Lifting strakes / strips ?

Which part of a planing boat hull this term widely used term referring to ?

I thought it was the submerged section s of strikes that may have started at the bow above the water as spray rails , and they moved aft behind the disruption zone , submerged perhaps changed shape .

Maybe taken to various lengths , some occasionally on faster narrower hulls to the transom? Tend to be horizontal to the planing surface ?


I am I correct ?

Thx for the reply .
Does the submerged part commonly referred to as a lifting strip / stake / rail in certain circumstances contribute to stern lift ? When it’s fully submerged .

Blue is submerged taken to the stern , but sometimes falls short .

red the disruption area(s) where the majority of hull lift takes place

Yellow the strake commonly known as the spray rail .Spends it time above the water when the boats running deflecting spray , reducing drag and somewhat also adding a little measured lift .




I know theses submerged strakes in “certain circumstances “ primarily are there to add stability, and reduce drag , but can if correctly shaped and dimensioned add lift at the stern?

On a deep V like this 23 degree, the middle set run to the transom and are quite pronounced.It cruises comfortably @ 1800 rpm with MAN s at 30 knots
There’s a lot of flat surface part way down the hull from the chine .
Do they contribute to additional lift , net lift at speed .
It’s got a bottom lifting pad as you can see as well .




Apologies for the pic rotation guys .

No Iam trying to understand exactly what theses strakes do .Particularly if those wider more pronounced ones running to the transom create any lift .
I think I have excessive lift .

The reason I ask is say up on the plane running at 26/27 knots .The boat responds to rudder like any other .
The boat runs very flat requiring zero tab .If a push the sticks Fwds more ( max speed is 38 knots ) the hull rises higher up , you can feel it lift higher and it low running angle say 4 degrees ( guess ) gets lower with out tabs .Tabs on Zero .
In fact the stern rises so much, along with the rest of the hull so it makes those rudders pretty ineffective.
For quick emergency type turns I have to pull the sticks back to effectively dip the rudders so they bite .
At 35 knots full rudder just adds drag the boat still tracks true or if anything deviates by a tiny degree hardly worth mentioning.

So where is the additional lift coming from ?

Yes I have been reading Reggie Fountains stuff .He used theses strakes underwater to the transom .Far faster boats so not as wide due to the speed advantage .But nether the less more lift means less drag of the hull in the water = more speed = win races .All the others like Donzi etc and most Ray hunt designs run the strake to the transom of very close .They call them lifting strikes , strips .
So as the name implies …….do they create lift ?


Also above a certain boat weight and size the lifting effect I understand is limited .Something to do with froude numbers
I quote this from a naval architecture forum .

“Another reason you don’t always see lifting strakes running all the way back .Or very pronounced.

. Boats with a volumetric Froude number less than 4.0 don't need lifting strakes... for example, a 55-foot boat weighing 60,000 pounds should only need strakes if it will go faster than 42 knots. Location and shape, again, is about finding the balance of the design.” [ end quote ]

Tend to see them running back to the transom / more pronounced, wider on deeper V more performance orientated hulls .

I realise something like this stuck on the stern underwater section about 2 ft down at the transom on say a San Lorenzo 95 chugging along at 18 knots isn’t gonna create anything .

Thanks for the reply s much appreciated as are others btw .

Yes that’s pretty much what I figured out .Not just the nomenclature “lifting “ .The boat runs very set btw .Nothing , waves , wake seems to take it off track once it up and running .Easy to drive as you hardly need to alter the steering once it’s set .

What is the physics out of interest of this additional lift ?

1- Extra Newtonian lift from the flat surface at speeds ?

2- As the water is deflected over the sharp edge of the strake , accelerated faster by the 30-35 knots and the deep V ( 23 degree deadrise ) the separation as well as reducing drag , the eddies create a pressure zone , decrease the stern suction ? So in effect add back lift .But only in certain circumstances, deep deadrise high ish speeds and not Uber heavy.

3- air at the disruption zone because they are deliberately pronounced, the air is drawn back some how lift is created as it trips over the sharp edge under water ?

I can’t quite find exactly how they create lift , wide ones extended far back .

But it’s widely reported they can add lift in certain circumstances .
As well as stability etc .

That movable hull vane is a great concept Hope it works .

Reminds me of dynamic suspension on cars , the shock rates adjusted every millionth of a sec ( or what ever ? ) to keep the max contact area of rubber on the road .