Paddle boat Tri Hull

Looks like the original doesn't have enough Water Plane Area (WPA) for its intended load. What this means is that the hulls sink too much with added weight, which can be a simple weight shift, from one hull to the other. This is what's causing your stability problem.

Two possible remedies:

1.) make the two hulls a little wider, leaving one propeller diameter distance between the hulls, and tapering the inner side of each hull outward about 3 in(7.6 cm) (this tapered protion would be about 1 ft (31 cm long)), or

2.) make the center hull nothing more than an enclosing of the space between the two hulls, but with the stern end of this enclosing rising up to the Waterline (WL) height, at a 1:4 (rise over run) taper. This will leave a short tunnel at the rear of the boat only, so water can get to the propeller.

In your original post, you said this boat was to be 6 ft wide. How wide are the hulls? It looks to me that they are only about 2 ft wide (61 cm), if even that. What's the propeller diameter?

Both solutions would allow water to get to the propeller, while increasing the WPA, which will make the boat much more stable. The 2nd solution would add more buoyancy to the bow than the stern, so might the boat to trim bow up, more than originally.

 

Daquiri, I want to setup an external propulsion unit like the following below. So it will be a bit easy to fit and maintain.
Video

 

Between the hulls: https://www.youtube.com/watch?v=ZmEuy4pA1pc

 

Hi Sharpi, sorry maybe type error, actually the old one was 4ft wide 8ft in over all length.

 

Since the overall length of the boat is going to increase anyways with that drive, you might make the whole boat more performant by streamlining the aft part of pontoons, like this:


The aft pontoon tails (blue) would serve as structural support for the wheel, while the central hull addition (green) would be shaped in order to give the required missing buoyancy and minimize the turbulence of the inflow to the wheel.

Just my thought, of course.

Cheers

 

Guys thanks so much, to have patience on my failed project. I have to rebuilt another paddle boat. this time I will have my nice friends in boat design as motivation. Thanks all, sorry I took your time to discuss about this troublesome paddle boat. Any kind of help I can offer within my range, it will be my pleasure to serve you. Thanks mates.