Dynamic lift or not with transom bracket

[jfblouin]

I tried to find information about use of dynamic lift or not with outboard transom bracket without succes.

What is the pro and con of this two type of design?

The bigger one with full bottom planing surface will add more buoyancy and aft lift but also add more drag.

The smaller one help to clean water flow for propeller.

[JR-Shine]

I am sure there is no dynamic lift from the bracket. It angles upward from the edge of the transom, if water flows along it that way, its will actually cause a great amount of suction and boat will not be able to get on plane. Picture an airplane with its flaps down, but upside down

There is normally a vertical gap between the end of the transom and the start of the bracket, this allows the water to "break free" and not follow up the bracket

Hope that makes sense.

Any added buoyancy is net zero gain due the engines being placed further back.

[jfblouin]

What can we think about this kind of bracket?

[LostInBoston]

Originally Posted by jfblouin

What can we think about this kind of bracket?

The design is couter productive. Its a straight shot back, so the drive needs to be mounted lower, which gives it more bow lift, which is couteractred by the extra planing surface.
JR-Shine, got it right, you want the water to break free of the hull and flow up into the drives without causing suction. Looks at the big, faster CC's the all have a notch before the drive. This allows the water to break free of the hull, airates the pocket to avoid suction and mount the drives higher to reduce bow lift and ride better.

[jfblouin]

Because the bracket plane is in-line with boat hull, why I cannot assume that it is just like a longer boat?

[tom28571]

Originally Posted by jfblouin

Because the bracket plane is in-line with boat hull, why I cannot assume that it is just like a longer boat?

I think I understand your english ok and nothing wrong with you reasoning either. Everyone's thoughts seem to be correct in a proper context.

I find the use of transom brackets a bit confusing. Is there a really good explanation of the working of these devices somewhere? I mean a thorough discussion with backup data of the different types of brackets on different types of boat hulls.

Just sticking one on an existing hull, and obtaining improving performance, seems to me to indicate that the boat was not designed properly in the first place. In one ecounter with a boat equipped with a bracket, the prop had a distressing tendency to ventilate at low speed in waves. This one thing would cause me to take it off regardless of any other good attribute it may have had. When it occured, the throttle had to be chopped until ventilation ceased and speed slowly built back up - a real nuisance.

[LostInBoston]

Originally Posted by jfblouin

Because the bracket plane is in-line with boat hull, why I cannot assume that it is just like a longer boat?

Yes, you can think of it that way. But adding a longer running surface liek that pushes the center of gravity further foward, but then the drive is mounted low to compensate for that. Like I said, they counteract one another. A bracket should allow the drives to be mounted high so the boat rides more level.