Tornado hulls with 25 etec.. Need design help.

First off, I've been lurking here reading for a while. This is my first post..

As I get older, it seems I dislike spending money on fuel for my boats less and less. haha. A sailboat is out of the question (I live on a canal with low bridges). I had read about a couple others using the 20' tornado class hulls for the platform as a powerboat. This had results of decent speed with only 9.9hp motors. I searched craigslist, and found a set of tornado hulls that were in great condition. I had a 7' x 11' nida core (sp?) floor made. I've collected an upper station box for a console, a small lightweight leaning post seat, 2 aluminum boxes with locking lids that are approximately 4' x 1' x 1', LED marker lights, steering helm, and just yesterday ordered a new remote control 25hp etec with 20'' shaft, electric start, and power tilt. It came with the controls, gauge, harness, and prop. The frame will be aluminum. Everything is lightweight except for the motor. I also bought a complete 18' hobie minus the sails.
What would the best hull configuration be for 2-4 adults and 2 children to run around the intracoastal waterways? It will stay in the water behind my home here in Sarasota County, FL (on the gulf). Would it be best to make it a catamaran with the 20' tornado hulls only, or use a combination of the tornado hulls and the 18 hobie hulls? I have to decide soon. It's at the shop, and they're waiting for instructions on how to build the frame. All advice is appreciated.
Some may wonder why I chose a 25 instead of something smaller. I wanted an engine that would push it at a decent speed. One of our favorite sandbars takes around an hour and a half to get to running around 25 mph. Granted, about half of that time is no wake zones. We just enjoy the cruise there.

 

With that kind of load on board, you're going to have real issues with available freeboard, especially aft. Tornado and H18 hulls are very clean through the water up to the speeds you indicate, but they can not be overloaded if you expect them to maintain their performance potential. Dragging the transom through the water will sap a good deal of the efficiency inherent in the design.

25 hp is more engine than you will need, but it can be OK if you find a way to give the hulls more displacement potential. Both of the boats you mention are not especially good at carrying the weight you describe. They are sport/racing cats meant to take two adults and that is their sweet spot when it comes to loading. There's no simple way to enhance the buoyancy of the Tornado hulls while still keeping the transoms clear. As it is, you'll need to position the engine somewhere toward the front beam in order to keep the boat balanced properly.

 

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The Tornado was designed to sail with two crew at approximately 340-360 pounds total. You can exceed that a bit but be wary of overloading the boat.
You might want to see if you could find a couple of Stiletto 23 hulls or just a used pontoon boat. Stilletto's were built over there ,if I remember correctly, so you might get lucky.
The picture below is of a Tornado mod done by Gary Dierking-he may be a member here or you could try googling him.

click on image----

 

That boat is one that encouraged me to take on this little project. He used marine plywood to build his deck. I figured I'd be saving a little weight, though I'm adding an extra 50 pounds or so from my engine selection.
I had planned on a 9'6'' beam, with an 8'6'' wide deck raised one foot over the hulls. When my floor was completed, he had made a mistake and made it 7'x11'. Now, I'm a little unsure of the beam. I originally wanted the deck to overlap the inside of the hulls. Now, I'm unsure..

Here is a video of Gary's boat..

http://exposureroom.com/members/vakaman/419485058b6647a7b148c2497e2ab986/

Others....

http://www.catsailor.com/wildthang/wild_thang.html

http://www.murrays.com/mm5/merchant...uct_Code=80-0011&Category_Code=&Store_Code=MS

http://www.biekerboats.com/Bieker_Boats/Skeeter.html


Those are some of the examples I've found so far. I spoke to the maker of the Wild Thang, and he's now running a 35 honda on the back of his 18 hobie. He said it runs around 30 mph.

 

Which ever hulls you chose make sure you make a good fairing for the outboard in front of the leg and as close to it as possible. Otherwise you will just make a lot of spray and won't go fast

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

I've been out on Russell Browns power cat a couple times-- tornado hulls with a pod seen on Paul Biekers website. I would echo Richard Woods comment about the importance of a engine fairing... Which Russell spent some time perfecting. Also, in regards to the Tornados displacement... Keep in mind that the sailboat is meant to take full displacement on one hull in that they are designed to fly a hull when at speed... Whereas the powercat could get away with twice the displacement because both hulls would always be equally loaded... At least we hope.
One hint I'm curious about... Why do you want so much beam?

 

Thank you for the advice about the fairing. Can those be purchased, or is there a link as to how they should be built?
I had figured the more beam, the more stable it would be. Although it is intended as a cruiser for the intracoastal waterway, there are many large boats that have little courtesy for those in smaller boats. During those times, I had figured a larger beam would be beneficial. Would there be much of a difference in stability between an 8' beam and a 9'6'' beam? Pros/cons?
The engine is now supposed to be in wednesday or thursday, the hulls were bottom painted yesterday, the nida core floor was delivered, and I bought a garmin 545s gps/sonar. The floor seemed heavier than I had thought it would be. They made it about 2'' thick, and it's very sturdy, but I would guess it weighs 120 to 150 pounds. I guess that just means the aluminum tube frame can be much less detailed saving weight. If the tornado hulls alone don't do what I want, I guess I'll have to change or add hulls. This is guess work for me, so if it turns out well, it would be a stroke of luck more than likely. It's a fun project though.
Doug Lord had mentioned the Stiletto 23 hull. I googled them, and come to find out it said their address is Laurel Rd in Nokomis, FL. That's where I live.. haha. I sent an email and it was no longer a working address. I've tried to call the number and haven't gotten a call back.

 

You would have to fabricate a fairing for your outboard. Another issues with using a single engine between hulls in a catamaran is that the motor is susceptible to ventilating between wave tops. So you will most likely need to submerge the leg deeper to compensate. You could have as much drag from your outboard leg as the hulls at 15 knots if you do not fair the motor... (outboards are really meant to operate behind a transom)

8' beam should be plenty for this type of boat in that you do not have a tall sailing rig to contend with... and you might as well make it highway legal. The most likely way you could capsize it, is a pitchpole while running with a following/quartering sea... although you would really need to push it to make this happen...something like going 17 knots down a steep 8 foot+ wave and stuffing the bows.

Weight will be the biggest enemy to your boat. Russell Brown did an amazing job at making his boat as light as possible...his entire superstructure-- beams, pod, seats, windshield-- weigh about 150 lbs. As for performance. With a 15 hp Honda 4 stroke motor he can reach 17 knots with one person... 16 knots with 2 or 3 people at wide open throttle. At 2/3 rds throttle he is at 14 to 15 knots. At 1/4 throttle he is at 12 knots.

 

Mike Lenneman at Multimarine in California has done quite a few of these things so it would pay to add him to your list.
Steve.

 

I just spoke to Mike at Multimarine. He was very nice to speak to. He actually had his 20' tornado hull powered by a 15hp motor there to give me measurements off of. It also has remote steering. He's sending pics so I'll have a better idea of placing the weight. He said his with the 15hp runs 20 knots with 2 people on board.

 

Can you post a picture or two... I would be interested in how the motor was mounted, if the was an engine fairing, and what the overall weight was.

 

I haven't received the pictures from Mike yet. The person doing the welding and bending of the frame had to go in for oral surgery yesterday, and the etec hasn't shown up yet. Mike had told me to mount the motor slightly forward of where the rear connecting bar would have went across if he had reused it. He said as far as motor height, to keep the cavitation plate inline with the bottom of the hulls for best results. As far as weight, I believe he said total weight was around 450 to 500 pounds. Don't hold me to that though. I've read so much lately, I sometimes mix up my info. He said he gets best performance with 1 or 2 persons on board, more than that and the performance starts to go down. When I have pics, I'll try to post them..

 

I visited Ron and Andy at Stiletto again today. They're delivering a kevlar 23 to me tomorrow.. I know I'm getting a little carried away, but it's interesting. The tornado hulls were ready to mount the frame today, so hopefully I'll be able to find someone that wants them. I don't think weight will be much of an issue now, which eases my mind. This will more than likely create a week or so holdup, but should be worth it in the long run.

 

Stilletto 23

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Wow! That is really cool-way to go ,Morse. Pictures when you can. Good to hear the Stilletto guys are still around.

PS- you might want to start a Stilletto 23 thread?

 

This might be the leg Mike is talking about

I took this photo a couple of days ago of a L7 outrigger powercat conversion in Marina del Ray

Richard Woods of Woods Designs

www.sailingcatamarans.com