Fuel consumption - An interesting comparson

[Kern O]

Steve, you have no idea how much this has bugged me since the pilot gave me the stats on the airplane. Boeing is proposing a 787 which will use a lot of carbon fiber and the target is an additional 30 percent reduction in fuel usage. Yet, the guys with a single on about 20 feet of boat can get something like 5 mpg, but add twins and 5 more feet and you're looking at 3 mpg. Get over 30 and you are lucky to be in the 2's.

The SeaHunter 35 is laid up much differently than most other boats and uses both a lot of carbon and kevlar. As a result, the boat is significantly lighter and stiffer. John (Darbikrash) has one on order. The boat gets better than 2, in spite of being 35 feet. I think it is about the most economical thing for its size out there. I seriously considered their 29, but the lack of a transom door kept my checkbook in my pocket. But while the SeaHunter is better, I still wonder if we all are missing something fundamental (yes, outside the box) that can translate to a real improvement.

I was at the gas station yesterday and regular fuel is just under $4.00 here in Maui. If I can get 2 mpg, that's still two bucks a mile for fuel. I could take a cab for the same price. Something needs to change.

Diesel boats do better because of their lower operating RPMs reduce frictional losses and diesel has more energy in a gallon of fuel. But even there, the situation is better, but still way off................

[fishbard]

I believe hydrofoils do considerably better than regular boats with hulls in the water. The problem is that there is a limit to how rough the seas can be with this set-up. Again, I think the real problem is how thick water is compared to air, without being thick enough to roll wheels on. The other fly in the ointment is the fact that water won't just lie there nice and flat--it has to get all roiled up from wind and tides. Since my favorite place to fish is the Atlantic Ocean off Hatteras, that "flat planar surface" is seldom present on my fishing trips. Your semi wouldn't do nearly as well if it had to travel off road all the time. Now if we could just figure out a way to pave roads over the seas to all our favorite fishing spots, we might be on to something. Of course, you could always get a sailboat, and then your fuel mileage would be great. A lot of this stuff has already been thought of, in fact, Phillip Rhodes designed a couple of custom sailing sportfishermen that were actually built and used.

[Bullshipper]

http://www.goldcoastyachts.com/suncat32.html

This company no longer lists their prototype 39' wave piercer that could carry 20 passengers at 30 lnots with a pair of 115 twin outboards at 30 knots. but look at the 47 footer wapve piercers using twin 200's.

The whole equation has to do with planing lift and resistance.

Hydrofoils will lift and give less resistance, but are highly unstable in water. So long thin sponsons that plan over much over their length, but pierce te waves at their tips are much more pratcial in terms of stability and lack of resistance, and you can also go wider in the tunnels without adding horsepower.

Another example is to compare a 27' wide mono hull that gets 2 mpg with a beam of 8'6, to a deep vee panga getting 4 mpg with a beam of 7'7". 10% less beam = 50% power reduction.

[welder]

So bull, what your saying is , Boating is a drag !

How bout an Alloy panga ?

Lester

[Kern O]

Lester: As you know, Pangas are very efficient hulls. The ones with the little Merc diesel in them get numbers like 8 or more. But they do that because they are light. Weight, surface area and speed are the enemies of boating. Almost any hull run at an idle does pretty well when it acts a displacement hull and does not create a pressure wave in front of itself. But displacement hulls run up against what is know as "hull speed", which is all the faster they'll go in spite of adding more power. Some of the displacement and semi displacement cats, like the Glacier Bays run up against that. They have a limit to how fast they like to go. Adding more power only eats more fuel, but does not push them much faster. The first Pangas I saw were in Cabo San Lucas and were launched through the surf as fishing charters. I spent many hours on them. They are low on comfort, put will go through anything and return good mileage. They have a very good length to beam ratio, which makes them good in the chop.

I have seen pictures of what appears to be a really big Panga with a full cabin. But, while I like the idea, I'll bet the mileage goes away as the weight goes up.

[welder]

Kern O , I will say you are correct, it take ponies to push pounds.

One thing I have noticed is like on my Pacific 23 I run the BF225 and with one prop I can run 30 MPH at 3000 RPM's and burn 4 or 5 gallons an Hour.

And some guys with smaller motors have to run WOT to do 30 to 35 MPH and burn a lot more fuel.

I guess what I'm trying to say is don't under power your hull , cuz smaller motor's don't save money in the long run.

Lester

[Kern O]

I followed Bullshipper's link to the boat. I have no doubt that it would work and work well. I might have a bit of a problem putting it on a trailer and heading down the highway with it. To get adequate wing height, you need beam. The Suncat has a 16 foot beam which is going to make for a very smooth and stable ride.

The only problem I see is that it is about as handsome as the back of a radio......

[Capt. Fred]

Yup, that look would take some time to get used to. Maybe a couple hundred years.

What about reducing friction with slime. I've read that when engineers calculate the top speed of dolphins that it just doesn't compute. They shouldn't be able to go that fast and they think it's the slime on them. ALso, I know that when a Posieden missle leaves a sub it does so with an air bubble in front of it and it travels to the surface through a pocket of air. What if some of the horsepower was directed into laying down a stream of bubbles along the hull to break the bond of the water to the hull.

Or, when I mentioned the hull changing shape, could there be an inflateable ski that would be inflated along both sides of the keel to provide more bouyancy and a flat surface to plane on. Imagine a bellows type arrangement along each side of the keel that fits into pockets in the hull. As the tubes inflate the rigid underside extends out till it flattens out the bottom of the hull. The air in the tubes could also act as a shock absorber.

[welder]

I think thats the reason the invented SHARK SKIN to paint oh your hull.

Lester

[Bullshipper]

Water adheres to all surfaces and creates a thin laminate that doesn't move. The surface molecules of this veener gets thinner when the surface it adheres to is smoother. Laminar flow is the condition when this fixed water molecule becomes the sheer plane that the other water molecules move against, so this condition in pipes and on hulls naturally creates the slime you are talking about creating.

I have some drawings at home of a 40'x 16' wave piercer with a bolt together floor and tower structure that makes her look every bit as attractive as the lines on a Hatteras, and it can be assembled after transport to the water on an 8' wide trailer, then moored to an anchor, and serviced by beach landings or a zodiac.

Wide set motors make them turn on a dime, eliminating the problems created by the sponsons that stick out 18 feet in front of the cabin area. They also back down well, and the wave piercing tips reduce the total vertical bow movement and speed by more than 50%. Add to this the ability to stay out overnight on a stable 16' beam to double the fishing time per gallon of fuel and this 6 mpg 40 footer will only burn around 25 gallons in 2 days off offshore fishing with up to 8 people comfortably in climate controlled conditions This is $4 person per day in fuel.

Add in a 25' tower to help the captain and his radar keep you on the fish.

These would be extremely cheap to build using strip plank sponsons under epoxy or all alloy plate and pipe.