Bertram 25 Stringers - How to test if bonded well?

ktm_2000 · Post by **ktm_2000** » Jul 18th, '18, 15:42

Hi All,

It's been a long time since I've been on the site, I had an account years ago but haven't posted much any-where online in the last several years.

I have a 64 Bertram 25 and the I/Os finally put me over the edge last fall and I sold them for parts.

I am planing on converting my boat to a single 300-350hp outboard along with a doghouse in a multi-year migration. Currently it is setup as a center console with radar arch

Year 1 - gut deck, fill transom, new fuel tank, new nida-core deck, re-attach existing CC and buy new outboard, minimal cosmetics.
Year 2 - build Doghouse, buy leaning post with integrated livewell
Year 3 - paint hull sides
year 4 - paint top cap

Desired look - https://photos.app.goo.gl/p2uMZoWRzqQ54WdA8

As of now I have most of the deck out and the wood removed from the transom (the bertram folks who did that layup should be congratulated as it was rock solid and a b$tch to get out). I left the lip of the deck intact around the perimeter so I could land the new deck on it.

I'm concerned with the stringer system being bonded well, a couple of years ago I wasn't paying attention going to the vineyard and passed near the cans out side oak bluff and ran through the rip at 24 kts and hit a series of 6' waves, cut the first, launched off the second and landed mid boat on the third. There was some crunching going on but nothing visible from outside the hull.

Some folks here have mentioned that the stringers can come unbonded, and it is relatively easy to fix. Since I have the hull opened up, now's the time to address it.

How would I tell if they are not bonded? I look at the line of woven roving outboard of the stringer and can't see obvious failure

I was planing on doing 3 layers of 1708 on both the inside and outside of the stringers, if the original bond wasn't good would that thought be wasted?

deck aft of drop down out
https://photos.app.goo.gl/TEZKBbgymnf8bGkKA

Outboard of stringer
https://photos.app.goo.gl/CSW57mWzGRkrzTHb8

ktm_2000 · Post by **ktm_2000** » Jul 18th, '18, 15:52

also let me know if you can see the image, I'm not sure I shared it correctly from google photos

ktm_2000 · Post by **ktm_2000** » Jul 18th, '18, 20:06

Well I answered my own question tonight, I cut out the drop down section and found that there is about a 30" section where the stringer broke off at the flange on the port side. The starboard side seems to be ok.

New questions

Should I grind off the flange and remove it?
How should I prep the stringers? grind off gelcoat and put a 40 grit grind on it so the resin has something to hold on to?
How many layers of 1708 on both sides?

Tony Meola · Post by **Tony Meola** » Jul 18th, '18, 20:49

Are you replacing the stringers with Coosa board or something similar?

To get a good bond you will need to grind back to clean glass. I will let the experts chime in on how many layers of matt to use, but I believe you might need 3 layers. Two 1708 and one heavier.

Check out the links below to see if they answer your questions.

http://bertram31.com/proj/tips/epoxy.htm

http://bertram31.com/proj/tips/epoxy.htm
http://bertram31.com/proj/tips/hull_repair/index.html

http://bertram31.com/newbb/viewtopic.ph ... air#p47186

ktm_2000 · Post by **ktm_2000** » Jul 18th, '18, 21:23

I hope to use the original stringers and reinforce them so they are as good as new. Long run I hope to fill in the area outside of the stringers with a closed cell foam before the new deck goes down.

I've been reading posts here that others have had issues with the port side stringer and the bond between the stringer flange going bad. I'd hate to do a lot of work to add glass to the joint then have the substrate break free under the glass I put down.

I'll post pics tomorrow, my home laptop won't see any pics from my phone

ktm_2000 · Post by **ktm_2000** » Jul 19th, '18, 08:23

Here's the pics of the dammage
https://photos.app.goo.gl/dGQLpCHGwB2RSHo79

https://photos.app.goo.gl/mgvCKMz19vAEF4Yz7

It appears that the flange is bonded well, since others have had issues with this area in the past I am inclined to grind it off and layup new glass

scot · Post by **scot** » Jul 19th, '18, 12:12

6-8 layers of 1708. That will be 1/4 to 3/8" thick. The box stringers are 1/4" thick.

BTW use epoxy. That is a structural bond.

ktm_2000 · Post by **ktm_2000** » Jul 20th, '18, 10:13

Scot,
Ok, I got it on the epoxy, I have a 5 gallon kit I was planning on using to glue in new marine ply into the transom and put 4 layers of 1708 to seal it in. The balance could be used on the stringers, I'm guessing that I will need a bit more resin than what I've purchased so I will probably work on the port side stringer first then get more resin then do the starboard side which doesn't have any apparent issues.

The boat is sitting on a trailer, should I come up with some type of method on the outside to press the hull side in the 1/2" -3/4" to close in the gap prior to glassing?

Any suggestion on how to accomplish this?

Other questions, why only the port side? seems like a lot of folks only have the issue on the port side.

CamB25 · Post by **CamB25** » Jul 20th, '18, 17:58

That's bizarre. I would go forward and find the start/end of that separation.

Break out the 4.5" grinder and the 36 grit disks! Here's a picture of mine after grinding. We used one layer of 1808 glass overlappping all the way down the outside and inside of the main stringers to reinforce everything. Mine were not damaged, but I decided to build in some insurance. Here's a picture"
https://www.amazon.com/photos/share/eLv ... VYJi7ClYEk

I doubt the hull is distorted, but you could run a string line to check.

Cam

CamB25 · Post by **CamB25** » Jul 20th, '18, 18:02

You were wise to save the perimeter of the old deck. Here' s a picture of my foam outboard of the stringers
https://www.amazon.com/photos/share/Dil ... 1cxXubrvFq

ianupton · Post by **ianupton** » Jul 23rd, '18, 07:51

I always heard the the port side stringer issues are result of old twin non counter-rotating engines which will tilt you to port underway.

Possibly also because when you pass an oncoming boat port to port and go over its wake you will be stressing the port side to a greater degree.

Ian.

ktm_2000 · Post by **ktm_2000** » Jul 23rd, '18, 09:18

All the folks from the old B25 board are here

I am still taking the boat apart to figure out what is wrong + redesigning it. Friday I took a chunk out of the top cap making the area where the windshield used to be much smaller. I need to finish that to figure out where the cabin floor can be cut to. I'll post another topic on the top cap modification.

It looks like it might not rain tomorrow night so I'll probably break out the grinder as Cam has suggested and start prepping.

ktm_2000 · Post by **ktm_2000** » Jul 25th, '18, 08:45

lets just say my back hurts this morning, sanding the stringers to prep for new glass is no fun because angles of the stringers and no good place to position your body without bending over while balancing.

I got the inboard side of the port stringer done and a portion of the outboard side in a little over an hour of grinding with a 36 grit flap disk. I am impressed with the Norton disks as they move material pretty quickly.

I didn't grind the flange and the material covering it yet and I think I will need to take it off on the inside but plan on leaving it intact on the outside.

no pics, will take some after another grinding session tonight.

DanTaylorB25 · Post by **DanTaylorB25** » Jul 25th, '18, 18:05

on the 25 I have just started the port side also has some area mid ship with the stringer separating from the hull

ktm_2000 · Post by **ktm_2000** » Jul 26th, '18, 08:50

didn't get any grinding done , but here's a pic of progress
https://photos.app.goo.gl/3KFbeg47dyFPtiCu6

the flange in front of the part in front is loose and will need to be cut out and re-glassed, I'm thinking of taking out the flange the whole way and re-glassing.

as Cam has mentioned I am now thinking the hull isn't out of wack, the stringer is, If I step on it, the gap closes so maybe a few bags of concrete will hold it down while glassing

ktm_2000 · Post by **ktm_2000** » Aug 27th, '18, 08:19

In preparing to reinforce the stringers, I am looking at this section of stringer that is molded in and thinking that it will be a royal pain to glass over

what was the intended purpose? on a moppie it was under the drop-down, in other models is it used?

https://photos.app.goo.gl/ymPiFBY6BuA5b5W66

since I am reinforcing the stringers anyway, could I cut it out to make it easier to glass?

CamB25 · Post by **CamB25** » Aug 27th, '18, 09:19

I have yet to discover the purpose for that piece. I would leave it in place and glass around it, not over it. Are you glassing both sides of the stringers? I would not glass over the tops, just run strips up the sides.

Cam

Wholelife · Post by **Wholelife** » Aug 27th, '18, 09:43

Oh NO! I am currently repowering my '62 moppie with a bracket. Completely redid boat several years ago with palm beach pod and marlin tower. Volvo 3.0 ltr never ran worth a flip. Always broken down. Yanked them out and hence my ongoing project. Just finished install of stainless marine bracket. I was noticing a slapping sound on my port side midships whenever a slight chop. Does that sound familiar? I can not imagine what kind of project this will be to fix the stringer assuming that is what the noise is. Getting ready to dump some serious money into the outboards.

ktm_2000 · Post by **ktm_2000** » Aug 27th, '18, 12:23

I am glassing both sides of the stringers, I don't plan on glassing over the top but will be adding material to it to keep it the same height of the outside lip. I saved the deck that I cut out and was planing on cutting strips of it and putting it on top of the stringers. I'll have to check the height of it to see if it still works as I ground off about 1/4-3/8" of putty from the top of the stringers, I might have to do strips of 3/4 marine ply instead.

That area that we don't know the purpose is cracked as well, about 4" in from the front of that piece of material. The bottom of it is not bonded well to the boat. If I have to reinforce it, it would be a pain to glass over all the turns in the material.

The area between the stringers will be finished as a fishbox, my plan was to put 5 or more layers of 1708 from the tabing of the center stringer up to the top of the outside stringers on the inside. On the outside make the glass have equal grab on the hull as it does up the side of the stringer. It would probably be overkill but I only want to do this once.

Wholelife - the only time I noticed this was in the one instance I described earlier, I've put at least 100 hrs on the boat since that event and didn't notice it

ktm_2000 · Post by **ktm_2000** » Aug 28th, '18, 08:20

Did some more grinding last night and cut out that section. Once I cut around the perimeter the piece lifted off with no prying. I was able to grind the edge glass holding down the flange, get a chisel under the glass then pry it off. The putty was in big globs up to 1/2" thick and not bonded very well on the top but seems to be holding well to the hull. Still using a chisel I was able to cut chunks of the putty out then finished by grinding it cleanly.

It will definitely be easier to glass the whole section at one time with that section removed.

The area forward still has a line of putty and some of the glass which held down the flange, I'm going to try to go at it with a chisel to save time as that area will take about 1hr to grind clean.
https://photos.app.goo.gl/46LEiqDcAwB92DHSA

For the starboard side which remained intact, I think I am just going to grind a good surface on the existing flange and hull and glass over everything
https://photos.app.goo.gl/sZ2i99qiuH3WNm9L9

CamB25 · Post by **CamB25** » Aug 28th, '18, 09:24

Nice work!

ktm_2000 · Post by **ktm_2000** » Sep 5th, '18, 09:27

How good is good enough on preparing the glass surface for extra reinforcement?

I've been grinding most nights for an hour or so for the last couple of weeks. Right now I think I am in a good place with most of it but am struggling with the very front of the boat where the stringers go under the portion of the v-birth that I am not removing. I've cut out the little cubby hole storage bins and have ground as far as I can reach sticking a 4.5" grinder in the recesses. It seems ok on the inboard side of the stringers but the grinder doesn't fit on the outside. The very front is not un-bonded.

I would prefer to not remove any more v-birth, so is there a point of diminishing returns?

Could I just put more reinforcing glass on the area that I can access?

CamB25 · Post by **CamB25** » Sep 6th, '18, 09:56

Well...I wouldn't stress too much about. I think the key is to get the stringers secured aft. The bending forces up in the bow are minimal given the sharp bow entry. The flex in the hull is obvious in the area of your problem and back along the hull. From my memory of delamination anecdotes, I think the majority are towards the stern. I also don't think you need multiple layers of glass because the load is well distributed over a large area. More wouldn't hurt, but probably doesn't buy you added insurance. The shear strength of one layer of 1708 is probably significantly greater than the VE goop that Bertram used to set the stringers.

I didn't have any delamination issues on my boat. We used one layer of 1808 on either side of the outboard stringers. Overlapping square-ish tabs, not one long run of glass (too hard to lay up).

It's all an experiment anyway!

ktm_2000 · Post by **ktm_2000** » Sep 9th, '18, 20:17

I've had enough grinding for a while, ok, maybe for a couple of days......

I glassed the outboard side of both of the stringers and got the inside of the port stringer done saturday. It was upper 50's today with rain in the forecast for tomorrow so I didn't glass today.

Here's some pics
layup schedule for outside the stringers, 2 layers of 20" wide, 1 layer of 16" wide, 1 layer of 10" wide 1708
https://photos.app.goo.gl/DZy3gsWFD8QyHDQJ6

test fitting and trimming the glass
https://photos.app.goo.gl/4jSVvFi3vNzA16qu7

Port side
https://photos.app.goo.gl/SNmHkZntfdK3hW7Z8

starboard side - was a real pain, spent almost 1hr removing air bubbles in the area where I cut out the drain to allow water to flow inside the stringer
https://photos.app.goo.gl/ScBABRFu4duKxjuG7

Inside port - pic doesn't show it but the glass goes up 2' underneath the v-birth. This side went horribly wrong for me. I had taken a lunch break after finishing the 2 outside portions and tried to get away with using the same paint tray and roller as well as the plastic covering the layup table. I did put the paint roller in denatured alcohol and that worked ok, but the left over resin in the paint tray started to kick the new resin too fast, the wet out glass was sticking to the layup table causing the stitching to come out of the cloth dragging behind me and causing major fits until I could cut them all off. I had to re-setup my layup table with new plastic mid layup as well as throw out one 5' section of wet out cloth which kicked. The back portion was also a pain to get to sit right with all the turns. The layup schedule was 3 layers of 26" wide and one layer of 16" wide 1708
https://photos.app.goo.gl/9eyixccvBRNerZnj6

CamB25 · Post by **CamB25** » Sep 10th, '18, 08:58

Looks like it's VERY reinforced now! Ready to do battle!

In my experience it is sometimes easier to wet out the substrate with a slightly thickened patch of epoxy to fill surface irregularities. This alows the fabric to bridge these areas. Thickened just enough to stay where you want it...let it start to kick, then work with the fabrics.

ktm_2000 · Post by **ktm_2000** » Sep 10th, '18, 16:05

Cam,

I'm using a similar technique to you, I mixed the resin and then rolled it on to the parts of the hull, got out of the boat and then wet out the glass, then climbed back in and positioned the glass and removed air bubbles. While wetting out the glass, I would roll on with a epoxy safe paint roller, then use a squeegee to move the excess. Once the first layer was saturated, I'd add another so as it would suck out any excess and wet out the 2nd layer faster. When I layed out the panels I offset their lengths so there wouldn't be a consistent joint.

After I tab in the bulkheads I'm probably going to put a 5th layer in the center and 1.50z mat on top of it to make a smooth sanding surface. It is probably overkill but I don't want to mess with this ever again.

btw, do you remember how much foam you used outboard of the stringers? I foamed in another boat like you did yours and it made quite a bit of difference in the sound characteristics.

CamB25 · Post by **CamB25** » Sep 11th, '18, 09:39

I would buy 5 gallons, at least. Mix in relatively small batches. Install bulkheads around your fuel lines.

ktm_2000 · Post by **ktm_2000** » Sep 27th, '18, 08:33

I did this a little while back but forgot to post

got the starboard side done
https://photos.app.goo.gl/bDeVnzfQDvvsE5Hd6

put 4 layers of 1708 in the old battery box area
https://photos.app.goo.gl/Sk3jfLTki4P8GzQu9

Also prepped the area to fill the transom, there was a gap between the stringers and the inside hull lamination, I didn't want water to potentially migrate into the new transom core so I put a layer of glass to seal the wood and the joint.
https://photos.app.goo.gl/3jmqfDffQkjRVbh57

I've been holding off putting the transom core in until the boat was shrink-wrapped. hopefully I will get to it soon...

No pics but I've laminated 2 panels of 1" nida-core with 2 layers of 1708 on the bottom side and 1 layer of 1708 on the top side. I am going to try to laminate the other 2 deck panels this saturday

ktm_2000 · Post by **ktm_2000** » Oct 6th, '18, 15:52

I got the 1/2 of the transom core glued in today, while test fitting both pieces I noticed that I couldn't easily get at the gap around the perimeter of the first board. I wanted to make sure the gap was filled completely so I am doing it in 2 steps. I used 6 bolts to clamp everything together and will fill the holes with thickened epoxy before glassing.

Inside shot
https://photos.app.goo.gl/bdSneg7ACFTyf4Dw6

Transom clamps to spread the load of the bolts.
https://photos.app.goo.gl/bsduhCMjYgcNYfY27

ktm_2000 · Post by **ktm_2000** » Oct 6th, '18, 16:00

I also started to make the bulkheads which will go around my fuel tank. I left them tall as I will probably be putting 3/4" meranti on top of the stringers to match the height of the original deck which I left around the perimeter.

the back of the fuel tank panel was the first one I layed up in 5+ years so the quality of the laminate isn't my best work. The bulkhead isn't structural so I really don't care. I was also test fitting the board which will extend the fuel tank base in front of it.
https://photos.app.goo.gl/vyEkYt3CvNAN4e159

The front of the tank bulkhead
https://photos.app.goo.gl/G45efy3WJjMm8QAk6

Overall view
https://photos.app.goo.gl/xTKRmmwzUdumvaHU7

Hopefully I can figure out the deck height, cut the tops to size and then tab them in monday.

ktm_2000 · Post by **ktm_2000** » Oct 11th, '18, 08:14

no pics but I got the 2nd 3/4" plywood panel glued in last night

hubris definitely got me, I didn't treat the bolts with any non-stick so they were stuck into the first panel. I had to put a blow torch on each of them for about a min to heat it up to be able to get them out. I also had to re-drill the holes to open them up to put the second panel in.

I also didn't mix up enough epoxy filler to fill the perimeter gap so I will need to come back and fully fill the seams when I fill the bolt holes.

ktm_2000 · Post by **ktm_2000** » Mar 24th, '19, 17:53

resurrecting this thread as Springtime allows me to start work again. I can't wait till it gets a bit warmer, still too cold for glassing so I am trying to get any work done that I can.

I templated and made up the front bulkhead out of nida-core which has a layer of 1708 on both sides then measured out the remaining space back to the fuel tank. From the fuel tank area up to the smaller cabin is 87" so it wouldn't be practical to leave all that space for a fishbox, I had thoughts of needing to crawl under the deck in fish slime to clear out the drains so the next thoughts where to divide up the space. I put marks at 48", 60" and 66". 48" is clearly too small, and I can't decide on 60 or 66".

I made a template which fit both 60" and 66" and cut out the part out of Nidacore and here's a pic. https://photos.app.goo.gl/pqbbbiSozTcgNYMC6

Big question, what to do with the space behind the fish boxes? At 60" back as shown in the pic, there is 27" left?

I have no current need for the space, what would you do with it?

bertram31.com

Bertram 25 Stringers - How to test if bonded well?

Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

Re: Bertram 25 Stringers - How to test if bonded well?

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