SD vs Planing vs Displacement

[Gludy]

No - you need the extra long keel option plus a set of legs.

All I can go on is my own experience of planing boats. I really do not think that the skill of the helsman is a factor. Sure, you certainly cannot do it with a carp helsman but, even with a good helsman, it sit eh limitations of the boat I am talking about.

What do others experience say going at 25 knots in calmish seas with their planing boats? Can thir family members wander around the boat with ease?

 

[Mike21]

Since we,ve managed to make hot tea and coffee( without spilling them /forums/images/graemlins/grin.gif) and Julie's managed to cook bacon butties for 10 on a P52 at 25knot in a F5, planing hulls can't be that bad, and in flat calm seas, you should have no problems /forums/images/graemlins/smile.gif

Unless off course as Whisper says it's down to having a good helmsman /forums/images/graemlins/grin.gif




Or helmswoman /forums/images/graemlins/smirk.gif

 

[BarryH]

"I really do not think that the skill of the helsman is a factor.".....I was gonna answer, but I'll bow to your superior knowledge.....umm yes I'm being sarky!
Its one of the main factors in any boat you plum. I could take Dame Ellens boat out and wreck it in five mins because I woulodn't have a clue. Yet it capable of buzzing round the world in a couple of weeks in her hands!!!

 

[Gludy]

Barry
What I was saying, if you read the post, is that I am not talking about the skill of the helmsman but the limitations of the boat assuming a good helmsman.

If you could just try opening your mind here instead of always trying to be sarky and score, we may be able to have a reasonable discussion about the subject and leave everyone's ego out of it.... actually have a valuable discussion.

So either grow up or stop responding to my posts.

 

[Gludy]

I think Julie deserves a medal for managing to make bacon butties in a P52m in a f5 at 25knots!!

It is as if we are talking chalk and cheese here .... I am sure you are sincere but my experience to date would rate that bacon butty making as deserving of the ultimate praise

 

[BarryH]

I'm sorry but I can't agree with you. Statemnets like "the helmsman isn't a factor" is utter rubbish. If anything the ability of the helmsman is more important than the hull.
Conversely you seem an intelligent person so take off the blinkers and look at the bigger picture!

You've purchased a boat with stabilizers. IMHO they're akin to ABS on a car. A system to compensate for driver error. A pro driver in a car not equiped with abs will be far more capable than a novice driver in an ABS equiped car. IE the pro driver knows his and the cars limit.....not a good analogy, but an easy parralell!

The same is applicable to boats to a certain extent. Tho your comments on being "comfortable" and being able to cook drink or whatever while underway, makes me wonder wether you pursuing the right hobby!

The sea moves due to weather, tides, topography of the sea bed etc. Its rarely going to be totally flat so get over it or live with it. If your unhappy with the way your boat feels while crossing it says volumes. Either the weather is a bit blowy and the sea is moving a fair bit or your trying to move to fast across it for the conditions......which can only be down to you the helmsman!!
Even if you've got stabilizers on your new boat, if you can't use the thing properly in the first place, they ain't really gonna be much use to you.

Have you ever thought that you've moved or entered into boating at the wrong end of the size scale? In smaller boats you have immense respect for thye sea. I'm wondering if by "going large" straight away you've missed out on a big part of the learning curve.

As for the various merits of the hull forms. Each has its pro's and con's. They've been developed over a period of time to get where they are now by experts in their field. Yet you feel that after your boating experience your qualified to pass comment on whats good and whats not. Sorry but again I think you need to wake up and smell the rose's. Whats makes you think that its long enough for you to gain the experience?

Ok so you've asked the questions and got answers. Yet, I'm sorry, but you don't seem to be digesting the info your getting. From comments you've posted your taking the info that suits your situation and ONLY applying that so it fits your decisions and ignoring info that doesn't. Do you now feel that the desision you've made is a wrong one?

Maybe the thread should be re titled "Gludy, This hobby isn't like the piccy's in the brochure"

I didn't really want to reply with a "bitchy" post or score "hits" as you put it. But your reply really got my heckles up. I'm no expert in boating terms but I have a bit more experience than yourself being raised around boats. Yet I don't consider myself the font of all knowledge when it comes to boating, but I am willing to learn and learn from my experiences and from others. I could go on but frankly I don't think you'll take in whats being said! Gludy, you've gone down in my esteem.

Sorry if anyone finds what I've said offensive or it seems I'm on my high horse but some comments made need to be addressed

 

[steverow]

Re: Horses for Courses.

I dont think that many people are actually going to agree on this.
Each type of vessel evolved differently, and evolved for a particular purpose, so therefore they are suited to a particular application better than others.

The Displacement hull is esssentially the same hull as a fishing trawler, which is itself a development of the round bilge form which has been around for centuries.
A highly stable form when driving forward, as it "beds" into the sea for stability as it displaces, but rolls like a pig when beam on, paticularly when anchored, thus the requirement for lateral stabilisation on large leisure vessels, such as the Nordhavn.

Semi displacement vessels are a development of the above, by narrowing the hull, flattening it out aft,adding a half keel and chine, and much bigger engines, you have the Nelson, and all it's variants, with a reasonable turn of speed by virtue of the larger engines.
Very stable in most seas including much better lateral stability than the displacement, 'cos of the keel.
It's not a "compromise" as some people would have it, but it evolved and developed into the pilot and coastguard vessels that we know so well today.
It is uniquely suited to this purpose.
The leisure vessels of Trader, Broom and Birchwood, are simply leisure versions of this form. Most vessels in this category have less beam in the hull than their planing or displacement counterparts, making them a bit skimpy on accomodation, with the exception of Traders and the like, however this is compensated for on these vessels by having a deeper than average keel, and flattening the hull out sooner to give the stability.

The planing boats are just that, developments of 1960's racing powerboats, which are themselves evolutions of later 2nd world war torpedo and patrol boats, designed to lift out of the water and present as little of it in the water as possible, except for the aft end to maintain the drive.
Because of this they are naturally susceptible to hitting the tops of waves as they
skim over, giving the slamming motion.
However, they are hugely successful and popular, and if you enjoy the fun of "driving", making a large wake, getting there at speed and generally enjoying the fun side of life then this is the boat for you...and why not??
However, there is little stabilty in the hull at displacement speeds, in any sort of sea, because this is not really the design criteria.
The other downside is that because of the planing angle it is difficult to drive from inside with reasonable or safe visibility, making them particularly unsuitable in heavy weather when you dont, for your own health and safety want to be on the flybridge unless of course it's in the 70 ft category or has an enclosed upper helm.

Nobody is going to agree on this thread because everybody thinks that their hull form is the best, and rightly so. You should be proud of your own boat because you chose it for your own reasons, and it obviously does what you want it to or you would have flogged it by now and moved on to something else.

So unless some enterprising designer comes up with a round bilge one third displacement, keel formed planing hull that doesnt move at a 40 degree angle, that we can all agree on, then I'm afraid we're all stuck with what we've got.
Of course the more well off amongst us could always go out and purchase three boats, one for each type of use then there is no argument....and NO Paul you cant keep Drumbeat as well!!

For me , well, In a force 8 or 9, If I'm unlucky enough to ever have to deal with one, I know which hull form I'd like under me......ask the Pilots, CG or RNLI why.

Steve.

 

[Gludy]

Barry
Your point about the helmsman is nothing short of absurd - we are comparing the characteristics of boats here and therefore need to assume the characteristics assuming they are helmed well. If you cannot, in effect see the simplicity of that point then frankly it is not worth discussing anything with you.

"You've purchased a boat with stabilizers. IMHO they're akin to ABS on a car. A system to compensate for driver error. A pro driver in a car not equipped with abs will be far more capable than a novice driver in an ABS equipped car. IE the pro driver knows his and the cars limit.....not a good analogy, but an easy parallel!"

Utter nonsense again - given a boat with the same good helmsman the one with the stabilisers will be far more stable. The discussion, I repeat is not about the degree of helming but about the boat characteristics.

"The same is applicable to boats to a certain extent. Tho your comments on being "comfortable" and being able to cook drink or whatever while underway, makes me wonder wether you pursuing the right hobby!"

I have become used to your inability to stick to the point and so your relentless need to resort to personal attacks like that. I have no doubt that Julie made the bacon butty - the point is she would have had a much easier time making it at 25 knots in an f5 on a boat with stabilisers.

"The sea moves due to weather, tides, topography of the sea bed etc. Its rarely going to be totally flat so get over it or live with it. If your unhappy with the way your boat feels while crossing it says volumes. Either the weather is a bit blowy and the sea is moving a fair bit or your trying to move to fast across it for the conditions......which can only be down to you the helmsman!!"

You are simply absurd and so blinded by prejudice that you cannot see the simplicity of the point. I have every right to choose an alternative hull form to give my family a smoother ride without you arrogantly accusing me in such a way.

Are you totally incapable of seeing the most simple point? Regardless of the helmsman I would much rather cross the Atlantic in a Nordhaven that in a P52. That is not a reflection on the helming ability of the person with the P52 but with the differences in the boat design and how they behave.

"Have you ever thought that you've moved or entered into boating at the wrong end of the size scale? In smaller boats you have immense respect for thye sea. I'm wondering if by "going large" straight away you've missed out on a big part of the learning curve."

Again you have to personalise the matter, totally incapable of conducting a reasonable conversation about the subject without going right of the point to make personal and frankly silly attacks like that.

"As for the various merits of the hull forms. Each has its pro's and con's. They've been developed over a period of time to get where they are now by experts in their field."

Agreed and that is what I have already stated.

"Yet you feel that after your boating experience your qualified to pass comment on whets good and whets not. Sorry but again I think you need to wake up and smell the rose's. Whets makes you think that its long enough for you to gain the experience?"

I certainly have a right to pass comment and a right to ask questions. I also have a right to seek clarification of those questions and that is all I ever do on any thread or have done on these two threads. I am stating what I and my friends have found to be true .... you seem to think that learning is about just accepting the status quo without any questioning - I do not. I learn a lot by questions and comments and you certainly have no right whatsoever to deny that to me. Nor is it arrogant of me to do this - it is very arrogant of you to try and deny it to me and to make personal attacks on me instead of dealing with the subject.

"Ok so you've asked the questions and got answers. Yet, I'm sorry, but you don't seem to be digesting the info your getting. From comments you've posted your taking the info that suits your situation and ONLY applying that so it fits your decisions and ignoring info that doesn't. Do you now feel that the decision you've made is a wrong one?"

I am beginning to feel you are losing your marbles with that nonsense.
All I am doing is asking further questions. I have stated why I have purchased the boat I have and I am happy with the decision - I have stated there is no right or wrong to this and that it, in the end is a personal decision - I have stated that very few people can ever hope to gain the experience of all the boat types and engine/stabiliser combinations .....I have also stated that learnt from a few posts naming you and Kim as posting posts I had learned from - I am imposing my views on no one and you are not going to bully me by the use of personal attacks to change the way I peruse the subjects one little bit.

"Maybe the thread should be re titled "Gludy, This hobby isn't like the piccy's in the brochure"

You really are on a roll of personal stuff aren't you? I shall not even lower myself to answer such a stupid question. If I were you, I would calm down a bit because you are way over the top.

" didn't really want to reply with a "bitchy" post or score "hits" as you put it. But your reply really got my heckles up."

Well you have been bitchy and personal and I agree that your hackles must be up.

"I'm no expert in boating terms but I have a bit more experience than yourself being raised around boats. Yet I don't consider myself the font of all knowledge when it comes to boating, but I am willing to learn and learn from my experiences and from others. I could go on but frankly I don't think you'll take in whets being said! Gludy, you've gone down in my esteem."

You are doing what you accuse me of ... you are closing your mind, all I have done in these last two threads is seek information, pass comment and invite discussion. As it happens it was the post from you and Kim that I learnt most from and I clearly stated that - see the previous thread. In effect the only logical reason for your anger on this subject must be because you do not like being questioned ... you seem to want me to roll over and accept in blind faith. I cannot do that and never will.

"Sorry if anyone finds what I've said offensive or it seems I'm on my high horse but some comments made need to be addressed "

But you did not address any of the issues did you? You did not state a single comment that i made and then point out how it was in anyway wrong. You simply went into personal attack mode. In fact you cannot have really read my points and that is sad, very sad.

 

[ArthurWood]

What's Machholz? I'm having a lot of trouble keeping up with things in this new format and I hate the fact that replies aren't notified by email. IT call it progress, like wot when I was working.

 

[ArthurWood]

Re: Machholz

Excuse my ignorance - just looked it up. I haven't been doing astronomical things for a while. Mus t get back to it. S'pose I've missed this one by now, from what I've just read.

 

[BarryH]

Gludy, I pressed the reply button to answer your post in full, but now I find that to be honest I'm finding this rather a bore.
You carry on the way you see fit. I've got rather more important things to worry about.

 

[Gludy]

That is fine with me Barry. A sort of hit and run tactic without ever dealing with the issue gets the thread nowhere.

As I see it, the issues are:-

What is the difference between a planing hull with stabilisers and an sd hull with stabilisers? The answer would probably be speed specific. What are Ferreti claiming?

What is the easier boat to make a bacon butty and cup of tea in at 25 knots - an sd boat with stabilisers or a planing boat (without stabilisers)?

From my experience and what I have learnt from others to date, there seems little doubt to me that the planing boat has a far harder ride and is much more difficult, for most people to enjoy the ride on the way. Howeverm the planing boat gets you there faster for the same fuel consumption.

Overall the best sea keeping boat is the SD boat (versus Planing) although you may have to watch it in a following sea, especially if you do not have enough speed to keep ahead of the sea as it were.

It has been pointed out that pilot boats and for that matter lifeboats are sd boats and that surely is because they offer the overall best sea keeping?

On fuel efficiency, the sd boats wins hands down at the lower speeds and the planing boats at the higher speeds. There is a crossover speed. That is when comparing same size planing and sd boats, there will be a speed in the SD boat when fuel consumption would be the same as the planing boat - in my case this is about 18 knots. Below that I can, by choosing the right speed, reduce fuel costs by up to 3 or 4 times. This option does not really exist with the planing boat.

Their is no one boat that is going to do it all. Its up to the individual to set their own priorities but it would be nice if we could agree on the facts of the differences so that each individual could choose based on facts not myth or a range of clashing opinions.

So I ask everyone - what have I stated that is wrong in the above?

 

[Mike21]

According to Nordhaven, their hulls are full displacement, not semi.
Their desciption here about displacement and semis makes interesting reading.

I was also pointing out that your assertion that you could not move around a planing hulled boat at speed was incorrect

 

[Gludy]

Mike
I never claimed that Nordhaven were SD, just that if I were to cross the Atlantic I would choose a Nordhaven not a Fairline Squadron as the hull to go in.

I never claimed that you could not move around, I stated that you could not easily move around. The issue here is that I claim it is much easier and more comfortable to move around at 25 knots on an sd hull with stablisers in a f5 than it is with a typical planing boat of the same size. Do you agree or disagree?

 

[Gludy]

From Nordhaven Site:-
--------------------------------------------------------------
While full-displacement designs are capable of extraordinary range due to their fuel-efficient hulls, they are limited in speed by their hull length. A full-displacement hull simply cannot go faster than a function of its waterline length, regardless of how much power is applied to its prop or props. Boats in the size range of Nordhavns (40 to 62 feet) are most efficient and comfortable running at between 7 and 10 knots. Consequently, their range varies from about 2750 to over 4500 nautical miles, certainly enough to safely cross oceans.

P.A.E., however, recognizes that not all owners or prospective buyers need the incredible range of these passagemakers and instead would prefer to go a bit faster during their coastal cruising. A sensible, pragmatic approach to providing faster speeds without sacrificing seaworthiness is to design a boat with semi-displacement characteristics. This design allows the hull to get partly out of the water when sufficient horsepower is applied and to get out from the grip and limitations of its own bow wave. The boat essentially begins to "plane."
----------------------------------------------------------------

An important point they make here is a point I have been making that the sd design is generally speaking a more seaworthy design than a planing hull design.

Another quote:-
-----------------------------
These designs are meant to cruise in the low-to-mid teens (knots) with moderate fuel consumption, yet when throttled back to typical displacement speeds of 7 to 9 knots, they can achieve remarkable fuel efficiencies and extended range.
------------------------------

Again a point i have been making.

Of course the other point I amde was that I I had to cross an ocean it would be a Nordhaven with its full D hull not a planing hull - why because of the sea keeping qualities.

So i honestly do not know here you are coming from Mike?

 

[Mike21]

Well originally said didn't see point of sd hulls, then in defence of them you'd rather use sd hull than planing and but would cross atlantic in Nordhaven.. implying that Nordhaven were sd hulls. But Nordhaven are full displacement , yet you,ve been argueing about sd hulls being the best /forums/images/graemlins/confused.gif

 

[Mike21]

Re: Horses for Courses.

[ QUOTE ]
I dont think that many people are actually going to agree on this.
Each type of vessel evolved differently, and evolved for a particular purpose, so therefore they are suited to a particular application better than others.

[/ QUOTE ]

Not going to argue over that one

But from what i've seen, most sd hulled boats create a much larger wash and seem to run at more of a bow up angle above displacement speeds than a planing hull.

But would also agree would not really enjoy F8 - F9 in a planing hull, would probably prefer if I had to be out in that weather to be on a reasonable sized yacht /forums/images/graemlins/blush.gif

 

[Gludy]

Mike you stated that your saw little point in SD hulls ...

"Too be honest, don't really see the point of them as they aren't nearly as stable as displacement hulls, and are much slower than planing hulls with worse fuel consumption. "

I replied, referring to sd hulls
"They offer the choice of cruising speed, overall better sea keeping and a very comfortable ride compared to the planing hull. I am not saying they are for everyone, that is down to the individual, I am saying that your description of them is grossly unjust to this hull type and misleading."

an

"So when we talk of superb sea keeping with any planing hull, I really think that it will be a long time before such a boat crosses the Atlantic whereas the Fleming and the Traders have on a number of occasions."

Then in response to
""in displacement mode, imho, and their seakeeping isn't that different at disp speed from a SD or D"

I responded about the Nordhaven crossing the Atantic - that is to the point that in displacement mode the sea keeping of either a sd or d hull not being that different in sea keeping at displacement speed!!!

So my response was to directly to the point that compared both d and sd to planing.

Mike- are you serious ... are you still maintaining that the sea keeping of say a 60 foot Fairline Squadron is the same as a 60 foot Nordhaven in crossing the Atlantic?

Are you still saying that a displacement hull, a semi-displacement hull and a planing hull all have about the same sea keeping properties when at displacement speed????

If you are, then you go against every hull designer and every book ever written on the subject. So please let us know if you have changed your mind or still maintain this?

 

[Mike21]

Well Paul, I'll leave you too it, since it now seems any opinion you don't agree with has now been attributed to me.
Mike

 

[Gludy]

Mike
Please be fair, all I did was quote you and ask if you still beleive in what you had stated.