TOPIC: Fiberglass construction from scratch

I'm all about original and preserving the past as it was. But I believe I'm going to have to improve a design on my boat. I'm nearing the end of the stringer repairs and the transom. This is next before I can move to body work.

Currently

After the back seat is installed this will create a closed area to the rest of the boat but open to the elements, sight, wind on the trailer, and possible fuel from the engine. I want to close this in, accessed only by pulling up the back seat. Fuel tank will have a cap and filler neck.I want to build a splash well (is that correct terminology)
Something similar to this renken

Here's my questions:
Where do I start? Do I need to build a permanent frame then glass over it? ( what material? Marine ply, solid wood)
A temporary mold(slick sheet metal, plastic wrapped wood, something will be removed and left only with the glass)?

Attaching to the existing (black) deck seems straight forward, slip part in front of or behind and glass together. . but What is the right way to attach at a 90° angle to the transom? I want this to be structural not only cosmetic.
With the tag "Recommending" a 90hp, my 135 will be pushing it. That shelf boxing in the transom and tieing it in to the deck has got to be stronger..right?
Probably why that renken is rated for a 100hp.

What does that "recommend" tag mean anyway? If it took a 50hp to plane out, but a 150 would snatch off the back, I would recommend to you that a 100 sounded nice. Is that similar to what they had in mind? It doesn't specifically say MAX.

Just wondering.

You need to create a splashwell...

All depends on your talent as a craftsman and ability to finish fiberglass.

You could make a mold and pop out a molded fiberglass part that would minimize weight when finished, but requires you to make a mold.


You could build a frame out of plywood and simply install that into the boat and cover it glass. But that means you'll leave the plywood and its added weight in the boat.

Both ways require the new work to be blended into the existing.

I dont think the US Voast Guard was recommending a 90, it was stating that a 90 was the max allowed hp for the boat.

Several factors determine max hp, the boxing shelf, whatever that is, isnt among them.

Google USCG max capacity if you want to see the wways to calc max hp ratings.

When you say mold, do you mean a removable frame work installed to support the glass as it drys I to that shape? Or mocking up a pan to build on a bench then put in the boat?
I have a surplus of sheet metal and I used to do Industrial duct work. That could work as a lightweight flexible mold/frame that could be removed if coated with something non stick.

A main concern is how to tie into the transom. Jus glass to the new glass splashwell going to be enough?or does it need something stiffer and more substantial?

USGC Max HP rule of thumb(boats under 20') appears to be length of boat(includes the 0utboard) times Width times 2 minus 90.
(LxWx2)-90
I'm coming up with around 120HP max on mine.

While on the subject, what happens when you have twins? From my research my particular boat with the wide open trNsom would have been availble with the option. With 90 recommended, can I only hang 2 40s? What would be the advantage to twins if not horsepower? For lack of better terms, is it just for traction? Like putting a truck in 4 wheel doesn't increase HP, jus helps distribute it to the ground?

Redneck_davis wrote:

When you say mold, do you mean a removable frame work installed to support the glass as it drys I to that shape? Or mocking up a pan to build on a bench then put in the boat?
I have a surplus of sheet metal and I used to do Industrial duct work. That could work as a lightweight flexible mold/frame that could be removed if coated with something non stick.

A main concern is how to tie into the transom. Jus glass to the new glass splashwell going to be enough?or does it need something stiffer and more substantial?

You can build a mold separately and add the part to the boat after construction, or build the mold in place and remove it once completed. There are some good articles in the Research/Restoration section of this website, see the tool bar at the top of the page. Also many good video's on the subject, one source is the Jamestown Distributors video series such as;
www.totalboatshow.com/wordpress/2015/11/11/fiberglass-repair-using-gelcoat-over-epoxy/

To tie it into the transom or side walls is called "tabbing", numerous layers of fiberglass increasing in size as you go. Again, a technique that gets much easier as you get used to working with the materials. It seems a little daunting at first, but really gets to be quite fun (just my two cents) after you get used to it.

Ive looked over the research section a few times. Very helpful.
I'll have to research that "tabbing" further. . thanks for the reply