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choosing the right resin for the job

6K views 55 replies 11 participants last post by  Boatbrains 
#1 ·
I have recently been able to get my hands on a female boat mould and I and in the research stage of the "how to" on building a boat out of a mould like this

my first question is out of the 3 basic resins available on the market (polyester, vinyl ester, and epoxy) what type should I use to hand lay (laminate) fibreglass into the mould. I will be applying gel coat to the mould prior to laying the fiber and resin

I have heard that gel coat will not bond to epoxy well but again I will be using a mould where I will apply wet resin to the gel coat so I'm not sure what could be the issue here.

IF anyone could assist me in any way on making the right choice about resins I would greatly appreciate it. I am aware that the ploy resins are much cheaper than epoxy but I want a job well done and i am going to do much research about this project before I begin, I have worked with polyester before in the past to do small repairs on my other boat but still could use some assistance in picking the right resin for this application
 
#36 ·
39 hull floor +48 Sq ft hull walls. boat hull total of 97 sq ft

Back deck 14 sq ft )Will be 3 feet long starting from transom)

Front deck 16 sq ft (7 feet long)

Back bulk head 6 sq ft

Front bulk head 6 sq ft

Mid way front bulk head 4 sq ft (under front deck)

This leaves me with roughly 6.5 feet of floor space inside the hull with the back and front deck at those Lengths

Sq ft is a rough estaminet and as another member suggested having bulk heads that function as rod holders is a nice idea if I am going to make gunnle walls with decking all around the boat like a true flats boat. ( I didn’t calculate having gunnles in the sq ft)

To confirm the hull is 15 inches deep in the stern and rises to 17 at the start of the front deck (7 foot off the stern)

I am still considering having a stringer system and false floor in the area below the front and back fishing decks even though I only have 15 inches of walls

I am also considering not using gel coat and going through the proses of faring and painting after the hull is popped out but I guess that will depend on the amount of time and money I want to spend getting the mold surface as pristine as I can.

I have probably said this before but I will power this boat with a 25 hp tiller handle outboard

I also want to ad flotation foam under the back and front decks most likely
 
G
#37 ·
Ok, give me a bit to do some “cypherin” and I’ll get you a close resin estimate for the hull layup I reccomended. I’ll try to come up with a layup plan for your decks and bulkheads too just bare with me, working 40hrs a week at day job and trying to start a business wears a person out a little!
 
G
#38 ·
Ok, if your measurements and my arithmatic are correct. For the layup schedule I provided with the cored bottom, and decks...
25 gallons resin and a 5 gallon pail of gelcoat will complete the job. I provided for a little waste. Remember that layup should go...
Gel coat
Skin coat, let cure!
Lightly abbraid skin coat with 80grit
Layup rest of bottom and sides all at once, let cure!
Bond core, let cure then fair
Glass over core
Laminating/ no wax added gel on mold surface.
Add wax or duratec high gloss when spraying/ rolling inside of boat.
You will be mixing/ using a lot of resin at one time so make sure you have plenty of help and cut/ dry fit your glass before pouring the first drop of resin. Keep your overlaps at least 8” and you will have a nice strong boat.
Also, if you use wood core the estimate will go up and wood and polyester don’t do well together as has been said by many before. Hope this helps.
 
G
#41 ·
One more thing, that mold has been sitting a while and needs a lot of work. I’d put several coats of mold release on it followed by 3 fine coats of pva before doing first layup. Then after hull is pulled, another couple coats of mold release and pva again for a few hulls. After that, if hulls are pulling good you can skip the pva.
 
#42 ·
ok sounds good and now I have a good idea of what I need to start this project. Thank you for your time and calculations. The reason I don't want to use gel coat is because I'm afraid it will crack later on down the road due to the hull flex, but it would be easier to sand and paint over then fiberglass if I needed
to. I also don't have the spray system to spray gel coat into the mold and I don't want to spend the extra money on one. I can spray paint thought. I read on chrismorejohns blog that when hand laying fibers like 1708 and 1700 its very hard to get the air bubbles out and he suggest woven roving for hand layup projects.
 
G
#43 ·
The biax materials are a little more difficult but not too bad. Your hull is a very basic design without a lot of tight corners so I wouldn’t worry to much about getting the air out, you can do it. The gel coat can be rolled and brushed into the mold, no need to spray. It will be a mirror image of the inside of the mold so make the mold glass smooth, the hull will be glass smooth. As far as cracking goes, get a mil thickness gauge and keep gel around about 20 mils and you should be good there also. I don’t see much hull flex with the lam schedule I gave and your layout with the deck/ bulkhead placement.
 
G
#44 ·
Also, If Mr. Morejohn offers advice/ changes to my schedule take them. He is a great guy with a lot of knowledge. Send him an email showing the layup I proposed and ask his thoughts. He will get back with you as soon as he gets a chance. His email is on his blog if I remember correctly.
 
#45 ·
I’m currently discussing a set of plans for a new 18 footer with Chris via email. He will tell you the old hb builds & most of his poly builds were (from outside int)10oz cloth, 1.5oz chop, then either another 10oz glass or Kevlar, then 1.5oz chop, one layer of 3/4in H80, the 1.5oz chop and inner cap of 10oz. Then stringers and other reinforcements come into play at strategic areas. Just remember resin doesn’t make it strong. You want about a 35-45% resin content.
 
#46 ·
If you’re hellbent on epoxy, then wax and pva the mold, wet it out, go to a 6oz sglass,10oz kevlar, 4oz s glass then core and dual 4-6oz s glass interior. Sand it after she cured then cut/fit some h80 for bulkheads and wrap with a dual 6oz. Epoxy in, then apply epoxy fillets. (Add stringers & floor as well at this point) then pop her from the mold, flip, sand 120g, prime, sand 220, then first finish coat of awlgrip, sand to 800 and spray final top coat. She would be light. Stiff, fast, and damn near indestructible.
 
#47 ·
There sure is a whole lot of different answers for one question, some bad advice and some good advice. Im going to be honest with you, if your still relatively new to fiberglass, resurrecting a mold and building a part is not for a first timer, especially a complete hull mold. I would suggest a couple smaller mold projects first. Trust me.
Also, i still dont see how that is a mold. I believe what you have is the plug that built a mold. When laying up a hull in a mold the work is done on the inside to build a part (hull).
Lets get that figured out before even discussing laminations
 
#48 ·
The boat is a mold it comes from a old man who did fiberglass work in south Louisiana it was apparently used to lay up boats in the past but the person I got it from painted the red gel coat on the interior with brown roll on paint from a hardware store and he used it to get to his duck blind. With that being said it doesn’t have cracks from stress. It is relatively strong and the paint will pressure wash off for the most part. Yes I am a first timer and I have never done a large project like this. My extent of fiberglass knowledge is fixing cracked panels in my larger bayboat where the storage hatches are. My request for information was to get a better understanding on what exactly it would be like as for cost, time, and amount of supply’s needed. (Which where answered) I am well educated on the steps of laying up a mold now that I have had help from members on here. I have also read the book called the elements of boat building (which is a perfect book for a project like this) I appreciate everyone’s openions and what they would do for something like this. I do have a smaller project that I am about to start this summer. It’s a 14foot jonhsen type skiff. I have decided to deck this Johnsen skiff first before attempting to build a boat out of a mold or what may or may not be a mold ha. It has been a desire of mine to build a boat for quite a while now, the time I spend learning and researching on this is enjoyable to me. I am also a college student working part time and running my own lawn care and landscaping service so my boat building funds are not huge but doable!
 
#51 ·
Whether it's a mold or not, and what resin to use and what layup schedule is best are all the wrong questions. What I see is an unremarkable hull form that would require a ton of work to make into a mold, and a ton more work to pull a good hull out of that mold. At the end, after much expense and many hours of labor the result would be an unremarkable boat. There are enough of those floating around already.

The important question is: Is all this effort and cost worth the end result? Granted, the OP will learn a lot, but wouldn't the learning be better gained on a more worthwhile project?
 
G
#53 · (Edited)
As far as that all goes, many of us that have rebuilt boats know that at the end of the day we could have bought a ready to fish boat without all the sanding! It’s the experience and satisfaction of producing something from raw materials that drives some folks, not saying ya’ll are wrong... but there are a lot of folks pretty much just saying don’t do it, it’s not worth it, ect... For me, I’ve made a decent living from boat and motor repairs. If anyone wants to try to build they’re own boat, I say go for it! I’ll try to help as I can.
 
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