Last step on a stepped hull question

[SamSam]

Originally Posted by tuantom

I think Jiggerpro is still a little misunderstood here. Pretend the boat in the pictures doesn't have that engine bracket on it - poof - it's gone. If you look, especially at picture #1, there is a step in the keel starting ~ 3 or 4 feet in front of the transom.
You would think this would disturb the water right in front of the prop. Why not?

If you pull up the site of the bahama 31 Jiggerpro posts in post #8, especially the 6th photo down in "building a bahama 31", there are no steps in the hull. (I put the photo down below) The only thing is the engine pod bracket extension thing. You can see how the center of it angles up a lot from the plane of the hull, so it can't be for water contact. I'm no NA, but it seems anywhere there is a real step in a hull, the hull after the step is at the same plane as before the step. It's like one straight hull with notches cut in it.

Even if there were a step way back there, I wouldn't think any aeration of the water would go deep enough to aerate the water the propellor needs, but that's just a guess. As is the above about the notches.

[EStaggs]

In using a 21' Campion (my neighbor's boat) in the usual blustery Juan de Fuca strait, I was impressed with the effectiveness of the bracketed outboard. The boat acted like it was 24' long, with better rough water manners and more stable handling. In 4' swell we never ventilated the prop, which is odd considering this place is well known for steep seas when wind opposes tide.

I think the ideas such as longer theoretical LOA, less wetted surface area vs LOA, and cleanliness of the water being offered to the prop, not to mention reduced draft compared to an IO (but comparable to a traditional outboard) are what drive it.

On our lake here at home, the extra length makes close quarters maneuvering more difficult due to the extra length, but thats the only detractor we have found.

E

[jonny250]

OK, I'm a newbie to the forum so I hope I observe proper protocol, etc..
Here's my take on the 'aft step';
The step is acting as the 'original' transom, the position of the props is sufficient to ensure they are running in clean water streaming from the transom. The hull aft of the 'transom' is not meant to be wetted at planing speed and should not affect the props.
The primary benefit of in effect 'moving' the transom further forward is that the centre of pressure and centre of gravity are better balanced for higher speeds; i.e. the centre of pressure of the running wetted surface is relatively closer to the CG and this reduces wetted surface area and hence frictional drag. It will also increase the speed at which dynamic instability occurs, hence making the boat more dynamically stable.
In the past a clever guy (E. Clement) designed a re-entrant 'Vee' hull which had the same characteristic. The idea was to try and benefit from a 'Vee' cut in the planing surface and the more efficient shape of the planing area. He also used a large adjustable stern stabiliser as an additional planing surface.

I quite like the idea that it gives you longer boat and so the builder can charge more too :-)