Stepped Hull and Hydrojet

[Rémy]

Hello

I have got a question about the possibility to associate stepped hull with hydrojet propulsion on a fast motoryacht.

I am planning to build a 1m long model boat looking like a Sunseeker Predator, but I would like to combine both stepped hull and hydrojet.

I have drawn my hull on MaxSurf and then on Rhino3D, with sprayrails obviously, and one step located a bit aft amidship. As you know, step creates an air cushion below the hull, and this is precisely my problem: is not that going to make my hydrojet cavitate ? If the inlets suck more air than water, it may be a problem...

As I said, my model is 1m long, the inlets are located 22cm from transom, and the step is located 40cm from transom. Do you think the 18cm clearance between them are sufficient for the air cushion ?

Thank you for your advices

Rémy

[Ilan Voyager]

Hydrojets hate to suck air and looses immediately all capacity of pumping water. It won't work.

On the other hand, surface propellers need to suck air so theorically it won't be a problem and seems better suited to a stepped hull.

The design of this kind of hulls is not a simple task. The Nasa internet site has a lot of data about these hulls which were used on the boat planes (hydravions)

The use of a model is a very good idea, and will give you some idea of where the step has to be placed. You have to make a model at the scale with a similar displacement and center of gravity as the planned scale one boat to have some accurate results.

Good luck.

[tspeer]

Why not locate the inlets in the step?