Too all Coosa guys

[LegacyT]

Im replacing the transom in my boat. I figure might as well since the motor n drive are off... I plan of using coosa. The transom core is 27 x 25 x 1.5". My question; is it stronger to lay up 3 x 0.5", 2 x 0.75" or just get the 1.5" stuff. I know I plan on using the bluewater 26lb. Also for the actual layup to the hull can I use thickened epoxy? I already have a gallon of west epoxy and 403 microfiber adhesive filler. Will this bond roughened coosa to roughened FRP adequately? Finally should I sleeve the through bolt holes for the transom plate with aluminum/brass tubing?

Thanks,

 

[tpenfield]

Re: Too all Coosa guys

Wow . . . change of plans ?

Last I recall, you were doing a patch on one side of the transom. Are you now replacing the entire transom?

Anyway, I am not sure if there is much or any Coosa board experience on the forum, but maybe. From my research on Coosa boards, it seems that they are layered fiberglass and foam. So, I'm not sure that laminating thinner pieces together would make much difference versus just a single piece.

 

[jigngrub]

Re: Too all Coosa guys

Anyway, I am not sure if there is much or any Coosa board experience on the forum

That's probably because at $329 per 4'x8'x3/4" sheet Coosa Board it isn't worth it... especially when you can get a sheet of kiln dried CCA plywood of the same size for $100 or less, and it comes with a lifetime warranty!

You can get this stuff cheaper elsewhere, this is just an example and for specs:
3/4" Marine Treated Decking

 

[jbcurt00]

Re: Too all Coosa guys

I thought you were planning to use the coosa competitor's product:
Space age synthetics transom

How much of a 4X8 sheet will you be using for your transom? If I had to guess, you'll probably only get 1 layer per sheet since it's such a large transom. Unless you piece it together, which doesn't sound like a good plan, IMHO.

 

[LegacyT]

Re: Too all Coosa guys

Been reading around guess coosa is proven in many current production boats. I don't want wood in there for peace of mind.
I found a retailer in Maine that will cut a sheet up to a customers needs since they deal it so much. Just wondering whether to get 4x8 of 0.5" n use the scraps for other things or just get a custom cut 1.5" The transom is only 27 x 25 inches

 

[Willyclay]

Re: Too all Coosa guys

The transom is only 27 x 25 inches

I don't see how that is possible on a 23ft boat. Any pix?

 

[ondarvr]

Re: Too all Coosa guys

The strength isn't going to be much different, so it comes down cost and hassle, plus what you may plan to do with any left overs.

Using multiple layers requires more work and money (materials to bond them together), so is there a difference in total cost to you between the two methods? Are you actually going to be able to use the leftover Coosa board from the thinner sheet?

 

[Woodonglass]

Re: Too all Coosa guys

Make sure and KNOW what epoxy sticks to that stuff. Its kinda particular. I still don't understand your thinking. Properly Prepped, glassed and maintained plywood will last 30+ years in a transom. I seriously doubt you'll own that boat in 30 years. Are you sure you want to go to this expense. I see NO reason to do so. Plywood will do the job and do it really well and save you a LOT of money.

 

[LegacyT]

Re: Too all Coosa guys

Heres a pic; basically where the carboard is.... The transom is separated on its own from the rest of the stern with 1/2" solid laminate. I plan on keeping the boat for a loong time. Its been in the family since 1995 and don't really justify putting in an (not to offend anyone) inferior product when modern much better substitutes are available...

 

[Woodonglass]

Re: Too all Coosa guys

Here's what I know about what you call an inferior product. My wood transom is 52 years old and still going strong. I totally expect it to be that way for my grandkids kids. It's your boat and your money so do what you want but it's not needed IMHO

 

[jigngrub]

Re: Too all Coosa guys

If it's just 27"x25" get the custom cut 1.5" piece if you're sure you want to use the Coosa.

 

[jbcurt00]

Re: Too all Coosa guys

There seems to be a few problems w/ your boat that were never posted as resolved:

What did you do to replace the 1/2" balsa core you found rotted on the starboard side. Damage from unsealed trim tab screws if I remember correctly? Last I heard you wanted to fill the area w/ epoxy & glass, rather then the suggested that the repair be done w/ materials & methods similar to the original coring.

How did the hull blisters that formed AFTER paying to have the hull blisters repaired & the boat bottom painted get resolved?

I ask because rather then jumping around finding & fixing small areas of concern, it might be beneficial to step back & treat the boat as a project in it's entirety. If you need to pull some of the interior, do so. Once the stuff that can 'easily' be removed via some screws, nuts & bolts has been removed, re-examine the boat. You may find more stuff you'd like to repair while in dry dock doing some rehab.

If you spend more on the transom for Coosa board & it's associated costs in installation materials, you may find that you might have been better served spending those dollars on new motor mounts. Just an example, because I know you posted that the mounts were recently redone, again, after a bad repair job 2 years ago, in a thread here somewhere.

IMHO, piecemealing together high end materials scattered across several different repair areas are of little substantive value. Unless you've done IT ALL. I do understand the desire to NEVER have to be concerned about those areas again.

I think you even mentioned in 1 of your threads that you were more then a little frustrated that

'there's always something w/ this old boat'

or something to that effect.

My $0.0175 :watermelon:

 

[LegacyT]

Re: Too all Coosa guys

The boat is serviceable. Was last summer ran all over the place with. And I do consider it a project hence going through repairing these things. Materials are ordered for the coring, transom is serviceable but I'm replacing it now while in there. Floors and motor mounts have been repaired . I just want to know how guys that have worked with coosa or the like have mounted it to fiberglass. With cloth in between or just thickened epoxy. And whether the coosa should be pre-wetted...

 

[ondarvr]

Re: Too all Coosa guys

For best results pre-wetting any surface is desired, but epoxy putty between Coosa layers doesn't really need it. Cloth won't do much between layers, but it doesn't hurt either, so whatever makes you feel better.

 

[ondarvr]

Re: Too all Coosa guys

Just read your blister thread, it's a common outcome. Epoxy paint and "epoxy" can be very different animals, while they may share some chemistry, making epoxy into a paint can drastically compromise many of its best characteristics, and this includes water resistance.

Like Pauloman said, the blisters that showed up later were most likely already there, just not easily noticed on the surface. Once the boat was placed back in the water they just continued to grow at about the normal rate. Using a true epoxy barrier coat would have slightly reduced the chance, or at least slowed down the development of their return, but water had already permeated the laminate and the clock had started ticking. This is why the it’s such an involved process to fix a blistered hull, by the time blisters are noticed in one area it’s normal for the rest of the hull follow along, it might be right away, or delayed due to certain conditions, but very likely.

Repairing just the area first affected (noticed) does nothing to stop the rest of the hull from possibly blistering in the near future. This is why I feel waiting and watching at first, or even doing nothing can be the best solution. If at some time the owner decides to do the repairs it should be a complete repair of the entire hull, removing all the gel coat and affected laminate, then rebuilding with epoxy.

 

[Willyclay]

Re: Too all Coosa guys

Heres a pic; basically where the carboard is.... The transom is separated on its own from the rest of the stern with 1/2" solid laminate.

Thanks for the picture. I just could not wrap my old geezer brain around the written description of the transom design. Good luck!

 

[gddavid]

Re: Too all Coosa guys

I have worked with Coosa before and if you don'd mind the expense the stuff is great. I would use the three sheets of 1/2" and laminate them together with 1 layer of 3/4 ounce CSM between each sheet. This will be stronger because the layers of mat provides tensile strength which creates a strong beam when separated by the thickness of the coosa, having more layers creates a stiffer beam. If I had my choice I would use vinylester resin but epoxy will do fine, epoxy isn't the first choice because it does not break down the adhesive holding the mat together however this isn't a bit deal if you aren't trying to form the mat in a 3 dimensional shape. The adhesive may interfere slightly with the bond between epoxy and glass fibers but the greater strength of epoxy and mechanical bond would overcome this. My 2 cents.

 

[ondarvr]

Re: Too all Coosa guys

Here is the thing about layering core. While adding layers of glass between 1/2" layers of core does add some strength, adding that same glass to the outer skin adds far more stiffness and strength for less cost and the same weight. The closer these added layers of glass are to the center of the laminate (center of the core), the less benefit there is, when placed in the center of the laminate they are almost just along for the ride. This is why if possible a single thickness of core is used in an original design. Mat would add little to the physical properties when used with epoxy, other types of glass would at least offer strength, even if they weren't used in the optimum way.

 

[Woodonglass]

Re: Too all Coosa guys

Also don't forget, this is an I/O transom and you have to be + or - within 1/4" of the tolerances for your outdrive and it has to be flat and parallel. You're gunna have to take this under consideration when calculating how to fabricate the finished thickness of the transom.

 

[LegacyT]

Re: Too all Coosa guys

I plan on doing it from the inside so I'll just re drill the holes from the outer skin. I called both coosa and west. Guess bluewater 26 1.5 has been used by boat manufacturers for transoms for 15 years with no issues. West recommends it as well. For the guys thinking of going this route:

Sand both surfaces with 60 grit paper. Wet out both surfaces with unthickend epoxy then mix up epoxy with 403 microfiber filler to the consistency of soft mayo. Apply and clamp. No grassing over required but I will just for good measure.