BWC Flying Fish I/II – Enclosed Centerboard Case Narrowed, GRP Walls Bowed Inward

[Toky]

Hello everyone,

I own an older BWC Flying Fish [I/II] and am having a problem with the enclosed centerboard case. The centerboard has become very difficult to move and can no longer be pulled out freely because the case has become too narrow in several places.

The inner GRP walls of the centerboard case are visibly bowed inward. There appears to be foam filling behind these walls. The material looks similar to polyurethane expanding foam or construction foam. However, I am currently unable to determine whether this foam was installed originally by BWC as buoyancy foam or as part of the double-skin construction, or whether it was added during a previous repair.

The restriction does not appear to be caused merely by dirt, paint, or isolated resin residue. It looks more as though pressure from the foam-filled cavity behind the walls has permanently pushed the GRP surfaces inward into the centerboard case.

My questions are:

Are similar deformations of the centerboard case known to occur on older boats of this construction?

Could old, damp, or incorrectly applied polyurethane foam exert enough pressure to deform the GRP walls in this way?

Could the problem instead be caused by delamination, frost damage, or a previous improper repair?

How would you open up this part of the structure without completely separating the upper and lower hull shells?

Would it make sense to open the cavity locally from the cockpit, remove the foam, realign the centerboard case using a straight former, and then rebuild the area with a suitable core material and new laminate?

I do not want to simply grind the walls thinner from inside the centerboard case, as I am concerned that this could weaken the structural and watertight GRP layer. Forcibly spreading the walls apart or heating the cured laminate also seems risky.

I would particularly appreciate hearing from anyone who has repaired this kind of boat, a similar double-skinned hull, or an enclosed foam-filled centerboard case. Photographs of the original construction, old shipyard documentation, or information about typical weak points would also be very welcome.

Thank you very much for your help and advice!

Best regards,

Toky

 

[HelmutSheina]

Cannot speak specifically of centreboard cases, but that cheap crumbly brown two part urethane foam has too many issues on boats to be of much usage.

It readily absorbs water, which negates its use as a flotation aid; and crumbles apart, blocking the passage of limber and pump inlets. Plus it can easily deform and destroy structures due to rapid expansion prior to curing.

A lot of early sailboards were made of it, coated in a thin plastic skin. A pin hole in the skin led to a huge repair job. Or another very expensive wreck on the pile.

I would imagine your best option would be to build a new case.

 

[Toky]

Cannot speak specifically of centreboard cases, but that cheap crumbly brown two part urethane foam has too many issues on boats to be of much usage.

It readily absorbs water, which negates its use as a flotation aid; and crumbles apart, blocking the passage of limber and pump inlets. Plus it can easily deform and destroy structures due to rapid expansion prior to curing.

A lot of early sailboards were made of it, coated in a thin plastic skin. A pin hole in the skin led to a huge repair job. Or another very expensive wreck on the pile.

I would imagine your best option would be to build a new case.

Thanks for the introspective, I will try to open it and check it from inside

 

[Toky]

Cannot speak specifically of centreboard cases, but that cheap crumbly brown two part urethane foam has too many issues on boats to be of much usage.

It readily absorbs water, which negates its use as a flotation aid; and crumbles apart, blocking the passage of limber and pump inlets. Plus it can easily deform and destroy structures due to rapid expansion prior to curing.

A lot of early sailboards were made of it, coated in a thin plastic skin. A pin hole in the skin led to a huge repair job. Or another very expensive wreck on the pile.

I would imagine your best option would be to build a new case.

I am planning to separate the deck/cockpit shell from the lower hull to gain access to the centreboard case. Do you have any advice, or do you know of a guide or forum thread explaining the best way to do this?

 

[Toky]

Hi everyone,


I’ve now opened up the entire hull and have access to the inside of the centerboard case. I’m attaching some photos. The centerboard case is visibly narrowed, and the internal filling also appears to be compressed or deformed.


Does anyone have experience with this kind of problem, or any advice on how best to repair it so that the deformation does not happen again?

 

[fallguy]

The centerboard case is not looking too good.

It is either compromised glass or compromised wood. The only way to know is to cut into the side and see.

It will require a rebuild, and the foam must be removed from the hull as it, too appears done from here (disintegrating).

As for the case, if wood; once it gets wet it swells. If glass, once it delaminates; it, too grows.

To me, it looks like it would be far easier to rebuild the case and tab a new case to the hull. At the same time, make sure the cb is also not swollen and compromised in some way or you’ll be building a new case for a garbage cb.

For construction help; you can ask here. For a wood case; epoxy is best because very waterproof. For a nonwood case, you would need to do quite a bit of laminating over the centerboard plus margin…no experience with that..

I have only helped repair a wooden (all wood) case that had opened a bit.

 

[wet feet]

Few people would have undertaken such a major exercise on a small boat of some vintage.It must mean a lot to you.I completely agree with the comments about 2 part foam being of little use,but it does help those who turn out boats in a hurry and who don't expect to see them again.
If I had to do something with the boat in it's dismantled state,I would begin by Inserting as many battens as I thought necessary to hold the sides the correct distance apart.How do you determine what that distance might be?I would expect the intention was to have flat sides that incorporated a draft angle for moulding.The width at the bottom shouldn't be too hard to measure,getting a sensible dimension for the top will be a bit more challenging.With a sufficient number of tapered battens in place and the entire case braced central to the boat.I would then add external reinforcing strips (quality foam if possible or decent hardwood as an alternative) of sufficient cross section to fit within the deck moulding but leaving about 10mm clear for a glass laminate.
I would cover the reinforcement strips with a couple of plies of 450gsm mat and polyester resin.No doubt somebody will tut-tut and insist that 1708 and epoxy is the only choice but the epoxy will cost more than the boat is worth and won't make a great deal of difference.At this point you will have dealt with the original problem and still have to come up with a viable plan to re-assemble the mouldings.
The hull to deck joint is the easy part,securing the other areas will not be easy and I expect the original builder will have used an assembly jig once he realised that more than a handful would be sold.Taking the remarks about filling the cavity with 2 part foam into account,I would suggest using slabs of polystyrene foam on the underside of the cockpit floor and bonded in place with a reliable mastic,perhaps 3M 5200 or Sikaflex.It only needs to support itself as the slab(s) will be quite light.Whether it would add sufficient stiffness is an unknown as we don't have any information about the weight of the boat users and it might mean that bonding a plywood panel to the surface first would be necessary-sealed of course.
Putting the deck back in place would be easier with a group of volunteers and they would need to be advised of the need for care and speed in the process.A dry run is a good idea and would be a good time to investigate where gaps might be using small conical mounds of modelling paste,we would use plasticene,and if the gaps are excessive,add foam and glass to reduce them.Only when you are sure that the sections can be assembled with sensible gaps for the bonding paste do you proceed.With clean bonding surfaces and the application of enough cash,I would use Plexus but you need to be confident of completing the assembly rapidly before the cure starts.You could use thickened epoxy and a slow hardener but would need to experiment with achieving the right viscosity before doing the job.

Is the boat really worth all that?