Need to Hire a Designer - Power Cat

I need to hire a designer.I have a 50 foot catamaran hull. It is a displacement hull made for a sailing cat. Very high performance. Very lightweight. Foam core.

This hull can do 18 or 20 knots under sail.

I want to hire a designer to put larger diesel engines in it, large props, and reach hull speeds using diesel engines.

Additionally, if anyone is an expert about using canard type foils to assist with lift and get it a little higher out of the water to gain more speed, that would be desirable as well.

All comments on the project are welcome in this thread. And anyone that you could all recommend for me to hire for this project design would be great. Thank you.

 

Not clear what you have (spelling doesn't help!) do you mean you just have hulls or do you mean it is an existing sailing catamaran that you want to turn into a motorsailer cat? About 30 years ago we fitted twin 90hp outboards to a 35ft Banshee catamaran for a customer in Florida. It did 19 knots under sail and 22 knots towing a waterskier under power

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Thank you, Richard. Certainly happy you picked up this thread.

The post was made from my phone so I apologize for any confusion regarding spelling.

The boat is a 50' x 25' sailing catamaran. Unfinished. No rig. Has small outboards currently. Currently weighs about 7 tons. It's already an underpowered displacement power cat. It's already in the water.

Would like to go through the exercise of power boat design on this displacement cat hull and implement the design in the coming months.

Need to determine tankage, range, outboard or inboard, top speed, cruising speed, prop specification, etc.

Also, I'm wanting to run it like a power boat with lots of electrical power and full climate control.

 

Is this thread in the correct section? Should it be under multihulls?

Richard, would you be interested in the design project?

 

I think you need to identify the boat, or supply the lines plan, and place that is the hands of the designer, to assess the practicability of your idea, it generally agreed that sail cats are a more likely proposition that sail monos to convert to a power boat, but still not ideal, after all sailboats don't travel directly upwind, but powerboats do, and it could turn into a hobby-horse nightmare. That is just one consideration, of course.

 

Thank you. This is the type of discussion I was hoping for. Why it won't work.

I have a 50' mono sailboat and this 50' cat.

I'm trying to get together a boat I don't need to sail that can get me places quickly.

I already own these boats outright so I'm trying to find the best way to get to the goal:

A climate controlled, stable and comfortable platform at sea that gets from one harbor to the next quickly. With good range and speed.

I am thinking since I already own the cat, it's the best hull. Just picture a 50' tornado or early Gunboat. That's what the cat hull is like. It's a very light, high performance displacement sailing cat with no mast. Already in the water.

Otherwise, I was looking at power boats under $100,000 in the States and yuck. They didn't seem very good compared to the cat I have.

Are there various things I can do to make it more "power cat"-like?

It's a 50' tornado Catamaran for all intents and purposes. Also it has reverse bows so that seems to dampen the hobby horsing some as the bows are depressed into the water. But like most sailing catamarans, those bows seem to like to leap out of the water with ease while the sterns always stay put.

 

Any conversion can be made to work.
It comes down to the simple issue of - how deep are your pockets!

 

It really does sound like it might be a problem, up-sea. Or even with the nose at 45 degrees to the oncoming waves, you have lost the damping effect of sails, and the thrust is along a much different line. I reckon a tornado cat pointed into the seas, under power, would hobby-horse badly. A sail boat has design considerations such as easy tacking, good light air performance by limiting wetted area, leeway etc, a power cat needs more volume in the ends, I think, to lessen pitching.

 

make an exact scale RC model and test it is a little chop. If is looks like it is about to go into orbit...…….

 

Conceptually, at least, it sounds reasonably feasible to me. At least initially, and without a look at a set of lines or some photographs of the hull, I don't think I would fret too much about problems with upsea performance. My concerns would be more about whether you have enough weight carrying capacity to convert to a powerboat, at least with much in the way of range. Fuel is pretty heavy to feed a couple of big diesels for days. Not that big diesels will be required to push a boat like that to 18 to 20 knots, however. My other concern is about the budget. $100,000 to finish out a custom 50-foot powercat sounds very aggressive unless you are planning to do much of the work yourself or have located a yard with high levels of capability for low levels of cost!

 

As to pitching, it currently does 8 knots with one 30hp outboard engine on providing power. Then the outboard over revs. The prop pitch (hi thrust prop) delivers good thrust at low speeds but seems to be pitched wrong as it runs out of top end.

Going 8 knots into wakes and chop the boat mostly just sits there flat. It seems to soak up all wakes, including ones from 60ft sport fishers that would nearly capsize typical monohulls.

I have yet to see a wake that would move this boat at all. Same goes for chop.

However, I have not had it out in any real steep swells or tried to motor into them. It's workable on the water but not ready for open ocean conditions quite yet.

Rather than building a model, maybe I can just use the current 30hp engines and perform some tests motoring into chop with higher pitched props?

Would there be a good indication of performance doing this even though speeds wouldn't be as high as with larger engines?

 

Yes, I plan to do nearly all the work myself. $100,000 is the parts and materials and possibly not a completely finished interior. It already has solar, batteries, lpg/propane, refrigeration, stove, oven, gasoline/petrol generator, fresh water system, hot water heater, anchor/windlass, 150 gals fuel tanks, 100 gals water tank, etc.

It needs cabinetry, headliners, lighting,better steering system, some glazing/window work, hatches and ports, general finishing of bare fiberglass inside and to make all of the items that are the main focus of the thread work.

Answering the post by Ad Hoc, my pockets are deep enough to finish this, but not deep enough to finish it twice. So I'd like to get all the numbers right the first time, hiring a qualified designer to have a look, then make the changes.

 

So, now you have made that decision, i would go ahead to engage the services of a NA and remain focused on that. Otherwise you'll get too many comments from armchair designers that will probably guide you down a wrong path, as you're unsure yourself. You need facts, not one-liners simply to sound knowledgeable.

 

Oh, I don't know about being guided down a wrong path, I think what I said first-up, made sense......
"I think you need to identify the boat, or supply the lines plan, and place that is the hands of the designer, to assess the practicality of your idea". No good signing up for a major spend, unless you can get a consensus from several experts that it will work properly. I make no apology for pointing out a potential pitfall, that it could turn into a bucking nightmare, driven up-sea at the wrong speed, if the hull shape is unsuitable. And I meant "bucking" starting with "b", but that could change in the mind of the owner if it turned out badly.

 

Is your 30hp engine centrally mounted? I assume so. You won't get much over 12 knots due to aeration unless you fit a deep nacelle. You need props behind/under the hulls for speed. In general you need fuller hull aft on a powercat. In part to create space for the engine itself. And in part to stop squatting at speed. See photo of the Banshee towing a waterskier with unmodified sailing hull.

The Multihull Centre in Millbrook UK has nearly finished the Gunboat Rainmaker conversion from sail to powercat. But it would have been more cost effective to start from scratch as they had to cut off the bottom of the existing hulls

Richard Woods of Woods Designs

www.sailingcatamarans.com