Planing

[Tommy c]

Will a t27 plane easier or not than a t32 with the same engine 2 up?

[chipko]

Unfortunately no. The longer the wetted area the sooner it will get planing for the same size motor. Plus a T38 will plane earlier than a T32.

[Steve509926]

Originally Posted by chipko

Unfortunately no. The longer the wetted area the sooner it will get planing for the same size motor. Plus a T38 will plane earlier than a T32.

Hi Chipko, why? Not doubting, just interested in the physics behind it.

[Pikey Dave]

Originally Posted by chipko

Unfortunately no. The longer the wetted area the sooner it will get planing for the same size motor. Plus a T38 will plane earlier than a T32.

Caveat:- I’m more than willing to be corrected/educated.
I thought that the longer the wetted area, the lower the planing speed. BUT the more hp required to achieve the speed.
I.e. yup, a longer hull will plane at a lower speed, but it needs more horses to get there.
So it depends on the OP’s base engine. If the engine is high enough hp to get the longer hull to planing speed, then the answer is yes. But if the hp isn’t sufficient to move the hull fast enough with the additional drag, then no.

Like I said, I’m happy to be corrected.

[chipko]

Originally Posted by Pikey Dave

I thought that the longer the wetted area, the lower the planing speed. BUT the more hp required to achieve the speed.
I.e. yup, a longer hull will plane at a lower speed, but it needs more horses to get there.
.

Can’t argue with that PD [emoji106]

To plane, especially to initiate planing, the power-to-weight ratio must be high, since the planing mode of operation involves moving the hull at speeds higher than its natural hull speed. As speed increases, hydrodynamic lift increases, and the hydrostatic (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.

Agree once planing a longer sib will be slightly slower than the shorter one, but in practice quicker/easier to climb out the hole with the same motor, particularly those of marginal power. This is probably due to the negligible weight difference of only 5 to 15kg between shorter/longer sibs (T27/T32/T38).

If you then factor in the total running weight, loaded the same, the percentage difference is marginal, so the supported weight (force) over the much larger surface area is considerably less and lift will occur quicker. There is also the benefit on a longer boat weight shifting forward to help ‘get out the hole’ is more effective.