What exactly is a 'stepped' hull?

[speedchaser]

Hi... This may seem like a basic question, but what exactly is a stepped hull, i.e. a stepped-mono as opposed to a single-mono? I thought I knew what this ment, but since looking at recent threads I'm not too sure now... Does the 'step' go lengthwise, or...? Thanks for any help :confused:

[CG Bob]

Here's a stepped (http://www.lesliefield.com/other_history/speed_boat_developments_from_the_past_into_the_fut ure.htm) hull description. The step runs athwartship, from port to starboard; it is usally located in the after half of the hull bottom. The description of stepped hulls is about 1/3 of the way down the page.

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[speedchaser]

Many, many thanks CG BOb!! And thankyou for the url... I've had a look - and well, I'm glad that I posed the thread... For some reason, I assumed that the 'step' in a stepped-hull, ran lattererly and not lengthwise, but now I realise the error of my assumption (an easy one to make, I guess...). I also thought that a surface-drive and a direct-drive was two different ways of saying the same thing - I now realise that they're not... So what I've gathered as a result of your help is that; a hydroplane, or a rigger, is also a form of stepped-hull (?), which is what (a hydro-rigger type) I'm trying to put together. the point being, that almost right up untill I posted the thread, I was going for a hydro-rigger type boat with NO step at all involved, but couldn't at the same time understand why it was that (in CAD drawing's, etc) I couldn't in theory at least, get the right angle for even a surface drive, never mind a direct drive. Some of this reply might be a bit 'in-coherent', but I'm sure you understand where I'm comming from... Once again, many thanks - I was otherwise literally a few days away from making a big blunder with the central 'tub' of my hydro-rigger concept... Cheers! :)

[CG Bob]

I'm glad I could be of some help.

I also thought that a surface-drive and a direct-drive was two different ways of saying the same thing - I now realise that they're not...
In a direct drive setup, the motor is connected to the prop shaft with some sort of universal joint; motor rpm equals shaft rpm. There is no transmission or gear s in a model direct drive system.

My first duty station (in 1977) in the USCG was the Columbia River Lightship, off the west coast of Oregon. The main engine was a direct drive direct reversing Diesel engine. To shift from forward to reverse, we had to stop the engine to shift the cam, and then restart the engine.

[speedchaser]

Yep - so I gleened from your much appreciated url... I've also realised; going back to the stepped hull part, that the lower-rear of the step, i.e. directly beneath the transom or thereabouts, must hang much lower down beneath the waterline relative to the horizontal than the beginning of the step when the boat is idle, so that when the boat gets up on a plane, there is still enough prop in the water, otherwise I can see how the entire prop would be out of the water... Otherwise I still don't know.... Many thanks

[martin richards]

There's another point in favour of stepped hulls which the link didn't have much to say about and that's airation. Getting some air in the water around the step breaks surface tension and lets the boat run freer. In many cases, especially the multi-step designs, this has supposedly more effect than the changes in geometry. Some boats even have means to introduce air in the region of the step(s) e.g., http://www.fastelectricsrfun.co.uk/miss_stress_2.htm

[speedchaser]

Many thanks 'mr'. I didn't know about air inlets in the bottom of hulls before, that's a good idea, although I wonder if the weight of the water going through is also a counteracting factor... The builder gives clear illustrations in the url you gave, it's interesting to see though that the two stepps in his design are not running full width of the hull (probably because it's a mono), however I can see how some of it could equally apply to a hydro type. All that said, etc, I still have a slight conundrum so to speak - which is that heart-of hearts, and this is probably going to let the whole 'kettle of fish' out of the bag, I want to go, not for a hydro-rigger TYPE, but simply a Hydro-Rigger period. That is, a Rigger with full length sponsons, or in other words, an 'unlimited hydroplane' without continuous cross-sections, the idea being, that it wouldn't flip over because there's nothing for the trapped water/air to push against, and at the same time give me similar (maybe not quite) performances to a conventional rigger. But I've been erring on doing this without any steps at all (not the sponsons or central tub) for reasons of ease of construction, i.e. borrowing from or adding in tunnel hull principles but of course the problem with this was getting the angle for a surface drive - hence why I posted the thread. I now think I probably have to have a step whether I like it or not unless I use a flexi-drive, but I've been warned against this... Cheers once again, sorry for long reply

[Ron Olson]

Hey CG, I know you don't I! The city and Bob gave you away :D
Maybe I'll get to see you more next year at the races and the Toledo Expo.
OK, now, back to the show.