Question re: Rudder Shelf Replacement

[JohnV8r]

Is there any reason why I could not use 1.5" or 2" Coosa Bluewater 26 for a replacement rudder shelf as opposed to building a composite shelf per Capt. Patrick's building tips? I'm just wondering if there is anything inherently stronger with vacuum bagging smaller 1/2" Coosa Bluewater 26 versus off the shelf Coosa board in a thickness that is equal to or thicker than the thickness of the built out composite board in the building tips.

Thanks in advance!

[CaptPatrick]

John,

Using Coosa Board in lieu of plywood is perfectly acceptable. Use the same construction technique, 2 outer fiberglass skins over 2 pieces of Coosa separated by a layer of fiberglass. All three layers of glass should be 1208 or 1708 biaxle. edges can be a couple of layers of 1 1/2 oz mat. A final layer of 1 1/2 oz mat over the top will give you a fairly smooth surface ready for fairing.

[Rick Kral]

Hello Cpt.,
I don't want to step on Johns post but i was curious if you had a similar problem/experience. Your response may help with Johns lay up. I have noticed when working with Coosa that bonding 2 sheets together is more difficult than it appears. Coosa comes through with a hard flat surface face. Obviously, Coosa does not have a poorus surface similar to plywood that allows the expoxy to get an agressive bond. There are some voids in the Coosa surface but those are random. I have found that i have to use a heavy (50) grit paper to really scuff up the bonding surfaces when layering Coosa. I realized this after i drilled out my rudder deck (fabricated with Coosa). I was able to break appart the core between the lay up with my hands. It appeared as though the epoxy was not able to penetrate the Coosa and where it did the surface was easily ripped away (shallow penetration). I did use a slow cure West system Epoxy and 1708 biaxle between the sheets of Coosa.

Thank you,
Rick Kral

[JohnV8r]

I just sent an email to Coosa Composites and asked them to review this thread and provide some feedback. Let's see what they come back with.

[CaptPatrick]

Hello Cpt.,
I don't want to step on Johns post but i was curious if you had a similar problem/experience. Your response may help with Johns lay up. I have noticed when working with Coosa that bonding 2 sheets together is more difficult than it appears. Coosa comes through with a hard flat surface face. Obviously, Coosa does not have a poorus surface similar to plywood that allows the expoxy to get an agressive bond. There are some voids in the Coosa surface but those are random. I have found that i have to use a heavy (50) grit paper to really scuff up the bonding surfaces when layering Coosa. I realized this after i drilled out my rudder deck (fabricated with Coosa). I was able to break appart the core between the lay up with my hands. It appeared as though the epoxy was not able to penetrate the Coosa and where it did the surface was easily ripped away (shallow penetration). I did use a slow cure West system Epoxy and 1708 biaxle between the sheets of Coosa.

Thank you,
Rick Kral

Rick,

Depending on the thickness of the Coosa Board, one side may have a slick pebbly surface, be deep black in color as opposed to the dark charcoal gray of a milled surface. This black surface was either the top or bottom and in contact with the platens used to press the sheet. There was a mold release used to keep the sheet from sticking to the platen, and must be sanded away before a bond can be made.

For larger pieces, a portable belt sander with 80 grit should knock that slick surface down nicely. After any necessary sanding, additional tooth can be developed with a hand saw by dragging the blade sideways across the Coosa surface to leave a slightly grooved surface.

Another technique to improve the resin bond is to prime the surfaces with un-thickened catalyzed resin. Wipe away excess resin with a clean rag and allow the resin to gel until tacky. Then do the layup with the glass, making sure to wet it out well and roll out all bubbles. Lay the second primed sheet onto the lay up and either weigh it down well or vacuum bag it. (Generally, I prefer weighing down rather than bagging...)

Added delamination strength can also be had by running a grid pattern of screws with a spacing of about 10" between screws. Since these screws will be totally glassed over, it's not necessary to use stainless screws.

Now, round over the top edges to about a 3/4" radius, smooth down the radius with sand paper, and prime the top surface and edges, and allow the resin to tack up. Lay up the fiberglass and let drape all the way over the edges. Once that surface has cured, turn the work over, trim up the excess fiberglass, and round over the edges. Lay up the bottom side, again allowing the glass to drape completely over the edges. This will give you two layers of glass all the around the edges.

[JohnV8r]

Thanks for that Capt. Patrick!

[JohnV8r]

Here is what I just got back via email from Coosa Composites. Capt. Patrick's recommendations should make this stuff bullet proof.

Sir,

Our boards are very well suited for any marine application where you would like to remove plywood or wood with a product that is lighter weight, will not rot, no mildew and does not absorb water.

Additionally, I have read the post and can say it is not difficult to bond our boards together. It does not say what he used, but I have attached our adhesive list that work. Please note that you would need to use a structural adhesive or boards can be easily be separated. The West Epoxy System and 3M’s 5200 are widely used with no problems. Water based adhesives do not work with our boards as there is no place for the water to evaporate. No additionally sanding is required, but you do need to make sure that boards are free from any contaminants.

I believe this answers your questions. If you need further assistance, please let me know.

Thanks,

Tamara Fee

[Rick Kral]

Hello John - Cpt.
Thank you both for the follow up. My experience would say that the Cpt. has definately hit the nail on the head. In the reply from the Coosa supplier he stated i did not mention the bonding material. Please note my last scentence which stated i did use West System epoxy. I did not tack the surface of the Coosa prior to lay up or rough up the surface. i did however have a good lay up free of air that was well clamped during the dry period. I had done some research and could not find any other posts on other sites that mentioned bonding conditions for Coosa. The product is an excellent product but like others out there certain proceedure need to be developed. I am happy to hear that i was not the only one who has experienced this condition.

John - good luck with the project. My rudder deck came out great and is about half the weight of the plywood version.
Rick

[Rocky]

Hi John,
I just want to say what I have learned from Capt Pat is to try to treat Coosa in this case where there are a lot of side loads and other loading on rudder table, like a core material. The strength is gained through sandwiching the core between glass and IMO is the only way in this area to create strength needed. If you want I can walk you through some measurements and we can produce/duplicate like below, I didn't build that 700 lb fiberglassing table for nothing! Lots of restaurants around Sonoma too or we could BBQ at my house and work on it if you'd like. Just Coosa and Glass/resin should be all we need. Rocky

[JohnV8r]

Thanks Rocky. I appreciate the offer. I owe you a phone call and look forward to getting together soon. I was looking at your shop and drooling!

[John F.]

Nice work and nice shop Rocky.

[Rocky]

Sounds good John V8r, hope to talk soon. Thanks John F, I'm finding it hard to leave boat alone while saving for diesels, like having a Bertram bug!

[Stephan]

That is beautiful!
S