Fiberglass Repair Option

I had a boat shop come to look at my hull of the Ranger Tug today . His opinion to repair is a modified outside repair . He believes the amount of interior shell to cut out would be more time and money than the gain would be . Please give me your opinion on this repair idea and what price tag a repair like this would be ( they charge $95 per hour ) .
-- Grind bad area beyond to good areas -- cut out bad area , wide and long enough to get in hand(s) with mini hand held grinder/sander and feather inside hull edges back , inspect with camera , make fiberglass backing plate to insert up into hull which is bonded with the West Epoxy system . Screws ( from outside )would pull down the backer plate into place . After curing , the outer repair would be done with mat in West Epoxy system , then gel coat . His said it would be stronger that the factories questionable makeup and thickness . I would appreciate opinions . Thank you

 

Not a fan.

Here is why.

1. The original laminate was weak. The best way to fix a weak laminate is bulkhead to bulkhead, remove gc or paint and laminate 3 layers of 1708 with epoxy. Feather grind the old laminate outside after the new is inside and step the repair pieces small to big. Switch to an ester for gc on the last layer.. It'll never break this way.

2. The long crack. Does the long crack cross a bulkhead or floor? How would you tab it properly from below if so. If not, then a crossmember floor would be smart. Unless it is only delam..., but if there is a crossmember, you can't repair delam around structures without tabbing.

3. If he thinks feather grinding the inside is smart, he doesn't really get it. The inside does not require feather grinding, only the outside so you can build back the laminate bigger to smaller pieces. The inside requires grinding to 60 grit or less and removal of all gc/paint/chop/roughness.

4. Is he suggesting epoxy? If not, forget it. There is no reason to save $75 on resin here. Sorry-you said epoxy..

show him my reply; he may do a lot of glass repair, but yours is a serious structural deficiency to start

 

If he can get three layers of 1708 bonded well with epoxy to the inside and there is no tabbing repair, then let him do it. If he needs to cut a few access panels above to get the bonds done well; that would be wise. He would have to make a clear form of some kind over the cutaway areas so he could see and that form would need a step the thickness of the hull for the outside laminates.

(it would be easier to do one layer, but the next two would be really difficult)
You said the hull was 1/8" thick iirc, this is too thin to support even a few hundred pounds let alone a forklift prong and the hull weight.

When you are done, you want about 0.250-.375" of glass verus that 1/8". This is 6 layers of 1708. How can he get 6 layers with cleats?

You have no glass experience at all, correct? I think you need to have someone specify the work and ask the repair guy if he'll meet the spec versus him saying I can fix the damage.

 

Fixing the damage can be done by grinding the edges on the inside and epoxy bonding a glass cleat all around the holes. This is a very poor repair because the bond strength is based on the cleat dimensions and substrate quality. A one inch cleat means 1/2" is on the old stuff which may be polyester. Then you have a 500 psi or lower bond rating which is very poor on the say 1/2". I can tell you, based on experience, I painted a locker, then applied a cleat to the edge with 40 grit sanding. The bond was about 1/2". I never anticipated much load and thought I could get away with it. But I was working in the locker one day and push my 200# o to the cleat and broke it off! So, the width of the cleating is really important and it can't be wide against a bulkhead or stringer..coming up against structures is done by putting the glass vertically-impossible from below. I suppose you can bond angled cleats to structural members, but will he? I'd say you need about a 3" minimum width cleat on the existing boat, but the repair is not as good as adding glass inside.

 

Pretty hard to comment without a clear idea of where the damage is, in relation to internal structures.

 

Thanks Fallguy , here are some answers - I said feather the inside , I think he just said grind , --- when you say 3 '' overlap of cleat , do you mean the backing fiberglass plate ? -- 3 '' overlap bond inside on all 4 sides ? -- crack does not cross a bulkhead ( cracked area is behind bulkhead , was blocked behind bulkhead ) --- hull is 6.3 mm thick - I have no fiberglass experience ( was welder/fab guy ) -- Have my Lab results back - Resin burn off , ash content 55.8 % -- UTS 18.3 ksi tension - 29.2 ksi compression -- 15 ksi yield strength . -- polyester resin - at least 2 fibers , one is 10-12 um , other is 29-22 um , I am learning the expensive way about fiberglass . To access the inside of the hull , the width of the center walkway up the center of the pilothouse , the Starboard seat /microwave area glass width area , would have to come out to get the waste tank out , maybe the water tank also . There is also a fiberglass liner that is below the tanks which would have to come out . Currently about 2.5 '' -3 '' space between the liner and inside of hull .

 

That figure of 6.3mm (quarter inch) is thin for a boat that size.

 

Definitely on the bottom of the range I'd say.

@bucketlist

I am not specifying 3"!

I am saying some minimum amount of bond of the cleat would be needed and that the cleats would make it so you don't/can't make the area any stronger.

The old layup is probably polyester or vinylester and so a very short bondline of cleat to existing hull is not going to be the strength of epoxy, but the strength of the existing substrate. And so, this must be considered. And the repair must not be weaker than the original.

My experience is enough to tell you a glass cleat say one inch wide is pitifully weak here. And if you are up against a structure, a repair guy might do that.

I am merely saying 3" is probably closer to the need and I am trying to get you to understand the potential problems with such a method.

I am not writing your spec here.

 

Definitely - especially as I think it is in way of the turn of the bilge, where the hull is attached to the keel.

 

Yes , looking through the two holes with a boroscope is hard to see the curves , edges etc where the backing plate would sit . Here are two pictures of the floor , seat area that would have to come out , ( picture is port , but starboard driver area would have to come out , to get tank(s) out .

 

Here are the two photos in Bucket's zip file above - I don't know why the second photo is sideways. I saved it to my computer right side up, but then it got posted like this.

 

The forces must be very well understood.

It is outside my cv to do it. I know some accounting.

If you use a force of 24000 pounds and apply that force to an area of cleats for a repair of 12x12, something like this is the math...

cleat area 1/2" bond all around is 2" total surface times 12" or 24" total area, then you have 1000 psi and the old ester bond to cleat interface will fail, double it to one inch, 500 psi still fails the old bond or a dirty or painted or gelcoat surface

I don't know the areas, the substrate, how to apply a flying boat force properly. I only know enough to tell you the pitfalls. And that you ought to find someone to spec the repair who is not the repair guy.

 

The issue I take here is you are trading doing the repair well and right for the cosmetics inside.

Who cares if you put a cleat in and have a 1/8 caulked gap in the footrest for the helm chair that can be done with 5200 versus fixing the hull issue right?

Me. I tear out the floor above, grind it out, lay in some new fiberglass and epoxy over a mold or something to hold the hull shape. Then grind the glass and secondary bond repair layers with epoxy up to needed finish.

The repair guy is worried you are going to want to make everything inside perfect and you need a return to function. The hull is first. A small cut line in the production molded interior should get repaired and you ought to let them fix that fast with cleats in there!

 

It seems relatively doable, just a case of having a backing to glass against, glassing upside down isn't that difficult.

 

The issue is the backing. If you don't get much bond surface on even one edge of a 12x12 repair, all the load in a wave impact will end up finding the weak spot. Obviously, you have the feathering of the exterior, but I'd say there is a rational limit on hole repairs... ?

I wonder if we can get @rxcomposite to give an opinion. Most likely @bucketlist, he will want to know how big the anticipated hole(s) are, speed and weight of the boat.