blacklabmarine

Gents,
Our DNA is in moderate speed outboard boats (think 50 knot top speed).

We have a requirement for a 42' x 10' deep-vee, monohull with diesel power. We (obviously) will be making the hull out of marine-grade aluminum alloy but are starting today to look at powering the hull.

What I would ask of you folks is the following:

1) If you had to have diesel power and needed to push this boat 60-65 knots (70 mph+) What powerplant would you use and how would you get that power to the water?

2) Our general group of naval architects and engineers will all tell me that they have the knowledge/expertise to do this project although none of them specialize in high-speed boats.

I'm sure that there are some specialists in high-speed design for both hulls and propulsion systems - any suggestions would be helpful.

3) Stepped hull or no steps?

This boat because of its mission profile will be heavier than the hulls you guys are used to. For a 42' will be looking at @ 12,000lbs w/o power or fuel.

Lastly, we're using the 60 knot number as a minimum - looooove to go faster.

ScottB

If I was building a diesel mono hull, I would call this guy
for advice on going fast

http://www.fbdesign.it/fabio%20buzzi.php

Jassman

Hi Jay..how you been.. The last diesel 43 Nor-tech I had was with the 480hp Yanmars with Arneson ASD-8 surface drives..boat ran 74..weighed in at 15k..The other diesels Nor-Tech has done have been with the Cummins power..

Fenderjack

iTrader: (2)

If all your looking to go is 70s, I would slap a set of hopped up duramax's in there matted to a B max drives... If you have a huge budget it is endless


John jr

Westcoast

That might be a good match for the new BUCK marine diesel

Jassman

the duramaxes are not out as of yet...and B-max is in the good, the bad, and the ugly section. too many problems, I have many friends with them on this board.

Arneson with the Yanmars, or Cummins with the NXT. These are the two optiona that work and give resale value.

stirling

12000 lbs without power /drives /gearboxes /fuel ,that is going to be a heavy boat wich needs a lot torque to move it at the speed you want ,if there,s no budged I would say a set Cat C 15 Acert with Arneson ASD12 ,and a set ZF 2 speed transmissions ,or triple Cummins 480 with ASD 8 ,s .
12 K in weight without power /drives /gearboxes /fuel is at least 19-20K with 2 big diesels with drives /boxes and fuel,which is a pain to reach those speed levels,Maybe Joe Gere can chime in ,he has a ton experience with this

A.J

Hot Stepper

How about a turbine engine?

carcrash

Listen to Jazzman on powerplants.
Absolutely use steps. There is no way to justify not using steps in your application: better fuel economy, better ride, better structure.

Remember that the point of steps is NOT to "aerate the bottom." Its to (1) increase the aspect ratio of the lifting surface (shorter for length), and (2) to give each planing surface a 2 to 3 degree angle of attack without undue bow rise and (3) to prevent porpoising by making the lift come from two widely separated areas on the bottom, instead of just one.

A planing bottom is like the bottom of a hydrofoil, it works exactly like a super-cavitating hydrofoil. That's the mathematics you use. A high aspect ratio foil (wider than long) gives more lift for a given amount of drag: less of the boat is in the water for a given amount of HP. Therefore, you go faster.

A lifting surface requires angle of attack to generate lift. On a long bottom, the first few feet of the boat hit the water at an angle, so lift is created forward, but as the water moves along the boat, and the pressure wave from the bottom affects the water, the angle of attack goes to zero (the water starts moving downward before the hull gets to the water), and so there is no lift generated aft, only drag.

By putting in a step, the aft end of the boat looks to the water like another boat -- the aft planing surface has an angle of attack, and so lift is generated aft as well as forward.

Nearly all airplanes have two horizontal airfoils -- the wing near the CG, and the horizontal stabilizer aft. That is a stable orientation. By having two lifting points on the bottom of a boat, rather than just one, the boat is far more stable fore-and-aft, and is therefore far more resistant to porpoising.

I strongly suggest you go tape a Fountain 47 bottom. While a tape measure won't show you right where the CG is, you can tell by the trailer axles that the steps are just forward of the center axle on a triple axle trailer. Note well that the aft corners of the two steps line up with the lower corner of the transom.
Your designers should know about the "crouch" formula, formulated in the 20's by the designer of several of the Gold Cup racers including Baby Bootlegger. His formula was derived from observed performance of many planing powerboats, with steps and without, during the period from 1905 to about 1930. This simple formula remains today as the most effective predictor of performance.

The formula uses the "Crouch factor" that is a constant for different bottom configurations. The higher the factor, the more performance for a given amount of weight and HP. The Crouch factor for Fountain hulls is the highest in the industry, and therefore the bottoms to learn from. Stepped bottoms are substantially higher performance than un-stepped bottoms at all HP, weight, and planing speeds.

Oddly enough, stepped bottoms are also more efficient at displacement speeds due to the wave energy (shorter waves), even though there is more turbulence.

One other thing. Note that Fountain bottoms have a "pad" where the foot or so on either side of the keel has much less deadrise. This actually makes the ride smoother! While this seems counterintuitive, there is a huge amount of data from Naval and NACA research that fully supports this. The lower deadrise near centerline ONLY works because its NARROW. If the entire bottom has low deadrise, you get beat to death, of course. The "pad" combined with longitudinal chines really makes the bottom a variable deadrise, less deadrise near the centerline and increasing deadrise towards the chines. This is what gives you the smoother ride than a constant deadrise from centerline to chine, and it also gives you more lift (and that means more speed for a given amount of power).

The way to think of the pad is to imagine re-entry into the water. First, the pad hits the water. Its a long a narrow planing surface: its very highly loaded. A highly loaded surface simply crushes the waves. But it does start to slow the vertical velocity of the boat. Then, the next portion of the bottom is in the water, now the pad, out to the second set of strakes. Still, the bottom as seen by the water is only 2/3 the beam of the whole boat. So again, its more highly loaded than the whole boat, so crushing the waves. Finally, after the boat is barely going downward (its fall has been broken), the full beam is in the water.

The mathematics behind the pad and the strakes (the variable deadrise) shows that smoothness is a non-linear factor of beam: one half the beam results in a MUCH smoother ride, not just twice as smooth. That's why all these offshore boats are narrow. The pad bottom is the same thing -- a MUCH narrower bottom that comes into play in rough conditions.

The above are the reasons why Fountains are so fast. You want to learn from the best.

BenPerfected

We made some progress on our bottom just hacking around....think what might have been if we had known what we were doing. I am a firm believer that speed is all about the bottom. It is a interesting that more HP boat manufactures don't spend more on R&D $ on bottom improvements.