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[nsa66]

Does anyone have any experience of modifying a commercial GRP hull to create a different vessel?

I wish to modify a Metcalfe Mouldings Manxman hull to form the basis of a model of the 1962 car ferry Manx Maid. Both vessels were built by Cammell Laird  and have broadly similar hulls of approximately the same form. The principal differences are:

1. The Manx Maid does not narrow in a taper towards the stern. The beam is maintained right up to the semi-circular cruiser stern. This would necessitate a progressive widening of the whole after section of the hull for approx. 2/3 of the length. I have various ideas about how to accomplish this. Options are:
a) build up the width entirely using externally applied filler. This would probably create serious deadweight issues as up to an inch of filler would need to be applied at EACH side of the hull, and the completed vessel has very little draught (only just over an inch for her 48” length on my King Orry built on same hull).
b) remove the existing after part of the hull above w/line level and create a new structure (plank on frame?) Below the waterline could probably be filled and sanded to meet with the new upper hull.
c) create a new outer skin (styrene? Liteply?) over frames attached to the existing hull. This would have the benefit of maintaining the original strength. Added weight would not be quite as high as option (a) and may be able to be compensated for in superstructure construction.

2. There is a slight “knuckle” in the bows, presumably to maintain width on the vehicle deck as far forward as possible. This is barely visible on all but the most detailed photograph and it is tempting to apply a little artistic licence (but I’ll know it’s wrong!). This could probably be added with filler but I think it will be bl…y awkward to fair it in to the hull with any accuracy.

3. The overall beam of Manx Maid is 3’ wider than Manxman (about 0.5” at scale). Again this could be conveniently overlooked or a couple of inches could be taken out of the length and the two halves rejoined.

Anyway, I would welcome any advice from people who have carried out such alterations. I don’t mind experimenting with different techniques but I would hate to destroy a perfectly good moulding.

Cheers.

[HS93 (RIP)]

I would go for C as the hull would retain it's strength and if you where not happy at first attempt you can go back to square one and try again. you could stick on foam blocks and shape then glass cloth it to shape it would be strong as well. whatever way you must roughen the surface to get a good key , also clean with acetone before applying the glass to the fiberglass, test the foam first to see if it melts..

Peter

[Perkasaman2]

C looks good. It's certainly possible to carefully cut the hull moulding lengthways - splitting it  along the keel with a jigsaw (fine tooth scrolling or metal cutting blade fitted) and enable the hull to be opened up to gain the extra width towards the stern. Internal frames could be added to re-shape the hull x sections/maintain the altered beam widths and also give support to the deck/superstructure. The alterations in option C will be well hidden.  

[Circlip]

By the time you've done the cut and chop and molding of "C" you could have gone for the "D" option of got a block of Blue foam, carved and shaped a plug and made your own hull. Can't help thinking that applying an "Overcoat" and getting it to fit properly will be far more hassle.

  Regards  Ian.

[longshanks]

Got to agree with Ian. Quicker, simpler & more satisfying to make your own hull.

Your main problem is going to be top weight. The shape of the vessel (Slab sided passanger accommodation) above a shallow draft !! I think you are going to have to keep everything above the waterline as light as possible or you will have no stability.

[nsa66]

Thanks for the advice guys it really is much appreciated. I'm new to the forum having been away from the modelling scene for several years due to family and work commitments. I'm currently asking a lot of questions on several sections of the forum to try and help me decide which of the many long-contemplated projects to pick up first.

In this case, there are several reasons why I'm avoiding option D.

Firstly, I do like playing around with new ways of doing things although I'm quite happy to take advice which will avoid costly mistakes.

Secondly, I have an idea for a future project which will involve a more intricate modification than this and would benefit from a bit of prior experience.

Thirdly, although I have built up hulls in various ways before, I do not find it a particularly enjoyable part of the modelling experience. I find most satisfaction in the technological stuff - radio, running gear, accessories etc.

Fourthly: I already have the hull !

With regards to stability, this could definitely be an issue if not well thought out. The King Orry was my first non-kit build, and I made several mistakes which hopefully I have learned from. I made all the decks out of relatively heavy ply and had various installations (smoke generator and fan, loudspeaker etc.) mounted far too high in the superstructure. Although tank testing proved that she will recover from all but the most ridiculous situation, the heel angle in a strong wind looks pretty alarming, although the high viewpoint exaggerates this a bit. Unfortunately the Manx Maid/Ben-my-Chree WERE far more slab sided although the larger enclosed volume does allow for a lighter construction.

I think I'll probably go with option C and try and lighten the original hull sides as much as possible between the new frames without sacrificing too much in the way of strength. It will probably be a while before I start as the "Orry" is in need of a pretty substantial refurbishment as a result of a 3 foot TID tug being dropped on her!