will it plane or displace?

[dkubiak]

I do I figure out if a hull will plane or displace? If it will plane, how I do figure out at which speed/horsepower it will plane?

Thanks,

Dan

[Danielsan]

I might need the same info, I did draw a boat which should be a planning one I hope. I do not know at what speed or HP. As I compare with oter boats I should have at least 140-160HP.

[Dutch Peter]

Look at this thread:

How much hp to plane?

[jfblouin]

First determine your relative speed.

Relative Speed = Speed (in knots) / Square roots ( WL (in meter))

Below 2.7 you are in deplacement mode.
Over 6.5 you are in planning mode.
That are average for standard boat.
Between 2.7 and 6.5 your are in the hole. This range of speed is not for your boat. It run in non-effective speed with bow up.

Now for planning speed, you can use this formula

HP needed= Total Weight (Kg) * Speed (in knots) * Speed/13500

13500 is a average constant for standard boat. You can change it for your boat if you know a spec for your boat.

Example: A boat with 7.0 m of WL is in displacement mode up to 7.1 knots. In transition mode up to 17.1 knots and in planning mode over that speed. This is approximation. A deep V can plane only at 18 knots and a flat boat will plane at 17 knots.

If I want to reach 30 Knots with my boat of 3000 Kg (included passager and fuel), I need 200 HP. This always a average but I post theses formula in a other forum last year and everybody will be in 10% and many one in 5% range for their boat.

[jfblouin]

Plus for planning, you need a flat transom to force the water flow to continue straight. Elsewhere the succion will keep your boat down in water and you never plane.

[Frans X L]

Just to add to the above posts.
When looking at a hull, a simple check for hull type is as follows.
Look at the profile(side view) of the keel and bottom.
If the rear half is horizontal and straight it is a planing hull.
If the rear half curves up to the waterline it is a displacement hull designed for low drag.

[Thunderhead19]

If the deadrise angle is too aggressive, it won't plane either. Well, that is to say that you'd need a gross amount of horsepower to do it. Anything will fly if you put a big enough engine on it.