planing hull with a keel?

good day!
i am trying to understand if a hull that has been given to us is a planing hull or not. it has a keel, but what worries me is that the the hull towards aft rises and flattens out, to accommodate the shafts and props. a flat aft is good for planing obviously, but what about the fact that it rises?from the front it looks the business: sharp entry, hard chines.
any thoughts?

 

post some detailed pictures of what you got !!!

Easy to post pictures so we can see what you are talking about !!
boats with Keels will plane just the dont like turning to much and like to go in a straight line

 

Yep, boats with keels, skegs and other appendages can plane off fun, though as with everything there's a trade off, often as Tunnels mentioned, directional stability.

 

Lets have a look at it.

MM

 

Hello all!
Thanks for the replies!we decided to go along with another hull (still keeled as the customer requires it) but at least i am sure this is planing, and i will be sending you pics shortly!
Can anyone tell me how to calculate resistance? i guess Savitsky is ok but i think this requires a modified version. I have found an online calculator http://illustrations.marin.ntnu.no/hydrodynamics/resistance/planing/index.html

but this does not take into consideration the resistance of the keel.

Any suggestions please???

 

Some drawings or sketches would be really useful

 

A planing hull with a keel would make a nice ferry. Slowly point it to its destination, then open the throttle and have a beer.
No crosswinds allowed of course.

George K, does your customer understand that a planing hull with a keel behaves like a train?

 

The exact value of added resistance due to a keel will depend on the speed, keel shape and the amount of marine growth on it's surface.
As a rough guide, with a drag coefficient Cd=0.006 (corresponding to a airfoil-like keel in mid-summer, with some marine growth on it), you might require roughly up to additional 60 HP of engine power (30 HP effective power) for each square meter of keel lateral area, at 30 kts speed.
Since the power required to overcome friction is speed^3 dependent, it means that - assuming the above friction coefficient - you can calculate the additional power (due to the presence of the keel) via the following formula:
EHP,add = Vkts^3 / 900
That power, re-calculated for each given speed, has to be added to the results of that on-line Savitsky calculator you've mentioned.
Cheers

 

DE boats have keels some are relatively fast most fall into fast semisplacement catagory. I think poster is really in that catagory without drawings or pictures we may never know.

 

Several people have suggested a sketch or drawing be submitted to make it easier to understand what is being discussed. I have been designing sail and power boats for about 40 years and one skill I have never mastered is reading minds. Keels come in different shapes and sizes, as do boat hulls.
One thing I will offer is large keels on a fast boat can often affect the handling. In 2 instances, removing a keel (large skeg) turned the boat from a totally unmanageable beast (ie: dangerous) into a manageable one.
Wishing you all a Merry Christmas

(ps: if I have missed a sketch- my apologies)

 

I have a strange boat here. No good picture of the underside. But it has lifting strakes and sharp chines that angle down. Is it a proper planing hull?

But it has a 110mm x 70mm rectangular cross section keel underneath.

Pictures here:
https://www.dropbox.com/sh/ifki7w8gzvz7dmq/AAB3c82Nt9JyMOj9fXpE67CLa?dl=0

What to think about its performance?

 

Looks like a planing hull, you should be telling us about the performance ! You may need to do some work with that exposed fibreglass, no good to have that exposed to water.

 

Ill try to make a test run next month. Sanded, cleaned, filled and painted the whole hull from outside and inside. That old boat had so many layers of bad paint on it. Heavy work. But fiberglass showed no cracks and strong.

 

Help to get performance info

Hello; i have an amphibious vehicle hull in thevworks (posted on search engine (Richard Gray) hope to get help on hull design > contact rickgray@telus.net if you can consult me thanks Rick