Q1: what is the purpose of the 8-inch circular impression on the foredeck just above the locker on my older 13-foot Boston Whaler boat?
[Moderator's note: this thread has been moved to THE GAM forum as it seeks information about the construction of a Unibond hull.]
Circular Impression in Foredeck of Older 13-footer
Re: Circular Impression in Foredeck of Older 13-footer
You are probably talking about the SPRUE HOLE. A sprue hole is an area in a mold into which the liquid material is poured and then later escapes when the mold is filled to capacity and overflows.
The process of making a Unibond hull in a Boston Whaler boat is to use the hull and the deck liner to create a mold. Into that mold a liquid material is introduced at the sprue. The liquid undergoes a chemical reaction that converts it into a solid material will a plethora of air bubbles (a closed cell foam) as the reaction continues to its equilibrium point and the new material cures into a hard solid.
In the case of Boston Whaler boats, as the foam expands and fills every part of the open area between the hull and liner, the orientation of the "mold" puts the sprue hole at the highest point, so it is the last part to fill. Typically the mold is closed at that moment, and the expansion of the foam is then stopped, so the density of the resultant foam created is kept somewhat more dense than if it were allowed to just expand against air pressure.
After all the foam has cured, any excess at the sprue hole is cut away so it is flush with the deck.
In the early days Boston Whaler hull production this foam in the sprue hole was left sitting exposed. In later production epochs the sprue opening was covered by a circular laminate section, usually attached by an adhesive. Sometimes these covers become loose and were lost.
You may benefit from reading my article that recounts a tour of the Boston Whaler factory. See
BOSTON WHALER FACTORY TOUR
Where Legends Are Made
https://continuouswave.com/whaler/reference/factory.html
The section under the head "The Unibond Hull" explains the use of the sprue hole.
The article is located in the REFERENCE section of the website. The continuousWave website contains a great deal of information outside of its forums, generally in the form or well-researched, well-written, illustrated articles. The index page for the REFERENCE section can be found at
https://continuouswave.com/whaler/reference/
There are more than one hundred articles available.
The process of making a Unibond hull in a Boston Whaler boat is to use the hull and the deck liner to create a mold. Into that mold a liquid material is introduced at the sprue. The liquid undergoes a chemical reaction that converts it into a solid material will a plethora of air bubbles (a closed cell foam) as the reaction continues to its equilibrium point and the new material cures into a hard solid.
In the case of Boston Whaler boats, as the foam expands and fills every part of the open area between the hull and liner, the orientation of the "mold" puts the sprue hole at the highest point, so it is the last part to fill. Typically the mold is closed at that moment, and the expansion of the foam is then stopped, so the density of the resultant foam created is kept somewhat more dense than if it were allowed to just expand against air pressure.
After all the foam has cured, any excess at the sprue hole is cut away so it is flush with the deck.
In the early days Boston Whaler hull production this foam in the sprue hole was left sitting exposed. In later production epochs the sprue opening was covered by a circular laminate section, usually attached by an adhesive. Sometimes these covers become loose and were lost.
You may benefit from reading my article that recounts a tour of the Boston Whaler factory. See
BOSTON WHALER FACTORY TOUR
Where Legends Are Made
https://continuouswave.com/whaler/reference/factory.html
The section under the head "The Unibond Hull" explains the use of the sprue hole.
The article is located in the REFERENCE section of the website. The continuousWave website contains a great deal of information outside of its forums, generally in the form or well-researched, well-written, illustrated articles. The index page for the REFERENCE section can be found at
https://continuouswave.com/whaler/reference/
There are more than one hundred articles available.
Re: Circular Impression in Foredeck of Older 13-footer
Jim—Interesting. Thanks for the information.