Bonding balsa core with vinyl ester

[79hydrostream]

I'm looking for some guidance with my first boat rebuild. The boat is a 79 hydro stream V-king with a paper thin hull. I'm looking of imputs about bonding the core down with vinyl ester . I was Told by my resin suplyer that bonding with vinyl ester mixed with any additives will be to brittel ,and will eventually crack and fail, is this true ?

This is what I'm planing to do as far as lamination is concerned
1. Grind the entire inner hull with a 36-16 grit grinder
2. Clean entire hull with asitone
3 lay down 2-3 layers of 1708 or 24 ounce try axle or a combination of the two? ( overlapping along the Kiel)
4. Bed in the balsa with ??????
5. Apply 2-3 layers of 1708 or try axle over the balsa

Douse this seem right ? I'm trying to overbuild the boat because the boat may see 2-3 foot chop at times as my lake can get ruff

 

[gonzo]

Are you replacing damaged core?

 

[waikikin]

Hi Hydrostream,
Sounds like lots of glass, core materials need to be in a balances laminate outside to inside with the inside no less than 80% of the outer. Using a core bedding putty is the most reliable way to install contour balsa without the extra complexity of vacuum bagging it in, you MUST also resin prime the core surface, it's also possible to bed in wet chopstrand mat but less reliable especially on old/lumpy(?) work. Great care needs to be taken in install to get continuous and consistent bonding.
This link http://www.airexbaltekbanova.com/downloads.html
scroll down to BALTEK processing guidelines
Not sure what size your hull is but there's a lot more to hull specs than throwing bulk at the structure. The idea of cores is to minimise the amount of glass/laminate to create a weight efficient & stiff structure.

Jeff

 

[79hydrostream]

Are you replacing damaged core?

Yes I have removed all of the old core and stringers

 

[sugarloafer]

be sure to keep the balsa in low humidity environment.

balsa will wick moisture out of the air and prevent it from bonding........also it will cause it to 'potatoe chip' or curl up......this is very important!
put it in your air conditioned house, take it out only right at use time.
if it curls up you can dry it out in the AC'd house also.
when putting in balsa core, set sheet on laid over 55gal drum, wet out with resin, turn 90degrees wet out again.
the balsa blocks must be individually coated with resin all the way around.....water migration will some day ruin it if it is not sealed.
there are lots of Carvers [and others] in landfills from water ruined balsa core.
just setting balsa in putty is not enough.

also, that sounds like you are adding too much glass.

 

[79hydrostream]

Hi Hydrostream,
Sounds like lots of glass, core materials need to be in a balances laminate outside to inside with the inside no less than 80% of the outer. Using a core bedding putty is the most reliable way to install contour balsa without the extra complexity of vacuum bagging it in, you MUST also resin prime the core surface, it's also possible to bed in wet chopstrand mat but less reliable especially on old/lumpy(?) work. Great care needs to be taken in install to get continuous and consistent bonding.
This link http://www.airexbaltekbanova.com/downloads.html
scroll down to BALTEK processing guidelines
Not sure what size your hull is but there's a lot more to hull specs than throwing bulk at the structure. The idea of cores is to minimise the amount of glass/laminate to create a weight efficient & stiff structure.

Jeff

that was a great link with lots of good info

 

[sugarloafer]

guidelines can be a 'fits all' explaination.

small boats need stiff panels only with enough laminate on the outer surface to not 'dent'......and enough tensile strength on the inside to not fail on deflection.

the failure of small boat panels comes from the crushing of the core and outer skin on deflection....the tensile strength of the inner laminate is much higher than the compression strength of the foam and the outer layer.

you just need to stiffen your hull to cut down on deflection in your lake chop.

the inner laminate should be 40-50% of the outer, especially since you are coring a boat that was designed as a single skin boat.....you already have an outer skin.

i would bed the core in bonding putty right to the existing laminate, [completely sealing balsa with resin if thats your core] and glass it with two layers of 10 OZ cloth [a high tensile strength layer thats affordable.

you put too much weight in that style boat it will not perform correctly.

also remember no matter what you do, you can destroy it with improper driving.
i've seen doctors go out and crack up 54' bertrams because they do not know when to pull the handles back, as long as their beer doesn't take out their teeth, they assume the boat can handle it......head engineer at Bertram Lee Dana showed me these boats...

for instance, i'm currently building state of the art flats boats.......the hull is 3/4" 5lb core cell with an 1 1/2" OZ mat and 1 layer of 10oz on the outside and 3/4 oz mat n 1 layer 10 oz on the inside.........its a 500lb 18' boat that runs in 2-3' chop all the time......the hull IS the floor [no stringers]

 

[79hydrostream]

be sure to keep the balsa in low humidity environment.

balsa will wick moisture out of the air and prevent it from bonding........also it will cause it to 'potatoe chip' or curl up......this is very important!
put it in your air conditioned house, take it out only right at use time.
if it curls up you can dry it out in the AC'd house also.
when putting in balsa core, set sheet on laid over 55gal drum, wet out with resin, turn 90degrees wet out again.
the balsa blocks must be individually coated with resin all the way around.....water migration will some day ruin it if it is not sealed.
there are lots of Carvers [and others] in landfills from water ruined balsa core.
just setting balsa in putty is not enough.

also, that sounds like you are adding too much glass.

That's a great idea about the drum , unfortunately everything you said not to do with the balsa I have already done .however the balsa has not started to curl so I guess it would be a good idea to take it out of my basement at the cottage and bring it home to the AC .the reason i'm adding so much glass to the boat is because the boat was originally designed as a light weight race boat .the hull is only 1/8 two 3/16 inch thickness with the gelcoat which to me seems extremely thin also in areas where there is no core or wood to give support there are lots of very fine stress cracks from bow to stern along some of the lifting strakes Thankfully the cracks don't go through the gelcoat and into the laminate

 

[sugarloafer]

i still would not add much outer laminate, in fact, none.......the lifting strakes focus the deflection on themselves.
you will be surprised how much stiffer it will be with a core........it will be VERY much stiffer with a core and minimal interior laminate.......3-400%......and thats what you want.......stiffness......not strength necessarily.

i'm 70 yrs. old.........i've done this all my life.

the balsa will dry out no problem.

 

[gonzo]

How are you keeping the hull from deforming? Usually, coring and laminating the interior layer is done while it is still in the mold.

 

[79hydrostream]

i still would not add much outer laminate, in fact, none.......the lifting strakes focus the deflection on themselves.
you will be surprised how much stiffer it will be with a core........it will be VERY much stiffer with a core and minimal interior laminate.......3-400%......and thats what you want.......stiffness......not strength necessarily.

i'm 70 yrs. old.........i've done this all my life.

the balsa will dry out no problem.[/QUOT

I should start off by saying the hull doesn't have core spanning the entire beam of the bottom it stops 2 inches before the lifting strakes,also the floor is then set into the ledge of the strake. witch then creates a hard spot. So now as the cored section of the hull now deflects ,the thin flimsy hull between the edge of the core and the floor flexes which is why I'm getting the spider cracks ,also the hull above the strake with the floor bedded to it has spider Cracks running the length of the floor. There is no core after the lifting strake

 

[79hydrostream]

How are you keeping the hull from deforming? Usually, coring and laminating the interior layer is done while it is still in the mold.

I have the hull resting in a 2\4 jig that is on the trailer

 

[sugarloafer]

long as the deck is on the boat and you have supported the hull as to not change bottom configuration, Gonzo's good exception pointed out should be taken care of.

so under the floor is cored and stiff , the core stops 2" before and then the floor is glassed IN a lifting strake .......then the exposed uncored bottom is used as a 'sole' or 'floor'.

cracks are along hard spot lifting strake and in exposed bottom 'sole' up to the chine.

*****************

long as you remove the floor, core the rest of the bottom, and replace the floor you're good to go for sure.
just coring the exposed 'sole' results in a 2" uncored band around and under the floor edge....that is not acceptable.