# choosing the right resin for the job



## jacques lemaire (Apr 17, 2018)

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


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## No Bait / Lures Only (Apr 10, 2011)

Little to no fumes with epoxy also more flexible. You can purchase different curing time/temperature hardners with epoxy. My latest repair/refurbish job was on a 20 year old polyester resin skiff/pirogue 13'-6 x 45". Repaired the rollover gunnels as were cracked thru in 7 locations. Used 1708 biaxel 6" wide tape, also rebuilt transom with 1/2" coosa boar reinforcement and layered 1708 under and over. Worked great very strong. How big of a boat is the mold?


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## Fishshoot (Oct 26, 2017)

I bet you could reach out to morejohn on this one. Or even see if he has something posted on his blog already. He has probably forgotten more than most of us know in regards to skiff building.


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## jacques lemaire (Apr 17, 2018)

No Bait / Lures Only said:


> Little to no fumes with epoxy also more flexible. You can purchase different curing time/temperature hardners with epoxy. My latest repair/refurbish job was on a 20 year old polyester resin skiff/pirogue 13'-6 x 45". Repaired the rollover gunnels as were cracked thru in 7 locations. Used 1708 biaxel 6" wide tape, also rebuilt transom with 1/2" coosa boar reinforcement and layered 1708 under and over. Worked great very strong. How big of a boat is the mold?


The mold is 17 feet long with a beam of 56 inches it’s some what similar to a gladesmen in the shape


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## jacques lemaire (Apr 17, 2018)

Fishshoot said:


> I bet you could reach out to morejohn on this one. Or even see if he has something posted on his blog already. He has probably forgotten more than most of us know in regards to skiff building.


I’m new to this forum thing. How would I go about doing that ?


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## DuckNut (Apr 3, 2009)

There are many people who will tell you to use epoxy, but there is a reason that there is like 2 manufacturers who build boats with it and then it is vacuum infused. Epoxies place is in repair.

Vinylester is what boats are being built with. Roller the gelcoat on and then start the layup.

There is a website www.boatdesign.net and those guys can give you the layup schedule for the whole build.


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## Fishshoot (Oct 26, 2017)

http://chrismorejohn.blogspot.com/?m=1

He is also on here you might be able to pm him.


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## DuckNut (Apr 3, 2009)

Fishshoot said:


> http://chrismorejohn.blogspot.com/?m=1
> 
> He is also on here you might be able to pm him.


I think he is sailing for the next couple of months. A response may be slow coming.


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## jacques lemaire (Apr 17, 2018)

I would like to lay up this mold with solid fiberglass and no core for the hull. I have been doing some research on this and I also purchased a book called the elements of fiberglass strength to get a better understanding of the lamination schedule since it changes from hull to hull and also depends on what the boat will be used for. I understand that the transom will need a core and I fully intend to use a core for that part but as for the rest of the hull I am leaning toward solid glass. Is there anything wrong with this as long as I have a proper glass thickness?
I guess what I'm trying to do is something like a gheeno hull where its all fiberglass.


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## yobata (Jul 14, 2015)

jacques lemaire said:


> I would like to lay up this mold with solid fiberglass and no core for the hull. I have been doing some research on this and I also purchased a book called the elements of fiberglass strength to get a better understanding of the lamination schedule since it changes from hull to hull and also depends on what the boat will be used for. I understand that the transom will need a core and I fully intend to use a core for that part but as for the rest of the hull I am leaning toward solid glass. Is there anything wrong with this as long as I have a proper glass thickness?
> I guess what I'm trying to do is something like a gheeno hull where its all fiberglass.


There is nothing "wrong" with using fiberglass without core, but there are disadvantages. Core is used to give the laminate strength, without it, you will have to use more fiberglass and resin usually resulting in more expense and (maybe more importantly for shallow water boats) more weight. Can you take a photo of the boat mold and post some dimensions?


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## jacques lemaire (Apr 17, 2018)

Here are some pictures of the mold. It will all be sanded and resurfaced before I start the layup. It’s in good shape but the guy who had it before me painted it. It’s about 17 feet long and Has a beam of 56 inches I believe. The sides are not very high at all, probably about 15 inches tall. I don’t have exact measurements right now of this since I am not home. The bottom of the hull is completely flat and come to a small v in the front. I plan to power the boat with a 25 hp outboard and as for a deck I will deal with that once I figure out what I need to do with the hull.
the mold is almost like an oversized pieroue


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## DuckNut (Apr 3, 2009)

I don't see a mold, I see a stripped boat hull. If that is truly a mold there is a tremendous amount of work ahead before you can use it as such.

Back to your question. If you use just glass you will have a flimsy hull just like the Gheenoe. Every wave you hit will flex the hull. Sure, it can be done but you would be better off laying down some glass and using a 1/2" core of some sort.


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## jacques lemaire (Apr 17, 2018)

It has red gel coat under the rolled on brown paint that you see in the pictures. I know it looks like a stripped boat hull but its half an inch thick of fiberglass and one inch thick in some places. It weighs about 700 pounds as it sits and that's not an exaggeration. There is no flex in the structure walls. I will brace the mold before I use it.

this is basically a one off project and i don't expect to pull a hull out of the mold that will be free of flaws. Im fine with fairing and sanding it after


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## RunningOnEmpty (Jun 20, 2015)

jacques lemaire said:


> I would like to lay up this mold with solid fiberglass and no core for the hull. I have been doing some research on this and I also purchased a book called the elements of fiberglass strength to get a better understanding of the lamination schedule since it changes from hull to hull and also depends on what the boat will be used for. I understand that the transom will need a core and I fully intend to use a core for that part but as for the rest of the hull I am leaning toward solid glass. Is there anything wrong with this as long as I have a proper glass thickness?
> I guess what I'm trying to do is something like a gheeno hull where its all fiberglass.


Boats built without a foam core are much more durable. The only downside is some extra weight.


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## Guest (Apr 27, 2018)

Ok, I’ll take a stab too. If I were doing it for a single hull and for my own use I’d probably just use polyester. My boats are never left in the water for more than a day. Polyester resin has been used in a lot of boats that have lasted 40-50 years. Nothing wrong with it, just know it’s limitations and you’ll be fine. If it’s gonna be in a wet slip then do skin coat in vinylester and you should be fine, many manufacturers do this. If money is no problem then vinylester throughout. As far as layup goes, core would be best but you can add stringers and subfloor to stiffen it up too.


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## Guest (Apr 27, 2018)

After looking at pics closer, here are my thoights. In order to have any freeboard I’d go with a 1” core. Here is how I’d lay it up.
Bottom and transom
3/4oz csm in VE allow to kick
3/4oz csm in pe
1700 -45/+45
3/4oz csm
1700 0/90
3/4oz csm
Core board
3/4oz csm
1700 0-90
3/4oz csm
1700 -45/+45
3/4oz csm

Sides
The skin of 3/4oz csm plus
3/4oz csm
1700 -45/+46
3/4oz csm
1700 0/90
3/4oz csm
Layup hull bottom and sides allow to kick, set core in bonding putty of your choice (i’d probably set in 3oz csm and weigh or vaccuum down)
After core is bonded follow with final five glass layers. You’ll need to add some stiffeners in the gunnels, “good job for rod holders to double as”.
Lay up will be around 1/8” thick on the sides and around 11/4 thick on bottom with core. You will need a couple bulkheads fore/aft to prevent twisting. These can be in form of seats, deck suppots, bow storage, ect... as long as they go from side to side and reach the floor.


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## Guest (Apr 27, 2018)

One more thing, overlap your joints 8”-10” The more overlap the stronger the bond.


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## jacques lemaire (Apr 17, 2018)

I looked at plastics honeycomb to use as a core. Would that be sufficient for this project? http://www.carbon-core.com/store/product-category/honeycomb/


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## jacques lemaire (Apr 17, 2018)

Also could someone give me an approximate amount of resin that would be needed ?


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## Guest (Apr 27, 2018)

The honeycomb should not be used to core a hull bottom. Use one of the many foam cores. If you can calculate the sq ft of the layup, I can get you close as far as resin amount goes. I can get you gelcoat amounts too. Let me know


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## jacques lemaire (Apr 17, 2018)

The sq ft of the lay up would = the Sq ft of the mold Xs the layers of glass right ?


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## Guest (Apr 27, 2018)

Sq ft of mold, sq ft of deck/seats, bulk heads, plus sq ft of the cored area on bottom of hull. I’ll give you resin amounts for the layup schedule I posted. Or if you have another layup schedule, I can estimatethat as well.


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## jacques lemaire (Apr 17, 2018)

Ok I’ll get this measurement when I get a chance. I am away for the next 2 days. Thank you for all of your help so far!


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## DuckNut (Apr 3, 2009)

Boatbrains said:


> After looking at pics closer, here are my thoights. In order to have any freeboard I’d go with a 1” core. Here is how I’d lay it up.
> Bottom and transom
> 3/4oz csm in VE allow to kick
> 3/4oz csm in pe
> ...



Thank you for the clarification. The mold looks like a stumpknocker and those were built by a chopper gun. Yours is going to be a tank. Bonding the core down you can buy bonding putty or use a notched trowel and spread epoxy peanut butter and weigh it down.


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## Guest (Apr 27, 2018)

Good eye Ducknut, it does look like a stumpknocker! That very flat bottom is why I reccomended that layup schedule and the 1” core. It should weigh about the same as a chopper built hull “maybe lighter” but will be 4 times as strong with a whole lot less spider cracking down the rd if built right.


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## Guest (Apr 27, 2018)

Ducknut, I have had good success in new builds just bonding core in 3oz wetout csm also. Just cut mat to size. Wet out, roll out air, using cinder blocks as weight over a sheet of plywood, allow to cure, fair in core and glass over. Never been a big fan of putties as I’ve seen a lot of different cores with cracked boding putty under them. Again, my way works best when doing a whole build when you can bond the core as soon as the hull layup kicks, makes a true one piece product.


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## jacques lemaire (Apr 17, 2018)

would you stay away from brushable gel coats ?


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## Guest (Apr 27, 2018)

Use no wax gelcoat in the mold, you will be glassing over the gelcoat in the mold and the wax will rise to the surface causing bonding issues with the gelcoat and skin coat. You can purchase a wax additive or duratech high gloss additive to mix in with the same gelcoat for the inside of the hull. I never buy any gel with wax already added.


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## Guest (Apr 27, 2018)

Jacques, the second best advice I think I can give you is this... get about 2-3 guys together that want a boat like you have and buy in bulk. I pay right at $800 for 55gal pe resin. Big price break from 1&5 gal pails. But I use it also. I buy fg in rolls not yds, again a signifigant price break.


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## predacious (Sep 1, 2016)

Boatbrains said:


> Use no wax gelcoat in the mold, you will be glassing over the gelcoat in the mold and the wax will rise to the surface causing bonding issues with the gelcoat and skin coat. You can purchase a wax additive or duratech high gloss additive to mix in with the same gelcoat for the inside of the hull. I never buy any gel with wax already added.



correct - laminating gel,when working in a mold...


the gentleman that suggested epoxy with a thickener/adhesive additive - epoxy means you need to either complete all the repairs/laminating with epoxy,or you will need a separation coat.NOTE: chopped strand matt isn't compatable with epoxies...


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## predacious (Sep 1, 2016)

Boatbrains said:


> Ducknut, I have had good success in new builds just bonding core in 3oz wetout csm also. Just cut mat to size. Wet out, roll out air, using cinder blocks as weight over a sheet of plywood, allow to cure, fair in core and glass over. Never been a big fan of putties as I’ve seen a lot of different cores with cracked boding putty under them. Again, my way works best when doing a whole build when you can bond the core as soon as the hull layup kicks, makes a true one piece product.


weight works,when the surface is flat - if the surface isn't flat,as in horizontal,weight doesn't work very well.clamping and wedges work well,when building a boat in a mold,laminating core,composite cores,with matt...

laminating wood with chopped strand matt and polyester resins - not the best approach,there's much better ways...

polyester based putties are brittle...


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## Guest (Apr 29, 2018)

Yes, you are correct about the weights. I prefer a vaccuum bag over everything else. If you look at his mold it resembles an old Stumpknocker and is about as flat of a bottom as one can get.


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## predacious (Sep 1, 2016)

Boatbrains said:


> Yes, you are correct about the weights. I prefer a vaccuum bag over everything else. If you look at his mold it resembles an old Stumpknocker and is about as flat of a bottom as one can get.


vacuum bagging is always the best approach - it assures no voids...

I didn't look at the whole thread,he's coring the bottom of the hull ??


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## predacious (Sep 1, 2016)

no need for a core on the hull's bottom - stringers and bulkheads - these will stiffen the hulls,as well as provide a platform for the interior deck to sit on...

honeycomb core - formally known as "nidacore",these are used by a whole lot of boat mfgs,as coring for hull sides,and decking...

me - I would run stringers from coosa board and bulkheads from coosa as well - bond these to the hull and glass with 1708.

another option is to make "boxes" out of glass - cut them in half,glass to the hull and fill them with a 2 part closed cell foam - glass over the "blow out holes when the foam kicks - that's the lightest way,and will provide a strong backbone to the hull.run bulkheads,crosswise,glassed to the hull and the "stringers" you made up - nothing wrong with that...drawback is,it's a little time consuming 

always more than one way to do something....


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## Guest (Apr 29, 2018)

He only has about 15” of freeboard as it sits, add stringers and floor and he’s got even less. That’s why I reccomended a cored bottom with a 1” core. That thickness should prevent hull flex with his 25 he plans on running. I prefer stringers myself but with that flat bottom and short sides I say core it.


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## jacques lemaire (Apr 17, 2018)

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


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## Guest (Apr 30, 2018)

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!


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## Guest (May 1, 2018)

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.


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## Guest (May 1, 2018)

And if anyone else is interested, the formula for paint/ gel coat coverage estimating goes as follows...
Sf to be covered x thickness in mils divided by 1604. 
A gallon of liquid will usually cover 1604sf at 1 mil thick.


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## Guest (May 1, 2018)

If you go the rt of stringers and sub floor the hull core will not be needed, nor the glass over top of the core. The amounts will change, but only slightly.


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## Guest (May 1, 2018)

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.


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## jacques lemaire (Apr 17, 2018)

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.


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## Guest (May 1, 2018)

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.


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## Guest (May 1, 2018)

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.


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## Rick hambric (Jun 24, 2017)

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.


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## Rick hambric (Jun 24, 2017)

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.


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## Cut Runner (Jan 25, 2017)

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


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## jacques lemaire (Apr 17, 2018)

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!


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## Guest (May 4, 2018)

I just got in a 15ish ft Stumpknocker for a transom job. This hull has a 1/2” cored bottom and three bench seats. The core is factory.


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## yobata (Jul 14, 2015)

jacques lemaire said:


> 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!


I think its a great idea to start with a re-build of the 14' johnsen first. You will learn a lot!


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## Vertigo (Jun 3, 2012)

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?


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## Rick hambric (Jun 24, 2017)

very good point @Vertigo , he could buy a set of conchfish plans for $300 and build a nice 16-18ft skiff for 4500.00 +-


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## Guest (May 4, 2018)

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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## Monty (Jan 10, 2018)

My brother ruined a nice boat hull trying to make a mold. Didn't apply enough wax and release agent. I know you have a mold. Buy a 55 gallon drum of polyester resin.


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## jacques lemaire (Apr 17, 2018)

Monty said:


> My brother ruined a nice boat hull trying to make a mold. Didn't apply enough wax and release agent. I know you have a mold. Buy a 55 gallon drum of polyester resin.


Now that had to be one expensive mistake! I will start my deck over project this month on my 14-foot skiff. I will make a new thread for it.


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## Guest (May 10, 2018)

Looking forward to the build Jacques


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