Reinforcing layer on unsound hull

[Paul75Participant @paul75]

Hello Everyone.

I bought a 1/96th scale HMS Solebay only to later discover that it has an unsound hull.

It was made in the early 1980s when SLA batteries were the only choice and, because of this, it had its GRP hull deepened to accommodate the weight. To do this the builder sliced the hull horizontally in much the same way as a sponge is sliced to make a Victoria sponge cake and used thin plywood (or perhaps balsa) to fill the join and deepen the hull.

Unfortunately, over the years this arrangement has weakened making the joint flex, albeit only slightly. This causes the paint on the surface of the hull to crack along the wood/GRP joins which is unsatisfactory.

Other than this issue it's a nice model boat and worth saving.

Can anyone please advise me how I might go about reinforcing the hull from the outside (i.e. without removing the deck which is sealed to the hull and has fittings including handrails attached) without losing all of the detail on the hull surface (deck plating etc)?

Are there any very thin GRP sheets available which could be layered on the outside of the hull and set with resin to cover the joint and prevent the cracks from forming?

Any advice would be appreciated.

Many thanks,

Paul.

[Paul75Participant @paul75]

[Ray Wood 3Participant @raywood3]

Hi Paul,

If it's taken this long to crack the paintwork, it may only be filling from the outside with epoxy & re paint?

You didn't mention how thick the infill ply layer is and how accessible the hull is through the hatches but if possible warm up some laminating epoxy resin so it flows, and slosh it around inside carefully to improve the joint between the grp hull and the ply. Don't be tempted with polyester resin as it doesn't have the same sticking properties as exoxy.

Interesting dilemma, some photos would help 😀

Regards Ray

[ashley needhamParticipant @ashleyneedham69188]

I would go with what Ray says. To be honest, unless you strip the hull and apply glass/resin to the outside it is muchly your only option. Perhaps scraping the cracks slightly might help get more (glue essentially) epoxy in the joint, along with removing some paint either side.

The cracking may only be some differential expansion and shrinkage of the different materials and nothing more, unless the cracks ARE worse than that?

Ashley

[Paul75Participant @paul75]

Thanks for your replies fellas.

The cracks are only fine (less than 1mm wide) but when filled (I've tried epoxy resin and Isopon) the cracks reappear when the model is handled due to slight flexing of the hull. Since the whole hull was cut to deepen it the horizontal cracks tend to run in certain places along most of the length of the hull.

I think the limited access through the hatches might mean that Ray's solution could be a bit difficult to achieve. I might give it a go though because it doesn't visibly affect the outside surface of the hull. Could you recommend a good low viscosity laminating epoxy for the job?

Many thanks,

Paul.

[ashley needhamParticipant @ashleyneedham69188]

Paul. It sounds bad, to be honest, for cracks to open so easily and does not bode well for long term stability.

. I would be looking at stripping the hull and recovering with fine glass cloth and Z-poxy resin, or normal epoxy resin. You can get glass cloth very fine, woven is best, it is like silk.

Simply running resin inside, while great for certain things, it not likely to give you the strength you do seem to need in this case

Ashley

[Ray Wood 3Participant @raywood3]

Hi Paul,

Sounds like your Victoria sponge cake has had her day in the wet stuff !!

How about a new grp hull and use the superstructue and running gear from your old boat??

Regards Ray

[Ray Wood 3Participant @raywood3]

Hi Paul,

Dean's Marine produce a kit @ 1/96th scale for Solbay, maybe they would sell you just the hull??

Regards Ray

[Charles OatesParticipant @charlesoates31738]

Hi Paul, what a horrible but interesting problem. If I can add my twopenny worth, I think your only option is to strip the model down. The amount of handling the ship will get in rubbing down the hull, repairing, sanding and painting is likely to cause a lot of damage otherwise. Any repairs to the outside only are likely to be unsightly, and may not last.

Real strength will only come from having a sound structure and reinforcement on the inside. That's a lot of work, but not difficult, it's more a matter of biting the bullet and getting on with it. You might also find that when you can properly see what's been done to the hull you would be better off with a new hull from Deans, as has been said.

Whatever you decide, why not create a picture album on here and share some photos of the work, we would all be interested.

Chas

[Paul75Participant @paul75]

Thanks again for your replies chaps.

I will upload some photos in due course but the model is currently in mothballs in the loft whilst I plan / get advice on a solution.

I think perhaps I'm painting a worse picture of the model than is actually the case. The cracks are fairly superficial and I've sailed it a few times and floated it in the bath without any water ingress. It's just that I would like to paint the hull to make the model presentable without the cracks then forming and spoiling it.

I've contemplated buying a new hull at £80 from Deans Marine but, given the cost and the time it will take to try to remove the existing deck and replace it on the new hull, I think that sort of refurbishment is beyond the scope for this model. It was only bought to provide a "quick fix" model that would be easier to transport to the lake to sail than my much larger HMS Duke of York. I would rather buy a whole new kit of the boat and start again from the beginning.

Could anyone recommend any thin glass fibre cloth that would fit the bill – the thinner the better?

Many thanks,

Paul.

[Paul75Participant @paul75]

Just had a thought.

Since the cracks only run horizontally about halfway down the depth of the hull sides, do you think simply gluing a thinnish strip of 0.25mm plastic sheet along the sides of the hull would solve the issue? These strips could be blended into the rest of the hull easily enough with filler.

I'm mindful that GRP sheets are more than 1mm thick and since the cracking is localised it would be surplus to requirements covering the whole hull. I suppose the main issue with using a thin strip of plastic would be the strength of the bond over time.

Your thoughts would be much appreciated.

Many thanks,

Paul.

[Charles OatesParticipant @charlesoates31738]

A sort of armored belt, why not. Cut whatever size, offer it up to the hull, mark around it. Then rub down the area it will bond to and epoxy it on. There's only a bit of time and cash to lose and everything to gain.

I'm not sure my idea of epoxy for plastic to fibreglass is the best way, hopefully others will have some ideas.

Chas

[neil hpParticipant @neilhp]

you could from the outside use grp surfacing tissue………it is a very fine gossamer type tissue impregnated with grp resin……or, for a little stronger patch, cut thin strips of cotton bed sheet that is past its best the equal width of the gap between the two halves of the hull, and impregnate that with grp resin…………….once it has cured overnight, skim the gap with car body filler and then sand smooth and level………….it is basically the same process as extending the length of a hull by putting some ply fillets in to a hull cut in half, only horizontally rather than vertically.

[Ray Wood 3Participant @raywood3]

Hi All,

If this was a full-size grp hull you would need the grind the layer of gel coat off and abrade the resin of the hull and roughen the surface, I'm still not sure how thick the make up strip which has to be bridged? But that will need recessing if possible and a new layer of woven glass cloth laid up from the outside of the hull with laminating epoxy resin, the light grade cloth is used for skinning model aeroplane wings, laying up tissue as mentioned is horrible stuff in my view 😮,

Regards Ray

Edited By Ray Wood 2 on 04/03/2020 20:08:14

[TelstarParticipant @telstar]

Hi Paul,

Could you "stitch" down the crack? Putting a cut at right angles to the crack about 20mm across the crack every few cms. along the length, (like stitches in a cut) with some thing like a Dremel with a cutting disk. Then ;glue in ridged reenforcement stripes , possibly carbon fiber **LINK** this would stabilize the crack before filling and sanding.

Cheers Tom

[Paul75Participant @paul75]

Hello Everyone.

Photos of HMS Solebay (or Lagos, to be exact), as promised. The first is the whole model (minus a few fittings to be reattached).

The second shows the side of the hull. The problem area about halfway down where the two halves of the hull are joined is about an inch in depth, as shown by the filler I had applied and sanded back again.

This next photo shows one of the cracks in the hull in the join area. It's one of many and more are prone to form with flexing of the hull. They tend to be less than 1mm in width but can't simply be filled because the hull flexing causes them to reopen. I've also tried epoxy resin and Captain Tolley's glue without success.

This last photo shows the region of the hull shown in photo 3 but from the inside. When the hull was deepened a reinforcing strip of thin wood (balsa?) was used to strengthen the join but over the years this has weakened allowing the hull to flex slightly, compounding the cracking issue. I've slopped a bit of epoxy resin on this wood strip to remedy some water ingress I'd spotted. I didn't notice this strip of wood when I viewed the model at the time of buying it and the join section on the outside was covered by the boot topping which was formed using adhesive tape – again not realised by me. A valuable lesson learned but overall I think the model is worth saving from the breaker's yard.

I intend to fit a strip of 0.25mm thick styrene sheet about 30mm wide down the whole length of the hull on both sides to cover the problem areas using a small amount of epoxy resin. I might push the styrene against the hull first and heat it with a hair dryer so that it moulds to the detail and shape of the hull prior to fixing.

I'll let you know how things go.

All the best,

Paul.

[ashley needhamParticipant @ashleyneedham69188]

Looking at that, I would run a 2 inch strip of glass cloth along the entire interior and resin it in place.

using strips and bits and bobs would be more time consuming and a big strip of glass should produce a permanent fix. When done, gouge out the external cracks generously and fill with P38 filler, itself a good glue.

Ashley

[Ray Wood 3Participant @raywood3]

Hi Paul,

I'd go with Ashley's suggestion but On the outside of the hull, as I guess you can't access all areas because the decks on. IMHO the styrene strip on the outside will be worthless structurally, and at a scale 1,000yds you won't notice?I

Regards Ray

[ashley needhamParticipant @ashleyneedham69188]

I think that if you can reinforce 2/3 of the hull inside it will be enough to stabilise it.

Ray is right, thin styrene like that not worth the effort and will deteriorate over the years in any case.

Ashley

[Charles OatesParticipant @charlesoates31738]

Thanks for posting the pictures Paul, now I can see the problem, I agree with Ashley, do it properly from the inside. I know you don't want to take the deck off, it seems like a massive job, but compared with repeated failed attempts to do it with filler etc, it will be worth it. It will also allow you to get the paint right as well and there's a lot less risk of damaging the superstructure and fittings while you work on the hull.

Chas

PS, it will also give you chance to put in some bulkheads that will lessen the flexing and strain on the hull sides.

 

Edited By Charles Oates on 18/03/2020 13:46:22

[Paul75Participant @paul75]

Thanks for your replies chaps.

With regard to epoxying a strip of fibreglass to the inside of the hull to stabilise it, do you think this could be done with the previous reinforcing strip of wood still in place? I'm not keen on removing this – I'd be splitting the hull again and it's too much work for this model.

Could anyone recommend a supplier for suitable fibreglass sheet? The web is awash with suppliers – it'd be useful to be pointed towards one that you've used before.

Thanks again.

All the best,

Paul.

[ashley needhamParticipant @ashleyneedham69188]

Leave the wood in but scrape well around it so the resin can get in there.

a woven fibreglass tape would be the easiest thing to use inside as it stays together well when wetting out. My preference is for epoxy resin as it dries tack-less. You can get resins which take several hours to go off, and these are fantastic to use, as you don’t have to over-mix quantities, you can simply mixup a bit more knowing the rest won’t start going off.

Ashley

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