Cat tunnel angles

[jfrabat]

Hi, guys. Need some feedback; a friend of mine saw my boat runs, and he also got hooked on boating. He is an architect, though, so he decided to design his own boat.

He asked me my opinions on the design, and I gave him some pointers, but one thing that caught my attention is that he designed the tunnel in a shape I have not seen before. If you look at the tunnel from the front, it looks lime \/------\/ instead of the traditional \| -------|/ (not sure if my text drawings work to illustrate my point).

Anyway, is there a downside to having the tunnel in this trapezoid shape?

[jfrabat]

Now that I am not on my mobile, let me share with you what I mean; this is the design he was going for (it is changed in the plans, as the tail was too long, but so you get the basic idea):

Whats-App-Image-2020-06-10-at-4-09-24-PM.jpg

He wants a Lambo type angular design. Now here is his design:

HOJA-1-CTAT-JB-Model.jpg

The 2 ESC position is to allow for room for balance (apart from the batteries in the pontoons). But the tunnel shape is the part I have never seen, and I am not sure if it would have any effects on performance. Not that B and D bulkheads are upside down...

[NativePaul]

It won't turn as well, as it will be trying to ride up that inside sponson when cornering rather than using it as a very low aspect ratio turn fin, so it will be a bit more prone to rolling over sideways, but with its narrow tunnel width I would guess that it isn't being designed for turning anyway.

I would be more concerned about the steps, they will be a hindrance as they are drawn and need some angle of attack to do anything productive, as little as 2 degrees will be helpfull, I have drawn it onto the last 2 steps, the front one should have some angle off attack too but MS paint doesn't have a pen tool for me to be able to adjust the up sweep of the nose to fit the new angle, hopefully he can figure out what I mean.

I would also increase the transom angles from 50 degrees or whatever they were, up to 90 degrees so they shed water as cleanly as possible.

It's too hard for me to draw, but I would also consider increasing the deadrise of each ride surface as they go forwards down the boat to compensate for them increasing in width.


Not To Scale.
Whats-App-Image-2020-06-10-at-4-09-24-PM.jpg

[Jesse J]

Probably want some ride pads and spray rails too. As drawn, it will have a squishy feel and will have more drag.
I’ve run one of my designs without and when I added the ride pads it ran a lot drier and more efficiently.