Planing bow hull and getting over the bow wave hump
I working on trying to get some "correct" sketches going for how a SES or Hovercraft gets over the hump. However my lack of understanding on how boat planes restricts me in some ways.
Please post a video or a sequence of drawings which illustrate how a boat gets on plane.
Examples may be anything you wish to share, from multi-hulls and hydroplanes to larger craft.
Feel free to ask questions.
I'm not trying to say boats get over the hump the same way hovercraft do, just looking to understand the boat side of things from this forum.
The second topic of "plow-in" as I understand it may also affect boats on plane coming into contact with wake and other waves. This is also of interest, and I hope not to confuse the two.
Here is an example for what I've been working on.
Link to original images:
Kach22, I can comment briefly on the 'plow-in' pehnomena as it relates to SES and ACV. Many (most even) early designs of both had their cushion air supply a the rear of the cushion. Many smaller ACVs still do..out of design necessity. What we didn't know early on was how large a pressure gradient is developed in the cushion as a result of forward speed and boundary shear effects. Lowest pressure forward and hghest aft. We found, through a series of cushion pressure measurements along the length of the cushion, surprisingly large pressure gradients that increase more or less linearly with speed..the net effect of which is to steadily move the lift center aft as the speed increases.
As the pressure gradient increases in magnitude, a secondary effect serves to amplify the pressure gradient and eventually result in the 'tip over' or 'plow in' event; as the lift center creeps aft and the craft trims bow down, the cross-sectional area of the cushion decreases forward and further restricts the 'duct' that the air is trying to move through to maintain the forward end of the cushion. (This may/should be less pronounced on lower L/B designs that characterize most ACVs..but is an issue with high L/B SES..)
I ignored windage effects here. they too can play a role; SES and ACV trim up some when headed in to the wind and trim down when running with it.
My SH-2 5-pass hovercraft had a huge problem with suden plow-ins when going down wind..and it had all it's air supplied from the rear of the cushion. The last SES I played with that had rear air supply and tipping problems was built more than 15 years agao..all since then have had the air supply all teh way forward.
The 'hump' discussion will have to be in another post..I think I already stretched the definition of 'brief' to the breaking point
Thanks BMcF, my goal is to apply a little boat common sense to hovercraft - just trying to start at the begining.
The things you know just astound me.
Trying to make sense of this.
This web-page lets you investigate the required thrust [kg] and horse power [hk] as well as trim angle and porpoissing stability for a given planing boat and a given velocity range.
I'm not sure a hovercraft which has lost it's lift power can get home on it's own, or if that would be a reasonable goal. Maybe just being towed by another reasonably sized craft would be a respectable achievement. The skirts would have to come off, I'm sure.
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