Where is the CofG of a yacht (roughly)!

I wouldn't stress about it. The guys on the crane should be able to guide you through it. Just make sure you have the tools needed to move the winchpost in case it needs to me moved away from the axles before finally positioning the boat. (Any movement the other way can be done away from the crane.)
 
Thanks for all of your helpful replies!

Regarding the nose weight, I have done a bit of searching around and it should be 175kg, however my Mitsubishi Shogun has a max noseweight of 115kg, so I'll go with that. I've towed a few boats before and noticed that they start to fishtail if the noseweight is a bit light at certain speeds, so I'm just going to take it steady.

Yes it's a new purpose built trailer, but as soon as I've found the right position for the boat I'll move the winchpost and supports, never to be moved again!

I've heard of people using a stabilising bar, haven;t got one for tomorrow, can anyone comment? I've seen pictures but don't really understand how they work.

Once again, thanks!
 
You have a good towcar there, so should be okay. 115KG noseweight is more than most cars can handle. I once read you should aim for 10% of the trailer weight on the ball, but most cars can't handle that with a large trailer. What does your trailer and boat weigh?

I wouldn't use a stabiliser, IMO they are gimiky things aimed at people towing too large a caravan with too small a car. They work by introducing friction to try and dampen any tendency to sway. It's really only hiding the problem, rather than fixing it.

At the moment I can't tow the boat over 50mph, but hope that will improve when I can alter the trailer to increase my noseweight.
 
Safe delivery!

Just to let everyone know, the lift went very well (driver was very skillful in getting his lorry into an extremely tight space!).

The noseweight ended up being approx 100kg, I could tow at 60 mph (and a bit more on occasions!) with no fish tailing whatsoever.

I have a few questions about towing, but I'm going to put them on a new thread.
 
seanfoster said:
I'm going to be lifting my yacht onto a trailer for the first time tomorrow and need to get it sitting evenly as much as possible.

I'm assuming that the centre of gravity is at the mast, would I be correct (generally)?

The boat is a bulb keel Dufour 1800 and it's going on a twin axle trailer, I'm thinking that the line of CofG should be somewhere between the two axles.

Could anyone comment?

Any help gratefully received!
Click to expand...

Listen Guys, I'm sorry I never saw this until after the event but everyone seems to be busy trying to make this difficult.
One reply nearly got the answer with his cardboard cutout, but try thinking a bit bigger...
Assuming this isn't a boat lift with two independant strops - when you hang the BOAT up by a string (crane) the cable will point directly down through the centre of gravity - however I suspect the crane driver knew this
 
Towing and CofG

It is all over now for the OP.
However my experience has been with fin keel types. We don't see twin keels here. (small tides)
Anyway the typical fin keel yacht will be aft heavy when sitting on the keel tip. Some manufacturers will make a fin keel that angles aft which helps a bit but usually you need a rope from bow down to cradle just to stop it toppling backwards. Obviously twin keel and shallow draft tend to have a shallow long keel so not so much problem.
Nose weight on a trailer is recommended to be 10% of total weight. As said if it is too little in nose weight then you get fishtailing. This is in my experience a problem when decelerating. Going fast and accelerating no problem but if you try to slow down especially on a downward hill it is very scary. Trailers have been known to overturn often taking towing vehicle with it.
I have just bought a Ford called a Territory.(Australian made) Just 2 wheel drive very ordinary but I was impressed by the towing capacity of 2600Kg (max nose weight 260kg.) My boat on trailer is about half that so no worries now.
Stabiliser bars A name often given here to load leveller bars. In fact I have never seen the friction type. The load leveller bars 2 sometimes 4 are about 1 metre long with a right angled bend in the front of the bar. The bent end fits into a special casting bolted under the tow ball. Imagine without a trailer the bar is fitted into the casting and lifted at the back end. It effectively levers the car front wheels down back wheels up. or tips the car body nose down. This effect is used by attaching the tips of the bars to the draw bar of the trailer. Often by 2 chains hanging down. You lift one bar then the other up until the chain loosely attaches. The effect is to reduce the sag of the back of the car while maintaining a high nose weight. Alternatives might be helper springs on the back of the car.
good luck olewill
 
I can understand your description, but have never seen a load-leveller over here. Our trailer nose weights are limited (by law on post-1996 cars) to whatever is on the type approved towbar. The French police are really into stopping caravans and boats, and sticking the jockey wheel on a set of scales. They'll give you an on-the-spot fine if you're over the odds. It's rare to find a European car with a max noseweight above about 100kg. Most ordinary cars are between 50 and 75kg, big MPVs and 4x4s nearer 100kg.

On the subject of "anti-snake" bars, they work to try and stop the trailer snaking. Our last trailer-sailer was an Evolution 22 and no matter what I did with it, it snaked like a pig. Scared the life out of me on a couple of occasions! I ended up getting an old Series III Landrover and it even tried to "wag" that a few times! I bought a cheap friction one from Towsure and was AMAZED at how well it DID work! You can adjust the degree of resistance by tightening the friction disc. It absolutely killed the snaking stone dead. I was really impressed!
 
Brup - no need to run and hide: you are absolutely right.

The position of the mast tells you nothing at all.

The card cut out method is irrelevant to finding the CG. The CLR has no relationship to CG other than it may also be generally amidships...

... but then why not just divide the LWL in two? Actually the CG is likely at 50-60% of the waterline.

The 'load to trim' method described will find you the CF (Centre of Flotation, also the centre of the waterplane area) not the CG.

The only way to find the CG is to find the CB (Centre of Buoyancy) for which all you need is a lines plan.

Measuring the areas of the sections and using Simpsons Multipliers (a formula) you can find the designed CB.

Providing she's floating on her designed lines the longitudinal CG will be exactly below the CB.

The problem is not that the boat is not of equal density (the water being displaced is!) but that the distribution of volume is three dimensional (not two as in the card cut out).

Fine lines forward will require a CG further aft and vice versa.

An example of this is the Cutlass 27. If you're not careful they have a tendancy to fall on their bows when drying out. The 'fine' lines of the stern require a CG that's further forward and too close to the front of the keel than is comfortable. The solution would have been: move the CG aft... but in order to stop her trimming down by the stern, also give her a fatter bottom. However the lateral profile would have remained unchanged...

The CG won't move just because the boat is in air not water either...
 
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Personally, I think I prefer the "moving-it-about-a-bit-while-it's-on-the-crane" technique! Lot less hassle!

Interesting bit about the Cutlass. Did you own one once? That's exactly what ours does - falls on its nose as it dries out! I've got a samson post you could pick the boat up with! Also, there's the other problem where the lovely fine stern lines mean that as soon as you get a couple of lardies (like me!) in the cockpit they trim noticeably stern-down!
 
We love ours to bits! Lovely, sea-kindly, exactly what you'd imagine given the hull shape (which also means there's stuff-all space down below and it never goes astern the same way twice)!
 
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