Power needed for planing?

Hi,

I have been reading the forums for a while and this site is a wonderful resource. I have been playing around with ideas for boats for a few years. I am not in a position to have a boat now however, I am looking at it as a possible home and escape vehicle. I started out thinking I would convert a OSV or research boat, the speed or lack of and cost is too great and the issues with asbestos, low ceilings and ancient machinery.

That brings me to the yacht world. I like sail boats and don't mind the speed if I am not burning 7 tons of MDO a day but, to have the internal volume I want I am looking at 90' plus boats. The crew would be a couple and while I know many live on smaller boats comfortably I can't see it myself. The sail boat is still at the top of the list however I do like the Lobster boat on steroids idea and some fast hardtops like the Sunseeker Predator and Fairlane Targa.

Both the Lobster boats and fast Hardtops in 55-75 foot range have the living space that equals a 90-100 foot sail boat. In the sail boat we could sail anywhere and on the speed boat we would be at the mercy of yacht transport but that is not the end of the world. The bigger question is just feeding the fires on a power boat to go anywhere. I would like to get a better understanding of large planning yachts and the efficiency of them.

I have thought about using a diesel electric drive on any boat. In looking at ad's for the Sunseeker they show tankage and range that is while high in fuel flow nowhere near BSFC fuel flow for their rated horsepower. Could two 600 KW electric motors get a 35 ton boat on plane and keep it there? And once it is on the step how much power is needed to keep it there in moderate seas?

The boats would all be on the Pacific coast of North America initially in Los Angeles. The radius of travel would be from Cabo to The Puget Sound.


Steve

Hi Lars,

I am not saying that the technology is cheap, but there are some new concepts in DE power that may work in smaller boats. Say a 50-60' that weights 15-20 tons. In this example a set of motors and gen sets to drive them could be had that weigh about 6400 pounds. While that is heavier than an inboard set up it is not that much more and it includes ships power in the package. A set of Yanmars or Volvos with gearboxes would weigh about 5000 and you would still need a generator. The cost up front is higher; how much is debatable but, over the course of a few years the fuel saving could be greater IF the numbers are correct. This is an idea that could go either way, the gen sets may not prove reliable over the long haul or it could prove to be the wave of the future.

That said; how do the power curves look on bringing a heavy boat up on plane and then keeping it at it's best planning speed. Do you need 2500 horse power to launch it on the step and then once on plane only need half that power to maintain speed? As an example the Sunseekers say they have a max speed of say 34 knots and curise speed 28 knots. Would you still be on plane at 20 knots or are you sinking back into the sea? I understand the pressure as lift, at what point is a planning hull at its best L/D?

I am looking at this from a total cost aspect and fuel is a huge part of the cost. Paying a bit more up front to greatly reduce on going costs is something I would do, the distances involved warrent the effort.

Steve

Hi Lars,

The model I used has three gen sets, I would like to think that two at curise speed would be enough to do the job. That is not an optimized set up to be sure and there could be more gen sets. I see this as a great way to save wear and tear on prime movers as well. When you are in a harbor one generator is moving the boat and running with a good load on it. Thinking out of the box is one of my strong suits I am kicking tires here and this is just the begining.

I have admired your designs, have any 60-70 lobster boats in the portfolio? Can you tell me if a 50-70' boat would be lighter in GRP or Alloy at the same strength. I have looked at a lot of boats and I see things in every boat I would do differently. I mainly would like more room in the galley and social areas and fewer guest cabins. I also want a nice size workshop. I would be the chief engineer as well as the Skipper.

Steve

One more thing on the generators that I was talking about, yes they are demand driven. They run at the speed needed to supply the power required on the entire bus. They are quite thrift and they are on the same bus so load sharring can be maximized.

This is not a giant EMD on a tug

Steve

No; they are load sensitive. From what I understand they throttle up and down depending on the load. I don't have any hard fast data on this system, I have talked to these folks about their design and I do think it makes sense. I am just not sure that it has been validated in use. The issue in these systems has always been weight and complexity, this seems to address both. The engines and generators are rated as prime movers per IMO specs and the weight per KW of the gen sets is about 30% of traditional gererators. Sounds too good to be true but, they have a real product. I am not in any way part of this organization and they shall remain nameless but I am very impressed by the specs and power systems they offer.

Steve