doing it from both sides is better - but not by a ton if there is no core - it just feels neater mostly!  Sometimes avoiding inside grinding is a big deal. Your only real reason to consider infusion is that doing a bagged wet layup of 12mm of material is not ideal - its hard to get air out and lots of layers!  You can of course break it up into two cure cycles and do 6mm at a time.  If it were a much larger repair and the boat was built using infusion - then an infused repair with matching materials would be a much more attractive idea. So I guess it totally depends on the boat, the location on the hull, access, engineering, materials, etc...

If you have never done infusion before, you will be more likely to get a good result with bagged wet-layup - its just easier to get right. 

Do you have any pictures of the holes?

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Chris Rogers - 7/7/2020 2:39:38 AM

Oh - that is kind of a big hole in an important spot!  Did you remove a saildrive?  If there was a hole there already then it is important to tie it back together will but unless you cut some internal structure (looks awful thick up front there!) then a structural skin repair should be adequate.  Generally a boat like this is built with a bit of chopped strand mat mixed with either woven roving or stitched material - but usually plenty of mat!  An epoxy repair scarfed in well - which will get you into the keel landing zone a bit - should be more than adequate.  When in doubt go with an equal amount of fiber reinforcement in all directions - and no need to use mat with epoxy.  You can repair any internal structure the same way.  If there is some heavy keel structure at the end of that hole (forward I think) like a grid or a keel floor then you'll need to do most of the laminating from the outside to lap onto existing material. 

Given the potential porosity of the laminate and the issue of bagging around bonded internal structure I think infusion would be a challenge here - probably doable but maybe not satisfying or ideal!  Two bagging operations of 6mm of wet-laid glass in epoxy should be fine.  If you need to you can stack up the wet plies of material off he boat (rolled really well and cut to shape) and lay it on the vacuum bag and belled stack and then press the whole thing up into place onto wet out surface. Might take a helper or a sheet of cardboard and some tape to get it done.  Set up another vacuum bag with a plastic shape former / sheet on the inside too and you'll be good to go.  Second operation (a day or two later) and you won't need the internal bag because it'll be (hopefully) vacuum tight.  You can clean up the inside and do a ply or two just to tidy thing up if you want.   

Just an educated guess here from one picture: if you grind a taper and lap 15:1 or 20:1 (180-240mm) out onto that hull you should be in good shape unless there's something seriously structural that got cut out - or I'm missing something.  Could go with less on the smaller hole - especially if you do half from the inside and half from the outside.