Is this an innovative concept?

[FAST FRED]

"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

[kengrome]

Your first boat will have to drag a huge "hole" behind that open triangle, box thingie.

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.

It would never get up on plane with reasonable amounts of power per pound ...

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:

The last hull has as much drag as the second ...

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.

Consider just the need for additional surface to plane on.

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.

With the exception of a couple of Atkins very small box keel boats (I have one of John's last box keel designs), they never really got over 2.5 S/L. They only did so with higher power to weight ratios than are practical in larger craft (my boat is 40'), but this is fairly easy in a boat two guys can lift into a pickup.

Again, your box keel does nothing except disrupt water flow to the prop. The box keel offers shoal draft and efficiency without resorting to great beam. The engine can live very low in the hull, the shaft angle is much straighter, freeboard can be kept low and the bulk of the craft's displacement is carried in the box.

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!

[kengrome]

Since that keel is wedge shaped it is going to act like a displacement hull and will only pierce the water and will not want to plane. It is only going to displace the water. It's shape does not promote lifting the hull up on the water.

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.

A boat on the plane does so on the aft third or less of the hull, usually around a meter. If that boat for some reason does get on the plane on that keel I suspect it is going to be very difficult to keep it steady. The slightest sidewave is going to grip either side and throw the boat.

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.

Also, again IF you get it on the plane, a planing boat rides up and down to find balance. The first time that nose moves down, nothing is going to keep it up because there is no support surface, and it is going to make a spectacular nose dive.

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.

[kengrome]

My sailing club had a four metre Avon Searider RIB as a rescue boat. The aperture through which the water entered and left was a circular hole of about four inches diameter in the transom ...

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 would suggest using a similar concept as the flow patterns with the proposal would almost certainly create a huge amount of drag.

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

[kengrome]

I drove a 12 passenger Burtram that had flooding holes in the transom similar to what "wet feet" discribed. It worked pretty well and planed after a slight delay. To me this makes more sense than having any holes forward. Less wetted area, and much less drag.

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.