[hordos]

I would like to know if you can make a plaining hull work like a displacement or semidisplacement by lengthening or adjusting weight to keep the boat level as it pickes up speed.

[AMG]

Hi,

A stepped hull is normally keeping it´s level at high speed if this is what you were asking.

[FISHTIGUA]

I think what Hordos was asking is can you make a semi-displacement hull from a planeing one.

Yes you can but you loose all advantages of both types and gain non of the benefits.

Fish

[Ju52]

Are you looking for a displacement glider ...

like this http://www.alsphere.at ??

A nice wekend to all
Gerhard

[CODOG]

If I understand your question correctly, then yes you can. But as already stated above, you will begin to lose the benefit of a planing hull design, and also not have the full benefits of displacement / semi-displacement hull design. Your requirements as to size and maximum speed would be a major consideration in this question too.
It is possible to design a planing hull that does not sink by the stern / rise at the bow as it gains speed, climbs the hump and comes up onto the plane as a normal planing hull would, either by adding considerable length or moving the LCG a long way further forward...but this design would therefore not be able to plane in the accepted sense. It would begin to plane due to its basic design, but the amount of hull surface still in the water would have high drag, its flat running angle and weight biased fwd would tend to force the bow to push the bow wave out of its way (rather than riding up and over the top of it) and the net result would be a higher power required to drive it at a relatively slower speed, and rather inefficient fuel consumption. This is by now a 'planing' design so compromised that the designer would have probably changed tack toward some form of semi-displacement design some time before.
There are artificial means that can be employed to 'flatten out' a planing hulls natural running angle (trim tabs / wedges / transom plates etc), but anything that will effectively lift the stern / push the bow down is normally used just for slower speeds, before or just on the hump (this is what I'm guessing you are getting at) Also, at higher speeds, too flat a running trim on a planing hull may result in bow steer, chine running and straight line tracking problems.
There are a million permutations ranging between full-on displacement right up to fast craft that run high speeds with only the tips of the props and the tip of the keel and chine in the water...but they all compromise one or more qualities for the reward of excelling at others. Planing hulls will rise up at the bow in their attempt to climb the bow wave in order to ride atop the water rather than through it...its what they do...if you deliberately design one that doesn't, it will suffer in other areas of performance / economy / handling too.
This brings us back to the size you have in mind and the speeds you want from the hull ? The design requirement you hinted at in your initial post suggests a decent speed but with minimal change between static and running trim angles ? So far its leaning toward a chine-bilged, semi-displacement hull with waterjets.

[KCook]

Methinks the best practical example would be tournament ski boats (Nautique, Mastercraft, etc). They do plane, with VERY little bow angle. But as already stated, this results in greater wetted surface, greater drag, less speed, and more fuel needed. Can be done however.

The other example would be high performance catamarans, which is not likely what the OP had in mind.

Kelly Cook

[Seafarer]

Originally Posted by FISHTIGUA

I think what Hordos was asking is can you make a semi-displacement hull from a planeing one.

Yes you can but you loose all advantages of both types and gain non of the benefits.

Fish

^^ This.

Huckins (ok, ok, I already hear the groans) builds planing hulls that are designed to run from a standstill to top speed with no more than 3 degrees of bow rise. They are also fairly fast and fuel efficient boats.

[penta]

So maybe will be better to share my idea in this theme. I hope.
http://den-k-den.livejournal.com/10318.html

Something like:
<10 knots - displacement
10~20 wavepiercer
>20 - cat



P.S.: sorry for my Eng. - it's very difficult for me to use it.

[Capt J]

Stretching a hull will increase the displacement speed. I run a 75' hatteras that was stretched 10' from a 65'. It picked up almost 2 knots at displacement speed and will do 10 knots at displacement speed up from 8-8.5knots. Cruising speed has slowed down a little. Weight and balance can slow down or speed up displacement speed.

[84far]

hi there

check out the 'Mochi Long Range 23'. it does what your after i think. interesting hull design. and im starting to see a few boats come out with a similar shape/idea.

a Hobie Cat is a good example of a twin hull form.

but everything is a compromise. what u gain in one thing, you'll loose in another. fine out what u need the most in the design and head down that path. maybe a hydrofoiled boat?....

far.