20ft Fibreglass boat repairs help & advice needed

Discussion in 'Fiberglass and Composite Boat Building' started by stuee, Aug 27, 2012.

  1. stuee
    Joined: Aug 2012
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    Location: Australia

    stuee Junior Member

    Some photos of the hull cleaned up and ready for the stringers.
    from the back of the boat to the beam going across its 2.95m then the cab after that,
    how fat apart should i put the bulkheads?

    Also the photo of the slit where the previous person almost cuts through actually held water in the boat for over 24hrs and only wept but ill still glass over it and put a little matting on it.
     

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  2. stuee
    Joined: Aug 2012
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    Location: Australia

    stuee Junior Member

    hi tunnels.

    I have made custom sub boxes for a friends car a bit ago and helped a friend make a fiber box so have a fairly good understanding about glassing and how it goes.

    Im not doing any glassing till probably end of next week and we have 2 days nextweek of 30+c so it should dryout nicely.

    When i put a long straight edge under the boat and the top is seems to look sort of ok, but the traider skids seem to be about 40mm away from touching it? this could be due to the previous person setting the trailer up when it had rubbish and some water in it?

    i will check when i get home on the situation of the straightness. What would be the leniency for the hook or rocker and what problems does this cause later if its too bad?

    I will clean up around the hole as you mentioned about 100mm and glass a new strip over it.

    I will take some pick of it when i get home with the straight edge on it so you can give your opinion too.

    Thanks again.
     
  3. tunnels

    tunnels Previous Member

    ok
    Quick look and see loads of strands of glass that never been rolled down when the boat was sprayed with a chopper gun . all really bad stuff but getting there ,the gray coloured bog where the old stringers sat looks like you need to get a sharp wide chisel and see if you can get as much or it out as possible . if its not stuck its not going to do anything when you fit the new stringers and try to attach them to the hull .
    Do you know how to make bog out of just plain resin ??
    In your case for sticking things in and coving the corners TALC and AEROSILL mix is completely ok .
    Just use the plain poly resin and about 2 parts talc to 1 part aerosill . talc has guts, aerosill only thickens !!.
    The consistancy is best when you can turn the container on its side and it just starts to move but dosent slump or try to runout of the container !!
    You will need quite a bit so id mix in a plastic container some where in the 4 to 6 litre size , 1/3 fill with resin and use a baked bean tin to do the measuring of the talc and aerosill !! a battery drill and a paint stirrer add the powders slowly and stir at the same time you add them remember the consistancy !! still but not hard if you add to much powders and it gets hard to mix just add a little more resin to bring it back to a better consistancy
    After you make the bog let it sit for a couple of hours before you use it just the make sure both ingreadiance are 100% saturated with resin you will notice its stiffer than when you first mixed it When you put a blob on the surface and then remove it and the surface should have a damp or wet looking patch where the resin is on the surface . that way you get a really good bond to the surface you sticking to . when you not using the bog cover airtight or it will skin with a hard crust and is useless so make sure it airtight !!

    Ok this is important !!
    After you have cut and fitted the stringers and its ready to be stuck in make sure you have lots bracing to hold them secure in place lift the stringer out and brush a coat of catalysed resin all over the wood and let it soak in!! Dont mix the resin so it goes hard quickly beause you are defeating the object if wanting it to soak in to the wood !!.
    When its hardened a second coat specially the ends and the edges that were cut and shaped . The resin coats are to seal and help preserve the wood so it will last for long time AND give a good bonding surface for the glass and bog to stick to as you can see from the old bog thats still there its was a sad atempt at sticking the wood down . To get that amount of bog id use a plascit bag and partly fill with the catalsed bog and use it like a icing bag the cake decoraters use and pip the bog in a even and consistant thickness so it ooozes out from under the wood all the way along both sides then use that and more bog to cove the corner bothsides from end to end . Coving and being able to roll you glass into a radused corner add a lot of strength to what you are doing . makes a neat tidy job as well . so many people never cove !! coving is important and make a smooth job always it is possible to use a plastic screw off end off a cartridge and cut it so its got a big hole and put that inside the bag before you fill it with bog and you can use that to fill and do the cove all at the same time .doing the job properly is the key always and making a neat job , glassing and bogging people make a terrible mess sometimes and get overed in the stuff . if your neat and tide you dont make a mess !!
    The glassing !! what will you use and how much ?? My choce would be 2x 450gram csm and a double bias glass with a csm on one side ! the csm is easy to roll and gives a good sandwich resin layer under the bouble bias thats got a ton of strength !!. the csm on the d/b would go to the outside!! its possible to get the d/b maybe 600 gram or 800 gram in precut rolls in all differant widths the csm needs to go to the top of the stringer but the d/b just 100mm onto the hull and a good part way up the stringer is ok (Maybe 3/4 of the height or more .) your glass bond to the old glass on the hull is really important and 100mm i would strongly recomend !!
    Keep the pictures coming they are good to see what and how you doing !!
    and if we see something that you might have missed can let you know !!:D
    How fast will you be hoping for ?? what sized motor ???? :?:
     
  4. stuee
    Joined: Aug 2012
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    Location: Australia

    stuee Junior Member

    Hi tunnels.
    Ok i think i got what you was saying and when get home will digest it and repeat back for your confirmation.
    I will try a chisel out the old filler over the weekend and also need to go over all the hull with the grinder to prep it for the new glass to bond.

    Im hoping to have this done for xmas, i have all the wood and glass now so just the case of getting it all put together.
    I do have a 200 yammy to go on the back too, the boat was recommended for a 180hp but the old transom was 15mm and imm replacing with a 18mm so 200 should be fine.

    Cheers
    Stuee
     
  5. tunnels

    tunnels Previous Member

    wow 200 hp!!!!! thats one meaty motor !!!

    wow if you having that much power your transom will want to be a minimum of 50mm thick at least and really solidly put together and glassed inside and over the top etc etc with knees down to mate up with the new stringers that you are putting in and bolted together and some strong glass
    Man this thing is going to fly . yougoing to have to take that fron piece of floor out as well to check the glassing and take the stringers wau forward !!
    ok the glassing for the stringers has changed dramaticly !!
    Cut the timber for the stringers and by then i will have a revised layup for you stringer system . but will have to have extra glass under the stringer as a bedding laminate then the stringeron top and then they get glassed as well .
    Did the boat have a keel of any sort inside ?
    i cant remember !! what tanks uo going to have ??
    underfloor or just your tote tanks ??
     
  6. stuee
    Joined: Aug 2012
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    stuee Junior Member

    Hi tunnels,
    What height would you recommend for the stringers,


    the the end highest to the floor can only be 65mm, the next 166mm but the next gap to floor is 249mm and the middle to floor is 269mm, it also has no keel.

    cheers
     
  7. wooky30014
    Joined: Jun 2012
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    Location: East of Atlanta Ga

    wooky30014 Junior Member

    Tunnels, I have a question (still on my learning curve here) the bog recipe you mentioned, I understand the 2 to1 mix of talc and aerosill, then mix the resin in and let it sit in a covered container, hardener is mixed in just as you are about to use it correct ? do you measure hardener for the measured resin or to the resin/talc/aerosil mix ?
     
  8. tunnels

    tunnels Previous Member

    PLastic container !
    1/3 FILL WITH RESIN
    Use a smaller conainer big baked bean tin or simular to measure the talc and aerosill into the resin as you are slowly stirring with the paint stirrer !!
    If you just pour the talc and aerosill in and then start to mix it could be lumpy !! so mix and pour at the same time !!
    OK?

    Do not add any catalyst at all untill you are ready to us some of the mix . remember keep it covered when you not using !!

    Its easyer to use some of the premix you just made in another plastic container then add the catalyst and t thoroughly mix ,you will notice it changes color slightly so all needs to be the same colour.
    the more catalyst you add the quicker it goes hard !!it up to you what you use !!
    Your looking for a gel time of about 30 minutes!! gives you time to work with it and time to clean up etc etc for smaller mixes it can be don on a square of plywood just make a hole in the middle and pour you catalyst in there and mix with a putty knife . thorough mixing is very important or you get hard and soft patchs and or even patchs that never go hard and never will , ever !!,
    :):D:p
     
  9. tunnels

    tunnels Previous Member

    The top of the stringers will be where the floor sits on top of so use a straigh edge fron side to side and measure down the spacing apart is important to divide into equal spacing . the keel it could be just a 50mm x 75mm with a rounded top to be glassed over , if you want to be able to use the under floor space for a tank of with liftouts to place all maner of things in there . skis and ropes etc etc . or its just wasted space . if you put a tank in there it needs to be attached to the side stringers with a 25mm gap underneith NOT sitting on the hull !!!:p
     
  10. stuee
    Joined: Aug 2012
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    stuee Junior Member

    Hi Tunnels.
    Thanks heaps for all your knowledge input, i wouldn't be doing this by myself without it.


    For the stringers i cut the 2 upper ones to floor height and the 3lower one and keel one to 200mm high,

    I was thinking about the tank of making a cut out in the keel stringer to leave about 70mm thick and about 1.2m long so i can make a box shape in the floor for the tank to fit in, that way the floor is supporting the tank and not the stringers and i can also access it if any problems.

    With the transom,
    i did some measuring and i can go a max of 45mm from outer hull to when the top sits back on.
    The hull wall is 6mm thick and i will put a 18mm ply + 15mm ply, im guessing that will be more than enough for the motor.

    I still need a little info for the joining of stringers as i read that scarf joints at crap and a think of the past and now a sister joint is better? (it seems easier too )

    and a answer for the bulkheads. what is your recommended spacing for them.

    Cheers
    stuee
     
  11. tunnels

    tunnels Previous Member

    Always remember the bottom of the hull moves up and down the tringers will even bend a little so if you sit anything on the hull or what ever its needs space for the hull to move or the push from the hull goes on the tank and who knows what will happen over time!!, the tank could get stressed enought to fracture panels and you will get leaks where you really dont want them!!, like i said you will need to do some major bracing because of the size of the motor you have . !! i will do some sketchs this morning how i think you should do the bottom of the hull under the floor to the back and knees for the transom . If you not taking the stringers to there max height to lay the floors onto its ok but remember you have to support and hold the floor up one way or another !.
    Back later today !!:idea:
     
  12. tunnels

    tunnels Previous Member

    200 hp is one mean motor !!

    Ok The hull bottom !
    Under the stringers where they were and the new ones will be placed they sat inside the strakes !!
    Strakes are a weak part of any hull bottom and a place that has 3 corners on each strake ,, they bend and work and always get cracks and the glass layers separate and the first place you go looking if the boat has a leak !! along side of the strakes is also a place where like your situation you have a stringer sitting inside and just out from each side the gel coat get stress cracks if the boat hits waves and the bottom flexes each side of the strake that has a stringer inside . so Need extra glass in there yet still alow it to bend but not as much as before and distribute the bending loads over a wider area so the bending is more gradual !!
    I have drawn the extra layers of glass using double bias glass as 100% of the strands will work for you right to the line where it finishs , 200mm each side of the stringers both sides full length , No woven roving should not be used !! Its next to useless in that situation !! Same with the stringers themselves they to have Double bias glass 150mm down onto the hull so its staggered back 50mm from the First layer , never end multiple layers of glass in one place !! the edge of where all the layers end is a weack point and most likely to fatigue and break in time . The top of the stringer nees just the chopped strand mato to go up and over not the double bias the floor can be glued and screwed down though the glass . so many time when you open up a foor the glass is away fron the wood and the wood can be sinply pulled out because it has delaminated away so take the glass up and over the top and it all stays together !!
    I hope you have a good close look at what i have drawn as theres lots detail .
    wood set in bog ,
    bog is coved each side full length of the stringes and the keel ,
    the glass cone 150mm down onto the hull stepped back 50mm from the first extra layer and all way to the top of the sides of the stringer just the Chopped strand goes over .
    Like i said before this post ,coat all the wood with resin and when it hard second coat again specially any end grain .
    Dont make the resin go hard to quickly as its needs to soak in and thats what the glass will stick to !!
    Theres enought work there to keep you busy for a while . i drew in a tank just incase . Nothing is to scale it just ideas thats all !!.
    The glass panels between the strakes and the keel are the ones that take all the pounding and stress when the boat is going . slow speeds they just move up and down gently but as speed increaces the bending becomes more severe and harder !! shock loads are the dangerous ones that do the damage . A shock load is like a really hard slap one when the boat jumps and spray goes out the side a long way . When that happens just once Its time to throttle back or you could be swimming home !!
    200 hp is one mean motor !! :eek:
    I hope you took note of the transom thickness i recomeneded and it should have knees down onto the stringers !!
    next lot of details to come !!
     

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  13. stuee
    Joined: Aug 2012
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    Location: Australia

    stuee Junior Member

    Nice work...

    It makes sense now.
    like you said, that will keep me busy a little while now.

    :)

    Cheers
     
  14. tunnels

    tunnels Previous Member

    Its all common sense really , nothing to taxing to worry about !!:p;)

    Did the bog thing make sense ??:?:

    The strake thing i have done so many repairs over the years i lost out !!.
    Starts as a slow leak and gradually get worse as time goes by !! all you see outside is a few stress cracks in the gel coat but the water gets in through the cracks under pressure

    The use of bouble bias glass !!
    The way the strands are laid is what gives anything its strength!! If strands are laid across a loaded area then it get stiffer !! If it runs with the stress does absolutly nothing !!! So If you use woven roving 50% of the glass you put in is doing nothing !! so use double bias and all the strands are long and going across and carries the load each way and alows it to bend but much stiffer that it was !!

    The bigger boats we have we always glass in extra glass then fill with high density foam and glass over and then carry on with the rest of the hull . have done this for years and never ever had problems !!, strakes also the first things to get damaged if the boat hits something !!. With smaller boats when they sit on the trailer the rollers or bunks are where the strakes are most times !
     

  15. wooky30014
    Joined: Jun 2012
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    Location: East of Atlanta Ga

    wooky30014 Junior Member

    Tunnels, the bog recipe makes perfect sense now, I knew about the adding a little talc and aerosil at a time and yes absolutely a plastic container.

    On my boat it looks like I'll have to put a second set of stringers on the outer strakes and a keel board (didn't have them there before nor a keel board). Let me finish a rough sketch of how I had planned for the underfloor "frame" with the stringer location it had before so you'll see what I had in mind with "bulkheads" going in between the stringers and from the outer side of them to the outer side of the hull. I'll post a pic of what I had it down to before I moved. After the pics were taken I cut the tops off the stringers to remove all the rotten wood in them. Like I said before I'm still in the planning stages of this since putting the project on hold. And yes, I know I still have some sanding to do before getting anything mounted back in place

    And Stuee, thanks for letting piggyback a little here as I think we both have our work cut out for us :cool:
     

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