Planing surface more important than hp?

[BoatFisho]

Ive been looking at guys trying to get their 4HP planning their infltable dinghies.

What it occurs to me is that you need a large planning surface, of course you can through my HP at it, but weight up front and planning surface is the way forward for them.

I look at a 2.5m inflatable and it just displaces, yet a 3.1m with properly weighted boat does plane with a 4hp.

So the larger boat planes partly due to larger planning surface? At some point there must be a stop in the extra surface being important, ie a 12foot inflatable might not plane.

So is planing surface or the boats length part of the equation?

 

[UncleWillie]

The answer is YES!
More Surface, Less Weight, Less Drag, better Hull Shape, or More Power will get anything to plane.
The 3m might have 50% more surface but only 25% more weight than the 2m dinghy.
It is not a simple problem.

 

[H20Rat]

As the uncle mentioned, it isn't that simple. More planing surface also means more wetted surface, which means more drag.

 

[bonz_d]

But a flat piece of plywood will draw less water that an 8"x8" post of the same weight.

 

[Maclin]

Look at Smart Tabs by Nauticus, they have tabs designed specifically for boats like that. Might be other brands also.

 

[dwco5051]

But a flat piece of plywood will draw less water that an 8"x8" post of the same weight.

But that 8 x 8 has wetted surface on both sides which is parasitic drag and does not help lift the boat. The load per area of planing surface is increased which effects the equation. Fluid dynamics can be very complicated.

 

[UncleWillie]

But a flat piece of plywood will draw less water that an 8"x8" post of the same weight.

A flat piece of plywood will draw (Displace) exactly the SAME amount of water as an 8x8 of the same WEIGHT.
The plywood will will have a lower foot print pressure (Pounds per Square Inch) than the 8x8 and will plane at a lower speed.
Think... A Water-skier on Skis weights more than he does when Barefoot skiing. Bare footing requires a much higher speed.
As stated, it is not a simple enough phenomenon to reduce to a single variable, or even two or three!

 

[bonz_d]

A flat piece of plywood will draw (Displace) exactly the SAME amount of water as an 8x8 of the same WEIGHT.
The plywood will will have a lower foot print pressure (Pounds per Square Inch) than the 8x8 and will plane at a lower speed.
Think... A Water-skier on Skis weights more than he does when Barefoot skiing. Bare footing requires a much higher speed.
As stated, it is not a simple enough phenomenon to reduce to a single variable, or even two or three!

I think you described what I was trying to say better than I did!

Though I believe they will Displace the same amount of water I also believe the 8X8 will draw more depth in the water than the flat plywood. In other words the bottom of the 8X8 will be deeper into the water than the wider board at rest.

 

[NYBo]

No Title

 

[bonz_d]

That works!