Stretching and widening a ski boat

Hi fellow boat builders, as I’ve stated I’ve got one hell of a question and so far I’ve found next to no information on how I can do it.

So my question is, has anyone out there ever stretched and widened a ski boat? I have an amazing body of an Everingham Ski boat. It’s a 69 fibreglass bottom, timber top ski boat. It’s 5mtrs long approximately 1.8mtrs wide (excuse the measurements for my US readers)

I’d like to bring it into the 20th century and add some length and width to really build it out. Ideally it’s a cut down the middle and across as well. Then I need to work out just how much glass and shape will be required. Once I have that it should be a case of building a mould and dropping it all in to glass and harden. The top I will replace so that’s a non issue. Has anyone ever heard of anyone doing this or even someone who knows how too? It would be a true waste of this boat to not work with its shape and the cost would go up significantly if I had to do it from scratch.

I’d appreciate any comments that help me find out more information. Cheers and look forward to speaking to you further.

 

... think it would be easier, not that much more expensive and better if you just build from scratch but in either case you should make sure your new design is going to work like you want it too.

 

Craig you are contemplating an enormous job that may result in a boat less capable than the one that you have. The boat in the pictures is typical of a standard tournament type ski boat. I live in the worlds capitol of water ski activity so I see a lot of ski boats. Your boat is a classic that should not be messed with. If you want a different boat then get a different boat but please do not wreck the jewel that you have.

One of your pictures shows a V8 engine that could very well develop excessive power and weigh more than the boat needs or wants for a ski boat. It will probably go faster than a standard tournament boat. Why would you need to go faster if skiing is the main function of the boat?

You have a reason for needing a longer, wider, boat. Please tell us about those reasons.

 

Some boats can be widened fairly easily, that one would be very difficult to get right. As said, finding a boat that fits your needs would be much easier and cost less.

 

No.

It would be EXTREMELY difficult to adapt the old hull into new lines. It would require making a plug and then frames. The transom would be discarded in all likelihood.

The reason for few responses is it is simply not done. There are people that have lengthened boats, but widening and lengthening is sort of unheard of.

When people remove a transom for repair; it is always a concern the boat lose its shape. When cutting the boat to the degree you suggest; it could only be done if you made a plug and frames from the old hull and then results would be even spurios; perhaps ugly.

Boats are not square or straight rectangles; when you try to lengthen these odd shapes; they distort.

Consider 2 squares. One is 2’x2’. The other is 1’x1’. They are 1’ apart and connected. Now move them another foot apart. The angles of the intersecting lines all change. Some hull forms are static enough in a section to make this possible without great distortion, but not all. When you add widening; they all become a twisted question.

For the effort required; you’d be much further along building any type of boat from scratch from a foam sandwich to a strip boat to a new boat in a plug even; although that would not be done for one off typically.

Leave her alone.

Buy or build the hull you’d prefer, or retreat from I wish she were bigger.

 

This can be done, but as others have warned, it's a job, a big job and the results may not be what you've hoped they might be. You don't need a mold, though some form of jig to make the hull longer and wider will be necessary to lay the fabrics and/or core on, for the laminating process. You can do it with a male or female mold. The female mold would be how the manufacture did it, but you'll spend as much money as building a whole new boat, just in the female portions of the modification. A male mold would be easier and I'd recommend a foam core to make this part easier.

In all honesty, I don't think this is a particularly wise idea. If you were to just widen or just lengthen her, the process would be much easier, but to do both, means cutting the boat into 4 separate pieces, aligning these to the new length/beam and making transitions from each piece to each piece, all the while incorporating these into shapes that will not kill the performance, looks and abilities of the current boat. I don't think a novice can do this, without considerable knowledge in hydrodynamics.

I'm not sure how much additional beam you'd like, but if it was me, I'd cut her down the centerline, on either side if the little centerline keel and space the two shell halves apart the distance you want. Next, I'd I'd make athwart shapes to continue the deadrise to the new centerline and lay in some foam. Working with the hull upside down, I lay on enough fabric to equal at least 2/3's of the current hull's thickness. With the bottom faired and smoothed and leaving the temporary deadrise molds in place, roll the boat over to apply the remaining fabrics on the inside. Lengthening her is more difficult, as you'll need to find the line that is at max beam in plan view and profile, which often isn't on a vertical line, but angled quite a bit. So, you'd have to make a diagonal, V shaped cut on the bottom and likely on the topsides as well. Spread out the two hull halves and fill in the distance with more of the same technique. With the lapped topsides, making smooth transitions on the laps will be all but impossible, but it is doable. In short, to make it right and look good, you're talking about hundreds of hours of work, which rivals just building a whole new hull of similar shape just wider and longer.