SD vs Planing vs Displacement

[martinwoolwich]

Firstly let me say out the outset that I have been boating for nearly four years and know very little!

My experience is limited to semi displacement boats only - Broom 38, Fleming 55. I have been on a planing boat once only (thanks Ian Ainge) and never on a displacement boat (at sea).

Looking back on recent threads it strikes me that my understanding of benefits vs limitations of the various hull types is far too simplified and probably wrong.

I am not trying to wind anyone up, I'm genuinely interested. (although one or two of my statements may be just a little tongue in cheek - for fun not for offense)

My view was:

Displacement: limited speed (calculated by some sq root of something, divided by something, multiplied by something), excellent fuel consumption, brilliant sea keeping (although may be wet) - by sea keeping I mean, not rolly polly, needs more than a mountainous sea to worry you, you can make a four course meal, whilst knitting and playing tiddlywinks without being aware of the big nasty weather out there. Typical owner has been boating for over 100 years, used to be a fisherman, sailor, submarine commander or Dutch!

Planing: Jolly quick - horrible fuel consumption, skips around all over the place, slams a lot, everyone grabbing hold for dear life, don't fill the wine glass more than a third full or you'll get bad stains on your polo shirt. It's more about getting there than the trip itself which is just a bit of an inconvenience and if that star trek transporty thing was available they'd all buy that. If the weather turns bad you got two choices, slow down and wallow like a hippo 'cause planing hulls just don't do slow down, or speed up which means slamming even harder. Really a mentality that says let's have a really nice second home that can change it's location whenever it feels like it. Typical owner is someone without much spare time on their hands who socializes a lot and only drinks bitter when watching England being thrashed at Rugby.


Displacement: Big compromise between both, not jolly quick but quicker than displacement, OK'ish fuel. If you want to make a big breakfast, slow down to displacement speed and it'll nearly be as good a full DS. If the weather is coming in, you can speed right up and be nearly as good a planing (although in my experience the weather is ALWAYS coming toward me so all I do is get to it quicker). Not swanky, more practical. Typical owner is compromise in hull and compromise in nature. Not a bad thing just wants the best of all worlds and know that's not possible so gets a close as they can

My only caveat to all this is that I believe the characteristics get significantly better on all types of hull as the boat gets bigger. (That's why I now have a 55!)

Based on what I've been reading recently here, I now see that many of these pre-conceptions are totally wrong, please advise.

 

[gcwhite]

To help Duncan I am now talking about hulls whereas before I was talking about adapting to conditions.

Planing boats have significantly different charactaristics depending on hull design and length. Assuming the same length then the design can make an enormous difference. Sunseeker (Sam Snead), Princess and Fairline ( 'Osolenski') all have superb seakeeping hulls and can perform well in quite big seas without slamming. My experience of Sealine is that they don't perform nearly as well.

 

[tcm]

doesn't seem a milion miles off, and the summary of typical owner alarmingly accurate.

I am coming to the view that only boat-testing journo's who get on a few different boats every weeks can sensibly differentiate between the pro's and cons of all the hulls etc. But the boat testing journos haven't got a real grasp about value/price/ownership, because, since they're boat-testing journos, they've never actually bought a decent boat cos they're a bit skint. So, nobody knows everything.

 

[Mike21]

Probably correct on displacement boats.
On planing hulls, depends on size and manufacturer, but it tends to be sterndrive hulls that skip , shafts are much more stable.
As for horrid fuel consumption, think you'll find semi-displacement are a lot worse than equivalent sized planing hull.
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. /forums/images/graemlins/grin.gif

 

[Mike21]

In defence of Sealine /forums/images/graemlins/blush.gif think you'll find some of the latest hulls are much better than the earlier ones

 

[gcwhite]

Mike
I am sure you are right my experience was 6 years ago, although in my marina there is a Sealine S42 and if I step on the bathing plaform it seriously lists whereas the same size Fairline or Sunseeker doesn't move. I have also obseved 42 ft Sealines cruising down the channel and when the crew move about the boat lists with them. This simply doesn't happen with the other main manufacturers.
I agree with the earlier comments what is the point of a semi?

/forums/images/graemlins/laugh.gif

 

[Gludy]

Eyeno
When you say that fairlines have superb sea keeping hulls compared to Sealines - a claim I do not dispute ... is not the real issue how they compare to SD or D hulls?

From my limited experience the planing hull, really has to go at planing speeds and no matter what you do you are skipping over the water like a stone and hence hitting it hard all the time.

Mike21

"As for horrid fuel consumption, think you'll find semi-displacement are a lot worse than equivalent sized planing hull."

That is too simplistic. For a start the option of going slower that is truly there with the SD hull offers a huge decrease in fuel consumption. In my case I save fuel below 18 knots ... up to 3 times less at 10 knots, consume the same at 18 knots and use more fuel over 18 knots in the SD boat ... I have the option of getting over 1500 miles range if I want it.

"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. "

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.

Taking some folks on my last 3 hour trip in the squaddie, I realised that all everyone does is sit - if the move they have to really hang on, a trip to the heads is an adventure and doing anything else is almost impossible and that is not in very rough conditions.

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.

All hulls are a compromise but I happen to think that Martin has made a wise choice with his Fleming. If he ever wants a trip out on a planing boat he is more than welcome to pop over to swanbsea for a day this summer and I will treat him to one. I frankly think it would not take long before he realised that its a totally different animal and probably not to his liking.

 

[gcwhite]

Gludy, yes you are right.

Actually I have never experienced an SD. A new friend aquired a Flemming 60 someting last year and promised me a trip; I'll remind him this season.

I've heard they can roll a bit when underway, is this true?. A planing hull once on the plane is relatively stable in anything up to low end of moderate.

/forums/images/graemlins/wink.gif

 

[stuartw]

In defence of Semi-planing cruisers

I am somewhat bemused by the comments from various people, that they cannot understand why semi-planing boats exist. Try explaining that ,to the likes of Broom, Birchwood and even Fairline (the late lamented Turbo 36).
One huge advantage is their stability in non planing conditions, particularly at anchor or berthed. I have witnessed on many occasions, the gyrations of a Sealine F33 next to me in Haslar. The owners wife eventually refused to stay on the boat it was so bad. In a heavy swell, where planing is perhaps impossible or would be extremely uncomfortable, a deep vee hull will have very little directional stability, and be rolling all over the place, particularly if it has outdrives. The small keel that most semi-planing hull have, does work.
I have to accept the argument about fuel economy is justified, but it's not a huge difference.

All I am really saying is, do not exclude semi-planing based on comments by a few deep vee hull boat owners. There are a lot of nice comfortable semi-planing boats out there.

 

[gcwhite]

Re: In defence of Semi-planing cruisers

The Sealine F33 and in fact all Sealines relative to their size are very frisky in any sea. A good planing boat will be ok in a moderate sea even if forced to come off the plane. I have on occasion had to cross the channel at about 12kts in such conditions and whilst there was, ofcourse, considerable longtitudinal movement rolling was very limited.

/forums/images/graemlins/smirk.gif

 

[duncan]

Always appreciate help.

Not quite sure what a famous golfer has to do with Sunseeker? Should this also have benefitted from 'commas' to indicate an approximation for the actual hull designers name (Don Shead), in the same way as 'Osolenski' is presumably an approximation for Olesinski?
I have to ask this as a question because I am only to wel aware of the possibility that I have missed the real point you were making completely - could it really be that Sam Snead was a Sunseeker lover becasue of the ride qualities of their hulls?

 

[Mike21]

Having only ever been on a sd hull in flat conditions , can not comment on their seakeaping, but they do seem to roll a lot more than a a planing hull, when above displacement speeds.
Only time I,ve had difficulty moving round a planing hull was in a F7 with wind over tide.
Do know that sd hulls are a compromise, and comments were a bit simplistic, but still don't see the point of them, although will not knock anybody's choice of boat as that is down to personnel preference.

Was just having a tongue in cheek go at Martins rather negative comments on planning hulls. /forums/images/graemlins/tongue.gif
And I'm sure some 90 year olds will be upset about his description of displacement hulls too
/forums/images/graemlins/laugh.gif

 

[jfm]

Martin I think that's broadly right but it compartmentalises boats too much. They aint really that different. Planing hulls will work perfickly ok at low speed and in displacement mode, imho, and their seakeeping isn't that different at disp speed from a SD or D. All this talk of fundamental differences is grossly exaggerated imho and -ignoring stabs- there wouldn't be much difference in ability to brew tea between your boat, ours, Gludy's new and old, and a 56foot fishing tub, at 8 knots.

The fitting of stabs is what causes the significant difference, not hull shape. As a practical matter you currently only get stabs on D and SD hulls, so on that basis I agree SD and D are better for making tea (referring to Gludy's test). But a stabilised plnaing hull is the best sort of boat in this size range imho, namely a ferretti with gyro stabilisation (and that's what I''ll be aiming for as next boat). This has stabilisation at low speed, the ability to run a bit faster to stabilise (where appropriate) by planing or semi planing, and at-anchor stabilisation. Miles better than Gludy's choice, imho.

This talk of planing hulls slamming also just doesn't accord with my experience. We can drive nose into a large swell, and as the hull jumps off the swell then lands, pushing masses of spray sideways, the landing is soft. A good modern V hull above say 30 tonnes will land fairly softly

So, imho the best of all worlds in your/Gludy/my size range and the next size up (say 70feet) is a stabilised ferretti planing hull. Besides the ferretti 731 has an interior to die for

Gludy, not picking a fight, you may disagree, that's fine.

Tcm is right that very few folk have wide experience. I certainly dont. It's invariably the case with boating that you need to work a lot to make the £££ to buy the boat, and family etc dont always want to spend as much time on it, so experience can be limited.

 

[ArthurWood]

I can only comment that here on the normally relatively calm Gulf of Mexico the 50-80ft Hatteras/Fleming types don't like going out in more than 3ft seas because of the rocking and rolling, whereas we planers don't have problems, unless we want to drink chapmpers en route, in which case we slow down for a while and still get to or destination long before the rest.

 

[oldgit]

Have you mentioned your observations with regard to Hatteras to that bloke on Boatsurvey. /forums/images/graemlins/smile.gif
Changing the subject entirely.Did you get a chance to look at Machholz ?Good views here despite all the clag.

 

[whisper]

Sorry, but surely displacement hulls can be decidedly roly poly. Or atleast all the ones I've been on have been.
The point is that by choosing semi D or Planing, over pure D, you will have to endure less time in roly poly mode, albeit with higher fuel costs.

 

[Gludy]

Yes- they can still roll a bit but the new stabiliser fitted with the latest software really do stop this - I turned the boat across its own wake with a f4 in the bacground at 25 knots and it did not seem to bank 1 degree or feel anything - its like switching the sea off.

 

[Gludy]

JFM

I have chosen my boat because:-

1. Comfort of ride for everyone is manyfold better than the same size planing boat - there is simply no comparison, even without stablisers. Wit stablisers, the difference is even more marked.

2. Size of usable accomodation - at least 50% more.

3. Ability to dry out - I can now visit all those little harbours and have increased my bolt holes by a factor of 20

4. Long range option with economy - a range of up to 1500 miles. A planing hull really does not offer that option. A choice of what speed I go V what fuel consumption I have.

The above are the main factors.

"in displacement mode, imho, and their seakeeping isn't that different at disp speed from a SD or D"
I strongly disagree - if I was crossing the Atlantic, I would prefer a Nordhaven to a Fairline Squadron.

I have been out in many conditions in a number of planing boats and they all sit on top of the water with a hard ride that precludes easy movement arounf the boat - I am amzed at any comments that are different to that. Its my obersavtion and that of many of my friends.

I agree that stablisation does make a huge difference in preventing rolling on D and SD hulls. I can see some sense in putting them on planing hulss for low speeds and for at anchor use - but it would still be a planing hull and hence would still have ahard ride on top of the water.

"This talk of planing hulls slamming also just doesn't accord with my experience. We can drive nose into a large swell, and as the hull jumps off the swell then lands, pushing masses of spray sideways, the landing is soft. A good modern V hull above say 30 tonnes will land fairly softly "

Not my experience and in particular not so with a Squadron 58 - they are simply not easy to walk around in any conditions whilst planing and still plane on top of the water giving a hard jolting sense.

I agree wie all must lack experience in that we do not gain the experience of multiple boats/hulls/stabliser options etc.

An article in the mag that looked into this subject in depth swapping a planing boat and sd boat - a sort of family boat swap - so that each could comment on the other would at least be interesting!

 

[whisper]

"I am amazed at any comments that are different to that" I respectfully suggest that you are sadly lacking in your experience by not having travelled by Botnia Targa. Our boat is but 26ft long O.A. I can guarantee that you can safely move around it whilst on the plane in smooth or slight seas. In moderate to rough seas the same applies provided that you are a)going with the waves which are running reasonably constantly b) have a skilful enough helmsman.
I appreciate that Botnia do not make a boat large enough for you so in your case this is all rather academic.
Re. the ability of a Trader ( super boats, by the way) to dry out. Are the props and stabilisers protected enough to do so without using legs?

 

[BarryH]

"have a skilful enough helmsman."........finally, about time too!