56' MY can it plane>

[Freeebird]

Ya'll are extrapolating too much. That formula is a general characteristic. It's empirical, and has other factors that contribute to the outcome...such as hull shape, water density, etc.

But more importantly, what is all this talk of plane? I don't get it....how about a nice easy cruise at 18 knots at 1800rpm?

Extrapolation, pontification, let's just call the whole thing off... plane.

Whose boat is that?

[Pascal]

Huh?

Yes, a boat will stay on plane at a slower speed while decelerating from a speed above minimum planing speed, but it's not going to stay on plane there any longer than if you bring it up from zero. Not sure I get your point.

Some boats, especially if underpowered may not get on plane at for example 16 kts and still be pushing a big a wake yet once they get on plane eventually after reaching 17 or 18, if back down a little they will stay up at 16.

Because the hull is already out of the water it takes less power but also less lift/speed to stay up

That said, the difference is small and not very relevant to the real world

[Toronto]

Could it be as simple as fuel starvation? I watched my RPM's slowly drop
on one cruise, and when the throttles were moved forward, little increase in RPM.
Might be a good first step to change engine and main fuel filter.

2 N JOY 52 CPMY

[saltshaker]

Ya'll are extrapolating too much. That formula is a general characteristic. It's empirical, and has other factors that contribute to the outcome...such as hull shape, water density, etc.

But more importantly, what is all this talk of plane? I don't get it....how about a nice easy cruise at 18 knots at 1800rpm?

That's about what mine runs but I prefer 23Kts at 2000rpms. Although I would much rather have your fuel burn!

[kjcampos]

good morning all sorry did not respond yesterday was on the move from Ocean City MD to Hampton VA long day on the water 12 hrs from untying to tying up ...ran the boat at 1800 RPMs for a while and just pushed a lot of water and ran 11 - 12 knts with the Trim Tabs all the way down...at least gauge said they were down....all i did was burn lots of fuel and no speed pulled it back to 1350 and ran between 9 - 10 knts a lot less fuel burn and just a longer day ....thinking of adding new longer Trim Tabs see if that will help...what is the Hull Speed on a 56' MY does anybody know??

[Scott & Malina]

good morning all sorry did not respond yesterday was on the move from Ocean City MD to Hampton VA long day on the water 12 hrs from untying to tying up ...ran the boat at 1800 RPMs for a while and just pushed a lot of water and ran 11 - 12 knts with the Trim Tabs all the way down...at least gauge said they were down....all i did was burn lots of fuel and no speed pulled it back to 1350 and ran between 9 - 10 knts a lot less fuel burn and just a longer day ....thinking of adding new longer Trim Tabs see if that will help...what is the Hull Speed on a 56' MY does anybody know??

Hull speed in knots equals 1.34 times the square root of the waterline length in feet (HS = 1.34 x √LWL).

Happy motoring!

Scott & Malina

[saltshaker]

Should be around 9kts. If your only getting 12kts at 1800 you are just burning fuel with little gain. Did you try running WOT to get on plane and then pulling her back? You're still going to need a bit more throttle to stay on plane than 1800rpms. Probably need to run at least 2000-2100. Not a good idea if you can't hit 2300 and don't
Know why. Do you know what injectors you have? Could be someone replaced them with smaller injectors to detune the engines. What HP are your engines?

[Pascal]

Hull speed on the 53 is 9.2 so I m guessing 9.3/9.4 for the 56

One thing that s critical to realize is that your fuel flow will be close to double at 10 kts vs 9kts. The difference is huge once you reach hull speed. It's something you don't quite realize until you have flow meters.

Another thing I forgot to mention earlier about wake and being on plane is that if you look back in calm waters you will see that at the transition point, either getting on or off, you wake width will change. Almost like a step on each side. If you don't see that sudden narrowing of the wake, you're not on plane

[SKYCHENEY]

That boat will not plane at 1800rpms. You essentially have two speeds; 9-10 kts at 12-1400rpms or 16-17kts at 21-2200rpm. 1500-2000 will just waste fuel and push a big wave.

That's how my 53 runs with 6v92's and that's how my friends 60MY runs with 8v92's. I would imagine yours would be the same.

[oscarvan]

Just for general information I did some research as to what "on plane" really is. It is not, as I first thought, the moment you exceed hull speed. Here's the definition:

When it is at rest, a vessel's weight is borne entirely by the buoyant force. At low speeds every hull acts as a displacement hull, meaning that the buoyant force is mainly responsible for supporting the craft. As speed increases, hydrodynamic lift increases as well. In contrast, the buoyant force decreases as the hull lifts out of the water, decreasing the displaced volume. At some speed, lift becomes the predominant upward force on the hull and the vessel is planing.