Hi,
I was able to find a second (complete) copy of this kit on eBay, so I decided to do a little kitbashing with this initial kit (that I bought knowing it was missing a few small parts).
Looking at the original boat, you can see that it is a bit short and stocky (Length overall/Beam overall of about 42/12.83 = 3.3 or so). I started thinking about making the boat longer, but noticed that for a lot of power boats the L/B seems to go up a bit as length increases. In general I noticed that for the hull, its bottom rake (slope) varies constantly over its length. However, I found that if I cut the boat roughly in half I could add some mid section while smoothing over any discontinuities in the bottom since the bottom slope/rake was very low in that area.
The next issue though was that I couldn't really change the beam by much very easily, and that a beam of 12.83ft (or about 2.75in for the scale model) was kind of narrow for anything larger than the original boat size (of about 42ft). I began to realize though that if I changed the scale of the model a little I could make a model of a bigger boat without adding too much midbody.
In addition, I also realized the a larger boat would likely have a bit more hull depth, and that if I added some additional "strakes" above the existing top of the hull, the beam overall would go up a little more since the hull has a bit of flare in it.
In the end I decided on changing the scale to 1/87 (HO scale) as opposed to its original scale of 1/56 since my (semi-) local hobby store stoicks some model train related stuff in 1/87 scale (including platic ladders and railings)
The pictures below show where I was earlier today, with one side modified, and the other still only partially done. One issue that I ran into was that when I cut the model in half I found that the basic hull was a bit asymmetric in shape with the sections being a bit concave on one side of the keel but a bit convex on the other side, as shown below.
As such I ended up gluing a thin sheet of styrene to the bottom of the hull to etither side of the keel to try and hide this weirdness in shape and to also help hide any "discontinuities" or flat spots in the bottom of the hull due to the added midbody. In the end I also added a thin sheet of styrene to the modified sides of the hull too, to help clean up the relatively messing joints in the hull and to also add strength to the lengthened hull, as shown below (sorry that the images turned out a little fuzzy).
GThe 1st picture shows the port side of the hull with some strakes added on top to increase the hull depth and with its "outer plating" while the 2nd picture shows the starboard side before I added the upper strakes to increase depth and without its outer plating to make it look cleaner. In this second picture you can also see the inside of the prt side of the hull where I added the extra strakes to increase its depth.
I was able to finish up the starboard side today, but am still working to clean up the "styrene sheet" joints and such.
In general, I'm hoping to try and make something roughly similar to the boat in this link, but not necessarily exactly the same as that boat.
Pat