I think the COG also depends on what boat. Series 1 boats have a lot of heavy wood built into them that is higher up than the latest woodies or glassfibre boats. I know my Series 1 has a sold mahogany centreboard trunk and stern where the later boats used thinner ply and put in more “ballast” down low to keep the weight legal

• This reply was modified 6 years, 4 months ago by Arthur.

I can’t be sure about the CoG,  and it would be worth looking up a measurement form to see what (if indeed anything) is measured.   But I think it highly probable that Jack Holt would have originally had at least some idea of the CoG position,  whether or not he fully worked it out.

What I do know  –  and this provides a minor insight into recent class history  –  is that the principal Moments of Inertia have never been specified,  or definitively measured for the class,  and we have every reason to think it most likely that they vary between different versions of the boat.    This became in issue in 2009/10,  while I was serving on Committee,  when we were alerted that for good reasons modern build was coming out with a weight below our minimum weight specification,  and builders were then having to incorporate additional materials into the construction purely to bring the weight up to specification.

The light construction arose from two parallel causes.  With the plastic boats it was the move from polyester resins to epoxy resins,  which are very much stronger for a given weight;   so epoxy boats were coming out of the moulds both stronger and lighter than their polyester predecessors.   With the wooden boats,  the cause was the disappearance from the market of traditional boatbuilding hardwoods,  particularly mahogany,  so builders were having to use alternatives which are available nowadays,  and these timbers turn out to have slightly lower density.

Committee accepted that in order to maintain a level playing field for the racers the weight needed to be made up somehow,  but became concerned that we did not want any particular distribution of this extra weight to give a competitive advantage.   Particular concern focussed on potential changes to the moments of inertia,  and a complicating factor was that these had never been measured,  or specified anywhere in the Class Rules.

So we decided that we (the Association) would specify what form these additional weights,  to be known as Association Corrector Weights (as distinct from the ones added beneath the thwart to bring the build weight up to the sailing weight),  were to take,  and where they were to be installed.    We wanted to ensure that so far as reasonably possible they would have a neutral effect on the moments of inertia of the boat.

David Rowlands asked me to do the maths for this,  which I duly did;  we then met to discuss it at the 2010 Dinghy Show,  David then did the design from my maths,  and if I remember correctly it was adopted at the next Committee Meeting.

Oliver

• This reply was modified 6 years, 4 months ago by Oliver Shaw.

that sounds like trial and error with the launching trolley. I imagine you would want just enough “forward” to keep the bow down when it is sitting, but still be comfortable enough to easily move around. You could even go the other way around, with it being Bow light so it always sits stern down to allow any water aboard to drain. I would be careful putting it in that position though, no sense in damaging the boat if you lost your grip and dropped it

I asked a similar question and here is the answer…

While i didn’t follow this to the letter I can post a photo of what i ended up with next time I’m at the boat.

The weight is light enough overall that a few inches either way will not make much of a difference.

I have just measured up,  as best I can (because the boat is currently jacked up at the bows,  and access is obstructed),  one of my vintage GP14s which is sitting on a Chris Brown launching trolley.   That is a clone of the excellent and once near ubiquitous West Mersea combi units,  with the twin cradle design.

I make it 245 cm from the axle to the bow snubber.     Although that distance may not be exact,  because of the limitations of access,  it will be within a very few cm.

That is designed to give modest nose weight,  and the trolley can if desired take a jockey wheel.   If the boat is placed on the trolley not fully up to the bow snubber she then can become neutrally balanced.

There would appear to be some room for experimentation around (and a little below) this 245 cm in order to achieve the desired balance.

My personal preference on the rare occasions when I need to pull a GP by hand is slight noseweight.    I can manage with the noseweight of one of these trolleys if I must,  but I prefer to use the jockey wheel.   But negative noseweight,  i.e. the boat being stern heavy,  is actually quite awkward for manoeuvring because one has to push down at the same time as pulling;   and zero noseweight (i.e. perfect balance) is almost as bad.  Slight noseweight is ideal,  and precisely how much is optimum is a very personal judgement.

Another consideration is that the aft support should ideally be some distance abaft the axle,  in order both to ensure that the boat sits securely on the trailer without the bow tending to lift off the bow cradle or chock,  and to at least reduce the long length of unsupported hull abaft the trolley.  The West Mersea design,  now cloned by a number of other builders,  was possibly one of the first designs to offer this feature,  and if you are designing your own trolley it is a feature well worth copying.

Yet another consideration (for optimum noseweight) is attitude,  and stability,  when parked.   Most of us tie our boats down if using club dinghy parks,  and many insurers require this anyway,  as it is usually best practice.   But even when tied down,  it helps if the boat is inherently stable in her berth,  whether the bow is propped up or not.

Hope this helps,

Oliver

• This reply was modified 6 years, 4 months ago by Oliver Shaw.

Yet another consideration in the context of a combi unit is the stability of the load when the outfit is being towed at speed on the road.    That may well be part of the reason for the nose weight of a combi trolley.

A possible alternative solution would be to use the original axle position but have an additional removable clock to the bow snubber.  That would enable to boat to be further back when in everyday use at the sailing club,  but pulled forward again for towing.

Oliver

250 cm, bow snubber to axle is the correct distance for the launching trolley. The aft cradle is often 30cm back from the axle, making the boat less “tippy” on the trolley.

Nose weight wants to be between 9 and 16 percent of gross trailered weight.