This is our Old Site for reference purposes only.
Active Site:

The George Blog – Design 160 Weight Estimate & Comments

Return to Recent Topics
Alternative WC Compartment for Design 119 posted in Design
Design 035 - CNC cutting files posted in Design
Design 168 – Deben 4¾ -tonner posted in Design
Deben 4¾ Tonner Plans posted in Design
New Design No. 178 – Starfire 23 posted in Design
Instructions Book 5 for Design No. 165 posted in Design
Re-caulking Dazy posted in The Odd Word
Addition/Extension posted in The Odd Word
Deben 4-Tonner posted in Design
Deben 4¾-Tonner – New Design posted in Design
Design (10 most recent)
The Odd Word (10 most recent)
News (10 most recent)
Recipes (10 most recent)
Design (Archives)
The Odd Word (Archives)
News (Archives)
Recipes (Archives)
Favourite Blogs & Sites
The British Humanist Association
Richard Dawkins
The Freethinker
Mercy For Animals

Design 160 Weight Estimate

We are now reaching the stage of the design where I have to start to fill in the weight estimate.

I have to make an estimate of the weight of everything, large and small, and estimate their centres of gravity longitudinally, vertically and transversely. I have to say this gets a bit boring!

It's both interesting and sometimes a bit daunting how the weight builds up as each new item is added. Eventually it all has to work out somewhere pretty close to the original assumptions that were made when designing the hull shape. If it doesn't, or can't be tweaked to do so, then it's back to the drawing board to make changes to the hull shape and/or the arrangement of the structures.

We do have some tools in our armoury – the most effective of which is to move or alter the ballast keel in some way to bring the longitudinal centre of gravity in line with the longitudinal centre of buoyancy. These have to coincide for the vessel to trim level.

The shape of the keel also has a big effect on the vertical centre of gravity. We want this to be low enough to give the yacht good stability, but not so low as to produce a very quick sharp roll period – which is uncomfortable. But the planform of the keel has a big part to play in the sailing balance of the boat, in conjunction with the sail plan, so we can't just move it around willy-nilly – unfortunately!

Any heavy item – engine, batteries, tanks, anchor cable, and so on – is a candidate for adjustment to the centres of gravity. And we look very closely at the rig in particular because rig weights are high up and even little changes there have a large effect on the vertical centre of gravity and stability of the boat.

That's why designers (well this one anyway) get really mad at builders or owners who increase rig sizes unnecessarily!


This article does not have any comments.

Post a comment

You need to Login to post a comment. If you are not a member you can Register.