What is the most economical boat type to do at least 12 knots with?

Question

I want to build my own commuter boat to commute 8 miles across the Otago Harbour in southern New Zealand. The only roughness I encounter there will be winds up to about 50km/h and a 1m-chop. Sailing and solar are probably not an option.

So far, I've been contemplating these concepts:

1. A 6m aluminium planing boat with an enclosed cabin and a Yanmar outboard diesel. I feel this may not be economical enough.

2. A 6m diesel launch with a 5HP inboard diesel. Perfect, except for the speed, which is probably less than 8 knots.

3. A 6m catamaran with a Yanmar diesel outboard.

4. A very narrow, 12m displacement boat with an inboard diesel of about 5HP.

Does anyone see any possibilities I may not have seen here yet?

Answer 1

Crazy idea, not the most "economical", but since you do your own designs, have you looked at the guys in FL from Solomon with their "Electric Wheel" ? (patented planetary drive with two integrated electric motors, would also allow interconnection to a Diesel engine).



I am somewhat serious, do not know their price, but with your University affiliation/ design credentials, they may have an interest to put a foot down in NZ.



You would run the boat on battery power, recharge during the day, while you teach, manage and think, and again recharge at night, when you sleep, or feast and drink "organic"..



Gruss aus dem sehr winterlichen NJ

Answer 2

A displacement boat with a diesel is the most economical set up. You will need more that 5 hp to move a 12m boat at 12 knots. More closer to 40 hp

Answer 3

A collegiate crew racing hull can barely achieve your performance requirements, but building something that long, light, and stiff is neither cheap nor easy.

Lightweight skiffs, inflatables or sail-type catamarans with planing hull shapes can achieve planing speeds with about 1 horsepower per 50 pounds pushed. If you are very careful about weight and wind drag you can probably build a weather shelter on one of those hulls, hang an outboard, and still carry one person at 12 kts with 15 horsepower. Youl'd better plan on sitting down and chugging along at 6 kts or less when the chop comes up unless you want to get beat to death on a rig that light.

Please note that if you're willing to settle for 6 knots all of the time, you can carry friends and a small pub's worth of cabin space along with you and still burn less fuel that what is needed to go fast some of the time.

Answer 4

50kmh winds and a 1mtr chop is rough if it kicks up. Cheoy Lee makes some good boats. Use the old Hull Speed Formula:

A displacement-hull boat whose waterline has length L (in feet) will have a ``hull speed'' that is K SQRT(L) knots, where K is a number between about 1.2 and 1.4 for most conventional cruising hulls. Small planing dinghies, large planing sleds, scows, and other designs (including catamarans) will not fit well into this formula, so you should ignore it. The formula assumes a lot of things, but all in all it does pretty well for figuring whether your Bristol 40 will keep up with a Catalina 30 in moderate winds (or vice versa).

http://www.cs.brown.edu/people/jfh/boats/FAQ/node19.html

And:

http://www.antrimdesign.com/articles/hullspeed.html



http://en.wikipedia.org/wiki/Hull_speed

The most commonly used hull speed constant is the wave propagation speed for the hull length, and it serves well for traditional sailing hulls. In English units, it is expressed as:



\mbox{knots} \approx 1.34 \times \sqrt{l \mbox{ft}}



Or, in metric units:



\mbox{knots} \approx 2.5 \times \sqrt{l \mbox{m}}



In reality, speed/length ratios of real hulls vary from as low as 1.18 for blunt hulls such as barges to over 1.42 for long, thin hulls. Also, since hull speed takes into account only the wave making resistance, large hulls (over 200 ft or 60 m) will be more limited by other forms of drag[1]

Go Deep Draft that is more Self Righting, I would. A 28'-36' Sloop with a 6'-7 draft'. Many sloops can be easily motored and have a proven design for weather.

They can be sailed in almsot any weathers, but that is up to the skippers ability and sometimes careless regaurd for self.

So far I have found about 50+ for sale from 50k to 300k GPB.

To build your own, go Sharpie. I have seen some and sailed on one, a 58'er out of New Orleans , she was BIG, but Sharpies have plans in many sizes.

The Sharpies have a good reputation and are decent in materials costs. Marine Ply and Glue. add about 100 extras to that and you got yerself a boat!

Have Fun,be Safe.

Answer 5

There are hydrofoil sailboats that will do over 40 knots.