Designing a 16' power cat

[SouthernComfort]

I'm not overly concerned with flipping my boat. My pontoon is 24'x8', with an 8' tall thin walled steel tubing dance floor, covered in 3/4" flooring. Even with such a high center of gravity the biggest waves on the lake never made me feel as if I was going over. It seems that lowering my center of gravity, with the same width, would only approve its stability in a worst case scenario. And I did not consider the small scale of my boat effecting weight placement in such small increments. It does make perfect sense. I was more looking for ideas as a way of construction for building the full size boat. I will not use the boat for testing in hopes of getting real life numbers. Thank you for your insight. If I don't decide on Richards design I will build a larger scale model. I appreciate the insight, as was my hopes for posting on this site. I believe i'm slightly ambitious in my boat building project. Thoughts of islanders building boats almost a thousand years ago made me feel with todays technologies it would be so much simpler. I so easily overlooked the skill and knowledge of these boatbuilders of long ago.

[SouthernComfort]

I have been working on my model over the weekend. I made a major error. The front bulkhead hulls should have been inset to achieve the symmetrical shape I had originally planned. I narrowed the hull width to accomodate for the error, but it wasnt nearly enough. Oh well, the learning curve. The more I think about it, the more i'm leaning towards Richards Skoota. But since i've come this far, i'll finish my model. Thanks for everyones advice, it is much appreciated.

[Mark Cat]

SouthernComfort,

Richard is correct in pointing out the challenges of payload and load distribution for boats in the 16 to 20 ft range.

I have attached an inflatable brochure to give you a feel for size. The Great White is 18 ft long. Notice the weight and engine power available. Also, have a look at the hull design for the inflatable.

I have been doing layouts for Aluminum Hull + Composite Console Power tenders in this range. It is possible but not easy to design for payload and speed. The key is to determine the position of payloads and passengers, in the various configurations, for the crafts various functions. It is possible to increase the beam, relative to the inflatable, and modify the hull design for more displacement and better planning performance, usually just a single chine is all that is needed.

So to keep the craft on its lines, which the inflatable does not do well, and really is not expected to do well, I have been looking at three basic configurations (yours may be different):

1) High speed pilot only. 1 person.
2) Yacht owner couple medium speed ship to shore ferry. 3 people + small supplies or 2 bags luggage.
3) Low speed supply and/two couple ferry. 2 people (Pilot+Helper) + supplies, or 5 people no supplies.

So everything has its place and its designed weight. So passengers must sit in specific locations in the proper distribution from 1 to 5 (and depends on their weight above or below 180 lbs average), and supplies have specific storage locations in the hulls or on deck for heavy very low speed operation.

Challenges:

Engine position and power to weight.

My focus engine was a Yamaha 60HP 237 lbs (see attached).

Gasoline tank size and position.
Pilot, Engine and Console position.
Best way to distribute passengers and supplies.
Hull design, cross between a power CAT single chine and tunnel shape. V to \| |/ to ish shape single chine (Many options).
For my designs so far the beam is always greater than inflatables.
Light weight aluminum + composite construction.
For the 18 to 20ft use an outboard jack plate.
Minimize frontal, console, hull and tunnel windage.
Ask about special 25 inch outboard shaft options this allows the engine to be completely clear of the tunnel (bridgedeck). Tunnel is aerodynamic for resistance but not for lift.
Console+pilot+Outboard are in an aerodynamic pod (Pilot is sitting, outboard directly behind).
Design hulls for beaching.

********Every item is on a diet*********

Mark

[SouthernComfort]

Hey Mark, thanks for the info. I'm looking more into option number 3 that you mentioned. Low speed cruising, comfortable for 4 in the cabin. Maybe flush mount seat anchors to mount fishing seats on the back, or even better, make identical brackets for the backseat and the back of the boat, whereas the rear bench seat could be used to sit and fish from. My model shows almost 8' in length and 6' in width for the cabin area, but still allowing for 3' in the front that could be used to lay and and catch some sun while at anchor. I'm thinking of sealing the bottom 2' of the hulls, and using the bulkheads and crossbracing as walls for storage along the upper 2' of the hulls, accessible from a central hatch on top, or smaller hatches inside. The rear could be used to store water jugs, gas, and other items, as well as large tents. I'll probably end up building Richards boat, but this is still fun.

[Mark Cat]

SouternComfort,

I really enjoy working on tender designs.

After reading your post I just wanted to make my self clear on the three configurations for the tender. The Catamaran/Tunnel tender design I talked about needed to accommodate all three configurations (uses).

The challenge was how to do this and properly distribute the loads per operational speed and purpose.

I guess you can also tell that for this tender we were really not concerned with fuel economy. The focus was more on unloaded or lightly loaded performance. Engine size was all about getting up on plane. Obviously, the pilot needed a lot of skill, and if you berried the hulls into a wave at speed things could get a little rough.

Mark

[SouthernComfort]

I now understand what you were saying. A hull that performs marginally well for your intended use, but adaptable to other configurations. I'm not overly concerned with speed, although efficiency is always on my mind. The best weekend I have had on the lake thus far was when we backed the houseboat into a sandbar, and the prop spun itself off. Happened friday afternoon. We partied for 3 days in that spot. But enough of that, fuzzy weekend. I have decided to go with Richard's Skoota plans. Makes much more sense. But this website and those involved have sparked many ideas in my head, and i'd like to thank everyone for their input. It is much appreciated.