modifying transoms

[bigwow]

I am about to start on the modification of BigWows transoms, I’m lengthening them and putting in steps.
The way I see it there are two ways of doing it; I can either laminate several foam sandwich panels on a sheet of glass and laminate them together in situe on the transoms, or
I can build a wooden mock up on one transom take a mould from this; laminate up two new transoms from the mould then stick them on.
Either way I will not be removing the old transoms which will in effect become another waterproof bulkhead, inside the new transoms.
Anyone any experience of doing modifications like this?

 

[boatmike]

Yes, similar things loads of times! Its a good idea but I can tell you now... Never assume a plug for port will match starb'd. If you make up a cardboard pattern of one it's no guarantee it will match t'other. Try it, it might, but don't rely on it. Your most difficult job will be fairing the hull externally to match the existing without seeing a join. Possible but difficult.
Far easier to make a plug of either side, and match the hull shape to the existing, then take a mould off that with CSM reinforced with timber. then layup the job in the mould with a flange on the hull mating face that you can bolt or screw to the existing transom. You will see a join of course and its up to you to decide if you want to fill and fair it or leave it as is.
Sounds like a lot of work but if you do it this way it is surprising how easy it is. laid up with panels and faired later will always look like thats exactly what you had done!

 

[bigwow]

Both hulls came off the same frame so surely must be identical? The only place they might be different is below the knuckle where they were faired with Filite, but that would have to be ground off down to the glassfibre in order to make the join.

"laid up with panels and faired later will always look like thats exactly what you had done! "

The whole boat was built this way, it took 6 weeks of 12 hour days to fair the foredeck and coach roof because they were only laminated on the inside of the foam, to get the curves, before fitting, then the top skin was laminated then faired with bucket after bucket of filite, a lot of which was then sanded off.

 

[Talbot]

assume you are doing the standard sugar sccop mod to the Flica - have you considered trying to get a mould of another factory moulded one.

You are lucky if the two hulls are symetrical. I considered doing this mod to my catalac, but the hulls are asymetric and costs/benefit could not be assessed as it hadnt been done before. not like the Flica which appears to really benefit from this mod.

 

[bigwow]

[ QUOTE ]
assume you are doing the standard sugar sccop mod to the Flica - have you considered trying to get a mould of another factory moulded one.

You are lucky if the two hulls are symetrical. I considered doing this mod to my catalac, but the hulls are asymetric and costs/benefit could not be assessed as it hadnt been done before. not like the Flica which appears to really benefit from this mod.

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Yes Mark I’m going to make BigWow into a Flica 37. Trouble is I don’t know anyone with a 37 I could take a pattern off so I’ll have to make it myself.
At the moment the transoms are in the water all the time, all the weight I’ve added, and it causes drag. Adding another 3 feet will bring them well out of the water and I’m hoping we will go as fast as we used to do.
John

 

[boatmike]

OK then if you fair it the same way you are right.. should look the same. I had thought the boat was made from a one piece plug and mould. Didn't realise it was an upside down job on frames. If they came off the same plug or frame, even if they are not exactly symmetrical they should be the same so you are right.
In this case I would tend to make the new bit deliberately small and fair it in rather than size to size (if you see what I mean) I still think however that making a plug and mould and laying up conventionally would be better than bending panels around the outside of a frame for the new bit though as you will find that it is then "inert" and will match the shape exactly. You could bend foam around a frame, pin it down, layup outside, remove from frame and layup inside after but I hate doing that. Everything fights you when trying to get it accurate. Far easier especially as you need two the same in my opinion to put the work into a good plug and mould. Plus the fact that if anyone ever shunts you up the bum you can easily make another

 

[oldsaltoz]

G'day John,

Have you considered using foam aligned by battens off the hull, this method reduces the fairing, no mould required, no plugs to be made, can be any shape or size.

You also need to look at the extra weight you will be adding and compensate for it with additional floatation to ensure you waterline remains the same and you don't have a bottom step under water. This is also a very good opportunity to lift your point of exit and leave a clean wake, and a lot less noise.

Let us know if you need more info.

Avagreat08......

 

[Talbot]

Your location doesnt make that easy, but have you considered asking Richard Woods if the moulds are available and can be hired????, or whether they have one available in the south west that you can sneek a quick mold from /forums/images/graemlins/smile.gif

 

[Bajansailor]

A couple of powerboats here were recently 'stretched', each by about 3' - in each case they built a simple mould using Formica sheets attached to the hull, following the shape of the hull.

They did however remove the existing transoms first, and laminated onto the hull interior with a good overlap, effectively canti-levering the extension off the original hull.

If you want to keep the existing transoms as bulkheads you could perhaps still use the formica panel mould method, and 'butt joint' the extensions on to the hull.
And then laminate over the joint on the hull exterior with a suitable overlap. This would be the only bit that would subsequently need any serious filling and fairing.

For added strength, you could perhaps cut some apertures in the current transoms and run longitudinal timber stringers (more cantilevers) through them into the hulls, to help support the extensions.
One disadvantage of following the curve of the hull like this is that you would extend the rocker, and the bottom edges of the new transoms might then be higher than desired (?).

Difficult to explain my thoughts in words, sorry.
However way you go about doing it (all methods described above are good) it can only be an overall benefit with more buoyancy, waterline length and load carrying ability.
The extensions will probbaly improve her overall appearance as well, by making her appear less boxy.
(I shall quickly add that I think the Flica is an attractive design - all of Richard's cats are!).

 

[boatmike]

If it was made as an externally faired job over a frame jig in the first place, there probably aren't any moulds available and the frame jig for the boat with sugar scoop stern might not be the same as his, making a "return" off someone elses boat not quite a match for his. In any case the only thing that needs accuracy is the outside form.

What I visualise is "transfer fairing" and looking at my previous posts I have not been clear how this can be done so I will start again.

1. Make a thick plywood pattern of the transom and screw it in place over one transom on the boat. (holes can be filled later)
2. Cut several pieces of lighter ply that are oversize to the shape at this stage to form horizontal sections of the final form (visualise lines cut parallel to the waterline at about 9 inch intervals)
3. Cut vertical ply formers the same. one on C/L and at least one either side (still oversize)
4. Cut half slots in the vertical and horizontal ply bits so that they fit together like an egg crate and screw this lot up to the transom plate.
5. Using a long batten, "transfer" the lines of the hull to the plywood so that you have the finished shape marked out.
6. At this stage decide what you are going to clad the outside with (plywood is OK but dont use MDF-its not stable and subject to moisture retention) and deduct its thickness from the shape you have drawn plus about 1/8" all around.
7. Cut the form in the vertical and horizontal formers to this line and clad in the ply screwing down at 6 inch intervals.
8. You now have a plug that is undersize to the boat that you can "bog up" with fairing compound and sand to the exact shape you need including the "end" shape where you can develop a nice curve with radiused ends and a short internal flange for the inside edge of the face that will form the steps. Finish off with either gel-coat or 2 pack paint and buff to a good finish. This is where the hard work is but you only need do it once.
9. Take the plug off the boat and screw a plate to the back of the transom to form an external flange.
10. Layup your mould with a generous right angle flange to the plate. (assume you know how to polish, use release agent etc but if you don't you can get this from a book)
When cured add more reinforcement where necessary before releasing mould from plug.
11. Screw a plate to the flange to pretrude inside the mould which will form the boundary angle. (best to use bolts to make it easily removable for release.)
12. Polish and prepare the mould (dont forget the flange) as you did the plug and layup your moulding
13. You now have a piece that can form the outside of the transom extension and it is very easy to line out internally with foam, make your steps, and glass over if you want.

I have tried to make this simple to describe the principle. In practice you could refine the principle as follows.

When you are making your plug you could easily adapt this method to include the steps in the plug and mould and "face up" the foam to the inside of the moulding when finished if it requires it and glass over. With a little imagination the steps could well be the horizontal plug formers.

When laying up the moulding include a strip of thin UPVC about say 3 inches wide inside the skin profile adjacent to the flange. UPVC sections have a good external finish and are easy to release. If it doesn't its very soft anyway and will break away easily. This will give you an undersize band to fair in to your hull.

If you have tight curves that ply wont go around look for "bendy ply" which has slots cut on one side.
You could of course make the mould with formica sheets etc straight off the boat as others have suggested. Perfectly valid but not quite as easy as it sounds..
I think a conventional transfer moulded plug and mould is the way to go though for several reasons.
1. The woodwork is not difficult and you don't need to be a cabinet maker to do it.
2. Most of the work is in fairing and polishing the plug, any other way you will need to do this twice.
3. It is the only way IMO to achieve a truly professional finish with a continuous outside moulding.

I hope this has helped.
It will at least give you food for thought.

 

[Talbot]

Didnt think of that - I would love to assist and learn on stuff like that. My fibreglass expertise is just at the repairing holes level. Vacuum bagging and stuff like that ought to be adult education rather than flower arranging.

 

[boatmike]

Didn't know you were adept at flower arranging dearest. /forums/images/graemlins/smile.gif

 

[Talbot]

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Didn't know you were adept at flower arranging dearest. /forums/images/graemlins/smile.gif

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My velvet arrangement is nice

But you should see my Oriental Fantasy!!!!!!!!!!!!!!!!!