There seems to be a strong consensus among Houdini experts that the best way to create the effect of a ship's wake is to create a pump at the bow of the ship that lifts water up and to the side. Searching through Vimeo and the Houdini Forums will provide a lot of wonderful examples of this:

- https://vimeo.com/93243750 [vimeo.com]
- https://vimeo.com/123026523 [vimeo.com]
- https://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&t=35468&highlight=ship+wake [sidefx.com]

I've been able to get the bow pump working successfully; jeff's post in there helped me out, as did a scene file from Graham Collier which I found elsewhere.

However, I've run into a bit of a brick wall. I'm a bit stubborn, and really wanted to figure this out on my own, but I've been working on it for an embarrassing amount of time, and can't seem to get over this hump.

When working with a small fast moving water craft, that sort of lovely wake seems to appear quite easily when one uses the aforementioned bow force. But since I've switched to using a much larger vessel (150 meters long) travelling at a moderate speed (15 knots / 7.7 meters per second) - and trying to simulate it the correct scale - it all seems to change.

Instead of creating a nice smooth trail of straight lines behind my ship, I get the curvy soup seen in the attached images. It's as if the water coming off the bow is swirling in a stagnant pond rather then falling elegantly behind the ship with the beautiful lines we want.

If the scale is correct, it should take approx. 480 frames for the particles from the bow to reach the stern; so iterating through different settings is painfully slow, even with a 20 core box. Since the final product needs to feature two destroyers - starting from a distant shot and zooming in till we're close up, I also need to have a very large amount of pre-roll to establish the long wake to stern, as well as enough extra frames that would allow my to duplicate the cache & offset it so that I can use the same cache on both destroyers with enough variety between the two that no one will see the difference.

I've tried increasing the ship's speed to 30 knots in order to help the process along, but the client is based in the Navy, and their eyes are sensitive to speed differences like that (“for this sort of operation, the ship would be moving much slower than that”), so speed and scale have to be accurate. Ironically though, the artistic shape of the foam is a bit more flexible, but what I have currently is a no go as it looks quite unrealistic - what I've seen in the same videos linked to above would be great.

I've included some basic scene information below; one thing to note is that all of my transform data (including camera position & rotation) is being imported from an Alembic file - meaning that I have to adjust my scene scale & settings to work with whatever the alembic file is providing in terms of model size, etc.)

Grid: 30m x 0.25m x 100m
Hip File Scale Settings: 7m & 7kg
Particle Separation: 0.06
Particle Radius: 1.2 & 2 (I've tried both, had slightly better results with the lower number)
Grid Scale: 2
Water Particle Density: 2000 / 1000 (also tried both, had slightly better results with the lower amount).
Collision Velocity Scale: 0.25 - 1.25 (tried varying amount of this; higher numbers created an undesirable tidal wave that went ahead of ship, lower numbers created more of a stagnant soup)

I'd love to attach a HIP file, but much of the scene is integrated with external files (Alembic caches containing client provided files). So it's difficult to extract the necessary information & remove client data without breaking it.

If necessary I can give it a shot, but I was hoping that someone might be able to see the information I've posted & provide some info that would point me in the correct direction.

Thanks!
Luke