A fellow who built one of the GISs wanted to shrink the boat because of limited building space and that someone gave the poor fellow the advice that …
“Generally it is OK to shrink a boat by a factor of 10 or 15%”
So my customer went ahead only to find out that this is really, REALLY bad advice.
Also the sailmaker changed the sailplan a bit – but didn’t bother to decrease the sail area for the much shorter and less stable boat.
The poor builder had a terrible time trying to make the boat work.
In the end I reviewed the situation and made some relatively simple suggestions about getting it all to work OK.
Just a bit too frequently lately I’ve read various postings on the net along the line of:
“Generally it is OK to increase or decrease the length of a boat by 10 or 15%”
It is bad advice for a motor boat and really, really bad advice for a sailing boat.
How does the person making the claim know how close the designer has gone to the limit on a particular boat? And will that line be crossed with the change.
Also are they allowing for the different relationships of the parts as in a sailing boat. Centres of effort, gravity, buoyancy, lateral resistance.
Do they know that by reducing the size of a boat by 15% all round the stability is reduced to 50% of the original?
So I’ve added three things to my webpage.
1/ A preamble to the problem
2/ An actual case study of someone who built one of my Goat Island Skiff (GIS) designs but changed a number of things because someone advised that it is “an OK” thing to do.
3/ Some advice about how to make the changes more safely in some boats.
The articles are here on my FAQ article
Some experts deserve a big kick up the bum.
And that is the end of my rant!