An armchair naval architecture poll

The longitudinal position of boat CoG is around...

  • Total voters
    37
MapisM

MapisM

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Thanks in advance folks for your views on this matter:
Where would you expect the CoG of the following boat to be placed, longitudinally?
I didn't include any placement astern of "1" or in front of "6" because I think it would be unreasonable, but feel free to comment and/or ask for further details.
I'm not sure that I'll be able to answer every question, but I'll sure try... :encouragement:

XH0DObyz_o.jpg
 
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P.,

next time try to make it harder by posting a plan that not only has all the levels of the boat from e/r to bimini, but also depiction of the sea bed (make it messy) and shows the seagulls above (maybe go to stratosphere and add a few satellites, or galaxy level as well, would be nice...)
That's a horrendous plan, saw it first on the 5inch screen of my mobile, no luck still don't understand wtf those boxes amidships are, where the tanks are (probably on the sides of the engines?) etc...

cheers

V.
 
As a hoist operator, it amazes me how big name boat manufacturers get the LCG wrong and put the hoist stickers in the wrong place.
A hoist should lift with +/- 10% on front or rear sling sets. Although with a suitable capacity hoist slippage is not an issue a it would be With a crane if you get the lcg wrong.

Generally look where the engines are, where the fuel tanks are, water tanks and whether there is a large tender an the swim platform as well as asking Hof full the fuel tanks are.

In this case the engines are on V drives and it is not clear where the fuel tanks are.
 
You can find the total displacement ( DP 58 ? Right ) , the engine s / G box Kg,s ,tankage too .
Prob is how full are the tanks - that’s all , fuel ,water ,Black .
I,am thinking a cubic M of water is a metric ton ,i realise fuel is bit different but near enough for the sake of answering this .

So ps give an indication—— say 1/2 full fluids ? Or full , or as sea trialled when new ?

If the main fuel tanks are lateral to the engines , then full asopposed 1/4 full will I reckon move the CoG @ least 1 place towards the stern .
Any hugely extra chain + upsized anchor may come into play over std spec .
It’s positioned right fwd way above the W L when runing so that cantilevered effect will multiply any Kg,s in so much as effect the CoG spot .
A massive tender sat on the bathing Platform will have a similar effect shoving the CoG rearwards in the other direction.

So for me there is not one answer ie a fixed line co responding to a number from the info given so far —- a range from X to Y would be a better Q imho .

Having said that I,ve opted for 1 based std spec ground gear and @ least 1/2 tanks full .
How ever fuel tanks empty and black / water full which I think looking @ the plans it may move Fwds to 2
 
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vas said:
That's a horrendous plan
Click to expand...
Sorry V (et all), I'm aware of that, but it's the best I've got.
I was hoping that it would have been clear enough for what I was asking, but in hindsight I realize that it's clear to me because I already know the real thing...

I just replaced the original drawing with another one, with the three fuel tanks in red and the water tank in blue.
The latter has a 1000 liters capacity, and the same goes for each of the side fuel tanks. The central fuel tank can hold 700 liters.

I hope this helps... :)
 
I originally thought one, so just forward of the engines. But I voted two because MapisM probably has several hundred feet of chain in the locker
 
No side view I'm afraid, but how can that be relevant for the LCG estimation?
Ref ground tackle, there's 80m of 10mm chain, plus 25Kg anchor.
Another element which might be worth considering is that the boat is overall heavier (by at least a couple of tons) when compared to similar size boats of the same era - even those with a reputation for non-light construction, like the Prin57, Sq58, Ferretti 57...
And at a guess, most of that difference is in the living spaces.

PS: for the records, "4" is placed just about at the boat longitudinal center.
So, even if as of now I see one vote for 4 and one for 5, gut feeling tells me that the LCG is bound to be somewhere astern of 4, mostly due to sheer engines weight...
 
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MapisM said:
No side view I'm afraid, but how can that be relevant for the LCG estimation?
...
Click to expand...
A boat floats with its Centre of Gravity directly below its Centre of Buoyancy. A side view would give a good idea of where the centre of buoyancy is.
 
bedouin said:
A boat floats with its Centre of Gravity directly below its Centre of Buoyancy. A side view would give a good idea of where the centre of buoyancy is.
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Fine, but wouldn't you need at a 3D model rather than just a side view, to estimate the CoB?
Regardless, that's all a bit academic, since unfortunately I don't have a decent side view - let alone a 3d CAD model...
 
MapisM said:
Fine, but wouldn't you need at a 3D model rather than just a side view, to estimate the CoB?
Regardless, that's all a bit academic, since unfortunately I don't have a decent side view - let alone a 3d CAD model...
Click to expand...
Side view would be a big help if the hull is of conventional shape, in fact more important than the plan view. For a displacement hull the CoG it likely to be a little back from half way along the waterline., for a planing hull it is likely to be 2/3rds or even further back
 
Well, I still struggle to understand how a side view could help a lot, but below is the closer thing to a proper side drawing that I can offer, if that helps... :)
IZc8M1lu_o.jpg
 
I think it’s relevant to see the super structure.kinda access how much wieght is fwd , and indeed shifted back on the FB
Having seen this I,d revise my choice to the end ,rear most port hole, which looks like near line 2 in the 1st pic .In fact a handy fitting just above the WL , silver dot in the midline of the rear most porthole .

There are 6 ports on the 1 st schematic and 7 on the side pic ,presume heads at the back stb side has an extra porthole ?
At least the end ones seem to match up .

Any how as said variable cos of tankage state ( s) between 1 and 2 .
 
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Portofino said:
There are 6 ports on the 1 st schematic and 7 on the side pic
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Wow, well spotted PF.
The drawing is correct, but I flipped the pic horizontally to keep the same orientation of the drawing.
In other words, the pic actually shows port side, not stbd. No differences aside from the portholes, anyhow!
 
The side view matters a lot because the centre of gravity and centre of buoyancy are intimately related. You can assess the centre of buoyancy purely from the underwater shape (i.e. it is the centre of gravity of the water it displaces) so that is easier than worrying about engine weights/locations etc.

So you need to assess the CoG of a shape the same as the underwater shape of the boat if made of solid wood. Purely by eye I would put that about the aft port, or maybe just forward of that. If the starboard ports on the photo correspond with the port ports on the schematic that puts in in 2 tending towards 1.
 
Well, thanks everybody.
Even with all the understandable guesswork involved, I believe that somewhere between 1 and 2 is a very reasonable estimate - btw, that's just about at one/two thirds from the stern/bow respectively, which as bedouin said is rather typical of P boats.

For clarification, the reason behind this thread is that while thinking about the possible alternatives for a gyro placement, I was wondering about the effects on weight distribution.
I have a few other minor gyro-related doubts, but I'll follow up if and when I'll decide to go ahead with it.
Not a short term upgrade anyway - the aim is to thoroughly test the boat next summer first...

The poll result is more than good enough for the moment - thanks again! :encouragement:
 
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