Keel planing

Hi everybody

On some Norwegian forums, searching for some speed vs. power results, of traditional Scandinavian boat design ( double-ender, spitzgatter..) I find term " planning on keel ", describing behavior of (typical) semi-displacement hull with keel, when power is increased .
I am familiar with tendency of such boats to " dig " stern , but, is "keel planning "something different ?

thank you in advance

 

Your Google search would be upset by the wrong spelling of "Planing", ( not Planning)

"Planing is the mode of operation for a waterborne craft in which its weight is predominantly supported by hydrodynamic lift, rather than hydrostatic lift"

This is the closest thing I could find on the internet, and even they spelled it incorrectly



https://www.researchgate.net/figure/Inverted-keel-planning-boat-design-front-view_fig1_313800627

 

dear Rwatson

yes, it is misspell, but, i search for the term even with proper spelling.
with your help, I find some (already known) facts about semi-displacement boats with keel, during planning. Like hard maneuvering ( due to a long keel) , and, especially problematic, stern digging. As a "countermeasure" in mid9 80's thy add a little tongue on the edge of the stern ( where bottom going upward) . Later on instead of just flat bottom from midships to stern, they start adding some "volume foot" , a mimic of V bottom . In last 20 years, an entire platforms are added (i.e Menorquin) . So I belive that only issue with rounded stern "traditional " form in the world of planing boats is lack of volume on stern.
But know, I found this new term " keel planing " .

 

Well Zoran, there are a few misunderstandings involved. First, if your focus is on a hull that is mainly supported by dynamic forces, then please use the correct term, namely: planing (NOT planning; you may be planning to build a planing hull, but that's something else!).

Then, what it is all about when it comes to "keel planing", is that a hull with a keel (like traditional hulls, both double-enders and transom type) tends to rise to a point where it loses transverse stability, then leans to one side and keeps planing on one bilge surface plus one side of the keel. In this mode it resembles a "soft-chined inverted vee" hull.

For a double ender with round buttocks aft to reach planing speeds it is necessary to create a straight buttock aft with a sharp cut-off. This is done by adding a horizontal panel to the extreme aft of the hull. This is a means to achieve planing speed, but it should not be confused by the consequence of planing with a keel.

 

Hi baeckmo
Thank you for nice and detailed explanation.
I am relatively familiar with this phenomenon, only name for it is different. And, being in region where semi-displacement boats are rare , our local experiences are related either on fast planing boats, or slow-mowers . Anyway, particular type of boat is mid-80's Windy 26SN . In fact, this boat is not pure round -bilge, but it is modified to reach speed above typical displacement speed . Namely, following "tricks" are applied : aft section of the bottom is flat; end-tip of the haul is not to sharp ( canoe ) but nice rounded ; chins are not rounded, but have distinct edge ; in the aft section of the bottom, some side bilge-keels ( diffusor, longitudinal stabilizer, fin...) are added; on the stern, a small panel (spoiler) is added .
According old ( factory new) and some newer ( rebuild, repowered) tests, boat is fine with 65-75HP engine for 13kn top speed, and 8-10kn cruising. On user declare 19kn with 120HP , but also, tendency to surf on keel .
I am planning ( now , this is a plan ) to repower baot, with roughly 140HP . Speed will increase, for sure, but I want to have smoth and controlled ride .
My doubt is following :

• can overall behavior on speeds over 13kn be improved by adding trim- tabs or interceptors ( assuming next step)
• will some modification of the currently modest "tongue" shaped stern platform, too full-width one, improve handling ( in Scandinavia, such platforms can be purchased as per-type aftermarket part)
• or , I need to consider more significant/radical modification, typical for European "traditional" boats, after 1990? Meaning, more volume on stern , with bottom slightly V-shaped and integrated extension /swim platform ( as seen on Sciallino, Mimi, Menorquin boats)

Aware the fact that picture speak more than thousand words , I try to attach some picture, but it seems too complex (so far) .
So, here is the link to one, that shows bottom of the boat: https://photos.inautia.com/barcosOc...-solcio-34988010171056556750565751654566x.jpg

 

Zoran, boats like this one have been built by QUORNING BOATS, Skaerbaek, Denmark before they switched over to MULTIHULLS. As far as I remember they were able to do something like planing. But if you want safe infos, try to speak (e-mail) Jens Quorning: http://www.dragonfly.dk/http://www.dragonfly.dk/
But please don´t forget, planing boats have to have a special structure and should be light and...

 

Another approach: A planing keel design by Phil Bolger (NA).

 

Bolger Box Keel, found in "BOATS with an OPEN MIND", Philip C. Bolger, International Marine, Camden, Maine, 1994, pp 287. Great Book with more samples of Box Keels, good house for the motor and the legs in the cabin.

 

An interesting solution of Athol Burns (Who is Athol Burns? https://www.boatdesign.net/threads/who-is-athol-burns.38688/ ), slightly hollow stern to give hydrodynamic lift at minimum drag when the boat is moving (Bern0ulli). This can reduce squatting and might allow something like semiplaning (Halbgleiter) if there is sufficient power.
Google:
"A semi-displacement hull is a hull design that combines features of the displacement and planing hull. It displaces water at low speeds but is able to generate lift at cruising speed. It is more stable than planing hulls, and faster than displacement hulls. It planes at lower speeds than regular planing hulls."

 

Please moderator a little help with the title when you have time.

I have to admit total confusion.

First a keelless boat and then a picture of a large keeled boat.

Which is it? Or did I skip reading something important?

 

Yeah, like you missed the whole conversation. It has covered the full gamut of hydrodynamics for non Planing boat hulls, ending with a comment on an unusual stern design.

 

This discussion could be helpful: Definition of Planing https://www.boatdesign.net/threads/definition-of-planing.45248/

 

Maybe we should start a revolution spelling it……

plane-ing!

who’s with me?????

 

Um. The misspelling has been mentioned a dozen times. If THAT doesn't work, the "revolution" is a non starter.

 

Hi Zoran - I have the same boat. Please reach out as I'd like to discuss my refit with you.