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Polymerman Boat Build: Temptress
After finishing the two Stringer, I discovered that the stringer Bryan and I made matches the curve of the jig, and the stringer that I made myself has less of a curve. I assume this is because I flexed the jig when I laminated with the jig perpendicular to the floor. Anyway, I now need to either fix or remake the stringer that I made myself.
Question: Should I try to Steam and Bend this Stringer (above the Glass Transition Temperature of the epoxy)? Or any other ideas how to fix this?
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For the stringer, I tried steaming and bending. But did not help much, if at all.
Now I have clamped the jig to stringer #2, and then clamped stringer #1 on top of it. As you can see in the photo, I can bend them to the same shape. I will try steaming with this configuration next.
Open to ideas.
Bob
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Thinking out side the box here, could you cut some relief cuts in bend to achieve proper curve and then fill any gaps with wood piece filler and epoxy??
The 2nd round of steaming overnight while clamped helped a lot. I am going to go with this.
Now I just need to store this clamped while it dries.
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Sorry it took me a while to reply on this one Bob. I am a bit late now but I probably wouldn't have recommend steaming as the first fix, what that's probably done is soften the epoxy and allowed you shift the laminations ever so slightly, altering the curve. Good that it's worked but I'm not sure as to the long term effect on the epoxy's strength once this has been done, I'll double check with West on this one. It probably depends on what temperature you can take the epoxy up to safely before it begins to affect it's long term properties, I don't know this off hand.
The difference is quite fixable though. The only critical edge of the stringer at this stage is the inside one, the one that fits against the jig. This is also the one that runs in the bulkhead cut outs when it comes to setting up the boat on the strongback. The other edge gets bevelled away and is dictated by the framing of the boat, lots of scrap wood there that will be removed so we don't need to worry too much about that right now.
I would consider gluing an additional lamination on this inside face, probably not the full length, just enough so you have material to cover the spring back. You could possible even taper this out with an electric hand plane to thin it down for the sections aft that don't need any extra material. Either that or it could then be cut to the correct curve internally, using the jig as a guide. I'd probably try and taper it first personally.
This is just my initial thought though, if you are ok warming and resetting the epoxy with steam then this could be an easier way to go. Overbending it may be necessary, by means of putting a block in between the jig and the lamination, just back of where you need to increase curvature, giving you extra room to overbend the curve may get you to where you need to be in the end. Let me run this by West re the temperature and get back to you on it.
There is also a third fix; the stringers can be shifted slightly, their position raised within the boat by cutting a bit of material out of the bulkhead cut outs to move them further up (when the boat's the right way up, down on the strongback of course). The extra material the stringer requires is just taken up within what you remove (or don't) when bevelling the bottoms, there should be plenty there. However these stringers want to remain even really, I'd recommend this method if you had a bit of even spring back on both of them but not for fixing one as you'll end up with a non-symmetrical pair once the boat is finished.
I'll get on to West System on Monday and let you know what they say re steaming. Either way it's all fixable!
Cheers
Dan
Hi Dan – Thank you for the thorough response. I am very curious what West System tells you about my steaming the laminate. Four points:
1) The steaming and clamping did significantly improve the bend. I agree with your idea to bed the laminate too far to let if come back to the exact shape I want.
2) If you can, ask West System “what is the glass transition temperature (Tg) of the cured epoxy. Tg is the temperature above which a non-crystalline polymer transitions from a hard glass to a soft pliable polymer. I am curious, because I want to know if the Tg is above or below 100 degrees C, the temperature of steam.
Ideally, I would have added a dry heat rather than steam.
3) Based in the chemical structure of epoxy, so do not think that steaming would alter the properties of the epoxy permanently. I think that I just need to let the laminate dry for several weeks, so that all the moisture slowly exits the wood and the cured epoxy.
4) Though it was almost 25 years ago, I have a Ph.D. in Polymer Science. My research and dissertation were on epoxy. Hence, I am Polymerman Boat Builder.😄
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Hi Bob
Apologies again for the delay as I am sure you are keen to crack on with the build. I have spoken to West System about this. The tg of this epoxy begins at around 52 degrees C or 126 degrees F but perhaps the more critical one to consider here is the HDT or heat distortion temperature, the temperature at which this epoxy's strength begins to break down long term. This is around 59 degrees C or 138 degrees F. Either way, by steaming at circa 100 degrees C, probably less for the inner most laminations, you are well above these temperatures for the West System epoxy.
If this were a smaller lamination or less critical element, maybe a deck gusset or something then I perhaps wouldn't be soo worried. Given that this is a major structural element of the boat, I think leaving it as is would be risky. The work to re make it now is quite inconvenient I am sure but if you see this begin to fail once you start using the boat, the work to replace it then would be unimaginable. Not to mention the other potential damage a stringer failure underway could cause.
The ultimate decision lies with you and more than anything else you are the guy who can grab a hold of this thing, see how it looks and determine whether you think any damage has been done. Perhaps even try peeling off one of the laminations to see if the glue line easily separates?
I think if it were me though, at this stage, I would be looking to re make the part for long term peace of mind.
Thanks Dan. This is painful, but I will probably remake it.
Good lesson learned.
Yes it's not ideal, as we would say in the UK "a bit of a shitter!"
Do you know what might have led to the increased spring back in the one stringer? Was your approach for lamination very different in the two or was the jig stressed a bit too much? I seem to remember you saying you did them in different ways.
I wouldn't want you to make another one and have the same thing happen. It is fixable but it would be better if you have a matching pair straight off the jig.
Also what thickness of laminations did you go with on these?
Yes a bit of a shitter! But we me forward. (I am doing some testing, so I will have more to report on this.
The difference between the two stringer is that I mounted the jig vertical for the first and horizontal for the 2nd. When mounted vertical, I unintentionally put flex in the jig. When I laid the jig on the floor with no flex (2nd stringer and 2nd picture) it came out perfect. So the key is to lay the jig on the floor. I used 1/2" think boards for both stringers.
See the two photos.
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Hello - I have placed the starboard side stringer. I am attaching a few pictures to get advice if the stringer is seated deep enough in the bulkheads? I measured and it is very close the the 3D model. I was expecting the bottom side of the stringer (top side on the strongback) to be closer to flush with the buldheads on the side closest to the center of the boat.
Let me know if you have any concerns, or if I should move forward....
Next step, 3-coats of epoxy on the bulkheads and place the port side stringer.
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Hi Bob, I did chuckle watching this the other day, a very appropriate music selection for this one 😁
This is looking good. There will be some excess, quite a lot in some places on the stringer, keel and the stem. This is due to the fact that the lamination stack needs to be sized to be big enough to cater for the largest section, probably around frame 2 I would think. It means that some of the frames aft will have quite a lot of excess material there. The only way round that would have been to create a partial length lamination plan for the final layer which I just thought was over complicated and had potential for leaving you short somewhere.
The main reference here is the lower (as it is at the moment, inside the boat) edge of the stringer. Its position is set by the cutouts in the bulkheads and the upper edge that will contact the hull skin is excess and will pull its shape from the framing lines as it gets bevelled later on.
So in short, yes you have it right, no need to set it in further 👍
Thank you, Dan. This helps my confidence. I will keep moving forward.
And I will have friends help me with the port side stringer. On the starboard side stringer, I mostly wanted to see if I could do it by myself. The answer is yes, just barely.
Dan - Can you tell me the:
- Model number of your Becker vacuum
- Brand of the catch pot.
- Brand of your textured plastic film
- Size of your connectors the plastic. (The parts that got clogged with epoxy.)
Ultimately, I need to determine which system to buy.
Thanks,
Bob
Dan - On the stringers, there are two lines at Frame 2. At which line do I cut off the stronger?
I cut it off at the most forward line. But I believe that I should have cut it off at the 2nd line from the from.... so that the stringer will but up to Frame 2.
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Yes, cut off at the aft line Bob, this is the aft side of frame 2 which mates to the end of the stringer. The stringer should go through the bulkhead and then meet the frame face.
For the vacuum setup, my pump is a Becker VT4.1 with a capacity of 10/12 m3/h
It was quite an expensive one but I considered it an investment for my business as it will get a lot of use. You can get much cheaper pumps that will suffice, certainly for a 1 off project. I would aim for something with around the same air volume capacity. If you wanted to push things I would imagine that would keep up with doing a whole bottom layer on a boat such as Temptress in one go. You’d need a team to get all your planking placed though!
If your pump has a smaller capacity then just reduce the area you are doing in one session. I’d probably do half a layer of planking in any one session anyway.
This is my resin catch pot: https://www.ecfibreglasssupplies.co.uk/resin-catch-pot
Breaches and fitting etc can also be found here: https://www.ecfibreglasssupplies.co.uk/vacuum-equipment
These are much the same worldwide though and won’t make too many odds if they vary slightly.
The textured film is a little more specialist, made by Pro Set and called their teak deck bagging film: https://www.marineindustrial.co.uk/catalogue/product.aspx?node_id=d496f398-44a0-43b5-86ab-a6f101166e2a&ou=%2fcatalogue%2fvacuum-bagging%2fpro-vac%2fvacuum-bagging-films%2fpro-vac-vacuum-bagging-film
I’ve only seen it sold on a 266m roll which is circa £500! There are alternative systems where by you use a breather fabric underneath a flat film which could be an option. Failing that I could roll you 10 meters or so off my roll and ship it to you if you get stuck. Let me know how you get on finding those products where you are.
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Dan - Thank you for the advice and very thorough response on the vacuum system. Greatly appreciated.
I will start researching the vacuum pump system and textured film. I will go with a lower cost pump, but hopefully the same volume.
No need for you to send me textured film, though I great appreciate the offer. If I have to buy such a large roll, you may get the remainder for Christmas 2024....
Happy Holidays.
Bob
PS - Notching the stringers is a super scary step..
Hi Dan - Do you have an estimate of the weight of Temptress? I am adding support structure to the strongback, as I do not think the MDF strongback legs are enough.
Get three questions(not urgent):
1) How much will temptress weigh (just the wood epoxy structure, excluding the engine, etc)?
2) what will the total weight be when Temptress is running in the water?
3) What is the weight of each stringer?
Thanks,
Bob
Bob
I purchased a 8 cfm dual stage pump from to oh mighty Amazon For $189.00 they now have a 12 cfm pump for $269.00 the pump that Dan has is about 7 cfm the Becker pump is a awesome unit but very $$$. I use to sell vac pumps in my last life.
Thank you Greg. I looked quickly and will spend more time investing. I really appreciate the lead. The Becker pump is quite expensive.
I will let you know my decision…. And may have more questions.
Bob