New wood boat building question

So I am building my first wood boat and have some questions. I will start by saying there is no specs for this build because my grandfather drew the plans . I do not want to cheap it on this boat and will give a few details about it.this is a 18foot boat. The frames are 1x3 red oak 16 inches apart glued and screwed with waterproof glue and real stainless screws. The keal is white oak and transom is 3 layers of 1/2 ply epoxied together . Here are my questions/concerns

what is the difference between epoxy and polyester resin? I will be fibergalssing the whole outside and at least waterproofing the inside and painting but maybe fiberglass if inside was well

will 3/8 suffice or is 1/2 necessary for the hull

is 30hp to big? The whole inside of the boat will be pretty much empty except for a floor and maybe 2 seat in the rear

Matt or cloth for outside glassing and what are the oz differences in fiberglass mat?

how many coats of fiberglass on the outside to be legit?

do I need to fiberglass the inside to make it watertight or just resin and paint?

Are splashguards a good idea not so much for splash. It for stability?

thanks in advance I’d love to see this thread loaded with opinions and experience!

 

Well, I'm not a builder but I have done restoration and understand the importance of waterproofing. So I'll answer what I can and skip what I cannot.

Regarding epoxy versus polyester I'll post a link to a nice intro on the advantages and proper use of epoxy. The creator of the article was a prolific poster on this website and his advice was always spot on. Sadly he died in 2018 but luckily for you his work lives on. Do some reading. It will be time well spent. PARyachts: Epoxy Tips & Tricks http://paryachts.blogspot.com/p/blog-page_93.html

I always use epoxy. Always.

There are also epoxy use handbooks available for free from System Three Resins and West Systems. Do a search and you can download them and read.

Mat versus cloth? Cloth. Always. Mat has uses in laying up polyester hulls but that is not what you're doing.

How many coats of resin to be legit? That depends. I do it like this........

Without cloth: 3 coats of resin. The second applied within about 12 hours of the first and the third within 12 hours of the second. You can go a bit faster if it is hotter. The idea is to get a good chemical bond. Then 2 coats of Interlux Epoxy Prime Coat and 2 to 3 coats of Interlux Perfection finish coat.

With cloth: First 2 coats of resin as above. I set the cloth down with the third coat of resin. Properly applied the cloth will show a "weave". After the fiberglass is down apply a couple of more coats of resin, enough to fill the weave and give you a smooth surface. Apply in time to get a chemical bond. Once the surface is fair and prepped apply paint as above. This will require at least 9 total coats of resin and paint but it will be waterproof. Do the reading I mentioned and you'll come to understand that you need the film thickness the multiple epoxy coats provide in order to gain the waterproofing qualities you desire.

Do you need to fiberglass the inside of the boat? No. Fiberglassing the outside of the hull gives you abrasion resistance. You could even consider glassing the bottom of the hull and partially up the sides. I've built small prams and to keep them light just do the bottoms. This has worked out well for me.

Well, that's a start. My best advice is to spend some time at Paul Riccelli's website. There is a wealth of information there.

Best of luck and welcome to the forum.

MIA

 

Thanks for all the info it I very much appreciated! So I guess there is no way around paying about 120-150 per gallon of epoxy . Not the end of the world but certainly not ideal. So it wouldn’t even be worth fiberglassing the inside corners and gaps inside the boat? Maybe just make a epoxy pasts and roll the corners and gaps?

 

Other's with far more expertise regarding wooden hull construction will certainly weigh in. As for the cost of the resin. Epoxy is expensive but it does go on sale. I primarily use System Three and MAS Epoxy. There are many other brands out there. Look for sales. Hopefully you'll get some advise from other builders here as to what they use. Epoxy is much more expensive than polyester resins. Then again silicon bronze screws cost a lot more than stainless which is a lot more than galvanized. There is a reason.

MIA

 

I have built a couple of small boats and done repair on other older ones. Like MIA I have just glassed the bottom for abrasion resistance, and used fiberglass tape on the seams at the chine, transom and stem. I have almost always used System Three or West. I have tried some of the other less expensive epoxies and was not satisfied with them. Of course, your results may vary. As was said, use cloth. Mat has practically no structural strength and is used primarily in production boats as the first layer inside the gel coat to achieve a smooth finish. Most boatbuilders of wooden boats use cloth for it's abrasion resistance.

 

I only know the Polyester is more fragile and useful for temporary fixes, or low stress use. Epoxy is generally more expensive than resin, due to its strength and formulations requirements. Epoxy is more resistant to wearing, cracking and peeling or damage.

 

Product Listing ..Epoxies http://www.king-cart.com/cgi-bin/cart.cgi?store=epoxy&product=..Epoxies&cart_id=17449.391&user-id=&password=&exchange=&exact_match=exact
$128'for 1.5 gal. A bit better than you are thinking

 

Poly resin is much cheaper but is not generally used for bonding to wood as it is not generally considered an adhesive and will delaminate in time. For marine use, use only epoxy as it bonds better to wood. I use West but have used all the others at some point in time. For glass, it is more important to make sure that the treatment of the glass (sizing) is compatible with whatever resin you use. On you boat with flat surfaces, cloth will be best.