Stepped Hulls

NIC SURRY · 07-11-2009, 09:53 PM

I've read on many occasions that having a stepped hull is supposed to help prevent a boat from stuffing and Id like to know why the steps help this as surely the boat is normally air bourne prior to stuffing or is it that it helps it fly flatter ?

Jon Holmes · 07-11-2009, 11:46 PM

I have read that stepped hulls dont fly straight???

FLYING FISH · 08-11-2009, 09:12 AM

If a basic mono with no steps were built and then the same hull with it`s wt and power etc characteristics with steps introduced and used as a comparsion,then you may get your answer,but that just doesn`t happen in boat design.More often than not umpteen variables are changed at once,so you can never be sure which refinement has done it`s job.
You would think a stepped hull by virtue of it`s shape would move the buoyancy forward slightly to give more bow lift,but books will tell you a stepped hull will resist pitching and can be unconrollable due to the steps not ventilating in rough seas,so where does that leave you.
The buzzi and shead boats had rocker to keep the bow up,whereas the cigarettes and phantoms don`t,but that didn`t seem to hinder their performance.
I suspect that although steps have been around a long time especially for record breakers,when they came into offshore,it was quite often a case of incorporating the fashion,for I can`t say I have come across a case of somebody saying those steps have increased my speed by `x` knots,even though they must have have an advantage over non stepped hulls.
Another problem can be the rise of floor in the aft sections of the boat,for if your not careful,it will keep the bow down more than you bargained for,so it`s not a case of we`ll stick a step in and we`ll whip the arse of the opposition,you would need to be aware of of the other factors in hull shape that has been created in breaking up that nice clean bottom shape.

Jon Fuller · 08-11-2009, 10:21 AM

Quote:

Originally Posted by NIC SURRY

I've read on many occasions that having a stepped hull is supposed to help prevent a boat from stuffing

Never heard that.

increased pitch stabilty (with certain step configurations, not all), and speed gain, yes, but never anything about resistance to stuffing, ...don't really see how it could...except maybe the increased pitch stability lessens the likelyhood of a classic nose up,'trip & stuff'.

Jimboat · 08-11-2009, 12:55 PM

more on step design at this thread.

Cookee · 09-11-2009, 12:24 PM

I have to agree with JF that steps won't prevent stuffing, I can also confirm that steps do not prevent a boat from flying level - I have been racing one for 9 years as well as leisure version of the same hull and spent quite some time in the air without too many problems!

Jon Holmes · 09-11-2009, 12:35 PM

Quote:

Originally Posted by Cookee

I can also confirm that steps do not prevent a boat from flying level

I agree, steps do not prevent a boat from flying level.

However, poorly positioned and vented steps on large hulls can affect handling in windy conditions.

NIC SURRY · 09-11-2009, 12:49 PM

Never heard that;Quote
I'll try and locate the articles,its probably a journo who doesn't know what he's on about-current forum journo's exclued(Cooke)
Nic

Jon Fuller · 09-11-2009, 02:02 PM

Quote:

Originally Posted by Jon Holmes

I agree, steps do not prevent a boat from flying level.

However, poorly positioned and vented steps on large hulls can affect handling in windy conditions.

There's a shed load more to steps that just their position. I think the depth of each step, and more importantly the relative angle of attack of each running surface portion is where it sll happens, or doesn't.

More Witchcraft.

Jon Holmes · 09-11-2009, 02:38 PM

I agree Jon.

Cookee · 10-11-2009, 08:15 AM

Quote:

Originally Posted by Jon Holmes

I agree, steps do not prevent a boat from flying level.

However, poorly positioned and vented steps on large hulls can affect handling in windy conditions.

So what you're saying is that a badly designed boat can handle badly!

I think stepped boats come in for a lot of unnecessary stick - whilst stepped hulls do need to be driven with a slightly different style, especially in corners, they seem to have acquired all sorts of complete wives tale type myths that are totally untrue!

Jon Fuller · 10-11-2009, 09:18 AM

Quote:

Originally Posted by Cookee

S
I think stepped boats come in for a lot of unnecessary stick - whilst stepped hulls do need to be driven with a slightly different style, especially in corners, they seem to have acquired all sorts of complete wives tale type myths that are totally untrue!

Maybe, but some boats seen in the famous 'ejection' videos do seem to have bitten the arse of the drivers with little provocation.

I feel sure they can be just as much of a disadvantage as they can an advantage if they aint right.

Adam · 10-11-2009, 09:36 AM

Quote:

Originally Posted by Jon Fuller

Maybe, but some boats seen in the famous 'ejection' videos do seem to have bitten the arse of the drivers with little provocation.

I feel sure they can be just as much of a disadvantage as they can an advantage if they aint right.

Agreed and as per Cookees comment - a badly designed boat can handle badly. Also true for non-stepped boats - although certainly steps do introduce more critical areas to a design.

For me the greatest problems with stepped hulls and their repuation have arisen from boats that have been conceived or based on race boats then being used as leisure boats and as such used in a different way.

There are ways around this and this needs to be reflected in the step design as part of the overall design.

All interesting work.

Jon Holmes · 10-11-2009, 09:39 AM

"If it aint broke, dont fix it" - steps, tubes etc

Bus Pass · 10-11-2009, 02:01 PM

Quote:

Originally Posted by FLYING FISH

If a basic mono with no steps were built and then the same hull with it`s wt and power etc characteristics with steps introduced and used as a comparsion,then you may get your answer,but that just doesn`t happen in boat design.More often than not umpteen variables are changed at once,so you can never be sure which refinement has done it`s job.

Our XRS43 now has steps incoporated into it, so we do have a straight comparison. Dual Volvo D6 370hp, non stepped 46 knots, stepped 49.5 knots. However it has reduced the ability to change the trim.

The secret as Jon says is where do you put them, how deep, shape, angle etc.

Jon Holmes · 10-11-2009, 02:19 PM

Ok,

So if we were to agree that there are no comparison boats available then we must assume that the builder of a non stepped hull never thought that adding steps would improve his original design to any distinct advantage or else he would have incorporated this into his original design.

As Bus Pass has shown, by adding steps to an original non stepped design he has improved top speed. However, there is a penalty for this increase in speed.

All i know is that more stepped hull design race boats have been involved in more accidents during races than non stepped designs and more leisure occupants have been ejected from Ribs than hardboats. Further, not all speed records are held by stepped hull designs.

So whilst i am not against stepped hull designs (Though i am against Rib's), i just dont see a significant advantage over the traditional deep vee design yet.

No axe to grind, just horses for courses.

Jon Fuller · 10-11-2009, 03:13 PM

Well, If I were attempting to add steps to the 32 (which I'd very much like to do) the possible speed gain wouldn't be my main reason for adding them, though any increase would of course be most welcome.
For me, the bit Jeff says, and John (holmes) sees as a negative, is what I would be striving to achieve, ..pitch stability, using level trim. mannerfelt is I believe the master of this, and as such, I would be looking to emulate his step design, which is generally different to those found in most other designs, both from europe, and over the pond. There's no other boat on the planet that runs in the chop the way the V-24 does, it's pitch stabilty, at maximum speed is beyond belief/comprehension. their average race speed is regularly right up near their top speed, even in quite a sloppy seaway.

natural pitch stability is the doorway to high average race speeds.

JMHO

Quote:

Originally Posted by Jon Holmes

Ok,

So if we were to agree that there are no comparison boats available then we must assume that the builder of a non stepped hull never thought that adding steps would improve his original design to any distinct advantage or else he would have incorporated this into his original design.

As Bus Pass has shown, by adding steps to an original non stepped design he has improved top speed. However, there is a penalty for this increase in speed.

All i know is that more stepped hull design race boats have been involved in more accidents during races than non stepped designs and more leisure occupants have been ejected from Ribs than hardboats. Further, not all speed records are held by stepped hull designs.

So whilst i am not against stepped hull designs (Though i am against Rib's), i just dont see a significant advantage over the traditional deep vee design yet.

No axe to grind, just horses for courses.

TobyC · 10-11-2009, 03:18 PM

before we know it Swipes will have wings

Jon Fuller · 10-11-2009, 03:32 PM

eeeeerrrrrrrrrrrrr, no.

Bus Pass · 10-11-2009, 05:30 PM

Adding steps to our 43 has not given any real downsides, the restriction on trimming is only slightly less than without steps. The boat certainly flys flatter.
More speed also means more miles per gallon! We are in the process of stepping the 37 hull for next years model.

Jon will probably remember the 47 foot Patrol Boats we launched at Gill's old place back in 2001. Without steps we could not have met the performance spec and they ran very well in the rough.