Saturday, November 5, 2011

The Strongback - Advice from John Bridges

The CABBS blueprint of the strongback.
We received our plans from CABBS and started thinking about the first step to build the prams. My brother is in the process of cleaning out his garage for this project, and I haven't had a lot of time to go over the blueprints. It seems pretty clear that the first thing that needs to be done is the Strongback.

I contacted John Bridges who has been building Optimists since 1963.  I saw a post comment he made on the WoodenBoat Forum and traced that back to the work he has done with the Moraine Sailing Club
John (brown shirt) lifting a hull off the strongback.

"I first built Optimists in Trinidad back in 1963 using the plans as published in the Rudder magazine.  I think we just set up a pair of 2" x 6" timbers on the floor as a base to work from.  Since then I have built others in Chile, Colombia and Ghana.   Some where along the line I built the present strong back here in the USA  which has been used to build about a dozen Optis out of the 17 that I have helped MSC members to build. my strongback is on legs to raise the hull to a convenient height for working and avoid to much back bending. 

The first operation is to make the centre frame and two transoms.  These will have extended side pieces so that they align with the (straight and level) datum i.e. base of the strongback.   I have the cross bearer for the bow transom, bevelled so that the Bow transom can be screwed to this and it is important that the other two cross bearers are at the correct distance from the first one.

Strongback in use during one of John's group building projects.

I usually use ring shank Phosphor bronze ring shank nails to hold the plywood in place on the chines whilst the glue sets. Epoxy is messy stuff so we are usually using PL2 Construction adhesive these days. For several years we have used Lauan Plywood (Interior use but with Exterior glue) and have found that this lasts for at least 6 years without problems providing it is kept painted and stored out of the sun and rain.   

1948 Optimist Plans

It can be covered with fiberglass cloth which adds to weight and durability.  The USA made Pine plywood does not weather well.  For more permanence Marine Plywood is available for about $95 per sheet (cf 20 for Lauan) It is all a matter of, as we say in England "You pays your money and takes your choice".  (John's photos)

As we get started on this project we will be posting pictures and video of the Optimist project. We hope to create a good record of our mistakes as well as triumphs.

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