Michael Storer Boat Design 

FAQ - Can I shrink or stretch (expand or contract) an existing boat plan.

 There is a bit of a common saying round the net at the moment that it is OK to extend or shorten the length an existing boat design by 10 or 15% .

THIS IS COMPLETELY WRONG!!!!!!!!  Read more below.

Home Page - Plans, dozens of articles on building setup and sailing



Links
Boat plans sail paddle row motor fishing storerboatplans.com oz goose simple to build boat fast family boat club racer opengoose.com sailmaker inexpensive and nicely finished. Lug Gaff through to mylar sails canoe sails a specialty reallysimplesails.com


Contacting me

FAQ on Boat Building

BOAT PLANS LIST

A super simple and a classic plywood canoe how to choose ... storerboatplans.com

Goat Island Skiff, simplicity performance and stunning ... storerboatplans.com

Taal Plywood Stand Up Paddleboard SUP ... storerboatplans.com

Oz Goose simple to build, excellent performance, family or sailing club ... storerboatplans.com

Quick Canoe Electric Trolling Motor boat. Light roofrack super easy build ... storerboatplans.com

Beth sailing canoe. Quick build classic canoe with modern performance ... storerboatplans.com

Dayboat launch 23 or 27ft simple build plywood ... storerboatplans.com

Handy Punt simple to build plywood fishing boat roofrack ... storerboatplans.com

Free Paddle and Oar Plans

Free plans for Canoe and Kayak Paddles and Rowboat oars and sweeps
There is a bit of a saying hanging round the net at the moment that it is OK to extend or shrink an existing plan by 10 or 15% and it will be OK.

Or that it is OK to shrink or expand all dimensions by 10 or 15 percent.

THIS IS COMPLETELY WRONG!!!!!!!!

Here's why ...

The above statement is so completely wrong that anyone stating it and holding it to be true should wash their mouth out with cabosil.

What it should say is that an old time boatbuilder, apprenticed in the trade as a young man and now with 30 years of building boats can make the decision that such a shrinkage might be OK for a PARTICULAR hull.

Can I show you all what it does if you decrease the dimensions to 85% of the original.

Carrying capacity will go down 0.85 cubed = 0.61 - you lose 40% of the carrying capacity. - so your 14ft boat which carried one person now only carries 0.6 of a person.  Or that carries two people will only carry 1.2 people

Stability will go down 0.85 to the 4th power = 0.52 - so you lose half your stability.  So the O.6 of a person is very likely to get very wet.

And if it is a sailing boat the sail area is now 0.85 squared = 0.72.

So stability has reduced by 50% but sail area has only been reduced by 28%

Still with me!!!!

My sense is that the quote about increasing or decreasing length is a misquote.

THE ACTUAL ORIGINAL QUOTE IS SOMETHING LIKE:

THE LENGTH OF A BOAT MAY BE INCREASED BY 10 or 15% without changing the depth and beam without damaging the performance and handling of the boat and has some capacity to improve both.
Philip Bolger

And Bolger was talking about work that he was doing so he could adapt sail areas, mast positions and gear distribution.  It's not for anyone to just go ahead and do it for themselves even in the case of motorboats.

If any of you have read my article in the most recent Amateur Boatbuilder magazine - you will know exactly why I am over-emphasising this point!  

A client took it to heart with one of my Goat Island Skiff designs. It was unsailable and the client was asking me why (without telling me he had shrunk it initially).
You can read it here

So if anyone quotes that one at the top to you ... ask them how they know it is true!


View My Stats