I'm rebuilding the passion for the twins, it's been a bit of a break but there was a plan.
I've just deleted a bunch of diatribe, I'll give the simple version. I've worked around Marine Engineering for most of my life and for a total of some 21 years at a place that makes high speed motor yachts. I used to be a test skipper and believe you me we test them hard, you kinda pick up things regarding the properties of planing hulls when your pushing 65 tons around the bay at 35 knots, I'm in Supplier Quality Management now but I reside in the Engineering and Design department and I'm surrounded by designers, naval architects and other specialists in Laminating, Vibration, and not least hull performance.
So, up to some years ago I'd made loads of airboats that were basically flatties with hull sides like a powerboat. Now sadly almost all of my photos have been lost but this one image remains of the typical boats I was making for maybe 20 years or so:
Some of them had slight tunnels, some one, some two, and when I came back to make some more it was with the sole intention of eliminating torque roll which plagued me on all of these till the later two tunnel versions. When I made the little red boat it was to try the glass over foam thing for the first time, but to help me with that I generated some of the shapes that that I planned to encounter on the true boat. The freak of this is things like the tunnels on the red boat are that wide because I wanted the offcuts to make the cockpit, being a materials miser
Add to that my noticing that the SI3 was such an accessible boat to make that worked so well, I figured there was stuff to learn from these two boats so held off on the twins to see what prevailed. The net result is a significant number of changes to the planned twin, I'll be changing attack angles and worrying less about weight, tunnels are to be deeper than planned, steps are to be introduced, and sponson profiles are to be quite different.
The way I derive this however is entirely in my head, I try to consider Bernoulli's theory and how that works and pull that into my scratchbuilds. I mostly visualise construction before starting, but often make little test pieces to prove one thing or another. The SI3 was the first time I had ever built a model from plans. I don't use any software or anything and usually shape things 'in the hand', with no drawings other than templates for matching sides. The key difference between my way of configuring hulls and the SI3 is that I like lift strakes and longitudinal steps to control lift and side movement, the SI3 works well through a fairly unique property of railing on the outside sponson in a turn, mine rely on lifting the outer sponson and dropping the inner to rail on a lift strake or tunnel edge.
What I learnt from the red boat is that I could go a lot narrower in wetted area than I'd imagined. It's tricky to see in these vids, but it is actually totally on the surface of the water under way, we purposefully arranged to take this photo in clam waters to show that:
With the right level of power that boat will skim much better, but it'll turn like a pig at higher speeds I reckon due to being too narrow, we'll see. With steeper AoA's it would be less demanding on power too I figure.
So right now I'm pulling all of this stuff together to reconfigure the Twin. The only firm decision is that I'm not going to be making an Electric version, I've seen too many hassles with that stuff for it to interest me. I believe I'm close to the final arrangement of the boat, but there won't be any drawings etc to see until I know what I'm making and want to make up templates, for which I use a Vector Graphics program (CorelDraw) and draw out the shapes with a sign plotter configured for pen plotting.
One other thing I'm changing is getting back into my fun thing of having novelties and fiddly bits that may not contribute much to perfomance but can be a grin to have. Gyros are on board and with a new radio combo I've just bought I've a world of ways to include active features, like weight compensating trim tabs to balance fuel weight loss etc, active rear wing, maybe split to enable roll resistance, all just for the hell of it cuz I likes making models
And that was the non diatribe version