Aft End Design

For a towed barge, where there will be no propulsor at the aft end, what is the main criteria to consider for the aft end design.

It stands to reason that the fullest aft end design will maximise cargo; what affect does the fullness of the aft end have on resistance?

Why is it not possible to carry a midbody section to the aft end and have a fully submerged transom?

What are the towing stability consequences of a design without a skeg?

Appreciate any thoughts you may have - If you can include references and/or design hyperlinks I will be most appreciative.

Regards

Julian

 

If you have a barge train, square ends work fairly well if they are towed close together. Also, some barges have square sterns where a tug fits against. The water flow can, more or less, make a continuous run from the bow of the first to the stern of the last.

 

Ship Shape Stern

For a towed barge, a "ship-shape" aft end spells disaster with respect to yaw. If you decide on a sleek stern, your barge will dance from left to right while the tug tries to pull her straight. The only way to deal with this is a set of large, ungainly skegs.

Harry Benford of the University of Michigan (1955) had this to say of stern design:

"More serious than the problems created by the bow are those brought on by improper shaping of the stern. There is no need, even in sea going barges, for a ship shape stern. Tests have shown that while the bare hull resistance of such a stern may be less than with a normally raked barge type, the interaction between the skegs and the ship's sides is so detrimental that exceedingly ungainly skegs are required with consequent loss in speed. In a recent test the skegs doubled the resistance!"

He goes on:

"A stern, if made nearly box shape, may have enough drag to stop yaw without aid of skegs. There are special circumstances under which this might be justifiable, but ordinarily a raked stern with skegs will show considerably higher speed."



Joshua N Straume
(504) 832-3952

 

I think it is always bad business to make a stern that is faster than the bow, but having vertical transom that goes deep is the other extreme. Ride a planing powereboat that is trying to go slow (3 to 4kts) and see what the skipper has to go through to keep it going straight. The wider and deeper you go, the worse the problem.

Phil Bolger has often talked about taking his famous 'brick' sailing scow design and ending a bottom that is re designed to be dead flat at the stern with a verical transom in hopes that the shallower rocker then needed to get the same displacement would actually have less drag.

So far, I haven't heard of him trying that.

He has, however, designed some 'fast motor sailers' that use the dead flat run and vertical transom, but they tend to be shallow, narrow, or both. And the word fast seems to describe the motoring more than the sailing.

Bob

 

Can't you maintain hull depth to control yaw, but round out the waterlines a little?