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[jpdenver]

Greetings.

I acquired a MH&B Topaz Kit.  As it was shipped from the UK to South Africa and then to the US, there were
numerous chances for the contents of the box to shift and damage each other.

Today I finally got a chance to open the box and spread out the contents.
To my dismay I found that the hull had suffered damage.

The cracks do NOT go all the way through to the inside. 
Here are some pics:

The big question is how to repair and smooth the hull for paint.
The second question is WHEN - at the very first?  or after inner bulkheads and supports?

Thanks for any suggestions - I am hoping for help from someone who has actually done this before?

Regards,
Jim Pope
Denver, CO
USA

[derekwarner]

Hullo Jim......[& the 4 legged family ].......all is not lost, however some serious work will be required

You must define the hull material......[expanded styrene? .....fibreglass????]
You must ensure that the repair process will eliminate the full profile of the crack within the parent material
Full scale engineering repair processes will be required
If the individual cracks do not protrude into the inner hull, this is only a visual assumption.......
The following is only one method of stitch welding as a reclamation method to provide a totally sound mechanical hull surface & section

1.Find the visual starting point of a crack on the outside of the hull...drill a 1/16" diameter hole right through the hull
2. Repeat this at the other end of the crack
3.Depending on  the length of the crack, drill the same 1/16" diameter holes at say a nominal 1/2" spacing
4.With a V   shaped scraper, chase the crack on the outer hull until approx. 1/2 of the hull thickness
5. Repeat this on each & every external visual crack....

6. Repeat the steps 4. & 5. from the inside of the hull, until you are confident that the inside & outside V scrapings are near to joining

7. The area surface adjoining each crack will need preparation to be completed in accordance with the actual hull material
8. Mask with PVC tape the length of each individual internal chased crack
9. invert the hull and flood the viscous liquid/paste repair medium.......
10. Repeat the process as at 10. on the internal sections of chased crack

In reality you need to ensure that the hardness of the 'welding fluid' is similar or the same as the hull. This will ensure minimal surface removal of the hull material when completing the surface sanding process

Good luck..........Derek

[grendel]

I wonder if the uv cure liquid plastic they advertise on tv that you can get in asda and the like could be used in situations like this, apparently you apply it and give it a 3 second burst of uv light and it sets stronger than the original material, it seems to me it must have some use to us modellers.
http://www.jmldirect.com/at-home/home-accessories/lazer-bond-uv-activated-liquid-plastic-adhesive-and-filler/
note I am not recommending this stuff as I havent tried it, but from its description it might have some uses in cases likethis

[jpdenver]

More details:

1. The Hull is GRP - Fiberglass

2. The thickness is approx 1.5 - 2.0 MM  hard to measure due to gunwales.

3. The cracks DO NOT go all the way thru.

Derek -
The girls say hi! (well not really - but if you give them a cookie - they will say anything)

Questions -
If the cracks are not present on the inside, do I need to create them by gouging out?

What to use to fill?   in the US we have a number of possibilities - these I know how to use:
1. Bondo - Body Putty  (the one with the little tube of hardener)
2. Bondo with Glass Fiber.
3. The Red Body putty used for the "top"
4. Two PART EPOXY  - various cure times
5. UHU Acrylic (powder and tube of goo)

I have never done true fiberglass but I assume it is like epoxy,
with two parts.   with and without "glass?"

So what is recommended?

Thanks,
Jim

[Stavros]

Right then just to be on the safe side I would lay up some tissue on the inside of the hull .


On the outside of the hull it is the gell coat that has cracked and the simple soloution is very simple really and this is what I would personally do....build the hull up till you are ready to paint it and simply use a wood chisel and chase the cracks very carefully and sand the edges of the craks down and the surrounding area with some 180 grit and fill them up with some Bondo rub down and paint as normal...hope this helps you.
Personally I wouldnt bother with anything else to repair it 




Dave

[Liverbudgie2]

It looks to me as though the box has been crushed in transit this has resulted in the gel coat cracking; all is not lost though far from it.
Follow Dereks advice 1 to 5 though with 4 you could use a sharp blade to cut to loose gel coat way.
If as you say the Interior GRP matting is undamaged and sound i.e. does not wobble or deflect under light pressure. Use a fine car body filler to fill the damaged area and then rub down with a fine wet or dry paper used wet with a flexible block as support until the area is flat and smooth throughout.
If there is any deflection in the area and, even if there is no obvious sign of damage behind the damage I would reinforce the area with a fine GRP cloth and epoxy resin.
While you're doing this you should ensure that the hull retains its shape you could do this by using sacrificial bulkheads I suppose, or by using a couple of lengths of wood internally across the hull in the way of the damaged area and held in position by using superglue or fine brass screws, the holes of which could be filled in with the same car body filler as I mention previously.   
As for the gunwales these do as has been mention previously but ensure that you have a nice straight line otherwise it will stand out like a sore thumb. The underside should be finished off with a fine jewellers file rather than paper.
All this should be done before you carry out any other work on the hull.
LB
Who built his Topaz almost twenty years ago.

[Fastfaz]

   Hi,
      I had a similar problem with a hull on one of my tugs Stav is right if it hasn't cracked all the way through its not a problem. I repaired my hull (if you flexed the hull in the cracked area it opened up inside although without flexing it looked undamaged) by fibreglassing over the damaged area with glass mat and resin then do what Stav said with a sharp chisel I would lift under the crack edge to make sure that its undamaged then sand it fill with car body filler sand it all down until you are happy its ready to paint, be aware though that car bodyfiller is not waterproof. My tug is used for competition towing and gets lots of bangs and bashes the repair is fine with no sign of any leaks or hairline cracks in the paintwork. Hope this helps.
     Cheers,
           Pete.

[derekwarner]

Hullo again to Jim & the Girls.......

I am often taken to task for suggesting full scale industrial solutions for scale model work

This I acknowledge, however it is offered with the best intent.......

I concur with bluebird  that it is possible to only chase the crack externally......however cracks in any material can and often do probergate further than the human eye can see

Now I am not suggesting you use any industrial Dye Check System  ......but with fibreglass, you could use a few drops of RED cochineal food dye + 1 drop of dish washing liquid ...add it to 100 ml of warm water and gently stir....when you think the crack is fully chased, blow the dust away, lightly brush on a smear of the dyed water, wipe it off with a paper cloth, then blow dry on hi heat the cracked area with you good partners hair dryer

If the crack is fully chased all visual evidence of the crack will be gone....if there is still a red line visible......the crack still exists

With respect to the filling of the chased cracks, I would still suggest to discount any car body filler option and go belt & braces with an epoxy resin/glass manufacturers actual reclamation process for such imperfections......this will ensure that the hull is physically mechanically sound, and not just visually repaired

What ever you do, don't forget those  1/16" holes at the extreme ends of the cracks........they ensure that the crack does not continue on through fatigue.......[even the resonance from an electric motor+ coupling+ prop shaft can create harmonic vibration & fatigue]

Derek 

[jpdenver]

Everyone,

Thanks for all the advice.
It is too cold in the shop right now and with the holidays coming I will have
to wait until the new year to attempt my repairs.

I will post the process and the results.

Happy Holidays to all.

Regards,
Jim Pope
Denver

[jpdenver]

Greetings and Happy New Year.

I started the repairs.
First I lined the interior with a layer of Fabric and Resin as advised.
Then I chased the cracks, and made sure to pay attention to the ends.

When I chased the cracks I basically tried to "erase" them.

Using "Bondo Spot Putty" I applied multiple layers, sanding between each one.

I now think that the hull is stable enough to proceed with the build,
I'll be taking care of any minor spots as I go.

Thanks for all the advice, and please watch my build in that area of the forum.

Regards,
Jim Pope
Denver

[Stavros]

like the way you store your planks darned good idea


Dave

[jpdenver]

Dave,

Thanks for the complement.
The build for her is on the steam forum.

I separated the planks by type and size
just to keep my sanity.

Regards,
Jim Pope

[martno1fan]

When repairing gelcoat cracks the best way to do it is to get a dremel with a small round tipped tool and follow the cracks rounding over the edges as it goes this gives a better profile for the filler or gelcoat which is what i use to adhere to ,this way it will not crack or eventually fall out over time which can happen if its not done right.Clean out the crack using acetone then fill leaving it a little proud,i use a cocktail stick to put the material in then leave it to set before wet sanding smooth,if done right it wont even be noticeable after .