Is this an innovative concept?

"The hook Atkins used was to keep the bow down when the hull was pushed past 1.4 S/L ratio."

Not so sure,about the "hook",

The reports I read of a boat that was plans built ,
and then swopped to a much larger engine was the boat BOW STEERED .

Atkin simply added a set of chines forward to lift the bow as much as the stern at the much higher speeds.

A true plain hull is probably best over SL-3 but below that the ability to motor fast WITH efficiency is of interest.

Would be interesting to see what Atkin would do today with very light weight engines and hull materials cheap enough for the home builder.

FF

 

That open triangle box thingie is in the shape of a Seaknife high speed planing hull. This hull shape was designed and pioneered by Peter Payne decades ago. Seaknife hulls are know to perform very well.

The only difference in my design is that there is no back panel on the keel to close it off. I left it open to allow water to flow through the keel so it does not block water flow to the prop at low speed. When the boat is planing it shouldn't make any difference that it is open because water will peel away from the transom bottom there rather than flood the box keel.

I'm curious why you believe this. Is it because the aft end of the box keel is open?

I don't know how much power Seaknife hulls require to get up on plane. Maybe they require "unreasonable" amounts of power, but there is no question that these hulls plane exceptionally well at high speeds:

That hull is something I designed a couple years ago for a very different boat and a very different purpose. I only posted the picture to illustrate the concept Loafer mentioned. Once again, the design I am considering to refine, build and test is the first one -- the one with the free flooding box keel in the shape of a wedge.

The original hull (without the box keel) has way more planing surface than necessary. If my only goal were to design a planing boat I would leave the box keel off completely. But without the box keel the original hull will pound like crazy when trying to go fast in anything but smooth flat water.

I added the box keel -- in the shape of a Seaknife hull -- specifically to allow the boat to plane on a much smaller surface, just like a Seaknife hull planes on its narrow triangular bottom. Planing on a smaller surface smooths the ride and prevents (or substantially reduces) violent pounding.

Creating a boat that planes smoothly in less than ideal conditions is one of my primary design goals here. The hull without the box keel will plane but it won't plane smoothly unless the water is very smooth and flat. I want this boat to ride nice when the water is neither smooth nor flat.

I know about Seabright style boats and their semi-planing advantages. I even built one in the Philippines a couple years ago. They do not go fast and I want this boat to go fast. Without the box keel it might go fast but not comfortably. With the box keel it should go fast and ride well.

I acknowledge the fact that there may be better ways to deal with the low speed flow of water to the prop. There may also be ways to reduce surface drag from the free flooding box keel while retaining its desirable characteristics. This is why I posted here ... so others can see the concept and make suggestions to improve the design before I build it.

Thanks for your comments PAR, they are very much appreciated!

 

Good point Fanie, thanks for the constructive comment!

I have considered changing the shape of the free flooding box keel so that its bottom is angled up from back to front (similar to the angle of the bottom of the box keel in the second image). This will provide a lifting surface to help the boat get on plane more easily. One side effect (and a possible advantage) is that it positions the box keel in its natural planing attitude which would reduce the upward pitch of the boat as it transitions from displacement to planing mode.

If I had not studied the hydrodynamics of Seaknife hulls I might agree with you. But Seaknife hulls -- which are precisely what my wedge shaped free flooding box keel is -- are very stable at speed. The reason is because the sheets of water thrown up along the sides of the hull have a laterally stabilizing effect.

Please look at the attached Seaknife images (not just the thumbnails but the full sized images) because some of them have captions that refer to this stabilizing effect. There is lots more written about this effect online, some of it in the patent applications by Peter Payne, but I don't have the references handy. If you're interested Google can probably find more for you rather quickly.

I disagree ... but all I can do to argue this point is to direct you to the literature regarding Seaknife hulls which have apparently been performing predictably at high speeds ever since they were first created.

Seaknife hulls may be uncommon and little known but they are not experimental. They work (and they work well) according to the literature. I'm just applying this success to my own small boat design ... or trying to anyways.

 

I understand how your RIB works but my concept seems to be significantly different. Since my prop moves up and down it will be directly inline with the box keel in the "up" position. In this position the prop can draw water from within the keel rather than only from around the sides and below the keel.

I think that when the prop is aligned with the middle of the box keel less drag will result from an open ended box keel than from a closed one.

I have an idea that may improve efficiency at low speed. I will post a rendering after I finish it. If it meets with favorable opinions here then it may resolve the low speed friction and drag issues

 

My theory is that holes forward in the keel (or further aft in the keel) allow water to reach the prop from within the keel. My other theory is that water going through the prop will get there via the most efficient manner.

If these theories are correct then it seems to "makes sense" to retain the holes ... just in case the easiest way for water to get to the prop happens to be through the keel.

Personally I think that some of the water through the prop will get there from within the keel, and the rest will get there from outside the keel -- but in either case it will get there via the path of least resistance.

Am I wrong about this? If so please explain, thanks.