Bedding stringer question
Printed From: CorrectCraftFan.com
Category: Repairs and Maintenance
Forum Name: Boat Maintenance
Forum Discription: Discuss maintenance of your Correct Craft
URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=23135
Printed Date: November-19-2024 at 3:28pm
Topic: Bedding stringer question
Posted By: Manny
Subject: Bedding stringer question
Date Posted: August-17-2011 at 4:05am
|
I just registered in this forum, but had been reading the posts since last December when bought a 1985 2001 SN. It had been of great help. Now SN is in process of total restoration of stringers. Port side floor and secondary stringer removed. Primary stringer coming out in pieces.
My question is: what material should be use for bedding the wood stringer to the hull? Every post in this forum says to use epoxy and two layers of mat. In contrast, experts advise not to attached the wood stringer with resin to the hull because it needs a more flexible material and cushion to avoid stress fractures. I was inclined to follow CCfans recomendation until last weekend when I removed the secondary stringer and noticed there was a layer of foam aprox. 1/4 inch height sandwich between the hull and bottom side of the stringer. Even filling any voids, stress will be concentrated along the stringer. Help please. |
Replies:
Posted By: uk1979
Date Posted: August-17-2011 at 7:12am
|
Manny I would stick to what you found on here,if there is a problem it would have come up with the number of boat that have been restrung...I think you have been talking/reading old school ways.
I had dabs of foam under my old stringers too I think they used it to hold them in place while they wrapped in glass back in the day. Others will chip in with there thoughts,welcome to CCF. ------------- Lets have a go 56 Starflite 77 SN 78 SN 80 BFN |
Posted By: 8122pbrainard
Date Posted: August-17-2011 at 8:28am
|
Manny,
You need to think about the total stringer "system" more. Once the stringer is glassed up from the hull and up the sides, it becomes a ridgid system without any flex. Where are you finding this other info? That layer of foam was simply a gap filler due to CC's poor workmanship!!  ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: TRBenj
Date Posted: August-17-2011 at 11:34am
Come on now, Pete- thats not fair! Yes, the foam was used as a gap filler. The whole point is to reduce stress concentrations created by high/low points between the stringer and hull. Getting a stringer shaped perfectly to the hull is a nearly impossible task, as Im sure you know! Thats the same reason most of us are bedding with mat or thickened resin. We have the benefit of taking our sweet time when rebuilding... the factory had a pace to maintain and its not like they were cutting the stringers with a CNC machine. 
While the foam seems to be an acceptable approach, there is no question that bedding the stringers with mat or thickened resin is stronger and more rigid. This may in fact be the way to go in areas that deserve more support (like primary stringers). Pieces that dont need such rigid attachment may be candidates for lighter bedding schedules, or none at all. ------------- |
8122pbrainard wrote:Posted By: Morfoot
Date Posted: August-17-2011 at 11:46am
|
Composite 101 will tell you to use resin and microballons as a filler for your gaps and for bedding the stringer. We use this mixture to bond replacement honeycomb core to panels in place of damaged core that as taken a hit from FOD here at DAL. Very strong bond and way much better than foam! ------------- "Morfoot; He can ski. He can wakeboard.He can cook chicken.He can create his own self-named beverage, & can also apparently fly. A man of many talents."72 Mustang "Kermit",88 SN Miss Scarlett, 99 SN "Sherman" |
Posted By: 8122pbrainard
Date Posted: August-17-2011 at 11:55am
It's not as "nearly impossible" than you may think. If you really want to get close, you place carbon paper betweenthe hull and pre shaped stringer. Move the stringer around some and the carbon paper black spots will show the high spots.
BTW, carbon paper isn't easy to find anymore. The last time I got some, I had to buy a big box of it!!! ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: TRBenj
Date Posted: August-17-2011 at 12:27pm
|
Pete, clearly you have better skills (and a higher degree of OCD!) than me. If I can get the gaps down under 1/8", Im happy- the bedding can take care of the rest.
Tim, I totally agree that bedding something down with thickened resin (or even mat) is going to be much stronger than foam. Of course, its also much more rigid. Whether or not that is "better" depends on the application! In some situations, bedding a structural member will result in strength far in excess of what is required- and the decreased flexibility may be a detriment. Just something to think about. ------------- |
Posted By: JoeinNY
Date Posted: August-17-2011 at 12:47pm
|
He is not reading old information or bad information. Firmly bedding a stringer to a hull is in general bad form in boat building or composite construction in general. Relative to a flexible hull a stringer can be considered essentially rigid and some where between flexible and rigid a bunch of energy must be dissipated or it will cause problems. Some of the methods and materials described here are far from best practice.. however there are a few things that keep this from being a critical error. One.. the hull on these boats in general is very think relative to the size of the span between the supports, this creates less flex and more ability to withstand the stress concentration. Two, the foam being poured into the hull further limits the motion of the hull, making the fact that the stringer is rigid less of an issue. Three the lengthwise orientation of the stringers is perpendicular to the direction of the cyclical loads and the full bunks generally employed on trailers and lifts with these boats are helpful. I do believe that should a few of the rebuilds I have seen on here end up on a rock at somepoint the point loads would not be tolerated as well as a more flexible mounting system.. but with a foam back up even that might not be critical.
I have used foam stringers in my rebuilds so I have been less concerned about their absolute rigidity, but the vertical fiberglass walls are also a significant rigid load. I deal with this as best as I can by tapering the joint with overlapping layers of glass over 6 inch area. I have also gone to great lengths to not bed or very rigidly mount the various supports I have added perpendicular to the stringers… and certainly to keep them close enough together to limit the hull flex.. Anyway if you were building canoes, sailboats, or any craft where you were concerned about getting as much strength as possible with the weight of the materials you were using you would indeed not try to create any rigid (relatively) structures .. but with an old correctcrafts these rules are much less rigid because the boats are much smaller and more rigid. It is fallacy to declare them out of date though anyone coming through auburn I can show how firmly bedding stringers in a classic sutphen will cause some serious trouble. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: JoeinNY
Date Posted: August-17-2011 at 12:51pm
|
BTW, Sutphen didnt screw up the stringer system.. the "professionals" who were well paid to restore the boat did.. now it goes into the backlog of things for this hobbist to repair. ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1477 - 1983 Ski Nautique 2001 1967 Mustang 302 "Decoy" http://www.youtube.com/watch?v=cO5MkcBXBBs - Holeshot Video |
Posted By: uk1979
Date Posted: August-17-2011 at 4:51pm
Joe if you have time post some pictures of the problem boat it would be good to see the issues. My thinking on this is back in the day the gap was good under the stringers or filled with foam, as the stringers soaked up water through the polly they would swell stressing the glass around it till they rot and letting off the stress + us in cold part will have freezing too adding more stress. When I took my old stringers out I found places where the glass had parted from the hull along the stringers. As you point out these boats have strong hulls and thick glass so flex is not a major problem unlike other makes. The way I see it now sealed up cpes wood stringers and epoxy glass in, swelling is not going to happen (this is dependent on how well its done in the rebuild ) But if your going back with polly then a gap would be good to let any swelling over time have somewhere to go if your using wood stringers. From a UK hobbist  ------------- Lets have a go 56 Starflite 77 SN 78 SN 80 BFN |
Posted By: daddyo
Date Posted: August-17-2011 at 7:28pm
| Interesting thread for someone like me who has a stringer job in his future. So are the stringers more to support the engine and floor, the hull, or both? |
Posted By: 8122pbrainard
Date Posted: August-17-2011 at 9:05pm
It's a weight and stress distribution "system". The stringers and hull work together. ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: Manny
Date Posted: August-18-2011 at 1:20pm
|
Thanks for the replies. Still with doubts. I know that foam is not a choice. Wood stringers are more rigid than fiberglass hull. Boat will not be use in lake. I live in the south side in Puerto Rico and from the marina to the ski spot, it is open sea, so you can experience high seas.
For the info not recommending bedding stringers to the hull, see: www.yachtsurvey.com/HullFailPart2.htm. and www.masepoxies.com/video/Replacing_Stringers.htm/. This last video, is also available in Jamestown Dist., go to Mas Epoxies How to: Stringers |
Posted By: uk 1979 part2
Date Posted: August-18-2011 at 7:02pm
|
Manny, if your boat has spent most of its life in salt water you may find the stringers are good just some rot on the floor side where the rain has been,they will be wet and all fixings will be bad but salt water soaked wood will not rot like fresh water soaked stringers.
Here is a pic of mine over 30 years old but used in salty water  ------------- lets have a go 2 |
Posted By: 8122pbrainard
Date Posted: August-18-2011 at 7:48pm
|
Roger,
You never cease to amaze me!! Man, you are more OCD than I am!! But, I also feel you may have more free time available than I do!! ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
Posted By: uk 1979 part2
Date Posted: August-18-2011 at 8:13pm
Pete when I have one of my boats finished and it comes somewhere close to your CC I might just match you on the OCD top table ------------- lets have a go 2 |
Posted By: Manny
Date Posted: August-19-2011 at 6:13am
| I wish mine were like yours, at least port side. Primary Stringer port side is completly rotten, is coming out in flackes. Secondary was not that bad, but not close to yours. If salt water doesn't rot wood, it was fresh water from washing the boat and rain. Starboard side doesn't seems to be that bad. I will find out this weekend. Hopefully, I may use starboard stringer as template. Did you set (bond) the stringers to the hull with epoxy and cloth? |
Posted By: uk 1979 part2
Date Posted: August-19-2011 at 2:23pm
Manny sorry to hear you have no luck with your old stringers, its mostly cold here so wet wood tends to stay wet............I guess it’s much hotter in your neck of the woods, as for bonding stringers to the hull I can’t help you on wood as I used Glass fibre sheet and fabbed up mine, as at the time it’s all I could find here ,Joe and Tim have used Cooser Board as a core in there builds, which is much better than my way as the weight is much less. Joe showed me some at GL so I can see what I miss out on living in the UK 
The way I see it using wood the key thing is to seal it up well with CPES if you can leave the wood out in the sun to warm up but keep turning it to warm all round then coat with CPES it will help to penetrate deeper, as for bonding the underside of stringers to the hull it’s your call........ to me the stringers are not that wide and epoxy mat ,cloth , and most fillers all give epoxy a bit more flex but also seal the hull stopping water hydroscopic into that area keeping it all nice and dry, each side will be flared then bonded with cloth build up again it’s your call if you won’t to add biax too. The sides will be in as one to the hull so the gap of 1’1/4 on the main and ¾ on secondary is small along with a thick hulled small boat everything works out, yes if you pin point load the hull in some way a problem may occur but it will on a unbonded stringer boat too just down to luck. If you won’t to try something different and bed the stringers in you could use 3m 5200 but I think it’s Polly based so will not bond that well to CPES/epoxy or bed using 3m 2216 B/A flexible epoxy, whatever way you go it will be superior to the way it has been for most of its life. Keep us updated on your build, Pictures please lots to read up on here and share your findings with us. This is how thick a 77 SN hull is around the drain hole,13.25mm Cheers Roger. 
 ------------- lets have a go 2 |
Posted By: Manny
Date Posted: September-10-2011 at 4:32am
|
Roger, thanks for your advise. Tomorrow, I expect to resumed restoration work after a brief pause. Knowing the CCFs, critics against, I haven't tell that I will use poly resin, instead of epoxy. The only place I know selling epoxy In Puerto Rico is West Marine, it is too expensive and they only have 1 gallon buckets. Further removal of the stringers revealed, not just foam between stringer and hull, also traces of poly. It seems that the poly just flowed underneath the stringer, not put there intentionally. I'm planning to set the stringer over few plies of tape and fill any void.
I'm struggling in how keep in place the stringer while resin dries. I'm planning to make like a wood brace to keep the stringer from moving. Any recomendation. I will try to post pictures, but first I need to review the other posts and instruction to learn how to do it. |
Posted By: uk1979
Date Posted: September-10-2011 at 11:13am
|
Hi Manny, yes its a real pain for us living outside the USA getting supplies at good rates,may be worth dropping a line to US composites to see how much to buy and ship everything you need,but as always need to check how much import tax your Gov adds on, here its + 20% on personal import.
If they don't ship I have used http://www.ipsparcel.com/ - IPS they will pick up and ship to you and can give you a US post address so you can buy from number of suppliers they will pack them all up at there hub then ship to you,and you fill out the shipping doc's online and send to the supplier to print off and stick on the box
But if Poly is your only way you need to seal your wood with something other than CEPS as its not a good poly to epoxy I would look at a Pre-Cat or AC sealer for Poly. As for setting the stringers in look at the old glass where it meets the hull once you have ground off the gel as one of the guys said it needs to be like a honey colour, some here have left the bottom 1/4 inch on the hull to give you channels to lay the new into or just leave tabs at each end and 1 or 2 along the stringers to line up the new then as you say brace the tops so there upright some weight on them to set is good but don't go overboard with it,we do like to see new things used so far its been kitchen sink to beer packs ------------- Lets have a go 56 Starflite 77 SN 78 SN 80 BFN |
Posted By: BuffaloBFN
Date Posted: September-11-2011 at 1:27am
|
At least on my boat, the factory bedding and filleting had dry spots that were full of dirt and oil so that leaving the 1/4" or even tabs was impossible. I cut back to the glass from the mold and that made a good surface for the stringer to match to. I did my best to make my fir stringers a part of the hull rather than just glued to it. I think it's key to do the entire lay-up of a main in 1 step so that everything is chemically bonded as well as mechanically(glued) attached.
Tech tip-don't cut the width of your stringer until you have the bottom mated. For keeping them in place, we've seen some nice notch jigs made here. What I did was reliable, but not as fancy. ------------- http://correctcraftfan.com/diaries/details.asp?ID=2331&sort=&pagenum=12&yrstart=1986&yrend=1990" rel="nofollow - 1988 BFN-sold "It's a Livin' Thing...What a Terrible Thing to Lose" ELO |
Posted By: Manny
Date Posted: September-12-2011 at 3:34am
|
I knew sanding down would be a messy task, but wiith 90+ F temperature, I was exhausted and it was only the port secondary stringer. After all that labor, I'm re-thinking usimg epoxy, not poly. I ordered the cloth to US Composites, so I will call them for resin quote.
My doubt with poly is if after encapsulating the wood with cloth and resin, does humidity builts inside or it just absorbs water. If the problem is that absorbs water, does a final coating of epoxy over the poly solve the problem. In this forum, there is a materials list which says: 5 gallon 3:1(medium) + another 5 galon of 4:1(fast), total 10 gallon. Does the stringer rebuild, including the floor, takes 10 gallon? Why not using resin 2:1 (slow)? Greg, thanks for your tech tip. I did just that. Also, I did a jig. I will look for those nice notch and reliable jigs. |
Posted By: uk1979
Date Posted: September-12-2011 at 7:37am
Manny, your thinking is right on absorption,but not only will it come from inside the boat through the bilge gel/poly but from out side the hull all be it very small along with no CEPS to seal the new stringers as it will not stick with poly it will start the same cycle you have now, may be a bit slower as I think today's Poly may be slightly better, if you go back with all Epoxy it should be set for good and will not let moisture through if done correctly. Keep reading all the builds on here lots of great info,one way to do the change over is to work your way across the boat setting 1 stringer at a time and using the old to brace using ply with slots in that fit snug over old and new, this helps keep the hull shape as a SN will flex a good bit, more if your big boned like me also good to have the hull up on stands not just on the trailer bunks.
Yes 10 US gallons is what you need,as for speed check with US composites as it sounds hot were you are and it will speed the kick time up if its very hot. How about some pictures of the build easier to see what your up to. ------------- Lets have a go 56 Starflite 77 SN 78 SN 80 BFN |