SD vs Planing vs Displacement

[Mike21]

No you added quotes from others as well, but have stated that planing hull would not be my first choice in rougher conditions, but would prefer a displacement hull.
As for crossing Atlantic would prefer QM2 or QE2 ( both displacement hulls /forums/images/graemlins/smile.gif ) or ideally a 747 /forums/images/graemlins/grin.gif

Mike

 

[Gludy]

I apologise if I have misquoted you, it was not intentional.

Certainly my response with the Nordhaven was in response to a point being made on both D and SD hulls.

 

[whisper]

"An important point they make here .........more seaworthy design than a planing hull" Nowhere in this paragraph from the Nordhavn site does it say this /forums/images/graemlins/crazy.gif
Please, please desist from making crass generalisations and accept the following indisputable facts <font color="red"> </font> .
a) In expert hands some <font color="red"> </font> planing boats can be as comfortable as an SD or D one.
b) The ability of the helmsman can <font color="red"> </font> play a major part in both the seaworthiness and comfort of any <font color="red"> </font> boat.

Come on England /forums/images/graemlins/shocked.gif

 

[Gludy]

It seems that some folks cannot manage to see a simple point, no matter how clear it is made.

Nowhere in any thread have I ever disputed that the helmsman makes a big difference ... nowhere.

What I have stated clearly is that for the same assumed good helming standard we are comparing the qualities of the boat - its that simple. If you cannot manage to intelligently discuss the characteristics of a boat in isolation than that is your problem not mine.

As regards the ability of a helmsman playing a major part in the seaworthiness and comfort of any boat I totally agree and have never stated anything different anywhere ... but this is not the point being discussed - the thread is about comparing displacement, sem-d and planing hulls. In order to do that you keep the variable of the helming constant whilst you see how each hull performs .... its that simple. To do otherwise would get you nowhere as there would be a muddle of skill and boat characteristics.

So Whisper, if you cannot manage to see the simplicity of this point, that I had already stated in a previous post, then please do not bother taking part in the discussion.

""An important point they make here .........more seaworthy design than a planing hull" Nowhere in this paragraph from the Nordhavn site does it say this "

I think if you properly read and digest what the Nordhaven site is saying, I know you seem to have problems with this skill), you will see that they rate their d hulls as the ultimate in sea worthiness. Any move a way from that is towards less seaworthiness.
I am even willing to be a bottle of your favourite plonk that Nordhaven has the clear opinion that d hull boat offer the ultimate in all round sea worthiness and are far better than planning hulls - do you wish to make a public bet? I can send an email and we can all see their answer.

You know besides wrongly accusing me of crass statements, you have not managed to actually express your view about the subject in the last post - direct question - do you believe that given the same good helmsman and the same length/weight of boat, there is no difference in the sea worthiness of the three hull type? Please give us the benefit of your simple answer to this question.

 

[Its_Only_Money]

"if you properly read and digest what the Nordhaven site is saying....they rate their d hulls as the ultimate in sea worthiness."

Well I for one wouldn't take any manufacturer's comments to that effect as gospel, after all I've never heard Ford claim that Vauxhall's are more comfortable /forums/images/graemlins/confused.gif /forums/images/graemlins/grin.gif

Never been in a war zone until this thread.....

"incoming!" /forums/images/graemlins/cool.gif

 

[Gludy]

Ok, I agree you should be careful about what manufacturers claim but that is not the point - the very point in question is what Nordhaven are claiming on their site - my answer was in response to a point made about that.

The facts are really very simple and all around us to see.

Lifeboats are semi-d hulls because they have to provide the best sea keeping and that means having a seat in the sea not siting on top of it PUS they have to get to the scene as fast as possible.

If planing hulls were so good at sea keeping then ask why life boats are not planing boats - sure they would have a much higher speed so why do they not all use Deep V planing hulls?

The answer is that they need better sea keeping than any planing hull can manage and that is with well trained skilled helmsman.

Getting to any simple well understood point like this on this forum is more difficult than getti blood out of a stone. I am starting a new thread on that simple questions about lifeboats.

 

[powerskipper]

Hay boys,

each to their own, go with what you like and trust.......

 

[jfm]

What is it that makes SD good at seakeeping?

I've just had a look around on the net and have to admit I'm confused by your proposition Gludy that there are fundamental seakeeping differences between SD and planing (ignoring stabilisers)

Exactly what is th difference between the two hull forms? Taking your 575 as the SD representative and our same-length Sq58 as a planing repr, they both have hard chines, flat sections underneath, a hard edge at the transom.

The SD has a keel (not sure about the shape, couldn't find it on Tarq website) and is heavier (loaded) for the same hp, so doesn't go as fast. Is it just the lack of speed that makes a boat SD rather than P? Is a SD just a planing hull with less power than needed to make it plane fully, and some tweaks to the hull shape to minimise any hump effect (though on this size boat with a modern hull there is no hump - you transition from disp thru semi-pllaning to planing, without any hump).

So is a trader575 like a Sq 58 but with less power/weight, quite a lot more forward beam (very flared bow and wide foredeck), keels to slow it down a few knots, and flatter hull sections/less V to make it semi plane more easily?

Seems to me this is how it is. At least, if there is a fundamentially different hull shape/hydrodynamics set up, can someone tell me what it is, cos I cant see it

So at slower speeds, say 12 knots in heavyish weather, what is it that makes SD better seakeeper than P? Is it the heavier bow that makes you crash thru headon waves with less lifting of the bow as you would get on the Sq (which is several tonnes lighter in the bow?) Or is it just the stabs? Is the seakeeping differnce just due to the fact it is ok to fit stabs on the 575 but not practical on the Sq58?

I think there's a load of exaggerating going on here, and the differences aren't huge, except for the stabs. Gludy you say esp the Sq58 doesn't allow walk around in any weahter, I dunno what sea conditions you have been out in but that really isn't right. It's 26tonnes loaded and while there comes a time when moving around isn't wise, for normal boating you can walk around freely, prepare food underway, etc etc. Also this 150% accommodation claim seems odd. There are no crew cabs on the Trader. It has a big aft cabin but otherwise the accom gain is I think more elbow room in the cabs rather than 150 more accom. Max is 4 cabins, we have 5, though I accept some of the 575 cabs will be bigger. The flybridge accom on the 575 is much less than Sq58, though whether you care about that depends on climate

Anyway, help me out, what is it that makes SD hull seakeep better than P? If you had to cross the atlantic (ignore range issues), exactly what is it about the 575 hull that makes you to prefer to be in that than the Sq58, apart from stabs? /forums/images/graemlins/confused.gif

 

[hlb]

Re: What is it that makes SD good at seakeeping?

You thick or what!! It's better cos Gludy says it's better. Would have thought you would know that by now!! /forums/images/graemlins/laugh.gif /forums/images/graemlins/laugh.gif

 

[Gludy]

Re: What is it that makes SD good at seakeeping?

JFM
Thanks for a post that actually deals with the subject.

On my Squadron 59 I have twin 600hp Volvo engines. It weighs in at about 26 ton.
It reaches 31 knots top on a good day 29 knots on a bad day but will cruise happily all day at 25/26 knots.

On my new Trader I have about the same weight and even more powerful engines - twin 715hp cats. Top speed is 25 knots - it will cruise all day at 22knots but you will pay a price for that - in fact anything over 18 knots uses more fuel.

So clearly there is a difference. The keel on the Trader is very deep, the whole profile of the hull is different, the angle of the bow is very different. etc.

I am currently working so I cannot spend time at this point but I shall return later with photographs and a detailed explanation.

As regards the extra accomodation - The Trader offer me at least 50% more usable accommodation:-
Main Bedroom - about 50% larger with walk around queen size bed, enough room for an office area.
Main bahtroom - slightly bigger but not much.
VIP bedroom - large double bed the same size as the master cabin on the 58 and this is very much bigger than the small twin bed cabin on the Squadron.
Third bedroom- full head height twin cabin with office - larger and more usable than twin bed in Squadron.
Galley - twice as large as the Squadron with all utility machines within it -eg washing machine etc.
Aft Deck V Cockpit - about 5 time bigger with fixed seating for 10 dining, a full aft deck galley and lots of walk round room.
Saloon - same size but without lost galley space but - to be more usable space.
Flybridge - seems smaller on the Trader but seating for 13 and decpetive. Crane with rib storage on top. Total area is actually larger but I have to admit the flybridge of the Squadron 58 is a dream.
Bathing platform - much larger on the trader (I have the foot extension) and totally free of ribs etc - a curved staircase to the aft deck.
Walk around area - much bigger and safer on the Trader.
Crew room - none on Trader but only used by me as a store room and there is ample storage on the Trader.

So overall, in terms of comfort of living in the trader is much larger and tuned in for live aboard.

I will return on the details of the hull - I have some photos of a 575 out of the water in a sling and this would help to explain.

 

[jfm]

Re: What is it that makes SD good at seakeeping?

Gludy that wopuld great if you could post the pix of 575 in slings. Would like to see. There has to be something making the difference between SD and P. If you're in a mad hurry email the pix to me and I'll put them up on the net. Thanks

 

[Gludy]

Re: What is it that makes SD good at seakeeping?

Give me you email address and I shall pop them over to you.