Designers....hydrodynamic question

[jlapratt]

I ran across a wooden mullet boat today (sorry, didn't have my camera, so no pics) that has me wondering about the hyrdodynamics of the design. These tradtionally are built as flat bottom skiffs with a motor well amidships, but this one had the motor well further forward (about 2/3 forwards) with a tunnel running to the transom. I know that flats boats have been designed with a tunnel to facilitate a shallower draft and are designed with hydrodynamic differential pressures dictating where the tunnel starts in relation to the prop.

I am thinking that for this mullet boat, that the tunnel does two things,1)provides sufficent delta P to limit prop caviataion and 2) provide lateral resistance to limit slippage while turning as a skeg would.

Has the wine I had with dinner buggered up my thought process or am I on the right track as to my thinking?

I am trying to understand the evolution of the design of these boats, and the expertise of this forum is invaluable. I welcome your comments!

[ 12-20-2002, 07:36 AM: Message edited by: jlapratt ]

[Mark Van]

I don't think there was any scientific thinking behind the mullet boat design. The motor was put far forward so it wouldn't be in the way when casting.

In Cedar Key, Florida they are called "bird dog boats", apparently because the go the direction the motor is pointed.

[ 12-20-2002, 09:32 PM: Message edited by: Mark Van ]

[Tom Lathrop]

Mark,

I was wondering if someone would come up with a scientific reason for the tunnel and engine placement. I expect that you are completely correct. Anyway, since the boat with engine forward steers by the bow instead of the stern, the lateral resistance of the tunnel sides is not relevant. Probably, the mullet fishermen would not know a delta P unless they met one in the bar. We have lots of well boats around here and they don't steer as well as a transom mounting.

[jlapratt]

That's funny Tom! I'm sure that this design has just evolved from practical usage, but I don't know the hydrodynamic effects of the tunnel.

I haven't seen any delta Ps in a bar, but have met a few static heads there.

Jeff